Thread: 8-71 blown big block,questions

Tweet

Originally Posted by Fastnuf

QUESTIONS How much boost is safe to crank into this engine?

It's kinda hard to tell how much more boost can be safely added without knowing the static compression ratio (or better yet, the dynamic compression ratio) and cam specs.
That being said, I would use the pulleys that give you 8 lbs of boost and slip in the 3.89 gears. Work on reducing your short times. They should be alot better than 1.58. They should be in the 1.4 area.
IMHO, I would not overdrive the blower without having a second keyway added to the crank. I have personally sheared stock woodruf keys and split dampers (including fluidampers). I had a guy who didn't even make it out of his driveway with a stock damper!

My static compression is 8.3 to 1,the cam is a crane powermax #134561 hyd. flat tappet,specs are 236/246@.050, .553/.571 lift, 112 LS, I dont know how to calculate dynamic compression, I noticed the 60' slowed at least a tenth when I switched from small 174 B&M blower to the large 8-71,however top end charge much better,I beleive the small blower was very responsive at lower rpm's but became less efficient at top end, I am a bracket racer so a slow consistant 60' is a good thing,and I like the big top end mph,I broke the sprag in my $800 4800 stall, BTE 9" race convertor mid season and borrowed a TCI 10" that stalled lower(4000),made no difference in 60', my current 3.70 gear/1.76 glide is not a lot of gear for this 3450# car,leaves like a snail,cross finish line at 5800,I need at least a 3.89 gear,or maybe 4.11,I have been making small changes,went from 3.50 gear to 3.70 ayear ago,60' improved a tenth,so I figure change to 3.89 should get me another tenth,I dont want to make alot of changes at once because I won 2 out of the17 races in no box modified at my track last year,combo is working well for racing,but not optimized. The car varied from 10.68 ET@near sea level density altitude on my perform-air weather station to 11.35 in mid summer @5000 density altitude,leads me to believe I should maybe put some smaller jets in there for mid summer hot weather racing,plugs always look perfect