Static Compression Race/Pump.
It's not really just about how much CR you can run on a certain octane either, since you can run crazy high compression but have to pull a bunch of timing and go backwards, making less power...
As a general rule, people run ~12:1 on pump gas, maybe ~12.5:1 if they trust their local gas station and get good quality 93...not that west coast **** water
. 14.8:1 would be no problem on a straight 116 fed LT1. SBCs run that compression on race gas and our reverse cooled heads allow a bit more leeway then a standard smallblock.Not sure what someone would be building to need anywhere near that much CR though. A happier medium would be something closer to Gregrobs 13.4:1 E85 build that can run off of much cheaper corn and not be nearly as tune sensitive as a nearly 15:1 monster on race gas.
Last edited by Puck; May 7, 2012 at 11:54 PM. Reason: further explaining
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Verdad Gallardo First off you can go much higher, and its done regularly.
Second why would I not get an increase in power? I havent dynoed it on E85 but it runs just as strong or stronger than 110 octane.
You cant just say "E85 is 105 octane" on some fronts it acts MUCH higher than that. Read up on latent heat of vaporization. On some other fronts, its nowhere near as good as race gas.
Long story short, E85 can make a lot of power in high comp or boosted applications, but you dont blindly treat it like race gas, or believe the BS you hear that it "loves more timing" etc. It doesnt.
99% of the bad info out there you hear about E85 is from people who have never even ran it!
Second why would I not get an increase in power? I havent dynoed it on E85 but it runs just as strong or stronger than 110 octane.
You cant just say "E85 is 105 octane" on some fronts it acts MUCH higher than that. Read up on latent heat of vaporization. On some other fronts, its nowhere near as good as race gas.
Long story short, E85 can make a lot of power in high comp or boosted applications, but you dont blindly treat it like race gas, or believe the BS you hear that it "loves more timing" etc. It doesnt.
99% of the bad info out there you hear about E85 is from people who have never even ran it!
First off you can go much higher, and its done regularly.
Second why would I not get an increase in power? I havent dynoed it on E85 but it runs just as strong or stronger than 110 octane.
You cant just say "E85 is 105 octane" on some fronts it acts MUCH higher than that. Read up on latent heat of vaporization. On some other fronts, its nowhere near as good as race gas.
Long story short, E85 can make a lot of power in high comp or boosted applications, but you dont blindly treat it like race gas, or believe the BS you hear that it "loves more timing" etc. It doesnt.
99% of the bad info out there you hear about E85 is from people who have never even ran it!
Second why would I not get an increase in power? I havent dynoed it on E85 but it runs just as strong or stronger than 110 octane.
You cant just say "E85 is 105 octane" on some fronts it acts MUCH higher than that. Read up on latent heat of vaporization. On some other fronts, its nowhere near as good as race gas.
Long story short, E85 can make a lot of power in high comp or boosted applications, but you dont blindly treat it like race gas, or believe the BS you hear that it "loves more timing" etc. It doesnt.
99% of the bad info out there you hear about E85 is from people who have never even ran it!
Does E85 have any negative effects on the fuel system or engine in general?
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The reason I'm asking is boost obviously "adds compression". If you have a static compression of 10.4:1, 10psi roughly acts like ~13.4:1 compression.
At least from my understanding. Because I am going to start building a 385" forged engine and am debating on compression ratio, I plan on running meth/water injection. So I was wondering at what compression I would want the meth to kick in. Well boost level.
At least from my understanding. Because I am going to start building a 385" forged engine and am debating on compression ratio, I plan on running meth/water injection. So I was wondering at what compression I would want the meth to kick in. Well boost level.
i ran my good old treefiddyfive at 11.3:1 CR on 93 pump with an agressive tune all day long.......
i tried sunoco 104 in this motor and it gained 0.....
i ran my 385 with three different compressions so far with the following fuels
13.2:1 on Sunnoco 112...it ran on 110 the same didn't slow down to 112 so i ran the 112 for extra protection in hot weather....this combo slowed down significantly on 116
14.2:1 on VP114 (but i think it actually needed a hair more with the agressive tune i had in it on launch)
now im 14.7:1 on VP C116....
i tried sunoco 104 in this motor and it gained 0.....
i ran my 385 with three different compressions so far with the following fuels
13.2:1 on Sunnoco 112...it ran on 110 the same didn't slow down to 112 so i ran the 112 for extra protection in hot weather....this combo slowed down significantly on 116
14.2:1 on VP114 (but i think it actually needed a hair more with the agressive tune i had in it on launch)
now im 14.7:1 on VP C116....
