Fuel for higher compression

[MarkSS]

My LT5 is 12:1 compression as modified by Lingenfelter back in the 90s. I have only driven it about 40 miles so far, but will be driving it regularly soon. So, will 92 octane unleaded be enough or do I need to add some kind of octane boost, and if so, what product is recommended?

[BYEBYE2U]

Did you get pinging with the 92 so far ?
If you dont hear it when you're running hot n going up the hill on high gear, you will be ok
Knock sensor may be taking care of it....
12:1 on aluminum engines is not that high n if you are running 4:10s it helps take load of engine-Ferraris n Ducatis are pushing 13:1
Push comes to shove you can buy 100GT Unleaded fuel at your local drag strip or local distributor from Sunoco, VP Fuels, Unocal to name a few
Mix accordingly to stop the pinging
Also keep an eye on your spark plugs for what looks like pimples n broken porcelain : Signs of detonation....n black smoke under hard acceleration when piston rings gets rattled n lose sealing...

[Paul Workman]

I have 11.5:1+ after porting and shaving the heads .020" and I'm not having issues here where we're approx 600± feet above mean sea level (AMSL).

You may not have a problem, or timing could be "tweaked" (or the ECM will do it anyway, if knock is detected).

Marc Haibeck did my dyno tune, and I believe he even bumped the timing calibration a degree or two above "stock". No problems with knock.

If you are living in the mountains, or high planes, for example where AMSL is higher, 92 octane is typical (due to less dense air helps prevent knock) I'm guessing you'll be OK as well (Mine runs fine during the Appalachian and Rocky Mtn runs on 92 and even 91 octane.)

One way to find out would be to put the car on a dyno and see what the knock counts do at WOT. Then you'll know if you need to back timing off a degree or two, OR find an outlet offering 100+ unleaded octane. (The ROUTE 66 DRAGWAY is nearby. So, there are several stations nearby that offer the higher 100+ octane "race gas" (for a price)).

That said, and based on experience with my ~11.5:1 I'm guessing you won't have a problem at 12:1 compression with 92+ octane. YMMV.

[lfalzarano]

Try Boostane as Insurance.


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[EvanZR1]

I've been running 93 on my 391 cubic inch motor with 12:1 here in Texas with no problem. I'd imagine you'd be fine on 92 in MN, but if you need to up it, you can add some Boostane or Torco. Don't bother with parts store octane "boosters" as they move the octane typically 1 "point", which if you read their fine print they define as .1 (so from 92 to 92.1). Torco and Boostane will move it full numbers based on the mix ratio you use. I used Torco on my '13 GS with a blower when I was in areas where I couldn't get 93, and it worked great. Only thing with Torco (not sure on Boostane) is it will turn things orange (i.e. plug tips). It doesn't hurt anything, but if you're not expecting it, you'll be surprised.

[tpepmeie]

Fwiw, on my 427 build 1, 12:1. I ran 93 on the street for “normal driving”. I was never brave enough to romp on it without a 50/50 race gas mix. And that is what we dyno’d the motor with.


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[EvanZR1]

I hammer mine every time I drive it, and have run 1/2 mile and 1 Mile event, all rnnng 12:1 on 93.