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Just interested to know what kind timing guys are running with this kind of setup on 93 pump gas, no meth
setup - lsx b15 create- comes with a ls7 cam from factory (9.0.1 CR), twin turbo, borg warner 62's, 93 pump gas, with intercooler, but no meth etc, 15psi of boost at present, 11.3/11.4 afr at high rpm wot and timing is 27 to start with at 100kpa, then ramped down to 16 at 205kpa(15psi), using holley dominator to control everything
I run 14 degrees at 14 psi and 10 degrees at 20psi. with meth and i think that is about the safe level without it was well...but I am limited to 90octane at best. I went off of Denmahs old picture/chart for the most part when I was tuning at different boost levels. I never had any issues with them. Most of the time for street cruising i just leave it at 10 degrees and run it at max of 14-15psi. Still to many ***** for the street like that.
There is no right answer. That's a great pic above BTW and should get you close.
What you have sounds like it's in the ball park. I'd drop timing to 12. Check all your plugs and see if you can find the leanest cylinder. Then pop a new plug in that cylinder and do a pull at 12* and 15lbs. I'd think that would make some serious power on the B15 motor... Assuming you can get a nice long pull at that power level, do it. Then shut the engine off right a way. jump out and pull the plug. Adjust timing up or down depending on how the plug heat markings read.Bump 1 degree and and do it again. Pretty much the only safe way without a chassis dyno IMO.
Compression ratio and cam choice matter when trying to get the timing right. Starting at 10 to 12 degrees is a good starting point. And READ THE PLUGS!
where should target afr be at say 14psi?? on 93 pump, intercooler etc, my IAT always very steady at 75 to 85f depending on outside temp, read so many ideas from 10 to 11,8 afr on that level of boost, thoughts?
The prefect AFR for your combo will be the one that nets the most power... as with anything, it varies... But for the most part it isn't going to vary much. On a gas scale you don't want anything below 11.3 IMO, and even that is out of the peak power window by quite a bit. Too much fuel isn't a good thing. even 11.3 is over a full point out of the peak rich power window. Strictly using the extra fuel to help with cooling. Much more than that and you can cause detonation VS prevent it. If you see detonation at 11.3:1 and not at 10.8:1 your timing is to advanced. Over advancing timing to compensate for an overly rich mixture is just bad tuning. a little water/meth inj goes a long way and its dirt cheap w/ easy installation. I'd just buy the parts though. Most basic "kits" are overpriced IMO. Shouldn't cost you more than $150.
Last edited by Forcefed86; May 22, 2020 at 07:48 AM.
The prefect AFR for your combo will be the one that nets the most power... as with anything, it varies... But for the most part it isn't going to vary much. On a gas scale you don't want anything below 11.3 IMO, and even that is out of the peak power window by quite a bit. Too much fuel isn't a good thing. even 11.3 is over a full point out of the peak rich power window. Strictly using the extra fuel to help with cooling. Much more than that and you can cause detonation VS prevent it. If you see detonation at 11.3:1 and not at 10.8:1 your timing is to advanced. Over advancing timing to compensate for an overly rich mixture is just bad tuning. a little water/meth inj goes a long way and its dirt cheap w/ easy installation. I'd just buy the parts though. Most basic "kits" are overpriced IMO. Shouldn't cost you more than $150.
Thanks for your post, this is my point, everyone has a different idea on the correct afr, but your post does make complete sense, so its all about getting timing right, how much power could one lose out on say 1000hp, say your making 1000hp on 12.5afr, then you made it richer to say 11.5, how much hp would you lose approx?
Thanks for your post, this is my point, everyone has a different idea on the correct afr, but your post does make complete sense, so its all about getting timing right, how much power could one lose out on say 1000hp, say your making 1000hp on 12.5afr, then you made it richer to say 11.5, how much hp would you lose approx?
A lot depends on the fuel used and the consistency of that fuel. Pump gas has a smaller window for peak power AFR's than say E85. So smaller changes in AFR will make more noticeable power gains. Something like E85 and you may see a 1-2% power difference going from 10.8 to 12.5. While on pump or race gas you may see 5-6% differences. There is no magic rule or number unfortunately. The engines VE, head design, bore, piston speed,compression, valve events, inlet temps/density and a hundred other things all play a big role. Its not a matter of power lost or gained with a turbo car in most cases. You aren't talking big power numbers relative to another lb of boost. Its about being as far away from the knock threshold as possible... being "safe". 12.5 may net you 15 more hp at the crank than 11.5. But you may be right on the edge of detonation, so it's not worth it...Better off to be rich and retarded as they say, lol. Then throw another lb of boost at it.
You can only go so rich with pump fuel before you do more harm than good. In my 91/93 pump gas experience 11.3:1 was that number on multiple engine setups I shot for based on knock sensor feed back. Also I noticed teh lower the compression, the less efficient the engine was and the more fuel it wanted. I would hit my best trap speeds at 10.8:1 on my 7.8:1 383. Yet my much more efficient 2.0 liter with a 4 valve head liked 12.5:1. (e85) and 34psi. WHich if you read on those forums is the "go to" AFR target for e85 on a baby motor.
Last edited by Forcefed86; May 22, 2020 at 03:52 PM.
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Timing curve with 93 pump gas 
