just a rebuild - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

*SaintlyCharBoy* · 02-05-2002, 01:28 PM

i am, as i have said for a while now, looking to buy 2 cars, one with hella lots of miles, one with slightly fwer and a 5 speed

but, if i want to up compression to squeeze some more horses out of the KA (dohc), what kind of numbers should i look for, i want a relaible daily driver, so i am thinking about going compression pistons and rings with forged arms...

what are your thoughts on overboring?

and what kind of prices should i be looking at?

any help is greatly appreciated
Sean

oh... would i need to upgrade cams?

*sykikchimp* · 02-05-2002, 03:50 PM

I would not recommend boring out the 240.  The cylinder walls a Very skinny as is.  Hopwever I seen people bore it out to like 2.440 liters.

Miles on the KA block don't really matter seeing as it is Iron, and pretty much bullet proof from the factory.  You will want to replace the crack, pistons, rods, etc. If it's miles are too high.  For the reliable High compression engine, everything should be forged.  

As for upgraded Cams.  PDM makes some and so does Jim Wolf Technologies.  Nismo too.  (nismo's is just two 91' exhaust cams.  one repinned to fit the intake side)  I've heard the JWT's are nice because there is almost no low end torque loss and they are made from blanks, whereas you get more HP on the top end with the PDM's, but loss of low end torque, and they are re-grinds.

Depending on how much work you wanna do, you can get around 250 hp out of an NA 240 with about 7-10k from what I hear.  That includes EVERYHTING.  Sorry I can't be more specific.

**West** · 02-05-2002, 04:20 PM

A cheap alternative to running higher compression is to get your 5-Speed DOHC and swap in some pistons from a SOHC into your car. It will increase it to 10.5.1(could be wrong) and give about a 5% gain. Not alot but its alot ezier and cheaper and if you run higher compression then that on the street then have fun stopping and going out of the way for 103 octane gas every time you need gas. Its just not very practical for a daily driver. Even with the higher compression I would run a higher octane like 95, and in states like mine that is hard to find. You will have to stock up on octane booster for when you fill up.

misnomer · 02-05-2002, 04:42 PM

Don't bore out the engine, it will screw with your cooling system, something you don't want in a daily driver. Compression all depends on what you want to put into the car. 10.0 to 1, give or take, is about as high as you'd want to go to prevent detonation on pump gas, go much higher and you'll need to use additives to increase the octane level. If you're increasing compression, you'd prolly want to combine that with new cams. Add on top of that your intake, headers, exhaust, and an ecu reprogramming, and you will prolly have some decent performance.

wherezmytofu · 02-05-2002, 04:51 PM

</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote </td></tr><tr><td id="QUOTE">Quote: from misnomer on 4:42 pm on Feb. 5, 2002
Don't bore out the engine, it will screw with your cooling system, something you don't want in a daily driver. Compression all depends on what you want to put into the car. 10.0 to 1, give or take, is about as high as you'd want to go to prevent detonation on pump gas, go much higher and you'll need to use additives to increase the octane level. If you're increasing compression, you'd prolly want to combine that with new cams. Add on top of that your intake, headers, exhaust, and an ecu reprogramming, and you will prolly have some decent performance.</td></tr></table><span id='postcolor'>

arg!!!!!!!! im sick of this...i's 12.5: 1 on 93 octane, the nsx is 10.6:1 and runs on 93 octane....look at the new rsx ......11.5 stock............

wherezmytofu · 02-05-2002, 04:55 PM

</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote </td></tr><tr><td id="QUOTE">Quote: from WeST on 4:20 pm on Feb. 5, 2002
A cheap alternative to running higher compression is to get your 5-Speed DOHC and swap in some pistons from a SOHC into your car. It will increase it to 10.5.1(could be wrong) and give about a 5% gain. Not alot but its alot ezier and cheaper and if you run higher compression then that on the street then have fun stopping and going out of the way for 103 octane gas every time you need gas. Its just not very practical for a daily driver. Even with the higher compression I would run a higher octane like 95, and in states like mine that is hard to find. You will have to stock up on octane booster for when you fill up.
</td></tr></table><span id='postcolor'>

i dun want 2 go against a mod but.........are you sure that you can take pistons off a soch and put it in a doch because the soch is 3 valves per cylinder and the doch is 4 valves per cylinder, the valve relief on the soch pistons should be different then the doch pistons...so the exhuast valves would line up and will hit.......

