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School me on PSI????

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Old Nov 10, 2006 | 06:19 AM
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Default School me on PSI????

Harold is wanting to know how much boost I plan to run. I really dont know that much about the amount of boost turbochargers put out. I know about the SC's. I guess I am doing it bass ackwards.
I am still reasearching as much as I can, but he needs the info now.
I was thinking somewhere around 8-10 on the street and 14-16 at the track. Most of yall know my motor plan but here it is again.
All forged rotating assembly, -31CC JE pistons, T-76, PortPros Stg III H/C/I.
CR is going to end up around 8.6:1. Alvin will be dyno tuning it when its done. I am using a JGS 40MM WG if it matters. I havent deceided on a BOV yet. OBX intercooler, and ASM monobalde. Id be happy if the car puts down 650ish to the wheels. I have the weekend to get as much info as I can so please help out. BTW its an LT1 based.


This car is not a DD.
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Old Nov 10, 2006 | 06:24 AM
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Turbos arent really set like superchargers, you decide how much boost you would like to run through a boost controller or by the spring in the wastegate. You can push a turbo beyond its thermal effeciency range which will generate more heat and not gain power but I don see that happening with the set up you plan on doing. A T76 should be fine on 16psi with your combo and I think your numbers will be easily obtainable.
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Old Nov 10, 2006 | 07:57 AM
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15-16psi will get you 650rwhp no problem...
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Old Nov 10, 2006 | 08:15 AM
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https://ls1tech.com/forums/forced-induction/208864-turbo-faq.html
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Old Nov 10, 2006 | 11:10 AM
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Well I have been running numbers all morning. And best I can guess I may need to step up to a T-88. I am using a 383 @6800 RPM and I just cant hit a good spot on the T-76 map.
Using a T-88 @ 10psi I am in about 77% efficiently and even that comes on real low.

I guess Ill just tell him between 10-16psi.
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Old Nov 10, 2006 | 11:13 AM
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Originally Posted by SWINGRRRR
Well I have been running numbers all morning. And best I can guess I may need to step up to a T-88. I am using a 383 @6800 RPM and I just cant hit a good spot on the T-76 map.
Using a T-88 @ 10psi I am in about 77% efficiently and even that comes on real low.

I guess Ill just tell him between 10-16psi.
Why do you want to spin the engine so high. Let the turbo make the power... not the rpm's.

Nice to see the thread unlocked.
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Old Nov 10, 2006 | 11:18 AM
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What do you think is a good RPM? 6000? I am sure you know, but the RPM is the first number I need to even start looking at the maps.

Edit: I got 65% efficiency @ 3/4 max RPM on the turbo using 16psi on the 383/T-76 @6000RPM's. And given the Hp=airflow lb/min x 10, thats 827Hp at 85%VE.
I think I am worrying to much about the numbers. I have to get some sleep.

Last edited by SWINGRRRR; Nov 10, 2006 at 11:35 AM.
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Old Nov 10, 2006 | 11:19 AM
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Originally Posted by SWINGRRRR
What do you think is a good RPM? 6000? I am sure you know, but the RPM is the first number I need to even start looking at the maps.
Absolutely. PM me the cam specs so we can talk more. The longevity of the engine will be better. Shoot for peak power ~5800-6000rpm and shift @ 6200rpm.
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Old Nov 10, 2006 | 11:37 AM
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turbos like RPM as it puts it in a better spot on the effeicncy range

i only have a 347 but spin my combo with the PTE88 about 7000, will problably spin higher next season.
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Old Nov 10, 2006 | 11:41 AM
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Originally Posted by smokinHawk
turbos like RPM as it puts it in a better spot on the effeicncy range
Thats too generic of statement that doesnt hold true alot of the time. Its based upon airflow consumption (c.i. and rpm) and the efficiency map of the turbo (sizing of turbo). If he spins the T76 past 6000rpm on a 383ci it will start to fall off the compressor map and become less efficient. Your statement would be false in this situation. Now in your case, more rpm probably moves your turbo into a better efficiency range based on YOUR C.I. and RPM and the size of YOUR turbo.
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Old Nov 10, 2006 | 12:13 PM
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Originally Posted by SWINGRRRR
I think I am worrying to much about the numbers.
I agree. Keep in mind also that the T76 units that are sold flow better than the old Garrett T76 compressor maps that everyone passes around on the internet. I've heard the newer stuff flows about 10% more and is more efficient.

Also keep in mind that guys are making 950 - 1100 fwhp with the T76 on 350 - 390 cid, while keeping the rpm under 6000. 650rwhp is a piece of cake for the T76GTS. Unless you're looking for 1000+ rwhp, you need not move up to a larger, harder to fit, slower spooling turbo.

Mike
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Old Nov 10, 2006 | 10:51 PM
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I know its hard to explain but I am extremely **** about the car. I obsess about the numbers. I have to be able to see the math.

Thanks for all the input guys. I am going to tell Harold 16psi with the mac RPM's around 6000.
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Old Nov 11, 2006 | 08:45 AM
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Originally Posted by RealQuick
Thats too generic of statement that doesnt hold true alot of the time. Its based upon airflow consumption (c.i. and rpm) and the efficiency map of the turbo (sizing of turbo). If he spins the T76 past 6000rpm on a 383ci it will start to fall off the compressor map and become less efficient. Your statement would be false in this situation. Now in your case, more rpm probably moves your turbo into a better efficiency range based on YOUR C.I. and RPM and the size of YOUR turbo.
yes it was a somewhat quick statement, and there are alot of varibles,
but if you look at the shap of the maps they have a high teardrop shape, so smaller engine gets up there in the map further if you rev it out, and all the turbo combos ive had wanted more and more rpm
and yes when you get a bigger engine it wont be able to get into the same regions so you have to rev it a little lower. but i just like to spin mine
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