CAM choice

[Stevo302]

Hi guys,
Thinking of getting one day a new CAM for my 1971 Vixen 2500.
I have so far, stage 2 head, 6 branch manifold with custom system, STD HS6's carbs.
All I want to do to the engine is up-rate the carbs to HS7's with matching inlet manifold, Up-rate ignition to Mega Jolt (Or something like that) and up-rate the CAM. That is plenty, then rolling road it.

Which CAM would be recommended for the above, any ideas welcome, even if i am waisting my £time. This is for a road going car.

Cheers,
Stevo.

[Slow M]

From memory, the cam that felt the most aggressive (poweful, torquey, push you back in the seat) was a Kent 282. I fed it via 3 dual throat 42mm SKs.

I would recommend, that you also look at Richard Good's triple carb manifolds.

Best,
B.

[Mr Tiger]

Hi Stevo,
I'm very interested in your post. I've got a 1971 Vixen 2500 too. I've had mine about nine months so I'm in no position to offer advice sadly.

I've been considering a tubular manifold (amongst other things) and was wondering if any will fit and clear chassis rails without any bending?

What compression ratio does yours have and do you know the bhp and torque it's currently developing?

Mine's mostly standard (excuse the pun) except for HS6s and K&Ns. You mention HS7s, do you mean 2" HS8s as fitted to E-Types?

Is yours the blue one with gold wheels on the Vixen Register?

Cheers,

Chris

[Stevo302]

Ive sent you mail Tiger. Same car but with black wheels now and better std fitting tyres.

What about the TR5 CAM heard that one is good......but where would you get it from?

Regards,
S

[Slow M]

Stevo302 said:

Ive sent you mail Tiger. Same car but with black wheels now and better std fitting tyres.

What about the TR5 CAM heard that one is good......but where would you get it from?

Regards,
S

High ratio roller rockers will accomplish a performance gain. The up-side is that you would only have to remove the head, to perform the work. Could go for a little shave, while you're at it. Also requires an external line to be added, for additional oiling.

Best,
B.

[Hansoplast]

Slow M said:

igh ratio roller rockers will accomplish a performance gain. The up-side is that you would only have to remove the head, to perform the work. Could go for a little shave, while you're at it. Also requires an external line to be added, for additional oiling.

Best,
B.

Hi there,
Being a long time TR driver, I have heard from the Triumph technicians that a external oil feed to the header is no good.
Every time you start the engine there is not enough oil for the head and crank.
That will lead to extra
But I also know that some others have another idea.
Feel free to do what you like.
You won't find roller rockers in racing TR's either by the way. Their max ref is not that high and the cams not that sharp. (6 cilinder I mean)

Good suppliers are TR Revington and Restorations. They are happy to inform you and both well known on the circuit.

Hans

[Slow M]

Hansoplast said:

Hi there,
Being a long time TR driver, I have heard from the Triumph technicians that a external oil feed to the header is no good.
Every time you start the engine there is not enough oil for the head and crank.
That will lead to extra
But I also know that some others have another idea.
Feel free to do what you like.
You won't find roller rockers in racing TR's either by the way. Their max ref is not that high and the cams not that sharp. (6 cilinder I mean)

Good suppliers are TR Revington and Restorations. They are happy to inform you and both well known on the circuit.

Hans

Hans,

In doing my due diligence and my research, I spoke with Glen Effinger, and J.K. Jackson, as well as Lanky Foushee. There are few individuals so steeped in the canons of Triumph racing, in the US, as those three. I also spoke with the (uncredited) designer of Crane's Gold roller rockers, one of the most successful such product ever to be sold.

First of all, there is no minimum RPM, where roller rockers become effective. Having said that, you should know that I've heard the glorious sound of a TR6 engine screaming into the high 7s.

Here is a fact to consider: an old paper, published in the annals of the SAE, stated that as much as 80% of engine wear occurrs within the first couple of minutes after start-up. This is universal among all internal combustion engines, and relates to the fact that oil, being a liquid, likes to drain away from the parts it's intended to lubricate. It does so, especially, in an engine that's been warmed up properly, and it especially hates to pump when it's cold. This is not a unique feature to Triumph engines, or to the TR6 unit.

One work around, is to install a pre-oiler, such as an Accusump (I did), which, when used at start-up, pre-pressurizes the oil galleries, before the engine turns over. Another, and the one I prefer, is to install an electric pump, with a one-way valve.

The actual worst effect of installing increased ratio rockers, be they roller tipped or not, is the increase in pressure on the cam lobe. None the less, this is probably offset by how much deeper into the base circle a lobe would have to be ground*, to arrive at similar valve timing events. Furthermore, and much more importantly, roller tipped rockers are a performance enhancement, because they reduce friction. This is the result of a three-fold effect.
1. The friction of the rocker tip dragging across the valve tip is virtually eliminated.
2. The resulting side loading of the valve stem, and the associated stem and guide wear, are greatly reduced.
The reduction in parasitic drag, or elimination of frictional losses equates to freeing up lost power.
3. The friction reduction on the valve train reduces the forces acting on the cam lobe.

In a straight six that has the camshaft driven from one of the ends, this means an increase in distortion of the valve timing events, as you look further along the camshaft. This is why you frequently see long, skinny camshafts driven from the center. (Ever looked at a bike?)

Another positive effect of an increased ratio rocker, is that it effectively increases the lobe ramp angles beyond what can reasonably be accomplished at the lobe/follower interface.

In summation, the net effect would be a positive one, on the valve train, rather than a negative one, on the crankshaft.

* For a long time, there were no Cam blanks available, and people only offered regrinds. This meant grinding deeper into the base circle, locally reducing the camshaft diameter, and thereby its ability to resist torsional forces.

Now, having ranted to my pedantic little heart's desire, I will also disqualify myself, from being in a position to advise on building a "proper" Triumph big six, and would suggest, that the people I originally spoke with, would be the ones to contact.

Best,
B.

Edited by Slow M on Saturday 1st March 15:16 -added summation

Edited by Slow M on Saturday 1st March 15:17

[kermit1300]

Try Moss Europe they do a fast road 83 cam which is not too radical and ok for general road use

[Hansoplast]

Wow B,
Your answer gives so much technical knowlegd that mine is overshadowed.

Mine is based on hearing and reading stories from others.
I think you will find the right way.

Happy to hear how the Triumph engine will be up graded.
What I have seen on the circuits the four cilinder are quicker.

Have Fun.

Hans.

[Slow M]

Hansoplast said:

Wow B,
Your answer gives so much technical knowlegd that mine is overshadowed.

Mine is based on hearing and reading stories from others.
I think you will find the right way.

Happy to hear how the Triumph engine will be up graded.
What I have seen on the circuits the four cilinder are quicker.

Have Fun.

Hans.

Hans,

That was years ago. Now, I'm on to the V8.

Best,
B.