calculate hp with boost? - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 22 Old 09-28-2011, 03:58 PM Thread Starter
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calculate hp with boost?

hey guys, I was wondering how low you can set the max boost? I have a stock block 347 that will probably make maybe 350rwhp and i have a turbo kit i want to add on soon. I know its risky with stock block but I was just wondering how low can you regulate the boost to?

Any way to calculate how much hp you would gain per lb of boost so I can maybe get a estimate on what I would make with low psi based off around 350rwhp on motor? Maybe 5-6 psi? how low can you go?

here is the combo:

ptk turbo kit w/ on3 70mm .86ar
internal balance 347
rhs 215 heads
holley systemax
custom turbo cam .576/.565 lift 230/228 dur.


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post #2 of 22 Old 09-28-2011, 04:31 PM
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5 pond spring in the waste gate should work....

what ive heard is every 1psi could equal upto 20hp every combo is different. also depends who tunes it.


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post #3 of 22 Old 09-28-2011, 04:36 PM Thread Starter
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could it be de-tuned to safely stay around 450 or so? I want to install the turbo pretty bad lol

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post #4 of 22 Old 09-28-2011, 04:45 PM
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probably

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post #5 of 22 Old 09-28-2011, 09:45 PM
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Could only "detune" my 331 w Trick FAC heads to 497 rwhp. Used a 5lb spring and the car made 4.6 psi. We kept timing to 20deg total and still split the block in under 100 miles. Hope you have better luck than I did.

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post #6 of 22 Old 09-28-2011, 10:52 PM
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Could only "detune" my 331 w Trick FAC heads to 497 rwhp. Used a 5lb spring and the car made 4.6 psi. We kept timing to 20deg total and still split the block in under 100 miles. Hope you have better luck than I did.
what was your tq?

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post #7 of 22 Old 09-28-2011, 11:50 PM
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Boost is controlled by the waste gate, the looser the spring the less boost/force it takes to open and stop boost from building. Most usually have a 4-8psi spring in them. HP per PSI VARIES a TON, it's completely dependent on the motor efficiency and turbo setup efficiency. Some make 12hp per PSI, some make 25hp per PSI. My setup makes 27whp per PSI.

I'd hold off on the turbo till you can afford a better block. That motor is gonna make a ton of power with a 70mm hanging off it.

fmyth, someone couldn't tune your car or you spun it past 6000rpm too much. My car made 488whp/504wtq on 13psi. I have put over 10,000 miles on my stock '91 bottom end and it's held up fine.

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post #8 of 22 Old 09-29-2011, 01:32 AM
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what was your tq?
Heres the dyno chart from our last (5th)pull. HP was down 10 because the car was hot. I am running an elec fan with no shroud and it was not cooling very well.


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post #9 of 22 Old 09-29-2011, 01:49 AM
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Originally Posted by ManicMike View Post
Boost is controlled by the waste gate, the looser the spring the less boost/force it takes to open and stop boost from building. Most usually have a 4-8psi spring in them. HP per PSI VARIES a TON, it's completely dependent on the motor efficiency and turbo setup efficiency. Some make 12hp per PSI, some make 25hp per PSI. My setup makes 27whp per PSI.

I'd hold off on the turbo till you can afford a better block. That motor is gonna make a ton of power with a 70mm hanging off it.


fmyth, someone couldn't tune your car or you spun it past 6000rpm too much. My car made 488whp/504wtq on 13psi. I have put over 10,000 miles on my stock '91 bottom end and it's held up fine.



So do what I say not what I do huh? Your telling the OP not to go turbo while your pushing 13psi through your stock short block making 488 rwhp for 10,000 miles?

Comparing a turbo 302 to my turbo 331 is not comparing apples to apples. Stock stroke vs. a 331 is a big difference. The car was never spun past 6k and it was tuned by Devin at PSR who is one of the best in the South West.

Many, many stock blocks have been cracked at lower hp. Stock stroke engines(like yours) tend last longer at elevated hp levels. Increasing the stroke creates more stress and cause the blocks to fail sooner and at lower RWHP levels. I have another turbo car with a stock stroke 306 that has been going strong and has made many passes over the last 2 years with no problems. I have also owned a procharged 302 and kenne bell 302 that survived many, many miles of abuse wo cracking the block. Turbos + stroked stock blocks = cracked block.

