High gear timing retard

I run an alky sbc, all iron, dry, 10-71 blown dragster as follows: 10-71, cam = .629/,669 280/290 @ .050, 112 lobe sep, 10.5 static CR, 180 glide, MSD 7AL3 w/trigger, 1750 lb wet, 33 deg lead, shift @ 7500, traps at 8000, ET +/- 6:80 @ +/- 196 I want to pull some lead out at the top end to relieve detonation possibilities so my questions are: 1) given that I clear the traps at about 8000, at what RPM should I pull the timing back and 2): how many degrees should I pull out as a starting baseline? Any help would be appreciated. Thanks ITA

 

Is it hurting bearings?

I used to pull 1 to 1.5 starting around 4 seconds to try to calm down a combo that was unhappy. I never figured out why it wanted to detonate, just eventually changed enough stuff that it quit. I don’t recall 1.5 out on the backhalf making a substantial improvement but I think it helped a little.

When I finally changed enough parts to make it happy it went a lot faster (almost .2) without pushing oil and hurting bearings and didn’t need the timing out at the big end.

 

Last engine I ran I had 35 deg lead and when I tore it down the splayed mains were hammered. This engine I'm going to back down the lead to 32. I don't really care about picking up mph or ET...I just want the engine to be totally happy. 32 lead isn't by any means radical on an sbc, so maybe I just should leave everything alone

 

What are you running for an A/F ratio @ 7000 to 8000 rpm and what size blower hat ?

 

Do not have an AFR gauge. The hat is BAU tall 3 x 5" blades

 

What does the spark plugs tell you. They have the complete story....

 

Made only 1 pass in 2020...hung a valve because of a tight guide, but the timing plug witness stripe was right on the money on 7 @32 lead... but I ran it real fat to get the fuel tune-up right, so we didn't even touch the cad. I think before I start messing with retard, I'm going to run it straight up at 32 until I get the plugs the right colour, then I can start to play with timing. I was only concerned about top end timing because on the old motor we hurt the caps and flattened the bearings...but I was running 35 degrees. 32 is more conservative, so I might just leave it alone and not try to re-invent the wheel. Won't know until we take some hits in Spring....if the tracks open up

 

I ran blown SBC for a long time .My weak link with a iron block was the main caps would walk and transfer material.The bearings looked perfect you could scotch brite them and re run . This was with Chevy bowtie race and the olds race block.never fixed the transfer issue Just flat filed the hi spots off and ran it. I ran 32 max timing with a 14-71 @ 45 psi think with the 10 71 had 35 psi .Any more timing it would try to lift the heads and push the gaskets out .

 

Completely agreed...

 

Right now the proposed plan....after I get the fuel balanced, to set lead @ 33 with shift @ 7500 and pull 3 deg out @ 7600 with a 7950 trap rpm. which is consistent +/- 50 rpm. Make sense?

 

Hi Mike , what performance difference does this make ?

 

I don't believe there will be any performance advantage at all....either ET or mph. It's simply easier on the engine at WOT to take away timing that it doesn't need. It's just an engine longevity issue for me