Topic: RAJAY B40 vs F40

[Cb750 Racer]

Currently I'm building up a turbo engine for my cb750 and in search of a the right turbo for the build. I currently have a RAJAY b25 from an old ATP kit but I think it'll be a little small paired to one of Mike Riecks 1000cc billet blocks. I would really like a RAJAY F40 turbocharger but I found a B40 on ebay. Does anyone know the difference between the two, is it just the compressor housing??

[Captain]

 It's the exhaust housing

 Captain

[PeWe]

Forum member Ilja might know which turbo to use. He has a turbo thread.
http://forums.sohc4.net/index.php/topic,127179.0.html

[Cb750 Racer]

It's the exhaust housing

 Captain

I appreciate your response Captain. That's what I was thinking, not sure why I wrote compressor housing I meant turbine housing.After further research I found that the B25 and B40 have the same exhaust housing so a B40 would be a useless upgrade to me as the tiny turbine housing is the main reason I need a larger unit . The RAJAY F40 should be the perfect turbo for this build. Now the real challenge will be finding one 

Forum member Ilja might know which turbo to use. He has a turbo thread.
http://forums.sohc4.net/index.php/topic,127179.0.html

I'm a huge fan of his turbo build. The videos of him riding his bike on youtube is actually what inspired me to pull the trigger and start my build. He's a really smart dude I think anyone looking to do a turbo cb750 should check out his thread.I'll have to shoot him a pm and see what he thinks would suite the build best.

[NitroHunter]

I believe the B25 is a fine, reasonably quick spooling turbo for a street bike. Looking at the compressor maps you see it efficiently moves plenty of air, far exceeding the flow capabilities of even the trickest SOHC heads with any big bore on the road for real - world riding applications. 
My experience with both is the 40 compressor will make more manifold pressure than your boost gauge has numbers, and do it quicker than you can say "RODS THRU THE CASES". 

[TurboD]

I know the thread is a little older, and don't know if you are still interested in info on the Rajay.

To start.
The B - F- E is for the compressor (intake) sizing, small to larger in that order.
The .25 - .40 - .60 is the turbine (exhaust) side, small to large in that order.

As others have said, a B25 would be fine for a quick spooling CB street/strip bike. A F40 which is common to find on KZ1000's is a little lazy to spool until the rpm is up.

[MRieck]

I believe the B25 is a fine, reasonably quick spooling turbo for a street bike. Looking at the compressor maps you see it efficiently moves plenty of air, far exceeding the flow capabilities of even the trickest SOHC heads with any big bore on the road for real - world riding applications. 
My experience with both is the 40 compressor will make more manifold pressure than your boost gauge has numbers, and do it quicker than you can say "RODS THRU THE CASES". 

That is all you need to know. Personally I'd run more static compression and less boost on the street. It isn't lazy putting around and will still rip when boost is in. I know it sounds glamorous, exotic etc etc saying you are running 15 or 18lbs of boost but shoving that amount of boost in a street SOHC 750? Looking for trouble IMO.

[TurboD]

Haha, at around 10-12 pounds of boost my clutch says time out.

[754]

 Nitro Hunter was hitting 30 plus.l

[MRieck]

Kawasaki have used the higher static CR less boost concept on their Ninja SX series (supercharged). They run 11:2 CR to maintain good bottom end.

[Cb750 Racer]

I know the thread is a little older, and don't know if you are still interested in info on the Rajay.

To start.
The B - F- E is for the compressor (intake) sizing, small to larger in that order.
The .25 - .40 - .60 is the turbine (exhaust) side, small to large in that order.

As others have said, a B25 would be fine for a quick spooling CB street/strip bike. A F40 which is common to find on KZ1000's is a little lazy to spool until the rpm is up.

Thanks for the info turboD! It really does help a lot it looks like a b40 is the turbo I need or atleast the .40 turbine and housing. Not too worried as the unit I saw on ebay looked like it had sat outside for the better part of its life.The Bike will be run N/A for a few months or until I source the parts I need to finish it up. I'll be installing the Cycle X Lock up clutch So hopefully clutch slip isn't a problem I'll face.

I believe the B25 is a fine, reasonably quick spooling turbo for a street bike. Looking at the compressor maps you see it efficiently moves plenty of air, far exceeding the flow capabilities of even the trickest SOHC heads with any big bore on the road for real - world riding applications. 
My experience with both is the 40 compressor will make more manifold pressure than your boost gauge has numbers, and do it quicker than you can say "RODS THRU THE CASES". 

That is all you need to know. Personally I'd run more static compression and less boost on the street. It isn't lazy putting around and will still rip when boost is in. I know it sounds glamorous, exotic etc etc saying you are running 15 or 18lbs of boost but shoving that amount of boost in a street SOHC 750? Looking for trouble IMO.

15-18lbs sounds very glamorous but would be very short lived no doubt.I'll be more then happy pumping out 10lbs of boost on 93 octane but something around 8lbs sounds more likely just to be safe even with the low CR.If I wanted to play it safe I would have got a nice used ZX14 for the price of what i'll have just have in the engine 

[TurboD]

A B40 is not what you want, I would go with a B25 or if you can find someone that has put together a F25. A B40 would be slower to spool and have the smallest compressor.

I need to buck up and buy a lockup for mine, at least I could use it. I can easily install super heavy springs, but with a no bar street tire bike controlling the slip by hand would be very very hard for good 60 foot times.

