ESE's works engine tuner

[DoldGuy]

What to expect with the Sub/Auxiliary Exhaust Ports opening at TDC (approximately 3mm on a 76mm stroke) ?

Main Exhaust open at TDC (1mm-2mm on a 76mm stroke) ?

[wobbly]

Aux ports open at TDC you loose a ton of power, main port open works to make power on a 180* twin with a common pipe, but would be impossible to jet without
pumper carbs and a shitload of jetting change.

[jonny quest]

Does anyone have any experience with the Aprilia Ditech SR50 scooters, 2001 year?

More specifically the fuel injection system. Looking to build a big bore stroker... around 100cc. I'd like to use the fuel injection system on it already, but don't know if I can modify it to work

[peewee]

What if you water-cooled the SS?

im sure that's a great idea if you already have water up near the spigot and can tie into the water source, like wobbly has shown several times. but like many older cylinders, mine has water only around the bore. if I didn't have fairly fresh nikisil I would see if it was feasible to weld on some water channels to the spigot. on the side of the cyl I could install some nipples and small water hose connected to the spigot but I don't think the pumping action would be very effective and the center portion of the exh passage would still be air cooled so how much would I really gain

[tjbw]

What to expect with the Sub/Auxiliary Exhaust Ports opening at TDC (approximately 3mm on a 76mm stroke) ?

Main Exhaust open at TDC (1mm-2mm on a 76mm stroke) ?

Not sure if I understand the question, as I can't imagine why anyone would want to do this.

If you take a conventional two stroke, but move the exhaust ports up to near the top of cylinder, then when exhaust ports close just before TDC most of the mixture will have been pushed into the exhaust pipe. Compression would be very low, so very easy to kick over, if it fires expect flame exiting the exhaust pipe. Power would be very low.

Well that's what I think, anyone else have any thoughts on this?

[ken seeber]

Want more transfer port area? Just raise them so they are as high as the EO. No (not really) back flow cos they are timed with matching holes in the piston skirt and cyl wall to prevent flow to the crankcase. Obviously it will exhibit exh (combusted) flow into the passage and also obviously it could be done in conjunction with lower “conventional” timed transfers. The idea was shown to me by a dude called Arthur around 20 + years. 10 ms on EngMod might show that it be of any value, but there it is.

[lodgernz]

I'd appreciate some more advice about exhaust ducts please.

My 50 has an exhaust port window area of about 500mm2. The exhaust duct is only about 40mm long. If I extend the duct to twice the bore, i.e. 78mm, and steadily reduce the CSA of the duct so that the outer end is 90% of the port area (assuming I can even achieve this), then the total volume of the duct would only be about 38cc. Does this sound too small for a 50?

I realise it's impossible to predict the volume of the washed-through mixture, but I'd like to know if this sounds to be in the ball-park or not.

[Pursang]

Not sure if I understand the question, as I can't imagine why anyone would want to do this.

If you take a conventional two stroke, but move the exhaust ports up to near the top of cylinder, then when exhaust ports close just before TDC most of the mixture will have been pushed into the exhaust pipe. Compression would be very low, so very easy to kick over, if it fires expect flame exiting the exhaust pipe. Power would be very low.

Well that's what I think, anyone else have any thoughts on this?

Even a 3mm by-pass hole someway between EPC & TDC will dramatically reduce the static compression. Common mod on 350 Bultaco Alpinas, Way back when.
Little detectable power loss under normal operating conditions.

[Pursang]

Want more transfer port area? Just raise them so they are as high as the EO. No (not really) back flow cos they are timed with matching holes in the piston skirt and cyl wall to prevent flow to the crankcase. Obviously it will exhibit exh (combusted) flow into the passage and also obviously it could be done in conjunction with lower “conventional” timed transfers. The idea was shown to me by a dude called Arthur around 20 + years. 10 ms on EngMod might show that it be of any value, but there it is.

Read a report , years ago, of a 1950's racer who got to ride, race & win on Walsh Bantams. He towed one home, after a meeting, with the exhaust pipe removed. He and his mate spent a lot of time looking up the exhaust duct (they weren't game to pull the head off). The piston skirt was 'Full of Holes'. He tried to reproduce the same with his own Bantam. It ran, but was Very peaky and pretty powerless. He suspected it was probably "free porting" out the exhaust. The Walsh Bantams, on the other hand, were capable of running with contemporary 500cc racing 4 strokes.


My Favorite vintage racing pic.

cheers, Daryl.

