This is Roy's, It must be good enough for the track !, Cheers Bill.
Exhaust
- Thread starter Monkeypants
- Start date
Roy provided me with some good info on exhausts. He pointed out that Horner Bros have their own dyno and have done more dyno testing of exhaust types for hotrod Vincents than most anyone. They always come back to the same system which is a two into one. He has the exact dimensions of their system, but Horners did not want that divulged, so I had to guess at it from various photos. That info, along with the numbers provided by Terry all seemed to point toward the 2" going into the merge then 2.5" after.
As Greg said in his comment on the racer exhaust, you have to start somewhere!
As Greg said in his comment on the racer exhaust, you have to start somewhere!
Bill, I get 3.53 sq. inches for two stock pipes sized 1 5/8" (.060" wall) A single 2.25" outlet gives 3.56 square inches, so that would be a good match for that size.
For my setup, the 2.5 came close to the same area as the two 2". The 2.5" is the actual ID thru the muffler, whereas the 2" pipe is smaller by the wall thickness, so it all works out, more or less.
Glen
For my setup, the 2.5 came close to the same area as the two 2". The 2.5" is the actual ID thru the muffler, whereas the 2" pipe is smaller by the wall thickness, so it all works out, more or less.
Glen
I used to sprint with a bloke with a stock 900Kwacker 4 pipe, We were about the same, 12.5 sec, He turned up with a Tuned !! 4 in to 1, He was slower !! Me with my big mouth said "David that outlet hole is too small ", Next time he had made the hole bigger, I could not get near him after that, Cheers, Bill.
This is a very interesting thread. I have not run the numbers with an engine the size of yours, but the formula requires so many decisions about the conditions under which you want to operate, it is difficult to do a rough calculation. What rpm do you want to shift at, what is that in piston speed, what mean port velocity are you shooting for 250, 275, 300, etc. After you have done all the calculations you get to the dyno and you are not impressed with the results, maybe.
I will say that the fastest Vincent single road racers I know use megaphones. I would think that Terry's heads would like them more than the stock heads because the stock heads have such a terrible exhaust port. Having said that I would prefer to use a straight pipe. There is plenty of torque, but not much high up, which is fine for road racing. I think the Factory stuck with straight pipes for the same reason.
Greg, I am sorry about the pipes, but you are not alone. Every racer has a similar story. One of the advantages that Roy Robertson and Glen have is they are running an Egli frame. The motor is so much higher than stock that you can get away with a low system with greater ease. I tacked up my system with the springs removed and the bike leaned over at 45 degrees in order to make sure it worked:
The next race was at Miller Motorsports and I went off the track in the Attitudes and bashed the pipe on the curb. That is when I decided a high pipe was mandatory. Of course, the reason I had made this pipe in the first place was because they had instituted a catch pan rule. They had not yet instituted a silencer rule, but I decided that I was not going to invest in expensive parts that could be made redundant with a stroke of a pen. With a high pipe I did not have to worry about mounting a silencer.
Irving-Vincent:
David
I will say that the fastest Vincent single road racers I know use megaphones. I would think that Terry's heads would like them more than the stock heads because the stock heads have such a terrible exhaust port. Having said that I would prefer to use a straight pipe. There is plenty of torque, but not much high up, which is fine for road racing. I think the Factory stuck with straight pipes for the same reason.
Greg, I am sorry about the pipes, but you are not alone. Every racer has a similar story. One of the advantages that Roy Robertson and Glen have is they are running an Egli frame. The motor is so much higher than stock that you can get away with a low system with greater ease. I tacked up my system with the springs removed and the bike leaned over at 45 degrees in order to make sure it worked:
The next race was at Miller Motorsports and I went off the track in the Attitudes and bashed the pipe on the curb. That is when I decided a high pipe was mandatory. Of course, the reason I had made this pipe in the first place was because they had instituted a catch pan rule. They had not yet instituted a silencer rule, but I decided that I was not going to invest in expensive parts that could be made redundant with a stroke of a pen. With a high pipe I did not have to worry about mounting a silencer.
Irving-Vincent:
David
David, I remember laying my l/ning over with side by side 2" pipes, And thinking I was never going to get it that far down, Ist corner, 1st race, You have guessed it !! I loved the sound of them, But had to go to 1 5/8th twin pipes, That bike was never fast ! But I went quicker than my Special round the tracks because I did more races, Cheers Bill.
Glen, i'm only on 998 I figure this to be "sufficient " for posing on the street! A wellknown called C R Axtell(norton guy ) reckoned to have "done worn-out my dyno "proving that 2 into one pulls better out of the turns .
Just measured the angle of contact at the megaphone, which would be the first part of the exhaust to contact the ground. Contact happens at 70 degrees from vertical, so I should be OK to lend the bike out to Dani Pedrosa, his shoulder will touch before the exhaust does.
One tip I can offer to anyone contemplating building their own exhaust system is to first purchase some cheap automotive flex pipe.
I bought enough to do a mock up for $25. This way you can quickly discover what fits and what doesn't, also what looks right and what doesn't.
If you are working with mandrel bends then make sure that any curves used in the modelling are a match to the radius of your pre-bent items, then go to it. Lean angles, clearances and intersections points between curves and straights can all be determined quickly from the flex pipe model.
Glen
I bought enough to do a mock up for $25. This way you can quickly discover what fits and what doesn't, also what looks right and what doesn't.
If you are working with mandrel bends then make sure that any curves used in the modelling are a match to the radius of your pre-bent items, then go to it. Lean angles, clearances and intersections points between curves and straights can all be determined quickly from the flex pipe model.
Glen
Attachments
Marquez would be a better test, but that was the great thing about the Egli when it was introduced. There were owners who loved the bike, but wanted to go around corners a little easier. I assume that was not measured at full compression?
David