Seat boring thread

[Oldschool]

A search did not turn up too many hits.

So question:
Those of you that do put larger than 25mm valves in Clone heads. How much can you bore from the stock seat before they become a weak point. I read 27mm quite often but lately I saw something a bit bigger at 27.5 on something. What do the experts bore the seat out too is what I am asking, and if you go larger how much of an interference fit do you need on these heads ( .005 range? )

So all things being equal what difference in flow does the leap to 27mm intake have or is the porting on the clone head the real limiting factor.

BTW this is a cut and paste of the same question I posted at Bob's 4 cycle.
Seems quite reasonable to ask in both places and see what those more clever than I have to say.

In particular I would like to hear from you Olajoe808, your very tight lipped on these subjects.

 

[Oldschool]

For those interested follow along here,

4 Cycle Karting Forums - Big valve conversion

 

[Mr.Blue]

thanks man ive been watching this close

 

[olajoe808]

Depends on what you are trying to achieve. If I were shooting for 20+hp I would shoot for no less than a one inch I.D intake. For something less I wouldn't worry about it too much to me it's splitting hairs on a hot rod minibike application. A lot of it also depends on the entire combo and how well it is tuned. You could have a head with a 27mm intake and that motor is not dialed in and it will be out performed by a completely stock size head due to setup.

 

[minidragbike]

I answered the question in detail, but the guys over there always like to bust my balls for posting detailed info. They say that they know it as well, but they just keep it to themselves.

 

[Atsownz]

The hell with it, just send a head to Charles, and a blank check!!! LMAO, you will have a small stroke when you get the head back! His work is second to know! Best to do it right the first time!:thumbsup:

 

[Oldschool]

A clone engine is as I see it an open platform no one owns. So its only fair and honest to share information on it.

Again thank you for the informations shared.

 

[minidragbike]

I don't own anything
Since the clone came 4 years ago new builders have popped up out of no where. I have already been building the Honda 3 years before the clone. So that is why I'm years ahead of those guys.

I like to always say it's easy to build a 20hp motor when you have experience building that same motor to 30hp. But it's extremely hard to build a 20hp motor when you only have experience building a 10hp motor.

 

[Oldschool]

I don't own anything
But it's extremely hard to build a 20hp motor when you only have experience building a 10hp motor.

Yes that sounds right..

How do you build a 20 HP clone thats going to be abused all the way up and down its RPM range and violently shocked and shaken in the process?

3 things stop these bikes MDB.
Cracked frames.
Parts torn off.
Burned clutches and broken jack shaft and drive parts.

Engines to this point were not turning fast enough and hard enough to do much more than throw a few rods or in my case smash up a wrist pin.