FCar2000TA

iTrader: (7)

I am starting to finalize the parts list for my build, and I am trying to decide what pistons I want to get. The motor will be 4.155" bore and 4" stroke, with LS7 style heads. I will also have piston oil squirters installed by Katech.

So, what does everyone think will be a safe compression with 91 octane gas? I think that I read somewhere that 12.5:1 was the max, but that was on a smaller bore motor. I think that the piston oil squirters should allow higher compression too.

Corona

Oil being squirted underneath Pistons helping with Compression and Pump gas...Wow never thought of that.
Fake News.

Your cam shaft dictates what's allowable.
91 octane and 12.5 =
A cam with more than 260 degrees @ .050
Top of my head math from reference builds.

Oil Squirter's 🤣

Corona

93 octane is what's being used with anything above 12 points of comp and sometimes with a

Fuel additive

Got Corn fuel?
And or a thicker head gasket to lower compression.

G Atsma

I think the real reason The LSA/LS9 use piston squirters is to keep the pistons cool enough to stave off being barbecued under lean conditions, not so much for low octane tolerance.
But that is just me speculating....

Corona

Sounds Correct to me! Read this around the time GM High tech was around.👍

G Atsma

I might have read the same thing..... lol

FCar2000TA

iTrader: (7)

the oil squirters keep the piston head cooler. I just assumed that would result in more knock resistance.

FCar2000TA

iTrader: (7)

flex fuel is planned, but I would still need to be able to run 91 octane in a pinch.

Corona

Thing is 8000+ rpm is needed with 12.5 on 91 octane.

Corona

Lower comprescompression or
Meth injection...

Best thing I came up with in a Pinch 😉 like U.
Use a thicker head gaskets Till u ready for a better fuel...

Winning either side of the coin flip 🙃👍

FCar2000TA

iTrader: (7)

Wiseco K463X155 would put me at 11.9:1.

Mickyinks

I’m at 12.3 : 1 and specked the cam so I could run on 98. It’s borderline in the hotter months but have flex fuel as back up
as stated earlier your cam will dictate how high compression so mayb 1st work i out how big a can you can live with and work from there

84ta406

iTrader: (6)

We spec'ed my 403ci build with 11.8:1 in mind. Tony said anything more and I would have to detune it with regards to timing, which defeats the purpose of more compression. He also said during the heat of the summer it might be good to toss some octane booster in for good measure.

Che70velle

iTrader: (6)

Not fake news at all. Figured you knew this? Why bother to cool the piston with oil? Coated pistons, coated valve faces, coated combustion chambers....all tricks on upping detonation resistance that work. Keeps heat in the chamber, which makes more power, and allows more static compression to be applied if there’s a fuel limitation. If no fuel limits, waste of time and money.

Double06

iTrader: (1)

I run 11.9 on 93 with about 21-22 degrees of timing and the cam is 246 / 258 on a 114 with an intake closing at about 80 degrees. Its a 454 - 4.185 x 4.125 with Brodix LS7 heads done by Advanced Induction. Car is light at 3,100 pounds with half tank no driver. I think I could run more timing but I kept is lower to factor in some cushion and or bad batch of gas. Cam timing, gearing, transmission, car weight and how good your head is are all factors.

showdog75

iTrader: (8)

I'll respectfully disagree with you on using thicker head gaskets to lower the compression. A tighter quench will be more octane friendly.

Corona

So run 91 octane @ 12.5 vs Adding a thicker head gasket for something like 11.5' ish. The hell with a .038 quench The Compression Must Be Lowered or run a Unusable street 8k+rpm cam because of trying to bleed off cylinder pressure? Do you know of guys running 2 head gaskets to try to Lower compression? I do and quench is not a thought.

The young man with the thread came up with the plan of the Century.. Get pistons that lowers the Comp.

As is with the pistons listed he could:
Later with E85 have the heads Milled $ vs removing the Thicker gssket and going with a thinner gasket that gets the 12.5 compression back Cheaper and not having to send the heads out 🤔😱

FCar2000TA

iTrader: (7)

What about carrying a quart of denatured alcohol in the car, incase I am forced to use 91 octane?

spanks13

iTrader: (5)

Boostane shots. Cheap insurance.

FCar2000TA

iTrader: (7)

I could just buy some E98, and keep a half gallon in the car.

half gallon of E98 plus 5 gal of 91 should end up at 95ish octane.