421 on stock cylinders?

[williamjernigan]

Someone I used to ride with just had his engine hopped up. He said that it was a 421 or 420 but that it was on stock cylinders. He says it has a 4mm stroker and it has 44mm alky carbs. Out of frame drag pipes and undercut or override transmission with a lockup clutch. What kind of hp numbers are we talkin here, and how fast could it really be on a stock frame thats just lowered.

[Bansh-eman]

Someone I used to ride with just had his engine hopped up. He said that it was a 421 or 420 but that it was on stock cylinders. He says it has a 4mm stroker and it has 44mm alky carbs. Out of frame drag pipes and undercut or override transmission with a lockup clutch. What kind of hp numbers are we talkin here, and how fast could it really be on a stock frame thats just lowered.

dajo correct me if im wrong, but a stock cylinder cant make it to 68mm and still have bore left? i think you can only go out .080 and thats a gernade waiting to blow... unless he had some work done to fit a new sleeve i dont think its a 421.. a 396 is more likely...

[BigRed350x]

I wouldn't say that .080 is a grenade waiting to happen. I ran .080 on my 87 shee for almost a year with no problems. I know a couple people who are at .100 and still do ok.

 

I agree though, without a big-bore sleeve, he can't be at 420 or 421. He would need a sleeve capable of 68mm to go with the stroker to get that displacement.

 

His power and speed etc depends a lot on his porting and rider ability. I keep up with a lot of piped cammed and intaked YFZ's on my YFZ and all I have done is a simple little intake manifold, nothing else. Its usually more rider ability than what they have done. If a slower bike can get the jump out of the hole they might have enough to stay ahead of a bigger bike.

 

If I had to guess based just on what you said, I would say he is probably somewhere between 75 and 100hp. Probably in the 80's range if he has a good port job and a big bore cylinder.

[Bansh-eman]

I wouldn't say that .080 is a grenade waiting to happen. I ran .080 on my 87 shee for almost a year with no problems. I know a couple people who are at .100 and still do ok.

 

I agree though, without a big-bore sleeve, he can't be at 420 or 421. He would need a sleeve capable of 68mm to go with the stroker to get that displacement.

 

His power and speed etc depends a lot on his porting and rider ability. I keep up with a lot of piped cammed and intaked YFZ's on my YFZ and all I have done is a simple little intake manifold, nothing else. Its usually more rider ability than what they have done. If a slower bike can get the jump out of the hole they might have enough to stay ahead of a bigger bike.

 

If I had to guess based just on what you said, I would say he is probably somewhere between 75 and 100hp. Probably in the 80's range if he has a good port job and a big bore cylinder.

bigred what are you doing on this early! get to work! lol

[dajogejr]

.080 is ok, but...that's only a 66mm piston. .100 would be 66.5mm, which would only be a 383 on stock stroke crank.

 

421 is usually attained by 4 mil crank, 5mm longer rod (110mm stock, long rods are 115mm) and a 68mm bore.

 

So...if he had a 4 mil long rod crank and punched .100, he'd still be at 410 or so...maybe a little less.

 

I'd feel pretty comfortable on an .080 OEM jug if the bore was done right, and the clearances are ok...however, after that, I'd be as nervous as a long tailed cat in a room full of rocking chairs!

 

I'm probably gonna get flamed for saying this...but....oh well.

 

If you're gonna put a sleeve in a cylinder to make it a big bore motor, I feel there's better choices out there, a la cub or cheetah cylinders (plus...a lot more, of course)...

 

By the time you spend the cabbage on a re-sleeve, porting, etc., you're probably at the same cost of a good set of aftermarket cylinders.

 

If you're gonna big bore it...might as well well port it, right??

 

Also, I'd say depending on who did his porting and how well, with Alky....he could very easily be over 100HP...

[Bansh-eman]

however, after that, I'd be as nervous as a long tailed cat in a room full of rocking chairs!

 

lol u fukin redneck!

 

If you're gonna put a sleeve in a cylinder to make it a big bore motor, I feel there's better choices out there, a la cub or cheetah cylinders (plus...a lot more, of course)...

 

By the time you spend the cabbage on a re-sleeve, porting, etc., you're probably at the same cost of a good set of aftermarket cylinders.

 

If you're gonna big bore it...might as well well port it, right??

 

Also, I'd say depending on who did his porting and how well, with Alky....he could very easily be over 100HP...

id agree to cost of putting a big bore sleeve in there having it ported and getting big bore pistons, u might as well get some cubs and get the power your paying for..