my .02 on cams for boosted motors

[spooled240]

I kind of agree with this, but I think it depends on how the car is driven. If it's seeing 7K rpms drifting and drag racing then I'd say fuck the low end..but for a daily driven street car that's mostly going to see about 3K rpms, low end is going to be used about ALL the time.

i have a daily driven s14 ka-t running about 8-12psi of boost (240-280whp) on the stock 232's and my power drops off around 5700 lol, low end torque around 3K when the turbo spools is a monster though

I'm thinking about swapping to the s13 cams, since I don't wanna lose much of that low end torque..so I'll still be on stock cams persay

[CrazyRob]

i think the thread title should be "my .02 on cams for brainlessly tuned boosted motors"

for drift, drag, and circuit having top end power is key while not sacrificing torque at the low end. in my opinion a motor should be tuned to the transmissions difference in rpm per gear. pretty much when you upshift the motor should be just past where it torque band kicks in. if you can afford a boss transmission you tune the engine however you want and change the trans to suit the powerband. with most peoples applications i would raise the redline and make sick top end power then change the diff ratio to keep the same mph per gear while making the engine not work so hard to get there. cams and turbo selection in a boosted motor comes down to what the cars overall setup will be.

on a street car racing style top end matters very little and on-demand passing power is king. so depending on the the hp/turbo efficiency/rev limit/headflow cams could be a good option for a boosted motor.

if someone is serious about racing, cams and tuning should be a first upgrade besides full cooling system upgrades.

if someone is serious about daily driving passing power they should increase their boost and leave their cams for a near last mod.

imo.

[Z U L8R]

Originally Posted by jspaeth

dave, I agree with you wrote here, but in THEORY the ignition timing that gives MBT could itself be a function of HOW much air is coming into the engine at a given RPM, as well as the air's temperature and pressure

Thus, in theory, optimum ignition timing at a given RPM probably changes when you change cams.

(I don't have ANY experience tuning cars, but this seems reasonable based upon my physical intuition).

i agree with you . however, optimum ignition timing sometimes has to come second to allowable ignition timing. and in order to keep from blowing things up sometimes ignition timing does have to change when you change cams, i agree

down low to mid range power of this xyz aftermarket camshaft per say is gonna be less efficient than the factory turbo cams, therefore reducing hp and torque.

high mid to high rpm range the longer duration bigger lift is gonna be more efficient than the factory turbo cam. so it's going to allow the ingestion of more intake charge because it's holding the valves open longer, therefore to compensate for this slight increase in air you would increase the fuel (injector pulsewidth).

thus your major adjustment would be in the fuel tables to acheive your target air fuel ratio. as far as the ignition timing table, because you're at high rpm / high load you're not even truely able to get MBT ignition angle because with that added pressure something's gotta give or kaboom. so where this cam profile is shining you're only able to run enough timing to stay below your knock threshold. because your now weakest link is how much timing can be in the motor before the heat and the pressure cause knock/detonation.

as far as tuning the car, you need to balance that margin of safety of whether you should add fuel only, add fuel and add timing, or add fuel and take away timing. if you add timing and get diminishing returns, leave it alone cause it's safer to make a few less hp/tq than blow up the motor.

and in the same way, with these xyz aftermarket "turbo" camshafts, down low where this camshaft is less efficient than the factory turbo cam, you can increase the ignition timing to MBT because the cam's efficiency is lower. but that's really a given anyways because the VE is lower, the load is lower and all that.

so here's also where a car with cams and a stand alone surpasses the same car with just an air fuel computer because here where you're losing VE, you can try to optimize performance by advancing the ignition angle.

on a similar note. i've noticed that if you log the boost and do a pull, then do another pull this time with the ignition timing advanced a little more, it will not make as much boost, therefore indicating some truth to what your inclination was, [paraphrasing you] "that adjusting the ignition timing did somehow affect how well the motor flows the air....i will say though, that i've only noticed this when tuning a car that has the base timing too retarded. once i advance the timing to where it needs to be, then do the pull, the boost drops slightly.

why does this happen? well think about it. it's an engine, a big air compressor, would changing the ignition angle closer to optimum from not optimum increase it's efficiency? of course. but also advancing the ignition angle from too retarded is also lowering exhaust temperatures therefore not creating as much pressure to spin the turbine......for the most part though no change in boost theoretically should be noticed since boost is regulated by the wastegate.

would changing how long and when in the rotation the intake and exhaust valves open and close make the motor more efficient therefore requiring a change in ignition angle? Yes, no, but not necessarily. if anything a reduction in ignition angle may be necessary to avoid knock/detonation due to the added cylinder filling at that same tuning point as I explained earlier.

