Who's Vincent/Hrd has the most power?

johnmead

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The headwork I am doing is not that radical. Just shortening and smoothing around the guides. Also, making the back of the port, at the intake valve is 90 degrees to shoot the intake directly at the edge of the valve. On the exhaust I am sutting down the guide and polishing the top of the port. I will measure the id of the ports and let you know what size they are.

The flow numbers on the stock TPV heads is not that great. Intake was 170fpm at 11.0mm and exhaust was 137fpm at 10.5mm lift. Both numbers were taken at 72 degrees F and 28 pounds test pressure. These numbers are what stock Chevy 350ci heads flow.

John Mead
 

vibrac

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I havent done a port for a while and before I do I would like to swat up on latest thinking but I am sure I read recently (perhaps in MPH) that a "straight port" was now considered more benificial than carving away the material from the wall above the seat directly facing the flow (which apart from making an apple shape round the guide is what we used to do) if thats is not the area you call 'the back of the port' I apologise. I do have a vested interest in all thoughts regarding inlet ports as I have a brand new head I have to give the treatment to this winter
 

johnmead

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The area I am referring to is the wall of the intake port where it curves down to the valve seat. Number 5 in the picture. This is a automobile head and taller than a Vincent head, but the idea is to point the flow directly at the edge of the valve to increase flow at low openings.

John Mead

0210hpp_flow04.jpg
 

Monkeypants

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There is the old school way of looking at porting and that is , "If in doubt, Port it out". A Norton tuner by name of Jim Comstock has turned that thinking on its head.
For some time now, he has been collecting heads from modified and stock Commandos to establish a flow test database.Thru dyno testing he has also learned that flow without adequate velocity creates a situation where density of charge is low, as is power output. Some of the heavily modified heads produced high hp at high rpm but very little in the middle. Some produced so little power in the middle that , when used for racing , were unable to attain the high rpm where thetheoretical big power level was.
The main thing learned was that he and others were placing too much emphsis on flow volume and not enough on flow velocity. By increasing flow volume thru porting, flow velocity is often lost. A little of this is OK, but there is a point where the density of charge becomes too low and power is actually lost due to the overly great port size.
People from all over the world have been sending their heads to him for testing and the results are really interesting. Using this information, he just built a 1007cc Commando engine which produces 85 hp at 6800 rpm and 97 ft pounds torque at 4,000 rpm!. One thing that concerned me early on about these Prince/Trease heads is that, combined with the MK5 cams and other items, the engine would be a high revving racing engine with little midrange. From anecdotal evidence it seems my fears are unwarranted. These heads are said to produce great wads of midrange power plus a healthy dose at top. They are the result of Terry's 50 years experience, John Trease's design work with a bit of Steve Hamel thrown in for good measure. That is a lot of R&D! Glen
 
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johnmead

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I have a question for this group. Has anyone enlarged the pivot hole in the rockers and pressed in an offset bushing to give more lift?

John Mead
 

bmetcalf

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Due to my inexperience, I am not able to think of a way to ensure the proper alignment of the offset. How would you do that?
 

greg brillus

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I have a question for this group. Has anyone enlarged the pivot hole in the rockers and pressed in an offset bushing to give more lift?

John Mead
Hi there John, well you could try the rocker set up that John Trease here in Australia has done to a worked Comet engine using 1.6:1 rocker arm ratios.....this works very well, but the normal type of cams and followers won't last.....must use roller tiped solid type cams/followers and a much improved full pressure oiling system to cope with this set up......mind you, this engine puts out over 58 HP Greg.
 

Brian Thompson

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Both kits have the CP pistons. The early ones are 350 grams v/s 300 grams for the later.You can see into the pistons under the crown and see machining marks from them being lightened. Also the early kits are stamped. I know i have 273 on one kit.I believe there was 350 top end kits in the first batch. Don't quote me on that.
Also the the later kits need the wider sealing surface of the liner to be filed away for the cylinder studs. Aren't the 2 piece studs a work of art? As is the 30mm crank. Almost to nice to hide away into the cases.
Cheers
brt650
 

Monkeypants

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re the crank- it is a good idea to check for runout. Mine was out four thou on one side, two on the other. Total indicated runout should not exceed 2 thou , according to Richardson. Maughans like to see 1/2 thou.
Dan Smith and I spent an afternoon beating on the crank with a lead hammer, didn't really move it.We also put in in the hydraulic press at up to 7 tons , but it was a very insecure position ,so did not want to go beyond that. The final descision that day was to leave it and run it as is. A day later and armed with info from Dan on crank truing, I had another go at it in my shop. It took fourteen tons pressure in the press to move it, but now it sits under 1/2 thou total indicated runout one side, 3/4 thou the other. I have read about people getting cranks "perfect" and considered having another go at it, but will leave well enough alone! Glen
 
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