JWT vs Enthalpy ECU comparison dyno results!! *Another* 400 whp CodyAce Built Car

[HemiCharger]

Originally Posted by TurboB15sentra

That last time I saw/spoke to Rob, was back in 2003, at one of the Mossy Nissan Oceanside car shows. I don't think he's working for Garrett any longer.

Yeah, the GT28RS was the turbo that really started the revollution for new/updated compressor/turbine technology. It showed that you could, in fact, have your cake, and eat it too. Quick spool up, and big power.. The "Disco Potato", known as the GT28RS, was originally designed by Rob and a few other guys, for a Miata engine. It was such a great turbo, that they turned prototypes over to people like JWT, Coleman, etc.. and those guys were the first to test with it on the SR. They also tested it on the QR25DE, which proved to be awesome. It started making boost at about 2K rpm, and made 325+whp on pump gas. I've personally taken one out to 350whp, on a low comp/built QR.

Anyways.. I'm rambling.. lol..

Travis

Yeah but wasn't the GT28RS designed specifically for FWD sentra's? I have not seen any RWD SR guys running them. I like everyone else on here is running a GT2871R. I wish I would have gotten the GT3076 instead. You can always make more power with boost. I understand the desire for top end in our cars but why would you pick a .63 A/R over a .83 or whatever A/R? Is the peak really that BIG of a difference?

[jspaeth]

Originally Posted by HemiCharger

Yeah but wasn't the GT28RS designed specifically for FWD sentra's? I have not seen any RWD SR guys running them. I like everyone else on here is running a GT2871R. I wish I would have gotten the GT3076 instead. You can always make more power with boost. I understand the desire for top end in our cars but why would you pick a .63 A/R over a .83 or whatever A/R? Is the peak really that BIG of a difference?

From the results I've seen/heard, 0.63 vs 0.86 is maybe 500 RPM difference in spool up time, but I think the 0.86 will keep breathing for at least another 500 RPM higher than the other one.

Again, high RPMs is good, because you always want to be in the lowest gear possible at a given speed (given that the torque is not dropping off super fast).

[codyace]

Originally Posted by 4x4le

Sorry. Im not trying to fill this thread with my results, I just want to clarify a few things. I didnt go back and optomise my low end, I actually didnt touch it much. Most of the pulls were started at a much higher rpm but this was the final one just to have a fuller graph. I know there is more work to be done and I will be back for more. I doubt I will do cams to be honest but I may some day. I think hitting numbers like that on a Dyno Dynamics with stock cams is just too impressive to add cams.

It almost seems unreal on stock cams, considering everything I've ever seen with SR's (and that' nearly 8 years now myself, as I was KA before that). I can't think of a single other dyno near your 'power' (even with the big boost) on stock stuff hehe.

Originally Posted by 4x4le

When I go back we will play with the load on the dyno to make the turbo spool more like how it does in real life and I will start the pulls at about 1800 rpm and go to about 5500 rpms and optomise all of that part of the maps.

I do like the ability to load on the DD dyno...this is my single biggest complaint with the Dynojet we use.

Originally Posted by 4x4le

After I go tune the lower rpms I will have a much more usable power band. Then If I were to add cams I would just be shifting that power band in favor or a higher hp number (which I have enough of right now).

See, to ap oint...with the SR you can run a smaller duration cam and probably gain some 'airflow' in the midrange...not needing to boost as much would provide much less stress on the engine for sure...but then again at 9:1 with E85, 24 psi is nothing.

Originally Posted by jspaeth

So, even if your torque drops off to say 250 ft-lbs in 2nd gear at high RPMS...you will be ACCELERATING equally as fast as when you are making 375 ft-lbs in 3rd gear.[

I myself, did not grasp this until I sat down and tried to understand it......unless your torque is dropping of REALLY fast, you ALWAYS (in our cars) want to rev all the way out to redline (due to the way our trannys are geared).

While I can grasp your point, wouldn't we also need to figure in a 'time vs RPM' aspec to this? Having more power in a gear is nice, but lets just assume 3rd gear is a 2.5 ratio, and 4 is a 1.0. Even though you'd think the mechanic advantage in power production vs gear would be better in 3rd, could we also not argue that the time in gear in that 1.0 4th be better for total speed? (If this makes any sense)

Or is it just another factor in it all? Or am I just completly wrong hehe.

Originally Posted by TurboB15sentra

It's tough to compare the transient response/spool up RPM, from dyno to dyno (even with the same car), as loading can vary wildly.

Travis

Ah, another issue with 'dyno fights'...the time aspect. I love comparing some cars over 'time' in WinPep but even that is hard due to different start RPM and the sort between different dyno's. A lot of people don't understand that the 'big hp' number may be impressive, but once you change that lower variable to time (instead of speed) all sorts of new things can appear.

Originally Posted by HemiCharger

Yeah but wasn't the GT28RS designed specifically for FWD sentra's? I have not seen any RWD SR guys running them. I like everyone else on here is running a GT2871R. I wish I would have gotten the GT3076 instead. You can always make more power with boost. I understand the desire for top end in our cars but why would you pick a .63 A/R over a .83 or whatever A/R? Is the peak really that BIG of a difference?