basically aftermarket turbo cams are just going to open and close the same exact valves a little longer and a little later/sooner than stock. the valves are still the same size. the ports in the head are still the same size. the displacement is still the same size. therefore you're basically borrowing power/torque over here, to make power/torque over there. that's it.

with things like vtec and vvt , you have the best of both worlds.

as far as stock turbo cams go. i'm not speaking for EVERY stock boosted engine because some boosted motors from the factory get really restrictive shitty cams. And some manufacturers build factory race cars. But for the most part the manufacturer's intent was drivability (street car first, race car second). most people's swapped cars are their daily first, and their race car second.

therefore intent and purpose should go into whether or not cams are a good choice based on the intent and purpose of your car. and that goes for EVERY mod on the car.

now on to NA cams.

The majority of factory NA cams are totally restrictive. this is because the motor's typically built around longevity, emmissions regulations, and the manufacturer's r&d budgets FIRST, then performance as the byproduct. then you go over to the more sports car minded NA cars, this will be less of the case and the profile will be a little more aggressive than it's commuter brethren, along with probably a better flowing intake and exhaust design.

however upgrading to a more aggressive NA cam will definately yield improved performance if the factory cam is restrictive...but again, there's a balance. when you get too crazy with the cam, then it's the same, you're robbing peter to pay paul, borrowing power here, to get it there.

and if going from NA to turbo, then totally getting a set of turbo cams will improve performance, as said earlier.

now truely, if you really want the power and efficiency out of those magical cams that just move the power around without any loss down low. increase your engine's efficiency. port the head so it'll flow more, do a valve job so they seal better, get a better exhaust and induction system(intercooler/piping included).

it's an engine, everything works together. but FIRST, it's a boosted motor, it makes it's power because it's turbo'd, wouldn't the best upgrade be a more efficient turbo? of course!

cliffnotes:

cam's rob peter to pay paul. I like Peter AND Paul (no homo)
parts on a motor work together to improve performance
i still don't like big ass cams

if you WANTED Paul to have the upper hand then your cams did exactly what you wanted them to do and there's no reason you should feel bad, you did the right thing!

disclaimer:

don't go cranking up the ignition timing down low just because your cam's not doing shit down there. Don't blame Dave for irrational/non-observant tuning methods lol. MBT is MBT.

Dave

[jspaeth]

wow! informative hahah

[codyace]

Originally Posted by smelly240

264/272 HKS step 2s are a fantastic setup for a larger turbo (30r or 35r)

I used 264s before this and up top i picked up a considerable amount changing to staggered - with no real losses down low.

You'd gain more with straight 272 and cam gears if you're looking to play with the intake side of things. Again, you need to look at lobe separation angle when it comes to 'turbo' setups. Obviously as close to zero is best, yet a big seperation helps with response (while killing top end). With a car that uses a huge turbo, I'd shoot for the lowest LSA, rather than the bigger gap for response.

VVL heads are great -- I have little experience with RWD, but in FWD they are a gift. Obviously most setups also involve a full point of compression, but the flow characteristics remain the same. awesome stuff. But for 600 whp, I would much rather go with displacment, rather than boost...just my preference though. Nissan certainly isn't giving me any trophy for doing well with their shiz.

Originally Posted by chituntang

Stop talking about trap speed, or any drag race thing because you are not really using your powerband. You put your feet on the gas pedal, and get it to the shifting rpm, then shift. You will not have your engine reving at like 2.5k rpm.

Trap speed is the single most important indicator of how well a car accelerates, drag race or not. When you measure 1/8th to 1/4 trap differences, or sectional speeed increase, you can get a true indication of how 'quick' a car is in the setup. Drag racing in the overal scheme of things may be lame to you, but the physics aspect it something you can't deny - a faster car will trap faster. Bottom line, if you trap higher, the car is faster. I mean, its' just how it is. Think about it:

a 300 hp car with stock 4.08's does XXX speed
a 300hp car with 4.6 FD does faster. Sure it may be slower to the 1/8th, but in all truth, 1/8th to 1/4 speed increase is the single best indicator of how fast it will be on track, or on street.

Originally Posted by chituntang

thing Dave is saying. You want to hit that 1000000000whp within less that 1000 rpm at the top, or have the turbo fully boost up at a lower rpm and hold it for 4000rpm.

But the point is, i'm not arguing for the big hp small powerband cars...they are geared/tire'd to stay in the powerband. I'm saying that a cammed stock car will be faster than a stock cam car. And it's always the case.

Originally Posted by jspaeth

Thus, in theory, optimum ignition timing at a given RPM probably changes when you change cams.

