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View Full Version : Raising compression on sr20det?



sillbeer
10-10-2002, 07:56 PM
The stock headgasket is .8mm on the sr20det and the compression is 8.5:1. I was curious as to what the compression would be if I where to install a .6mm metal gasket? Would I see any noticeable performance increases? What would be a reasonable boost level with an hks 2540, 550's, and z32 mafs? Would it even be worthwhile? It just made me curious when I read the post about greasers car with the high compression pistons and a slightly lower boost level.

neo_rambo
10-10-2002, 08:04 PM
you want to lower compression for a turbo application like a sr20det. you would want to increase the compression for a Na application but a turbo application you want lower compression so you could run higher boost..Am I right ASAD mister all knowing about silvias?

sillbeer
10-10-2002, 08:19 PM
I know the general rule of thumb is to lower compression and boost high, but I was just reading greasers post where he had the 9:1 pistons. I was just thinking of a slightly cheaper way of doing it instead of buying the wiseco pistons that he has. I'm also not looking to make anywhere near the same hp either. Somewhere around 340rwhp or so would make me happy and I know you can achieve that from some cams and a 1.4mm head gasket. I just wanted to do it a little differently. Maybe...Is this a smart way of doing it or would it be better to go the other route?

Greaser_
10-10-2002, 09:08 PM
neo rambo you are correct only in the fact that you state
"lower the compression to run more boost"

im kinda miffed that this is forcefed by alot of people when they hear turbo they think......turbo=Low compression.

His goal is not to boost high. it it to make power with said GT2540.

You can raise static compression with a thinner headgasket. How much you will have to measure for yourself with some simple fluid math before and after the HG install. i doubt it will be much. Higher compression does (at the limits) reduce the amount of boost you can run on pump gas. But why limit the power potential. I laugh at you if you lowered your compression to run 20psi on pump gas and make xx hp when i raise my compression to run higher octane with same boost and make 100hp more than you. if i was at that xx hp level where you would be at 20psi i would be at 15 maybe. ALOT better for the motor, the compressor is most likely more efficient all is well, thats why my setup makes more power (theory here not MY motor being quoted on)

raising compression has these pros:
better throttle response
higher torque off boost
higher torque on boost, higher hp on boost
lower specific fuel consumption(means less fuel at the same boost a lower compression motor would need)
higher hp potential

cons are:
less boost on pump gas
um.....


why run 8:1 compression with 25psi for 400hp when you could run 9 or 10:1 compression with 15-20psi for 400hp you could probably still get away with pump gas for said example above.


oh and i only raised it to 9:1. i dont know what it can be raised to with just pistons. There has to be some rotational testing with the cams in place and some putty, but for me thats way off. I fore see only 10:1 pistons could be used then the exta point i want will have to be chamber and valve additions. as an example: a freind with a b16 honda had stock motor with 7lbs for 244hp. dropped compression to 8:1 or 2.5 points and he got 243hp @12psi HAHHAHAHAAHAHAHHAHHAHHAHAHAHAHAHAHAHAHAHAH

Tran_Works
10-10-2002, 09:14 PM
Well I don't know what the compression would be if you got a 6mm gasket but I am assuming this is going to be street driven, so I think it would be safer to just get a slightly thicker gasket since it wont make that big of a difference and run a little bit of extra boost to compensate(sp?) for the extra few ponies or just keep the stock gasket cause i think its capable of withstanding 350hp. I think it would be safer to run with the thicker gasket since you only want around the 350 mark which is not to much to ask for especially with the hks 2540 turbo and 550cc injectors.

Tran_Works
10-10-2002, 09:22 PM
nicely said Greaser, beat me too it, but the only reason I said the things I said is because hes talking about a gasket and I don't think he wants pistons like he stated before but you are entirely correct on your statement.

97 S14
10-10-2002, 11:12 PM
9:1 Wiesco pistons are very popular for the 200SX/Sentra guys when turbocharging their FWD SR20DE motor's. I have a set for my SR.

garageEPIKtuning
10-11-2002, 12:51 AM
Destin,
This is exactly the way we went on the built GSR turbo that we have been working on for the last few months. I wont go into the gory details, but we actually built it with 9.5:1 JE pistons. We are using the AEM EMS though, so that is the only way that I would ever consider turbo'ing with that high of a compression ratio though. We have vicelike control over every parameter of the engine, especially timing. I dont think the Power FC controls timing, does it?

