Oddball engines and prototypes

[husaberg]

xrtra page

[Grumph]

Reading that long winded lot makes you wonder if he was paid by the word....Pic of complete bike is the F1/endurance genesis that raced in the Suzuka 8hr.
Engine pics are of the production 750.
If he later assumed that the ignition lead was compression dependent he was wrong. The problem is that the generally accepted flow pattern for a 4 valve haed is for two contra rotating streams of inlet mixture to form and follow the cylinder walls down...Superimpose a central stream on this and where does it fit in ? Answer - where and when it can. At some rpm, better than others...Hence the weird ignition curve with twin peaks. From memory, 42deg advance at 4500rpm and then drop back to about 36deg till 8500 where it has to jump to around 45 deg advance. It holds that for a very short time then drops steadily to 30 deg from where it drops back as a rev limiter.
The OW01 is even more extreme although following the same shape - I believe at max they see around 50 deg advance.
My read on this is that at certain rpm, there is either too much turbulence for it to burn or not enough....
What he didn't pick up in those pages anyway is that the center inlet cam is 5 deg advance over the outers - I've always assumed it was to try and get something flowing there before the outers opened...
Another problem is the very high surface/volume ratio in the inlets...there's a pic looking down the ports, I used to describe it as kerbing and channeling. Take too much out and you reduce port velocity too far...
The exhaust valves are really too small also - bigger exhausts always pay dividends in them

And lastly, cam timing...Right up to the 5 valve R1 they kept the inlet on 100deg lobe center, Exhaust usually on 110deg LC....What is it ? a british single from 1950 ? Even keeping std cams, they go much better on 103/105 lobe centers....

[husaberg]

Reading that long winded lot makes you wonder if he was paid by the word....Pic of complete bike is the F1/endurance genesis that raced in the Suzuka 8hr.
Engine pics are of the production 750.
If he later assumed that the ignition lead was compression dependent he was wrong. The problem is that the generally accepted flow pattern for a 4 valve haed is for two contra rotating streams of inlet mixture to form and follow the cylinder walls down...Superimpose a central stream on this and where does it fit in ? Answer - where and when it can. At some rpm, better than others...Hence the weird ignition curve with twin peaks. From memory, 42deg advance at 4500rpm and then drop back to about 36deg till 8500 where it has to jump to around 45 deg advance. It holds that for a very short time then drops steadily to 30 deg from where it drops back as a rev limiter.
The OW01 is even more extreme although following the same shape - I believe at max they see around 50 deg advance.

But as it needed a MAX advance of 50 is an indication it was pretty dire.
My understanding was it wasn't the comp that was causing the huge advance.
it was the resultant shape of the chamber that was a result of achieving a high comp with the engine.
The later OW it seemed to be they could rev high or have acceleration from a high comp, but not both.
Although one tuner from Italy could always get a shit load of HP out of it. Was it Bontempi that raced it? It was always a missile when it raced at the euro tracks.

In one of the street bike mags a guy in WA had one of the works FZ750 engines in a FZR frame.

[Grumph]

Characteristically, things like very high com Z1's with a poor chamber shape, need the big advance right across the range to burn properly.
The 5V yams need the big advance only in specific rpm bands. To me this doesn't indicate a poor chamber shape but that something is happening at those rpm's...
My belief is that it is the turbulence occuring at those points which is causing it.
Whether in fact conditions cause a stall in the turbulence or too much turbulence to sustain fire i don't know...But it's apparent the curves were dyno developed, just throw in advance till it runs right at a given RPM.

[husaberg]

Characteristically, things like very high com Z1's with a poor chamber shape, need the big advance right across the range to burn properly.
The 5V yams need the big advance only in specific rpm bands. To me this doesn't indicate a poor chamber shape but that something is happening at those rpm's...
My belief is that it is the turbulence occuring at those points which is causing it.
Whether in fact conditions cause a stall in the turbulence or too much turbulence to sustain fire i don't know...But it's apparent the curves were dyno developed, just throw in advance till it runs right at a given RPM.

I can't find the Italian tuners name but pretty sure the UKSB Boost bikes were pensioned off ones he had later did as well initially for WSB.

Found it Beppe Russo is the guys name he was the tuner for belgrada and had been working on the Yamaha 750's from 1986 onwards (I'm guessing with Bimota WSB first)
1994 YZf750 158.7 hp @13800rpm

[Frits Overmars]

My understanding was it wasn't the comp that was causing the huge advance.