Correct. Timing throws everythign off in regard to max timing advance and all of that stuff.

Originally Posted by spooled240

I kind of agree with this, but I think it depends on how the car is driven. If it's seeing 7K rpms drifting and drag racing then I'd say fuck the low end..but for a daily driven street car that's mostly going to see about 3K rpms, low end is going to be used about ALL the time.

But realistically speaking, the only time you are below 3k, is pulling out from a lamp. The car idles at 1000 for all intents and purposes....just watch where our car's rpm's are pulling out. It's sure great to have the ultimate low end power, but you never really 'use it' for anything performance related. I could care less about daily driving, so lon as MPG stays up.
[/QUOTE]

Originally Posted by Z U L8R

down low to mid range power of this xyz aftermarket camshaft per say is gonna be less efficient than the factory turbo cams, therefore reducing hp and torque.

Again, 'turbo' specific cams are aimed at real deal setups. JWT S3 and HKS 264 are not 'turbo cams'....but they work awesome.

Originally Posted by Z U L8R

as far as tuning the car, you need to balance that margin of safety of whether you should add fuel only, add fuel and add timing, or add fuel and take away timing. if you add timing and get diminishing returns, leave it alone cause it's safer to make a few less hp/tq than blow up the motor.

Certainly - but adding boost is also a potentially dangerous solution to lack of airflow. You increase detonation ability 100%, which to me isn't worth it.

The least amount of boost and timign required to make XXX hp is the best, and that's why cams are the best addition IMO.

Again, I could care less abotu the 2500-3500 rpm power band. This area under the curve in no way helps in the grand scheme. Hell a car that makes 10-20 lessin the the 2500-4000 range, yet makes 20-30 more in the 4000-7000 range is always the faster car, both on street, on track, and in trap speed.

Again, traction is that 'lost' thing too...a car that makes more torque, yet rolls the tires, is slower. For example: my buddies Lightning is a fantastic machine (road races it, so it's all abotu down low)...but in a normal circumstance, he makes 'to much' power down load, and ends up rolling the tires off....when the car with a better average powerband stays ahead.

Response rocks - i"m addicted to it...but when it's at the expense of acceleration, I'd rather aim for the powerband.

Originally Posted by Z U L8R

basically aftermarket turbo cams are just going to open and close the same exact valves a little longer and a little later/sooner than stock. the valves are still the same size. the ports in the head are still the same size. the displacement is still the same size. therefore you're basically borrowing power/torque over here, to make power/torque over there. that's it.

While the general 'entry/exit' paths may remain the same size, the flow charecteristics and the combustion process are not. The most amount of air flow per constriction will net the most power. Again, a low end powerband does not indicate a stronger car. Look at v8's with RV cams for example.

Originally Posted by Z U L8R

and if going from NA to turbo, then totally getting a set of turbo cams will improve performance, as said earlier.

Totally untrue. Again, LSA is a very important part of turbo powerband. A larger duration cam, with a better LSA will do better than a shroter duration with a crappy LSA.


Again, average powerband always results in a faster car. You can ahve all of the trump extracting, house pulling, grin inducign torque and resopnse in the world - but a car with better average power will always win the race, turbo, N/A or nitrous.

[codyace]

Lets not also forget the 'gear ratio' factor. Throw a hot set of gears in (4.3 or 4.6) and yo ucan get all the mechanical low end you want, and then use the big cams for the top end. Ooooh baby, what a nice combo.

[Z U L8R]

good! mission accomplished!

what started out as an opinionated and frustrated rant, turned into a great discussion on cams.

Originally Posted by codyace

Again, 'turbo' specific cams are aimed at real deal setups.

my point exactly.

San diego really is a nice place my little bro's stationed there on the U.S.S. Stockdale. i love pacific beach....i fell asleep at pacific beach for 15 minutes and woke up with all these hotties all around me tanning.....LOVE THAT PLACE! whale's vagina ftmfw

lol i know i'm a total car nerd...but i really am a sexy mofo, best watch yo girlfriend yo, i'll dazzle her with muh profile , lobe, and duration ya kno wha'msayin boiiiiiii!

how we do ATL style shawty ^_^

Dave

[codyace]

i'm glad i don't watch that many movies - i usually fall asleep but anchorman I watched


It's the same with any car type/engine type though- "turbo" cams are great for the 500+crew -- at that point those guy sknow what they are doing. For anything else, JWT S3 is best.

