Help w/ Turbo timing Question?

[Guest zcarbum]

OK,

 

I have all the basic knowledge of how the turbo system works, and how to incorperate it with my early Z..

 

BUT!!!

 

One Part I just dont quite get......... "Timing".

 

 

 

 

stock 76' is 8 deg. (+/- 2 )..... 81'-82' turbo 20 deg... and 83' is 24 deg.

 

 

1) Why would you Advance the timing on a turbo system???

 

2) Can someone help me understand why with a system that you dont want detonation!!, would you have the spark start sooner??

 

3) Is there something about the increased cylinder pressures that slows combustion??? or do I have something wrong in my thinking this out??

 

Any help appreciated,

 

aZcarbum

[Clifton]

OK' date='

 

 

One Part I just dont quite get......... "Timing".

 

 

 

 

stock 76' is 8 deg. (+/- 2 )..... 81'-82' turbo 20 deg... and 83' is 24 deg.

 

 

1) Why would you Advance the timing on a turbo system???

 

2) Can someone help me understand why with a system that you dont want detonation!!, would you have the spark start sooner??

 

3) Is there something about the increased cylinder pressures that slows combustion??? or do I have something wrong in my thinking this out??

 

Any help appreciated,

 

aZcarbum [/quote']

 

Stcok timing at idle is static,not total. The 8* on the 76 will be alot higher at higher RPMs when the mechanical advance increases. I would guess around 35* total. Total timing depends on boost. 30* total with 7 psi might work but 30* with 20 psi won't. The higher the pressure the less total timing.

[Drax240z]

The turbo engines run more initial timing to try to offset the results of a lower compression ratio, and gain back some of the low rpm grunt.

 

A NA engine has a curve that might start at 8-12*, ramp up to as much as 38* at ~3000rpm, and then carry on at that level until redline.

 

A turbo engine will have a similar curve, starting at 20* if it has significantly lower compression ratio, ramp up to as much as 38* total at ~3000rpm and stay there until redline. The issue with the turbo is that IF you are in boost, you will want to retard the timing WHILE UNDER BOOST ONLY. That's why a lot of people use the MSD BTM box, or similar. It allows them to retard timing dependant on manifold pressure. (ie: take out 1-3* timing for every PSI of manifold [boost] pressure) In that case if you are running 10psi of boost, you might be retarding 15* of timing, which would put you at ~23* of timing, but only while under boost at 10psi.

 

Hope that helps.