Scooterotica

it is not that I will port a barrel to this kind of mod, I ask if it makes sense to build an engine with these parts I have, as the bore needs honing and a new piston.
So question is if I should send the money or save it for other projects.

fishi

can anybody post some pics of a 71mm H2 750 Conversion, either Taffspeed or AF or selfmade with some details about timings, please.

fishi

fishi

The slot arrangement works OK on a boost port because the port exit is angled higher into the cylinder. The main transfers are supposed to flow lower and across the piston crown, and that is why most designs have an arrangement that is conducive to that end.

I think this design would cause a lot of extra turbulence where the gas is hitting the end of the port (where it turns into the bore). You'd probably find it would act more like a boost port too with gas coming out at the wrong angle.

There is a benefit in shortening the transfer wall, but not beyond the point where the small end casting is, when transfers open (if that makes sense )

Hi Tony,

if you took a closer view to this barrel for the PIAGGIO Ciao Moped you can see thet this kind of transfer design is still used.
This is a SIMONINI 90cc barrel with approx. 12 HP. So is can not be the wrong way, IMHO.





fishi

drunkmunkey6969 wrote:I've been thinking about this modification.....and im inclinded to believe that it wont improve top end power, nor will it impare it.....but i think because of the lack of 'inner arc' on the transfer wall (the one that been removed) it will reduce bottom end most and a little mid range.

Anyone have a thought/comment?

Ive found that grinding back the "inner arc to give a port tapering to a venturi at the cylinder gives better torque. I do recon that it needs a wall but this could be provided by boring the cylinder out and having it sleeved.

fishi wrote:Hi Tony,

if you took a closer view to this barrel for the PIAGGIO Ciao Moped you can see thet this kind of transfer design is still used.
This is a SIMONINI 90cc barrel with approx. 12 HP. So is can not be the wrong way, IMHO.


fishi

This one is a modern YZ250 and shows how far the ports sweeps out to get good flow and direction.

Every application is different and it may be that slots are fine some situations

That's a very interesting barrel photo as it is thought provoking and obviously delivers enough of a result to have made it beyond the drawing board.

Adam_Winstone wrote: ↑Sun Apr 18, 2021 11:06 pm That's a very interesting barrel photo as it is thought provoking and obviously delivers enough of a result to have made it beyond the drawing board.

I remember seeing one that scotty did a few years ago which was similar. I think it was based on a steel lined ts1 for one of the wwsc lads. Although it was years ago, so it could be a load of BS