Thread: 8-71 blown big block,questions

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Originally Posted by rabid rat

one theory of mine is it 60' is slow because I am underdriving the blower 20 percent @5# of boost,I think it will really wake it up if I bump up the boost,crane says cam is good to 10-12 # of boost,so I am running it at 5#,I think this is like putting to big a cam in a low compression motor,which would also be slugish off the line. Does this make sense to you guys?

well yes more boost will make every thing work better .i have a big cam idle it has 2inch,s of vac at intake at the carbs it has about 15 and the carbs work out of the box just fine carbs think they are on a mild engine the blower helps out

Originally Posted by rabid rat

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

I agree with your not wanting to make to many changes at once. One at a time.
5800 RPM is a tad low for crossing the finish line. Maybe the 4.11's would be better than the 3.89's.

I have been told by several people over the last couple years that my 60' time is slow relative to my finish line mph and calculated hp, one thing all these people had in common was they dont own or even know anyone that has driven a carbed blown car down a dragstrip,all their info comes from a computer program, I have recentlytalked to a guy with a simular combo,all steel 55 chev,427 9# boost best time 10.07@137,1.53 60' this looks right in line with my10.68@127,1.58 60' at 5# boost,in fact the guy with the 55 is running glide with a 5500 stall and a 4.56 rear gear,One could conclude giving my car more gear wont help my 60' much,but I think I need to talk to a few more people with a simular combo before I can consider this a fact,I dont think these computer programs are very accurate for blown cars,do any of you guys out there actually have a blown car that you run down a track,and have time slips,I would like to compare notes with you

Originally Posted by rabid rat

I have been told by several people over the last couple years that my 60' time is slow relative to my finish line mph and calculated hp, one thing all these people had in common was they dont own or even know anyone that has driven a carbed blown car down a dragstrip,all their info comes from a computer program, I have recentlytalked to a guy with a simular combo,all steel 55 chev,427 9# boost best time 10.07@137,1.53 60' this looks right in line with my10.68@127,1.58 60' at 5# boost,in fact the guy with the 55 is running glide with a 5500 stall and a 4.56 rear gear,One could conclude giving my car more gear wont help my 60' much,but I think I need to talk to a few more people with a simular combo before I can consider this a fact,I dont think these computer programs are very accurate for blown cars,do any of you guys out there actually have a blown car that you run down a track,and have time slips,I would like to compare notes with you

Here's my computer program!
http://www.calvertracing.com/gallery/gadavis.mpg
BTW, that was a 1.35 60' ON THE BACK TIRES!

Here's my computer program.
http://www.calvertracing.com/gallery/gadavis.mpg
BTW, that was a 1.35 60' on the back tires.
Bumper Scraping
My web site.
The Fastest Street Car in San Diego?

I was thinking my 3/8 truck rods could take a couple more pounds of boost(abuse)if I keep the rpm's under 6200,I think high rpm has killed more big chevy's than 8# of boost has,it is a calculated risk,how many rods have you guys broke under 6200 rpm?

Originally Posted by rabid rat

I was thinking my 3/8 truck rods could take a couple more pounds of boost(abuse)if I keep the rpm's under 6200,I think high rpm has killed more big chevy's than 8# of boost has,it is a calculated risk,how many rods have you guys broke under 6200 rpm?

i had one guy run 8 pounds of boost with a whipple charger on a 454 he drove evey day and pulled a big car trailer stock thumb rods but i seen a truck rod fail in a new boat so can you do it ? yes you could but your playing with old used rods that have seen how much ? i have used that same rod in many builds that gone past 6200 but with out the added power adder that is the acid test .i did that along ago the rods you can buy know and what i have seen done with the H beams i just will not bet on the stock rods for what your tring to do. i have seen the stock rods loose press on the pin and go thru the piston wall

Hay Pat how are the L-88 of the LS-7 Rods . Can they hold up to big HP Builds with SPS Rod bolts installed ?

Originally Posted by tango

Hay Pat how are the L-88 of the LS-7 Rods . Can they hold up to big HP Builds with SPS Rod bolts installed ?

i think for the money the H beam are still a better rod they could work you are talking the green rod if so the bolts are as good as or better then sps tango look on #7 i did go thru this but ? are you taking the old 3/8 dimple rods or the 7/16 dimple rods ? i still think them old rods are worth more to some one building a numbers engine and have to have them it takes alot of work to make them sexy