[Frits Overmars]

Does anyone have any experience with the Aprilia Ditech SR50 scooters? I'd like to use the fuel injection system on it but don't know if I can modify it to work

Aprilia has a lot of experience with their DiTech system, namely that it shouldn't have been put on the market so soon. There were so many problems that it almost did Aprilia in. In fact it did, because it rendered Aprilia insolvent (it coincided with a helmet-law for scooter riders that was introduced around the same time, which caused a collapse of the Italian scooter market, and with the acquision by Aprilia of the old Guzzi works that turned out to be almost worthless).
Aprilia was then swallowed up by its biggest creditor, Piaggio, snapping it from the jaws of also-interested Ducati, which incidentally was taken over shortly afterwards by Audi. We are still awaiting all-wheel-drive Ducatis.
OK, back to the business at hand:
the Ditech system may be suitable, but it'll take a lot of work, sweat and tears. And in any case it will be reluctant to rev because of the inertia of the air-valve.

What to expect with the Sub/Auxiliary Exhaust Ports opening at TDC (approximately 3mm on a 76mm stroke)? Main Exhaust open at TDC (1mm-2mm on a 76mm stroke) ?

If you take a conventional two stroke, but move the exhaust ports up to near the top of cylinder, then when exhaust ports close just before TDC most of the mixture will have been pushed into the exhaust pipe. Compression would be very low, so very easy to kick over, if it fires expect flame exiting the exhaust pipe. Power would be very low.

Tjbw, DoldGuy is not talking about very high exhaust ports but about ports with very low bottoms that are opened near TDC by the underside of the piston skirt.

My 50 has an exhaust port window area of about 500mm2. The exhaust duct is only about 40mm long. If I extend the duct to twice the bore, i.e. 78mm, and steadily reduce the CSA of the duct so that the outer end is 90% of the port area (assuming I can even achieve this), then the total volume of the duct would only be about 38cc. Does this sound too small for a 50? I realise it's impossible to predict the volume of the washed-through mixture, but I'd like to know if this sounds to be in the ball-park or not.

Ball-park .
If you can persuade your exhaust pipe to shove 38cc of washed-through fresh mixture back into the cylinder before the exhaust closes, you'll have a winner.
Of course even the washed-through mixure will not be 100% pure, but a long, narrow exhaust duct helps in this respect; it will provide for a small-area contact plane between the spent and the fresh gases. But while mixing is limited, the long, narrow tract offers an unfavourable ratio between duct volume and duct wall surface, thus increasing the heat transfer from the walls to the mixture.

[peewee]

frits i think you confused me for tjbw. but i do have alittle experience with exh ports opening under the piston at tdc. some old ktm were like that and i happen to have one of them engineering marvels . whether it was a bungled design or ktm was aware and just didnt care, im not sure. im not even sure how big of a deal it is. maybe at tdc the crakcase and pipe pressures are near the same so no mingling of fresh mix and exh gas takes place, i just dont know. since i dont know, i used different piston to keep exh ports closed at tdc

[Niels Abildgaard]

the old Guzzi works that turned out to be almost worthless).
Aprilia was then swallowed up by its biggest creditor, Piaggio, snapping it from the jaws of also-interested Ducati, which incidentally was taken over shortly afterwards by Audi.

Can we have the story why V2 Guzzis were worthless and V2 Ducatis are not?

[jonny quest]

Frits, the little I understand of the ditech 2001, it has a cam ground on the crank which times, and actuates an air pump. This air pump provides pressurized air to an already fuel pressurized direct injection system. It has a throttle body and tps, which just allows air into motor via case reed. Direct high pressure air and fuel is injected into cylinder head.

Is it water temp, baro pressure controlled also?

Apparently they run safely with a non original pipe and bumped up to 70cc.

[Muhr]

Is adjusting a little in the crankcase and a reflection I had regarding C transfers case meeting. Below I have two different options, have someone tested this or have any thoughts on it. (on side fed rotary valv)

Regards Muhr

[breezy]

Read a report , years ago, of a 1950's racer who got to ride, race & win on Walsh Bantams. He towed one home, after a meeting, with the exhaust pipe removed. He and his mate spent a lot of time looking up the exhaust duct (they weren't game to pull the head off). The piston skirt was 'Full of Holes'. He tried to reproduce the same with his own Bantam. It ran, but was Very peaky and pretty powerless. He suspected it was probably "free porting" out the exhaust. The Walsh Bantams, on the other hand, were capable of running with contemporary 500cc racing 4 strokes.


My Favorite vintage racing pic.

cheers, Daryl.

i wonder if maybe the holes were for extra lubrication ... i have plenty of experience with piston siezure in cast barrels!!! any extra lubrication is a very welcome.