fa2st cyclinder for mini quad

adas said:
What are the characteristics of having a high blowdown,
such as with raising the exhaust 1-2mm and not touching the transfers?

And what are the characteristics of having a low blowdown, by lifting the transfer by 2mm and the exhaust by 1mm?

Is one better for a midrace 11,500 rpm revving engine?
thanks

frank
Click to expand...

A low blowdown makes the engine less peaky. So you get a "smoother" power deliver. Also more powerfull in lower revs.

So a low BD = less power, but smoother
High BD = more peak power, but not so smooth.

For the 11.5k rpm engine I would take a BD around 30 degree.
 
Mr Big, something like this I think will fit? I will work some mm today. But, we were hoping to get the most hp we can. What do you think about the plates on the base to bring up the hight on the cylinder for the 45mm crank? Shoul I port diff if I use the plates or add the 20,30,40, or 50mm into the port map? Or nothing and use the stock gasket?
 
Test port map? What do you think on this one?
2ce6ss5.jpg
 
Once we have a good port map and it is tested we will be making 40 of them or so and putting them up at just cost. we can get them done for like 90.00usd and are going to make a billet one in 89.9cc with a L.A. sleeve that can be replaced when needed and it will be around 500usd with replacement sleeves for around 125.00 if al goes well. We are looking for a case mfg that can offer us case halfs at a good price. But we my also be switching to a Honda type shifter 85cc motor if I can get a contract with them for just the motor.
But, for now it is the jog motor setup!
 
Ok, so race went good and stock cylinder is ok but only around 8hp or less I would say. We set it up as a 70cc stock and 39mm crank.
It was slow at best stock. The max rpm we registered was 10200rpm? I hope with better port timing and porting this cylinder will rip. Right now it is R.I.P. on my desk.........Here is what we know about the stock portiming.
2m64i38.jpg
 
So today at the track I got a look at a 70 that was just way to fast to be a 70cc and so I just had to go and look. Wow was the guy a @$$ hole big time. We went and got a blanket and put it over the bike after all 3 races. But, at the starting line I did see a spacer under his cylinder and noticed it was a little slow off the line. By the time it was 20 feet out of the gate it was roosting past all mini ATV even the 90cc stuff. I think it was running like 18000rpm and was like a chain saw sound. It had a lot of power and only a few cobras were able to beat him and they were shifters.
I did get a good look before he noticed I was looking at his motor. He was using a italkit and looked like what I got from the same supplier. He said a few mini ATV guys were getting this head and this guy is one of them. I found out that he is getting on 45mm cranks and the 70cc lc kits. He got 10 kits a month ago. 1 cylinder kit of each 70cc they had. Then he reordered the kit above. But, this time he ordered 6 pcs and put them on reorder status. I noticed a lot of epoxies on the out side of the cylinder but the spacer was fresh. We know a guy that has got 2 motors from this guy and he said that he was charged 30.00usd for a spacer and told he was at 85cc. I have to confirm this. But, the guy is a friend of a friend and said we can take a look at the motor next month at the race. So I know this can be done! Just need to confirm 20mm for the spacer and 5mm off the head!
 
Hm, that timing you gave on this paper:

2m64i38.jpg


Are not suited for 45 mm stroke use. The timings go thru the roof and you need a really, really, REALLY good exhaust to work with those timings.

A solution could be:

Making a spacer and install it on the top of the cylinder. Between cylinder and head. In this way the timings would be somewhere acceptable. Are you sure you measured the transfer timings right?? They seem alittle high for such a cylinder. Remember that if you are going to make a spacer on top of the cylinder it should be very precize.

Mounting a 45mm stroke crank with a spacer under the cylinder is not gonna do the trick. Or you should resleave/weld/retune it. Costs alot of time/money.

If you gonna drive with it, don't make the exhaustport that big. Your pistonring will fail and the gasreaction will suck.

I still think you should buy a MHR Speed 7T cylinder. Great cylinder and out of the box allready 20+ hp.
With the right tools and know-how, it's relative easy to get 22-23 hp out of it. And that's with a normal stroke!

Anyway, just let us know what you are planning to do.
 
