Topic: CB750 HP at 2,500 to 3,500 RPM

[chewbacca5000]

Does anyone know how much HP a CB750 will produce at 2,500 to 3,500 RPMs.  Just looking for a ball park figure.

Thanks!

[phil71]

why, are you turning one into a generator?

[phil71]

(about 23 Hp)

[chewbacca5000]

(about 23 Hp)

Your close air compressor.  Have you turned 1 into a generator?  At around 6HP per cylinder that would translate into around 22 CFM per cylinder.

Thanks Phi!

[phil71]

i have no idea how you could possibly come up with that # without taking weight of rotating mass, transmission etc. NOt to mention that compressors use reed valves, no camshafts..
I'd rather buy you a compressor than see you do that to a SOHC 750

[chewbacca5000]

i have no idea how you could possibly come up with that # without taking weight of rotating mass, transmission etc. NOt to mention that compressors use reed valves, no camshafts..
I'd rather buy you a compressor than see you do that to a SOHC 750

Just basing my answer on rated power for air compressors.  5 HP air compressor is around 16 to 18 CFM.  7.5 HP air compressor can do 24 to 26 CFM. To buy an air compressor that can put out in the mid 20s would run around 2 grand.  So the motivation is financial. 

This has been done in the 30s google "convert motorcycle engine to air compressor" and read the popular science article.  PG 71 is the overview and page 89 is the 20 CFM number.

[dave500]

if your using two cylinders to fire itll be half the power?

[750resurrection]

I'd rather buy you a compressor than see you do that to a SOHC 750

 Oh boy here we go. I guess you had better not watch then.
Better yet, offer him 5X the going price for that engine, you can "save it" and he can buy a nice compressor.

[750resurrection]

(about 23 Hp)

Your close air compressor.  Have you turned 1 into a generator?  At around 6HP per cylinder that would translate into around 22 CFM per cylinder.

Thanks Phi!

 I saw your other thread on this, or maybe it was in another thread, just letting you know it's a great idea, keep going for it, it's an honor to the cb750's versatility, and to your skills and ingenuity.

[750resurrection]

i have no idea how you could possibly come up with that # without taking weight of rotating mass, transmission etc. NOt to mention that compressors use reed valves, no camshafts..
I'd rather buy you a compressor than see you do that to a SOHC 750

Just basing my answer on rated power for air compressors.  5 HP air compressor is around 16 to 18 CFM.  7.5 HP air compressor can do 24 to 26 CFM. To buy an air compressor that can put out in the mid 20s would run around 2 grand.  So the motivation is financial. 

This has been done in the 30s google "convert motorcycle engine to air compressor" and read the popular science article.  PG 71 is the overview and page 89 is the 20 CFM number.

 Thanks for the article. I see they say directly a 4 cyl motorcycle engine is preferred, and they just removed the adjusting screw and locknut for #4 exhaust in the engine mod, and added a shock absorb spring, and it was 20cubic feet per minute at 400 rpm.

LOL - you might get more than that.

http://books.google.com/books?id=_icDAAAAMBAJ&pg=PA70&lpg=PA70&dq=convert+motorcycle+engine+to+air+compressor&source=bl&ots=qJFJkXhkqt&sig=kze2zOjI_XA_I7a5oXqf7wiA8DM&hl=en&sa=X&ei=4AiDUI2uOZLOyAHa_YG4Bw&ved=0CFYQ6AEwBQ#v=onepage&q=convert%20motorcycle%20engine%20to%20air%20compressor&f=false

[phil71]

of course it'll work, but with 2 pistons making power, and 2 used to squish air, you'll burn out crank bearings pretty fast from the uneven load.. and the primary chains will clack like an MF.
Is this project lined up for after the n2o 550 is completed?

[750resurrection]

 Glad you know all the ins and outs even after the magazine said they run great for a long time with no problems. Nice try though.

[Retro Rocket]

 Glad you know all the ins and outs even after the magazine said they run great for a long time with no problems. Nice try though.

Here we go again.....

[phil71]

believe everything you read.

[Bailgang]

Well you can always do what my father in law did. He took a 5hp Briggs engine and used it as the actual compressor driven by a 2hp electric motor. It was about worthless when trying to use any sort of air tool but it could put air in your tire.

[chewbacca5000]

if your using two cylinders to fire itll be half the power?

I am really interested in what Dave is saying here half the power.  In the article the engine ran on 3 cylinders and used the 4th for air.  Phil makes a good point about load / bearings. It may not be smooth enough.

