[charlie66]

If I were to build a 461 ci motor with 11:3 to1 base compression ratio that was tuned for E85 with intercooler and aluminum heads. what could I expect? Would it live at low boost levels , say 12 to 15 pounds ? What different characteristics would there be compared to a 8:75 to 1 motor? Would it make more power at the same boost levels, or would it be less efficient and be detonating ? I guess higher air intake temps would be more inherent right? I'm throwing this around because I have this motor built and all I would need would be a cam to get it up an running.. It would have twin Precision PTE6870's on it.....

[v869tr6]

Feed it E98 when you turn the boost up

[charlie66]

Originally Posted by v869tr6

Feed it E98 when you turn the boost up

What are you at with your compression?

[Tom Vaught]

At some point Charlie, the compression ratio limits your boost level that you can run with available fuel. You seem to be on a Max Boost quest.

The fact that you were running 35 psi with a 4 cylinder engine and had good durability and now assuming the same guidelines (except for fuel economy) what would be the benefit of going 3 full points higher in compression ratio with the same fuel, a V-8 engine, and twin turbos? And thinking that it would not have combustion stability issues with the higher static compression ratio. Corvettes tried that deal in production with direct injection and would up running very moderate boost because it was a street car.

Tom V.

[charlie66]

Originally Posted by Tom Vaught

At some point Charlie, the compression ratio limits your boost level that you can run with available fuel. You seem to be on a Max Boost quest.

The fact that you were running 35 psi with a 4 cylinder engine and had good durability and now assuming the same guidelines (except for fuel economy) what would be the benefit of going 3 full points higher in compression ratio with the same fuel, a V-8 engine, and twin turbos? And thinking that it would not have combustion stability issues with the higher static compression ratio. Corvettes tried that deal in production with direct injection and would up running very moderate boost because it was a street car.

Tom V.

I'm only thinking of this because I have my motor in my Ventura that is built with all the good stuff but has flat tops which brings it to 11.3 to 1. So i was asking because it would be really easy to just change the cam and not have to go and take the whole motor apart for new dish tops. Maybe I could use a thicker head gasket ? You know me , I like to experiment with things Tom.. If you think it will be a time bomb then I wont even think about anymore .. Just wanted to see what everyone thought of this idea..

[BruceWilkie]

Charlie do a search on Yellow Bullet... maximum compression E85 in both the NA and turbo sections. See what the extremes are. I think you'll be surprised. I DONT advocate trying the extremes but I'd consider something between the minimums and extremes and adjust accordingly.

BTW inlet temps shouldnt change from compression but turbine may behave differently. (Compression affects EGT). HEAT of COMPRESSED air/fuel will increase!

That said Id keep manifold inlet temps cool(close to ambient) if boosted(A/W intercooler) With compression up where you're at I'd add water injection to slow combustion rate some.

Bigger concern is keeping cylinders sealed and stock block alive.

With your present boost success with E85 on your 4 cylinder you might want to consider staying NA on the 461 and upping compression 2-3 points.

Continue doing your homework!

[charlie66]

Originally Posted by BruceWilkie

Charlie do a search on Yellow Bullet... maximum compression E85 in both the NA and turbo sections. See what the extremes are. I think you'll be surprised. I DONT advocate trying the extremes but I'd consider something between the minimums and extremes and adjust accordingly.

BTW inlet temps shouldnt change from compression but turbine may behave differently. (Compression affects EGT). HEAT of COMPRESSED air/fuel will increase!

That said Id keep manifold inlet temps cool(close to ambient) if boosted(A/W intercooler) With compression up where you're at I'd add water injection to slow combustion rate some.

Bigger concern is keeping cylinders sealed and stock block alive.

With your present boost success with E85 on your 4 cylinder you might want to consider staying NA on the 461 and upping compression 2-3 points.

Continue doing your homework!

I really want to go turbo with the 461.
I guess what I really would like to know is if some one can tell me what the cylinder pressure comparison would be with a 11 to 1 motor at 10 psi to a 8 to 1 motor at 35 psi, or is there more involved to think about? If its some of the same maybe it will be ok?

[BruceWilkie]

From Wallace site
http://www.wallaceracing.com/boost-c...ratio-calc.php

Note I used Altitude of zero!
Note from site says "2 Different Formulas Used For Answers
The first is the standard equation used by many,
The second may be the more reliable one "

IMO cam timing events will have effects on actual compression pressures seen! As will temperature. Plenty of unknown assumptions in the above calculator.

8:1 compression at 40 psi
"The Boosted Compression Ratio from your Boost of 40 psi is 29.77 : 1
The Effective Boosted Compression Ratio from your Boost of 40 psi is 15.43 : 1"

11.3 compression at 15 psi
"The Boosted Compression Ratio from your Boost of 15 psi is 22.83 : 1
The Effective Boosted Compression Ratio from your Boost of 15 psi is 16.06 : 1"

11.3 compression at 12 psi

"The Boosted Compression Ratio from your Boost of 12 psi is 20.52 : 1
The Effective Boosted Compression Ratio from your Boost of 12 psi is 15.23 : 1"

[charlie66]

Thanks Bruce. I guess when I see my friend with 10:5 to 1 with his 2JZ motor having zero issues @ 30 psi with 11 degrees of timing, I think to myself that maybe this would be possible . He thinks ill be fine. But then again he's just a turner guy with a way better design of motor...

[Tom Vaught]

10.5 assumed compression ratio might actually be closer to 10 to 1 on a production engine. Pontiacs historically were lower than 10.75 to 1 on their engines.

