Thread: HEI re-curve

Tweet

I know this isn't Club Gas Mileage, but a good running engine is efficient, right?
I have been trying to squeeze every last available MPG out of my son's 1976 Monte Carlo. (350/350, until recently completely stock) Granted, this car won't ever be an economy car, but our goal is to make it efficient as possible. We have dumped the worn out old 2bbl/cast iron intake, and single exhaust and installed a fresh eddelbrock 1406/performer dual plane intake, and dual exhaust. The car's mpg and performance is noticeably better, but I think we can do better.
After some checking, we found that the vacuum advance isn't working. This is a perfect opportunity to "tweak" the distributor. What do you suggest as far as weights/springs, adjustable vac. advance canister, initial timing, all in by xxxx rpm? I know my way around a car, but I have never tried to get the most out of a distributor. How would I go about making improvements rather than just replacing the parts with other OEM parts?

Ok, that is easy enough. Does this imply that the factory specs are "good enough" ?? What I was trying to determine is this; what direction should I go in to improve on the factory specs, and if this can be done with a simple weight/spring, advance canister change? Thanks.

You can make changes to the timing curve with new springs, weights, and a (working) vacuum cannister yes. But it will take a lot of experimentation to dial it in where the motor perofrms best. As Denny suggested, the factory specs are a good place to start.

JMO, but I have always heard that the smog era cars (your monte) ran the timing way retarded for emissions purposes and subsequently ran like pigs. So in the end, you may not land right on top of what the factory specs say.

Good luck with it. What your doing is a lost art amongst many who prefer to "bolt-on" their power and tune it "close enough" versus having everything dialed in to perfection for max performance from the existing combo.

You'll be a better technician in the end.

Good basic article to help understand what you are about to attempt. http://www.pontiacstreetperformance....distcurve.html

Thanks Nitro, Good stuff there.

That's because I screwed up the URL.......try it now.

Originally Posted by DennyW

I wonder how 65ny got through ?? What's that in the air ??

(sniff,sniff)...hhhmmm, smells familiar like something from the 70's....

Originally Posted by DennyW

I wonder how 65ny got through ?? What's that in the air ??

I googled "hei recurve" the first thing that came up was ponticacperformance. It was pretty easy, anyone can do it.

I smell something in the air too. I think it is sarcasm. Thanks for the help though.

Purely sarcasm......if we can't laugh at ourselves, we're in deep trouble

No Harm, No Foul. I was just jabbin back a little.

I bought an adjustable vacuum canister and a recurve kit. (Weights and springs) The vacuum canister was adjustable.....it provided between 29 and 34 degrees of advance......Way too much. The weights in the recurve kit looked pretty cheezy too. Maybe I bought the wrong brand. I just cleaned up the existing weights, used new springs, and got my $$ back on the adjustable canister.
I did quite a bit of reading on the subject and found that a SBC likes to have 36 degrees initial and 52 degrees total timing (if the cam doesn't have a lot of overlap)
End result: 16 deg base timing, 20 degrees mechanical starting around 1000 rpm, all in by 2800, and 15 degrees vacuum advance.
Doing this took me pretty much an entire weekend of fiddling around with the distributor, test driving, listening for detonation, fiddling around with the distributor some more, test driving……..over and over and over again.
So far, this has yielded the best results for me. I have about 50 degrees of total advance at 2200 rpm (my 60mph)
This tired old 114000 mile car runs better than new now, and the mileage has gone from a city/highway combined of 12.5mpg to 15city/20 highway.
I've had some naysayers say that timing adjustments could never make this much difference, but they CAN. I would even bet that I could tweak on it a little more and get better results, but for now, I think I'll leave it alone.

You know,

I really oughta copy 65 new yorkers,specs. Just for kicks. He seemed to have gone through the trouble and I seem to have the same car with the same manifold an carb.

I got a Mr Gasket advance curve kit so them weights are different an advance further physically I think. They didn't look too cheesy to me besides I used the old weights to steady a bench leg in 2002.

Ohh I forgot Idle, I got mine set at 950 in park, Makes it 650 in drive I think.

Hey New Yorker! The best I can do is the weakest springs that open at 900 and advance 20. But they don't even get close til 3000 rpm. Guess that'll be as close as I get.