Forced induction 100cc

[husaberg]

New crankshaft, back to 104cc? What's the limit on SC 100 fourstroke?

if you could live with 180 degree why not weld and destroke it. Although I think 360 degrees would be better for forced induction. (Plus sounds better)
one of the models.The rods are definitely 2mm shorter or longer on one of the models with the pistons pin location different to suit.
They have different cam profiles too from memory.
I have a fair few bits and bobs for them too Neil if you want anything (guts of two complete engines)

[Grumph]

We've discussed welding and grinding on here previously. Someone - Speedpro ? - knew who had Summit Engineering's submerged arc machine. But you've still got to get it ground - and good, as in very small workpiece, grinders are now very thin on the ground in NZ.
Given Neil's access to CNC equipment I'd say less grief all round to simply make a new crank. I think the primary gear may be detatchable, simple enough to cut it out if it's not, and shrink/weld it onto a new crank.

[husaberg]

We've discussed welding and grinding on here previously. Someone - Speedpro ? - knew who had Summit Engineering's submerged arc machine. But you've still got to get it ground - and good, as in very small workpiece, grinders are now very thin on the ground in NZ.
Given Neil's access to CNC equipment I'd say less grief all round to simply make a new crank. I think the primary gear may be detatchable, simple enough to cut it out if it's not, and shrink/weld it onto a new crank.

Lot of time and material in a billet plus it would have to be ground afterwards anyway wouldn't it?
The CBR250 crank if cut in half would give a 360 crank I think it has larger journals to start with too. But I can remember (The CBR250 are 27 and 27.5mm big end jounrnals) they are 48.5mm x 33.8mm bore and stroke
the FZR250 crank primary drive is unlikely to be pressed on. See below.
Later bugger the FZR250 is 27mm journals I just went and measured


This is the CBR250 crank

cylinders 2 and three are closer and could form a nice 360 degree twin with the primary drive gear from the adjoining cylinder already in place.

[speedpro]

The rule book says: "24.2 Engines must be derived from non-competition motorcycles. Motocross, Road Racing, Enduro and Go Kart motors and transmission parts are not permitted. There shall be no restriction on the make, type or design of carburettor, ignition, exhaust, piston, cam, valve springs or cooling system except for class eligibility. All engines must be normally aspirated except F4 4 stroke engines of less than 100cc capacity, which may be turbo or supercharged. F4 2 stroke engines over 104cc are restricted to carburation equivalent to a single 24mm carburettor, F5 4 stroke engines over 53cc are restricted to carburetion equivalent to a single 20mm carburettor."

"less than 100cc" - that's it.

[speedpro]

In my engine I use the original cylinders 3&4. I think it would not be too difficult to go with cylinders 2&3 and leave the bit of crank with the primary gear and cut the rest off, except for the capacity of course.

To make it "doable" for average guys with average stuff in the garage it would be a whole lot easier if 125cc was allowed. Some of the capacity restrictions make stuff extremely difficult to achieve. The realities in nearly every case is that even with a couple of extra "cc" they still aren't going to set the world on fire but simply make it possible by reducing the cost and complexity of execution/manufacture.

[jasonu]

To make it "doable" for average guys with average stuff in the garage it would be a whole lot easier if 125cc was allowed. Some of the capacity restrictions make stuff extremely difficult to achieve. The realities in nearly every case is that even with a couple of extra "cc" they still aren't going to set the world on fire but simply make it possible by reducing the cost and complexity of execution/manufacture.

But if it was too easy everyone would be doing it.

[Flettner]

OK, 99.9cc it is then.
What I want is ( I think ) a 360 degree parrallel twin ( even induction ) with a balance shaft forward, output drive running off the end of the crank driving a standard clutch and gearbox. Horrizontal case split, short manifold from supercharger to cylinders, wet supercharger ie injection on the supercharger inlet. Gearbox will be home made version of the YZ250 ( home made so it's within the rules and robust) I would like to start fresh on the cases and crank so I don't have to compromise too much and make things a little stiffer ( crankcase and cylinder / head studs for example ) for heavy supercharge, as 40 plus HP is technically possible. Weight will be an issue ( not just mine ).
Sound like a fun project ???
I have my foundry nearly ready, can't wait to cast some parts.

[Bert]

OK, 99.9cc it is then.
What I want is ( I think ) a 360 degree parrallel twin ( even induction ) with a balance shaft forward, output drive running off the end of the crank driving a standard clutch and gearbox. Horrizontal case split, short manifold from supercharger to cylinders, wet supercharger ie injection on the supercharger inlet. Gearbox will be home made version of the YZ250 ( home made so it's within the rules and robust) I would like to start fresh on the cases and crank so I don't have to compromise too much and make things a little stiffer ( crankcase and cylinder / head studs for example ) for heavy supercharge, as 40 plus HP is technically possible. Weight will be an issue ( not just mine ).
Sound like a fun project ???
I have my foundry nearly ready, can't wait to cast some parts.

Sounds like a fun project.
Back the frame question, a tZR250 1KT would be ideal.
Lighter than a FZR, and not too bulky around the engine and good size wheels.

Engine casing redesign, I've always loved the aprilia SVX/RVX with the heads basically mounting directly onto the casing (sleeve consumed as part of the casing) piss poor job of explaining that... Here's a link




You could make some serious studs to deal with the supercharger...
With your skills I'm sure you could make it work for a parallel twin.
I can't visualise what the castings would look like.

[Yow Ling]

probably look like half of this, with a supercharger

[Grumph]

Forget the balance shaft. KISS....and fercrissake it''s only a pair of 50's sharing a crank.
From vertical cylinders to 45 deg angle, use 70% balance factor. 45 to horizontal cylinders, use the reciprocal, ie 30% balance factor.
that'll be smooth enough to over 14 grand.

[Bert]

probably look like half of this, with a supercharger

Bingo... Yes that would do it.