comparison on ATC90 / ATC110 performance cams

[cb-viguur]

Hello, I'm new to the forum, sent here by a friend who told me this is where all the people would be who could have the info on ATC90/110 performance cams.

I'm sorry to say I don't really have a 3-wheeler, but I have an S90 racebike that I race in the Netherlands.

last year I managed to blow up my 100cc motor (S90 crank and 53mm piston)
After that I upgraded to 122cc with an ATC110 crank and 56mm bigbore. (riding in the 125cc class)
I am running this with a camshaft that has the markings KH96 but it is performing so well, I would like to have some more high end power.

What camshaft can I get that has more high end power then a KH96?
And would someone have one?

the rest of my setup, so the experts know what I'm dealing with:
- ported head
- racing valve springs with titanium keepers
- Keihin CR29 carb (might change to CR31)
- ATC110 crank ( ignition side modified to S90 specs)
- Rocky 56mm piston in ATC110 cilinder
- battery ignition, no rotor on crank
- 4 speed close ratio transmission
- stronger clutch springs
- oil cooler
And loads of mods to the running gear, but I guess that just hasn't got enough wheels for this forum.

[shortline10]

The Kenny Harmon 96 grind is a very good high rpm cam . Is it the roller bearing style ?
The next step would be a stroker crank and a 61mm BIG bore kit .

[Joseph Farrow]

Welcome! Cool Bike for Sure. Even if it does only have two wheels. lol

Mike is right. The KH 96 Grind is one of the best cams out there for all out racing. Mainly top end.
The fastest easiest way to increase power is to run a stroker. The next way is to increasing your piston size from a 56mm (max with stock cylinder) and go to an over sized sleeve in a stock cylinder or an aftermarket cylinder. 61-62mm. That is about as much as you can squeeze in between the cylinder studs. What this set up you have to have your center cases bored to accept the larger sleeve.

Here is a pic of the KH96 Cam. This is a single roller. They did offer it in a double roller.




Here is an example of a "Cheater Cylinder" Stock cylinder with oversized sleeve.


Pauter aftermarket. Came standard in 61mm with regular high compression or alky piston.


H&S aftermarket. Came standard in 61.5mm IIRC.


With a 61.5 stroker and a 61.5 bore you end up with about 180cc. Nearly double displacement.

Mike can build you one if the Price is Right. lol

[cb-viguur]

thanks for the advice
from this I reckon the KH96 is pretty much the wildest thing out there?
mine has no rollers by the way, normal bearing surfaces

I am running this in a 125cc class, so I don't want to increase the capacity. And as it is performing so good in a wide powerband I had hoped to find a cam for a higher power output, also in a higher powerband, my close ratio gearbox will allow it. Now running op to 11.500RPM max, shift at 10.500 where possible.
It just runs so easily that I feel I could get more out of it....although I am already the quickest 4stroke in my class, only being outrun by a couple of yamaha twins and a maico 2stroke.

Might want to build a second engine some day, with a CT110 crank, that has the shorter conrod and then add a very low 56,5mm piston that should fit in the original S90 alloy cylinder length, of course with a new sleeve.
Just so it will look like a 90 on the outside again, with 122cc on the inside.

I am currently building something similar for a friend who has an S90 for trial use, with a 54mm piston meant for atc70 type engines, in combination with the CT110 crank, will give 113cc with nothing visible on the outside.

@ Joseph, that type of cheater cylinder looks familiar, just made something like it for my C110 racebike


I have done some more strange things with small Honda's but they are all 2wheelers:
http://hondaclassicracing.blogspot.nl/

[ps2fixer]

Looks like a lot of run, and your blog is full of reproduction parts! Ever thought to produce parts no longer made for the 3 wheelers, since they are becoming collectables there seems to be a bit of demand for parts besides the typical pulled parts with plenty of wear. Looks like most of your parts are AL, I know 350x left side covers are ate up all the time from the chain and are hard to find one in nice shape. Shipping might be killer, but maybe sending 10 or so to someone in the usa to resell would make the costs doable? Just thinking out loud, either way you have talent those parts look great.

[Joseph Farrow]

The "Cheater Cylinder" will give you the appearance of "Stock" but increase your bore by 5+mm.
You use a Honda CB750 piston machined down.

thanks for the advice
from this I reckon the KH96 is pretty much the wildest thing out there?
mine has no rollers by the way, normal bearing surfaces

I am running this in a 125cc class, so I don't want to increase the capacity. And as it is performing so good in a wide powerband I had hoped to find a cam for a higher power output, also in a higher powerband, my close ratio gearbox will allow it. Now running op to 11.500RPM max, shift at 10.500 where possible.
It just runs so easily that I feel I could get more out of it....although I am already the quickest 4stroke in my class, only being outrun by a couple of yamaha twins and a maico 2stroke.

Might want to build a second engine some day, with a CT110 crank, that has the shorter conrod and then add a very low 56,5mm piston that should fit in the original S90 alloy cylinder length, of course with a new sleeve.
Just so it will look like a 90 on the outside again, with 122cc on the inside.

I am currently building something similar for a friend who has an S90 for trial use, with a 54mm piston meant for atc70 type engines, in combination with the CT110 crank, will give 113cc with nothing visible on the outside.

@ Joseph, that type of cheater cylinder looks familiar, just made something like it for my C110 racebike


I have done some more strange things with small Honda's but they are all 2wheelers:
http://hondaclassicracing.blogspot.nl/