Anyway, the results on the GSR motor were satisfactory so far, if surprising. At .7 bar, only revving to 5600rpm on the dyno, we have made 319.2hp and 295.7tq. The 440s that we were using were very inadequate and went dead lean just into VTEC...picking up some 1000ccs and heading back to see what we can pull out of it. I havent even calibrated the Typhoon boost solenoid yet. I cant wait to get the bigger injectors and get back on the dyno, so we can rev all the way to 9k. I'm expecting 400hp at 7bar. http://forums.freshalloy.com/ubbthreads/images/icons/grin.gif

So, in a roundabout way, there is what I think. It can be done, but without full engine mgmt, like Greaser has, I would retard the static ign timing a degree or two for safety.

Good luck,
Jeff

asad
10-11-2002, 09:23 AM
</font><blockquote><font class="small[/img]In reply to:</font><hr />
I dont think the Power FC controls timing, does it?


[/QUOTE]

You can change the ignition timing with the PowerFC.

Asad

SRFiveTen
10-11-2002, 11:48 AM
most headgasket manufacturers advertize their 1.1~1.2mm thick gasket as the stock replacement.

by going with 0.6mm gasket on 86mm bore sr20det, they estimate the compression ratio to rise to 8.7:1 ~ 9.2:1 depending on the manufacturer.
best bet will be to calculate from actual measurements.

i believe when you go with different thickness gasket, you will need to compensate for the change in crank sprocket to cam sprockets geometry by investing in a set of adjustable cam gears.

when combining a thinner head gasket and higher than stock lift camshafts, you should check for valves to piston clearance.

sillbeer
10-11-2002, 04:28 PM
Thanks for all the imput. I was planning on getting a set of hks cam gears and 260-264 degree cams. I may have to go with some 256's for the clearance which would probably be adequate.

Greaser_
10-11-2002, 05:28 PM
actually go with whatever cam you want. The SR pistons are dished from the factory. the pistons i have are flat top (hence the raise in compression) and i have JWT S4 cams with no problem specs are 264degrees at 11.5mm lift.

i'm sure youll be fine, theres no way a thinner hg will reduced the amount of clearance the same as a set of flat top pistons.

SRFiveTen
10-11-2002, 05:41 PM
i think best advice here or with any other rebuild project would be, "measure, measure again. check, check again."

probably adequate, should be ok, oh i'm sure,,,, just don't go well with high performance engine, imo.

what are the famous words spoken before we hear "oh sh!t"?

terabyte
10-12-2002, 12:32 AM
Given this info about less boost more compression. Would it be better to get the N/A VG30E over the turbo VG30ET for my swap?

sillbeer
10-12-2002, 04:48 PM
Can anyone give me a formula for figuring out what the clearance would be for this situation? I don't want to go and buy some cams, get them installed and then do the checks with the head on and find out they won't fit. I will do the checks anyways, I would just like to figure this out ahead of time. I found a post here that had all the specs for your car Greaser. You didn't list what head gasket your running? Just curious.

ruf4play
10-12-2002, 05:10 PM
Like mentioned before, this is not for those afraid of blowing up their motor. The tuning window is going to get MUCH smaller.

I believe the correct answer for SRFiveTen's question is "Hey, check THIS out!"

sillbeer
10-12-2002, 05:20 PM
I'm not afraid of blowing my motor at all. SR's are a dime a dozen here. Just wanted to check out some #'s before I went out and bought the wrong stuff. Destin

ruf4play
10-12-2002, 05:25 PM
In that case, best of luck to you. I've been kicking around the thought of using a 0.6mm gasket too. Should bump compression up about 8.9-9.1.

Super13
10-12-2002, 05:30 PM
is the apexi stuff in japan sold on the street cheaper then what the common dealer asks for here &lt;need figures or guestimate?

asad
10-12-2002, 06:24 PM
You can guesstimate what thickness gasket will cause interference problems by finding out what cam lift value will cause problems. Subtract from that the stock cam lift and you'll get an idea of how much thinner a headgasket you can run. If you're running an aftermarket cam you can take that into account too by adding that difference in.

