ducatipaso.org

Over the holidays I was thinking about this topic and how it seems you don't really have a plan which imho shows in some things you wrote.
If you're serious about this and unless you're just randomly checking your options I'd suggest you stop and take a step back. The only approach that makes sense is to know exactly what you need (not what you want) and have a concept. To get there you'll have to answer yourself more questions.

But before getting there, you say you aim for 85-90 then 90-100hp. If the base is a 750 engine you should know that the 72hp that are on paper are actually 60-64hp at the rear wheel which can be seen on different dyno charts. Getting +30hp out of a 750 engine is not realistic and even if you can get over 20hp out of it the result will be an engine which is for sure not for everyday use. Forget max hp, that's not what you're after. If you'll be riding the bike on the street you want torque. If you aim for torque a hp increase will come with it automatically.

This should answer the question if a 750 crankshaft can handle 90-100hp. You will not get in that situation.

If 96mm pistons fit on a 750 engine ? The original ones are 88mm, the 780cc big bore kit is 90mm, the 900cc engines have 92mm pistons. 94mm pistons on a 900cc engine result in 944cc, 96mm in 960cc.
Take a 750 cylinder base gasket, measure the outer diameter of a 900cc cylinder and you'll see that doesn't make sense.

A 900SS engine has a 43mm inlet and a 38mm outlet valve, so can you fit a 44mm valve in a 750 head - no.
You can combine a 750 racing valve and a 900SS valve but you'll need a washer for the spark plugs. Lift and overlap have to be considered such as the clearance to the piston, even more if the pistons have a high dome and the cams are aftermarket.

900SS cams are not worthwhile losing time with btw. You can also read BikeBoy`s tests.

Every modification to an engine, exhaust or carburetion system will influence its performance, narrow or widen hp & torque output range and shift it up or down the revv range. You need to be clear about what you want. Some modifications only work in combination with others and some shouldn't be combined. The more there is done the more the whole characteristics of the engine is impacted and chances are you'll end up with an engine that shows a great result on a dyno but doesn't meet your expectations on the street.
For instance "lightening all the sprockets / flywheel and max porting on the heads incl racing cams" + large valves etc imo doesn't really coincide with a street used 750 engine.

I never really understood the appeal so many guys show for "race" parts. "Race" means the parts are designed for max performance at WOT and a revv range you will hardly hit on the street. Other parts like race brakes can also be the opposite of an improvement because they ideally operate at temperatures which you will not reach under normal riding conditions.

Coming back to the beginning; some questions you should ask yourself are:
- how is your actual riding style and how would an engine need to be to match that ?
- what is your budget ? A full engine modification can easily cost as much as your bike is currently worth. While the crankshaft will do you'll need aftermarket conrods, in consequence a crankshaft rebalancing, new crankshaft bearings etc etc
- does it make sense to use a 750 engine as base or directly go for a 900 ?
- how "street legal" do you want to stay ? Most mods may not be legal anyway but things like large valves do increase noise emission in a noticeable way
- do you want a bullet proof engine or just max power output (if it's the first skip a dual spark plug conversion)

sorry, got a bit carried away ...

G.

95HP was possible in the last 750 TT1 race Engines.
Just take a tone off money and build a Race Engine with a weekend lifetime

Race engines measure hours not miles!

I have an 87-F1 with some slight performance mods and it's very perky. Quite fun to ride too. But 90hp from a Paso engine will be extremely expensive and no fun on the street. Just as an example of what can be done to an air cooled twin, I have built a monster motor for my Multi. 1098cc 12:1 compression, knifed crank, slight porting on the heads, custom dyno tuning and she makes 95hp and 94 ft. Lb torque. It's street bike and it's a wonder to ride. Torque is where it's at for the street.

Hi G.,
That was a excellent recap of good old hot rod logic. I always thought for street use that a engine taken apart and "blueprinted" ie highly balanced, very good tolerances etc would be about as good as it gets for the everyday street.My experiences down that path has been with BMW's and I expect that a 750 would be the same.Regards Arch.