[Z U L8R]

i also wanted to clarify a little on my OPINION for ka-t set ups.

yes you'd have EXCELLENT response on a ka-t by just leaving the stock cams, or putting the stock s13 dohc cams in it (if you had an s14 dohc ka24de), but torque and powerband up top would drop off because of the profiles.

also because a ka is a 2.4 liter, displacement and static compression are higher than an sr therefore doing cams would not kill your powerband down low because it's plenty torquey. but EXACTLY the mildest 'turbo' cam like the s1 cams in my opinion would be a perfect choice because they barely impair down low (where by design it's already strong enough) but DEFINITELY help the motor breath better up top.

i personally haven't tried the s1 cams in comparison to stock but like i said, once all the other important details of my ka-t build were dealt with. if i still wanted more out of the car, i'd definitely start seeing what i can do to keep the powerband from falling off up top by experimenting with some different cams. obviously if the s1 wasn't a big enough difference, then i'd go bigger.

from experience i'll say that i wouldn't have peace of mind with pushing a stock ka bottom end passed 10psi, therefore i would have my own at 8 or 9 psi tops, and it'd last no problem. once i built the bottom end with forged pistons and rods, the added thickness of the ring lands of turbo pistons vs the n/a pistons as well as the strength of the material and cooling properties of them, i'd have no problem cranking that sucker up and puttin down some worthy power.

i know there's guy's on ka-t.org making 9 million horsepower on the stock bottom end and running 40 psi and what not....but they have the magical ka-t juice that only the magical leprechaun triplethurodon on the top of candy mountain possess. us regular folk don't have access to such marvelous wizardry so we're stuck obeying the laws of physics and properties of metals...

in the ka's the pistons are the weakest link, the rods and rod bolts are the next, therefore if you do one, do the other while you're at it, and have an overly stout set up that you can run at 50% of what it can handle, and that's how you'll get your fun out of it without blowing motors up every other month.

there are exceptions to every rule and everyone has that buddy that's running 15psi on a stock ka-t for 2 years with no problem....but in my experience, he's the exception, not the rule.

"seems like there's always enough time to do it twice, but never enough time to do it right" -Tim Coleman-

Cody thanks for being "devil's advocate" but definitely making some good points along the way. we're both saying the same thing for the most part is what i'm concluding.

Cody: my opinion on a turbo car is , less valve overlap is most desirable as it causes reversion, n/a car obviously more overlap is more desirable. how do you feel about that and elaborate in lay man's terms so other's can follow along.

also as Mr. Corky Bell talks about in his must read book


he talks about in the latter chapters where you're actually testing your set up. checking your exhaust pressure in comparison to your intake pressure. for a street car a 2(exhaust) to 1 (manifold pressure) ratio is ideal, however for a full race set up 1-1 is the goal.

by basically checking the pressure's and comparing them at your torque peak vs redline, you can see if you have a properly matched turbo on your car.

if you have a shit ton more pressure in your exhaust before the turbo than in your intake manifold then you can deduce obviously that your turbo's too small, a restriction, and the reason torque/power falls off as rpm increases. good example, t25 turbo at 14psi........(technically they don't hold 14psi at redline tho lol)

but here the restriction is the size of the turbo, NOT the cam shafts. just running a bigger turbo at lower psi will flow the same air to match the power down low, and be less of a restriction therefore freeing up the hp/tq up top.

this was the point i was making in context. upgrading the turbo as first priority addresses the size of the turbo being a restriction. upgrading the cams and leaving the turbo the same takes away even more usable power down low and though will make slightly more up top, still doesn't fix the restriction. it'd be like changing to a wider rim when your problem remains that the tires aren't balanced.

but the point is, you're losing power down low AND still running the same boost versus losing a little down low for the spool difference, but gaining efficiency, therefore able to make the same peak numbers as before, with better powerband up top at lower boost. obviously if you crank it up to the same 14psi you'd make even more power than before.

the other GREAT points Corky makes is about your intake system and intercooler piping. you can test for pressure drops after the air filter or after the maf and see pressure drops. these pressure drops force your turbo to work harder to move the same amount of air. therefore the pressure (psi) has to increase in order to flow the same amount of air, and with that pressure, comes more heat......totally the things we're trying to avoid.

same goes with checking your pressure drops in your intercooler and piping, even with throttle body. you can actually KNOW, test, and find out restrictions in your turbo set up to increase your set up's efficiency, and THAT'S how/why good and properly matched parts make all the difference.

a 2psi loss is tolerable. and 0 loss is impossible :P

woot woot

gearing is totally frickin AWESOME as well. the stock r200 diff in the 280z's are a 3.54 if i recall correctly (iirc), i was running an 83 280zx 3.9 open diff. i ran 11.92@ 125mph on 245/60/14 bfg t/a $50 s-rated pep boys tires with 1 wheel spinnin and a mighty suck ass 2.1 60 foot hahaha. my 4th gear would tap out at 120mph so right at the end of the 1/4 i had to shift into fifth.

