High compression and low boost?
01-31-2011, 09:43 AM
#21
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Brain i have seen it in person on a dyno customer came in and wanted to see what his new 5.0l mustang really put down so we put it on the dyno and he made 397whp. When we saw the numbers we were all amazed.
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01-31-2011, 10:28 AM
#23
If you can afford to replace your built motor if you blow it up, then I say high comp is the way to go. More fun out of boost. Spend money on headwork. Otherwise, I think the safety margin you get with stock or lower compression is probably worth it.
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01-31-2011, 11:09 AM
#29
All it comes down to is newer/more efficient technology.
Look at the s2k: they make ridiculous power with forced induction even without direct injection. Biggest reason? their heads flow more than a BP could even dream of. They get away with 500+ whp on the stock 11:1 compression.
So you take a well flowing engine, add vvt on both cams, add direct injection and of course you end up with a ton of efficiency/more power. Add boost and e85 to that and you've got yourself a damn near ideal setup.
If I was to "do it all over again" with a miata/bp, it would be with a 01+ engine with 10.5-11:1 compression, and a twin scroll variation of a 3071. On e85 of course. e85 is so best
Look at the s2k: they make ridiculous power with forced induction even without direct injection. Biggest reason? their heads flow more than a BP could even dream of. They get away with 500+ whp on the stock 11:1 compression.
So you take a well flowing engine, add vvt on both cams, add direct injection and of course you end up with a ton of efficiency/more power. Add boost and e85 to that and you've got yourself a damn near ideal setup.
If I was to "do it all over again" with a miata/bp, it would be with a 01+ engine with 10.5-11:1 compression, and a twin scroll variation of a 3071. On e85 of course. e85 is so best
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02-01-2011, 04:38 PM
#30
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I wanna play.
IIRC, going from 8.5 to 10.5 CR pistons was good for 22ft lbs of torque on a 7.6 liter big block making ~500ft lbs. The effect would be significantly smaller on our little motors. The number of pounds of air and fuel you can burn without detonation in a 10.5 CR engine is significantly less than an 8.5 CR engine if all other variables are controlled. Therefore, you have less potential for making power on the higher compression engine using pump gas.
On C16 or other race gas the detonation threshold is much higher, but eventually, given enough added air and fuel mass, it can be reached as well. And the lower compression engine will have more headroom there too.
It's almost like science and math or something.
So what if these high compression direct injection guys still have room for boost on top of stock power. How much more air could they get away with cramming in their engines if they were one or two points lower compression?
IIRC, going from 8.5 to 10.5 CR pistons was good for 22ft lbs of torque on a 7.6 liter big block making ~500ft lbs. The effect would be significantly smaller on our little motors. The number of pounds of air and fuel you can burn without detonation in a 10.5 CR engine is significantly less than an 8.5 CR engine if all other variables are controlled. Therefore, you have less potential for making power on the higher compression engine using pump gas.
On C16 or other race gas the detonation threshold is much higher, but eventually, given enough added air and fuel mass, it can be reached as well. And the lower compression engine will have more headroom there too.
It's almost like science and math or something.
So what if these high compression direct injection guys still have room for boost on top of stock power. How much more air could they get away with cramming in their engines if they were one or two points lower compression?
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02-01-2011, 05:35 PM
#33
What you consider small would depend on the compression ratio, fuel octane, and application.
But here is a better example:
3071 @ 9:1 small turbo, plenty of room,
3071 @ 10:1 medium, tuning abilities will be challanged.
3071 @ 11:1 big turbo, race gas, and very little room for error.
3071 @ 14:1 gigantic, and not sure if it is possible.
Of coarse this is just an example. What kind of compression a 3071 mounted to a bp will tolerate would need someone to do some painfully expensive experimenting.
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02-01-2011, 05:41 PM
#34
Minus what might be in the coilovers, this picture shows all 60's technology at play..... Our parents and grandparents know their **** on the track
Its always been my understanding from watching dyno pulls and talking to builders is high compression engines make a bit more power, but spike in cylinder pressures while doing it.
