X Lbs of boost = X Hp??
12-29-2008, 02:32 PM
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X Lbs of boost = X Hp?? hay guys im going to be going from 6.5 psi to around 13-14 , in a 9:8:1 347, stock 6.0 heads .232/241 .595/.608 114 LSA cam how huch power "should" i pick up?? on pump gas no meth stalled A4. also dont know if it matter but im swaping the rear gears from a 2:73 to a 3:73. sorry i did not have time to do a search. TIA
Ricky
Ricky
12-29-2008, 02:45 PM
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Depends on the turbo first off?? You can make more power with less boost and rpms if the turbo is larger....It could take x amount of pounds on one turbo to make x amount of power whereas it make take half the psi to make the same power on a larger turbo in other words.
Back when I had my 620HP Subaru Sti, guys used to always give the large turbo guys crap for the "lag" ect...but the fact is even though we wern't even at half spool in the turbos RPM range when they where already at full boost.....we were making more power at that point than they were. Needless to say a small jump was always worth it and very short lived.
I would def say we need to know the advertised CFM's, exhaust side (A.R.), and wheel size to make a good guess.
Back when I had my 620HP Subaru Sti, guys used to always give the large turbo guys crap for the "lag" ect...but the fact is even though we wern't even at half spool in the turbos RPM range when they where already at full boost.....we were making more power at that point than they were. Needless to say a small jump was always worth it and very short lived.
I would def say we need to know the advertised CFM's, exhaust side (A.R.), and wheel size to make a good guess.
12-29-2008, 02:58 PM
#3
3.73 is way too big of a gear for a turbo, i had it, going to a 3.08-3.25 now, dont do the gear swap.
also not sure what you hp is now but a 347 with 13-14 psi
and the 6.0 heads should be 600-650 id say with tight stall.
Thats assuming its a D1SC procharger.
Hard to say without the turbo, i was assuming your using a 67mm-76mm. mounted upfront. probably 675-700, what fuel system are you using?
also not sure what you hp is now but a 347 with 13-14 psi
and the 6.0 heads should be 600-650 id say with tight stall.
Thats assuming its a D1SC procharger.
Hard to say without the turbo, i was assuming your using a 67mm-76mm. mounted upfront. probably 675-700, what fuel system are you using?
Last edited by cjg454ss; 12-29-2008 at 03:03 PM.
12-29-2008, 04:48 PM
#5
If you are in the efficiency of the compressor it will gain more than if it was out of the map. 20hp/psi is a good gain. On a 35R TT setup, going from 7-10psi, I picked up 35hp/lb. From there on out, I picked up ~18-22hp/lb up to 17.
And x2 keeping the 2.73s
And x2 keeping the 2.73s
12-29-2008, 05:24 PM
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Us Turbo Buick guys generally stick to 3.42 unless we change tire size. I think most guys will gear up if they go higher than a 28in tire.
Generally you want to "keep the load" on the engine/turbo so I would recommend no larger than 3.55s. Ask around before you change your gears... in FI Bigger is NOT better.
Also the HP rule has many variables... We only average 8hp per Lb of boost in the turbo regals... but then again we can run 30lbs of boost with the right fuel!
Boost is not really a sign of HP, but a sign of restriction, so hp gains per lb of boost will change based on what your setup is... Lets say you change to better heads: you will make more HP at lower boost because of the better flow of the heads, your turbo will have to work less to more more air. Boost is basically how hard your turbo is working.
Generally you want to "keep the load" on the engine/turbo so I would recommend no larger than 3.55s. Ask around before you change your gears... in FI Bigger is NOT better.
Also the HP rule has many variables... We only average 8hp per Lb of boost in the turbo regals... but then again we can run 30lbs of boost with the right fuel!
Boost is not really a sign of HP, but a sign of restriction, so hp gains per lb of boost will change based on what your setup is... Lets say you change to better heads: you will make more HP at lower boost because of the better flow of the heads, your turbo will have to work less to more more air. Boost is basically how hard your turbo is working.
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12-29-2008, 06:00 PM
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sorry guys i shoould have said that im procharged. very sorry about that.does any one else use 25 crank HP pre lb of boost? im just looking fro soe thing ruff right now as a buddy and i are make a little bet.
12-29-2008, 06:08 PM
#9
It really depends on the NA hp. The optimistic calculation is:
hp gained/psi boost = NA hp / 14.7
...but this calculation assumes there is no parasitic losses, so it will overestimate SC hp and overestimate turbo hp IF the backpressure/boost ratio is greater than 1/1. The backpressure/boost ratio can be determined using a whole myriad of variables, and not very easy to calculate.
Not so coincidentally, assuming your typical 400 hp engine, 400/14.7 = 27, or slightly higher than the 25 number folks are tossing around.
Obviously, if you add 1 psi boost to a 1000 hp NA engine, it will gain much more than 25 hp.
hp gained/psi boost = NA hp / 14.7
...but this calculation assumes there is no parasitic losses, so it will overestimate SC hp and overestimate turbo hp IF the backpressure/boost ratio is greater than 1/1. The backpressure/boost ratio can be determined using a whole myriad of variables, and not very easy to calculate.
Not so coincidentally, assuming your typical 400 hp engine, 400/14.7 = 27, or slightly higher than the 25 number folks are tossing around.