just for shit's and giggles i put the stock 3.54 back in, now 4th gear went to 140...then there was fifth...keep in mind my tires were only rated to ~100mph.....scarey thing i tested this out indeed >_< (dumb ass)

went back to the track, and ran a 11.95 @ 122mph with a 1.99 60' . as far as the dyno sheet, boost kicked on about 300rpm sooner. but since i didn't spin as much on that pass the trap speed went down. i hated the stock 3.54. the same modded c6 z06's that i'd race with the the 3.54 i'd be dead even with, where as with the 3.9 i would beat by 2 cars. i quickly switched back to the 3.9.

ideally the z31 88 turbo 300zx has an r200 3.7 vlsd. i think that would have been the best compromise. not only was it the only direct bolt in lsd, but i could wind out 4th gear a little passed the 1/4 mile and eliminate that last shift.

all in all though, with better tires, if i could drop my 60 foot time to like a 1.6, the car would've probably done a 10.8-11 flat no problem based on the trap speed. every tenth off your 60 foot time is 2-3 tenths off your 1/4 mile.

i'm totally not a "drifter", but drifting is fun as hell....i prefer hwy pulls or the drag strip.

i just like the look on the face of the dude in the mercielago that got spanked by a 30 year old rattle canned datsun mauhahahaha.

i gotta keep this post semi 8 page, cause i gotta knock out this timing belt water pump on an elantra! YAAAAY!!

what's your thoughts "ProjectRDM" mr. RUSS!?! HRMM ^.-

Dave

[Z U L8R]

since we're on the discussion of cams, this is a FANTASTIC, how to on degreeing cams etc.

check this out when you get time.
www.ka-t.org :: View topic - How To: Setting Valve Lash/Dialing in Cams

that's that ka-t wizardry right thurr ^_^

Dave

[SrRaycer]

Overlap can be tuned with cam gears. Some of you are talking as if stock Nissan cams are magical. Talk about the stock cams lift and duration vs aftermarket options, all aftermarket cams aren't made for peak power, hence all the options available. There are cams made specifically for torque and midrange that outperform the stockers in the "usable powerband" department. WHAT about the stock cams make them the BEST for torque and spool?

[Z U L8R]

low lobe separation angle (LSA), which means low overlap as well as they have low duration as high duration and low LSA still creates more overlap. the design is around driveability and midrange power, as is the turbo that comes with it.

it's not that the stock cams are magical, and it's not that aftermarket cams are either. it's just that until you get rid of your biggest restriction in airflow and power which is the itty bitty turbo, there's no point in putting cams in there that are gonna still be restricted by the output of this same itty bitty turbo.

upgrade the turbo and do all the other supporting mods, THEEEN tweak the power band with some cams if you want to.

cams definately have their place and use in the scheme of things, there's just a lot of other more important things that limit the engines power output that should be dealt with before the cams need to be.

cams are more like the final touch to the engine build. the icing on the cake if you will. the proper cams will compliment the already thoughtfully upgraded turbo system.

if it's between upgrading the stock turbo versus the stock cams....deal with your weakest link first.

that's where my emphasis is.

Dave

[SrRaycer]

The point is you can't say they aren't necessary unless your trying to "tweak" the powerband for a few additional hp. They may not be necessary for YOU and your driving style as everyone doesnt like to rev, but some do. Isnt that what makes vtec in hondas fun? nobody complains about that. Some of us dont need full boost at 3200 and would like a higher powerband that hauls all the way to 8k+...
And you're supposed to match your cams to your turbo,there is a LOT OF MISINFORMATION AND OPINION being labeled as fact.

You keep mentioning should you buy cams vs an upgraded turbo or something, I am talking about whether aftermarket cams can be an improvement over stock for a responsive setup...you seem to be talking of a budget build.

[Z U L8R]

"I am talking about whether aftermarket cams can be an improvement over stock for a responsive setup" -SRRaycer-

the answer is no.....the only thing you could do is go even less LSA and less duration....then you WILL be getting into restricting power with changing the cams.

the reason hp and torque fall off up top with the stock sr20 set up is because of the turbo, not the cams. that's not my opinion, that's the facts.

the purpose for upgrading the cams is to help maintain power and torque at mid to high rpm....but when the size of the stock turbo is the reason your hp/tq is falling off...address the reason FIRST.

lol i dunno what else to tell ya sir. it's not about a budget build, it's about making intelligent decisions for modding your car.

what good is upgrading to a 3 foot carbon fiber racing spoiler when you're still running the stock engine and need to change your oil?

