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Terry Prince 1350/1360 on the dyno

Re: Terry Prince 1350/1360 on the dyno

Postby worntorn » Wed Apr 08, 2015 10:52 am

The MK5 cam from Terry Prince is the first computer designed cam for Vincents, as far as I know. It came about after Terry had a discussion with his godson, Fritz Egli Jr., son of the famous Egli frame designer. Fritz Jr. was lead engineer on the Mercedes Formula One racing team until recently and as such had use of the team's cam development program, a very expensive piece of software.
Fritz offered to use the software to design a high performance cam specifically for the stretched Vincent top ends that Terry builds. Terry gave Fritz Jr. all of the relevant data and Fritz plugged the numbers into the program. The result was this MK5 cam which both Terry and I have used on our 1360 bikes, but not many others have. I believe Mal Hewett also uses the MK5 on his Vincent racebike which just set a new speed record on Lake Gardiner.
Some of Terry's previous cam designs (he has tried a great many) used a lift at valve figure as high as .50" however the Mercedes F1 program said that there would be no improvement in breathing beyond a lift of. 440" for the rpm range and other parameters given, so that is where the. 440" number came from.

The MK5 cam when tested on dyno far exceeded power output from any other race cam Terry had tried. He was at first unwilling to sell them to me for street use, thinking they might be unsuitable in the lower rpm range. After running his racebike for awhile with the MK5s installed he decided they would be tractable enough at low rpm for street use. It turns out that the bike idles quite well, though it is a lumpy idle, and pulls away easily with very light throttle. From 2000 rpm on up it pulls extremely hard and throttle response in general is quicker than I am accustomed to on either my litre sportbike or the vintage bikes here.


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Re: Terry Prince 1350/1360 on the dyno

Postby WZ507 » Wed Apr 08, 2015 11:22 am

Regarding the head you are running, have you ever seen (or measured) the airflow curve as a function of valve lift, and if so, does airflow maximize by 0.440" lift?

Apologies for prying into every nook and cranny of your project, but every tidbit helps me better understand engine performance. Thank you.
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Re: Terry Prince 1350/1360 on the dyno

Postby worntorn » Wed Apr 08, 2015 6:28 pm

No apology required, I appreciate the interest, just wish I had more detailed info.

When I ordered the top ends from Terry he told me that the heads would not be cast until he had made changes to his existing patterns, which are an evolution of high performance Vincent heads he designed in the 1980s. He was in the midst of flow testing several new prototypes when I made the order. The best shape/design would be the type chosen for a batch of fourteen heads he planned to have made up, two of which were for my engine.
Terry has reconfigured the 1980s design several times over the years, then tested the results on his own bike both on dyno and on the salt. Around 2007 he sold smaller sized set of these heads (he has 84 & 92 Mm sizes) to the machinist/motorcycle racer Steve Hamel who wanted to revisit Rollie Free's Bomneville record of 1949. Steve wanted to see if he could break Rollie's record, but do it on pump gas rather than the alcohol fuel Rollie's Lightning ran. Steve revamped Terry's high performance heads considerably and upped the output of his 998cc machine to over 100rwhp then with further mods 120 rwhp. Here is his bike at the 100 HP stage. https://m.youtube.com/?#/watch?v=z6SpCobouDc
He did break Rollie's record with that bike.
This made Terry take notice, so he incorporated some but not all of Steve's modifications in another new design, the one he was busy flow testing when I made my order in early 2010. I received the heads in early 2011. Terry did not incorporate all of Steve's changes as Steve's is a/Bonneville racer, top end only type engine and Terry wanted to keep a strong level of midrange power with his design. I can attest to the fact that he got that right.

So all of the R&D has been done by Terry Prince and Steve Hamel , some of it going back to the 70s. That's what make these top ends relatively good value, it's not so much the foundry work and machining which goes into a current set as it is all of the expensive R&D that went on to get here., much of it trial and error I'm sure.

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Re: Terry Prince 1350/1360 on the dyno

Postby Bernhard » Thu Apr 09, 2015 7:27 am

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Re: Terry Prince 1350/1360 on the dyno

Postby ogrilp400 » Thu Aug 27, 2015 5:00 am

No, No, you are looking at it wrong. With the valve at .440 lift, the area around the valve available for flow is 2.76 sq" on a 2" circle, slightly less if you want to take it at the contact point with the seat. With an 1.3/8" port behind that valve, the cross sectional area is 1.48sq". So you can see the valve at .440 lift has the capacity to flow far more than the port will allow. Most likely the valve would be flowing max port flow at about .380" lift.

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Re: Terry Prince 1350/1360 on the dyno

Postby Buellingvincent » Wed Mar 23, 2016 10:37 am

Hi, found this video of a start up sequence with Terry. I assume this is the bike.

You probably all have seen this but I think it is a nice moment from Bonneville with Terry.
Terry Prince Love for Speed and Vincent Motorcycles: Bonneville Stories

/ Patrik
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