edit: west bought the idea that ka pistons are not domed....if thats true then there is no problem <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/biggrin.gif" border="0" valign="absmiddle" alt=':D'>

(Edited by wherezmytofu at 5<img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/wow.gif" border="0" valign="absmiddle" alt=':0'>8 pm on Feb. 5, 2002)

misnomer · 02-05-2002, 05:01 PM

Tofu: I was simply going off what my auto tech instructor mentioned. He has an old Pontiac that runs on 10.5:1 compression, and it detonates when he gets down to lower altitudes.

wherezmytofu · 02-05-2002, 05:04 PM

i know four itr the run stock except for 12.5 on 93 octane...also nsx,itr, s2k, rsx, have >10.1:1 stock i guess the timing is just different

(Edited by wherezmytofu at 5<img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/wow.gif" border="0" valign="absmiddle" alt=':0'>6 pm on Feb. 5, 2002)

whateverjames · 02-05-2002, 05:13 PM

</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote </td></tr><tr><td id="QUOTE">Quote: from wherezmytofu on 5:55 pm on Feb. 5, 2002
</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote </td></tr><tr><td id="QUOTE">Quote: from WeST on 4:20 pm on Feb. 5, 2002
A cheap alternative to running higher compression is to get your 5-Speed DOHC and swap in some pistons from a SOHC into your car. It will increase it to 10.5.1(could be wrong) and give about a 5% gain. Not alot but its alot ezier and cheaper and if you run higher compression then that on the street then have fun stopping and going out of the way for 103 octane gas every time you need gas. Its just not very practical for a daily driver. Even with the higher compression I would run a higher octane like 95, and in states like mine that is hard to find. You will have to stock up on octane booster for when you fill up.
</td></tr></table><span id='postcolor'>

i dun want 2 go against a mod but.........are you sure that you can take pistons off a soch and put it in a doch because the soch is 3 valves per cylinder and the doch is 4 valves per cylinder, the valve relief on the soch pistons should be different then the doch pistons...so the exhuast valves would line up and will hit.......

edit: west bought the idea that ka pistons are not domed....if thats true then there is no problem <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/biggrin.gif" border="0" valign="absmiddle" alt=':D'>

(Edited by wherezmytofu at 5<img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/wow.gif" border="0" valign="absmiddle" alt=':0'>8 pm on Feb. 5, 2002)
</td></tr></table><span id='postcolor'>

i've heard of it being done before. you have to grind down the tops of the pistons to get the 10.5:1 compression

240meowth · 02-05-2002, 06:58 PM

i was talking to  my friend about the 10.5:1 and i was wondering what he thinks, he told me that the new celica runs 11.5 (not very sure), so i'd assume it'll be fine

White240sx · 02-05-2002, 09:43 PM

</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote </td></tr><tr><td id="QUOTE">Quote: from SaintlyCharBoy on 1:28 pm on Feb. 5, 2002
any help is greatly appreciated
Sean</td></tr></table><span id='postcolor'>

Give Rebello Racing a call. They build N/A KA's and talking to them will be more enlightening than trying to get answers on a forum.

*BTW: I would recommend calling them only if you are serious about buying (willing to spend around $3000 or more). I wouldn't figure that they would be opposed to answering questions, but I’m fairly certain they stay busy over there so make it worth their time. I don't mean to sound gruff, but do you know what I’m saying?

*sykikchimp* · 02-06-2002, 02:54 PM

those car can run those compression rations on 93 octane b/c the have much different MAF's, and Fuel systems, and timing, and cams, different head designs, etc.  Without modifying the Fuel and air management in the car, (and several other factors) you WILL experience detonate with higher comp. pistons.  Thats why it's a lot more work than just throwing in different compression pistons.  

I know thats not any help, but I don't want you to leave thinking this is a simple as buying new pistons, cracking open the engine, and poping in new pistons

geeaj · 02-06-2002, 03:48 PM

I would have to agree with the last post. Just because a Toyota Celica is running high compression with 93 octane (compression higher then the 10.5:1 planned for the ka24 rebuild), doesn't mean jack.

