Horner Vincent engine modifications.

greg brillus

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The modified steering stem thread has some posts about the various mods the Horner brothers did to their Goodwood bike. Some of the mods are relevant to the steering stem thread and some to engine modifications. I have created this new thread to hopefully make it a little easier to follow the different aspects. Initially I will probably move some posts but some posts may be duplicated as they address both aspects. Eddy.
Greg Brillus wrote: Funny how to keep it fair the organizers decided it best if the Horner's not bring the Vincent back to race at Goodwood. We all pretty much know how "Modernised" all these new build Manx's are, what with modern fork internals, engines that put out 70 plus HP and so on. In reality the Horner's modernized the Vincent to some extent, and some parts at great expense. I was told the cost toward the front end changes alone was in excess of $10,000 plus the rear Ohlin's coilovers on the rear were $5000 worth. The upgrades to the engine were quite realistic but the costs involved well beyond the average Vincent builder including myself. But I can see how they got 96 HP out of the 998cc engine with no trouble except the primary chain not having the strength needed. The organizers at Goodwood were completely wrong with their assumption, though the capacity of the bikes should be separated like other categories. The changes to the front end are similar to what we have done, but ours at much lower cost. Remember too that they employed the help of a Bike suspension guru from Sydney for assistance with the upgrades, probably due to limited time to get the bike ready. It's a great pity that the bike is retired and just sits in their collection not being used any more.
 
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Bill Thomas

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Hello Greg, Maybe you can tell us , On another thread, How they got another 26 bhp ??, Not that I think they did !, Or needed to. I have been told , You can get alsorts out of a Dyno. Cheers Bill.
 

greg brillus

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Hi there Bill, Happy new year to you........sorry I didn't really want to drift off topic, although the suspension was the link. I was just comparing the difference between what the Horner's had created verses what we are discussing on this thread. I guess anything special as a "One off " is going to be costly, but given the Horner's have a full CNC machine shop, they can produce fabulous bits of gear, as anyone who has actually seen their bikes in person can attest to. This is one of the main reasons why they don't sell anything or produce road bikes, because they are very custom made, and spares would be near impossible to get and very costly to produce. I do know of some of the tricks they put into building the Goodwood Bike's engine, but I'm not entirely sure if I would be allowed to discuss it. Unless others out there can advise otherwise. Lets just say it had a lot more done to it than when I built mine, not stuff that's rocket science, but quite costly just the same. Cheers...........Greg.
 

Bill Thomas

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Happy New year Greg, You know I am always looking for More Power, Don't know why !.
Still can't get my head around those Monoblocs !!, I bored one out for my Comet, And it killed it stone dead !!. All The Best Bill.
 

greg brillus

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Yes Bill, I think sometimes we forget how delicate an instrument that a carby is. You probably lost some of it's Venturi affect, and that may be why it did not perform as you expected. I have seen Vincent's with 1 1/2 GP's on them, which for a relatively slow revving engine, seems over the top to me.
 

hadronuk

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There is a very interesting talk by the B.Johnston, who in 1978 was technical manager of AMAL Ltd here:

http://velobanjogent.blogspot.co.uk/2011/11/further-full-look-at-scientific-paper.html

Talking about the new Monobloc he explains that: “A substantial improvement was achieved by the introduction of bleed holes in the needle jet component. These served the dual purpose of assisting the compensation characteristics and allowing fuel to collect in the annular space around the needle jet to form a reservoir at small throttle openings which is available for acceleration.”
I found that with my completely standard Rapide engine the sharp intake pulses at tickover caused this fuel to be sucked in irregular splashes into the air flow, making the accurate calibration impossible. Starting and performance above ¼ throttle were first class, but this incurable slow speed problem made the Monoblocs unusable. It remains a complete mystery to me why Monoblocs work fine on some Vincents but not on others. It is interesting that Johnston also says that Monoblocs that did not work well with high performance two strokes. Perhaps this was also due to sharp intake pulses? One other point of interest. “The concentric, Fig 4, is a good example of value engineering. To achieve a major cost saving the jet block was sacrificed; as expected the resulting irregular bore shape reduced the absolute power by an average of between 2% and 4% depending upon application, but usually only at peak torque.”
 

champion

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I have read several of the post race interviews. One four page long article in Classic Bike Magazine. The second was an interview in an Australian classic motorcycle racing magazine (I believe it was on their facebook page for a while.)
From memory they spent a lot of time doing flow analysis through the head, used Prince castings which they then ported to their own design, including a much smaller inlet valve. One of the articles implied that the combustion chamber design was based on Australian V8 racing engine design.
The articles also acknowledged that standard front suspension geometry is incorrect on a Vincent which is why they modified it, one of the other main things they modified was the oil feed. Which the described as totally inadequate, especially to the cams. After 'accidentally' gate crashing the riders welcome party, I spent a lot of time talking to them at the Revival. The aspect of the bikes performance which they felt really was not fully developed for the start of the race was the front brake.

I have a few more photos of the bike somewhere, will dig them out at some point.
 

davidd

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I don't think the mods to get the HP were secret, they are just difficult. They did a lot to get the head to seal. They probably based the compression on the fuel they were allowed to use and the compression could have been very high. With only four head bolts and no bridge between the valve towers the Vincent head flexes quite a bit and leaks out precious power at high compression. Higher CFM's would give them certain power. Higher revs would help the cause also. Heat is the big problem and some oil jets squirting up to the piston crowns would allow them to keep more of the power they found.

David
 
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Bill Thomas

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In the late 70s, I had 12 to1 pistons on my special, On Petrol, But then we had 100 octane petrol at the roadside pump, I raced and used it on the road and it went very well !!, I used 24 degrees ign advance and maybe ran it a bit rich to keep it Cool, It was a nice bike to ride. Cheers Bill.
 

champion

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Sorry I feel the conversation has been dragged off topic, which was not my intent.
 

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