i keep reading that some engine setups have to low of a C.R. to be boost friendly!!!
so what is a good C.R. for boost???
thanks

 

Any of them are fine (under like 11.0 ) IMHO. Tuning is the key here. There is no reason to run a lower CR and have off boost performace suffer because you want to be able to run 15 psi or something. Just run lower boost and make the same amount of power with a lower CR.

 

9:1 compression is what I like and what I will always run on my boosted motor.

 

You really have to judge this based on the size of your motor and the rpm's you'll be pushing. First off, a 1.6 ltr honda motor will not be as off-boost friendly with a compression ratio of 8.5:1 as say...a SR20DET which comes stock with the 8.5:1 compression ratio. First off, its a matter of displacement. The SR is a 2.0liter motor, which gives its lower compression pistons just a little more room-to-boom out of boost. The smaller 1.6(im not choosing a motor series because its of little importance.) has to struggle to put out the same torque as the 2.0. Torque is effectively what your driving out of boost and technically in boost as well. Horsepower is a kind of measurement of torque with RPM(there's a simple formula for this that escapes me.). Broken down, Displacement generally builds torque. The second thing to remember is that the honda engines are more RPM oriented engines. They use smaller displacement motors coupled with higher RPM to build longer powerbands. This sacrifeces torque because the higher you rev up the motor to make the horsepower, the lower overall torque usually becomes. So if you have a 1.6liter honda reving to 8000rpm and a SR20DET reving to 6500rpm, you can see that the lower compression in the larger motor is balanced out by the lower rpm, which generates greater torque. While the honda usualy will have slightly higher compression and use greater rpms to build horsepower(Remember, a torque by rpm measurement.) Basically, if your going to run a 1.6 ltr turbo honda with high rpm's, going to 8.5 compression will lessen your out-of-boost power. Sure, you CAN run more boost, but your only doing it to make up for the lost compression and thats a poor choice unless you get to run 100+ octane all the time. If you have a 2.0liter honda, you could start to push the lower compression ratios, but still your going to be reving the motor up quite a bit, so whats the point. You'll be happy to have that torque when your launching your car. My recomendation would be a generaly 9.0:1 for most boosted applications. It provides with enough torque and a compression ratio that will provide you with safe boostability. If you want to run higher, by all means, but your pretty much just using the higher compression and taking away from your potential use of your turbos efficiency, so use a smaller turbo. No need using a 18psi efficient turbo on a 6psi motor. If you choose to run lower compression, thats fine too, just need a little more boost for the same power. Most important of all, tuning. Always with the tuning...

 

The ideal compression for a forced induction engine is 8.5:1. However theres a lot more too it. You can make a lot more power with high compression and boost. You can have an engine with 13:1 compression and run 25lbs of boost. Most people wouldnt, because building a low compression forced induction engine is a lot easier to tune. If you have a high compression forced induction engine, its a lot easier to blow it up with inproper tuning. But with a good tuner, a high compression forced induction engine can make double the HP of a low compression forced induction engine.

 

I'm partial to 10:1, and when the time comes to sleeve and rebuild I'm going to stick with 10:1

 

my D16z6 has a C.R. of 9:2:1!!! is this a good C.R.?
thanks

 

i'll let you know when im done.
10.5:1 here

 

from what i know.. (not much)
I would say around 10 to 1. if you can make more power on less boost.. why not. your charge temps are lower. making your intercooler more effective. and your turbo more effective.

i would be embarrased to say i run 15 lbs of boost and make 250 whp

 

There are way too many variables for there to be an ideal compression ratio, but generally for a street car i'd go 9:1. Don't think that all racers run high compression. We run less than 9:1 on Kenny's car...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by fast93accord &raquo;</TD></TR><TR><TD CLASS="quote">The ideal compression for a forced induction engine is 8.5:1.</TD></TR></TABLE>
Can you post technical data or a link to it? Thanks!

 

IMO, it really depends on the application. In my CRX, built mainly for autocrossing, I prefer high compression and lower boost, as it's easy to get out of boost while autocrossing. On a street-driven drag car, lower compressions start to make a lot of sense. It really depends on the application.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 1SIKCRX &raquo;</TD></TR><TR><TD CLASS="quote">my D16z6 has a C.R. of 9:2:1!!! is this a good C.R.?
thanks</TD></TR></TABLE>

Yeah man your engine is fine for boost. I will be boosting the same motor pretty soon.

 

I'd like to run the JRSC on a d-series. I like keeping the d-series cause it saves me 100 lbs up front, for handling purposes.

The JRSC isn't easily intercooled, on my budget. And I don't want to up the boost too much (they come stock 6PSI, and suffer if you push them past 8PSI). But I also don't want to slap on a JRSC on my d-series, and have power like a stock 99-00 SI. So I was considering upping hte compression a little. will I notice a big difference in power going from 9.5-&gt;10 CR Is it safe to push it further?

-PHiZ