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View Full Version : Compression ratio and detonation.



Snowboat
10-13-2001, 12:13 PM
I'm surprised I haven't found this forum before but I 'm glad I did. I see why the usage of Az-don's v drive forum has gone down. I'm new to blowers and I have a few questions. I'm running an 18 foot Biesemeyer V drive at 4400 feet elevation. The engine is a 461 BB Chevy with 4 bolt, steel crank, Bowtie signature heads with 2.250 and 1.88 valves, solid roller cam, .680 and .698 lift, roller rockers. The carbs are 4150 750's jetted fat. The blower is a 6-71 big bore at 10% over. The timing is 28 degrees. The block water temperature is 100 to 135 degrees. When I'm putting along the vacuum is 2 or 3. When I romp on her the boost goes to 12 to 15. Because of the fear factor and the location of the guage down by the v drive, near the passenger seat, I don't know if the boost stays at that level all the way up to 61-6200 rpms. I can't hear squat. I'm running AR 15 plugs with the short electode. Will they melt and missfire before serious detonation? The compression ratio is 8. I calculate the final compression ratio at 12.75 for 4400 feet @12 psi boost. I've read pump gas is good to 12.54 (from Blower Drive Service, I believe). Will I blow the sucker up? It isn't run WOT, at this time, for very long. Since it takes a good set I would like to hammer down longer, but snow is just around the corner. Thanks.

superdave013
10-13-2001, 12:39 PM
Snowboat, Glad you made it! I still stop by AZ don's now and then but it just seems to load slow and sometimes won't load at all! Kinda sad as he had a good thing going for awhile. I ran my turbo deal at 12 psi on pump gas but it was pretty close to sea level. So I am not getting in this one. I will say that the fuel is the cheapest thing in an engine and in my blown boats I ran race gas but also made lots more boost.
BLOWNDRAGBOAT is the one that I'm sure will come up with the good info you need. Mostlikely he won't just tell you what you need but also why you need it!
Look forward to seeing some of your posts in the v-drive section too.

skijake
10-14-2001, 06:55 PM
When you are talking pump gas you have to remember that most of the charts are set up talking 92 octane, Calif, Az, Nevada, and soon the whole west coast has changed to 91 octane. So be carefull when you look at charts.
This is due to a patent that Unocal holds. So do not buy 76 gas or race fuel because they are the ones making it hard on everyone

BLOWNDRAGBOAT
10-19-2001, 08:38 PM
Just emai lme Snow and I will help you with your setup. From what I can see, your already going in the wrong direction. Email me and I will forward my number for you to call me. Look forward to hearing from you.

Snowboat
10-20-2001, 11:15 AM
Thanks BLOWNDRAGBOAT. Home is mendenhall@newwaveis.com and work is mendenhk@triton-coal.com.