Looking for some DOHC horsepower

[seestheday]

I have heard that dropping in a cb900 engine is fairly straightforward, and is the best value by far for hopping up a DOHC cb750.

To put it in I've heard you just need to fab/modify some engine mounts.  That said, I've never done it.

[Re-run]

That may just be the easiest thing to do. Something I would entertain!

[TOOLS1]

Sounds like a good plan to me. That's what we used to do with the hot rods. Swap in a bigger engine.
TOOLS

[shinyribs]

Bigger engines are cool and a cheap and easy way to go faster.But the allure of making a little engine run as good-or better- than a big engine can be hard to pass up. Would you feel more satisfied outrunning a CB750 with a 1100GSXR,or would you rather have an ol' "750" that can hang with some of the current rides out there?Not that I think a CB750 would ever whip up on a 'Busa,but you catch my drift.

Personally,I'll take the later

And i put "750" in quotes cuz ain't nobody gotta know that your ol' "750" is now an 836...or biggerSleepers...its where its at!

[Half-Caf]

TOOLS1 wrote

Sounds like a good plan to me. That's what we used to do with the hot rods. Swap in a bigger engine.
TOOLS

But then you guys would kick me off the forum
As for it being a drop-in, I know that at least the 900c uses a shaft and hi lo gears. So I think I'd probably need to use the 16 that's on there and swap out the swingarm too -right?

[TOOLS1]

Only the C had the shaft. Use a K, or F engine.
TOOLS

[Half-Caf]

Hmm, guy just told me that I could have that 900 for $150 plus my old TV -very tempting  
This makes me wonder: is it possible to do a trans swap to keep the 900 a chain drive? Or would the 900 rear end be an easy bolt to my frame?

I could also just build off its guts, but I would feel like I was abandoning my first love for a new mistress
Also, I like the red

[shinyribs]

Get the 900-ride it-build your first love as time and money allow.
                              or
Get the 900-sell it for a profit-build your first love now!

[Half-Caf]

Here are some better pics of that 900c

[shinyribs]

Love the tank. Will those forks work on your bike? Are there any advantages to using those forks?

Shaft drive is not all bad. Low maintenance is never a bad thing!

If you get it and decide to part it out I might be interested in the tank. Especially if it fit a '78 frame,which I highly doubt.Never hurts to dream...

Which reminds me-did you say you were selling your clip-ons? Details and price please. I'm in the market for some.Black ones

[Half-Caf]

shinyribs wrote

Will those forks work on your bike? Are there any advantages to using those forks?

My guess is that the forks would swap right over. I'm not sure, but apart from the Honda logo, they might be the same thing...
As for the clips, I think I may be keeping them after all. I might spend the $150 I was going to put into the new front end on this instead. Certainly more lbs per $$

After doing a little reading, it looks like honda lengthened the frame (and shortened the swingarm) to accomodate the 900c trans. Knowing that, you can definitely tell by looking at the pics.
Also, I think my thoughts on swapping the trans was just wishful thinking. Engine/trans is all one unit, right?

That leads me to my next question: Could I just drop the whole 900 top end on my 750 base?
I guess in theory it's not that much different than a big bore and upgraded cams

[shinyribs]

Good question on the 900 top end swap. Since the other article you posted stated the mains of the 900 lined up with the 750,it doesn't seem too far fetched.THAT would be incredibly awesome,but just sounds too easy!

[Half-Caf]

sounds like the jugs on the 900 are slightly longer ...makes sense when you consider the crank has a longer stroke (yes, i mean CRANK this time ).
It looks like that might be the only issue. If it were an issue, I wonder if a little machining could overcome it

Tools, you said the cranks would not just drop in. I see how this is the case with the SOHC (being that everything is basically reversed) Is it true that they wouldn't work in a DOHC 750 either?
If this works, it could possibly be the best $150 I could put into my bike -I don't really care about the tv...

[shinyribs]

I really hope this works.Id love to see you pull this off

[TOOLS1]

I think it might be doable. Might have to have some machine work done, but not sure.
TOOLS

[Half-Caf]

Tools, you were just the guy I was hoping to hear from.
Looks like I'll be blazing a little new territory here
As far as I can tell, the crank would be the only issue. If I can't throw the 900 crank in there, I will have to worry about compression even if I throw the 900 rods in.
I'm not holding my breath on the crank -if it works I'm golden. If not, I wonder if maybe shortening the jugs a tad would do the trick.

Or maybe I could bore out my jugs for the 900 pistons and use the 750 cranks, rods, and 900 head. I guess that would, work as a backup, but I want as much 900 as I can throw in there

[Half-Caf]

Now I just have to see if my buddy doesn't mind me having another bike in the garage. I wonder if I could get it in my apartment

[shinyribs]

I wonder what the the bore and stroke of a factory built 900 is vs a bored out 750. What I'm saying is,900cc is 900cc. If the stroke is the same,and you are just gaining bore,then it wouldn't be worth all the custom machining.     DISCLAIMER: You WILL get extra cool points if you pull this off.Dont get me wrong.

Dropping the 900 cams into your motor is a cake walk obviously,so no discussion needed  there.

What about the head?The key to this whole 900 thing might be that all the horsepower is coming from a superior head design compared to your DOHC 750. Will the heads bolt on your jugs?

cdaiscool style cliff's:
- Bore your DOHC out to a 900 or 936(936 is common kit for SOHC,not sure about DOHC)
-install 900 head on your jugs,or port yours to similar performance
-use 900 cams
-same hp minus the headaches???maybe???

[cdaiscool]

My own personal style, aye? Lol, I see cliff notes on other forums, so I tend to keep that going on.

I wonder how much of a difference tuning will make. If you get a proper tune, you should be able to make decent power with either choice.

I'm in to watch as well. I'm in the same exact spot as you.








I wonder how difficult getting a turbo on my 750 would be. Still tossing the idea. I've got access to a serious veteran welder, and cheap (probably sub-100!) turbo. Just need a carb and way to change timing and fuel pressure...

[shinyribs]

Cda,there was some discussion about turbos a few month back. Samir was real gunhoe about it for a while. Check out the search bar and see if you can find it.There were some pretty good links there.