I realize this won't be 100% accurate because the higher-lift cams also tend to have longer durations, but that's OK because it'll give you a conservative estimate (I think).

Asad

J&J_SR20DET
10-12-2002, 10:44 PM
hii greaser i am impressed at your thoery so if a have some money and get my bottemend done for the sr20det like say get the motor bored out to like close to 2.2 liter and get forged pistons but stock rods just heat them. and run 9:1 compression with a big turbo and run it at like 15 psi will that give me close to 400hp and what about the torque keeping in mind i have stainless plumbing and sparco intercooler and a custom 3' down pipe head port and polish 550cc injectors and ecu retuned and the rest is stock. what will you sugest than can i run pump gas at 15psi and have no detatoion.

J&J_SR20DET
10-12-2002, 10:49 PM
oh yeah forgot to add i am also using trust 1.2mm head gasket will that make a difference

YellowS14
10-13-2002, 05:17 AM
"get the motor bored out to like close to 2.2 liter and get forged pistons but stock rods just heat them"

:::::heheheheh:::::: damn its early

White_240sx
10-13-2002, 09:58 AM
</font><blockquote><font class="small[/img]In reply to:</font><hr />
oh yeah forgot to add i am also using trust 1.2mm head gasket will that make a difference

[/QUOTE]

How are you going to use a Trust head gasket with the ~91mm bore of your hypothetical 2.2 liter?

J&J_SR20DET
10-13-2002, 04:31 PM
bore out the metal gasket to 2.2L why what do you have in mind.

J&J_SR20DET
10-13-2002, 04:32 PM
whats so funny troy what are you laughin at.

asad
10-13-2002, 04:34 PM
</font><blockquote><font class="small[/img]In reply to:</font><hr />
whats so funny troy what are you laughin at.

[/QUOTE]

He's laughing at the fact that you don't know what you're talking about. Running a 91mm bore on an SR20 will leave VERY little space between the cylinder walls.

The most common way to get a 2.2L SR is to run a stroker kit that lengthens the stroke (with a different crankshaft) and a slight overbore.

Asad

J&J_SR20DET
10-13-2002, 04:39 PM
hummmmmm sounds interesting
first of all i dont want to spend like 5000 bucks on a toda storker kit second of all i was wondering if i want to bore it to like 2.2l if i get custom pistons and rods will they fit on the stock crank though
what is the math

J&J_SR20DET
10-13-2002, 04:47 PM
the stock bore* stroke is 86 *86 right how much can i increase the bore with changing the crank you know what i mean

asad
10-13-2002, 05:12 PM
No, I don't know what you mean, because you're not making any sense. The bore has nothing to do with the crank. If you get custom pistons and rods, you get them made so they work with the stock crank. That's the beauty of "custom" parts.

If you resleeve the block, you can probably go to ~88-89mm. An 89mm x 86mm SR will give you 2140cc.

Asad

J&J_SR20DET
10-13-2002, 07:14 PM
hi asad thanks for your advice. anyways so you mean 89mm * 86mm sr will give 2140cc. that is good which means that i can use 89mm piston and use the same rod of 86 mm what will be the compresson will it be the same at 8.5:1 or will it increase to may be 8.6:1. and how did you calculate 2140cc thanks for you help http://forums.freshalloy.com/ubbthreads/images/icons/smile.gif))

john

J&J_SR20DET
10-13-2002, 07:16 PM
do you have any idea how much new seleves will cost for a 89mm bore

J&J_SR20DET
10-13-2002, 07:26 PM
are you sure that sr motor have seleves because i know ka do but i am not sure if sr motors have seleves in the cylinder walls

White_240sx
10-13-2002, 07:32 PM
</font><blockquote><font class="small[/img]In reply to:</font><hr />
1 can use 89mm piston and use the same rod of 86 mm what will be the compresson will it be the same at 8.5:1 or will it increase to may be 8.6:1

[/QUOTE]

Your compression ratio will be governed by the shape of the piston crowns, head gasket thickness, and combustion chamber volume you use, not bore and/or stroke.

</font><blockquote><font class="small[/img]In reply to:</font><hr />
and how did you calculate 2140cc

[/QUOTE]

Stroke * Pi * Bore^2

White_240sx
10-13-2002, 07:33 PM
Neither the SR nor the KA have sleeved cylinder walls.

