lookin for a couple tips to tune the BB in my 73. ive had the car a couple months now, and this is my first old school v8. i did work on pre 1970s airport equipment for 13 years, so im a decent wrench w most of the basic tools, ive got timing lights, dwell meter, etc

the block numbers id the engine as a 300HP big block(396 or 402) LS3 from a 71 chevelle. it runs good, doesnt use or leak oil, so im hesitant to disassemble it to check the head, cam or crank. its got an edelbrock performer 2.0 intake, and a holley 670 street avenger. idle is a bit lumpy, so im guessin the cam isnt stock. no idea on valves, porting, pistons etc

ive got her runnin pretty well, i got her with a well worn, sloppy non tach drive distributor, i purchased a used tach drive unit here, rebuilt it using info found on this forum(THX!) and installed it yesterday. i set the initial timing at 16, and found i could only get 32 deg mech advance, so rather than changing the stop bushing, i set the initial timing up to 20 degrees. at 20 deg she idled much smoother, and i got 36 deg total adv at 2900rpm. close enough - all setup done w vac adv capped

question: am i running any risks using the 20 deg initial advance? even though the idle sounds smoother there, should i change the stop bushing to a thinner one, and back down the initial timing?

question 2: i picked up a cheap vacuum gauge at autozone, and at idle the needle virates between 9-13 psi. after watching the holley vid

http://www.youtube.com/watch?v=NrnzD7PgoHI

i checked my ignition and all seems well. is this fluxuating vacuum reading anything that would cause concern, or should i disregard it?

the engine runs great to me, but being my first v8 ireally dont have anything to compare it to

thx as always!

 

1. If it starts when hot you can leave it at 20 otherwise you need the bushing. Even the factory set up had a plastic bushing.
2. Without knowing how radical a cam it's hard to comment on the vacuum reading. The Holley though should have a power valve that is at least 2 numbers below your lowest reading so if you are going as low as 9 you need a 7.0 valve.

 

If the fluctuation rate [when jumping from 9-13] is very regular, I would guess that is due to the overlap built into the cam. Thus, it must be a fairly aggressive cam. To make good use of that cam, the heads would need to flow better than stock pieces. Anyway, I think that's the cause of the fluctuation and there is nothing to worry about.

As long as your car starts and idles well, and it doesn't have any signs of pre-ignition (pinging) when at WOT, you should be good to go.

 

This website tells you how to diagnose engine problems using a vacuum gauge, it's pretty informative.

http://www.secondchancegarage.com/public/186.cfm


Scott

 

thx guys for the info. she starts fine hot, and ive been watching for any signs of pinging, havent heard or felt any yet. ill read up on that link, im always lookin to learn new techniques

thx! again