Thanks for the input. You're right. I've to get it sorted out. First my thoughts:

paso750 wrote: 1) how is your actual riding style and how would an engine need to be to match that ?
2) what is your budget ? A full engine modification can easily cost as much as your bike is currently worth. While the crankshaft will do you'll need aftermarket conrods, in consequence a crankshaft rebalancing, new crankshaft bearings etc etc
3) does it make sense to use a 750 engine as base or directly go for a 900 ?
4) how "street legal" do you want to stay ? Most mods may not be legal anyway but things like large valves do increase noise emission in a noticeable way
5) do you want a bullet proof engine or just max power output (if it's the first skip a dual spark plug conversion)

ad1) riding style is sporty, max 170 km/ph for short distances. Most of the time approx 130 km/ph on the freeway. This is the reason I'd like more torque between 5k - 7k.
ad2) I'm doing most of the work myself. Don't have a real budget. All the money going in isn't the best investment anyway
ad3) 750!
ad4) we ain't got no TUV
ad5) in the middle would be fine.

paso750 wrote:..But before getting there, you say you aim for 85-90 then 90-100hp. If the base is a 750 engine you should know that the 72hp that are on paper are actually 60-64hp at the rear wheel which can be seen on different dyno charts. Getting +30hp out of a 750 engine is not realistic and even if you can get over 20hp out of it the result will be an engine which is for sure not for everyday use. Forget max hp, that's not what you're after. If you'll be riding the bike on the street you want torque. If you aim for torque a hp increase will come with it automatically..

I've owned different ducati's and I just asumed that around 90 bhp would do the trick. Didn't think through it has only approx 62 hp at the back wheel. Now I realize it's allmost impossible to get it tuned this far and keep the engine in one piece for road use. The reason for upgrading the engine is that it could use more torque between 5k -7k and furthermore it is a "technical challenge"..

paso750 wrote:This should answer the question if a 750 crankshaft can handle 90-100hp. You will not get in that situation.

Got it. An std 750 crank it is.

paso750 wrote:If 96mm pistons fit on a 750 engine ? The original ones are 88mm, the 780cc big bore kit is 90mm, the 900cc engines have 92mm pistons. 94mm pistons on a 900cc engine result in 944cc, 96mm in 960cc.
Take a 750 cylinder base gasket, measure the outer diameter of a 900cc cylinder and you'll see that doesn't make sense.

At the time I didn't know the limits of the casing. I realize now that the studs and the opening of the casing got it's limits..

paso750 wrote:A 900SS engine has a 43mm inlet and a 38mm outlet valve, so can you fit a 44mm valve in a 750 head - no.
You can combine a 750 racing valve and a 900SS valve but you'll need a washer for the spark plugs. Lift and overlap have to be considered such as the clearance to the piston, even more if the pistons have a high dome and the cams are aftermarket.

900SS cams are not worthwhile losing time with btw. You can also read BikeBoy`s tests.

As far of the heads I've started reading "Performance tuning in theory and practise" by Graham Bell. Interesting stuff. He states that there is a certain balance between the amount of gas going in and getting it fully transformed into energy. If I understand correctly 41mm (1,6 inch) inlet and 35mm (1,37 inch) exhaust valves should be enough. Focus should be on the correct porting and valve lift.
This should give the following options:

Heads
Stock 750 paso heads as base, ported inlet and exhaust for an optimal flow between the 44 dcnf, combustion chamber and the exhaust.
I'll have to find out if the stock cams give enough lift though. Also I'll have to calculate what kind of diameter exhaust tubing I need.

