Blower Boost in relation to Compression

I'm a crew member for a NMCA Pro Street. And this season has had its ups and downs. I'm trying to better understand certain aspects of the motor so I can be more help to the crew.
We run a Veeney Headed Hemi, K-11 Blown, injected on alcohol, The blower is putting out about 38lbs of boost with 29% overdrive.
My question is this:
At what point should anyone be concerned about the compression of the motor and the amount of blower boost ? Explain ?
I had read the more boost you push through, you better off with lower compresion...
Thanks

 

Art

you, may want to consult w/car owner first he spends the $$$$

 

I do talk to the owner about alot of things. But I'm looking to educate myself on the subject of Blown Alcohol motors....

 

art

Ya, but can you put two main jets in again please

 

Go figure , Old Green Truck (OGT) ..... Let me guess .... with the comment of maybe you should just ask the owner....

Pete....

 

I figure I'll learn some things on my own, and leave the owner out of the loop since everyone and their brother asks him millions of questions, or tells him what they think is wrong..... No need to bother the owner...

 

Compression

The dynamic or running compression when using a blower is different than for a naturaly aspirated engine. In a blown engine the compression changes as the boost increases. When you add more overdrive to the blower it may not increase the boost pressure that much at maxium rpm but will increase the idle and lower rpm compression. Blown engines will usually have lower base compression because as the rpm goes up the boost goes up and thus the dynamic compression.
There are no dumb questions just dumb answers.

 

im a newbe

great site,hope i never need to ask that ogt for any info or help,geeeeeeeeezzzzzzzzzzz

 

OGT was busting me, he's a good friend, and extrememly knowledgeable.. I'm always asking him things , I figured I'd give him a break for once.

 

Thanks NitroHawk, Thats what I read, I was just wondering if there was a science, or calculation to determine good vs bad.

 

Go Figure???

There are so many variables that will effect the correct fuel to air ratio compression being only one that it is not practical to try to figure out. It you have a computer program such as the one Davenport sells and you plug in all the variables you might get close. The best way is to run the car and tune by the performance. Just remember there is only one best air fuel ratio for a given set of circumstances anything else you are leaving hp on the table.
A good barameter of the correct mixture is the cyl temps when you get the performance right. But since you don't have a computer you might consider useing one of the less expensive units even if it is just capable of monitoring one cyl. Just remember this. More blower / More fuel. An engine will run good on the rich side and not hurt itself but to lean and bad things happen.

 

Thanks nitro hawk, we do have a computer, and monitor many many variables, Exhaust Temp, blower pres, clutch rpm, driveshaft rpm, fuel flow, oil pressure, fuel pressure. We use the Racepack set up, and it works great. When we are tuning the car, I give him all the atmosperic #'s, first off the Water grains followed by corrected altitude. We like to have the exhaust temps around 1000 deg. After that we go get track temp, and look at the track to help with the initial clutch set up. The owner/driver of the truck has the tuning under control.

Thanks