2008 Stage 3 ROUSH - Rebirth...

[Pentalab]

How much compression (CR) will you be using this time around? The folks with the 11-14 cars....all have 11:1 CR.....and make 580-600 rwhp...with 10 psi and pump gas.

If you can run the blower at 10-12 psi, the IAT's should be cooler....and also less hp to drive the blower.

I see nascar uses 14:1 CR..and 93 pump gas....but they are NA of course.

There was some question as to where the 1st ring gets located. The engine builders want to move it lower a bit to reduce ring temps....(which will also decrease CR a bit). Ford wants to move it up a bit....to reduce emissions.

Although Roush used 8.5:1 CR and didn't stroke the engs on their 540H etc cars... they had to increase the boost way up to compensate. In NA mode, the 8.5:1 CR will result in a power redux....vs say 11:1 CR.

If it was me.... within reason of course, I think I would opt to stroke it, and also use the highest CR that is practical. Optimize the heads + cams next....then worry about the blower (and boost levels) dead last.

Plan B.... just buy the FRPP 11:1 302CI Aluminator...and slap your favourite blower of the week on it.

Jimbo

 

[AutoXRacer]

The JDM 302E setup is 9.8:1.
With the new heads I'll be running slightly less than the 9.8:1; probably around 9.6:1 or so.
Stock heads have a 51cc chamber while the new heads have a 53cc chamber reducing compression ratio by 0.2 roughly.

The problem with running high compression is fuel. I tune for 91-92 octane. If I would run higher compression, that would force me to run a lot less boost and use higher octane fuel and reduce my timing all of which would decrease my power potential.

The Coyote motors can get away with that due to their optimized variable cam timing, 4 valves, and better PCM.

 

[BadPiggy]

I see nascar uses 14:1 CR..and 93 pump gas....but they are NA of course

NASCAR uses E15...98 octane.

http://www.gosunoco.com/sunoco-racing/nascar/

 

[06Saleen E]

Need to be very careful with that JDM comp ratio (or other companies advertised comp ratios). Thats the spec that they have with pistons and crank stroke that's it (this has nothing to do with JDM) and That's the setup that I got, but when you calculate compression ratio and add to the mix Piston deck clearance, head gasket bore diameter, head gasket thickness, combustion chamber volume (and this can be very different depending on your type of heads configuration) the number will change. Based on this JDM spec 9.8:1 when all was set and done on my Saleen Extreme I wound up with 10.3:1 comp ratio. So, do the math the right way and don't assume only that's 9.8:1 because that's the piston/crank data.

The JDM 302E setup is 9.8:1.
With the new heads I'll be running slightly less than the 9.8:1; probably around 9.6:1 or so.

The problem with running high compression is fuel. I tune for 91-92 octane. If I would run higher compression, that would force me to run a lot less boost and use higher octane fuel and reduce my timing all of which would decrease my power potential.

The Coyote motors can get away with that due to their optimized variable cam timing, 4 valves, and better PCM.

 

[AutoXRacer]

How do you measure compression ratio?

 

[lito]

Initial volume/Final volume.

 

[06Saleen E]

There're a bunch of formulas around. You can use this......
http://www.summitracing.com/expertadviceandnews/calcsandtools/Compression-Calculator/

 

[BruceH]

How do you measure compression ratio?

http://www.wallaceracing.com/cr_test2.php

FWIW all of the frpp head gasket kits I've used have a compressed head gasket thickness of .031" when I measure them.

 

[AutoXRacer]

Cool thanks!!

Anyone know the specs on the JDM pistons; CCs?
Also, what's the gasket bore diameter?

And how do I get the deck height? Is that something the machine shop will have to provide?

(Fyi: I'm learning about all of this as I go... lol)

 

[skwerl]

Gerald, here's the spec sheet on my short block. Yours should be the same. Maybe some of these numbers will help.

 

[BruceH]

Cool thanks!!

Anyone know the specs on the JDM pistons; CCs?
Also, what's the gasket bore diameter?

And how do I get the deck height? Is that something the machine shop will have to provide?

(Fyi: I'm learning about all of this as I go... lol)

Deck height is .008" stock. Unless the heads are milled or the block was decked it should be about .008".

I was under the impression that JDM was using a -6.5cc dish but have nothing to back it up.

I can't find a head gasket right now. Just use 3.600". It doesn't make much difference in the calculation.