Cylinders
Currently I drive a californian model, with the "flat" pistons. As I mentioned earlier I've got the stock paso pistons with the higher domes on the shelf. These could be used in combination with 1mm squish.
Second option will be aftermarket 90mm hc pistons. I could go for wiseco, pistal etc. Point of concern is the extra weight of hc pistons that'll make balancing of the crank needed.

rest of the engine
stock overhauled engine as base, heavy duty clutch springs if needed, longer secondair transmission shaft (more offset front 15t sprocket), slightly lightened flywheel just for kicks.

exhaust
See above. I'll have to calculate what is needed for an optimum flow. If the stock diameter is enough, I'm still considering making my own exhaust. "Spaghetti" look-a-like of some sort

To be continued

ok, it will take some time! Have a nice job!

ducapaso wrote:ok, it will take some time! Have a nice job!

Tx. I'll have a go at a spare engine. It's one of the latest 750 models. Looks like crap, but a solid base to start from. In the meantime I can ride the paso with the current engine.

Léon

Brutus wrote: ad1) riding style is sporty, max 170 km/ph for short distances. Most of the time approx 130 km/ph on the freeway. This is the reason I'd like more torque between 5k - 7k.

That is what I was thinking

ad2) I'm doing most of the work myself. Don't have a real budget. All the money going in isn't the best investment anyway

In case you`re interested in a set of polished and rebalanced 750 conrods let me know

ad4) we ain't got no TUV

I know but Police will stop you for excessive noise. (specially if you come to Germany)

and furthermore it is a "technical challenge"..

that`s an arguement I can understand

Also I'll have to calculate what kind of diameter exhaust tubing I need.

Larger tubing will reduce back pressure and shift the torque to a higher rpm range.
A friend of mine has a custom header with a Quad D exhaust on a ST2 engine. The bike really pulls hard but only over 6.000rpm. Below that I find it a little boring, an original bike has more low end punch. That wouldn`t be for me but it`s ok for his riding style.

Point of concern is the extra weight of hc pistons that'll make balancing of the crank needed.

Many aftermarket pistons are actually lighter than the original.

Stick to what the experts say.Faloon and others such as ed milich have spent a lot of time building these engines for street / race , and are receptive to sensible emails. merry xmas and happy new year to all you duc enthusiasts. rgds J

PS No disrespect intended to any of the above posts,but there are so many variables involved in tuning a performance engine that unless you have considerable experience ,it can quickly become a nightmare

Thats a 30 year old book,a lot, no make that everything has changed since then

Ed I would listen too, when he knows you well enough to speak to you

Looking forward to watching this project progress. It's great that you can bounce your ideas and thoughts around in a forum like this.

I would agree that you should study the work of engine builders and tuners mentioned in this thread. Check their websites and examine the motor recipes they have used to see what modifications will achieve your goals.

Good luck!

Paso750 wrote:..In case you`re interested in a set of polished and rebalanced 750 conrods let me know..

Thanks allot. I'll have to check the crank that is in my spare engine.

Paso750 wrote:Larger tubing will reduce back pressure and shift the torque to a higher rpm range.
A friend of mine has a custom header with a Quad D exhaust on a ST2 engine. The bike really pulls hard but only over 6.000rpm. Below that I find it a little boring, an original bike has more low end punch. That wouldn`t be for me but it`s ok for his riding style

Ok, I'll look into that.

Paso750 wrote:Many aftermarket pistons are actually lighter than the original.

Any idea what is a good option for hc pistons?

Jayh wrote:Stick to what the experts say.Faloon and others such as ed milich have spent a lot of time building these engines for street / race , and are receptive to sensible emails. merry xmas and happy new year to all you duc enthusiasts. rgds J

Ok, good suggestion. I'll give it a try.

koko64 wrote:Looking forward to watching this project progress. It's great that you can bounce your ideas and thoughts around in a forum like this.

I would agree that you should study the work of engine builders and tuners mentioned in this thread. Check their websites and examine the motor recipes they have used to see what modifications will achieve your goals.

Thanks, will do!

750paso wrote:

A rebuild Indiana..? (750 offcourse)

Best wishes by the way!

http://forums.ducatipaso.org/download/file.php?id=678
Holy crap G ! you sure don't look like what I expected er, nice bike