precision 76gts?????
TECH Addict
Joined: Jul 2005
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They would all run pretty good. I have a 383 with the same turbo and it ain't slow. The turbo will go over 20 psi on my motor. HOWEVER, that turbo seems to work best in the 350 cid range at about 22 psi. You can make 1000 rwhp with a setup like that.
Definitely get the .96 A/R, though.
Definitely get the .96 A/R, though.
Shameless plug, but I have one for sale. .96 housing too.
https://ls1tech.com/forums/lsx-parts-sale/385038-fs-precision-t76-gts.html
https://ls1tech.com/forums/lsx-parts-sale/385038-fs-precision-t76-gts.html
How big is to big for a t76gts. I am running a 370 and i am planning on running the 76gts going to shoot for 600-650rwhp. It works by the numbers but there is a lot of unknowns
TECH Addict
Joined: Jul 2005
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370 cid and the 76GTS will easily get way over 650 rwhp. I'm at 383 cid with the 76GTS, a crappy log-header turbo setup, an "all wrong" blower cam, and an auto with a loose converter and it still made 680 rwhp at 19 psi.
Mike
Mike
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Originally Posted by 2nasty
i want to get about 7 to 900 at the wheels.
ed
too small for any of those displacements you will be stuck with less than 850rwhp unless you go with stock cid.. the turbo will go into compress or surge.
i'm not saying it because i figured it out mathematicly, it happened to me.
i'm not saying it because i figured it out mathematicly, it happened to me.
With a big CI motor the turbo will reach its choke limit. Surge limit is a turbo that outputs to much air for the engine to consume. Thats what the surge rings on the compressor covers are for.
Jose
Jose
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Joined: Jul 2005
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I've been thinking about the whole turbo size versus engine size issue alot lately. . .
I really don't think a large motor with a T-76 will limit it's power potential. An 1100 hp motor will consume the same amount of air and produce the same amount of exhaust gas no matter what the displacement. I'm sure there is some efficiency (BSFC) difference that gives the 180 cid Supra engines an advantage and somewhere in the 5 - 10% would be reasonable due to superior rod/stroke ratios and combustion chamber shapes. That can account for 50 - 100 hp at this level. But when 355 cid makes nearly the same power as a 180 cid motor, I just can't believe engine size is that big of a factor. Especially when 180 is good, 355 is fine, but 383 is supposedly just way too much.
I think the problem is mainly that of perception. We don't see many high-hp 383's with T-76's just because no one's really built a serious combo and dyno'd it. For instance, many people would say that 990 rwhp from a T-76 on a 355 is impossible - until Jose et. al. did it. Take my car, for instance. Sure, I "only" made 680 rwhp, but I did it at 19 psi through an auto with a loose converter with a "crappy" log header, an "all wrong" supercharger cam, and a "too small" vortech aftercooler. Perhaps if I dyno'd at 22 psi through a T56 with proper headers, a larger intercooler, and a turbo cam, it would have been in the upper 900's. . .
And as far as "choke" goes, 1100 hp worth of air will choke the compressor regardless of what size engine it goes to.
I really don't think a large motor with a T-76 will limit it's power potential. An 1100 hp motor will consume the same amount of air and produce the same amount of exhaust gas no matter what the displacement. I'm sure there is some efficiency (BSFC) difference that gives the 180 cid Supra engines an advantage and somewhere in the 5 - 10% would be reasonable due to superior rod/stroke ratios and combustion chamber shapes. That can account for 50 - 100 hp at this level. But when 355 cid makes nearly the same power as a 180 cid motor, I just can't believe engine size is that big of a factor. Especially when 180 is good, 355 is fine, but 383 is supposedly just way too much.
I think the problem is mainly that of perception. We don't see many high-hp 383's with T-76's just because no one's really built a serious combo and dyno'd it. For instance, many people would say that 990 rwhp from a T-76 on a 355 is impossible - until Jose et. al. did it. Take my car, for instance. Sure, I "only" made 680 rwhp, but I did it at 19 psi through an auto with a loose converter with a "crappy" log header, an "all wrong" supercharger cam, and a "too small" vortech aftercooler. Perhaps if I dyno'd at 22 psi through a T56 with proper headers, a larger intercooler, and a turbo cam, it would have been in the upper 900's. . .
And as far as "choke" goes, 1100 hp worth of air will choke the compressor regardless of what size engine it goes to.
Last edited by engineermike; Oct 3, 2005 at 04:49 PM.
Originally Posted by engineermike
And as far as "choke" goes, 1100 hp worth of air will choke the compressor regardless of what size engine it goes to.
I never understood that either, when people talk about engine size. I guess it's because 20psi on a 347cid motor is a lot less air than 20psi on a 422....therefore the 20psi on the 422 will be choked by the exhaust side before the 20psi on the small motor.....so even though the exhaust side chokes at the same amount of HP (airflow), this limit is at less boost with a bigger motor, and since most compressors hare more effecient at higher boost levels, it's better to use the smaller motor with a given turbo?
