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1970 Chevelle Malibu "400" Clone

Changed to a 76 jet, 13.8-14 at cruising. Unhooked the secondaries. Changed to .029 idle feed restrictor low speed still in the 11-12s looking at going to .027. Seems to be snappier. Probably need to look at the AF gauge less and use my butt more.


List 80804-1
PMJ-76 SMJ-92 With extensions
PMAB- .029 SMAB- .029
PIFR-.029L SIFR-.029L
PIAB-.066 SIAB-.066
PPV# 6.5 SPV# Plug
PPVRC-.069 SPVRC-.069
PE1 .029 SE1 .029
PE2 Plug SE2 Plug
PE3 Plug SE3 Plug
PE4 .029 SE4 .029
PE5 Plug SE5 Plug
Kill Bleeds-.012 P&S
 
I like the attention to tuning! I would be clueless how to achieve what you’re striving for! Nice work John and thanks for posting your changes.
 
Thinking the idle air bleed might be too small but it drives good. thinking about changing to a 8.5 pv. It honestly cruises on the flat ground at 17-18in/hg. The idle is only 12in/hg but it sure has plenty of cruising vac, enough so I think the pv needs to come on earlier.
 
So I have been just driving the car, twerking it here and there. Yesterday I drove it a hour+ to my friends shop with a chassis Dyno. Every pull except the last was in 3rd to keep from having to run the car to 145mph each pull (pulls were 2500-6200). First problem was it rattled hard with 17 initial and 36 total timing. backed the timing off 2 degrees at a time till we were at 11 initial and 30 total. The pointer might be off and it actually gain quite a bit of power. It was dipping into the 13 A/f at the top of the pulls. Changed the secondary jet. no real gain but the a/f started in the high 11s and went to the high 12s at the end of the pull. Pulled the cut outs and made a pull, it gained about 30hp but the a/f signal didn't work because of the short pipe length. Recapped the pipe and added a 1" spacer. picked up about 6hp and the a/f steadied out to 12.7. Put on a .5" shorter air cleaner to allow the hood to close and no HP loss. A bit of detonation started to reoccur at peak torque (4000). Found some slightly stiffer advance springs that delayed full advance till 4500 and the rattle was gone. Final pull was in 4th gear. The peak in 4th (least drivetrain loss) was 513WHP through my 2.5" full length duals with dynomax turbo mufflers. There might be 20-30 HP with cutouts open and a bit longer extension pipe. It starts to pop and bang because of valve float/lifter pump up right at 6200. I probably went overboard chasing a lean a/f number because it has a bit of lean buck on the highway and just off idle. I need to a bit of ass tuning to sort that out with the a/f meter put away.
 
Nice pulls John!

Did you ever find true TDC with your pointer and a piston stop? That seems like very low timing it wanted...
 
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I am pretty sure we did but the timing does seem low. Dyno says it is happy. I wonder if the vac advance adds some that is hard to see
 
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