driven87

iTrader: (1)

Posting this question for a freind of mine. he has an LS7 he is about to freshen up that he got in a trade. he was looking at a set of wiseco pistons that claimed 12.1 compression ratio with 72cc heads. looking at the stock ls7 heads they come in at 70cc, so im guessing this puts him somewhere around 12.4 or so with the 70cc heads? he asked about running a thicker head gasket but i saw a stock ls7 gasket is already .055 thick. his biggest question was shoull he look for a lower compression piston with the factory heads for pump gas? should he get a custom cam to make it work on pump gas? should he run a thicker head gasket to lower it down some to run pump gas? This is not a race car just something he wants to toy with. any ideas on which way to go would be great, thanks

Sales4@Texas-Speed

iTrader: (4)

I don't think that will work on pump gas. We usually cut the line at 11.5:1 for pump gas. I also don't think you could find a cam that would bleed off that much compression and still be desirable for power and driveability. I would try and find a piston that doesn't yield that much compression.

briancb1

Sounds like there was a reason someone wanted to trade those pistons....

You can get thicker head gaskets through various manufactures, so he is not limited to .055"....

But honestly even if he did get it to run at higher RPM with 12:1+, you wont be able to run much timing advance (less than ideal) on 91 or 93 gas.

He could see if the piston crown is thick enough to machine a small dome, just removing enough material to get to 11:1 or so.

Another not to far-out option is meth/water injection. It has been done and works for situations like this. Call SNOW performance and they will fill you in on the rest of the details if you care to investigate that route.

Good luck

Unreal

If you define e85 as pump gas then sure.

I know several ls7s running 11.5-12.0 on 91-93 octane.

Spdmn75

iTrader: (2)

who makes a thicker LS7 head gasket?

Pony Exp.305

iTrader: (6)

Go for E85. I have seen some guys with 11-15 CR using E85...
Need bigger injectors and fuel pump for E85.
Do search.

mike c.

iTrader: (1)

Me and a bud both have 11.6 comp and i have 29deg timing. I believe nick williams has 12.0 but i don't know how much timing he runs.

racer7088

Just get the right pistons its much easier and no 12.4 to one compression is not a smart idea for a real street car. Wise has an 8cc piston I think as well or you could cut the dome off if there is one to the comp you want.

Josh@PremierAutosports

iTrader: (11)

I have quiet a few customers running 11:8-12:4 on pump gas. You have no room for error on the tune up and I make sure the knows what they are getting into. You have to keep a eye out incase you get bad gas etc. I even have a customer with a 440 ls7 with 12:8:1 that makes 591whp. He could make more on better gas. We were planning on 12:1 for his build then after we had his new motor we found his heads had been milled before.

TransWS6Am

iTrader: (41)

wow 440 LS7 with only 591whp? I'm guessing that high compression is really hurting that number.

racer7088

You will make more hp with more compression if you can run appropriate timing etc. but in texas you wuill detonate unless you have really crappy heads and cam and intake killing your VE.

Most deals with this much compression unless they are a turd they can't run the right timing and actually make less power and are less reliable.

For example Stage7's big cathedral port 468 is only 11.2 to 1 and makes over 630 rwtq and over 670 rwhp. At 12.4 to 1 his engine would probably blow up and make less everywhere although on race gas yes he would pick up certainly.

We done sevral crazier 600+ RHWP cathedral port deals and all are under 11.5 to 1. Over that with a good cam and heads you usually have to detune down here in Texas at least and you lose the power.

No one runs 12.5 to one even in engine masters that is winning right now so that should tell you a lot about true pump gas stuff in general.

hymey

On some motors on engine dyno I have seen them increase 30 hp by upping comp from 11.8 to 12.8:1, this motor was running 33 degrees timing on pump gas. It was a Holden 355 Stroker using aftermarket cylinder heads with chambers similiar to LSX. Depends on the dynamic compression and intake centreline and overlap. I personally know of a LS7 that ran 11.8:1 on pump and could of handled more it made 708hp on engine dyno with a 240s hydraulic roller it now has a 260s solid roller and is getting 12.4:1. It depends on the cylinder head too. Most big solid roller engines in street cars in Aus all around 12-13:1 on pump fuel no issues. You can leave it on the table if its low. But as Eric said if you have to pull to much lead out to prevent detonation you have to much compression or issues elsewhere in your combo.

180ls1

iTrader: (4)

ya its doable but if the car is going to see pump gas there is not much of a point. You will have to tame the tune down and pull so much timing wont see gains from it.

racer7088

Hymey, I think you have better pump gas than we do as well down there!

ramairws6

iTrader: (33)

Your joking i hope.....

briancb1

He is referring to the fact it probably has very little timing advance with the "to high" compression.

LS6427

iTrader: (2)

Any problem with running 12.5:1 for a 100% street car + 200 shot....441ci.....down in hot south Florida.

If 103 octane was used full time? This gas is all over the place at stations down here.

Also.....if for some reason I had to use 93 octane in a pinch....if it was driven very casually, hot day, would it be just fine to drive it that way till 103 was put in?

.

racer7088

At low MAP you aren't making much real compression so you could run a lot lower octane for just cruising. Just don't get on it.

LS6427

iTrader: (2)

So 12.5 and a 200 shot with full time 103 octane is fine.........for racing?

.

racer7088

I don't know about that fuel but if we had it here yes I wouldn't be scared to run more compression if it's real.