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Old 05-16-2010, 08:18 PM
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? about advancing cam

I just got my rebuild back from engine guy, bone stock 350 .30over, stock manifolds, intake and exhaust, DUI dist. Jet Quadrajet, stock crank, stock rods, stock 4 eyebrows. I don't have the cam card in front of me but I'm pretty sure its .417 lift, It's been in the truck for a few days: here's my prob. from the stoplight to about 3500 rpm it's SO SO, but from 3500 and up it will snap your head back, a friend said I need more cam advance to move the powerband down. I remember the builder saying there is 4 degrees of advance ground into cam, I have a comp 9 keyway timing set I just ordered, how much can I advance the cam safely. I know I should use a degree wheel, but with the engine in the truck it's a pain. I was thinking I would only need 2 or 4 crank degrees, which I think is 1 or 2 cam degrees....right? At what point would I start interfering valves with pistons? If anyone can help a rookie I would really appreciate it.
Thanks Dave
and I would ask engine guy but the bum hasn't retured phone calls
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Old 05-16-2010, 08:37 PM
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What`s the rear gear ratio? what size tire? Where`s the timing set at? What intake manifold? Need this information so we can figure where the issue is.
If the cam`s lift number is that low then it`s not very big, so we need the true cam specs. Unless the cam is too big for the combo, advancing it isn`t going to help any, advancing the cam will only drop the power band by 200 RPM.
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Old 05-16-2010, 11:29 PM
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I don't know if the Chevy 9-way timing sets are like the ones made for Pontiac, but all of the ones I have seen have been off about 2 or 3 degrees. Maybe someone can tell us if the Chevy sets suffer from the same problem.

Each degree of advance dialed into the cam will only move the power band down about 100 RPM. So a true four degrees advance will only have the cam come on 400 RPM sooner.
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Old 05-16-2010, 11:40 PM
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Intake closing point is too late for the available static compression ratio. Determine exact static compression ratio and change cam to one that matches.
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Old 05-17-2010, 05:45 AM
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Quote:
Originally Posted by racingdave35
from the stoplight to about 3500 rpm it's SO SO, but from 3500 and up it will snap your head back
I'd recommend you set the timing curve as aggressive as the combo will handle w/o risking any detonation, then work on allowing the Q-jet secondary to come in sooner to see if that helped matters.

But as said, need all the info on the vehicle.
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Old 05-17-2010, 06:33 AM
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2.73 rear, th350, final 6.88 in first gear,4.14 second? I think, stock truck manifold,8 inch wheels 265/60/15 tires, 24 degrees static/36 full advance on the ignition, checked the plugs, no sign of det. I have a lower vac. choke pull-off so the quad comes in pretty early.
If I go the full 8 degrees on the timing set that would be 4 degrees additional cam advance, or only 400 rpms? Don't get me wrong, the truck runs well even from idle; I would just like to have what I have up top, off the line.

Dave
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Old 05-17-2010, 06:45 AM
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Quote:
Originally Posted by racingdave35
2.73 rear, th350, final 6.88 in first gear,4.14 second? I think, stock truck manifold,8 inch wheels 265/60/15 tires, 24 degrees static/36 full advance on the ignition, checked the plugs, no sign of det. I have a lower vac. choke pull-off so the quad comes in pretty early.
If I go the full 8 degrees on the timing set that would be 4 degrees additional cam advance, or only 400 rpms? Don't get me wrong, the truck runs well even from idle; I would just like to have what I have up top, off the line.

Dave
Dave, advancing the cam isn't going to help that much, especially w/o having degreed the cam to start with. Unless you know where you are now, you can't know where you'll be after changing the cam phasing.

What I see is a truck crying out for some gear! Something around 3.50:1-up.
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Old 05-17-2010, 10:29 AM
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Which intake? are you using a adapter or spacer? if so what type?
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Old 05-17-2010, 10:32 AM
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Quote:
Originally Posted by DoubleVision
Which intake? are you using a adapter or spacer? if so what type?
He said: "bone stock 350 .30over, stock manifolds, intake and exhaust, DUI dist. Jet Quadrajet, stock crank, stock rods, stock 4 eyebrows."
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Old 05-17-2010, 10:36 AM
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I seen that Cob, However I was just asking since I`ve seen guys put Q-jets on edelbrock performers and use a adapter plate and still call it stock. I certainly agree he needs gears, finding out which intake and how the carbs set up is important as well for low end development, even when he gets some gears for it.
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Old 05-17-2010, 11:40 AM
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Post the cam timing and lift specs. You probabily need a much higher rear gear ratio and a much higher stall converter if the cam is of any size.
Advancing the cam will not make a too big cam into a small cam.

As said you need to degree it in to see where it is at before attempting to chang e the installed cam phasing.
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Old 05-17-2010, 11:51 AM
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Quote:
Originally Posted by DoubleVision
I seen that Cob, However I was just asking since I`ve seen guys put Q-jets on edelbrock performers and use a adapter plate and still call it stock.

-----

He really needs headers, too.
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Old 05-17-2010, 08:52 PM
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Thank you everyone for the help, I'll do some homework and get back. Thank you all very very much!
Dave
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