The reason I'm asking is boost obviously "adds compression". If you have a static compression of 10.4:1, 10psi roughly acts like ~13.4:1 compression.
At least from my understanding. Because I am going to start building a 385" forged engine and am debating on compression ratio, I plan on running meth/water injection. So I was wondering at what compression I would want the meth to kick in. Well boost level.
At least from my understanding. Because I am going to start building a 385" forged engine and am debating on compression ratio, I plan on running meth/water injection. So I was wondering at what compression I would want the meth to kick in. Well boost level.
and when to inject water/meth really is determined on lots of factors: cam profile, flow of heads, flow of exhaust, timing, turbo or procharger, intercooled?
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You cant say that 10psi roughly acts like 13.4:1.... Boost pressure is not determined on what goes into the chamber. Boost is the measurement of restriction going TO the chamber. unless the piston is the only restriction to flow, boost numbers really mean squat when determining what the "real compression ratio is".
and when to inject water/meth really is determined on lots of factors: cam profile, flow of heads, flow of exhaust, timing, turbo or procharger, intercooled?
and when to inject water/meth really is determined on lots of factors: cam profile, flow of heads, flow of exhaust, timing, turbo or procharger, intercooled?
Added 10psi means you have atmosphere plus 10psi. So you have added 10psi into each cylinder. Which means you have more than 43.75ci of air per cylinder. So you have air that has already been compressed entering the cylinder with air that hasn't been compressed. The piston goes up, compressing the air but since air has already been compressed its going to be 9:1 + the compressed air. Which gives you a higher compression ratio.
Also the calculations doesn't give a static compression ratio its called Effective Compression Ratio.
When an engine of 350 cubes goes up on its compression stroke it has atmospheric pressure in the chamber. It then proceeds to compress it to its compression ratio. IE the air is compressed 9 times its orginal volume, 9:1 ratio. If an engine was 100% VE is means 43.75ci of air fills the cylinder each time. With a compression ratio of 9:1 that volume of air now becomes 4.861ci of air.
Added 10psi means you have atmosphere plus 10psi. So you have added 10psi into each cylinder. Which means you have more than 43.75ci of air per cylinder. So you have air that has already been compressed entering the cylinder with air that hasn't been compressed. The piston goes up, compressing the air but since air has already been compressed its going to be 9:1 + the compressed air. Which gives you a higher compression ratio.
Also the calculations doesn't give a static compression ratio its called Effective Compression Ratio.
Added 10psi means you have atmosphere plus 10psi. So you have added 10psi into each cylinder. Which means you have more than 43.75ci of air per cylinder. So you have air that has already been compressed entering the cylinder with air that hasn't been compressed. The piston goes up, compressing the air but since air has already been compressed its going to be 9:1 + the compressed air. Which gives you a higher compression ratio.
Also the calculations doesn't give a static compression ratio its called Effective Compression Ratio.
When an engine of 350 cubes goes up on its compression stroke it has atmospheric pressure in the chamber. It then proceeds to compress it to its compression ratio. IE the air is compressed 9 times its orginal volume, 9:1 ratio. If an engine was 100% VE is means 43.75ci of air fills the cylinder each time. With a compression ratio of 9:1 that volume of air now becomes 4.861ci of air.
Added 10psi means you have atmosphere plus 10psi. So you have added 10psi into each cylinder. Which means you have more than 43.75ci of air per cylinder. So you have air that has already been compressed entering the cylinder with air that hasn't been compressed. The piston goes up, compressing the air but since air has already been compressed its going to be 9:1 + the compressed air. Which gives you a higher compression ratio.
Also the calculations doesn't give a static compression ratio its called Effective Compression Ratio.
Added 10psi means you have atmosphere plus 10psi. So you have added 10psi into each cylinder. Which means you have more than 43.75ci of air per cylinder. So you have air that has already been compressed entering the cylinder with air that hasn't been compressed. The piston goes up, compressing the air but since air has already been compressed its going to be 9:1 + the compressed air. Which gives you a higher compression ratio.
Also the calculations doesn't give a static compression ratio its called Effective Compression Ratio.
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This is to determine what CR will work with what boost levels and then when to have water/meth kick on.
If your compression ratio is say 14.8:1 at 25psi obviously you are going to want run some form of higher octane fuel as its far past what most guys are running on pump fuel.
A 9:1 Compression with 25psi = 14.8:1. You're saying this calculation isn't true, but would you agree it would make the Effective Compression Ratio over 12.5:1? Which then you need to look into a higher octane fuel correct?
Last edited by F0x Slaughter; May 8, 2012 at 06:45 PM.
