I finished putting the HEI in today and took the stang for a spin. It runs way better but im still having some problems:

1) the exhaust (or something) pops when the RPMs get past like 2500. It doesnt seem like it would be a backfire, so im not sure what it would be. any ideas? I didnt plug the vacuum line when I timed it, would that make a difference?

2) it shifts before like 3k when on the floor. is that normal? It starts to lose power then, but it still seems early for some reason.

p.s.- engine is completely stock with an HEI dizzy.

 

i always figured there was a reason they told you to plug the line otherwise they wouldn't tell you to. I bet you are getting a small backfire. Retime it with the vacuum line plugged and see if that helps.

 

okay, thats what ill try when i get a chance.

one more thing:

What should I set the timing to? I have heard 8-10 deg or so. How far from the TDC mark would that be on the harmonic balancer? like 2 cm or so? I would like to time it for the best performance cuz I dont care about gas mileage.

 

it really shouldnt matter too much
at idle there is no vacuum on that line anyway

 

there is vacuum on that line at idle. Unplug that line when the car is running and tell me if your car stays running. Mine wont. I thought the point of vacuum advance is to adjust the timing at idle. I could be wrong though but that is what someone told me its purpose was.

 

from wikki-
"Manifold vacuum is an effect of choked flow through a throttle in the intake manifold of an engine. It is a measure of the amount of restriction of airflow through the engine, and hence of the unused power capacity in the engine. In some engines, the manifold vacuum is also used as an auxiliary power source to drive engine accessories. Manifold vacuum should not be confused with venturi vacuum, which is an effect that is exploited in carburetors to achieve a fixed mix ratio between fuel and air.

When the throttle is opened (in a car, the accelerator pedal is depressed), ambient air is free to fill the intake manifold, increasing the pressure (filling the vacuum)."

That line will have max. vacuum at idle

 

I have to disagree with this statement. the purpose of vacuum advance is to increase economy at cruise. There is no vacuum to the dist at idle, it increases as engine speed increases. Another name for it is "ported" vacuum. Make sure you are using a port above the throttle plate. Below the plate will be manifold vacuum. Start with 10 degrees advance, is your balancer not marked? Maybe you are experiencing a "miss"? How are your wires? Or maybe you have some wires crossed.

 

vacuum advance is for when you need your engine timing advanced not at idle.Sure its a pop or is it a miss?

 

ok, that means my car has the wrong port for the vacuum line used. That is weird because it also means the po used the wrong line with the stock distributor. I thought the mechanical advance took over after idle? Whats the point of having both then? Thanks for the info. Why do they make you take it off and plug it then to set timing? Since air is moving through the carb wont there still be a little vacuum? I believe you, i am just trying to understand more about how it works.

 

Your distributor will either have a vacuum advance cannister attached to it's side.... or no cannister. No cannister would signify that you had a mechanical advance distributor. Your distributor will not have both a mechanical and vacuum advance.

As stated, the vacuum line to the cannister should not have any vacuum at idle..... "should not". Just as a precaution, the vacuum line is disconnected while establishing base timing... just in case some minor amount of vacuum was pulling the distributor off of it's base timing.

Timing for every engine will be slightly different based upon what you want out of the engine.

For instance if you have a very high compression ratio and don't feel like running high octane racing fuel....... retarding the timing will help the car run "okay".

For those not concerned about fuel mileage/economy and are strictly looking for seat of the pants power.... advancing your base timing as far as possible without encountering detonation (pinging) under load will usually do it.

Dave