Compression ratio

[linuxman51]

Since this is always a touchy subject in the land of liberal thought but ultraconservative tuning (e.g. turbobricks), I figure'd I would pose the question here...

In whatever realm of performance you're involved in, whats the 'normal' CR for the peeps makin the power?

[roadracer4life]

NA 13.5:1
SC 11.0:1
Turbo 10.0:1

[Byrd]

Was 9:1 on the 2.0L (It was hard to tune though)

8:1 on the 2.4L

[1.8t]

10.7 here. All the boost vette guys run 9ish. All the n/a guys go for 11.5ish to 12. Evo boys stayed around 8.8~8.5. Honda boost guys went 9.0 to 9.5, see Brock for n/a applications.

[VR4Rob]

Stock 8.0:1

[Swine]

All the big hp subie boys go 9.0, a few 9.5, some of the real adventurous go 10.0 but their cars never run right.

If i was build a big power/big boost motor, i would go with what i know works and is decently relaible. 9.0 should get the job done quite nicely.

[VDUBNDizzy]

9.25 all day long.

[XSivPSI]

there is an evo9 on evom with an aluminum rod motor with 10:1 cr making a little over 500whp on the stock turbo.

[zmasterB]

I think around 9.0 is ideal........9.5 or higher makes the detonation "window" too small at higher boost levels, below 8.5 makes the engine lethargic out of boost. Lower compression looses some spoolability also.........

Its all kind of a balance really. How much boost, how big of a turbo, how much desired HP, desired response.

[Pegasus_Red]

From my standpoint I would rather have the reliability of an 8.5 with a well matched turbo and meth injection and an air to water intercooler rather than say a 10:1 with a larger turbo both making around the same numbers, just my take on things.

But what the fuck do I know, I run a 7:1 on stock engine that barely ever runs... fucking vac leaks.

[TheWill]

Most of the n/a guys for Honda are in the 12 + range for compression I know that King motor sports builds a few b16's and type R motors that are 13:1.

[DloveN]

Not like anyone on here cares but S4 N/A rotors are 9.4:1, S5 N/A's are 9.7:1, RX8 Rotors are 10:1, and I can't remember any of the other numbers. I know the big turbo guys have like 8.5:1 rotors, but I think most turbo cars have 9:1.

[linuxman51]

From my standpoint I would rather have the reliability of an 8.5 with a well matched turbo and meth injection and an air to water intercooler rather than say a 10:1 with a larger turbo both making around the same numbers, just my take on things.

But what the fuck do I know, I run a 7:1 on stock engine that barely ever runs... fucking vac leaks.

Why are you going to put all the helpers on the low cr setup? I'm not arguing about retardedly high CR's here, its just funny how things pan out in other (slower) forums.

[linuxman51]

I suppose its really a moot point, your average volvo "tuner" (and I use the term very loosely), despite YEARS worth of documentation empirical evidence in the forms of youtube videos, dyno graphs, etc.


... still struggles mightily to break 14.5 in the 1/4.
apparently thats a fast car over there these days. Glad I missed that memo.

[xamraci]

I do believe the F22b was 8.8:1 and it seemed just fine until the oil stravation issue and the klapow...that along with the many different turbos that died due to oil issues:patriot:

8.8-9.0:1 I would think is pretty damn good...

I wanna build a 10.5:1 forged turbo car one day...cause well...thats just baller:pimp:

[Obike]

When I build the tC I'm going to go w/ 9.0:1 CR pistons, although I have debated just using forged pistons that are the stock CR of 9.6:1.

[Pegasus_Red]

Why are you going to put all the helpers on the low cr setup? I'm not arguing about retardedly high CR's here, its just funny how things pan out in other (slower) forums.

You can run it on lower grade fuel, then switch up teh bewst when you want to run the premium stuff, think about how much you would save in fuel costs.

[linuxman51]

You can run it on lower grade fuel, then switch up teh bewst when you want to run the premium stuff, think about how much you would save in fuel costs.

actually the off boost performance gains from higher compression would yield better fuel economy than slumming around with a slug on lower octane.

[titec2]

You beat me to it....

[organic]

When i was building B18A1/ B1, I'd punch it out half a mil. = 81.5

With a GSR head (42.5 cc) it ended up being around 9.2:1

pretty good on and off boost.

There were some guys a couple years ago that found some crazy sweet spot in

a H22 around 17:1 :O

As far as sportbikes, The Hayabusa used to be 11.0:1 with 151hp
now they are 12.5:1 with 194 hp

When we turbo'd them, we'd drop them down no further than 10.0:1

[VDUBNDizzy]

actually the off boost performance gains from higher compression would yield better fuel economy than slumming around with a slug on lower octane.

Yup, people randomly ask if they can use 87 in the 1.8t forum on Vortex. You can, and the ECU will pull timing, and nothing will get hurt (at stock boost levels). But you'll end up getting worse gas mileage and negating the benefit of using cheaper gas in the first place. There's no reason to run less than 9:1 on a turbo motor. There have been a few 10:1 1.8t's lately, one that runs our software that pushes 27-29 psi daily.

[BlueBoostedTibby]

10:1 for most v6 tiburons, which is stock.

[linuxman51]

10:1 for most v6 tiburons, which is stock.

thats cool, where do they run out of steam at?

[LT16speedTA]

In the 240sx community, the KA-t guys making the most power typically are at 8.8:1.

[militarymustang88gt]

i know alot of mustang guys running boost are around 9.5- 10. i wanna aim for the mid 11 area.

[A418t81]

As its been said, for max power turbo apps 9-9.5, depending on application.

[roadracer4life]

In the 240sx community, the KA-t guys making the most power typically are at 8.8:1.

9.0:1 in mine and made good power till i shit a head gasket.. due to lack of fuel not because of the CR..

[LT16speedTA]

9.0:1 in mine and made good power till i shit a head gasket.. due to lack of fuel not because of the CR..

Yeah, your car made good power. Hell there have been a couple people to make 530whp on stock 9.5:1 pistons, just typically people are running the arias 8.8:1.

[Jnic335i]

335 is running 10.2:1 compression ratio.

[BlueBoostedTibby]

thats cool, where do they run out of steam at?


~10lbs is where its time to cut it open and start replacing things. Theres a few people (shop sponsored of course) with ross pistons and the like that are pushing 25lbs+ of course there are a number of options for 9 and 8 rating pistons from ross as well

[DloveN]

My Ski Nautique's 351 has 11:1, or it might be 12...I'm not sure. I do know that it could pull a damn house out of the water, with the right prop.

[Jess]

turbo 1.8 Miata guys usually run 9.0:1

[dixond]

Compression Ratio? Pump it up...
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[Drew]

8.5:1 in the Vovo 850R's/T5's

Playing it safe as usual I suppose...

[linuxman51]

8.5:1 in the Vovo 850R's/T5's

Playing it safe as usual I suppose...

they got to. seen the rods they put in those motors? :O

[Drew]

only from pictures guys take after snapping them like toothpicks :(

[ActiveAero]

Most off the shelf turbo Honda piston applications are around 9.1 or so. There are a good many that experiment by running 10+ as well that seem to have no real issues.

In terms of NA with B-series the norm for a good high hp street setup on pump gas was 12-12.5 with a few risky people running in the 13+ range. I think the race gas only engines were usually in the 15-16:1 range.

I'm not real sure on the K-series but I wouldn't be surprised if they can run a little higher compression across the board due to the bigger bore.