Short block…. Compression ratio?

K4fxd

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So again, I ask the question, if lowering the compression and increasing the air charge is indeed the magical solution, then why not just lower the compression to 1:1 and have a giant compressor slamming 25 bar of pressure into the motor?
You are missing the point and I don't have the paitence to type out 6 paragraphs to make it clear.

In the end, I'dd personally rather make 1000 rear on 17 lbs of boost at 12:1 than 25 lbs of boost at 9.5:1.
If it is a turbo car then yes, I would want as much compression as the motor will tolerate out of boost then live with the reduced ign timing under boost. The reason is turbo cars only make boost under load and most street driving is out of boost.

On the street with a PD blower I would want to run lower static compression and more boost for the peak pressure reasons engineer mike pointed out.

That's just me. You guys do what you want.
And I'll have a 100,000 mile engine
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Angrey

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You are missing the point and I don't have the paitence to type out 6 paragraphs to make it clear.


If it is a turbo car then yes, I would want as much compression as the motor will tolerate out of boost then live with the reduced ign timing under boost. The reason is turbo cars only make boost under load and most street driving is out of boost.

On the street with a PD blower I would want to run lower static compression and more boost for the peak pressure reasons engineer mike pointed out.


And I'll have a 100,000 mile engine
I'm not missing the point. If 10:1 is better, why not 5:1?
 

K4fxd

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Angrey

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Mike answered that question in at least 2 previous posts.
No he didn't he punted citing blower limitations.

I'm talking about from the ground up. And the question is rhetorical, but it flushes out the truth.

If 10:1 is better, then surely 5:1 is even MO BETTER. Forget about the blower you have NOW, if lower compression and crazy boost is so much better, and it's simply a matter of losing efficiency (which enthusiasts and race teams don't give a isht about) then why don't we see race teams running low single digit compression ratios with giant blowers capable of compressing the air to several bar of pressure?

I'll tell you why. Because of the quality of fuel. There's no NEED to run a ginormous blower and a zillion lbs of boost when you have quality fuel that's resistant to pre-ignition and detonation. Mike is stuck in 1995 when most street car guys were stuck buying 93 (if you didn't want dedicated race fuel for a trailer queen).

With E85, there's NO reason to run lower compression and there's plenty of people running 11:1 and 12:1 on comparatively decent numbers.

I'll concede that if you want to make 1500 hp+ then low(er) compression and more fuel/boost is the answer. But for all practical uses for enthusiasts on this forum, picking that motor just means you generate more blower heat, have to run a smaller pulley and eventually you run out of blower or intercooler (trying to spin that thing to the moon to keep up). Hence the 500 guys that are having to ditch the ported OE blowers in favor of a much larger 3.8 setup. We haven't even gotten to space limitations in the engine bay, etc.

The bottom line is, for 93, if you're wanting to make North of 800 rear, yes, one way would be to lower the compression and up the boost (and try to cool it as best as possible or add a nitrous or meth injection to cool that hot ass charge you've just created).

But most people wanting North of that are willing to concede to E85 which resets the problem and there is NO NEED to run a lower comp motor at power levels MOST people are wanting or capable of sporting.

Good day gentlemen.
 

engineermike

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No he didn't he punted citing blower limitations.

I'm talking about from the ground up. And the question is rhetorical, but it flushes out the truth.
You said, "At what point are you claiming lowering compression yields negative returns?" and my answer was correct; it's when you run out of air or fuel.

If 10:1 is better, then surely 5:1 is even MO BETTER. Forget about the blower you have NOW, if lower compression and crazy boost is so much better, and it's simply a matter of losing efficiency (which enthusiasts and race teams don't give a isht about) then why don't we see race teams running low single digit compression ratios with giant blowers capable of compressing the air to several bar of pressure?
You're clearly not understanding trade-offs when you boil it down to the simple term "better" and also clearly are not understanding the term "efficiency". I'm not talking about fuel efficiency. I'm talking about making the more or less power from the same air and fuel flow. As I have said repeatedly, more compression will make more power from the same air/fuel flow because it is more efficient, barring knock. Race teams running unlimited octane only sacrifice engine longevity by increasing compression, and gain power due to the higher efficiency of the high compression. Their engines are built stout and only run minutes (or even seconds) between overhauls. Compression ratio is a big bag of trade-offs and "we" aren't running race cars on unlimited octane so the same compression ratio is not optimal. So, for a race car with unlimited octane and frequent overhauls, higher compression is "better" because it will make more power under the given constraints. But in a street car with limited octane and high reliability expectations, lower compression is "better". One size DOES NOT fit all.

I'll tell you why. Because of the quality of fuel. There's no NEED to run a ginormous blower and a zillion lbs of boost when you have quality fuel that's resistant to pre-ignition and detonation.
Why are you talking about fuel quality again? The OP specified pump gas. If he specified 87 octane, that's his prerogative and I'm glad to discuss. If you don't want to talk about building an engine for pump gas, then why are you here?

