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Old 02-04-2013, 06:05 AM
damanx damanx is offline
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Help me fine tune my 3.4l with a Holley 390 cfm.

Hey all, hopefully I can get some help to nail down some tuning issues I am having.

To start, it's a 1985 S-15 with a 1993 3.4l v6 60 degree block. I've put on the Edelbrock 2 piece intake system and topping it off is the Holley 390 cfm carburetor. 700r4 transmission and 3.73 rear.

The ignition system is the original stock system from the 2.8l, which is a distributor and seperate coil.

So far, at 2900 feet, it's running at idle, a very stable 17" vacuum at 900 rpm. In drive with brake applied, it drops to about 15". Initial timing is at 12 degrees.

At cruise speed of 55 mph, 1950 rpm, vacuum is around 12". At this speed, timing is running about 42-45 degrees.

One of my issues is apparently getting the timing all in at 32 degrees, but where? I've read anywhere between 2500 - 3500 for mechanical. If I am cruising 55-65 most of the time, should I set mechanical to be all in at around 2000 rpm?

Fortunately, I have a timing analyzer that I have been using to watch what the timing is doing under different conditions and another issue I need to clarify is what am I wanting the timing to do as soon as I stomp the throttle? For example, at cruise when the timing is full mechanical and vacuum applied, it is at 45 degrees. When I get into it, vacuum goes away and the timing drops to 25 or so. Am I correct in assuming I need to put aftermarket weights and springs for the mechanical to stay at 32 above 2000 rpm?

Also, when I give it gas, with the vacuum advance hooked to the ported outlet on the metering block, it appears that I lose vacuum and maintain the max mechanical advance almost immediately. Should I place a vacuum delay inline to slow the drop?

Thanks for any and all help.
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