Topic: 1080...915 Over bore kit

[Buffo]

There was a post of a 1080 over bore kit. I cant seem to find it now.

Where does one find this kit.

Has anyone had any experience with said kit?

I have a 1978 CB750K8 does anyone happen to know if said kit is offered for my bike

Don

[MRieck]

That kit is alot of work. Arias made pistons which you can still get custom made. Dynoman lists pistons for that kit which I'm sure are custom made from Arias. The stock cylinder has a very hard time with those sleeves- they are simply to large. You need an aftermarket cylinder like RC used to sell. Obviously you can't buy them new . They were basically a crappy design with no air passages or fin area....just what you want when you increase bore size about 50% . You need rods and a million hopped up pieces. The head really isn't meant to sustain that many cc's either- the ports and valves are way to small. They break starters...both kick and electric. 915cc is the largest I'd go for practical purposes. Dynoman lists the 915cc pistons which are most likely made by Wiseco. They probably run the "XA" ring package which is a nice set of rings.

[Buffo]

would it be worth the nickels to buy a modern set of carbs if i were to install the 915 set up?

I havent been inside my engine yet, and i hope i don't HAVE to. so would you know how much the valves can be opened up without degrading integrity? Some heads can only be polished and not ported.

Does anyone sell a complete 915 it? Everything that would be needed to do the job.

Don

[Sam Green Racing]

Buffo,

31mm CR carbs will sort your first problem, and Mike can sort valves and porting, Its what he dose and Iv'e heard some very good reports of his work.

Good luck,

Sam.

[Buffo]

So Mike.. What do you say Ol' bean.

Point me in the proper direction if you would be so kind. And if you are so inclined

don

[Sam Green Racing]

Don,

Think Mike has gone off line.  Why not send him a PM.

[Zeke]

Yeah, the more Aluminum you lose, the more you're only good for the drag strip.

Goddamn, if you want 1000cc buy it, know what I mean?

Otherwise, these guys seem to have best luck with 836.

Zeke

[Terry in Australia]

Here's a pic of the kinda work Mike does, he built this stage 2 head for me (skimming, porting/polishing, bigger valves, new valve guides, kibblewhite springs, titanium retainers etc) and I am still blown away with the quality, it's almost too nice to mount on my engine, ha ha!

I've bought a new Megacycle 125/75 cam, an 836cc big bore kit, some 31mm flat slide Mikuni carbs and I'll get Megacycle engineering here in Oz to build me a pipe, and I'm hoping to get 80-90 BHP out of it. As Mike mentioned in his post, massive big bore kits, while possible, aren't a "drop in" deal, and will will not work well with otherwise stock components.

Just an 836 kit and a cam is a good start, but if you want big reliable horsepower, you have to look at the whole package, then of course, you need to take a long hard look at what you're gonna mount it in. Cheers, Terry.      

[MRieck]

So Mike.. What do you say Ol' bean.

Point me in the proper direction if you would be so kind. And if you are so inclined

don

Don
  Here's the website I mentiioned earlier   http://dynoman.net/engine/pistons.html   I have dealt with him in the past and he is a standup guy. That 915 kit will have to be custom ordered so you can anticipate a wait. Like I said earlier those blanks, 67.5mm, are an overbore size for CBR-600's. What's nice about that is they are generally cut for the XA ring pack. The XA rings are nice in that the top ring is only 1mm thick which equals low friction.The 2nd and oil rings are thin also. These rings are also made in Japan. Keep in mind you will need Carrillo or Falicon connecting rods. Polishing a port does very, very little to improve flow. The CB port isn't very good to begin with and needs a good deal of work to flow well. The valves are small and oversize pieces are needed with anything over 836cc.You will need a cam also- the Megacycle 125-75 is what I use in my 915 and it has put the engine in the low 90HP range. While that doesn't sound like much HP, ( my Hayabusa recently made 185.8HP with stock bore, my porting and Yosh drop in cams) BUT it is still about a 80% increase in HP. Torque was at 57LBS too. Carbs are a nice addition and I made the figure stated with CR-29's. I now have 31's on it. Hope this helps.   Mike

[Buffo]

Yes yes..thanks for the info. I emailed the folks at dynoman.net lastnight (friday night). I expect to get more info early next week. 

I will most likely go 915 when i do. But as i dont want an unrelialble machine, a great deal of thought and energy will go into making my bike everyday ridable.

This project will not start for a little while. I want to get my bike to look and act the way i want it to as it is. But I like to know what i am getting my self into and get as much information and advice as i can before i make any real decisions.

Thanks again

[MRieck]

The 915 is very reliable with good rods and some of the other parts I mentioned.

[Buffo]

got an email from the folks at dynoman.net and he says that... well here:

"Don, the 915 has been gone for many years, however we have had them made on a special order basis in the past. The problem is the old 900-915 pistons we had in the old days were not even close to the pistons we have today. We now have better alloys, CNC milling, and lighter forgings too work with. That means if we had an old kit, you might not want it anyway. As you probably know, you must bore the cases, and install larger sleeves in the cylinder block with this kit. You will also need rods, which are about $220 each. Add to that a good ignition and set of larger carbs and a better cam and you are drinking cheap beer for years. If you really want to go that route, we are happy to help you. We keep the HD clutches, top end studs, and HD cam chains etc. in stock. We are just telling you what you already know, but if your budget is limited, an 836 kit with good ignition and race carbs, will out run a 915 with stock carbs, for much less money. Please don't get us wrong, we love the 915 in your bike, but it depends on what you want to spend. If you just want more power, there is much more bang for the buck with other options. We try to put your money in the best place to get you the most power. If you can tell us what you have already done, it would help us to help you. After telling you all of this, the answer to your original question is Yes!     Have a great weekend and thanks for looking!     Best Regards,   BHA "

Rethinking my plan...but i do like the sound of CB915"

Don
 

[MRieck]

My 915 kit is one of the last made by Wiseco as it has the XA ring pack. Like I said they are special order with a long wait BUT the blanks are still being made by Wiseco. He's an honest guy...it's a commitment BUT if done right it's an investment (God, sounds like a commercial)! The 836 is a good kit and with porting, carbs and a good cam it screws. Good rods are nice too!!