Another eng swap thread:(Edit: no longer considering EFI, upgrading 750 engine

[koko64]

  FCRs are awesome.
41's shouldn't be too bad for an 800 with their 900 valves and higher comp?

[LowercaseJake]

41's are too big for a street 800/750...maybe even a 900. A full on race bike, or an 1100, maybe.

Just one guys' thinking.

You actually may be right...I was one of those head scratchers when I first installed em that said; "you kidding me, right? where's the wheelie fun and instant gratification?" hours of tuning later I liked em, but not before lots of tuning and lots of other mods. Open airbox and Dynojet kit on my original 750 was my first "wow what took me so long" mod

[LowercaseJake]

I did LOVE how easy to fiddle with they are/were

[koko64]

You, of all people, should know that I do have 41's on my bike.

Pardon me. I mean't for Jake to try his 41's on the 800 motor he plans to fit. If they're too big he can swap 'em for 39's. Or maybe Jake should shoehorn that 1000DS motor in and run the 41's.

[LowercaseJake]

Pardon me. I mean't for Jake to try his 41's on the 800 motor he plans to fit. If they're too big he can swap 'em for 39's. Or maybe Jake should shoehorn that 1000DS motor in and run the 41's.

The 1000 would actually be easier, since headers from the elusive M1000 would bolt up fine. Exhaust is my primary concern.

Never doing carbs again unless absolutely mandatory.

[LowercaseJake]

By the way, I found out 900 headers fit the 1000ds. I don't think Ducati has ever changed the bolt spacing.

[Speeddog]

By the way, I found out 900 headers fit the 1000ds. I don't think Ducati has ever changed the bolt spacing.

I'm pretty sure the actual port position is different, thus will not fit on an assembled motor.

[koko64]

/quote]

Fair enough, time marches on. Tapping a keyboard beats getting benzine laced fuel on your skin and breathing it's fumes not to mention the precise, multi dimensional tuning available with EFI. That said, I like carbrettors and I remember Chris at CCW saying 1000DS motors really responded to split single FCR41s. I guess tandem FCRs on long manifolds would sacrifice top end power for monstrous mid range torque.

[koko64]

41's are too big for a street 800/750...maybe even a 900. A full on race bike, or an 1100, maybe.

Just one guys' thinking.

True. I believe FCR39s give better part throttle respone than 41's, even on a worked 900, but at the expense of a few peak hp. 39's on my worked Superlight felt snappier at low/mid rpms than the 41's on my two worked Monsters. Better for many unworked streetbikes.
I figured if Jake wanted to keep his 41's it might make for an interesting motor recipe.

[LowercaseJake]

True. I believe FCR39s give better part throttle respone than 41's, even on a worked 900, but at the expense of a few peak hp. 39's on my worked Superlight felt snappier at low/mid rpms than the 41's on my two worked Monsters. Better for many unworked streetbikes.
I figured if Jake wanted to keep his 41's it might make for an interesting motor recipe.

41's are sold, and I'm going back and forth with Doug Lofgren on Mikuni 38mm mods. SUPER nice guy. I'm also looking at TDMR40's, they're $300 cheaper than FCR's, and...well...I like to go the road less travelled. Kaemna and FranksMX will even customize/tune a baseline for you based on your project, which is pretty cool.

Of course the easy thing to do would be follow through with the EFI swap. Especially since I already announced "I'm done with carbs". LOL

Mainly I want my bike back together NOW which means one of the dusty motors in the corner of my garage....a 600 and a 750.

[koko64]

The TDMRs have a choke iirc.

[koko64]

Maybe pop the 600 in for the moment and build a hot 750 with hi comp pistons light flywheel, Flatside carbs (of the appropriate size), (maybe 43mm inlet valves out of a 900), (maybe 900 V head cams), modified airbox and some porting. I was just telling a buddy here how surprised I was with how well the motor spun up, the acceleration and how smooth it was when I tested a 750 with similar mods. Fitting 800 heads would be even better from what I have heard.

[LowercaseJake]

Maybe pop the 600 in for the moment and build a hot 750 with hi comp pistons light flywheel, Flatside carbs (of the appropriate size), (maybe 43mm inlet valves out of a 900), (maybe 900 V head cams), modified airbox and some porting. I was just telling a buddy here how surprised I was with how well the motor spun up, the acceleration and how smooth it was when I tested a 750 with similar mods. Fitting 800 heads would be even better from what I have heard.

Wait, you're telling me 800 and 900 heads literally bolt right on? so the only difference when finished would be boreXstroke?

Edit: disregard, Google is my friend

[koko64]

I learned here from others here that 800 heads bolt on, but I dont believe 900 heads do. Others will confirm. Iirc, people here have fitted 620 and 800 heads, 800 heads being preferred for their better cams and bigger valves. You will need hi comp pistons too as the 800 has bigger combustion chambers, probably to unshroud the bigger valves it has. Iirc speeddog and Duckstew built one so pm those guys, as they specialize in the marque. The cams, valve size and low comp appear to hamstring the stock 750. Check out bikeboy.org.

Unlike 900's, I have only played with one 750 but Speeddog knows them well.

[ducpainter]

900 heads won't fit on 750 stud spacing