The Toyota has different fuel mapping and air/fuel programming then our ECUs. I suspect that the algorithms used retard timing during certain scenarios so that detonation will not occur.

What this means is that the compression isn't static, it changes based on the variables such as throttle input, air temperature, etc.

You can very well run 10.5:1 compression on street gas and still run like shit, your car pingin' for dear life on WOT. It all depends on the fuel/air management.

Given your situation, give Rick at Rebello motors a call. This summer, I plan on having them build a N/A ka24e running high compression (but not as high as what you guys are thinking).

Another aspect to consider is using forged versus cast pistons. You can save the money on forged pistons and use the money for porting/polishing (only worthwhile if ka24e...ka24de head are siamesed together so there isn't much metal to begin with.) *thx dpro/dave for that tidbit of info*

If your are not going turbo, forged pistons ARE NOT NEEDED. The cons of forged vs cast for N/A applications, simply outway the pros.

For one, there is cost. That is self explanatory.

Forged pistons have a very different expansion rate vs cast pistons. What does this mean in real day to day driving? Your motor will be noisier, it will not be as smooth.

Do yourself a favor and give the Rebello guys or Sunbelt motors a call.

02-05-2002, 01:28 PM	#1
SaintlyCharBoy Premium Member Join Date: Jan 2002 Location: Bow, NH Age: 43 Posts: 849 Trader Rating: (1) Feedback Score: 1 reviews	i am, as i have said for a while now, looking to buy 2 cars, one with hella lots of miles, one with slightly fwer and a 5 speed but, if i want to up compression to squeeze some more horses out of the KA (dohc), what kind of numbers should i look for, i want a relaible daily driver, so i am thinking about going compression pistons and rings with forged arms... what are your thoughts on overboring? and what kind of prices should i be looking at? any help is greatly appreciated Sean oh... would i need to upgrade cams?

02-05-2002, 03:50 PM	#2
sykikchimp WOW addicted Join Date: Dec 2001 Location: the moon Age: 44 Posts: 6,525 Trader Rating: (0) Feedback Score: 0 reviews	I would not recommend boring out the 240.  The cylinder walls a Very skinny as is.  Hopwever I seen people bore it out to like 2.440 liters. Miles on the KA block don't really matter seeing as it is Iron, and pretty much bullet proof from the factory.  You will want to replace the crack, pistons, rods, etc. If it's miles are too high.  For the reliable High compression engine, everything should be forged.   As for upgraded Cams.  PDM makes some and so does Jim Wolf Technologies.  Nismo too.  (nismo's is just two 91' exhaust cams.  one repinned to fit the intake side)  I've heard the JWT's are nice because there is almost no low end torque loss and they are made from blanks, whereas you get more HP on the top end with the PDM's, but loss of low end torque, and they are re-grinds. Depending on how much work you wanna do, you can get around 250 hp out of an NA 240 with about 7-10k from what I hear.  That includes EVERYHTING.  Sorry I can't be more specific.

02-05-2002, 04:20 PM	#3
West OMNOMNOMNOM Join Date: Dec 2000 Location: Denver, CO Age: 44 Posts: 6,456 Trader Rating: (0) Rides Gallery: West Feedback Score: 0 reviews	A cheap alternative to running higher compression is to get your 5-Speed DOHC and swap in some pistons from a SOHC into your car. It will increase it to 10.5.1(could be wrong) and give about a 5% gain. Not alot but its alot ezier and cheaper and if you run higher compression then that on the street then have fun stopping and going out of the way for 103 octane gas every time you need gas. Its just not very practical for a daily driver. Even with the higher compression I would run a higher octane like 95, and in states like mine that is hard to find. You will have to stock up on octane booster for when you fill up.

02-05-2002, 04:42 PM	#4
misnomer Nissanaholic! Join Date: Jul 2001 Location: Nevada Posts: 2,293 Trader Rating: (0) Feedback Score: 0 reviews	Don't bore out the engine, it will screw with your cooling system, something you don't want in a daily driver. Compression all depends on what you want to put into the car. 10.0 to 1, give or take, is about as high as you'd want to go to prevent detonation on pump gas, go much higher and you'll need to use additives to increase the octane level. If you're increasing compression, you'd prolly want to combine that with new cams. Add on top of that your intake, headers, exhaust, and an ecu reprogramming, and you will prolly have some decent performance.

