Anyone,

Using the ARAP bin w/Vortec's is this too much advance 47Deg total? for vortecs. SDPC used 15 deg base timing to get the 360 horse power in their SDPC 360. is that in the chip or base timing? Basically can I run the arap with 6 Deg base W/ 91 octane (California) gas on vortec heads. Mags say they want 32-35 w/ a carb. I'm using the tpi w the knock sensor functional, anyway I don't want to hurt perf, or internals due to too much timing.

Any advice would be appreciated.

Thanks

K

 

There is alot more to consider in terms of timing, looking at the biggest number in the table tells you very little.

However you are correct in the idea that they dont really like anything over 36* total.

 

i heard that the best should be around 33*-35* max advance.

nebu.

 

The "total" number in the BIN isn't the same thing as "total timing". The 32-35° number you see given in race tuning is measured with zero vacuum, i.e. max load, or WOT; the high number in the BIN is for high vacuum, i.e. light load, or cruising.

The 2 numbers are the analog of static + centrifugal timing, as compared to static + centrifugal + vacuum advance, in a mechanical distributor.

Don't modify it until you understand it better.

 

Exactly right.

In general terms ARAP is very hot. Probably too much timing for the Vortec head needs in all situations, both cruise and WOT.

It might be in your best interest to spend some time in the DIY PROM forum to gain a better understanding of how a .bin supplies timing to an engine at different load levels.

Below you will see some actual dyno data from my motor. The blue line shows total timing at WOT to be 36* the red line shows total timing at WOT to be 34*. You will notice that nice gains were had from the 2* increase up until 4900rpm. After 4900rpm adding more timing did nothing for power output, the motor didnt want anything more, end of story, I dialed it back down to 34* after 5000rpm. 38* was then tried in pull 11 below 5000rpm and nothing changed, so the final timing is set to be 36* until 5000rpm and 34* beyond 5000rpm. You will however notice a slight power jump at 5700rpm, this is due to the fact that I pulled some fuel from the PE Vs. RPM tables as she was a bit rich up there in pull 9, ~12.2:1 AFR.

What does this mean? It means that in a ECM controlled environment the motor may very well want different timing at differnet RPM, which is fine as you can very well dial it in to what the needs of the engine are. So all this talk and speculation of what is best from rumors that carb guys pass out is just crap until you start gathering actuall output data.

Oh, I dont run Vortec heads though, I run E-Tec 170 heads with the SDPC base and a Superram plenum runner setup. The heads are kinda similair but not exactly.

You will also notice the different slopes of the power curve. This is also something you can directly atribute to the Tuned Port philosophy of a long runner setup, IE: TPI or Superram. Hence what I believe to be the difference in timing to make max power at different RPM levels.

The results were also had with a stock 48mm TB, which is currently a choke point on the motor as there is manifold vacuum at WOT. #s are RWHP

 

E-Tec 170, ported and polished, for those who assume they are the same as the Vortec head, they are clearly not the same or not really even close.

 

Other than the valve guide and the spark plug boss, those look nearly identical to my Vortecs.

 

Spark plug boss
Valve guide boss
Short side radius
Larger eghaust valve
Larger exhaust port
Cleaner bowls overall
80% E/I Ratio

Are a few of the differences that require additional machine and porting work to acheive with a set of box-stock Vortec Heads.

Ask me how I know, oh yeah, I have had both heads in hand for direct comparison.