VetteNURSE

What initial timing are people running with moderate cam .490 lift 242/262? Manifold vacuum?

Thanks,
Mike

bluedawg

If 242/262 is total duration, id say 12 degrees initial.

VetteNURSE

I am getting some surging at idle in first gear in a parking lot when I let the clutch out. Could it need retarding?

Mike

Jeff_Keryk

Sounds like a lean A/F condition.

VetteNURSE

Should have added it runs perfect otherwise. No hesitation at speed, great throttle responce. If I add a few rpms at idle it smoothes right out.

Mike

jackwabbit703

along with excessive timing.

MelWff

What is your current timing set for? Are you running vacuum advance ported or manifold and how much is it? What is your idle rpm set for?

VetteNURSE

My idle is set at 750, ported vacuum to the vac advance after much discussion with my engine builder. He insists thats how it was designes and how it should stay. I'm not convinced after reading Lars" papers so im totally confused on that one. The initial is now around 12.

lars

If I were tuning it with that cam, I'd set it up for 18 initial, 36 total, with a 2800 rpm total advance curve. Then I'd customize a vacuum advance to produce about 12-14 degrees of vacuum advance and run it off manifold vacuum. This will give you about 30-32 degrees of timing at idle, which will make it run exceptionally well.

These engines were certainly not "designed" for ported vacuum. Nonsense. These engines were designed for full manifold vacuum, and were "Band-Aided" to pass emissions by eliminating the vacuum advance at idle in order to get the timing retarded far enough to get the emissions down. If your goal is to pass an emissions test, run ported vacuum. Obama will be proud of you.

Lars

7t9l82

Lars as usual is 100 percent correct, however as a side note i have never been convinced that retarding the timing actually " helped " emissions.it seems as thats what they thought,but if mileage and performance improve with advanced timing how can emissions increase too? an i hope obozo isn't happy.

VetteNURSE

Thanks so much for the reply Lars. If I go much ovevr the 12 initial I get detonation, by advancing my initial do I understand that I am advancing the total as well, past 36, the way I have it set up now? My total is 36 at 3k, should I use lighter springs? I'm still frustrated after spending a small fortune on this rebuild with someone that was supposed to set it up too. It does run pretty good now so I can't wait till it is set up right.

Oh ya, there is no emissions for cars over 25 years old in CT.

Thanks,

Mike

jackwabbit703

Something does not sound right here. Set your initial timing to 16 and try driving your car without vacuum advance to see if it still detonates. If no detonation, your vacuum advance is supplying way more than 16 degrees of advance which is common. Go well over 52 degrees during part throttle will cause problems. I'm sure someone have cover this many times but you can just set your total timing to 36 and let initial far wherever also.

My mallory HEI gives out 22 degrees advance instead 14 degrees written in the instruction and specs so I'm in pursuit of purchasing a new adjustable canister.

I do not know the laws in CT but in Virginia, if you want regular plates instead antique, you will need to pass emissions even if your car is 25 years old. Also, if your car came with cat converter (post 74' cars), you will have to install a cat converter to pass emissions.

scottyp99

If you have 12 initial, and 36 total, you've got 24 degrees of mechanical advance. The only way you will be able to increase initial timing, without also increasing total timing, is by reducing the amount of mechanical advance. Unless.......you switch to manifold vacuum for vacuum advance. Just try it, and see how it works, easy to change back if you don't like it. BTW, it sounds like whoever you have working on your engine is a knucklehead. JMHO. Also, there are 3 things you should never do: don't **** into the wind, never play pool for money with someone who brought his own stick, and don't argue with Lars.


Scott

tgcattle

Lars helped me a lot. I set up timing as he said. With no vac installed. Gave him my vac reading at idle and he hooked me up with a vac can they gave me the correct vac at cruise. With manifold vac. I set timing to 36 total ended up being 18 Initial hooked full vac 52 degrees @ 3000 rpm. It hauls butt now

VetteNURSE

OK so heres the update. This saturday I was going to get this if it took all day. I set the initial to 18 with advance plugged and I had all in 36 degrees at 3000rpm. I then used manifold vac instead of ported and WOW what a difference! the idle rpm went up but it got alot smoother in a hurry. I found that I had 20 degrees of vac ontop of my 18 degrees of initial. I then put on the vac adv limiter, ( ya its an MSD, sorry Lars) I set it to 14 wich gives me 32 degrees at idle. I was on a roll so I played with mechanical springs and got the all in 36 degrees to come down to 2500rpm. I then tuned in the carb, set idle and A/F to get the most vac, which BTW increased 30 percent!

Now it idles much smoother, still sounds lumpy but the car doesn't shake as much. And Lars, it does now run "exeptionally well". It has huge power and it will roast the tires, no hesitation at speed.

so now I'm wondering if the all in rpm of 2500 is too low, should I play with the springs to get it to 2800? Ya and I agree the motor guy is a knuckle head.

Thanks to everyone for the advice and double thanks to Lars for the #s he really is a tuning guru!!!

Mike

scottyp99

This is why you hear abut people who bolt a bunch of speed parts onto their engine, and it's still a turd. It's all in the tune, man! VetteNURSE, I think you've got it down, if you're not getting any detonation, leave it alone and drive the tires off it. BTW, good call on re-tuning the carb after changing the timing, it's always the last step. Congrats!

Scott