Horsepower based on fuel consumption

is there a formula that tells what the approximate amount of power you are making based on fuel consumption?

 

Blown alcohol with roots will use somewhere around 1.8 pounds of fuel, per hour, per horsepower, but this can vary pretty dramatically. A good Pro Stock motor will burn less than .4 lbs of gas.

 

For a blown alcohol engine a safe tuneup is a BSFC of .0053 GPM per HP. That should get you close for a starting tuneup. .3 gallons per pound of boost is pretty close also.

 

So 13.5 gpm is roughly 2500hp? Is my math right on that?

 

Yes, that should be pretty close at 8000 RPM's.

 

I don't think that you can go by fuel consumption because of so many other factors like ignition,cubic inches and camshaft,cylinder head and blower efficiency.

Say you were to make only 1000hp with 375 cubic inch smallblock chevy with a screw blower and a mild cam and a set of alan johnson symmetrical port heads and promag.
Then say you make 1000hp with an old flathead ford pumped up to the same cubes with a some old school 6-71 blower and a huge flat tappet cam and a vertex mag.

Are you telling me that the sbc that isn't even coming to life and is capable of making that hp normally aspirated is going to use the same amount of fuel as the flathead with it tongue hanging out?

 

Mike, I use this with a screw and do the usual test hits to even everything out and read the plugs. I find that it's usually about a gallon less for a good roots blower, but close enough to start some testing. If the engine has a flow meter, I check these numbers at 8000 RPM's because thats all some of the top dragster/sportsman guy's turn there's.

 

I think if both of them engines are built for drag racing and turn them 8000+ and some how get that AJ engine to only make a 1000 HP, they would require close to the same fuel, less the difference in Hp required to spin the blower. I use this on engine's with between 20 and 50+ pounds of boost and it works for me. I'm sure there are plenty of combo's that neither of these baseline formulas will work on, but I haven't built one yet.

 

so if you go up 10 pounds of boost you need 3 gallons of gas? is there a formula for percentage that you overdrive a motor if you have your baseline already?

 

I'm sure it would make a difference if your going from 10# to 20# are from 30# to 40#. Either way, 10# would be a major HP gain. I would estimate around 400 to 500 HP if the other componets are correct. Depending how close to the edge the tune up was before the pulley change, it should require between 2.5 to 3 gallons more. The VE of the engine and the blower would also play a part in the amount of fuel required. This would be a BASELINE tune up only.

 

is there any rule on percentage on jet sizing? say if you were 30over and went to 40over or 40 over and went to 50 over? jeremy

 

Mike! This information is exactly why I really like this site! We "new" ones to this sport certainy appreciate feed back from ones that have "been there and done that"!

Again, thanks for all of the tech info that everyone here helps us with!

 

About 20 years ago Steve Plueger told me that if the alcohol guys could figure out a way to burn as much fuel efficiently in their motors as the nitro motors use it would make the same power. I thought he was on drugs.

His prophecy has come to pass, though. Many years ago the nitro racers were running 5.60's with a single Enderely pump. Even back then Steve was real big in trying to cram more fuel in the motors. From what I know, todays alcohol motors are burning roughly the same amount of fuel that the nitro cars were consuming back then. It takes the latest screw blowers and everything else to do it on alcohol, which was what he meant by figuring out how to do it efficiently. At any rate, the alcohol cars are going as fast as the nitro cars were back then when they ran close to the same amount of fuel we use today.

A quick comparison to todays alcohol funny cars compared to a nitro funny car of the past would be Steve Plueger's Bucky Austin driven NFC. Small cubic inch, limited fuel pump, and running 5.70's like clockwork.

BTU's

RG

 

yes i have to agree thank you for all the info want to learn as much as possible and it helps when you learn it from someone that has already done it. thanks again jeremy

 

Thank's for the HP to boost numbers, Mike. I wouldn't think the HP numbers would go up that much. Thats why I recommend the .3 per pound deal and it seems to be a very safe starting point. It also eliminates the the problem some have with the BSFC formula when they have incorrect predicted HP numbers that sometimes aren't realistic. Do you have some dyno figures with different boost levels on the same engine are did your numbers come from on track runs?

 

How much power does a screw blown motor with 60psi make?

 

how big is the sky?

I would think it would depend on the CI amongst a host of other factors.