capacity engine

[Brutus]

Gents, this summer I'd managed to get my hands on a milling machine. Now the winter is coming I'm playing with the thought to make an engine for my 750paso with approx 85-90HP at the rear wheel. Got no clue what the engine casing can manage. Any weak points where it could crack? Also I've got a good crank of an early 851 on the shelf with all te sprockets. Is this an easy fit? Would be great if this will go straight in, some adjustments to the casing to fit bigger cilinders and HC pistons (96mm?), lightening all the sprockets / flywheel and max porting on the heads incl racing cams.. Any feedback is welcome..!

[paso750]

I don`t know how realisic 85-90hp at the rear wheel are on a 750. That`ll take extreme modifications and you may end up with an engine which is fine for track but not for street use.
However, one thing you could do is fitting the crankshaft, conrods & pistons from a 800 series engine. The 800SS pistons are high compression. That`s the basis of the Thersby 804cc F1/TTs.

[Brutus]

I don`t know how realisic 85-90hp at the rear wheel are on a 750. That`ll take extreme modifications and you may end up with an engine which is fine for track but not for street use.
However, one thing you could do is fitting the crankshaft, conrods & pistons from a 800 series engine. The 800SS pistons are high compression. That`s the basis of the Thersby 804cc F1/TTs.

Thanks, I'll look into that.

[ducapaso]

Maybe you'd rather to switch to a 904 fuel injected from a Cagiva Elefant and tune up this

[Brutus]

Maybe you'd rather to switch to a 904 fuel injected from a Cagiva Elefant and tune up this

Tx. good idea. I'll look around if any is for sale for a reasonable price.

[paso750]

I don`t think it`s such a good idea.
The 900ie (1B, Lucky Explorer) has a 5 speed gearbox and cylinder heads with the small valves of the 750 engines. Many Elefant riders swap the cylinder heads with the ones of a 900SS.
An engine from a 900ie GT (1BE) has a 6 speed gearbox. I don`t know which valves this engine uses, probably also the small ones which matches their concept of being offroad bikes.
900ie GTs are rare and more expensive than the others but you will always have the problem that the swingarm won`t fit unless you modify the engine case and some engine mounts may also not be at the right place if you put a 900 engine instead of a 750 in the frame.
Imo if you`d go this way it would be better to find an engine from a 906 or 907ie or if you don`t mind making an engine fit and converting to water cooling one from a ST2 (944cc). (In case of the ST2 change the pickups & bracket so you can use your old Kokusan ignition and put on a FCR carb. Set it up correctly and then you will have fun.)

[ducapaso]

Anyway, you need to put some money in the swap: My idea requires to modify heads, the 906/907 water cooled needs to increase weight end put a water cooler, an M900 engine reqiures to machine the gearbox (Lcerani did this)

[Brutus]

Thanks for the reply. I'm still considering to use a late 750paso casing with a stock gearbox. Don't know how strong the crank is. Could it handle 90 - 100 hp? I could fit an 851 crank instead with approx an 2,5mm alu base gasket (home made). From there I could go for hc pistons with some serious porting of the heads. Max diameter valves etc. I know I've to rebuild the sprag, cause of the splines of the crank. This shouldn't be a problem. Can't say if the clutch will hold, though..
Another option is to use the stock pistons, raise the cilinder a bit more till the chamber pressure is approx 8 bar and make myself a custom exhaust with a garrett turbo. Heads can be stock also. The dcnf carb should manage it well, as it is also turbocharged on earlier vw beetles..
One thing that troubles me a bit, is if the stock paso casing is strong enough for the hp + torque I'm aiming at.. Any feedback is welcome..!
Léon

[ducapaso]

In my opinion the clutch will not hold enough, this is the reason they switched to the standard configuration with the 6 gear engine. The box should be strong enough as 650 pantah was tuned for racing with quite high power levels. You considered a dual spark modding? It's one of the cheapest modding to the stock heads and will let you install hc pistons and special cams with less output troubles!
About turbo, I think this will make you face very big temp troubles: pistins can MELT in just a while!!!

[Brutus]

In my opinion the clutch will not hold enough, this is the reason they switched to the standard configuration with the 6 gear engine. The box should be strong enough as 650 pantah was tuned for racing with quite high power levels. You considered a dual spark modding? It's one of the cheapest modding to the stock heads and will let you install hc pistons and special cams with less output troubles!
About turbo, I think this will make you face very big temp troubles: pistins can MELT in just a while!!!

Thanks, I think you're right. The stock setup of an oil/air cooled paso engine is just enough to keep the temperature at an acceptable level. If I'd go for the hc pistons / ported heads and spec cams, what would be sensible? I'm aiming for 90 bhp with an 750 engine. I could fit the 851 crank which will give an additional stroke >> 64mm 851 crank; 61,5mm 750paso crank. 88mm hc pistal pistons? Compression ratio? 900ss cams?

[ducapaso]

I think that the 2,5 mm spacer will reduce the structural strenght of the engine, more there will be some trouble with gear and clutch assembling... More you will have to machine the alluminium near the frame attacs. So installing a 900 from a SS or a monster will become easier than this.
The easiest way to get a result is alwais the best one, so what's the target of your project?

[ducapaso]

About the temperature, the cheapest way is to install this: http://www.ebay.com/itm/DUCATI-BEVEL-TW ... 1004479619

Also try to squeese oil into the heads from the cooler putting a jet in that cover

[paso750]

Brutus, what are you aiming for ? That`s the most important question. A race engine for track days or one for the street?
If your go for dual spark plug heads you`ll have to reduce ignition timing advance or you will ruin the engine.

[Brutus]

Good point. I'm aiming at 80-90 bhp with the max torque between 5k-7k if possible (street use). Also I would like to use a paso 750 engine with the 44 dcnf weber. I still got those early paso pistons lying around though. I believe these got approx 14k km's on it. They have a higher dome, but don't know the compression ratio. Maybe with a new set of piston rings would be enough in combination with some upgrading of the heads. Don't know the max capacity of the 750 heads. Will 44mm inlet valves fit? Will 900 cams give more lift? Like to know about your experience.
Before I forget; I'm only considering an 851 crank because I asume the stock 750 paso crank can't handle 90 bhp and a higher torque. Am I right?

Léon

[koko64]

Check out J D Hords website for his hot 750SS (795 motor).
Also Bikeboy.org for his hot 750 with big valves and 900 cams.

Guys on the Monster forum tell me that hi comp pistons and 695/800 heads work well. They say the 695/800 heads bolt onto 750 barrels, but you need higher comp pistons due to the different combustion chamber.

Brad Black has a narrow case 900 crank that might be for sale. He was thinking of putting it in his 750. A hi comp, big bore kit (Fast by Ferracci USA), narrow case 900 crank, 695 heads (better ports, big valves), should give you over 800cc, big valves, better cams and heads. Brad would know the details involved.

Very interesting project.