[Namor]

1)do the 851 (the bike) cyclinders match up to the 748 or 916 crank cases and heads to make a quick swap?

2)do the 916 cylinders match up to the 748 crank case. 2) can 748 heads match that cyclinder or do they need 916 heads. 4) if so can i just run the FIM 851 chip to match up.

i know that the 916 can be turned over to a 955, 5) can that set up fit the 748 crank case? disregard if the 748 head won't match.

6)i know that the 996 head/cylinders can fit the 916 but wonder if the area where the rods fit through need enlargment? if so can a 748 case match the 996

in sum is the 748, 916, 996 crank case essentially the same? someone please remove the scales from my eyes.

....(sigh) then the throttle bodies...

 

[OldBaldy]

The 996 cylinder stud spacng is wider than the 748/916, thus will not fit a 748 case, unless you do the Veetwo mod, which is quite pricey.

Best bet - sell the 748 motor and buy a used 996 motor - total cost will be less than $1K, for MUCH more torque and some more power. Transforms the bike!

You also get a better base for more power, if so desired.

 

[Namor]

i'm not to into power for now, all i am after these days is info.

now that i know the 996 is a separate entity from the 748-916, can someone speak up on the smaller bkes.

 

[Synergy]

Here is an equation to calculate 2 cylinder displacement in CC
Lets use a 748 for example.
Bore = 88mm
Stroke = 61.5mm

Bore(mm)*Bore(mm)*Stroke(mm)*.0015708

88*88*61.5*.0015708 = 748.1

Bore/Stroke of all recent SBKs
916 : 94/66
996 : 98/66
749 : 90/58.8
749R : 94/54
999 : 100/63.5
999R : 104/58.8

Now most common 748 big bore kits are using 94 mm slugs

94*94*61.5*.0015708 = 853.6

I have seen 95 mm used which will give you an 872, now you are pushing the barrel wall thickness to its limits. Too high of compression and a lot of high revs could lead to a cracked barrel.

I went with the standard 853 kit which will run fine with my stock cams and valves for now. Next years project is bigger valves/new cams. If your going to increase displacement you need to help the motor breathe. 872 you better run bigger valves from the get go. There are also other options for the 748. Fox Performance makes a 890 kit. That involves all new custom barrels. You can run high comp pistons. Stock compression on a 748 is 11.5:1. Also what OldBaldy recommended: 996 motor. You can drop a 996 into the 748 frame. You can transplant the 748's close ratio transmission into the 996. Had my motor damage been more severe I would have got a 996 put the 748 tranny in it and run it stoke bore with high comp pistons. I just couldn't sacrafice a 748 motor with 8k miles on it just because of 2 bent valves and 2 cracked guides.

Now with the big bore kits, bigger valves, hotter cams, you need to get exhaust out with less restriction. I would recommend at least 50mm full system for the 853....Remember its only money and you cant take it with ya!