Mallory HEI Tuning

[houston54]

I just replaced the GM HEI unit with a Mallory HEI and have noticed an improvement in the performance of the motor.  Is there any other tuning I should considered for general street use?  The Mallory came with a allen wrench and extra springs but very little information as to why or when they should be used.  I am assuming the allen wrench is for adjusting the vacuum advance but I can find no information on this.

[39deluxe]

I got the same unit for my stepside but the new engine hasn't been fired up yet. You're right. There isn't much tuning info with the product.  As for adjusting the vacuum advance, if you are not getting any part throttle pinging it is probably ok as is. If you are getting pinging tighten it up just to the point where it stops. That's assuming you are using the right grade of gas  and not trying to use an adjustable advance to compensate for too low of octane.

As for the advance curve, I don't know what comes in the unit. It's probably a compromise that works well in most mild street engines but is better than the GM HEI. I think that you want about 34-36 total degrees all in by 3000 rpm. That is with the vacuum advance disconnected and the hose plugged. If you have an adjustable timing light or a degreed balancer this is easy to check and swapping springs to dial it in is easy. It might take a combo of springs to get it right on. My used balancer was good so I bought one of those Pro-Form balancer covers from Summit. Jegs and others have them too. For under $30. I have a full degreed balancer that is easy to read.

Tom

[wayne petty]

those distributers also come with a plastic KEY... look for something about 3 inches long... with steps... that is used to set the limit of centrifical advance... the different steps are to inserted through the breaker plate and something loosened.. then tightened...


there are a bunch of different adjustments on most distributers...

vacuum advance.. when it starts by ajusting the spring tension

there are ways.. to limit the amount of vacuum advance also..

if you noticed.. there are different diameter wires used in the springs..

the thin wires let it advance at lower rpms..   thicker ones increase the speed needed to advance to the same point...

on some.. you can vary the amount of slack on the secondary spring.. so the primary moves first.. then the secondary later..

there is a mechanical limit device on them.. that is what the plastic key is for... so you can set it... without needing to guess at it.. which is impossible..

there is a ton of guess work and educated guesses.. on how much how soon...   every motor combonation is different...  there are base lines that will work and be really close...

if anybody plans on playing with the advance rates...  it is best to screw a detonation sensor that matches a later model motor of the same kind.. with the indicator that can be had from places like jc whitney... similar to an air fuel ratio meter...  the detonation sensors are piezo microphones tuned to specific engine detonation sounds.. so they buzz the ecm when the motor starts making those death rattles..

a lot of speed shops still have a working distributer testing machine.. and most know how much curve to put in a motor if you can describe the parts you have..


in nascar racing.. they go as far as having movable reluctor teeth so they can look for that last fraction of a horsepower.. but this is on a dyno...with tons of time... and millions on the line...

hope this helps a bit.. i wish i had more numbers for you....


do you have degree tape on your balancer.. or an  an adjustable timing light... a tachometer,   a hand held vacuum pump...   a fuel pump vacuum testing gauge..    ( this last one has a larger dial so it is easier to see..) ((i really miss the large gauge i had on my marquette scope.. it fell over in the northridge earthquake and the push buttons will all caved in.. landed on a small block chevy))

with the above tools .. less the smashed scope...   you can figure out when it the mechanical advance starts... and how much it advances..  and how much the vacuum advance moves and when it starts...

you might also want to drive the car with the large vacuum gauge tee'ed into the hook up for the vacuum advance to see how much vacuum you have during different parts of your drive cycle..


here are a few links to read up on

http://www.circletrack.com/techarticles/139_0310_ignition_timing_tech_how_to/index.html

http://www.circletrack.com/howto/1842_ignition_timing_maximum_performance/index.html