[Cb750 Racer]

A B40 is not what you want, I would go with a B25 or if you can find someone that has put together a F25. A B40 would be slower to spool and have the smallest compressor.

I need to buck up and buy a lockup for mine, at least I could use it. I can easily install super heavy springs, but with a no bar street tire bike controlling the slip by hand would be very very hard for good 60 foot times.

I see what your saying TurboD a b25 like I have now or an f25 would be optimal for something close to stock displacement. I'm gonna be over 1000cc with the Wiseco 72mm pistons which is over the recommended displacement of the b25 so I'm looking for a larger turbine to reduce the backpreassure at the higher end of the rev range. Truthfully I wouldn't mind a later spool I don't think my lock up clutch would either 

[TurboD]

You have to keep in mind that these old Rajays are 40+ years old and very low performing and sluggish by todays standards. When I say slow to spool, I mean like close to redline when rolling into it in the first gear.

Understand that Kz1000's with 1000cc+ commonly use F40's and will take half of a gear to start building boost, The SOHC Honda even with 1000cc simply won't match the flow of the KZ because the head is nowhere near as good.

I always get a kick out of and love the SOHC Honda guys talking about going 1000cc and bigger like its something exotic. While I love the old SOHC Honda's, I own a few 836cc, 1000cc, and a turbo myself, they simply don't have the cylinder head to compete with the KZ. A F40 on a well tuned Kz1000 will easily near the 180HP mark.

My bike below has a F40 on it, it is 1428cc and made 250hp. If I was after all out performance like I once was I would install a E60, which may bring the numbers up another 50hp. The big CC coupled a slightly small sized turbo (exhaust side)makes for a much more fun ride.

[754]

That Kawi is set up quite similar to Nitro Hunters,  736 turbo that ran 10.0..

In the eighties..

[TurboD]

My old KZ1428 with a F40 ran 8.60 @ 160 in 91, it had stock valves in the head.  That's me, blue jeans and tennis shoes HeHe.

[Medyo Bastos]

My old KZ1428 with a F40 ran 8.60 @ 160 in 91, it had stock valves in the head.  That's me, blue jeans and tennis shoes HeHe.

Rebox? I always thought of as a Puma type


Sent from my iPhone using Tapatalk

[MRieck]

"I'll be installing the Cycle X Lock up clutch"....in general lock up clutches don't work well on the street. Trying to shift from 1st to 2nd etc can be impossible with any type of weight on the arms. Plus the arms quickly eat into the pressure plate unless steel buttons are installed (like an MTC unit).

[TurboD]

What a darn minute  , they run just fine, every KZ I have ever owned has had a lockup, no ill effects at all. The nice is thing is that you can use light springs, makes for a easy to control clutch. I use H1 500 springs in the Kaws.

[MRieck]

What a darn minute  , they run just fine, every KZ I have ever owned has had a lockup, no ill effects at all. The nice is thing is that you can use light springs, makes for a easy to control clutch. I use H1 500 springs in the Kaws.

to use a line from Bobby De niro in Goodfellas..."Good for you spida....good for you". I used an MRE unit on my FJ that was sprayed and it was miserable. It was with an APE spring conversion. Maybe if I had lightened the arms themselves it would have worked better but that long movement between first to second sucked. No matter what it put bad grooves in that conversion pressure plate. I hope you run an MTC unit. I took it out and went 3 stiff, 3 soft Barnett springs and the world was right. I took the nitrous off as it didn't have a progressive feed and would light up the tire at 5,000 RPM in 5th. It would make me poop my pants.

[NitroHunter]

Nitro Hunter was hitting 30 plus.l

Kawasaki have used the higher static CR less boost concept on their Ninja SX series (supercharged). They run 11:2 CR to maintain good bottom end.

Since I would be putting 30+lbs. of manifold pressure on an essentially stock motor that was targeted specifically for the strip, I built it fully aware that it was a rolling time bomb. Through multiple base gaskets the barrels got raised enough to lower the CR under 7:1. Cam chain had little use for a tensioner.
Talk about a torque killer especially with stock bore size. That thing wouldn't get out of it's own way unless I revved the hell out of it. Oh and there was the cost of the ERC 118 fuel that it ran, very specialized, and serious money in the '80s.
From about half-track it ran really good down the strip but absolutely sucked to ride around the neighborhood.

[MRieck]

Nitro Hunter was hitting 30 plus.l

Kawasaki have used the higher static CR less boost concept on their Ninja SX series (supercharged). They run 11:2 CR to maintain good bottom end.

Since I would be putting 30+lbs. of manifold pressure on an essentially stock motor that was targeted specifically for the strip, I built it fully aware that it was a rolling time bomb. Through multiple base gaskets the barrels got raised enough to lower the CR under 7:1. Cam chain had little use for a tensioner.
Talk about a torque killer especially with stock bore size. That thing wouldn't get out of it's own way unless I revved the hell out of it. Oh and there was the cost of the ERC 118 fuel that it ran, very specialized, and serious money in the '80s.
From about half-track it ran really good down the strip but absolutely sucked to ride around the neighborhood.

Building grenades Brother.

[eli]

Hi, if you're still looking for the right rajay turbo, I have rajays and parts for sale.
Michael

[Cb750 Racer]

Hi, if you're still looking for the right rajay turbo, I have rajays and parts for sale.
Michael

Pm sent Eli