Max Spark Timing for LT4s on E85
 

Would anyone be willing to share what they've heard about what is considered safe MAX TIMING is for E85 (E70, or so, in my area, apparently)? I know there's a point timing doesn't add power, and that E85 won't necessarily knock, but the engine, essentially, can mechanically knock, and beat the bearings up bad.

I'm seeing and hearing about 25* is about as much as LT4s will handle. Does that sound right? Is that for E-content for as low as, like, E70? I don't have a cam, so does that 25* matter for me?

I'm just looking for a good number that will take advantage of everything I've invested into what I'm doing. I don't, really, have a practical way to test the effects of changing timing, so I'm just hoping I could get some feedback into what others have found, or heard, from reliable sources.

Thanks, and have a great weekend!

25 is a good number, pretty much the point where we start to see diminishing returns on an LT4, you'll still make slightly more power up to 28-29 degrees as long as there is no knock, but you'll have plenty of smiles at 25...

Run stock LT4 knock sensor values once you're on E (not the Magnuson values), just gives you some extra safety margin as you push the tune further on E.

Basically, what I said to Chuck in a PM. 24-25 degrees is as far as I take a streetcar. You are getting 98-99% of available engine power and it's safe. Sure, if you are at a grudge race for 50k and ok that there is a chance your engine will meet the Reaper, then send it with 27-28 degrees on full E. But I am not setting up street cars that way.

Thank you all for reaffirming, gentlemen. I don't trust anyone with my car, so getting to a dyno I trust is a little tough. Seeing a safe limit, for now, is what I was hoping for.

Thank you both for your continued help :)

So I’ll reconfigure and run the humidity table similar to how gmpp has it setup.


I’ll run 25-26 in no humidity and 28-29 when it’s max humidity on a bolt on SS.

Seems to work well for me. What do you think about that

NA LT1 I would 28 degrees on E regardless of the humidity. That table is basically for pump gas due to the compression being high enough were 93 is still touchy due to the LT1's high compression. On E it won't matter.

Ethanol is like liquid intercooling in the cylinder. It drops cylinder temps hundreds of degrees during the combustion cycle. For that reason it actually likes a little heat. Also why gas stations drop the E content back in the winter.

Do you start bringing the timing up to 25* (LT4s) AFTER peak torque? That's been my understanding.

Depends on the setup. Bigger blower not spinning as hard, I bring it in early as possible. Stock blower being overspun I ramp it in. Small blower over spun hits harder, demands more fuel, harder on bottom end.

Something just occurred to me (forgive me)...

Would it be fair to say that I should be able to look back at my LOGS, running a 94-octane blend, and add a few degrees to that, in most places for E'? For example: if I see that the car was tolerating 20* of timing on 94-octane, it's probably safe to add a couple degrees in that same area on the FLEX SPARK table? I feel like the answer could be "YES"... I think I'm asking if I go back, and look at old 94-octane LOGS, and add a few degrees (to about 25* TOTAL SPARK at WOT, as I move into higher RPMs and higher across the AIRMASS scale), that's probably pretty reasonable/safe?

24-25 degrees on E50+ from 4k rpm on up should be perfectly fine on your setup.

OK. After taking more time to think about it, I wasn't too far off this time.

Thanks King.

:happy0180:

On E60+ I usually run up to 28 degrees on the LT4's before any modifiers( Humidity and IAT's) and 29 on the LT1's before any modifiers. Even in full humidity, the modifier pulls half a degree. Then if things heat up the logic will pull more timing. I choose the set this up like OEM logic. I know some tuners remove most of the logic and lock in on a lower number timing number for consistency. I'm not saying I am right or they are wrong. I just do things a little differently. I have quite a few cars running around on the street with this setup with no issues.

I've seen one reputable shop run up to 32 degrees on the dyno on the LT4's with E62. However, I'm sure they back it down once it's off the dyno. I can't imagine that living very well on the street.


If the car is boosted to the moon I'll back that number down to 26-27 depending on the setup. Cammed cars are a little different as well. So my above numbers are stock heads and stock cammed cars. Timing is ramped up on the LT4 from a lower value to a peak value at redline. The LT1's are a little different. They like more timing pre peak torque, then less timing during peak torque then more timing after peak torque. I don't desensitize the knock sensors either.

Thank you for the additional comments!!! :happy0180:

That is what I generally do except I am more conservative on the timing.

I assume when you say 29 degrees for LT1 that is NA which seems right. Just curious what kind of timing do you run for FI LT1's on E?

Yes definitely NA for the LT1.

Boosted LT1's I am very conservative on timing. Like 15-16 degrees on 93 and 19-20 on E even though I feel like you could get away with 21-22. I don't do much of the boosted LT1 stuff honestly because the pistons are so weak so I am definitely not as knowledgeable here. Even with a conservative tune these things can pop and then the tuner gets blamed. I actually turn down most work if it involves a boosted LT1 with stock pistons.

Me too lol. I have mine running between 19-20 on E and 12 on 93 even though I have yet to run it on 93 with FI. It's pretty much been on E its entire life even when it was NA.

What do you guys think about Lambda on E60-E70? Meaning, do any of you run leaner on E60+ than you would tune a customer car for?

I run my LT1 .82-.83. I try to keep LT4 stuff around .84-.85.

Same here. I've gone up to .86 on my LT4 without an issue on 14lbs but I moved it back to .84-.85. I get nervous about .86.

Clients LT4's I target .83-.84 unless a lot of blower/psi and meth. Then I target richer.

Do cammed cars like more or less timing than stock cammed cars?

Thanks

As a generality, typically larger cams need more timing in the lower RPM range since dynamic compression and/or efficiency is reduced vs the factory cam in that lower operating ranges. As for WOT timing, it all depends on the build. A bigger cam doesn't automatically mean it requires more timing at WOT. This is where it is beneficial to use a dyno to determine what timing the setup likes.

^Agreed