sure, spoilers have their role and purpose in the grand scheme of things...but aren't there more important things you can spend the same money on before you get a spoiler? if you're getting a spoiler because you want to grip the road better, then wouldn't a better upgrade FIRST be better tires?

that's my opinion. if my opinion is completely illogical, that's your opinion....and we can disagree, no biggie

"san diego means whale's vagina"

Dave

[SrRaycer]

"the purpose for upgrading the cams is to help maintain power and torque at mid to high rpm....but when the size of the stock turbo is the reason your hp/tq is falling off...address the reason FIRST." Z U L8R

You still seem to be talking about cams vs turbo. I understand that your saying upgrade cams when you have the appropriate turbo, but you also seem to be saying don't upgrade your cams with a bigger turbo so you can still have some low-end power.
I think this argument will just go back and forth so I give...lol

But I still stand by what I previously posted

[codyace]

Originally Posted by Z U L8R

from experience i'll say that i wouldn't have peace of mind with pushing a stock ka bottom end passed 10psi, therefore i would have my own at 8 or 9 psi tops, and it'd last no problem.
--
i know there's guy's on ka-t.org making 9 million horsepower on the stock bottom end and running 40 psi and what not....but they have the magical ka-t juice that only the magical leprechaun triplethurodon on the top of candy mountain possess. us regular folk don't have access to such marvelous wizardry so we're stuck obeying the laws of physics and properties of metals...
--
there are exceptions to every rule and everyone has that buddy that's running 15psi on a stock ka-t for 2 years with no problem....but in my experience, he's the exception, not the rule.

I wholeheartedly agree with this. When I see these guys and their magical '300 hp all day no issue' steups, I really question how 'driven' they are.

While my 240 experience is 95% SR related, I will say that my 'turbo nissan' roots were in my fun little 1994 Altima...that I turbocharged - what a great setup, and at the time (2002/2003, there weren't many turbo 'anything' out thrre (aside from DSM)...so an aftermarket, custom, turbo ALTIMA was super uncommon.

Our rule of thumb was, 10 psi - or 12 if you trusted the tune and didn't care if it blew up. Needless to say, my car lasted roughly 10,000 miles before my brothers blew it up once they raised the boost to 15(when I was deployed).

Nice to find someone else who realizes this. PS: 'Leoplurodon' was the magical dinosaur haha.

Originally Posted by Z U L8R

Cody thanks for being "devil's advocate" but definitely making some good points along the way. we're both saying the same thing for the most part is what i'm concluding.

Cody: my opinion on a turbo car is , less valve overlap is most desirable as it causes reversion, n/a car obviously more overlap is more desirable. how do you feel about that and elaborate in lay man's terms so other's can follow along.

No problem - I too think we're talking about the same thing, just go about it two different ways - there is always another way to 'bake the pie' as they say.

In regard to overlap, obviously the least amount = best 'technically' (and as you mentioned helps reduce backpressure ratio). BUT in the same response, that 'overlap' is also what helps make better average power. Certainly, there is no denying the fact that less overlap helps spool the turbo better -- but with anything, this 'spool up' positive, comes with a negative: lack of a 'hearty' powerband.

For me, unless I was making a 'race car', I wouldn't bother with striving for cams with less overlap/backpressure for a street car. I'm certain my ratio is near 2:1, but so long as your tune is safe and you don't run a bunch of timing, you really can't go wrong with it.

Originally Posted by Z U L8R

also as Mr. Corky Bell talks about in his must read book

Maximum boost (to me) is like the first testament of the bible. Great start, got the basics, and generally speaking - but it is severely out dated at this point. The concepts will forever be there, but with the advent (and accessibility) of better parts, tuning solutions, and shops, have also come new ways to approach the issues.

Originally Posted by Z U L8R

but the point is, you're losing power down low AND still running the same boost versus losing a little down low for the spool difference, but gaining efficiency, therefore able to make the same peak numbers as before, with better powerband up top at lower boost. obviously if you crank it up to the same 14psi you'd make even more power than before.

lets also not forget the often forget, and overly (if not the most) important issue surround dyno graphs: lack of a standardized graph OVER time. Sure a graph could look perfect, but if it's slow to respond and comes into power sluggish, that nice powerband really is nothing more than 'eye candy' to impress people on forums and car shows. When I look at my graph versus others (as well as other SR cars) in WinPep, trying to figure out a standard 'overtime' point, it's really evident. Sure those those steamy t28 graphs with full spool before 3000 look impressive, and seem fun, but once you look at the graph over time, you'll see how much that lack of top end really hurts, as it's SLOW SLOW SLOW at that point.

