timing and iat

[bct10985]

Those with centrifugals what kind of iats are you seeing and what is your total timing at wot?

[BullF-16]

My timing was about 17-19 deg at WOT with IATs at about 115-120.

Pat G, my tuner set it up to pull timing at IATs above about 55 deg C or 135F

Fully built/forged motor though!!!!!!!!!!!!!!

AFRs were very conservative at 10.8-11.0

[dan0617]

Timing depends on IAT in my tune. On a 65 degree day, I see IAT at the top of 2nd gear at 114 degrees and timing at 14.5 degrees. By the top of 3rd I see IAT at 159 degrees and timing at 11.5 degrees.

I am surprised to see timing pull that much with that temp but I guess that is what is safe. I'm also surprised to see IAT's climb that much, but is still better than the top mounts I've seen. This is with a Vortech Si trim ECS kit, 12 lbs of boost on a stock cammed L99.

What is everyone else seeing for IAT's after a 1/8th or 1/4 mile pull in 60 or 70 degree weather??

[bct10985]

My iats were getting up to 160 on the dyno and my tuner said it would only accept 8 degrees of timing before knock sensors would pull timing. He acted kinda shocked and asked what octane and where i got the gas from. Royal farms 93.

[dan0617]

I am at 11.2 AFR running 93 octane 10 percent ethanol. Gauge set for 14.2 stoich. I am down to 11.5 or 12 degrees timing at 160 IAT. 6200 rpms 12 psi boost. No knock retard.
Stock l99 stock cam.

8 degrees seems a little low. Make sure your AFR is no leaner than 11.7 with normal gas calibration and fuel that has ethanol blended.

[realcanuk]

Originally Posted by bct10985

My iats were getting up to 160 on the dyno and my tuner said it would only accept 8 degrees of timing before knock sensors would pull timing. He acted kinda shocked and asked what octane and where i got the gas from. Royal farms 93.

I dont think IAT's should get that high with a centri. Even with my eforce I never see 160.

I am running 94 octane, 10% ethanol, , 12 lbs of boost, 18 degrees of timing, and afr around 11.8 . This is on a forged motor and meth, which can obviously take more timing than a stock engine.
By 158 I am pulling a ton of timing, just in case but I never expect to see those temps.

[bct10985]

Matt from fsp thinks it could be that their dyno didnt have good enough airflow and that you would never see iats that high on the street. I dont know why im looking for more power the thing just blows the tires off as it is lol

[Padre]

With ported heads, 9.5CR, stage II intercooler, and 104 unleaded, I see 160* (at 6800 rpm and 130mph+ at the top of fourth) and 18* timing with no knock-reduction.

Padre

[dan0617]

I see 160 IAT on the street at the top of 3rd after a WOT pull starting from 1/2 way through 1st gear. Not the dyno.

[dan0617]

With an air to air IC centri, or with a normal intercooler on a top mount, I'm betting there isn't a setup out there that stays below 160 IAT on a 70 or so ambient day.

Everyone I see below 160 is fancy intercooler, AC setup, meth, etc.

[dan0617]

Originally Posted by realcanuk

I dont think IAT's should get that high with a centri. Even with my eforce I never see 160.

I am running 94 octane, 10% ethanol, , 12 lbs of boost, 18 degrees of timing, and afr around 11.8 . This is on a forged motor and meth, which can obviously take more timing than a stock engine.
By 158 I am pulling a ton of timing, just in case but I never expect to see those temps.

Cam and compression have ALOT to do with timing. Meth has ALOT to do with IAT. Turn the meth off and let us know what your IAT and timing is at the end of a 1/4 mile run just before you lift off the go pedal. Ill bet you see well over 160.

[Alvin@PCMofNC]

Originally Posted by bct10985

My iats were getting up to 160 on the dyno and my tuner said it would only accept 8 degrees of timing before knock sensors would pull timing. He acted kinda shocked and asked what octane and where i got the gas from. Royal farms 93.

I would make some changes ASAP. A good cam will allow you to run more timing at the same boost than the stock cam..Especially if you have a L99. Please let us know if we can help with the cam.

Other than that I would go up on the pulley size (less boost) I feel really uncomfortable if I cannot get at least 12-14 degrees of timing in a setup and the reason is this...

Combustion releases energy in a combination of two ways. 1. Expansion work (good) 2. Heat (not so good) The later the timing the more the combustion cycle misses out on expansion work because the majority of the expansion happens relatively soon in the cycle at around 28-35 degrees after top dead center. So what is happening the energy released misses its chance to be expansion work and so is only option is to become heat. This is putting more heat into the exhaust valve, plugs, headers/manifolds, cats, etc!

What I'm getting at is the later the lead, the more your going to start cooking everything else!

[realcanuk]

Originally Posted by dan0617

Cam and compression have ALOT to do with timing. Meth has ALOT to do with IAT. Turn the meth off and let us know what your IAT and timing is at the end of a 1/4 mile run just before you lift off the go pedal. Ill bet you see well over 160.

I had my supercharger without meth for over a year.... saw about 140 at the end of a run. .

[bct10985]

Originally Posted by Alvin@PCMofNC

I would make some changes ASAP. A good cam will allow you to run more timing at the same boost than the stock cam..Especially if you have a L99. Please let us know if we can help with the cam.

Other than that I would go up on the pulley size (less boost) I feel really uncomfortable if I cannot get at least 12-14 degrees of timing in a setup and the reason is this...

Combustion releases energy in a combination of two ways. 1. Expansion work (good) 2. Heat (not so good) The later the timing the more the combustion cycle misses out on expansion work because the majority of the expansion happens relatively soon in the cycle at around 28-35 degrees after top dead center. So what is happening the energy released misses its chance to be expansion work and so is only option is to become heat. This is putting more heat into the exhaust valve, plugs, headers/manifolds, cats, etc!

What I'm getting at is the later the lead, the more your going to start cooking everything else!

Its an ls3