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Suitable cam for 2.5 PI fitted with SU HS6 carbs


Mark GT6
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Hi,

 

I have a Mk3 GT6 fitted with 2.5l PI engine and SU HS6 Carbs. I have been told the engine will run better if fitted with a GT6 Mk2 cam shaft. Any idea where I might be able to lay my hands on one. Rimmer Bros advertise new a cam suitable for Mk2 and Mk3 engines. I though cams for Mk2's and 3's were different. Would any of the Kent cams be suitable.

 

Any help would be gratefully received. Mark

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teh mk2 and early mk3 are the same. 35 65 IIRC, and yes a bit smoother. 

However, which PI engine do you have? many of the saloon PI engines had that same cam, the TR5 and 150bhp TR6 had the racier cam, but that will work with carbs too. Just a bit lumpier at idle. 

 

Newman cams are THE cam people to go to at the moment......

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I have a Vitesse with a 2.5 PI engine and HS6 carbs.

With some head work,a decent manifold and being properly built it produced 172BHP at 5800Rpm on the rollers,its a really strong engine.It has a TR5 cam and a CR of 10:1.Its also not bad on fuel.

 

I fitted a saloon box and J type o/d along with a 3.27 diff with Jones/Bowler CV shafts.

 

To source a cam try Newmans in Bromley,they will do any grind for you.

 

Currently using a standard Vitesse distributor with no advance(it pinks too much)I plan to fit a 123 Tune soon.

Runs exclusively on Shell V Power fuel btw.

Steve

 

Clive beat me to it there,also the lumpy idle thing isnt true for mine,it will sit smoothly at 800rpm and pull from low revs no problem.

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Hello Mark

                I fitted one of these to my brother in laws TR6(US)

It has a 3 into 2 into exhaust about 9 to 1comp,  K&N s and a ported head

And it made 130bhp on the rollers.

 

http://www.chriswitor.com/proddetail.php?prod=CW3021EX

 

Chris Witor said stick to about 9 to 1 comp less chance of pinking and going to 9.5 to 1 only gains about 5bhp I think he said

 

I have now fitted Megajolt ignition and he says it is even better and smoother tick over.

 

Roger

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Thanks for all your help,

 

I bought the car with engine fitted and was told it was out of a saloon car. The only upgrades that have been done to the engine is the fitting of a stainless exhaust manifold and sports exhaust. The problem I am having is getting a stable reliable tick over, without the engine cutting. I have replaced the distributor and the electronic ignition module. The carbs have been rebuilt completely, plugs, leads and distributor cap have also been replaced. I have reset the valves and checked cylinder compression pressure and the tick over problem still remains, hence the focus on the cam. As I will be taking the gearbox and overdrive out shortly to be rebuilt, I thought it might be a good opportunity to deal with replacing the cam. I will take all your advice and contact Newmans for their views.

Are there any other performance upgrades that I could do without having to get the engine rebuilt. Would fitting a stage 2 head be of any benefit.

 

Thanks again for all your help, Mark

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Stage 2 is meaningless. You want to know what has actually been done.

 

First thing to do is find out what you actually have, so use the engine number to start with. Then measure the head depth, the figures are out there for the various type of head. That will tell you if it has been previously modified by skimming.

 

Finding which cam you have is harder, but can be done. Do your research.

 

If it is from a late saloon PI, it may have the 18/58 cam which is very "soft", lots of torque so ideal if in a saloon and towing a caravan. Less ideal in a sports car where you want it to give more performance and don't have to pull all that weight around.

 

Chris Witor is a handy chap, have a look at his website.

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Pete the MK1PI had teh mk2 engine fitted, hence 2.5. A very late development (test bed??)

 

A friend runs a MK1 PI (cr) engine in his GT6 on SU's. A std engine but well screwed together, plus a spawn of satan 6>2>1 manifold. That produces in excess of 130bhp on the rollers (think flywheel figure) so not shabby.

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http://www.chriswitor.com/cw_technical/camshaft_applications.pdf

 

that reckons you have the same cam as teh GT6/vit mk2

 

And I apologise, I slipped up earlier. The TR5 cam is the 35 65, wheras the Gt6 etc one you have been recommended is 25 65. 

I believe Witor does a special cam too, have a browse through his stuff.

 

But you should have the beginnings of a very decent engine there with potentially not a lot to spend.

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