Your compression, PSI, Turbo and Power.

[MetalSpikeRacing]

Hey guys,

As I get closer to buy parts for my engine, Im starting to get into choosing piston compression for the horse power that I'm looking for.

I was looking at my compression to be 9.5:1 until Chris at SOS recommended 9.2:1 . Im looking for no more than 500whp and I would like to know what psi would one have to run to reach those power numbers?

Hence the name of the tittle,what are your specs?
As my car sits right now:

Stock compression ---

Psi 9-10

WHP 452

Turbo PT-6266 BB

 

[E-Nough Logic]

They might be recommending the 9.2 not because of the compression ratio, but possible because the design of the piston is different, and inherently stronger, just a thought. You likely wouldn't notice a difference between 9.5 and 9.2 anyway. Since you track the car, I don't think a slightly lower compression is a bad idea unless you have e85 available.

My Engine:
Stock C/R
9psi
446whp
GTX3076r

 

[BATMANs]

9.2:1
Wiseco full skirt 2618 forged alloy
13psi on SOS SC
water intercooled
91 octane
430rwhp

Engine has been built to handle 700HP~ if I go turbo down the line.

 

[MetalSpikeRacing]

Thank you gentleman,
So I guess once the pistons are replaced with forged pieces the engine can take 12-14psi?

-MSR

 

[kookoo4nsx]

MSR, have you considered increasing the bore or stroke for more torque?

PS, last week you said you were good at 450 rwhp!!!!:smile:

 

[BATMANs]

Thank you gentleman,
So I guess once the pistons are replaced with forged pieces the engine can take 12-14psi?

-MSR

easily. I met a few people that are pushing 20psi with 9.2:1 CR. Dunno if that was with any trick fuel and/or conservative tune.

- - - Updated - - -

MSR, have you considered increasing the bore or stroke for more torque?

PS, last week you said you were good at 450 rwhp!!!!:smile:

It's pretty expensive to stroke a NSX. Certainly not as generous on the power to price ratio.

https://www.google.com/search?q=nsx+stroker+kit&oq=nsx+stroker+kit&aqs=chrome..69i57j0l3.7105j0&sourceid=chrome&ie=UTF-8#fp=22eba574080ae8c3&q=nsx+stroker+kit&tbm=shop&tbs=vw:l,p_ordd

And if u bore the correct way to do it is to have sleeves.

https://www.google.com/search?q=darton+nsx&oq=darton+nsx&aqs=chrome..69i57j0.1434j0&sourceid=chrome&ie=UTF-8#fp=22eba574080ae8c3&q=darton+sleeves+nsx&tbm=shop&tbs=vw:l,p_ordd

 

[v8killer]

Low comp. SOS rebuild (Pistons only) 9.2:1.

11psi 440rwhp 15.9psi 528rwhp.

PT-61 Turbo

Lots of track events (20+ weekends) and 27,000 miles since build.

 

[MetalSpikeRacing]

Ok, guys help me out here and lets be a little open.
If Im pushing 9-10psi on stock motor-compression and making 450whp, why would I not just keep the same compression 10.2:1, If I'm replacing pistons and head gaskets.My engine did not let go, Its just getting blow by and I want to refresh-rebuilt it closer to stock specs.

I'm afraid of losing spool time by dropping the compression that low, (9.2:1) Would stock compression with forged pistons at 10-12psi not be reasonable?

 

[BATMANs]

I would just keep that compression for 9-10 pis.

10-12 psi you may want to drop it down to 9.5-10 CR unless u have an adroit tuner.

 

[MetalSpikeRacing]

Yeah, seems like 9.5:1 is the compromise compression.
-MSR

 

[BATMANs]

I think the best thing to do is to look at the FI cars and their OEM compression ratios and boost.

A few cars you may want to research:

GTR
Porsche
ZR1

 

[cantdrive55]

9.5 cr
11 psi-480rwhp
15 psi-560rwhp

 

[blodi]

9.0 CR
13ish psi
RWHP - I'll let you know in a few hours. :wink:

Update:
[email protected] psi
423 ft/lbs
Mustang Dyno

 

[MetalSpikeRacing]

That seems like a lot of power for the psi, at what RPM and what turbo?

 

[blodi]

That seems like a lot of power for the psi, at what RPM and what turbo?

@ 7792 RPM for hp. 5698 for torque.

Precision 67mm.

 

[MetalSpikeRacing]

Most feel really nice!

 

[Lamini]

That seems like a lot of power for the psi, at what RPM and what turbo?

Precision BB Turbo 67 mm
http://www.nsxprime.com/forum/showt...-Turbo-Build?p=1686797&viewfull=1#post1686797

 

[MetalSpikeRacing]

Pistons are ordered, 9.5:1
And here we go! Last time I order an engine it made 552awhp on a 4G63. For the nsx I only want 450-500rwhp of reliable track power.

-MSR

 

[sca037]

9.0 CR
13ish psi
[email protected] psi
423 ft/lbs
Mustang Dyno

Now THAT's what I'm talkin' about!

Brian

 

[peiserg]

9.2:1 forged SOS stage II build
10psi making 500 rwhp
16 psi making 605 rwhp

fwiw I've got 15k miles on the build, and probably 10-15 hard track events totalling 1000+ miles

not sure of the turbo in there tho.

 

[MetalSpikeRacing]

How are you guys making such number in so little boost? I ran 10psi and only made 450rwhp on stock compression!!

 

[cptnsx]

How are you guys making such number in so little boost? I ran 10psi and only made 450rwhp on stock compression!!

Overly optimistic dynos or boost creep. 10psi if measured correctly and in the right location will not double the power of a stock NSX you need more than 14.7 for that.

 

[mrbozo1]

How are you guys making such number in so little boost? I ran 10psi and only made 450rwhp on stock compression!!

Better fuel. Better tune (more aggressive than stock), most guys also run headers, most guys that make the bigger hp numbers also run a standalone EMS . FI covers up a lot of flow problems of a stock system. My car has 500 hp on 10 psi , Stock compression. 630 hp at 14 psi. This tune is on E-85 and tuned by the same firm that tunes most of the NSX's in Phoenix. Done on a Dynapac dyno FWIW. I think the hp numbers are close because of the numbers I run at the dragstrip.

 

[cptnsx]

Better fuel. Better tune (more aggressive than stock), most guys also run headers, most guys that make the bigger hp numbers also run a standalone EMS . FI covers up a lot of flow problems of a stock system. My car has 500 hp on 10 psi , Stock compression. 630 hp at 14 psi. This tune is on E-85 and tuned by the same firm that tunes most of the NSX's in Phoenix. Done on a Dynapac dyno FWIW. I think the hp numbers are close because of the numbers I run at the dragstrip.

I don't agree especially since a ZR1 will trap at 130-131 with only 530rwhp. A 400rwhp NSX will trap at 120. It does not take 230 more rwhp to get 11 miles in the quarter (unless those are at the crank numbers in your post). Dynos lie all the time. I agree that E-85 allows more timing but who is running greater than stock timing at those psi levels.

There was an NSX in a past posting here at 630-640rwhp and that thing was at or close to 140 traps. Which is where it should be for the power and weight.

 

[onestepx]

Metal Spike I went with SOS 10.2:1 pistons on E85 pushing 24 psi making close to 800 rwhp