Ignition Timing after Head Porting

[ktm]

I am about to pull the trigger and get my cylinder head ported by Slover Porting and install an Isky cam. I've been searching for the better part of 2 hours trying to find an answer to my question to no avail.

 

Following porting work and cam installation, will the timing generally stay the same for a given boost (yes Tony, I know it's about flow) or does it decrease due to increase in VE and flow and thus power? For instance, I may run 20 psi to achieve 400 ft-lbs of torque, but following porting work I may be able to achieve that same power at 12 psi. My timing at 20 psi is, say, 18 degrees. Would I retune my setup for 18 degrees at 12 psi or would I be able to run closer to its current timing (say, 25 degrees)? I am talking about rough tuning.

 

The effective compression ratio has definitely changed considerably, but the mass of air has not correct? Air + fuel = power. For a given power level, you need a certain amount of air and fuel.

Edited September 28, 2010 by ktm

[BLOZ UP]

The timing can stay the same, but you can pick up power by retuning it--especially if you add a cam. I couldn't say whether you need to advance or retard it, I'll leave that for the experts and all their Maths.

[rossman]

You should be able to advance your timing. I think this thread answers your question.

[ktm]

Close rossman, it is that thread which prompted my question. Tony mentioned in passing running 10 psi with full advance versus 20 psi that is retarded for a given power, but it is only mentioned once. I've been trying to get my head around that statement for a while and can not quite seem to get it. If I am making the same power at 10 psi that I was at 20 psi, why can I run full advance at 10 psi? Shouldn't it be closer to the advance at 20 psi?

[DuoWing]

I'm no expert and don't claim to know much about turbocharging, but what I got out of Tony's post was essentially that don't look at it from the aspect that it's making more power as the reason to need to retard the timing, but rather that you're motor is being able to use the fuel/air combination much more effectively. So you have less friction on the air, less compression of the air from the turbo, so less heat. I can't be sure on this, but it also sounds like you don't need to the extremely huge injectors because there's overall less being stuffed into the chamber than when you were running it on 20psi. It all works out to build more power, with less likelihood of detonation. So in that respect you can then run more timing advance and with the port/polish, better turbo, etc make more out of less much more efficiently.

 

At least that's how I interpreted it. Mainly when he was saying about making 300hp+ on a stock j-pipe without the need of an intercooler is what gave me the way I took it.

 

Edit: I think this line from Tony best sums it up: Things that become mandatory at 20psi are not necessary at 8-10 psi.

Edited September 28, 2010 by DuoWing