Hello Big B,
I appreciate all info.
The engine is a 90 cc from the factory 52 mm bore x 42 mm stroke liquid cooled cast iron cylinder.
When you mention that the cases need to be machined for the crank, can you be more specific? What needs to be machined and why?
Anywhere near 18-20 HP would be a huge step up for us.
Does anyone know of a source here in the US for the Fabrizi products?
Thanks again all
Cast iron cylinder?? I thought the FHT kit was alu+nicasil.
If you use a 50cc engine, the stroke is 39.2. Fitting a 42 mm stroke crank, you will need more space in that 50cc engine to mount the 42 mm stroke.
So it should be made atleast 1.4 mm bigger. ((42-39.2= (2.8)/2)
Otherwise you crank will not fit.
That 90cc FHT kit should do atleast 20 HP. But the finishing quality issn't so super. A 2fast kit is cheaper and the quality is super.
Take a look at these pix (took them from other forum):
Crank + cylinder is around 900 dollar like said and makes 78cc.
Still this kit puts out 24 hp or more easy!
Hey Big B,
Thanks again.
The current engine is in an ATV manufactured in Taiwan (Minarelli copy).
It is 89.2cc from the factory with a cast iron liquid cooled cylinder. The cylinder is marked FRC on one side and A-ONE on the other.
Bore is 52 mm
Stroke is 42 mm
Revs to 9,500 and produces 12 RWHP on a Land and Sea Dyno. This is after a little tuning to the very minimal ports. Transfers are a joke with the front right transfer having a cast in divet/indentation (why I have no idea) that severely limits flow.
The 2 fast for race cylinder and crank seems a lot more affordable than what I was quoted for the Fabrizi 47.6 x 47 set-up.
I have contacted a friend in Italy for some help. Our first race is in 4 weeks.
Thanks again all
the Jog90cc engine for the quads you use have a 79,5mm inside diameter for the crankshaft & the 2Fast Minarelli crank only has 74,5mm diameter so no more need to machine the carters to make the crank fit.
Tiba,
Thanks for the input. Are you sure about the measurements you quoted? I am a little concerned that the clearances might be too much.
79.5 mm - 74.5 mm = 5.0 mm
5.0 mm / 2 = 2.5 mm (.098" for us in the U.S.) clearance from crank web(journal) to crankcase.
Will this cause a problem with low end pressure (too much slippage)?
Thanks,
In some cases, a bigger crankhousevolume is positive on HP's :evil:
yup, i'm very sure, the Jog90 engine is very common here in my place & we have been tuning this type of engine long before you guys hehehe.
i dunno how much crankcase compression will be with that big a clearance but i think with the 2Fast cilinder kit's huge transfer tunnels it won't matter that much, besides a well designed pipe can suck all the air/fuel inside the crankcase & the carburator.
you can always try to use a smaller carburator to compensate for the extra volume or do another crankcase from a 50cc Jog engine.
my 2Fast engine uses a 50cc carter & i had it machined to give a 0,50mm clearance (75,5mm inside diameter) but MT says to do it to 76mm.
Actaully i have encountered this problem, and dont suggest you use the 90cc case. I have used many, and they are great for the bigger cranks that are ment for it. To use a smaler crank such as the 2f4r or in my case a FHT, you are going to lower the case compression too low. Despite the high rpm and high flow transfers.
Yes the 2f4r and FHT have huge transfers and can flow the volume, but even with a rights sized carb you wont have the true performance you would if you ran a 50cc case with the recommended .5mm clearnence. There is a reason why manufacturers ( BIG 4) build bikes with the tolernece this way.
I have built so many engines its hard to remember them all, and we have 90cc cases and 100cc ones for that matter. I have access to pretty much everything, and my suggestion is to find 50cc cases.
If you want true power, try to find a Yamaha Vino scooter since you are in the USA. Then you can get the better instake reed valve that will give better power on the low end. You can go with any of the top bore kits including the 2f4r and see huge power over the set up you have now. Also as Tiba mentioned the true key is getting the right pipe. IN your case since you cant run the scooter pipes, i suggest looking for a ATV that will have a similar layout to that as you see on the scooters here, but ment for a ATV.
We built an ATV ( SMC/Kasea) that keeps up with Yamaha 200s but was 99cc. Smoked every other quad in the class. I have yet to test it against a Cobra 70cc shifter quad???? we see soon....
Well this is just my suggestion, you can run the 2f4r, its good, but take note to the case clearence issue. The one i built had 2mm clearence and ran fast, good and great power, but ran even better when i used the 50cc cases.
yes! i am the mang!
50cc crankcase measure 73,3 to 73,5mm, most crankshafts have a diameter of 71,5 to 71,8mm.
70cc's use the same crankshaft as the 50cc's.
then that isn't a real 50cc crankcase or he is talking bullshit, there is no production crankshaft for a 70cc with a 78mm crank diameter unless the Taiwanese or Chinese made it especially to fit the Jog70 crankcase.
those measurements i gave you came from a 50cc crankcase, to make a 70cc engine you just put a 47 or 47,6mm big bore kit, throughout my experience i have never seen a 39,2 stroke crankshaft with a 78mm diameter on a minarelli scooter engine.