boost vs. compression revisited...

dbusch · Post by **dbusch** » Tue Mar 22, 2005 5:56 pm

what has been the norm for compression ratio with blown non-intercooled applications with C16 fuel? I know it depends on what type of head is used, but there still must be a roundabout number that works the best. I know with inter/aftercooled blown motors up to and maybe beyond 11.0 compression works well, but what about with no cooler? Can extra rich air/fuel ratios allow for higher compression ratios? I have my own experiences with these combos but am wondering what other people have tried. Any thoughts or experiences here would be appreciated...

SteveS · Post by **SteveS** » Tue Mar 22, 2005 8:05 pm

As you suggest, head design and combustion chamber shape play a big role in establishing how much effective compression the engine can tolerate. The formula for determining effective compression ratios is as follows:

ECR=(14.7+Boost in psi/14.7)*Static CR

Altitude, fuel delivery and ignition also play a role in determining maximum ECR. For non-intercooled applications running C16, I would think a 8:1 to 9:1 static CR would be appropriate. Anything more than this would limit boost; anything less than this would compromise low-end performance.

Ron C. · Post by **Ron C.** » Wed Mar 23, 2005 4:24 pm

"Can extra rich air/fuel ratios allow for higher compression ratios?"

There wouldn't be any point to doing that if your trying to make power with gas. You'd be better off, power wise, to lower the cr and up the boost. If your trying to run with a higher cr you might want to take a look at VP's "Import" grade of gas. It's by far the best one for blower applications (3-5% power increase over C16 or NO2), but it's also twice the price. Water injection would be another way to squeeze a little more out of that type of combination.
I agree with Steve, 8 to 9 to 1 is generally the area for gas applications. With 8 to 1 or lower for the higher end boost and power.
At 9 to 1 cr and 20 psi your looking at a little over 21 to 1 effective cr which is pushing C16. Of course there are some varying factors that can make it work.
That's my thought's and experience anyway.

Grocerius Maximus · Post by **Grocerius Maximus** » Wed Mar 23, 2005 6:10 pm

If it is non-intercooled, and you can use it, throw a small shot of juice at it to cool off the intake charge. In many cases running at a boost level that keeps you in the 'happy' PR area and throwing a little juice at it is better than just throwing mondo boost.

STOCK 1090 · Post by **STOCK 1090** » Wed Mar 23, 2005 6:41 pm

Go with the lower CR and boost it.
I would also find a way to get some sort of intercooler on it.
In the past I was able to make almost 4hp per cubic inch in a V-6 drag engine with 9.1 CR and 28lbs with one turbo. It wasn't a bomb either.

Turbos are a bunch of fun!

dbusch · Post by **dbusch** » Thu Mar 24, 2005 12:04 am

this is a class car that cannot run an intercooler/water injection/ etc. I will check into the VP "import " gas. Over 25psi boost too!!

STOCK 1090 · Post by **STOCK 1090** » Thu Mar 24, 2005 7:56 am

Any rules on the pipe from the turbo to the intake? Material? Length?
There is always more than one way to read the rules.

Ron C. · Post by **Ron C.** » Thu Mar 24, 2005 11:24 am

For tech comparison go to VP's website and click on there "fuel spec sheets". Compare the "Import" to C16 and NO2 which would be best second choices. The "Import" is designed to be used with high mechanical heat induction. The distillation evaporation percentages are much more favorable for your application. If the rules allow it.....that is. Be prepaired to pay around $16.50 @ gallon in 54 gallon drum quantities. The "Import" will make 3 to 5% more power than the C16 or NO2.
Happy racing...........