Compression Ratio Dilemma . . .

Zero Signal · May 17, 2006

Ok, so I'm putting the car down for awhile to save for a 347 stroker. The only question left is, how much compression should I run? I would like to have the flexibility of being able to run a blower int he future. . . BUT that wouldn't be for a couple years down the road. So I'd like to get as much as I can out of the motor N/A in the meantime. . . .

Should I just go all out N/A and make the best of it? It seems like if I go with a middle of the range compression like 9.5:1 I'd be killing myself in both areas. Maybe I should just go for 11:1 right off the bat and stick with the N/A crowd. To be honest, I'm thinking I would be pretty happy with a motor that puts down >320hp to the wheels since I know it will have plenty of torque all around already.

SeventyMach1 · May 17, 2006

It's all your preference man.

Keep in mind that if you go with N/A now and plan a blower later on ... there are gaskets that allow you to lower the CR.

And if you go with a blower setup now and don't like it ... you can always mill the heads and stay N/A.

I know your looking to get the right setup the FIRST time (as we all do) ... but just letting you know that you have a margin to work with as well.

With that said .... I vote 14:1 N/A 347.

mytight95 · May 17, 2006

, i don't know if you could get away with an 11:1 ratio on pump gas, i think it depends on where you live and the octane you have access to.

i like the n/a setup myself, i am however gonna have a bottle just in case i need it....

I have also seen people with the above 10:1 or so, that run a small amount of boost safely with a forged bottom end, and a good set of head gaskets, and fat tune

jason

Killercanary · May 17, 2006

SeventyMach1 said:
Keep in mind that if you go with N/A now and plan a blower later on ... there are gaskets that allow you to lower the CR.

While it true that HG thickness can and will change the compression ratio, when you start adding thick HG's to lower the compression ratio the quench area is also changed and the resultant flame travel pattern can actually have the opposite effect of what you are trying to achieve, and that is to prevent detonation. A thicker HG is NOT the answer to lowering your CR.

A 9:1 347 with decent parts should lay down in the 320rwhp range with relative ease, and would support mild level boost, but the power output will RAPIDLY increase and you will VERY easily exceed the stock block's limits. If I were you and I was sticking with the strock block I'd either build a boosted 306, or a high compression 347. You should be able to get away with at least 10.5:1 with a decent set of aluminum heads and a good cooling system.

Daggar · May 17, 2006

Killercanary said:
While it true that HG thickness can and will change the compression ratio, when you start adding thick HG's to lower the compression ratio the quench area is also changed and the resultant flame travel pattern can actually have the opposite effect of what you are trying to achieve, and that is to prevent detonation. A thicker HG is NOT the answer to lowering your CR.

A 9:1 347 with decent parts should lay down in the 320rwhp range with relative ease, and would support mild level boost, but the power output will RAPIDLY increase and you will VERY easily exceed the stock block's limits. If I were you and I was sticking with the strock block I'd either build a boosted 306, or a high compression 347. You should be able to get away with at least 10.5:1 with a decent set of aluminum heads and a good cooling system.

I'm with him... anything within the 9.1 - 9.5 range will be good for N/A and give you boost options later on.

Grn92LX · May 17, 2006

Go with a high compression n/a engine. I run 11.045:1 with out a single issue. Pump gas street car I don't like the idea of supercharged strokers out of stock blocks. If you're going to be using the gt40 stuff you have on it then you'd probably be fine with a blown 347.

I just prefer n/a engines anyway. Less tuning headaches and when you do it right you can beat power adder combo's.

WhiteDevil · May 17, 2006

Im stickin with N/A and going with 10-10.5:1

Zero Signal · May 17, 2006

I'm leaning toward the high compression and sticking with N/A for mostly cost purposes at this point. In either case, my H/C/I will be a bottleneck with the stroker and will need to be upgraded anyway ($$$).

WHat fuel pump and injectors should I be looking at for this if I was shooting for 11:1 and maybe 325+ RWHP

Grn92LX · May 17, 2006

255 pump and 30lb injectors.

WhiteDevil · May 17, 2006

Grn92LX said:
255 pump and 30lb injectors.

I have a 255 pump and i think im going with 30s because i dont want 42s. Im shooting for 350-360 rwhp.

SeventyMach1 · May 17, 2006

Killercanary said:
A thicker HG is NOT the answer to lowering your CR.

True dat. The way I said that was way off, lol. I should have just said that HG's can lower CR .... but shouldn't be depended upon for that purpose. The engine should be set up right the first time .... so you don't end up trying to use them that way.

86bluecobra · May 17, 2006

i would say you would like the 9.0 - 9.5 to 1 compression ratio.
This gives you options.

Compression Ratio Dilemma . . .

Zero Signal

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SeventyMach1

Keep it lubed .... keep it straight .... and keep

mytight95

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Killercanary

The car that set the bar.

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Grn92LX

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WhiteDevil

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Zero Signal

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Grn92LX

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WhiteDevil

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SeventyMach1

Keep it lubed .... keep it straight .... and keep

86bluecobra

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