Got a question for you wrenchers. Do I need to make any changes to the heads If I install an 853 kit on a 748S? If so, what changes? TIA.
No, you don't have to, but it is a very good time to do it- inspect rockers, unshroud the valves and smooth out the ports a little. Probably worth between 5 and 10 rwhp, if tuned properly.
Otherwise, just going 853 will get 100-ish rwhp with stock heads...
Can you just put it back together with stock injectors, timing, etc. as well? I'm thinking of doing it also, but dont want to mess with all the ecu crap, etc!!!!
Can you just put it back together with stock injectors, timing, etc. as well? I'm thinking of doing it also, but dont want to mess with all the ecu crap, etc!!!!
The stock injectors/throttle bodies will be fine. The stock timing should be ok too.
You'll need to source a replacement ECU chip for the increased capacity. Talk to your local FIM dealer & ask them for a UM097DL chip.
After all is said & done though, good re-assembly & a good tune will go a long way to making you a VERY happy person.
Enjoy
__________________
... and NOW IT'S AN 853
The Road is There To Share. SO GET THE FCUK OFF IT & LET SOMEONE ELSE HAVE A GO
'96 853 - That pulls like a 12yo
'99 750 F4S MV Agusta - She's rather sick atm DUCK SHYTE
Here is the real question. How much compression do you get with stock 748 heads and a standard 853 kit. Most like to unshroud (open up) the combustion chamber so more valve area is exposed. This is the luxury of a larger bore.
WIth the stock heads wouldn't compression be well over 13? I haven't bothered with calculations just figured I'd ask since I believe Synergy went over this topic a while back.
I may have one for sale as my bike is a 748 sps and as I have found there is a 2mm difference in piston height when I pulled the bike to pieces.
So do I machine cylinders etc,buy new pistons more money or just put it back together
The kit I have is for the 748 standard engine bip, s.with the flat pistons.
The kit has only 500 miles on it from another owner.
Pic attached of the pistons.
Shot with DSC-P92 at 2007-09-24
if they're 2 mm shorter then they're 888 (or maybe 916) pistons. the dp kits at one point were just 888 pistons and maybe shorter cylinders. which would give you belt tension issues.
with the sp you need specific pistons with the big valve cutouts. all the 748 pistons are the same compression height.
The rod length of the 916, 888, & 748 is the same. The diffierence in pistons height is 1/2 the difference in stroke. 66mm (916) minus 61.5 (748) is 4.5mm divide by 2 is 2.25mm.
64mm (888) minus 61.5mm (748) is 3.5mm divide by 2 equals 1.75mm.
I had rods made that are 2.5mm longer so I had plenty of material to remove from a stock 853 piston.
I found that the rings relative to the wrist pin centerline are the same, that means that the difference in height is all above the top ring. That also means that you can machine the pistons tops and end up with the same distance top-ring-to -deck as the 916. (That dimension is important because of the operating temp of the top ring. If that dimension is too short, the rings will be operating too hot, but since it's the same as the 916, it should be liveable.)
Thanks Brad, Moperfserv.
The pistons are about 2mm shorter (853)but the cylinders are the same height in all respects.
So what is this kit, I brought it as being represented as a 748/853 bigbore kit.
Ok then, what is the correct piston for the sps application then, anyone know or have them.
This is starting to cost a lot of money
People should know what they are selling
Can you just put it back together with stock injectors, timing, etc. as well? I'm thinking of doing it also, but dont want to mess with all the ecu crap, etc!!!!
you should swap the chip to an FIM 853 chip, otherwise it'll be running lean. easy to change. you don't need to do anything but the chip.
__________________
Mark Buckelew
soon: 2008 Hypermotard
'01 BMW K1200LT
70's HD Champion Flattracker (winters project)
Here is the real question. How much compression do you get with stock 748 heads and a standard 853 kit. Most like to unshroud (open up) the combustion chamber so more valve area is exposed. This is the luxury of a larger bore.
WIth the stock heads wouldn't compression be well over 13? I haven't bothered with calculations just figured I'd ask since I believe Synergy went over this topic a while back.
I guess it depends on whether the pistons are flat top or domed. I put 748 heads (unshrouded) on my 851 (64mm stroke) using 95mm bore 916 jugs and Pistal flat top pistons, squish set to 1mm, (907cc). Carefully cc'd it has 12.3/1 compression. I would think that the 853 pistons would have to be pretty "lumpy" to get over 13.??
853 kit
more money or just put it back together
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