(apparently the SR does have OE sleeves, I stand corrected)

J&J_SR20DET
10-13-2002, 07:44 PM
thanks mason for you help you sound like a very knowlegable person http://forums.freshalloy.com/ubbthreads/images/icons/smile.gif))

J&J_SR20DET
10-13-2002, 07:50 PM
hi mason do you know about the jwt setup for the sr2Odet.

White_240sx
10-13-2002, 08:22 PM
I am sorry, I have no personal knowledge of it. Here is an old thread outlining it though.

http://forums.freshalloy.com/ubbthreads/showflat.php?Cat=&amp;Board=UBB9&amp;Number=45282&amp;Forum=UB B9&amp;Main=45282&amp;Search=true#Post45282

asad
10-13-2002, 08:33 PM
</font><blockquote><font class="small[/img]In reply to:</font><hr />
use the same rod of 86 mm

[/QUOTE]

&lt;sigh&gt;. The ROD is not 86mm. That's the stroke of the crankshaft. The SR20 rod is something like 136mm long.

Asad

SRFiveTen
10-14-2002, 12:55 PM
</font><blockquote><font class="small[/img]In reply to:</font><hr />
&lt;sigh&gt;.

[/QUOTE]

86mm x 86mm = 1998cc sr20, 87mm bore gasket
87mm x 86mm = 2044cc sr21, 88mm bore gasket
87mm x 91mm = 2163cc sr22, 88mm bore gasket

i learned of 87.5mm bore pistons for sr20, but never heard of 88 or bigger.

asad
10-14-2002, 01:12 PM
</font><blockquote><font class="small[/img]In reply to:</font><hr />
i learned of 87.5mm bore pistons for sr20, but never heard of 88 or bigger.

[/QUOTE]

The reason I say you can probably go to an 89mm piston is because the SR20 shares the same center-to-center bore spacing as the KA24...which has 89mm pistons. Custom 89mm-bore SR pistons would be no problem for any reputable piston company.

Asad

SRFiveTen
10-14-2002, 03:28 PM
</font><blockquote><font class="small[/img]In reply to:</font><hr />
Custom 89mm-bore SR pistons would be no problem for any reputable piston company

[/QUOTE]

why shell out on a set of pistons that won't work?
sr is aluminum block, not as strong as ka.
so, there just isn't enough support between the cylinders to accomodate big bore pistons.

tomei, toda, hks, apex-i, jun are reputable and do not offer pistons that don't work.
they've been doing this for a while.

when one has the means to bore and stroke his sr, wouldn't he look to get the best performance for his money?
how come there is no sr23 or sr24 or sr39?

asad
10-14-2002, 04:11 PM
Actually, looking at some pics of SR20 blocks, I can see why it won't work. It's not because the aluminum block isn't as strong -- it's because the sleeves don't actually touch each other since there's thin coolant passage between each cylinder sleeve.

One could possibly try and machine the block to accept a set of sleeves that butt against each other, like the ones Golden Eagle (and others?) make(s) for Hondas:
http://www.goldeneaglemfg.com/sleeves.htm
http://www.overboost.com/pix.asp?image=./images/464/full/DSCN8292.jpg
http://www.overboost.com/story.asp?id=464

If a system like that works for a 500-some-odd hp open-deck Honda motor, it should work on a closed-deck SR20, and would allow a larger-than-common overbore.

Asad

sillbeer
10-14-2002, 06:21 PM
I was also curious about cams. Why would you run a 264 in and a 268 ex? Also whats the benefit to getting cam gears? Are they worth the additional $300?

garageEPIKtuning
10-14-2002, 07:18 PM
adjustable cam gears are a necessity if you are considering the thinner head gasket. In order to keep the cam timing at spec due to the fact that it will be a few thou shorter.

dorimaster
10-14-2002, 09:28 PM
The reason to run a smaller camshaft for intake side is known to have a better idle. Usually 256 intake and 264 or 272 exhaust. Does anyone here run that? Is it true that on sr's that you need to have the same profiles or you need a shim or valve adjustment?

Pete

Super13
10-14-2002, 10:42 PM
that sounds painfull what exactly is a head readjustment?