as you know, i put a 350 in my 86 305H. what timing chain should have been used (for vortec truck motor or lt1) (vortec heads, lt1 cam). i jetted it down (750 cfm) and you have to advance the timing to like 20 to get it to smooth out. it runs bad on the low end, but good on the top end. any suggestions?
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86 Camaro (350)
79 Blazer (FI 350)
98 Buick Riviera (S/C)
96 Grand Prix (Sp. Ed.)
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It would be helpful to know what distributer type you are using. Whether it is points, HEI, vacuum advance, computer controlled, etc....
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non-computer controlled (nothing is anymore), HEI, vacuum advance, accel, gm coil86 Camaro (350)
79 Blazer (FI 350)
98 Buick Riviera (S/C)
96 Grand Prix (Sp. Ed.)
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OK, we are getting into artform territory. Dialing in a Vacuum and Centrifugal advance can be tricky. If you aren't breaking up on the top end and the low end is soggy, try switching the vacuum advance to a non ported source. There are two types of vacuum ports on the carb, ones that pull constant vacuum, ones that don't pull vacuum until a certain throttle angle. Try a constant vacuum source and see if it sharpens up the low end. It's been years since I tuned a carb/vacuum advance engine so on certain specifics, I would need a little brush up. There are also mechanical advance kits that allow you to change weights and springs to allow the centrifugal advance to come in sooner, adjustable vacuum advance pods that allow a fine tune of vacuum advance rates. Start by changing the vacuum advance source and let me know what happens, we can go from there.
BTW, when you re-jetted, are you sure you are on the money?Comment
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the distributor is not the problem. also ive had from .089 to .110 jets in it, so its not a carb problem (other reasons i know also)86 Camaro (350)
79 Blazer (FI 350)
98 Buick Riviera (S/C)
96 Grand Prix (Sp. Ed.)
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Well if you are absolutely sure that everything else is dead on, was the current chain installed straight up, advanced or retarded? Generally if a chain stretches, you lose low low end with an increase in the top end. Same scenerio if the cam is retarded. Hopefully the cam was degreed rather than simply lining up the dots. Without knowing the history of the motor, I would even run a compression and leakdown test to check for uniform figures in each hole. Problems in this area sometimes can be masked by higher rpms.Comment
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i took the timing chain off. its lined up right. i am going to degree the cam. im also going to reset the valves86 Camaro (350)
79 Blazer (FI 350)
98 Buick Riviera (S/C)
96 Grand Prix (Sp. Ed.)
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