So with anything, racing dyno graphs is certainly an interesting tool, but with so many differences in dyno type, load application, and correction - they should always be taken as examples. Strap my car on a mustang dyno and throw a load on it, and it'll spool like the street. On our dynojet, it spools later, but is much more repeatable in power. Which one is best? Depends on who you ask. I do know this though, the 'non load' factor is a best crappy for setting boost up on, as on the street you almost always see more.

Originally Posted by Z U L8R

the dyno sheet, boost kicked on about 300rpm sooner. but since i didn't spin as much on that pass the trap speed went down. i hated the stock 3.54. the same modded c6 z06's that i'd race with the the 3.54 i'd be dead even with, where as with the 3.9 i would beat by 2 cars. i quickly switched back to the 3.9.

The spool increase was from the extra load through gear, for those not understanding that aspect. Remember, load = turbos best friend at times.

BUT, one advantage of a small turbine is that they light fast, and are predictable. Hehe, I run a 4.6 - sure I loose some spool torque, but the mechanical advantage >*

[army240]

Thanks a lot on this fantastic discussion on cams!

What do you guys think about stagered cam setup? I'm about to install HKS 256/264 (int/exh), 10.5mm lift, on a stock internal, stock head, tomei expreme manifold, HKS GT2540, all support mods, on a friend car...

I ran the number throught the calculator on the KA-T site, here's what it give :

Overlap : 4.00 degrees
Intake Duration : 222.00 degrees.
The Exhaust Duration : 225.00 degrees.
The Inlet Cam has an Installed Centerline of 108.00 degrees ATDC.
The exhaust cam has an Installed Centerline of 111.50 degrees BTDC.

I've seen some nice dyno sheets with the stock intake cam, and BC 264 on the exhaust side, with T28... Not big number, but nice powerband all along the RPM range.

Anyway, i'm just curious what you guys think about stagered cam setup!

And again, this is a really interresting discussion!

Frank

[Z U L8R]

give it a shot Frank, if you can post up dyno graph at the same psi before and after and the only difference being the cams/tune then it'd be great to see your gains and how the motor liked it.

i'd give it a shot. nice/expensive turbo too btw

Dave =]

[army240]

Originally Posted by Z U L8R

give it a shot Frank, if you can post up dyno graph at the same psi before and after and the only difference being the cams/tune then it'd be great to see your gains and how the motor liked it.

i'd give it a shot. nice/expensive turbo too btw

Dave =]

Unfortunately, I won't be able to do a "Before" dyno sheet, cause i'll be installing the HKS at the same time as the cams(now it's on a S15 T28). Also, the engine is already out of the bay, and I don't have any dyno sheet. But I will surely post a "After" one

As with the discussion, I say that they're a lot of mods I would do before putting aftermarket cams in a stock SR. As for choosing which cam, I guess that's a lot of research, and it depends on what you want! Big number, or nice powerband... you choose, you can't really have both I guess!

Frank

P.S. Like I said, this is my a friend car I'm working on... I wish I could own his turbo haha!

[jspaeth]

Originally Posted by army240

As for choosing which cam, I guess that's a lot of research, and it depends on what you want! Big number, or nice powerband... you choose, you can't really have both I guess!

That's partially true....I would say having a "nice powerband" means having a relatively wide and flatt-ish torque curve.

If you start going with bigger turbos like a 30R or 35R, you NEED the bigger cams to help the motor breathe up top and you NEED headwork to raise the limit to AT LEAST 8000 RPM to even make it worthwhile.

The torque curve on my 2871R with 264/264 starts to drop off around 7000 RPM or so, maybe a little earlier.

I bet with a twinscroll 30R and 264/264 with the Greddy Intake mani, you could have a setup that spools early and makes 350 ft-lbs from 4000 RPM-7500 (8000?) RPM.


Now THAT would be a sick powerband.....


My buddy is running a 30R on his S2K.....it is retarded.....he makes solid torque from like 4500-8200.....

[Z U L8R]

ya, when i was at Lethal we put a 30/76r on an 06 s2000 (2.2L) and that thing was like insta spool, it was great.

honestly if i get to baller status once my 2j 240z is done and making 600hp i'll be going back to working on my ka-t datsun 510....i only want 400-450 outta that now since the Z can be my corvette killer, but if that ka blows up, it'd be bad ass to put an s2000 motor in the 510. uber rev, 6 speed, strong as hell motors (cept for the gay open deck block), and best of all boost AND V-ATTACK!!! lol

honda definately has the best flowing heads. of course that's what million's of dollars in R & D will get you they won't TELL you what they did, but it'd definitely be wise to COPY what they did

this definitely isn't a "closing statement" as i still wanna see more people's before and after dyno sheets of cams.

i'm glad i made this thread, and thanks everyone who posted in it.

keep it alive! post up your dyno sheets if you have any before and after just cams if you can, and make sure you give us a brief description of your set up, how much boost, and what cams.

thanks,

Dave

[renegade_ewok]

This is a hell of a thread...