You're right, sort of. It's not the compression ratio per se that requires the huge advantage; in a decent engine the higher this ratio, the less advance would be required. But a high compression ratio screws the combustion chamber shape up until it looks like a wet pancake, and that needs a lot of advantage in order for the flame to get to the mixture in all those nooks & crannies more or less on time.
It was even worse in F1 when they still had the 98 mm bore, 39,75 mm stroke high-revvers. These required over 55° advance at WOT and even more at part-throttle.

I can't find the Italian tuners name but pretty sure the UKSB Boost bikes were pensioned off ones he had later did as well initially for WSB.
Found it Beppe Russo is the guys name he was the tuner for belgrada and had been working on the Yamaha 750's from 1986 onwards.

I could have spared you the search Husa, but I was not paying much attention as you guys seem to be writing about foul-strokes lately .
I visited Beppe a couple of times because he was using my FOS dyno hard- and software. First run we did was a standard Yamaha 750. It said 150 hp on the brochure and it delivered 120 rear wheel hp on the dyno. Those Japanese PR-guys must have been measuring the power at the piston ring.
BTW: in case you wish to google: it's Belgarda.

[J.A.W.]

I was not paying much attention as you guys seem to be writing about foul-strokes lately

F-O wants 2Ts.. give 'im 2Ts..

http://www.enginelabs.com/news/video...-for-aviation/

[WilDun]

There you go, my very first motorcycle and a two stroke! (Trojan Minimotor)


And (below)my second motorcycle, also a two stroke! (Royal Enfield flying flea.)
BTW. Note the massive drum brake up front, the rubber band front suspension, and the expansion chamber!
This was the military model dropped into Holland and elsewhere for the paratroopers during WW2. - engine was a DKW clone (I'm told).

I am first and foremost a two stroke enthusiast of course, but if I wait till two strokes make a comeback and don't take an interest in anything else, then I'm going to miss out big time!

[ken seeber]

What goes around comes around

http://www.gizmag.com/dan-gurney-mom...-patent/39344/

Interesting is the power increase with a snazzy inlet passage shaping. Hard to believe. Maybe that's what Harry has done with all his transfer ports.

[J.A.W.]

Looks like 1/2 a square 4..

[husaberg]

What goes around comes around

http://www.gizmag.com/dan-gurney-mom...-patent/39344/

Interesting is the power increase with a snazzy inlet passage shaping. Hard to believe. Maybe that's what Harry has done with all his transfer ports.

Very hard to belive the hp isn't. Just that it is just a as result of the shape which is pretty generic motorbike.

Michael Cyst did the contra rotating crank but it sideways.

The contra cranks has its advantages but costs a lot more, with more parts etc.
also those primary gears have no hunting tooth.

[ken seeber]

also those primary gears have no hunting tooth.

Hooser, you're right, but there are a couple of ways to look at it. As the PCD is much larger than a normal sized primary drive gear, the tooth loading is much less. However, in this case he seems to be playing with 4 = foul strokes and I am assuming that only one of the two cylinders fires each rev. This being the case, the teeth in mesh at the time of combustion would see a load reversal on each consecutive revolution. ie, if the front cylinder was firing, it would be "driving" the rear cylinder, and the reverse would apply the next revolution. Yes, no hunting tooth, but certainly a load reversal seen by the teeth, half the wear? However this doesn't apply to classic tandem twin 2 strokes: Rotax 256 and Kawasaki 250s.

[husaberg]

Hooser, you're right, but there are a couple of ways to look at it. As the PCD is much larger than a normal sized primary drive gear, the tooth loading is much less. However, in this case he seems to be playing with 4 = foul strokes and I am assuming that only one of the two cylinders fires each rev. This being the case, the teeth in mesh at the time of combustion would see a load reversal on each consecutive revolution. ie, if the front cylinder was firing, it would be "driving" the rear cylinder, and the reverse would apply the next revolution. Yes, no hunting tooth, but certainly a load reversal seen by the teeth, half the wear? However this doesn't apply to classic tandem twin 2 strokes: Rotax 256 and Kawasaki 250s.

Yeah but the output too be more than a 250 twin or 500v or sq four.
im picking it 2 180 twins coupled together.
I can't see t being a goer for anything other than a TQ or midget kind of stuff etc.
A boxer likely does everything better cheaper. Other than gyro.

[WilDun]

I can't see t being a goer for anything other than a TQ or midget kind of stuff etc.
A boxer likely does everything better cheaper. Other than gyro.

Yeah probably good for racing stuff where it is being checked out regularly and where gear noise isn't a real problem, (high peripheral speeds) but for road going machines maybe not so good. .....Probably!

Only thing against boxers really is width.

[Frits Overmars]

Only thing against boxers really is width.

Not necessarily,Will.