Who does the best 740 kit

[Flatbed]

I have a couple of 670s' laying around and was thinking about doing a 740 conversion. Who in your opinion does the the best work. Also I heard some guys are boring out their 670's to 711 by using Pol. 700 pistons. Is this pushing the limits on cylinder wall clearance or what? Is the cost for the extra horses worth it on the 740 kit. Can I run the same pipes for the 670 on the 740. 7000 to 9000 feet. I realize it's alot of questions but there is alot of intelligent minds out there.
Thanks.

 

[DWHalverson]

If I remember right the Polaris 700 pistons make it a 720. The stock pipe works good, almost tough to beat it, unless you get really aggressive on porting. Some say a good ported 670 will make as much power for less money. I have a 740 and I think it runs harder than any ported 670 I've been around. So I say yes, big bore it. They are a tough engine with good power.

 

[H20SKE]

Union Bay/Fast Trax.

H20SKE...

 

[NoSecondChances]

I have a couple of 670s' laying around and was thinking about doing a 740 conversion. Who in your opinion does the the best work. Also I heard some guys are boring out their 670's to 711 by using Pol. 700 pistons. Is this pushing the limits on cylinder wall clearance or what? Is the cost for the extra horses worth it on the 740 kit. Can I run the same pipes for the 670 on the 740. 7000 to 9000 feet. I realize it's alot of questions but there is alot of intelligent minds out there.
Thanks.

Yep, Halverson is right the Pol 700 Liberty pistons make it a 720. 81 mm Bore instead of the 78. If you go with the 740 kit, yes, Fastrax (formerly Union Bay) will do it good. Also Crank Shop does one. You can buy the sleeves from LA Sleeve and someone else makes them too (i forget the name but its the other major sleeve manufacturer). not sure about the pin height or size, I know of a guy in Kamloops that did one, I can find out. A quick call to Wiseco will be able to tell you if the pin height and diameter will work. Might have to shim the cylinder up and cut the head to make it fit. Call Val Simmons, he built a few of them.

If I remember right the Polaris 700 pistons make it a 720. The stock pipe works good, almost tough to beat it, unless you get really aggressive on porting. Some say a good ported 670 will make as much power for less money. I have a 740 and I think it runs harder than any ported 670 I've been around. So I say yes, big bore it. They are a tough engine with good power.

 

[Sheriff]

I have a couple of 670s' laying around and was thinking about doing a 740 conversion. Who in your opinion does the the best work. Also I heard some guys are boring out their 670's to 711 by using Pol. 700 pistons. Is this pushing the limits on cylinder wall clearance or what? Is the cost for the extra horses worth it on the 740 kit. Can I run the same pipes for the 670 on the 740. 7000 to 9000 feet. I realize it's alot of questions but there is alot of intelligent minds out there.
Thanks.

I have one for sale, built by Split Second Performance 780-524-4330, Ralph can really make these work. He has done a 720 (Wildcat 700 pistonns) for me & I rode that thing hard for 3 years, for the 740 he was using Ski-Doo Watercraft Pistons...160 real hp.

 

[Flatbed]

Did he resleeve it for the 720 or bore the original sleeves. One guy did one around here with the original sleeves and didn't have a problem. Precision Performance In Idaho said the sleeves would be to thin after the bore job and would cause problems. I have some extra jugs that aren't much good. Maybe I'll have a guy here bore them out so I can see what I'm up against. Then I'll call Ralph and Union Bay and see what they can do for me. Thanks for the help guys.

 

[DWHalverson]

The recomendation on the skirts on the sleeves should be no less than 1/16'' for thickness when done. The 740 uses 82mm Sea-Doo watercraft pistons from an XP 718. I used Pro-X pistons in the one I built.

 

[Flatbed]

Thanks, DW, I was wondering how much sleeve I need to play with.

 

[NoSecondChances]

The recomendation on the skirts on the sleeves should be no less than 1/16'' for thickness when done. The 740 uses 82mm Sea-Doo watercraft pistons from an XP 718. I used Pro-X pistons in the one I built.

Whoops, was thinking about the streetbike and screwed up the #'s, this ^^^ is the correct bore - 78 mm and 70 mm stroke. sorry.

So the 718 is a 68mm stroke and 82mm bore, my question is this: If the 650's use the 68mm stroke as well, stands to reason that you could use the 80 mm piston from the overbore on the 650 and get a 704? Is the 650 piston the stock ring style same as the 718? This would mean getting over the 700 cc mark (little more jam if you wanted and had to overbore anyway) and still keep the stock liners. Not quite going to the 720 stage and running thin walls. Does anyone have the piston pin info for the 650? This might be another option. Flatbed, if you think that 740 is what you're going to do, I would just call Fasttrax or Ralph. The 740 is a re-sleeve and you have to machine the cases so you will be saving the cost of boring if you are going to re-sleeve anyway. You should be able to measure the cylinder wall without boring and determine if there will be 1/16th or not.

 

[Flatbed]

Hey guys, I called Fastrax and they no longer do these kind of conversions. They now only do big bore kits. When they bought out Union Bay, that was the end of the fun stuff; I guess you'd call it that. They gave me a number of one of the original starters of Union Bay, apparently he still plays with this kind of work, but he wasn't in when I called. I tried Ralph also, No answer. Will try next week. If you want Union's number let me know or Fastrax has it.

 

[BIG JOHN]

Hey guys, I called Fastrax and they no longer do these kind of conversions. They now only do big bore kits. When they bought out Union Bay, that was the end of the fun stuff; I guess you'd call it that. They gave me a number of one of the original starters of Union Bay, apparently he still plays with this kind of work, but he wasn't in when I called. I tried Ralph also, No answer. Will try next week. If you want Union's number let me know or Fastrax has it.

I'm your Huckleberry...

Still work on RV motors...BJ