Im chiming in on this cam discussion - Im running a T28 with HKS cams (256/264 split duration... at least thats what the timing chain guide had etched into it...) and the T28, down low, is a touch less responsive than an OEM cammed SR. I drove another SR and it felt more torquey <3000 RPM, but after that my car with the cams felt like it PEAKED higher in the mid range. I have no charts to compare unfortunately.

[redpotatoes]

Originally Posted by Z U L8R

there are exceptions to every rule and everyone has that buddy that's running 15psi on a stock ka-t for 2 years with no problem....but in my experience, he's the exception, not the rule.

I guess I am an exception because I am running 15psi on my stock block and it's running like a charm for the past years. A proper maintained engine and a good tune makes all the difference.

[Pacman]

Going back to my post about the adjustable gears, like you said later in the thread about making power here and losing there, the gears can bring power back into a more usable range, or bring power where it wasn't before verse just slapping cams in. Brings the power band back where its usable. Thats where I'm going with this.

Think like 248/248 swap on a KA, it makes power (I remember seeing the dyno of the comparison a LONG time ago) but its so high in the top end. Having the power that high is pretty much useless unless you sit at 5500+RPM all day. Timing them allows the cam to function as the designer wanted and makes the power come back to useable. I feel gears are good to have, not necessarily manditory, when upgrading cams. (Am I making sense or is the Norco clouding my mind [knee surgery]?).

Awesome thread. Read through the whole thing.

[army240]

Originally Posted by Pacman

Going back to my post about the adjustable gears, like you said later in the thread about making power here and losing there, the gears can bring power back into a more usable range, or bring power where it wasn't before verse just slapping cams in. Brings the power band back where its usable. Thats where I'm going with this.

Think like 248/248 swap on a KA, it makes power (I remember seeing the dyno of the comparison a LONG time ago) but its so high in the top end. Having the power that high is pretty much useless unless you sit at 5500+RPM all day. Timing them allows the cam to function as the designer wanted and makes the power come back to useable. I feel gears are good to have, not necessarily manditory, when upgrading cams. (Am I making sense or is the Norco clouding my mind [knee surgery]?).

Awesome thread. Read through the whole thing.

Adj. Cam gears are a good thing to have... give you flexibility for your application. If you have the budget for it, it's not a bad thing to have. BC 272s recommand using Cam gear, i'm using them, degreed to true TDC. With stock cam gears, idle is rough and there's low vacuum. So it's a good thing to tune them.

Frank

[jspaeth]

Originally Posted by army240

Adj. Cam gears are a good thing to have... give you flexibility for your application. If you have the budget for it, it's not a bad thing to have. BC 272s recommand using Cam gear, i'm using them, degreed to true TDC. With stock cam gears, idle is rough and there's low vacuum. So it's a good thing to tune them.

Frank

I agree that they can't HURT....but isn't "lower vacuum" a simple consequence of the increased overlap?

Meaning, if you install the cams perfectly, and they are perfectly degreed, (i.e. operating from a timing standpoint exactly how they were desgined to), wouldn't you still suffer a lower vacuum purely due to the built-in overlap?


Your post is making it sound like the OEM cam sprockets are the source of the decreased idle vacuum

[army240]

My bad, I meant is when my cam was set on "0", the idle vacuum was lower than when it was degreed to True TDC, according to the BC degreeing diagram.

Frank

[jspaeth]

I guess you are saying the vacuum can get even worse if the cams are not perfectly degreed?

That makes sense....but your original statement kinda made it sound otherwise.

Bigger, longer cams = less vacuum at idle bc of more overlap, it's just the way it is.

Sure you could change them to regain some of the idle vacuum back, but you would probably be doing more harm to the power output in other places.

[army240]

Originally Posted by jspaeth

I guess you are saying the vacuum can get even worse if the cams are not perfectly degreed?

That makes sense....but your original statement kinda made it sound otherwise.

Bigger, longer cams = less vacuum at idle bc of more overlap, it's just the way it is.

Sure you could change them to regain some of the idle vacuum back, but you would probably be doing more harm to the power output in other places.

Sorry, I'm a french guy, and sometimes my toughs are not well explained! /off topic

[midnight_rex]

i got JWT S4 cams with my t3/t4 (motor fully built from the top - down). what kind of street/response would i get out of it?