A couple weeks ago there was a thread discussing timing/split, and it brought my attention to the PFC base map. Most people that tune on here run a split of between 10-15* with say 12-15* advance at 15 psi.

It's generally known that lowering split raises combustion pressures and increases power at the cost of being more dangerous. It's also generally known that increasing IGL timing also increases power (up to a point) at the cost of being more dangerous.

So here we have 2 timing factors that can effect power/engine safety.
Looking at the PFC base map under high boost they choose a different method then most people here. They have very conservative IGL timing and very close split at high boost (20psi) The split goes as low as 4* under peak torque conditions. Generally a big no no, but maybe the low IGL makes this A/OK?

rob94rx7 or something like that on here has been running stock twins at 20+ psi on the PFC base map timing with no problems for a long time. it was in his thread that actually got my attention to this.

Is this a case where there is more then one way to skin a cat?
Do the 2 methods have the same effect. Both being safe just in different ways.
Will one method make more power then the other? Is one way more reliable? Has anyone done any testing in this area? I'm just curious what everyone thinks of this. Discuss.

-Brent V

 

I typically set split at 12 degrees. I have found that lowering it to say 10 makes really no difference in power gain and going lower only yields a couple HP overall.

Increasing the leading timing is where you can pickup a lot of HP.

 

Cool thats what i wanted to know

 

I think it depends a lot on fuel. People running alcohol injection (or high percentage/straight meth) tend to benefit much more from an agressive split than those running on straight pump. I don't know exactly to what degree, but advancing the IGL gives similar results to narrowing the split, so you have to work progressively on both to get a happy medium of power, proper EGT's and little/no knock readings. 12* across in boost seems to be the safe norm for pump.

 

It has everything to do with the fuel being used. That largely dictates the burn rate which dictates when spark can be fired.

Split is contingent on lead advance. 12* split with race fuel is almost a waste of split. Skinny it up to about 5-7* split and watch the difference. But, I agree with Jason that lead advance is obviously the guy to look at.

Zero (or even negative) split in vacuum; Zero split at 0psi in the manifold, ramp up to 5-7 by 15psi and keep static thereafter when using high octane race fuel. Zero split at 0psi in the manifold, ramp up to about 10-11* by 15psi, ramp up to 15* split shortly thereafter, then keep flat when using any kind of pump fuel.

B

 

How much gain did you see with your 25%+ Alcohol to change the split from standard 10-12 down to 5-7??

 

Don't know. Never did a before dyno to really see. I ran an aggressive lead advance (16*BTDC at 15-25psi) with a 6-7* split. At 15psi, if it were all pump, I would've done something like 13-14*BTDC with 11* split. /shrug

B

 

Only reason I ask is that I was talking with HC, he is currently running 12* split (because of his Safeguard) and plans on ditching the Box to narrow the split. I'm going to be running a safeguard this summer as well, and will have twin M6 nozzles with a 75/25 meth/water mix. I'm wondering for my smaller amount of alcohol how much a narrower split would really do, I'm looking forward to seeing what Howard nets by doing it.

 

No clue from me. If anything, I'd focus on lead advance rather than split as lead advance is what will yield the greater power and torque with what you're wanting to do. That's my 2 cents.

B

 

on 100 octane and 18psi I tried 12 split and then I tried 10 split. There was a difference of about 2 hp, so I just put it back to 12. I didn't try anything as narrow as 6 or 7 split. I really wish I had the dual EGT setup at that time.

 

Yup, 100%

On C16 at 20psi I am usually around 18 deg advance. I have played with the split from 15 to 12 to 10 to 8 and never noticed a major increase in HP, I actually lost HP and the air fuels changed quite a bit. I then put it back to 12deg split and left it alone. I agree with Jason.

There are guys out there that like high advance and a safe split, some like med advance and a closer split and some like 15deg advance and a simple 15 deg split, you will get a million answers when it comes to timing. The only way to really see what is best is to get a dyno and have some fun lol!!!

Next time I'm on the dyno, i might just vid the changes and the pc screen...

Anthony