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Old 08-12-2004, 07:23 AM
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Chevy 350/350 cam - poor performance

I have just completed the rebuild on my 63 corvette 327 340 HP motor. all stock specs 11.25 comp, Chevy L88 350/350 cam 450/460 lift 224/224 duration @50 (as close to factory spec as a could find),461 double hump heads, stock carter carb stock 2.5" manifolds and dual exhaust, 18deg initial and 18deg in distributor in by 2800rpm - no detonation and 185psi cylinder pressure with 5 pulses of the starter. Problem low vacuum 13'' at 800 rpm creates stumble off idle. Do I have to live with this? Any suggestions - maybe a different cam that might not create detonation and help the bottom end vacuum. Any experience with this cam? Is this a normal vacuum reading with this cam?

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Old 08-12-2004, 08:30 AM
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I`m curious to see how you got a L88 cam in a small block. The L88 was a 427 big block cam. anyways, 224 duration, 327 cubic inches = low vacuum. the stumble off idle is likely in the carb`s pump shot adjustment, the carb has to be tuned for the new engine combo as well. the spark timing should be 12 degree`s before top dead center, with 36-38 total all in by 3000 RPM.
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Old 08-12-2004, 12:30 PM
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i agree w/dv. bigger accelerator pump. but i am the world's dumbest mecheanic, i cant even spell it
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Old 08-12-2004, 06:32 PM
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You left out an important spec. What is the lobe seperation angle? The factory cam that you seem to be refering to is the LT-1 and L-82 cam. It was ground with a rather wide lobe sep. angle, 114 degrees. Chevy did, and still do, this a lot of their hot rod cams. The wide lobe sep angle allows a smoother idle and more vacuum at idle. Also, it will give a wider power band but less torque.
Many companies still sell this cam. They also sell cams with simular duration but with a tighter lobe sep angle. This gives more torque but a rougher idle, less cranking compression and less vacuum. Cams with tighter lobe sep angles tend to be more popular unless you're using nitrous. It appears that you might have such a cam. This would let you get away with mildly driving it without detonation. Don't be fooled by this you might still have detonation with agressive part throttle accelleration that you may not hear. Check your plugs for signs of detonation.
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Old 08-12-2004, 06:57 PM
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I ran that same cam (L82) years ago and was very pleased with it. The engine was a standard bore 350 (new short block), I upgraded the pistons from dish to flat tops, installed a pair of 041 heads and topped it off with an Edelbrock RPM intake and a 650 Holley and it ran 14.0's at 4400 ft elevation in a big boat Monty Carlo with 3.73 gears. I think that your problem is either total timing - which should be at 36-38 deg and/or the carb. Always start the tuning process with getting the timing right FIRST and then move to the carb. Set the total timing first and then check where the initial is. Adjust as necessary.
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Old 08-12-2004, 10:23 PM
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I have those cam specs listed as 222 @ .050 for both the in and ex with 111 in and 114 centers. Ur cam choice is all right {except its hydraulic} hehe. I had the same 340 hp engine in my 63 rdstr and ran pretty gd.Made 22 mpg with 3.70 grs.
Do u still have the stock aluminum intake for the avs?

Is the comp actually 11 to 1? or is that book specs. chevrolet tend to have wider lobe centers than aftermarket cams and should make gd vacuum. Id idle it up a bit to about 900 or 925 and recheck. Make sure uve got the idle screws adjusted and put in as much initial timing as it wants,then adjust ur dist to make the 32 -36 degrees total on a dist machine so u can slow the curve down as needed for load. Dont know if it will handle all in by 2500 with this stinky gas nowadays or not. You are running a 4 gear right? 63 means its a warner trans,but i cant remember the first gear ratio. Anyways ,just do things 1 step at a time remember ur base tune so u can go back to it if the next step doesnt work.
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