monster 620 bore increase

[POCO LOCO]

I own a 2006 Monster 620 Dark. Mods I have done so far is 14 tooth front sprocket, K& N air filter, Dan moto slip ons, i riidium plugs.I have not reflashed my ECU yet , because I hear that you can bump up displacement by swapping out 800 cylinders from a 2006 monster and slipping in  feracci pistons.Any opinions on this?

[Speeddog]

695/750/800 cylinders are all 88mm bore.
Basically the same though the dowel pin location on the base changed in ~'01-'02, so you'll have to watch that.

With your 620 crank (61.5mm stroke) that will get you 748cc.

Your cams are a little bit better than what was in the 750's.
So it'll then run a little better than a hi-comp 750.

That's not particularly spectacular, but it's better than what you have now.
Perhaps 6-8 HP more across the range.

Considering the cost of parts and labor, it may be more effective to slide in an 800 motor.
That would get you 10-15 HP more across the range, and a 6-speed trans as well.
Depends how much of it you're doing yourself.

[Duck-Stew]

695/750/800 cylinders are all 88mm bore.
Basically the same though the dowel pin location on the base changed in ~'01-'02, so you'll have to watch that.

With your 620 crank (61.5mm stroke) that will get you 748cc.

Your cams are a little bit better than what was in the 750's.
So it'll then run a little better than a hi-comp 750.

That's not particularly spectacular, but it's better than what you have now.
Perhaps 6-8 HP more across the range.

Considering the cost of parts and labor, it may be more effective to slide in an 800 motor.
That would get you 10-15 HP more across the range, and a 6-speed trans as well.
Depends how much of it you're doing yourself.

'06 620 is already a 6-speed BTW Mr. Speeddog... 

[The ModFather]

Considering the cost of parts and labor, it may be more effective to slide in an 800 motor.
That would get you 10-15 HP more across the range, and a 6-speed trans as well.
Depends how much of it you're doing yourself.

When my beloved 2005 Monster 620 engine gets to a point where some major engine work is required to keep it running this is what I'm-A gonna do!!

[Speeddog]

'06 620 is already a 6-speed BTW Mr. Speeddog... 

Hmmm... I guess I had the way-back machine set to 2004. 

[DarkMonster620]

'06 620 is already a 6-speed BTW Mr. Speeddog... 

'05 too . . . unless it was the Dark single disc . . .

[koko64]

Are there any considerations re combustion chamber shape and piston choice when doing this big bore upgrade to a 620? Are 620 and 750 combustion chambers shaped differently influencing choice of hi comp pistons?

[DarkMonster620]

Are there any considerations re combustion chamber shape and piston choice when doing this big bore upgrade to a 620? Are 620 and 750 combustion chambers shaped differently influencing choice of hi comp pistons?

620 is has better flowing heads . . . you can get more if a pro is doing the work, but, reliability will/might become an issue if you go full HC . . .

[koko64]

Has the 620 a tighter chamber? If so you think 11:1 pistons rather than 12:1 pistons to avoid piston to valve and piston to head clearance issues?

[DarkMonster620]

Has the 620 a tighter chamber? If so you think 11:1 pistons rather than 12:1 pistons to avoid piston to valve and piston to head clearance issues?

just regular day to day use . . the 12:1 are just too hot for city riding if PO is gonna do lots of canyon riding and track time, then, yes, HC and some head work . . .

my M620 ran great until it didn't . . . with 10.5:1 OEM . . . faster than a few 750 locally

[POCO LOCO]

695/750/800 cylinders are all 88mm bore.
Basically the same though the dowel pin location on the base changed in ~'01-'02, so you'll have to watch that.

With your 620 crank (61.5mm stroke) that will get you 748cc.

Your cams are a little bit better than what was in the 750's.
So it'll then run a little better than a hi-comp 750.

That's not particularly spectacular, but it's better than what you have now.
Perhaps 6-8 HP more across the range.
Considering the cost of parts and labor, it may be more effective to slide in an 800 motor.
That would get you 10-15 HP more across the range, and a 6-speed trans as well.
Depends how much of it you're doing yourself.

O.K. So what year cylinders, and off what size engine will I have to purchase to do this Monster 620 conversion ?

[koko64]

Be watching this with interest.
I was wondering about this (have a customer with an '06 620 Dark). Assuming the post 02 88mm cylinders are the same it looks like 03+ 88mm cylinders are ok from what Speeddog posted. I guess buying used cylinders in your part of the world is cheaper than boring and replating 620 cylinders? I don't even know if the 620 cylinders have enough material to do that, i.e. if they are small bore versions of 88mm cylinders. Sounds too like you need 10:1 -11:1 pistons with the 620 chamber rather than 12:1 for the 750 chamber which I assume is more open.
These guys will have to confirm.
 

[koko64]

If you go with a hi comp 750 conversion, PCV and an open airbox, should be a decent performance gain. Iirc Darkmonster is looking at doing this so he might have some good info for you.

[DarkMonster620]

IF and ONLY IF those cylinders fit the 620 crankcase I would then try to procure myself a set of said cylinders in order to install my 11:1 FBF pistons . . I would NOT have to redo my ECU, since, it would be able to handle it, sure, a reflash and dyno tune would be the best option but, in my side of the world, I don't have access to a bike dyno or tuning software . . . Since Ducati sells the cylinders with pistons  . . . I wanted the 750 cylinders

edit:
or, just get a set of 800 cylinders/piston and reflash ECU

[Speeddog]

I guess I missed the quick blast of posts last October.

Be watching this with interest.
I was wondering about this (have a customer with an '06 620 Dark). Assuming the post 02 88mm cylinders are the same it looks like 03+ 88mm cylinders are ok from what Speeddog posted. I guess buying used cylinders in your part of the world is cheaper than boring and replating 620 cylinders? I don't even know if the 620 cylinders have enough material to do that, i.e. if they are small bore versions of 88mm cylinders. Sounds too like you need 10:1 -11:1 pistons with the 620 chamber rather than 12:1 for the 750 chamber which I assume is more open.
These guys will have to confirm.
 

Are there any considerations re combustion chamber shape and piston choice when doing this big bore upgrade to a 620? Are 620 and 750 combustion chambers shaped differently influencing choice of hi comp pistons?

I don't know if there are any differences in the chambers between 620 and 750.
I suspect they're the same, as the valve part numbers are the same when comparing last year of 750 and first year of 620 ('02).
Cams are in the same spot, as are rockers, etc.
620 has slightly more lift on the cam, so they may have moved the valve seats.....
I wouldn't have moved the seats if I were in their shoes, so perhaps they did. 

I've got FBF 750 hi-comps and Mahle 91mm (makes a 750 into an 800) hi-comps, and neither dome is a particularly close fit in a 695/800 chamber.
And the fit of the squish areas aren't so flash either.
Which really annoys me, as they could have done it properly with a relatively tiny effort.
Mahle fits better, but still not as it should.
Perhaps they fit a 750 head better, but I'd be surprised.

800 and 900 valves are the same part numbers, at least for 8mm stem 800's.

I've compared a couple years of '02 and later 620/695/750/800 crankcase part numbers, and each individual year they're the same part numbers.
Can't compare cylinder part numbers, as OEM they come with pistons, which are different due to the different strokes.
From that, I'd say all '02 and later 620/695/750/800 cylinders will swap without issue.

You'll need to get the proper piston deck height to match whatever crank you run.
620 and 750 are same stroke, so that makes it a lot easier.
800 pistons are ~2.25mm shorter deck height than 620/750.