I have a '72 Vette with a 350 engine and automatic transmission. Now here is my problem. I cannot seem to get the engine to idle right. I adjusted the timing to where the manual says but it seems like it wants to take off as soon as I put it in gear and if i adjust it the other way it almost always dies. It produces some black smoke, I think mainly when the accelerator is pushed. I rebuilt the engine as a 383 stroker(400 crank), but I also had a 327/300hp cam installed. The rest of the engine has been redone also. I put a new distributor on it and had the Q-jet rebuilt. I wanted the engine to looked stock so I tried to keep everything the same. Could there be a compatability problem between the crank and the cam? Maybe something with the vaccuum? The guy that I bought the car from said that the tranny has already been rebuilt. Could the new engine set-up be causing problems with the torque converter that would make it shift hard? Please any information would be greatly appreciated! I am tearing my hair out trying to figure this out. thanks
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Re: cam and crank combo wrong??
The 327 cu in 300 hp cam will be marginal with respect to cylinder filling in a 383 cu in engine. It's a very poor choice of cams. Since the cylinders can't fill under wide-open throttle, the volumetric efficiency, hence torque, will suffer. You will find yourself with the gas pedal down significantly at all part throttle positions as well.
The 151 (327/350) cam works well in a 383 and with Rhodes lifters and a phase advance of a couple of degrees. A comp Cams 280 magnum straight up will allow you to cruise at 2500 RPM. (500 rpm into the power band) This is a very good hydraulic for a 383. Use Rhodes lifters.
Dale. -
Re: cam and crank combo wrong??
Scott,
I have built several "strokers" like the one you have. There is no compatibility problem between the crank and the cam, unless it was installed wrong (one tooth off). Since you've gone to a 400 crank then you have changed out the balancer and flywheel/flexplate too, as the 400 is internally balanced. Sounds like you have several problems to work on. The hard shifting is coming from a lack of vacuum going to the modulator on the transmission. The idle problem may be related. The cam doesn't sound all that radical but why don't you send us the lift and duration specs anyway. If the cam was designed for manual transmissions and short gears (large numbers) then that could have an impact on the motors ability to idle and operate at low RPMS. Did you change out the torque convertor? The black smoke is definitely coming from an over rich situation. You mentioned that the Q-jet was rebuilt. Do you know for a fact that the Q-jet was rebuilt correctly and operates as it should? Can you install it on another car to test?
--Corey #33787Comment
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Re: cam and crank combo wrong??
The 929 cam will work with a long stroke engine, but it will be like a truck engine - lots of low end torque, but low specific power output. The torque curve will shift to produce about the same peak torque and power at the same piston speed. The ratio would be 3.25/3.75 = .86, so the new torque peak will be .866 x 3200 = 2800. Likewise the new power peak will shift down to .866 x 5000 = 4300.
I know this doesn't solve your problem - just wanted to explain the effect of increased stroke. If you build a stroker motor, you need a longer cam to maintain the same peak torque and peak power points. Chances are your 383 doesn't produce much more top end power than a 327/300, but because of the increased torque, it will make more power at low and medium revs, so it will feel much stronger except above 4500 revs.
DukeComment
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I Agree
Specific power output and torque suffer in absolute value due to poor cylinder filling.
Dale.Comment
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