However, technically there is a reason to not run infinite compression ratio on race motors, and I've explained it already. It has to do with peak cylinder pressure and engine stresses.

Mike is stuck in 1995 when most street car guys were stuck buying 93 (if you didn't want dedicated race fuel for a trailer queen).
It's the subject of the thread. I have my reasons why I do it and it's not because I'm stuck in 1995, though I did have a 1995 Camaro that ran 9's at 146 on pump gas, but I digress... Anyway, who cares what the reasons are...it's what the thread is about. I ask again....If you don't want to talk about building an engine for pump gas, then why are you here?

With E85,...
I ask again....If you don't want to talk about building an engine for pump gas, then why are you here?

Do you participate in the diesel boards and tell them they're building their engines all wrong and they need to use E85 as well?

With E85, there's NO reason to run lower compression and there's plenty of people running 11:1 and 12:1 on comparatively decent numbers.
Engine stresses; see above. It's definitely not as strong of a case as if octane-limited, but it's not correct to say there's "NO reason".

I'll concede that if you want to make 1500 hp+ then low(er) compression and more fuel/boost is the answer. But for all practical uses for enthusiasts on this forum, picking that motor just means you generate more blower heat, have to run a smaller pulley and eventually you run out of blower or intercooler (trying to spin that thing to the moon to keep up).
Wait, wasn't it me that said the lower limit on compression ratio was when you run out of blower? And you said I "punted" but now you're saying the exact same thing.

And again, I'm talking 10 or 11/1 in a gen3. The GT500 is running 9.5/1 on a smaller blower and yet making awesome numbers on 93, well in excess of what an 11/1 or 12/1 Coyote is capable.

I'll point out again that with high compression and true pump gas there is a wall right around 700 rwhp where the Coyote becomes octane-limited. Predators are making 850+ on the same octane by using lower compression. If lowering compression is out of the question (for you), then how do I get to 850 on pump gas? Seriously, what is your solution?

Hence the 500 guys that are having to ditch the ported OE blowers in favor of a much larger 3.8 setup. We haven't even gotten to space limitations in the engine bay, etc.
Except that you have to lower the engine to fit the 3.8 in the S550.

The bottom line is, for 93, if you're wanting to make North of 800 rear, yes, one way would be to lower the compression and up the boost....
Yes, FINALLY...and definitely the most practical way. And by extension, if you lower compression and set it up for 700 hp, then the result will be more reliable rather than running on the edge of knock.

But most people wanting North of that are willing to concede to E85 which resets the problem and there is NO NEED to run a lower comp motor at power levels MOST people are wanting or capable of sporting.
Again, "NO NEED" is technically incorrect; more accurately it would be "LESS NEED".

But if this were a conversation about E85 vs 93, then this would be a relevant point. But it's the OPs thread and he specified pump gas very early on.

So.....If you don't want to talk about building an engine for pump gas, then why are you here?
 

K4fxd

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Next time I run into one of the street outlaw types who run 50 psi of boost on turbos, I'll ask what compression they run. I'll bet it is lower than 12.

Will I lose my dollar?
 

gimmie11s

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Next time I run into one of the street outlaw types who run 50 psi of boost on turbos, I'll ask what compression they run. I'll bet it is lower than 12.

Will I lose my dollar?
Yes you'll lose that dollar.
 

K4fxd

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Angrey

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Next time I run into one of the street outlaw types who run 50 psi of boost on turbos, I'll ask what compression they run. I'll bet it is lower than 12.

Will I lose my dollar?
Conceded. Now show me someone who runs a daily or street car with the chops to handle 50 psi. The GTR and Lambo guys do it because they dump $100k+ into their motors/cars.

So yeah, if you decide to run 50 psi, I'll tip my hat, you're not going to do it on 12:1 compression. Now show me someone running a street mustang with 50 psi.
 

LxMike

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Hmm, I wonder what the supra guys with 1,000+ rwhp run for boost and C.R...
 

engineermike

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Who’s suggesting 50 psi? I’m talking about 16-18 psi at 10-11/1 compression, which is actually really close to what a stock gen2 ecoboost runs (though it does it on 87 octane).
 

K4fxd

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Who’s suggesting 50 psi?
I threw that out there because some of these guys get 60 or more 1/8th mile runs before needing a refresh. They are making 3000+ reliable HP

So my question was what compression ratio do they run. I really don't know. I suppose I could call Sonny and ask
 

TKM Conbread

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I threw that out there because some of these guys get 60 or more 1/8th mile runs before needing a refresh. They are making 3000+ reliable HP

So my question was what compression ratio do they run. I really don't know. I suppose I could call Sonny and ask
we have a 4.6 bore space SBC that sees 75-82 psi… the motor has made 4000 to the hubs with twin 98s on Fueltech hub dyno…car runs 3.76 on a 275 tire… compression is in the 12-13:1 range…

there is no set answer to this question.. its a matter of trial and error.. testing and way more testing… no 2 motors will ever be the same..

and Also Sonny died last year…
 
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