LS6427

iTrader: (2)

Just on your typical stroker motor, say a 427-454 size LSx......

Nice size cam.....all else being equal pretty much, except a jump in compression.

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Gray86hatch

iTrader: (83)

4-5% is a good #

LS6427

iTrader: (2)

Thanks.

So is it about 4-5% for each point increase in compression?

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racerfox

iTrader: (4)

you cant run on the street unless you run race gas with that comp..

82cetuner

iTrader: (9)

thats not true its in the tune I have heard of people running up to 13 and if it really is a issue you can always swich to E85.

Pwebbz28

iTrader: (31)

Or e85 :-)

Yes, for every 1 point in compression you are looking at a 4% increase in power. I you make 700 with 11:1 you will make about 725-730 with 12:1.

LS6427

iTrader: (2)

Its a 100% street car.....will never see a drag track......weekend warrior, fun car. Maybe 2,000 miles a year.

I'm having a 441ci built...I was wondering if its worth it to go higher compression than the typical 11:1 or 11:3.1, and go 12.5:1 or maybe even 13:1....since using full time race gas is no issue for me. 101, 110, E85..whatever.

I also want to be able to spray a 200 shot though.....is 13:1 too high for that much spray?

Because to have what amounts to possibly 50 more HP (10% more from 11.3:1 to 13:1 cr) for N/A driving....why not......

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gnx7

iTrader: (28)

if you can get e85 it is less than 1/2 the price of 100/110/116 octane. I would run that.

LS6427

iTrader: (2)

Its easy to get here. Plus I was gonna do what my friend and his father do....they have a 200-300 gallon tank they fill up for their fun toys and it sits in their back yard with an electric pump.

They trailer it a station to fill it when it gets low.

***Can an engine set up for E85 also use 110...with no changes?

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good2go

Depends on the cam. Keep your dynamic compression ratio down with a big cam and you can get away with a lot. I'm running about 11.8 to12:1 static CR with pump gas, 24 degrees of timing, no knock. Because of my cam my DCR is only 8.5:1.

Bill00Formula

iTrader: (4)

Just out of curiousity, why wouldn't you take it to the track just to see how it runs?

LS6427

iTrader: (2)

Maybe I'd go up to Moroso for the heck of it some day, but its an hour drive up and an hour drive back......plus its not set up for 1/4 mile launches and I'm on radials. So it'll be very un-representative of its true potential. I really have no interest in drag racing to be honest, doesn't do it for me.

Isn't it safe to say with 800 RWHP the car would have 8 second potential...IF it was set up for drag racing?

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speedtigger

iTrader: (16)

This is not correct. It is not a simple percentage per point of compression. The gains diminish as the compression increases. There is a much larger increase from 8:1 to 9:1 then there is from 12:1 to 13:1.

This is true to a degree. This also is not a simple formula. Once the engine comes into it's range of volumetric efficiency, the cam is no longer bleeding off pressure. In fact, it is increasing it. DCR is a helpful tool, but it is only part of the equation.

Here is an article with a chart from Popular HotRodding that illustrates the diminishing benefits of adding compression.

Read more: http://www.popularhotrodding.com/tec...#ixzz1aUhiazku

The above chart is not perfect either. More of an example of the diminished returns. The dance is: static compression, dynamic compression and volumetric efficiency. Those factors all together produce the final answer. Because of this, I always temper theoretical ideas with real world experience. I look at what other racers have been successful with in comparison to the theoretical data as a double check.

LS6427

iTrader: (2)

I'm just wondering if the approximate 50 HP increase from 11.3:1 to 13:1 will be worth having to use race gas or E85 full time. Whatever the increase is will just be a bonus because running the race gas or E85 is absolutely no problem at all.


Another question: If I do go 13:1 does that mean 110 octane minimum?

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speedtigger

iTrader: (16)

I have no experience with E85. But, 13:1 definitely means racing gas all the time. Another resources is your cam manufacturer. They will also give you their compression recommendation for a given cam or vice versa. The whole thing is about volumetric efficiency in a given RPM range and cylinder pressures. The volatility of the fuel and the burn rate have to be a good match for your set up. You want to match your cam and compression closely. If I were in your shoes, I would consult the cam manufacturer and start talking to the guys on YellowBullet.com. It is a rough crowd, but that is the best place I know of to share practical experience with people running racing fuels and E85 on high compression set ups.

LS6427

iTrader: (2)

Cool, I'll check it out, thanks.

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