Thirdgen- That setup should make more torque (due to increased cylinder pressures)
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02-02-2011, 12:02 AM
#35
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Boost is a measure of the restriction of air in a space. A turbo creates flow. A byproduct of flow is pressure.
From the turboforums.com, saying a turbo makes boost is like saying a cow farm makes crap. It makes cows, but a byproduct is crap.
It's just that boost, or the restriction of air, is the simplest way of measuring the amount of flow.
To explain the restriction, I will say that my roots blower, on my previous GTP, which moves a set amount of air 90ci, if I remember correctly, per rotation, boost is lost when the blower is ported. Flow and power are not lost, just the restriction of airflow measured as a pressure. It doesn't really work the same for turbos because of the way they are controlled, but I think you get the pic.
I think that High compression, plus big turbo, plus e85 or aquamist water injection, and a lot of dyno time would make for the ultimate DD. HIgh compression means power before boost. Big turbo means that you won't use it unless you are getting on it(kinda like the C5 Z06 I got to drive), and the fuel stuff doesn't need an explanation.
From the turboforums.com, saying a turbo makes boost is like saying a cow farm makes crap. It makes cows, but a byproduct is crap.
It's just that boost, or the restriction of air, is the simplest way of measuring the amount of flow.
To explain the restriction, I will say that my roots blower, on my previous GTP, which moves a set amount of air 90ci, if I remember correctly, per rotation, boost is lost when the blower is ported. Flow and power are not lost, just the restriction of airflow measured as a pressure. It doesn't really work the same for turbos because of the way they are controlled, but I think you get the pic.
I think that High compression, plus big turbo, plus e85 or aquamist water injection, and a lot of dyno time would make for the ultimate DD. HIgh compression means power before boost. Big turbo means that you won't use it unless you are getting on it(kinda like the C5 Z06 I got to drive), and the fuel stuff doesn't need an explanation.
Last edited by Dust; 02-02-2011 at 12:32 AM.
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02-02-2011, 12:24 AM
#36
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In addition to direct injection, newer technology for combustion chamber design has also helped improve detonation resistance.
--Ian
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02-05-2011, 03:07 AM
#38
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The first post I ever made here was in regards to the suitability of boosting my 10.5 comp motor and i got flamed pretty good. Lots of research later and Im almost ready to shove some boost in.
My build includes a very well prepared bottom end (I rev it to 8500 rpm every day many times) big cams, big valves and extensive head work at 10.5:1 and a relatively small turbo. Im currently atmo on e85 and running stupid amounts of timing (well over 35 degrees in places) and when boosted i will lose some of that and hopefully 10-12 psi will take its place, but psi IS just a measure of restriction. And remembering this, 10 psi on my very well breathing engine (compared to most of the stock head cars here) could well be like pushing 14psi at the same AIT as many other cars here, certaintly in terms of actual air mass flowed.
Dann
EDIT: lets not forget how hard my 10.5:1 engine with highly worked heads will spool a small turbo, on the street and tarmac rally it should be awesome.
My build includes a very well prepared bottom end (I rev it to 8500 rpm every day many times) big cams, big valves and extensive head work at 10.5:1 and a relatively small turbo. Im currently atmo on e85 and running stupid amounts of timing (well over 35 degrees in places) and when boosted i will lose some of that and hopefully 10-12 psi will take its place, but psi IS just a measure of restriction. And remembering this, 10 psi on my very well breathing engine (compared to most of the stock head cars here) could well be like pushing 14psi at the same AIT as many other cars here, certaintly in terms of actual air mass flowed.
Dann
EDIT: lets not forget how hard my 10.5:1 engine with highly worked heads will spool a small turbo, on the street and tarmac rally it should be awesome.
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02-05-2011, 03:45 AM
#39
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Backpressure from an itty bitty turbine is a major cause of restriction. Restriction is heat. Heat is det.
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