The GT28RS was designed around the Miata, but adapted well to the Sentra. Remember that ugly brown 'disco brown' Sentra (hence disco potato) that was in every magazine ever 7ish years back?

Sure you can always make more power with boost...but you loose response. I'd take a faster spooling 400 hp anyday over a laggy 450. The numbrs may impress simple people, but it's all about performance in my spetrum.

A/R on the exhaust side is extremely important. If an engine doesn't breath alot, why run a big a/r and loose velocity? Run a smaller one, on a bigger compressor to make some good power. And is the peak difference that much? Not really...exhaust A/R in the 'generic sense' really doesn't in 'same family' turbos...not enough to make up for the lost spool up time. Now if you're throwing a turbo on a big cube car, then yes, you will then fight smaller A/R's choking motors.

Originally Posted by jspaeth

From the results I've seen/heard, 0.63 vs 0.86 is maybe 500 RPM difference in spool up time, but I think the 0.86 will keep breathing for at least another 500 RPM higher than the other one.

Again, high RPMs is good, because you always want to be in the lowest gear possible at a given speed (given that the torque is not dropping off super fast).

Yep. 500 to 800 rpm woth of spool up, with a 10-15 hp gain sometimes. To me, that extra hp isn't worth the loss of response, especially with a smaller frame turbo.

[jspaeth]

Originally Posted by codyace

While I can grasp your point, wouldn't we also need to figure in a 'time vs RPM' aspec to this? Having more power in a gear is nice, but lets just assume 3rd gear is a 2.5 ratio, and 4 is a 1.0. Even though you'd think the mechanic advantage in power production vs gear would be better in 3rd, could we also not argue that the time in gear in that 1.0 4th be better for total speed? (If this makes any sense)

Or is it just another factor in it all? Or am I just completly wrong hehe.

I could be wrong, but my perception of Newton's laws is that the fastest way to get from point A to point B is to maximize the INTEGRAL of acceleration over the entire trajectory.

This essentially means that you want the most possible acceleration at any point in time possible.

I have done the calculations based upon my dyno chart (and other peoples' will be similar)...

For example.....


Let's say my "dyno" shows that I make 300 ft-lbs at 6000 RPM and 250 ft-lbs at 8000 RPM.



If you do the caluclations, you would find the following "theoretical" accelerations in each gear (in ft/sec^2)...with stock SR/KA tranny and stock USDM 240 4.083 final drive:

6000 RPM (peak torque)

1 - 42.39
2 - 24.27
3 - 16.58
4 - 12.68
5 - 9.68

8000 RPM

1 - 35.81
2 - 20.51
3 - 14.10
4 - 10.78
5 - 8.18


Notice that the acceleration at redline in any gear is ALWAYS higher than the acceleration in the lower gear at the lower RPM (even at peak torque in that lower gear...).


This means that the OPTIMAL way to get from point A to point B fastest is to redline EVERY gear.


Now, in some cars, the torque drops off MUCH faster before redline....in CERTAIN scenarios, it MAY be beneficial to shift before redline.

This would require that the torque made at the NEW RPM (upon upshifting) multiplied by the ratio of the NEW GEAR RATIO/OLD GEAR RATIO is higher than the torque being made if you had just stayed in the lower gear.

Example:

2nd gear is 1.902
3rd gear is 1.308

Ratio of 2nd/3rd is 1.45!!!!

This means if you are in 2nd, and your torque starts dropping off....for it to be beneficial for you to upshift, the NEW torque you would make in 3rd upon upshifting would need to be 45% higher than the current torque you are making in 2nd.

So even if your torque drops off quickly and you are only making 200 ft-lbs in 2nd, you would need to make 290 ft-lbs at whatever RPM you WOULD be in 3rd if you upshifting in order for it to be beneficial to shift.

Summary

Like I said....with GT2871R setups and the shapes of the torque curves they produce out to, say, 8000 RPM or maybe even 8500 RPM, it is ALWAYS beneficial to just keep revving out in the lower gear....



As you can see, even at redline, the lower gear always has better acceleration then the next highest gear at it's PEAK acceleration point (6000 RPM)

[TurboB15sentra]

Originally Posted by HemiCharger

Yeah but wasn't the GT28RS designed specifically for FWD sentra's? I have not seen any RWD SR guys running them. I like everyone else on here is running a GT2871R. I wish I would have gotten the GT3076 instead. You can always make more power with boost. I understand the desire for top end in our cars but why would you pick a .63 A/R over a .83 or whatever A/R? Is the peak really that BIG of a difference?

Nope.. The GT28RS, will easily run on a RWD SR motor. Dave Coleman has one in his S13. It was originally tested on a Miata, and had great results. Rob Cadle introduced the turbo to JWT/Kojima, etc.. (the FWD SR crowd) Nissan's Steve Mitchell actually gave JWT a proto (no VIN) 2000 Sentra SE, to build with a GT28RS. The car was nicknamed the "Disco Potato", because of it's chameleon paint job, and the fact that it looks bulky/shaped like a potato. So, the name "Disco Potato Turbo" stuck to the GT28RS, and has been that way ever since.



This car was well rounded, and was brutally quick in the twisties.

Travis