Tried a search, hard topic to dig up, I am running an all motor h23 setup, what do you think the highest static compression ratio is for me to run it daily on pump gas 91-93 octane?? Any suggestions are welcome.
Set up so far
h23 block 88mm GE sleeves
crower rods
wisco pistons (running low compression h22 pistons in my h23, the engine builder wants to start low and then deck the block to bump it up)
milled head 50 thousandths
clay smith cams 284 lift 390 duration

 

Chamber depth and an 88mm bore diameter will limit you to about 12.8-1 on 93 octane with GOOD tuning.

 

what exactly is chamber depth

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 93ludeSi &raquo;</TD></TR><TR><TD CLASS="quote">what exactly is chamber depth</TD></TR></TABLE>
depth of your chambers...

13:1.

 

so the chamber depth is not something i can change then

 

not really.. you could but it would require some custom parts... and a lot of time, $$. I would guess max compression you would want to run 12.5:1

 

12.5 seems plenty high to me, i have to drive the thing everyday

 

ericks racing will tell you that 11-5-1 is the most he recomends in a street car on 91 octane.

 

I'm running 12 to 1 and on occasion get a little pinging.

 

11.5CR fully built no pingage (B18C).
Same motor with 12.1 pinged a lot.

Paul

 

http://members.uia.net/pkelley2/DynamicCR.html

Static compression ratio doesn't neccesarily determine whether or not you can run on pump gas. Cam specs have a lot to do with it. I don't know exactly what kind of dynamic compression ratio you'd need for a four cylinder to have an engine that's doable on pump gas but I'd guess if some people with higher compression ratios and different cams specs that can be run on pump gas figured out their DCR you'd be able to definately settle the whole 'will my engine run on pump gas' question.

It's a little bit tougher to figure out but there is a calculator on that link for it. If people that have high hp pump gas friendly engines figured out their DCR you'd soon be able to see what the max DCR is. I don't know if anyone would actually take the time though

 

thanks man, the link helps, i understand what my engine builder keeps telling me, he has a computer program set up that caluclates the dynamic compression.

 

.....but most camshafts that have enough duration to drop the dynamic cylinder pressure (in the lower rpm ranges) aren't idle, or emission friendly.

 

Some states don't have to worry about emissions at all. There are also ways of getting around emissions laws.

Also, what's a good idle is dependent upon what you can handle. I can have an engine idle at 400 rpm, or I can have an engine idle at 1100 rpm. Especially if it's a torque lacking engine idle its not that much of a problem, just gotta raise it.

 

12:8:1

 

yeah, i have been told the cams are pretty wild, emissions is not such an issue in CT at the moment anyway, and i think I will be running a test pipe as well

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Woofer &raquo;</TD></TR><TR><TD CLASS="quote">.....but most camshafts that have enough duration to drop the dynamic cylinder pressure (in the lower rpm ranges) aren't idle, or emission friendly. </TD></TR></TABLE>

i bet a good percentage of built motor won't pass emission... so thats not even an issue anymore...

and ask your tuner what the high CR he can tune w/ pump gas.