That being said, a 10 to 1 engine with 30 psi with 11 degrees of timing basically means that the combustion cycle is starting late therefore the cylinder pressure is lower tna it would be at 27 degrees of timing. Your engine was probably not giving up near as much cylinder pressure at 30 psi of boost even with 8.75 to 1 compression ratio. Off boost I bet it drives nice with 10-1 compression ratio even with late timing.

Tom V.

ps don't give up on going with boost on the V-8 engine. Just buy the right CR pistons as adding a thick gasket to lower compression ratio make the engine want to knock much easier.

Tom V.

[charlie66]

Originally Posted by Tom Vaught

10.5 assumed compression ratio might actually be closer to 10 to 1 on a production engine. Pontiacs historically were lower than 10.75 to 1 on their engines.

That being said, a 10 to 1 engine with 30 psi with 11 degrees of timing basically means that the combustion cycle is starting late therefore the cylinder pressure is lower tna it would be at 27 degrees of timing. Your engine was probably not giving up near as much cylinder pressure at 30 psi of boost even with 8.75 to 1 compression ratio. Off boost I bet it drives nice with 10-1 compression ratio even with late timing.

Tom V.

ps don't give up on going with boost on the V-8 engine. Just buy the right CR pistons as adding a thick gasket to lower compression ratio make the engine want to knock much easier.

Tom V.

I know the higher compression yields a lot less boost capabilities. That's why I'm asking what would be the max level of boost with e85 and a 11:3 to 1 motor. If I could get away with 10 - 15 psi , what kind of power would we be talking about. Would it be more then a 8: to 1 motor at the same level of boost? This is the question that I would like to know the answer to. That and would the motor be able to live ....

[v869tr6]

My compression is about 8.25 maybe 8.5 with the heads having been resurfaced about 3 times.
I do have a very small cam with no overlap so that must make some difference.
I run E85 most of the time on the street and run E98 at the strip just for some insurance in the 1/4 mile.

[Boostedbird]

The Butler's 482" in this story is at 10:1 and at this point was at 44psi. They were on alcohol though. Just something to read.

[Boostedbird]

http://www.hotrod.com/how-to/engine/...-engine-build/

[JSPONT]

There is twin turbo drag week car that runs on the street around our area Charlie, I won't use his name just incase he street races the car. It is a 540 c.i. Chevy, twin 88mm 10.25 to 1 runs 26psi on e85 with no issues per him.

Sounds like you have a good science experiment on your hands! A fast one too. My guess is at 10-12 psi the Ventura will not be able to handle the power with out upgrades!!!!!!!!!

[charlie66]

Originally Posted by JSPONT

There is twin turbo drag week car that runs on the street around our area Charlie, I won't use his name just incase he street races the car. It is a 540 c.i. Chevy, twin 88mm 10.25 to 1 runs 26psi on e85 with no issues per him.

Sounds like you have a good science experiment on your hands! A fast one too. My guess is at 10-12 psi the Ventura will not be able to handle the power with out upgrades!!!!!!!!!

Do you know this guy. I would like to talk to him if possible ..

[charlie66]

Originally Posted by Boostedbird

The Butler's 482" in this story is at 10:1 and at this point was at 44psi. They were on alcohol though. Just something to read.

Thanks. I have seen that article ...

[charlie66]

Originally Posted by v869tr6

My compression is about 8.25 maybe 8.5 with the heads having been resurfaced about 3 times.
I do have a very small cam with no overlap so that must make some difference.
I run E85 most of the time on the street and run E98 at the strip just for some insurance in the 1/4 mile.

Thank you.

I was also thinking for this case scenario a small cam with hardly any overlap would be the best way to go... I really do feel that E85 would work. That's all I've been using with my 4 cylinder even at 35 - 38 psi I have had not one detonation problem . So 10 psi on a 11 to 1 motor to me seems like a go. But what do I know really im just going off a feeling from what I have experienced ... But that's all I got, my experience's, and you guys..... and a appreciate and value all of you!

[Boostedbird]

Originally Posted by charlie66

Thank you.

I was also thinking for this case scenario a small cam with hardly any overlap would be the best way to go... I really do feel that E85 would work. That's all I've been using with my 4 cylinder even at 35 - 38 psi I have had not one detonation problem . So 10 psi on a 11 to 1 motor to me seems like a go. But what do I know really im just going off a feeling from what I have experienced ... But that's all I got, my experience's, and you guys..... and a appreciate and value all of you!

Charlie, I would think that as long as you had a larger good flowing exhaust with low backpressure a larger cam with some overlap would be the way to go. Not the same situation, but my car has 9.3:1 compression with 26 degrees of overlap on the cam. It's just a solid flat tappet. Seems to run pretty good I think. I would think that a small cam and no overlap would cause it to be prone to detonation at 11:1, especially when the cylinder pressure rises even more under boost. No expert though, just my thoughts.

[charlie66]

Originally Posted by Boostedbird

Charlie, I would think that as long as you had a larger good flowing exhaust with low backpressure a larger cam with some overlap would be the way to go. Not the same situation, but my car has 9.3:1 compression with 26 degrees of overlap on the cam. It's just a solid flat tappet. Seems to run pretty good I think. I would think that a small cam and no overlap would cause it to be prone to detonation at 11:1, especially when the cylinder pressure rises even more under boost. No expert though, just my thoughts.

Ok ill have to look into that one. Ill call Tim at bullet