Obviously, if you add 1 psi boost to a 1000 hp NA engine, it will gain much more than 25 hp.
12-30-2008, 07:43 AM
#11
373's will be fine long as you dont go faster than say 130 in 1:1 gear on a stock size tire or dont mind racing in overdrive gear.
i would hope for more like 20 / lb assuming your supercharger will not find some restriction (air filter/elbow too small) and your fuel system is capable
i would hope for more like 20 / lb assuming your supercharger will not find some restriction (air filter/elbow too small) and your fuel system is capable
12-30-2008, 09:18 AM
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It really depends on the NA hp. The optimistic calculation is:
hp gained/psi boost = NA hp / 14.7
...but this calculation assumes there is no parasitic losses, so it will overestimate SC hp and overestimate turbo hp IF the backpressure/boost ratio is greater than 1/1. The backpressure/boost ratio can be determined using a whole myriad of variables, and not very easy to calculate.
Not so coincidentally, assuming your typical 400 hp engine, 400/14.7 = 27, or slightly higher than the 25 number folks are tossing around.
Obviously, if you add 1 psi boost to a 1000 hp NA engine, it will gain much more than 25 hp.
hp gained/psi boost = NA hp / 14.7
...but this calculation assumes there is no parasitic losses, so it will overestimate SC hp and overestimate turbo hp IF the backpressure/boost ratio is greater than 1/1. The backpressure/boost ratio can be determined using a whole myriad of variables, and not very easy to calculate.
Not so coincidentally, assuming your typical 400 hp engine, 400/14.7 = 27, or slightly higher than the 25 number folks are tossing around.
Obviously, if you add 1 psi boost to a 1000 hp NA engine, it will gain much more than 25 hp.
12-30-2008, 09:23 AM
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www.tunercalcs.com seems to be pretty accurate, it was within a hp-5hp w/ mine
373's will be fine long as you dont go faster than say 130 in 1:1 gear on a stock size tire or dont mind racing in overdrive gear.
i would hope for more like 20 / lb assuming your supercharger will not find some restriction (air filter/elbow too small) and your fuel system is capable
i would hope for more like 20 / lb assuming your supercharger will not find some restriction (air filter/elbow too small) and your fuel system is capable
12-30-2008, 09:42 AM
#16
Ok well you have to give me something go go off of. You can't just say that any engine will pick up a set number. It depends mainly on the amount of hp the engine already makes. A 1000 hp engine will gain ~70 hp/psi, while a 400 hp engine will only gain 27 hp/psi. And that assumes a high level of efficiency of the compressor itself. If your compressor is nearly max'd out, then it won't be nearly as high.
12-30-2008, 12:43 PM
#17
I would think blowers also will vary on hp per psi depending on their airflow just like turbos. I guess the estimates of doubling atmosphere to 14.7 pounds roughly double existing engine hp.
I see this loading and turbo gearing thing a lot but don't really believe it. I see many many very fast cars on the old boosted lists and in other articles using 3.73 and 4.10 even of course you still have to gear for the traps if 1/4 mile is your main concern to insure you don't run out of rpm or have to shift up to overdrive gear which isnt' the end of the world but will cost a few tenths.
Also guys are forgetting off boost the 2.73 can be pretty wimpy although they might help traction.
I am most likely going with 3.54 as going to 4l80e swap would possibly have gone to 3.73 if stayed with m6. Also m6 cars like more gearing to help get them going off the line,better depending on the clutch also.
I have yet to see any real proof that really low gears give better times if you take traction out of the equation or have enought mph without having to go overdrive. Many smaller engine cars like my dsms use pretty high rear end gears course small four bangers have a lot less torque off boost than big v8s.
I admit I can easily destroy my current pretty much worn out nittos with stock 3.42s but the turbos spin up super quickly and can't see why would want faster spool up on my particular combo. Course also running 408 cubes which don't hurt and 9.5 to one compression which also helps some.
I see this loading and turbo gearing thing a lot but don't really believe it. I see many many very fast cars on the old boosted lists and in other articles using 3.73 and 4.10 even of course you still have to gear for the traps if 1/4 mile is your main concern to insure you don't run out of rpm or have to shift up to overdrive gear which isnt' the end of the world but will cost a few tenths.
Also guys are forgetting off boost the 2.73 can be pretty wimpy although they might help traction.
I am most likely going with 3.54 as going to 4l80e swap would possibly have gone to 3.73 if stayed with m6. Also m6 cars like more gearing to help get them going off the line,better depending on the clutch also.
I have yet to see any real proof that really low gears give better times if you take traction out of the equation or have enought mph without having to go overdrive. Many smaller engine cars like my dsms use pretty high rear end gears course small four bangers have a lot less torque off boost than big v8s.
I admit I can easily destroy my current pretty much worn out nittos with stock 3.42s but the turbos spin up super quickly and can't see why would want faster spool up on my particular combo. Course also running 408 cubes which don't hurt and 9.5 to one compression which also helps some.
01-01-2009, 02:50 AM
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Ok well you have to give me something go go off of. You can't just say that any engine will pick up a set number. It depends mainly on the amount of hp the engine already makes. A 1000 hp engine will gain ~70 hp/psi, while a 400 hp engine will only gain 27 hp/psi. And that assumes a high level of efficiency of the compressor itself. If your compressor is nearly max'd out, then it won't be nearly as high.