02-05-2002, 04:51 PM	#5
wherezmytofu BANNED Join Date: Nov 2001 Posts: 1,873 Trader Rating: (0) Feedback Score: 0 reviews	</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote </td></tr><tr><td id="QUOTE">Quote: from misnomer on 4:42 pm on Feb. 5, 2002 Don't bore out the engine, it will screw with your cooling system, something you don't want in a daily driver. Compression all depends on what you want to put into the car. 10.0 to 1, give or take, is about as high as you'd want to go to prevent detonation on pump gas, go much higher and you'll need to use additives to increase the octane level. If you're increasing compression, you'd prolly want to combine that with new cams. Add on top of that your intake, headers, exhaust, and an ecu reprogramming, and you will prolly have some decent performance.</td></tr></table><span id='postcolor'> arg!!!!!!!! im sick of this...i's 12.5: 1 on 93 octane, the nsx is 10.6:1 and runs on 93 octane....look at the new rsx ......11.5 stock............

02-05-2002, 04:55 PM	#6
wherezmytofu BANNED Join Date: Nov 2001 Posts: 1,873 Trader Rating: (0) Feedback Score: 0 reviews	</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote </td></tr><tr><td id="QUOTE">Quote: from WeST on 4:20 pm on Feb. 5, 2002 A cheap alternative to running higher compression is to get your 5-Speed DOHC and swap in some pistons from a SOHC into your car. It will increase it to 10.5.1(could be wrong) and give about a 5% gain. Not alot but its alot ezier and cheaper and if you run higher compression then that on the street then have fun stopping and going out of the way for 103 octane gas every time you need gas. Its just not very practical for a daily driver. Even with the higher compression I would run a higher octane like 95, and in states like mine that is hard to find. You will have to stock up on octane booster for when you fill up. </td></tr></table><span id='postcolor'> i dun want 2 go against a mod but.........are you sure that you can take pistons off a soch and put it in a doch because the soch is 3 valves per cylinder and the doch is 4 valves per cylinder, the valve relief on the soch pistons should be different then the doch pistons...so the exhuast valves would line up and will hit....... edit: west bought the idea that ka pistons are not domed....if thats true then there is no problem <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/biggrin.gif" border="0" valign="absmiddle" alt=':D'> (Edited by wherezmytofu at 5<img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/wow.gif" border="0" valign="absmiddle" alt=':0'>8 pm on Feb. 5, 2002)

02-05-2002, 05:01 PM	#7
misnomer Nissanaholic! Join Date: Jul 2001 Location: Nevada Posts: 2,293 Trader Rating: (0) Feedback Score: 0 reviews	Tofu: I was simply going off what my auto tech instructor mentioned. He has an old Pontiac that runs on 10.5:1 compression, and it detonates when he gets down to lower altitudes.

02-05-2002, 05:04 PM	#8
wherezmytofu BANNED Join Date: Nov 2001 Posts: 1,873 Trader Rating: (0) Feedback Score: 0 reviews	i know four itr the run stock except for 12.5 on 93 octane...also nsx,itr, s2k, rsx, have >10.1:1 stock i guess the timing is just different (Edited by wherezmytofu at 5<img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/wow.gif" border="0" valign="absmiddle" alt=':0'>6 pm on Feb. 5, 2002)

