620 + 695 = 750

[caperix]

The winter downtime has me looking around the garage and thinking of mods.  I have a working 620 monster and a 695 engine from another project.  The 695 is basicly a destroked 800, same heads and cylinders as the 800, the 620 has a 750 stroke with a smaller bore and similar heads to the 750.  It seams like putting the 695 cylinders and heads on the 620 should be a good upgrade.  I would think to get propper deck height I would need to use 750cc pistons, and it would def. need a good tune when finished.  So on paper as the big parts are allready on hand I think I can make similar power to a tuned 800 75 + hp for $1500 - $2000, about the same as I could sell the 620 for and buy a s2r 800.  As my 620 came with the 320mm brakes and I have allready upgraded the suspension, I feel like it would take about the same amount of money as the engine work for the 620 to get the 800 chasis to the level the 620 is at.  Any thoughts or ideas on this? 

[DarkStaR]

Sell both motors and get a 900 motor.

or

-620 + -695 = 900

[Duck-Stew]

88mm cylinders from the 695 coupled with the 61.5mm stroke of the 620 would yield a 750cc 2V engine that would require the 750 pistons (buy some hi-compression pistons for this to get the max bang out of it).  So, yes..your assumptions and math are correct.

But...the other poster has a valid point as well...  Could sell both motors and get one bigger one.

[caperix]

I have looked into engine swaps but they all seem to cost alot more money for not much more improvement.  A 900 from what I have read would require different exhaust, most motors don't come with the clutch adding more cost and the same amount of custom tuning to get it to run on the 5.9 ecu that is allready in the bike.  A 1000ds could use the same exhaust but motors are very expensive still, and also do not come with clutch.  Dual output coils would also need to be purchased.  The larger motors could be tuned to make more power than the 750 setup I am leaning towards but from what I can tell a 750 with the 800/695 heads and a good tune should make similar power to a 900.

[accrocker]

I would sell the 620, use the profits to install hi-comp pistons in the 695 engine (73hp stock) then use the rest of the cash for nemesis, microtek, whatever ecu you want, and dyno tuning.

[Raux]

i've been all over on this thought process as well. should i go with the longer stroke, larger pistons, etc. and finally said, let me get the most power with the motor i have.

so to that end, try something different. sell the 620 motor take the 695 motor, find 696 heads with the larger valves do a port and polish and swap them out, upgrade the ecu, intake and exhaust systems.

there are a lot of people wondering if this could be done

[brad black]

the 800 has a larger combustion chamber than the 750 due to the 900 valves, which would be huge on a 695.  how big are the domes on the std 695 pistons?

you'd need a nominally high comp ratio 750 piston to give it decent comp i'd think, as 750 chambers are about 15% smaller than 900 chambers.  the only 750 pistons available are ferracci or kaemna that i know of.  altho if you found some of the old gio.ca.moto ones they'd probably be ok - they were always excessive comp wise.

apart from the comp ratio bit it's just a bolt on.  dead easy.  get someone who knows porting to give the heads a clean up and surface texture - nothing too flash.  should go ok and lots cheaper than playing with bits from a different engine.  get your ecu reflashed with an 800 map too.

it'd feel better if you ran the 695 6 speed box - it's a closer ratio apart from 1 to 2.  are you going to split the bottom end?  no need too apart from gearbox swap i guess.

it'll go almost as well as a 900, but the 900 (if you get an ss motor) has the wide ratio 6 speed that's a bonus on its own.  you'll need headers and inlet manifolds and ecu.

what are the 620 and 695 motors worth?  i'm guessing not a lot.

[caperix]

Brad thanks for the info, I did not know about the different ratio gear box in the 695, and did not even think about the larger combustion chamber.  I have yet to pull apart the top end of the 695 to check out the piston design.  I had been thinking about the ferrachi 10.8 : 1 750 pistons but with that info maybe I need the 12 : 1 pistons.  My only other worry is piston to valve clearance with the higher lift cams.  The 620 has over 30,000 miles on it so I think both engines together may only just cover a stripped 900.
Raux, I have thought about the 696 top end as that seams to be the hot setup for the small case engine now.  They have proven very difficult to find though, and with the ecu's oil temp sensor relocation and redesign I do not know if they would read the same
or be able to be swaped.

[Travman]

Sell both motors and get a 900 motor.

or

-620 + -695 = 900

Sell both and get a 1000DS motor.  Chris at CA-Cycleworks has one for sale. 

[darkduc7]

my 2 cents, buy a new bike with a bigger motor, dont tear into things as tempting as it is. but of course, im jaded.

[scott_araujo]

IIRC the 800 and 695 have about the same power/torque with the 695 being a little smoother.  Sell the 620 and hot rod the 695.  PC3, exhaust, air filter or pods, custom map on a dyno.  Taking apart two engines to make one makes no sense financially.  You'll end up with a ton of parts that aren't quite an engine and still have to replace or refurbish many worn bits along the way.  If you want to tinker go for it but it think you could get a great engine from the 695 and don't face the headaches of getting all the parts of diff engines to fit together in a bike they don't belong to.

But I'm jaded too, I'd rather ride than wrench most days.

Scott

[caperix]

I have almost as much fun moding the bike as I do riding it.  I don't see any reson that a top end swap could not be done with the engine still in the bike making that the easiest way to go other than the more expensive buy a new bike method.  I think the only purchases needed will be high compression pistons and an ecu reflash, 800 map will get it going pc3 should be able to dial it it.

[scott_araujo]

Will take a little more fiddling with the PC3 and leave almost an engine's worth of leftover parts, but yeah, no engine pull required.  Maybe you can take the leftover parts and make a 500cc out of them. 

Scott