 

[AutoXRacer]

So if I used these figures:
Cyl: 8
Bore: 3.5540 (stock)
Stroke: 3.800
Head CC: 51 (stock)
Piston: 11cc (only number that gets me closest to 9.8:1; 6cc gets me to 10.75)
Gasket Thickness: 0.031
Gasket Bore: 3.600
Deck Height: 0.008

I get CID: 301.58 and 10.02:1

With my new 53cc heads and 3.5565 bore, that lowers the CR to 9.83:1 and CID to 303.70.
Seems like the larger bore increases compression???

I get the same number with the Summit calculator: 9.85:1 and 303.70.
Obviously all this is a rough estimate.

 

[skwerl]

I think our pistons are 6.5cc dish.

 

[AutoXRacer]

If thats the case then the effective CR is close to 10.67:1 (using stock heads 51cc).

With the FRPP std CNC/Ported heads (53cc): 10.38:1
With the FRPP Race CNC/Ported heads (48cc): 11.14:1
(all with std bore of 3.5540)

With my new +0.010 bore and std CNC/Ported heads: 10.44:1

How does increase bore, increase CR?
i thought less volume = high compression

 

[BruceH]

So if I used these figures:
Cyl: 8
Bore: 3.5540 (stock)
Stroke: 3.800
Head CC: 51 (stock)
Piston: 11cc (only number that gets me closest to 9.8:1; 6cc gets me to 10.75)
Gasket Thickness: 0.031
Gasket Bore: 3.600
Deck Height: 0.008

I get CID: 301.58 and 10.02:1

With my new 53cc heads and 3.5565 bore, that lowers the CR to 9.83:1 and CID to 303.70.
Seems like the larger bore increases compression???

I get the same number with the Summit calculator: 9.85:1 and 303.70.
Obviously all this is a rough estimate.

If all else stays the same then an increase in bore or stroke will increase compression.

Stock heads are 50.3cc btw. I've seen them listed from 50-53.

 

[AutoXRacer]

Gerald, here's the spec sheet on my short block. Yours should be the same. Maybe some of these numbers will help.

By the way Skwerl, all those numbers are inaccurate. When my engine builder measured my motor, he said all the measurements were all off. I don't recall by how much exactly, but it was significant; IIRC he might have said as much as 0.0020" or something.

 

[BruceH]

By the way Skwerl, all those numbers are inaccurate. When my engine builder measured my motor, he said all the measurements were all off. I don't recall by how much exactly, but it was significant; IIRC he might have said as much as 0.0020" or something.

Technique can cause different measurement. Having calibrated measuring tools helps keep the variances to a minimum.

Did your shop measure the bores and subtract the parts measurements?

 

[skwerl]

I think our pistons are 6.5cc dish.

If thats the case then the effective CR is close to 10.67:1 (using stock heads 51cc).

With the FRPP std CNC/Ported heads (53cc): 10.38:1
With the FRPP Race CNC/Ported heads (48cc): 11.14:1
(all with std bore of 3.5540)

With my new +0.010 bore and std CNC/Ported heads: 10.44:1

How does increase bore, increase CR?
i thought less volume = high compression

I wouldn't doubt 11:1 compression. I don't know how to convert it but my compression test showed 212-213psi compression. That's with the Stage 3 heads though.

 

[06Saleen E]

As you can see there's a lot people that can say you should use this or that. Go and measure yourself. No guessing here. The minute you start assuming room for errors grows dramatically. My cyl heads were listed at 51cc, however when I went ahead and measured it (2 times) came out to be 47.6cc. You measure the vol with a large pipet, like the one they use in the chemistry labs. If you don't know or don't have the tools, take it to an engine builder that knows what he's doing. As you see chamber vol is very critical. Once you have the real CR it will be a good number for your tuner to have and know about it. This will get him in a good sense as far as engine timing and how to be on the safe side of things.

If thats the case then the effective CR is close to 10.67:1 (using stock heads 51cc).

With the FRPP std CNC/Ported heads (53cc): 10.38:1
With the FRPP Race CNC/Ported heads (48cc): 11.14:1
(all with std bore of 3.5540)

With my new +0.010 bore and std CNC/Ported heads: 10.44:1

How does increase bore, increase CR?
i thought less volume = high compression

 

[06Saleen E]

Yes less vol= higher compression. However comp increases with larger displacement (i.e. More stroke or larger bore). They're different perspectives.

If thats the case then the effective CR is close to 10.67:1 (using stock heads 51cc).

How does increase bore, increase CR?
i thought less volume = high compression