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Last edited by fmyth; 09-29-2011 at 01:58 AM.
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post #10 of 22 Old 09-29-2011, 02:05 AM Thread Starter
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Thanks for the posts guys. I understand that its not a smart idea to turbo the engine. What would you guys say is a low enough HP on all motor to justify installing a turbo to use at minimum psi?

maybe if im lucky my engine will be a turd and need some boost lol...


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post #11 of 22 Old 09-29-2011, 10:47 AM
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Is the 347 assembled and in the car now? If so and you are ok with the risk go ahead and install the turbo with the lowest psi wg spring you have and get a tune. It may break on the dyno or last many years. If you still have the stock long block engine in the car why not install the turbo on it, make mid 400's and have fun til it breaks?

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post #12 of 22 Old 09-29-2011, 10:49 AM Thread Starter
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the 347 is in the car. if it was the stock engine i would not care one bit.

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post #13 of 22 Old 09-29-2011, 11:15 AM
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if you dont care if it breaks then do it. the best part of a turbo or s/c set up is you can use it on another motor. when it blows up by a bone stock 5.0 and just run higher psi to make the same power levels as the 347+turbo

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post #14 of 22 Old 09-29-2011, 11:57 AM Thread Starter
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if you dont care if it breaks then do it. the best part of a turbo or s/c set up is you can use it on another motor. when it blows up by a bone stock 5.0 and just run higher psi to make the same power levels as the 347+turbo
yea but i do care. its a fresh 347 not a stock 5.0 so I want to do it while being as safe as possible. I know 347 are even worse to boost on a stock block, but it is 0 balanced and has a main girdle (which might or might not do anything) so maybe it has a chance.

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post #15 of 22 Old 10-01-2011, 10:01 PM
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I also have a 347 , but with a Dart block. I made 347 on the motor with 375 lbs of TQ. With a 76mm turbo and 11 lbs I made 585 and 610. Doing the math, I made 21 hp per lbs of boost. A good rule of thumb is 20-25 hp per lbs. The other HUGE factor is how efficient the motor runs. After all, its just a pump itself.
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post #16 of 22 Old 10-01-2011, 11:03 PM
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here try this

Wallace Racing - Estimate HP From Adding Boost Calculator

1993 Reef Blue Notchback,Stock with GT40 Tubular intake, 70mm TB,AOD Tranny,3.73's,Full Flow Master Exhaust.
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post #17 of 22 Old 10-01-2011, 11:18 PM
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that isnt anywhere near accurate

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post #18 of 22 Old 10-02-2011, 12:27 AM
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that isnt anywhere near accurate
its pretty close,it was only 21hp off HLD-TYT's setup,20hp isnt a huge number diff

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post #19 of 22 Old 10-09-2011, 11:58 PM
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So do what I say not what I do huh? Your telling the OP not to go turbo while your pushing 13psi through your stock short block making 488 rwhp for 10,000 miles?.
I say NOT to do it because even with a On3 turbo kit the car would EASILY make 450+ on the WG spring. It'd be a real shame to punch a hole in that nicely built motor and take out the rotating assembly and/or heads.

My motor has ARP headstuds along with MLS gasket's, so it's decently turbo-safe. Plus if I window it, I take a trip to the local pick/pull and find me a new motor.

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post #20 of 22 Old 10-10-2011, 12:05 AM
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FWIW, Everything i've read says 14.5psi will double an engines hp.
example, add 14.5psi to 350hp na motor and it'll make roughly 700.
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post #21 of 22 Old 10-21-2011, 03:45 PM Thread Starter
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my engine also is ARP studed and am using cometic MLS gaskets.

god I want to go turbo but like ManicMike said, it would be a real shame to damage the engine.

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post #22 of 22 Old 10-21-2011, 08:07 PM
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I say NOT to do it because even with a On3 turbo kit the car would EASILY make 450+ on the WG spring. It'd be a real shame to punch a hole in that nicely built motor and take out the rotating assembly and/or heads.

My motor has ARP headstuds along with MLS gasket's, so it's decently turbo-safe. Plus if I window it, I take a trip to the local pick/pull and find me a new motor.
I was just messing w you. I do agree that running a stock junkyard short block makes more sense. You could sell the 347 and buy a half dozen 5.0 roller short blocks. I recently picked up a 92 HO short block w 47k on it for $250.

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