So, this sounds like bad news? The 45mm crank sounds like a no go......Let me go look and se what I have in the old box of stuff........OK I have a CB.68.112 in 12mm from Italkit but I am not sure of the stroke on it?
What would be the max crank size for this cylinder?
Here is what italkit told us "Cylinder Kit 70cc Minarelli Liquid Cooled Aluminum, 12mm Piston Wrist , Single Piston Ring , horizontal, Stroker ( Brings ROD 43mm Optional" But, they did not have a 43mm crank when I last talked to them in full circle and they said it would be a few months. So we had 10 of this 45mm full circle and I was hoping to use one in theses builds. lol
I measured a 2f4r and here is what I got from them starting from exhaust port
23.01
25.26
34.77
34.91
34.96
34.80
34.93
34.87
25.60

That was a mini kit?
I guess I can look for a dif crank?
 
If I were you I would definetly use the 45mm crank, but with a cylinder that is better matched for a stroke of around 45mm.
Like the 2fast for example.

Or you can use a cyl for 39mm stroke, but then you have to machine it a bit to get it right.

That would include a baseplate spacer or take down the cylinderbase (depending on which side you have errored in port duration) to get to healthy levels on all port durations (or port timings if you prefer that).
Machine all portfloors so they match up with the piston and portroofs to get to the port timings you want.
Then you would have to make a spacer for the cylinderhead to allow the piston to move higher, to make its full 45mm stroke.
Then you can only hope that the piston ring isn't too high up on the piston, or else the ring will have to move on the spacer, which i seriously doubt is going to work.
 
the cylinders we have said they were for a 43mm stroke? Where can I get a good 43mm crank?
or can a base spacer and some milling out of the head make the 45mm work?

kinda like this guy did
34oujig.jpg
 
the fabrizi FHT uses a 46 or 47mm crank, maybe you should try to get one of those if you want a stroker set up, or you can get a kundo 44mm crank, they are full circle cranks and come with a base plate spacer.
 
kundo 44mm crank?
Would this be a good option for the Scooter agua a 70 cc. (admis.carter) bulón Ø 12 - culata 1 pieza
47,00

CK.68.743.G1

I can get spacers made any size I need if that would help with the 45mm fitting. Where can I get a kundo crank at in the usa?
 
Going for the 45 mm is a good option, but not with the cylinder you have right now.

Also with 43 mm stroke, you gonna have hard time with durations with that Italkit cylinder.

When you put a 2fast on a std crank (with adapting etc) then it's low timed. But with the 44 mm stroke, the timing is good for that cylinder.

A bigger stroke with that Italkit cylinder is not a good idea. Maybe rebore it to bigger piston size?
 
I was told from Italkit that this was made just for a 43mm crank? I guess if I want it to work it must only be a 43mm crank..... Italkit I guess is not the way to go.
My friend got back to me on his spacer it is a 6mm and it is on a 70cc italkit? His set up must not be using a 45mm crank though and he was not finding any id numbers on the cylinder. If he was closer I would go over there and look, but he lives 300 miles from here. lol We have not opened it yet so I am still guessing. I will post a pic of his proting tonight.
 
the 2f4r cylinders are not in the budget just now. I have a feeling we are going to be way over on this project. Nothing is fitting right......lol We picked a crank first and should have picked a cylinder first.......Then a crank....ect....
I need to salvage this project some how.......Any one got a idea? Cheapest way out of this issue?
 
Can we mill the case down?
Can we mill the head?
And use a spacer at 5mm?
This is stuff we can do here!
Will this get us close to what we need with out scrapping the cylinders and cranks?
I know how smart you guys are on this page, there has to be something......
There is 2mm difference for what the factory calls for and what we have. They call for a 43mm crank and we have a 45mm crank.
Mr Big, will I be to far out on my portimings if I use a mill job on the case and a spacer and a mill on the head? Or can I get away with a spacer and port it high?
Just hoping for options with out getting more parts! We have a lot of this set up. lol
 
Yes, 43mm speed kit! We ordered a lot of this kit and were told 45 should not be a huge issue.......lol
We also have the 42mm Italkit and it is not the same as this kit much lower ports......
 

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