I need a drawing of ET84, exhaust nut

[johnmead]

The cams make maximum hp at 6800 so I am tuning it for 7500. Engine has a press together crank with two tapered roller bearings on the drive-side mainshaft to eliminate the bearing race walking problem. These cranks have been run to 9000 without any problems.

I got the exhaust pipes from Tim Kingham. They are copies of the 2-2 he is running on his racing Rapide.

John

 

[Howard]

That's going to be a short primary pipe.

H

 

[roy the mechanic]

If Mr Fueling was involved then it has to be beleived! But remember our motors were already obsolete when he went to "school"

 

[johnmead]

That's going to be a short primary pipe.

H

Yes, if I was not using an anti-reversion device. With it I can make the exhaust pipe any length I want and the engine will not be affected by the return pulse.

John

 

[davidd]

John,

I think that you can do exactly what you want with the design that I used. I am not smart enough to be left on my own with exhaust design. I know that Terry's heads had an anti-reversion device in the form of a "D" shaped port. Carleton's flow testing showed that it did not work for the high-revs he wanted. One of the issues that Vincent owners face with high revving engines is that the available cams will not produce power over 6000 rpm. Once you produce a cam to go over that barrier, your mean gas velocity requirements usually limit you to an 1-3/4" pipe as the 2" pipes do not generate enough velocity to prevent some exhaust gas from flowing backwards (reversion).

As to the sonic requirements, namely, the negative pulses, it seems to me these are a good thing in moderation, pulling in the intake charge during overlap. Most of the lore says that a Vincent does not like a megaphone, but I think it is just the opposite. In fact, I think, in a crude way, the exhaust sees a two inch pipe as a megaphone of sorts. Coburn always ran a megaphone for max power in the 60's and 70's. Carleton always got max power with a megaphone and Lindsay Kyle is getting 45 HP plus from his Comet with an 1-34" pipe and a megaphone with a silencer. I think that there was just no money for development.

I think what you are doing is very interesting and am looking forward to your reports when it is running.

David

 

[johnmead]

The cams I am going to use are Terry Prince MK4s. He says that they make max power at 6800rpm. The engine is almost together and after breaking in I will put it on a DynoJet and see what numbers I get. My pipes are 1 3/4 and I will be running them into modern Ducati Termignoni cans.

Did Carleton ever get any cams that would produce power at higher rpms?

I cleaned up the intake and exhaust ports but did not open them up as they seem to be almost too big for a 615cc cylinder.

John

 

[vibrac]

I tend to agree about 2" pipes I note Roy Robertson uses 1 3/4" the whole question of efficiency is a bit academic when the regs are asking for 105db I can only achieve this at the moment with a 4+ inch silencer with 2" adsorption and straight through perforated pipe and of course the only place for that is up high.
I do have some ideas for next year and once the silencer is smaller and lower a new pipe will follow
are the TP Mk4's still available?

 

[bmetcalf]

Here is the contact info: http://www.classicmotorbikes.com.au/contact.html

I wonder if he is going to Bonneville this year?

 

[davidd]

I think Tim is spot on about the pipes. When Carleton was running there was no silencer requirment in the rules. Now there is, so most of his exhaust system development is out dated for me. Terry's Mk4 cams are available.

Terry has had a raft of health issues this past year. He fell down an embankment, the tire on his bike exploded on the dyno and a chunk hit him in the head and he recently had an operation that was more involved than he had hoped. Despite this, he will be at Bonneville and the Rally. He will be with Pat Manning much of the time.

John, it sounds like a good set up. Carleton used John Renwick's cam, which I also had in my engine, which makes power up high, but more importantly, it does not drop off quickly. John does not sell retail because he makes them himself and he cannot do the quality necessary for such sales. Carleton and I have 500cc Prince heads, not the 600 ones. I have not used it as it is illegal in some of the venues that I run. If you run Vintage, you have to have original cases, cylinders and heads. They are not illegal in AHRMA road racing, so Carlton used his road racing. There were still a lot of hours and money spent to make that head flow. As I remember, the intake was pretty easy, like one day on the flow bench. He then spent more than a week on the exhaust port trying to balance the flow.

David

 

[Monkeypants]

Roy Robertson uses John Renwicks cams but with several small modifications added (trial and error). He tried the Terry Prince mk 4 cams, but lapped 2 seconds slower than with the modified Renwick cams.
Terry sent me his MK5 cams and radiused followers. I did not get a dyno graph from him, but my recollection is that on his race bike they produced an extra 12 hp over the mk 4 while lifting the valves a bit less. These are the cams that were designed by Fritz Egli jr using the Mercedes Formula one cam development program. They look to be rectangles with a bit ground off the corners!

Glen