UH-60DRIVER

Bout to pull the trigger on some AHR stage 4 heads along with a BTR stage 4 cam. Here in El Paso the best we get is 91 so I want to flex fuel tune my car. I know I need high comp ratio for E85 but it's not the best idea for 91. What would be the best for both worlds? Also is there a rule of thumb for how much each thousandths I shave on the head will increase the compression ratio?

jayyyw

Are you going to be running e85 most of the time?

UH-60DRIVER

Hmm. Good question. Probably. However I am in the military so I who knows where I could end up in the world.

MTPZ06

IMO, the compression really needed to take advantage of E85 would essentially render your car useless at 91 octane. You can do a mild mill (.010 - .015) and tune it as best as possible for 91, but E85 wont net you much of anything in gains at that point...probably less than 8 rwhp. Who knows if E85 is even going to be around for the long-term.

UH-60DRIVER

True....is a .030 mil too much for 91?

MTPZ06

Not necessarily...AZDave tracks his C6Z and did .030 mill and "tuned" his car for 91 (local fuel). He adds 100 octane at the track, and his rationale was that if he sells the car out of sate to someone with 93 available, they could car retune the car for some extra power. You'll just have to pull some extra timing...so it becomes a question; is the compression bump worth more power than the timing you're pulling? You said you're in the military, so conceivably you could bounce elsewhere with better fuel.

lt1z

Milling only effects static compression and quench which is only part of the equation as to what fuel will be adequate.

outhouse

AHP mine at .010 for 91 just for safety sake. The power difference is minimal for me and not worth the risk of getting a bad batch of gas.

AzDave47

^^ Accurate comment on my build. The tune was set rich as I do events at 600-800' and over 6000'. HCI with K501 cam, MSD, NW102, Pfadt 1 7/8" headers and more, 602/489 rwhp/tq, 7100 RPM peak power 7300 RPM FSO.

I know I'm not getting the benefit of the .030 mill (~11.7:1 CR) due to the tune on 91, but figured it was not much cost and if I sold the car to an area with 93, they'd just have to do a tune for their area and get 5-10 HP more for just the cost of a tune rather than yank the heads.

Unreal

This.

Zero mill could be crap for 91 or you can do 50 thousands mill and be fine. Since all it effects is static compression. Dynamic matters just as much or more.

Never had an issue on 91 with a 30 mill. Always seen solid 15-20rwhp gains. Yes the car will take 2-3 degrees less timing, but even with 2-3 degrees less timing it makes more power.

There is NO risk with bad gas unless your tuner is a nitwit and disables knock sensors and low octane maps. Bad gas the car switches over to the low octane map, just like before. That is the whole point of that system on the car. Tune it properly and zero issues.

MTPZ06

OP, just noticed you're going to go with AHP heads. Unless something has changed, I believe Kohle will mill up to .020 for no additional cost with his rebuilds. Milling .030 will come at an additional cost. How much, I don't recall...but if you cant take advantage of it, I'd just stick with the free .020 mill. Provided of course, this is still the case. Also, he gives a military discount, so don't forget to mention that as well.

Unreal

Disclaimer, it depends on who is doing the heads too. I've seen one brand of heads that knock if you look at them wrong. No mill and they won't take any timing. I have zero first hand experience with AHP heads, but with WCCH and a few others I would always do at least a .030" mill. They love it. Some other brands you can't mill at all, and need to run 100+ octane just to get any timing, and to those heads, I suggest never touching them and running far far far away from their crap.

Michael_D

I've always used SCR. It doesn't change, even with a different camshaft. DCR values go out the window as soon as the scavenging stage kicks in.

If you have bad fuel, (which is not only due to octane), I limit SCR to 12/1, aluminum heads. I also squeeze quench and smooth/polish the combustion chamber and piston tops. 11.5/1 for this engine should be just fine with 91 octane.

Also, make sure the low spark table is not a copy and paste of the high spark table and AFR is no leaner than 12.5:1.

The E38 ECM "learns" from KR, and will bias toward the low spark table values. It does not switch back and forth.

Meth injection can also be used.

jayyyw

I'd like to know who you think should be avoided.. You can PM me if you do not want to disclose the info in this thread.

lt1z

It is important how the chambers are done in the heads. I have tuned cars with heads from all the major players in stock LS7 head porting and definitely had to take note of the differences in timing they would accept with similar or the same cam designs.

Michael_D

And through your various testing of different chambers, is there anything obvious that you can identify that causes detonation? Or conversely, reduces it?

lt1z

Not as obvious to the naked eye as with a scanner