Staging Lane
Joined: Oct 2005
Posts: 73
Likes: 0
Originally Posted by engineermike
I've been thinking about the whole turbo size versus engine size issue alot lately. . .
I really don't think a large motor with a T-76 will limit it's power potential. An 1100 hp motor will consume the same amount of air and produce the same amount of exhaust gas no matter what the displacement. I'm sure there is some efficiency (BSFC) difference that gives the 180 cid Supra engines an advantage and somewhere in the 5 - 10% would be reasonable due to superior rod/stroke ratios and combustion chamber shapes. That can account for 50 - 100 hp at this level. But when 355 cid makes nearly the same power as a 180 cid motor, I just can't believe engine size is that big of a factor. Especially when 180 is good, 355 is fine, but 383 is supposedly just way too much.
I think the problem is mainly that of perception. We don't see many high-hp 383's with T-76's just because no one's really built a serious combo and dyno'd it. For instance, many people would say that 990 rwhp from a T-76 on a 355 is impossible - until Jose et. al. did it. Take my car, for instance. Sure, I "only" made 680 rwhp, but I did it at 19 psi through an auto with a loose converter with a "crappy" log header, an "all wrong" supercharger cam, and a "too small" vortech aftercooler. Perhaps if I dyno'd at 22 psi through a T56 with proper headers, a larger intercooler, and a turbo cam, it would have been in the upper 900's. . .
And as far as "choke" goes, 1100 hp worth of air will choke the compressor regardless of what size engine it goes to.
I really don't think a large motor with a T-76 will limit it's power potential. An 1100 hp motor will consume the same amount of air and produce the same amount of exhaust gas no matter what the displacement. I'm sure there is some efficiency (BSFC) difference that gives the 180 cid Supra engines an advantage and somewhere in the 5 - 10% would be reasonable due to superior rod/stroke ratios and combustion chamber shapes. That can account for 50 - 100 hp at this level. But when 355 cid makes nearly the same power as a 180 cid motor, I just can't believe engine size is that big of a factor. Especially when 180 is good, 355 is fine, but 383 is supposedly just way too much.
I think the problem is mainly that of perception. We don't see many high-hp 383's with T-76's just because no one's really built a serious combo and dyno'd it. For instance, many people would say that 990 rwhp from a T-76 on a 355 is impossible - until Jose et. al. did it. Take my car, for instance. Sure, I "only" made 680 rwhp, but I did it at 19 psi through an auto with a loose converter with a "crappy" log header, an "all wrong" supercharger cam, and a "too small" vortech aftercooler. Perhaps if I dyno'd at 22 psi through a T56 with proper headers, a larger intercooler, and a turbo cam, it would have been in the upper 900's. . .
And as far as "choke" goes, 1100 hp worth of air will choke the compressor regardless of what size engine it goes to.
The big thing with using a smaller turbo on a larger displacement engine is to open up the exhaust housing more. This can be done by going to a bigger wheel in the same housing or bumping up to a larger exhaust housing. This will allow lower back pressure and get you a bit less pumping losses.
So, if a T76 will make 1000 whp on a 355, it should do the same on an equally efficient 408, assuming it stays in the same efficiency range of the turbo. This HP will be achieved at a lower boost than in it will be on the 355, because the 408 is obviously breathing more air in.
A 76 will not support that much on a 408 unless you run a TV backside, which then becomes huge and is complicated to match a proper compressor cover with a thumper CHRA. Also you are now dropping the PR of the compressor wheel, which means the efficiency drops, which means the HP supported drops a well. As for exhaust housing or turbine wheel change, they will bandaid the problem somewhat, but still cause a restriction unless you do both properly. Also the name "compressor wheel" is just that. IF their is not a certain level of compressing of the air, the wheel will not efficiently work. That efficiency is dictated by X amount of air incoming at X turbine speed, then X amount of PR on the oulet side.
Staging Lane
Joined: Oct 2005
Posts: 73
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The PR on the exhaust is not extremely picky. Mainly it will affect spool up or if it is too small, cause a bottle neck in the system. That is why the T3/T4 setups work. They still put out good power, but you will end up with a bottle neck in the exhuast side before you outflow the compressor side on most of them. A bottle neck isn't a cut off point either, you just start to get diminishing returns. I have seen some small turbo's put out WAY more power than they were ever intended for and spinning 40k RPM more than they are supposed to. It isn't great for longevity, but they have lasted much longer than I thought they would. The stock turbo on the Mitsu EVOVIII is a great example, it got a full weight car into the 10's without nitrous. That is pretty amazing for a little 16g turbo (similar in size to a big T28).