650 cylinder vs 701 cylinder question

[SirWoof]

Not sure if this is the right place, but I have a 701 62T I’m getting ready to drop in my sn super jet. Pulled from a running couch, but it’s a little tired but a runner.
Recently I picked up a 650 cylinder that’s bored to a 701 with new pistons in a box, and a worked over cylinder head..the cylinder has also been ported and the quality work looks a lot better then a lot I have seen...
My main question is would it be a good idea to run the 62T case with the 650(bored/ported) jugs/pistons/head
Or is the stock 62t cylinder stock just as good. Not worth it? Waste of time?
I get porting the 62T would probably be better but I can’t afford to send it off + riding time is coming up quick.
Will try to get some pictures of the ported jug soon

 

[yamanube]

The 62T cylinder is probably better.

 

[Storbeck]

Stock 650 cylinders have SUPER tiny ports, stock 62t cylinders have kinda pretty decent ports, so stock for stock the 62t would be clearly the way to go. That means your decision would depend entirely on how the 650 cylinder is ported, and to some extend what you want the motor to do.

You can also buy a porting template from yamanube pretty cheap and do it yourself with a die grinder.

 

[yamanube]

@SirWoof send me a message if you want to get into porting your own cylinder.

 

[Storbeck]

What exhaust are you running and what was tired about the 62t?

What's the rest of the combo? Head, ignition, carbs and so on.

 

[kevbo]

The lower port engine is better with a stock superjet exhaust. If you have a pipe, use the 62t cyl and get the impeller right.

 

[SirWoof]

View attachment 410116

@SirWoof send me a message if you want to get into porting your own cylinder.

I actually have both your templates lol just a little intimidated on trying it myself, but this ported 650 jug fell into my lap

 

[SirWoof]

What exhaust are you running and what was tired about the 62t?

What's the rest of the combo? Head, ignition, carbs and so on.

Just starting to get a little low on comp, 125 each hole
The 62t i have for the ski is bone stock so dual 38s I believe
But I do have some parts ready to go on once I decide on if I’m using this ported jug or not.. lol
Coffman sizzler pipe
A ignition module that protec has modded and added a adjustable rev limiter
Has a stock water box and I believe a 14/17 skat trak impeller in a 90 square nose super jet

 

[SirWoof]

Here’s some pictures of the jug, so compared to a stock 650 jug I have it’s HUGE comparison, but it has a lengthened boost port and also a shortened the bottom of the sleeve, not sure how much that helps .. but let me know what you guys think just trying to learn and go in the right direction

 

[Storbeck]

I wouldn't use a top end that is low on compression, or at least I'd choose the top end that is LEAST low on compression, and I think the 650 will be a better match for a sizzler pipe, so I would use the 650.

But...i say that as somebody who has never run a sizzler on anything, so if somebody else has better experience to go on, listen to them, not me.

 

[mikidymac]

I would give the 650 a try since someone spent a lot of time porting it and it is a fresh 701 bore. with new pistons.

Worst case scenario is you don't like it and are out a couple gaskets.

 

[MTRHEAD]

The hot ticket way back when (90-95ish) was the 650 cylinder with the 4mm or 5mm crank with the 125mm rod. The non stroker or shorter stroke cranks benefited from the 118mm? Or 123mm rad rod. Most used 4mm or 5mm with OEM rods. The 650 transfers have more volume than a 701/760 cylinder and the timing on the transfers was decent with the stroker when the cylinder was lifted. The exhaust just needed to be ported to the right size and the exit also made appropriate. At the end of the day they perform equal if not better if ported the same because of the added transfer volume. A mod race era (785cc) Lamey stroker cylinder had smaller sleeves than a 701 for the same reason.

 

[Storbeck]

The hot ticket way back when (90-95ish) was the 650 cylinder with the 4mm or 5mm crank wih the 125mm rod. The non stroker or shorter stroke cranks benefited from the 118mm? Or 123mm rad rod. Most used 4mm or 5mm with OEM rods. The 650 transfers have more volume than a 701/760 cylinder and the timing on the transfers was decent with the stroker when the cylinder was lifted. The exhaust just needed to be ported to the right size and the exit also made appropriate. At the end of the day they perform equal if not better if ported the same because of the added transfer volume. A race day Lamey stroker cylinder had smaller sleeves than a 701 for the same reason.

What was the displacement limit in those days?

 

[MTRHEAD]

What was the displacement limit in those days?

785cc.
popular ski setups in mid 90’s Yamaha‘s 8mm stroker 81mm bore = 783cc. Kawasaki’s 3mm stroker 80.5 bore = 783cc

 

[Storbeck]

Ah, I was trying to figure out what the 4-5mm stroker 650's were shooting for, 81 bore 73 stroke is 752cc's.

For absolutely no good reason it seems cool to make something fast with the 650 cylinders that people don't want.

 

[yamanube]

He sent me pics of his 650 cylinder with one of my porting templates in it....it looks like the exhaust port has been raised 4-5mm.

 

[Storbeck]

If that template is lined up with the top of the cylinder like it is supposed to be that must be a really high exhaust port. Higher than a 64x.

Do you have a pic from the inside?

 

[yamanube]

If that template is lined up with the top of the cylinder like it is supposed to be that must be a really high exhaust port. Higher than a 64x.

Do you have a pic from the inside?

Just keep 'er pinned.

 

[SirWoof]

So I finally got the 701 template back from my friend @yamanube
I haven’t measured it with a caliper but it is very minimal port height difference
I’ll post both 701 & 650 template on here first 2 are 701 temp. Second 2 are 650..

 

[yamanube]

Port timing is similar to a 760 64x cylinder.