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406 tuning (not in a 4x4)

1K views 12 replies 6 participants last post by  66k1000 
#1 ·
So, Its not IN a 4x4 but there are a ton of gurus on here that might be able to help.

I have a 406 sbc, dart platinum 220 heads / intake, about 11.6:1 compression, hydraulic .525/.546 lift 241* / 249* .050 on a 110. Open hooker super comp fender dump headers. 950 holley hp. 3500 stall

Its in a 62 nova, but it sets next to my 68 scout with 383 sbc so its close. :rolleyes:

Here is my issue. It has a slight hesitation on the launch and a pretty bad popping in the exhaust on deceleration. the popping is after a pass or even after a hard rev in neutral.

Car runs well, 11.56 @ 118 so far but I think I might have a lean condition. I ran it all season and did fine. I parked it for a while then ran it again and it was running 11.90's and wanted to foul plugs. I checked my fuel filter and put a new element in it. I'm running 6.5 psi fuel pressure at idle which drops to 4-4.5 under hard load. jets right now are 76 primary 82 secondary. those are up from 72 primary 77 secondary. it pops with both those jets.

any input?
 
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#3 ·
hesitation is carb tuning... accelerator pump shot generally helps fix it... your carb is large, but not tooo large. should be close, but will more than likely need a smaller squirter on the accelerator pump.

also, make sure the linkage on the carb throttle shaft *(where the throttle hooks up)isnt loose on the shaft..
 
#4 ·
What if the first year I ran it, it ran great with no stumble. Then next season it starts acting funny with no change. Question, is it normal for fuel psi to drop under acceleration or should it be constant all the way through? My thought is it should stay constant in the upper rpm band so it's bot lean?
 
#6 ·
Seems to me that your fuel pump is showing its age. Right off the line, however, I think you need to have a look at the accelerator pump. I'm not quite certain a smaller squirter would fix it though...hesitation = not enough fuel, so...I think I'd have to disagree on that one. Your pump diaphragms might be getting worn out or are just plain old.

as far as the popping goes...it may still be pulling in quite a good bit of fuel when youre off the throttle... how long are your header tubes? the collectors?
 
#7 · (Edited)
1 3/4" primary hooker supercomp fenderwell headers with 3" collectors. full length headers, usualy around 30-33" or there abouts. Im leaning towards my fuel system is just getting worn out. I've ordered a new element for the filter and will crank up the pressure so it doesnt drop too far under load but I'll plan on replacing the pump soon.

I have heard that adding a piece of 3" exhaust pipe to headers like this about 12-18" long can help the popping and improve scavenging etc. Or even bolting a good high-flow race muffler to each one might help with a little back pressure. The engine is not THAT wild that a muffler may not help it..
 
#10 ·
in your opinion, would a track only car benefit E.T. and/or MPH from a muffler vs the weight of adding them?

I know big monster motors don't need them but with smaller cams with smaller durations @ .050 they like a little back presssure to help out the bottom end.
 
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