Just curious what kind of spark advance forced induction LT1/4 guys are running....

how much boost?

also are you using meth?

stock bottom end? or built, lowered compression, forged bottom end.

I asked this question on the C5 FI site and it seemed like most ran 15 to 19 degrees spark advance under boost - regardless of how much boost or whether they ran meth or not. They also seem to be making crazy power. (But dont forget some of our own: aks racing, tjwong, lcvette, are also making crazy power as well. )

 

I have read that you typically retard 1 deg of timing per 1lb of boost.

 

ok, so the time honored N/A spark advance for SBC is 36 degrees at WOT to redline.

So I should be running 26 degrees timing at WOT (for 10 psi boost, on a stock bottom end).

 

Good place to start. Other factors that affect the timing are fuel octane and intercooling.

 

ok. next question...Im still a little skeptical...

If 26 degrees if acceptable for an LT1 under boost....

Why dont the LS1 guys run that much spark advance?

26 degrees (LT1 under boost ) vs. 17 degrees (typical 17 degrees for an LS1) thats a big difference.

Why so much difference? It cant just be because of reverse-cooled heads....

 

Compression ratio becomes a factor. They may also be using a safety margin as well.

 

Dizwiz24,

On my 95 vette with p1sc, ported heads and intake, slightly lowered compression ~10:1 i would see knock at anything over 21* of timing on 93 octane pump gas, this was at 12 psi intercooled. lsx motors cannot be compared to gen1 or 2 small block chevy configurations as they have much better suited combustion chambers for flame propagation and require less advance for a complete burn. Our chambers require a little extra time to attain the same burn efficiency and is why you see advance numbers generally a bit higher. obviously the preferred method is less advance and better chambers, any advance not required to achieve the same burn equates to additional horsepower and the ability to raise the static compression ratio with less likelihood of detonation.

Hope this helps, my suggestion is to data-log your runs on the dyno/street starting with low advance in the 16-17* range in the extended spark maps above 100kpa, with our limited map function and 1 bar sensor this is about is good as we can hope for without the use of add on ignition modules and boost retard assistance. log each run once you have your AFR dialed in and increase advance by a degree until you see minor knock retard, back down your total advance in the areas this occurred and repeat until you have your advance dialed in through the RPM range at 100kpa+. this netted me 512rwhp using my engine and blower configuration and the car has been running strong and reliable at this level for the last 4 years on 93 octane pump.

Chris

 

Back when I was running my 396 I was at about 22-24. I was running a if I recall a 15 gallon per hour jet on Greg's Meth- injection system. My compression ratio was about 9.7:1 with AFR 210 heads and a pretty mild cam.

But there are alot of determining factors... If you are running meth injection how much are you pumping into it, when does it turn on and off and the outside ambient temps.

As Ice was suggesting as well almost every setup is a bit different so it is best to increase a degree at a time. I also had a memory set boost guage to see what I was actually making in boost.

When I was setting up my system, I would also have a copilot monitoring the spark knock with my laptop when I was was on the throttle and I would monitor this with Auto -tap or tuner-cat which ever...

I hope this helps ! good luck with your tune.

Mo

 

lcvette, mo_bandy,

thank you, these were the types of responses I was looking for.

yes, I agree. I feel my best area, @ 10psi boost, 12.0:1 AFR, is going to be around 20 to 22 degrees of spark advance on my stock bottom end 93 lt1. I am using meth injection (blower works kit w/ pressure solenoid)

I will target this range when tuning.

 

i was wondering the same thing i have a 96 lts im wanting to do a rear mount turbo and was wondering how much i would need to advance my timing and what a safe amount of boost would be on a stock motor and if i need to upgrade fuel injectors and pump?

 

Well first you will want to retard your timing. Not advance it. Also if you run 50/50 meth/water, that will help you not have to retard it as much.

Keep engine temps cool w a 160 tstat.

Yes you will want the bigger injectors (60 lb/hr minimum) and a big fuel pump (walbro 255/hr w hotwire mod as a minimum.

Good luck

 

ok thank you ive been researching everything before i get into it cause im a very low budget so i dont want to mess anything up then have to make payments on a blown up car and its my daily driver so i cant have that.