11:1 Compression not possible/recomended on pump gas?!?!?!?

[95ImpySS]

Finally got my LE2's to the machine shop doing the work on my short block. They needed to measure the combustion chambers to pick a piston. I requested 11.5:1 compression and the tech looked at me like I was crazy. Said you "cant run 11.5:1 with aluminum heads on pump gas". Says "you cant run 10:1 with iron heads on pump gas". You need race fuel. This being the second time being told this by 2 different employees, I felt I had to have a go with him. I told him about how many other builds have run 11.5:1 and higher without any problems on pump gas using aluminum heads. He said no way, either they are not really xx.x:1 or they are pulling timing that SBC's need to make power. Said you cant go that high without detonation. Explained to him various builds seen on forums and YouTube. And his response was "id have to pull the motor apart and really see if its xx.x:1".

Admitting defeat I told him to make it 11:1 and leave it there. If it melts down I will cut my losses and buy a Civic. What merit do these shop employees have saying its not possible to run 11:1 aluminum heads on pump gas without detonation? I know there are hundreds of LTx builds higher than 11:1 and stock they were at 10.5:1. What gives? The shop is very well known, been in business over 40 years and has many engine and chassis builds to their name. Am I wrong or are these guys clueless about new-age SBC?

[97firehawk]

They do not understand gen 2 small block's period hell I ran 10.5.1 on a gen 1 on 93 my LT1 has 11.1/4.1 on 93 no issues I no guys running 12.1 .

[97firehawk]

They just have zero clue.

[AChotrod]

Its a reverse cooled engine which cools the heads first allowing the higher compression ratios without detonation. Stock is 10.4:1 lol. Your builder is just used to Gen 1 SBCs. Mine is 11.4:1 and has been running pump gas for years now.

[faust]

my old 385 11.8:1 was and still is fine

[95ImpySS]

They just have zero clue.

That's exactly what I thought. But a well known shop, turning out 10-30 engines a week. Figured they would have got with the times by now. Well see. Don't know if I feel comfortable with them doing my turbo engine next year. Well see how this one turns out. IMO SBC I is not SBC II...

[Fastbird]

my old 385 11.8:1 was and still is fine

Ditto. My black car was at the same and fine.

Postin' on the go......

[97firehawk]

My builder was concerned as well till I explained to him . He has done mostly gen 1 builds but he built my cusins turbo LT1 and my nitrous LT1 and he did a awsome job although I picked my cam and heads mostly because he hasn't done to many LT1s .

[94Blackbird]

They may be a well know and respected shop, but if they haven't worked on LT's or don't have experience with LT motors, then they'll be just as clueless as your average tire kicker.

[proace4]

I know of 2 lt1's in wichita one is at 12.7:1, and my car is at 13:1. I have had it on the dyno a few times logging pulls and it never has any issues. Tuned on crappy kansas 91.

[BadBlackZee]

It blows my mind that this machine shop would say that. I am good friends with 95ImpySS and have spoken with the folks over at that machine shop. Hell, me and Impy built my 12.7:1 383 that you see in the sig. No problems on 93 octane pump gas...

According to the shop, I should have melted a whole in every one of my pistons within 15 minutes of running it. Going on 20 miles strong now :). Time will tell how it holds up

There should be no problems running in the mid to high 11:1 SCR while still maintaining pump gas. My logic is based on the same logic that ACHotRod is using. Reverse cooled heads helps to curb detonation, especially when you start upping the compression. Gen II LT motors are just a whole different ball-game than Gen I SBC...

[1badz]

Brad, looks like you need to invest in a few barrels of race gas for your 11:1 engine :jest:

[96LT1355Z28]

12.1 in mine on 91 octane. My engine builder was cautious at first, then admitted he wasn't familiar with LT1's. After seing mine run and talking to others he's changed his views.

[xdeified]

Talking to my family and builder they were all shocked I was doing anything over a 10.5:1 compression. They constantly kept telling me "your going to need to run racing gas if you plan on going over 10.5:1." I guess they don't realize if you have a good tune, you'll be fine on pump gas.

[Joker Z28]

Like said above, the reverse cooling allows for the higher compression. Older school guys just dont understand it yet.
Either way
<12.3 compression 93 octane all day

[joelster]

11.77-1 here and it runs just fine on pump gas. You have to run a big cam though to bleed off a bit of the compression. The dynamic compression is in the 9.5-1 range.