10 hp./per psi boost rule

[DCottrell]

In a recent post I saw a reference to the 10 hp. /per psi boost rule, and was wondering if that is anywhere near accurate as an estimate of hp? My pump and injectors are stock, and only mods are as listed in signature, and truck hits 24-25 psi boost. I find it a little hard to believe that I could be running 240 hp without touching the pump or changing the injectors. Truck does run strong though



Daryl

 

[Forrest Nearing]

it's a very rough rule of thumb for gassers... very rough... and doesn't really carry over to diesels IMO

 

[chuckwilson]

Yes, Daryl you are correct, for some reason 5. 9 cummins with single turbo seem to average about 10 hp. per pound of boost. There is an enginering term for it but I dont know what it is. I friend of mine at Cummins Bridgeway runs the dyno & told me about it!!!!!!

 

[TWorline]

Daryl:



How much difference in boost/exahaust temps did the CoolerTubz make?

 

[Forrest Nearing]

my old truck made 440rwhp at 45psi... my current truck probably makes 500rwhp at 45psi... Jim Fulmer's truck makes over 600rwhp at 45psi



all single turbo 12v trucks...



just doesn't mean as much on a diesel IMO

 

[Highfinance97]

i agree with forrest, there is some 7-800 HP trucks out there that run very efficently at 40-45 PSI





Michael

 

[DCottrell]

10 hp /psi rule

Tim,

I waited to install them till I had pyro installed and damned if the pyro wasn't defective from the start.

It went up to 250* and stuck there. Have sent it back to Danin, so no pyro readings. I got about a 3-4 psi increase in boost. I wish I could have had pyro readings before, but it might be up to 2 weeks before I get a replacement gauge, so could not wait to try the tubes. The truck seems to be a lot more responsive with the new tubes, seat of the pants feel I LIKE IT! Oo.

 

[MMiller]

IMHO there are some diesels that it applies to. I think when talking tractors, the old 1066 IH's were that way, to a point. Our 5. 9s are not. I'm running 32# of boost with my stock charger, and at most I'm running 250 hp. At 30 psi I was running 235 hp. I'm betting most of my boost is a result of higher then acceptable drive pressure.



Michael

 

[TWorline]

Tim,

I waited to install them till I had pyro installed and damned if the pyro wasn't defective from the start.

It went up to 250* and stuck there. Have sent it back to Danin, so no pyro readings. I got about a 3-4 psi increase in boost. I wish I could have had pyro readings before, but it might be up to 2 weeks before I get a replacement gauge, so could not wait to try the tubes. The truck seems to be a lot more responsive with the new tubes, seat of the pants feel I LIKE IT! Oo.

Daryl:

Well if the discussion topic here holds true that is pretty cheap for 30-40hp! I was much like yourself did to many things all at the same time, didn't have gauges etc... but the overall seat of the pants gauge felt real good!

 

[CSchafer]

I wish that was correct. Mine make's 40lbs

 

[dpuckett]

I read on the webpage for (I think) Diesel Injection of Pittsburg (or maybe TST?), that in stock form, the 12v 5. 9 engines made roughly 10hp per psi; 8. 3 about 15hp/psi. That changes even with exhaust housing swaps.



So, if you have a stock head (I doubt Jim Fulmer's is stock), a stock H1C turbo, (and intercooler), and are making 24psi boost, it is safe to say you are in the neighborhood of 220-250hp. Where that is depends on housing size to an extent. Smaller moves the power closer to the engine; larger back to the wheels.



Now, if you are like me, and running 34-38psi through a stock H1C, and a 14cm housing, it is more likely 270-300 at the flywheel. One has to consider the efficiency map of the turbo. My 91 (nonIC) could peg the 40psi gauge in 3-5th gears, and I doubt it cleared 300RWHP. MAYBE flywheel on a really good cold day on good #2 fuel.



Joe Donnelly made 800hp with <50psi didnt he? Seems like I remember reading that. But, he had done some extensive porting, which reduces resistance, and gives more MASS of air per psi boost.



Daniel

 

[glhs]

it's a very rough rule of thumb for gassers... very rough... and doesn't really carry over to diesels IMO

Huh?

If/when gasser engines make that much boost it's usually way more than 10 hp per psi.

A lot depends on the turbo. An hx 35/16 is probably pretty close to that rule; hp at the FLYWHEEL. A stock 92 makes around 15 psi and is rated at 160 hp. A stock 97 5 spd running a 16 cm housing would make around 22 psi and was rated at 215 hp.

Put on a larger turbo on your truck and maybe your boost would fall to 20(?) but would have approx. the same hp.

 

[RustyJC]

If we're talking about rear wheel horsepower, mine works out pretty close - 347 RWHP @ 34 PSIG boost with the stock HX35W-12.



Rusty

 

[pwerwagn]

I have had 3 different housings on my 35. A 12, 14 and 16.

the 12, with the wastegate plugged and an 11 plate and nothing else, would make about 33psi.

With the 14, it was about the same. The 16 dropped boost to about 28psi, but it pulled way harder on the top end.



Then with more fuel, the 12 had to be wastegated. I could make 45 easily. With the 16, the most I could make was 38psi, ever.



Joe D did make 800+ RWHP on around 50psi. but the denisty was way higher than the HX35 at 50psi.



--Jeff