02-05-2002, 05:13 PM	#9
whateverjames Nissanaholic! Join Date: Jul 2001 Location: St. Louis Age: 45 Posts: 2,263 Trader Rating: (0) Feedback Score: 0 reviews	</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote </td></tr><tr><td id="QUOTE">Quote: from wherezmytofu on 5:55 pm on Feb. 5, 2002 </span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote </td></tr><tr><td id="QUOTE">Quote: from WeST on 4:20 pm on Feb. 5, 2002 A cheap alternative to running higher compression is to get your 5-Speed DOHC and swap in some pistons from a SOHC into your car. It will increase it to 10.5.1(could be wrong) and give about a 5% gain. Not alot but its alot ezier and cheaper and if you run higher compression then that on the street then have fun stopping and going out of the way for 103 octane gas every time you need gas. Its just not very practical for a daily driver. Even with the higher compression I would run a higher octane like 95, and in states like mine that is hard to find. You will have to stock up on octane booster for when you fill up. </td></tr></table><span id='postcolor'> i dun want 2 go against a mod but.........are you sure that you can take pistons off a soch and put it in a doch because the soch is 3 valves per cylinder and the doch is 4 valves per cylinder, the valve relief on the soch pistons should be different then the doch pistons...so the exhuast valves would line up and will hit....... edit: west bought the idea that ka pistons are not domed....if thats true then there is no problem <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/biggrin.gif" border="0" valign="absmiddle" alt=':D'> (Edited by wherezmytofu at 5<img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/wow.gif" border="0" valign="absmiddle" alt=':0'>8 pm on Feb. 5, 2002) </td></tr></table><span id='postcolor'> i've heard of it being done before. you have to grind down the tops of the pistons to get the 10.5:1 compression

02-05-2002, 06:58 PM	#10
240meowth Nissanaholic! Join Date: Dec 2001 Location: torrance, ca Age: 41 Posts: 2,407 Trader Rating: (4) Feedback Score: 4 reviews	i was talking to  my friend about the 10.5:1 and i was wondering what he thinks, he told me that the new celica runs 11.5 (not very sure), so i'd assume it'll be fine

02-05-2002, 09:43 PM	#11
White240sx Zilvia Member Join Date: Nov 2001 Posts: 219 Trader Rating: (0) Feedback Score: 0 reviews	</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote </td></tr><tr><td id="QUOTE">Quote: from SaintlyCharBoy on 1:28 pm on Feb. 5, 2002 any help is greatly appreciated Sean</td></tr></table><span id='postcolor'> Give Rebello Racing a call. They build N/A KA's and talking to them will be more enlightening than trying to get answers on a forum. *BTW: I would recommend calling them only if you are serious about buying (willing to spend around $3000 or more). I wouldn't figure that they would be opposed to answering questions, but I’m fairly certain they stay busy over there so make it worth their time. I don't mean to sound gruff, but do you know what I’m saying?

02-06-2002, 02:54 PM	#12
sykikchimp WOW addicted Join Date: Dec 2001 Location: the moon Age: 44 Posts: 6,525 Trader Rating: (0) Feedback Score: 0 reviews	those car can run those compression rations on 93 octane b/c the have much different MAF's, and Fuel systems, and timing, and cams, different head designs, etc.  Without modifying the Fuel and air management in the car, (and several other factors) you WILL experience detonate with higher comp. pistons.  Thats why it's a lot more work than just throwing in different compression pistons.   I know thats not any help, but I don't want you to leave thinking this is a simple as buying new pistons, cracking open the engine, and poping in new pistons

02-06-2002, 03:48 PM	#13
geeaj Zilvia Junkie Join Date: Dec 2001 Posts: 357 Trader Rating: (0) Feedback Score: 0 reviews	I would have to agree with the last post. Just because a Toyota Celica is running high compression with 93 octane (compression higher then the 10.5:1 planned for the ka24 rebuild), doesn't mean jack. The Toyota has different fuel mapping and air/fuel programming then our ECUs. I suspect that the algorithms used retard timing during certain scenarios so that detonation will not occur. What this means is that the compression isn't static, it changes based on the variables such as throttle input, air temperature, etc. You can very well run 10.5:1 compression on street gas and still run like shit, your car pingin' for dear life on WOT. It all depends on the fuel/air management. Given your situation, give Rick at Rebello motors a call. This summer, I plan on having them build a N/A ka24e running high compression (but not as high as what you guys are thinking). Another aspect to consider is using forged versus cast pistons. You can save the money on forged pistons and use the money for porting/polishing (only worthwhile if ka24e...ka24de head are siamesed together so there isn't much metal to begin with.) thx dpro/dave for that tidbit of info If your are not going turbo, forged pistons ARE NOT NEEDED. The cons of forged vs cast for N/A applications, simply outway the pros. For one, there is cost. That is self explanatory. Forged pistons have a very different expansion rate vs cast pistons. What does this mean in real day to day driving? Your motor will be noisier, it will not be as smooth. Do yourself a favor and give the Rebello guys or Sunbelt motors a call.