[Retro Rocket]

Hey Chewbacca, i replied in your other thread mate.

You would need to close off the exhaust valve to stop air being forced out the exhaust port, that would mean altering the camshaft or doing something with the valve springs and timing. I also think it would run at a lot less than half the horsepower being suggested in the other thread because the 2 lazy cylinders would rob more power as they are being dragged around. The compressed air from the engine will be  hot and may contain engine oil.  This could be a problem for some applications like blasting or painting. You would need a separator to remove oil from the air and a pressure relief valve as well. It can and has been done but i don't think it will be very efficient and may cost more than its worth, primary chains will rattle their butts off...

[trueblue]

An old Volkswagen engine is great for this, simply remove the exhaust rocker and fit a one way valve into the spark plug holes of 2 cylinders, usually the rear 2.  Modify the intake so the carb doesn't feed the rear 2 cylinders, and fit a carb that is undersized for the remaining 2 cylinders, this provides more torque from the engine at the expense of top end power, also usually make them run more economically if done right.  This is about the only useful application for a VW engine .  If you want to get fancy you could also use a water cooled Subaru engine and perform the same mods to it .

[bjbuchanan]

people have done it with corvair engines too, for the same reason as the old vw engines

that boxer layout minimizes quickly mangling the bearings compared to other stuff. Ever ran a corvair engine on 3 cylinders inadvertently? smooth as butter but no balls. come to think of it its kinda like it on all 6 lol

[750resurrection]

An old Volkswagen engine is great for this, simply remove the exhaust rocker and fit a one way valve into the spark plug holes of 2 cylinders, usually the rear 2.  Modify the intake so the carb doesn't feed the rear 2 cylinders, and fit a carb that is undersized for the remaining 2 cylinders, this provides more torque from the engine at the expense of top end power, also usually make them run more economically if done right.  This is about the only useful application for a VW engine .  If you want to get fancy you could also use a water cooled Subaru engine and perform the same mods to it .

They make good dune buggies too. I rezzed one and it sold really quickly - after I scared the beejeebers out of my race car driver making air with him in the passenger seat. 

[dave500]

when i was an apprentice with the now defunct melbourne and metropolitan board of works they had those vw air compressors,boy did they make a racket!they were on a purpose built trailer and got towed everywhere,,im not familiar with the 750 engine but on the 500/550 even with the rocker screw removed the actual rocker will depress its valve a little,i think its the same on a 750?,youll have to remove the rocker arm if it is.

[cougar]

I won't get into the discussion about using one of our SOHC750 motors for another use (?) ! What about the fact that it's an Air cooled engine? If you're going to be using half of it as an air compressor, this will mean it will be stationary. Air cooled engines need to be in the wind to remove the heat they produce. How do you plan on dealing with this? Just wondering ! I would be more inclined to go with a water cooled engine like " trueblue" suggested.   ...cougar...

[bjbuchanan]

IIRC about adapting them you make like a solid setup. No tolerance, no valve lash.

The dune buggies have balls compared to the vw baby buggies lol. Easily airborne. The only problem with them is they eat up the differentials in those things

As for cougar, they just put a squirrel cage fan on them, its the same thing they do with a lot of smaller compressors. squirrel cage fan and a simple pulley setup. Its all do-able its just a matter of wanting to

[750resurrection]

I won't get into the discussion about using one of our SOHC750 motors for another use (?) ! What about the fact that it's an Air cooled engine? If you're going to be using half of it as an air compressor, this will mean it will be stationary. Air cooled engines need to be in the wind to remove the heat they produce. How do you plan on dealing with this? Just wondering ! I would be more inclined to go with a water cooled engine like " trueblue" suggested.   ...cougar...

 He already showed a 12V fan he has ready for cooling. A fan, you know, like air, that cools the air cooled engine...

[750resurrection]

i have no idea how you could possibly come up with that # without taking weight of rotating mass, transmission etc. NOt to mention that compressors use reed valves, no camshafts..
I'd rather buy you a compressor than see you do that to a SOHC 750

Just basing my answer on rated power for air compressors.  5 HP air compressor is around 16 to 18 CFM.  7.5 HP air compressor can do 24 to 26 CFM. To buy an air compressor that can put out in the mid 20s would run around 2 grand.  So the motivation is financial. 

This has been done in the 30s google "convert motorcycle engine to air compressor" and read the popular science article.  PG 71 is the overview and page 89 is the 20 CFM number.

 I have another engine as well I'd love to do this with. Keep at it Chewy, let the cabin fever work hard... 
 Since I'm counting on your superior skills to copy from.