Hi, I've updated the list of Dolomite Sprint cams and uploaded it on triumphowners.com. See here: Cams Dolomite Sprint
As before, all specifications are collected from various sources and as such are for reference purposes only. Note that the valve lift figures are a rough guide, as with some suppliers it’s not clear if camlift or valve lift is quoted and to make things more complicated, all suppliers use different valve clearances for the different cams they offer
If someone can add info or measured his/her camshaft, I’d be happy to update the list.
Thanks for the info, I have about 10 diferent versions in my about 40 cam stock, and ofcours my own mesuring data, so maybe I can give a few a name now.
You did not mention the F3 double lobe cams though.
The cam is basically the Group 1 STR cam with 2 profiles on it. The centre of the lobe, approximately 12 mm wide, is ground differently to the rest of the lobe. This leaves 2 outer sections on the lobe approximately 4 mm wide to operate the inlet bucket, and the rocker fits in between these outer sections and operates the exhaust at different (advanced) valve timing. The rockers would need to be narrowed slightly to run in the "groove". This would allow more overlap to be acheived and more exhaust valve advance.Swindon did this with their F3 engines. I had a cam ground to this profile locally, but have never got around to using it.
I believe that the F3 motors had air restictors which limited the horsepower to about 160bhp. I know that you said you have not used the F3 grind, but do you believe that there would be an improvemnt over a Group 1 if there was no restictor?
Hi Mark, I am thinking there would be an improvement. I know from parts I got from Holbay that they did a lot of work on rocker profile to try to improve exhaust valve timing. I checked a Sprint cam some years ago and found that the exhaust duration was quite a bit less than the inlet (from memory about 75-80%) and that the exhuast closed quite early after TDC, leaving very little overlap to assist in dragging the inlet charge in. My object was to increase the open time of the exhaust valve and thus the ovelap. One thing I was concerned about was the narrowness of the outer cam lobes and what effect they would have on wear of the buckets. I would possibly have fitted a spray bar to better lubricate the cam. Unfortunately I never got very far as other distractions cropped up. I certainly think it would be worth a go
Hmmm the inner exhaust cam must be small enough to fit entirely within the inlet cam so it must have a smaller base circle. Could mean the rockers are significantly different to normal then unless it can all be taken up in the shims & buckets. Interesting. I wonder if any of the design drawings exist still.
tinweevil wrote:Hmmm the inner exhaust cam must be small enough to fit entirely within the inlet cam so it must have a smaller base circle. Could mean the rockers are significantly different to normal then unless it can all be taken up in the shims & buckets. Interesting. I wonder if any of the design drawings exist still.
Unless the cams were made that way from the billet, when they would only need normal shims.
The two profiles are ground onto the one lobe and the base circle is not altered. the cam is ground as per normal, and then the centre track is ground using different timing with a narrow stone. Any alteration is in camshaft degrees which are effectively twice the cranksaft degrees. The cam is not altered that much.
In my stock there are 5 of these cams, one is still fitted in a complete F3 engine.
There are 2 types of rockers used, simply modified standard ones, grinded smaler, and total new ones machined out of a billet.
No I never used them, but my friend Bunkes from Hamburg did not find them from any use for his engines, becouse the F3 engines did not rev that high becouse of the air restrictor, as far I know that restrictor is 28mm ??
Bdw the base circle is smaler, and the cams (exhoust part) where griended with a special very narow stone.
On the used altered rockers you can see some wear, and I think for a road tracday car the wear will be far to much, meaby special light valves and springs is the way to go.
I will try them in the future, but the improvement with the coatings , H beam rods, Wosner pistons 12.5 comp ratio etc will go first after my hart surgery.
Hi Hans, I hope your heart problems were not caused by the stress of racing a Triumph. I hope your treatment goes well.I understand what you are saying re the F3 cams. The grind was to maximise torque, not HP at high revs. The F3 cams were not much different to a fast road cam in timing. When I ground my cam I had it ground to a Cosworth BD4 grind, which is very similar to a Group 1 cam. As I said my main concern was with wear on the rockers and followers etc, although modern oils may help that. The other thing was that the car was going pretty well as it was so there was no need to get into a whole new set of problems.The other modification I was looking at was to fit Kugelfischer mechanical injection off a Peugeot 504, but that was put on hold also.
10 years ago my car had a Road cam TT10104 installed. Recently I encountered a serious Cylinderhead problem. Valve guides have worked loose in the head, a spring is tired making contact between piston and valve. In other words, head scrab and I need a new one. My question is, does this cam really improves horsepower, as my car is as original, with standard carburettors and exhaust. What do I have to do to take the most bebefit of the cam? I need a new head, but I would want to retain the cam if it is of real benefit. I Can someone tell me what is the correct cam timing and how to establish the correct timing?
