[ud03803]

Guys - looking for an understanding here please. When my 2018 SS was basically stock with E85 and CAI, I got a mail order tune for it. It seemed to work quite well. When I was logging, I noticed timing would be 27.5-28 degrees WOT with zero knock across the board.

Now I have the car much more modified (see sig) with LT4 injectors and hpfp. My current tuner had it set at 25 degrees and it would get like .1 retard now and then. I raised that to 26 degrees and saw a couple of cells at .4 up to 1.5 degrees retard. How can I be much more modified, same fuel etc but have to run 2-3 degrees less timing? Trying to understand how this works - thanks!

[ud03803]

No suggestions? Actually, I did think of something. I now remember reading the datasheet on these ported heads - they are 12:1 compression so perhaps that could account for not being able to run as much timing as the stock 11.5:1 heads. Thoughts?

[Z0Tex]

I'm willing to bet the E85 you are getting (I'm assuming it is pump E85) simply just isn't quite "good enough" for that extra .5 worth of compression. You may have found the limit for the fuel you have if it was the exact same as when it was used on your first tune, or the quality of the E85 fuel you have may have gone down since you swapped your heads.

[ud03803]

Originally Posted by Z0Tex

I'm willing to bet the E85 you are getting (I'm assuming it is pump E85) simply just isn't quite "good enough" for that extra .5 worth of compression. You may have found the limit for the fuel you have if it was the exact same as when it was used on your first tune, or the quality of the E85 fuel you have may have gone down since you swapped your heads.

That's a good possibility. I am seeing 76% at the pumps now. Who knows what's in those tanks! Thanks for the feedback. I think I'll roll it back .5 degrees to be safe. That's only a couple of horsepower anyway and isn't worth the risk of damage.

[wookwook]

Dude, accept the new normal for what it is, be glad your not a turbo owner. after a "bunch of mods" and your looking at .5 ? And no your not losing HP it just doesn't equate that way. timing does not automatically mean HP if you've increased VE by any means.

[ud03803]

Originally Posted by wookwook

Dude, accept the new normal for what it is, be glad your not a turbo owner. after a "bunch of mods" and your looking at .5 ? And no your not losing HP it just doesn't equate that way. timing does not automatically mean HP if you've increased VE by any means.

Thanks, just trying to learn the ropes. A lot has changed since my LS tuning days.

[NickeyMatt1LE]

With the added compression and higher overall airflow with heads/cam/ intake, cylinder pressure is higher and less timing is needed.