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Gt6 mk3 cam decision?? Tr6 or mk2??


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Hey guys. I found my self in a rebuild after redoing the whole car. It's not a full restoration or anything just a refresh. 

Anyway. I found the cam pitted and lifters pitted. :(

bottom end is all good. Checked it out. But I'm in decision time on what cam to use. 

1# oem cam. Which is tough to find

2# mk2 cam. Which is a better duration cam. Was told no other items needed ( other then new lifters ) more of a drop in cam. Will work with the original carbs. Needs to be timed advanced. 

3# try cam. Which is a drop in cam, but needs shortened push rods, was told 0.30" rods needed. Also apparently wont work with the original carbs needs tr6 carbs or u.k 150s with adjustable mixture. Also timming needs adjustment. 

The easiest is the mk2 cam, I can get. The tr6 is more work, more cost due to added parts. Gt6 mk3 cam is tough to find. Stock. Might as well do the mk2? 

Any info on these would be great help!!! 

I am leaning towards the mk2 cam as cost and time is an issue. Carbs are expensive. 

I'd love to hear what I have to do to install mk2 cam and a tr6 cam. 

If I'm missing anything.

Thanks

Cheers.

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For a minimum hassle upgrade on a street driving car, I would say that the the Mk2 308778 cam is a great option if you can get one.

For a slight variation on that, Chris Witor sells one with the same timing, but increased lift, which is reported to work well. 

Or a Newman PH1.

When you say TR6, there are at least 3 different ones used.

PI 150 (CP series) which won’t play nicely with CD carbs.

PI 125 (CR series) & at least one US spec one, neither of which brings any advantage over the MK2 cam.

Don't see why any of the TR6 cams would need different pushrods.

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Thanks for the insight!!! Much appreciated.

I was told that a tr6 injection cam is a mild cam upgrade. Some say that the lift is more so would need push rods to be shorter, was told others have shimmed the rocker shaft for the extra space. I'm not sure. Reason for need answers. As I'm ready to get one to finish the engine. 

With that was told the 150 carbs o have are u.s carbs not u.k so I dont have ability to adjust them so wont work on this tr6 cam. 

I was leaning on the mk2 cam as I'm told it's a drop in with no replacement of other parts. Except the lifter of coarse. 

It is a street car, would do an odd track day for fun but it's more a spirited driving car not a race car. All stock drive train with a swing spring out back. 

So with the mk2 cam. What's needed to use it in a mk3? 

I've heard the timming needs to be advanced abit? Other then that it should be a straight install? 

Appreciate the feed back. 

Also it's a flat top piston engine. Was told that's a u.k? Then heard the u.s models had that as well? They are better then the cone etc.?? 

Oh also, I have 10 thous end play on my crank, most say that's good. Some say it's in spec but shim it. What is your take. Vid posted.

Cheers.

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Hello Superman,

 

different length pushrods are used for different head thickness, e.g. the P.I. head has  a smaller overall height than others so uses shorter pushrods to maintain the rocker adjustment.

Don't shim the rocker pedestals, again this was used when heads were skimmed but it was a mistake and did nothing except upset the rocker geometry.

Without checking the manual, but off hand I would say that's too much and can only get worse. Selective assembly with new thrust washers  would be my route.

Alec

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Agree with the above.

All factory cams have the same base circle. Aftermarket cams ground on new blanks are also likely to. Re-profiled cams will have some reduction of base circle and for these there is a weak argument for longer pushrods. In practice there is plenty of adjustment at the rocker and the difference in geometry is negligible.  Bottom line.... use the pushrods that match your head thickness.

The later TR6 injection cam has the same timing as the later GT6 Mk3 cam but 20 thou more lift. Good for low end torque but it’s all over by 4,500 rpm. The early one is a lot more aggressive and has a fair bit of overlap so will give a very rough idle and bottom end with CD carbs due to reversion.

I note you say your engine has flat top pistons. This makes it a very early Mk3 or possibly a transplant from a Mk2. Can you find a part number on your old cam?

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

As regards the endfloat, I’d be very happy to see that number on an engine that has been run. However, a bit less happy on an engine in build because experience suggests that you usually gain a 2 - 3 thou more during the bedding process. I like to see 5 - 8 thou. 10 is a bit of an awkward number as even a 5 thou oversized washer risks making things a bit tight. I have been known to use a used washer (the front-side ones are usually in good shape) to gain the odd thou.

If any of the washers you have are more brassy coloured, use it on the harder working flywheel side.

If your ocd is fierce then there is this

http://www.customthrustwashers.com/

posting as a satisfied customer 

 

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On 2/21/2021 at 5:28 AM, 2.5piman said:

Hello Superman,

 

different length pushrods are used for different head thickness, e.g. the P.I. head has  a smaller overall height than others so uses shorter pushrods to maintain the rocker adjustment.

Don't shim the rocker pedestals, again this was used when heads were skimmed but it was a mistake and did nothing except upset the rocker geometry.

Without checking the manual, but off hand I would say that's too much and can only get worse. Selective assembly with new thrust washers  would be my route.

Alec

Thanks alec

Yes I finally got the proper specs. 4 to 8 thous. I'm going to use standard shims and .005 to get to around 5 or 6 thous. 

No, I will not shim the rockers. It was just said to me in chats. Was told by tony lyndsey-dean that the cam will go right in with out shorter rods. My head has no shaving done. So should be normal thickness. I double and triple checked lol. Was told no it will work with out that. 

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On 2/21/2021 at 6:14 AM, Nick Jones said:

Agree with the above.

All factory cams have the same base circle. Aftermarket cams ground on new blanks are also likely to. Re-profiled cams will have some reduction of base circle and for these there is a weak argument for longer pushrods. In practice there is plenty of adjustment at the rocker and the difference in geometry is negligible.  Bottom line.... use the pushrods that match your head thickness.

The later TR6 injection cam has the same timing as the later GT6 Mk3 cam but 20 thou more lift. Good for low end torque but it’s all over by 4,500 rpm. The early one is a lot more aggressive and has a fair bit of overlap so will give a very rough idle and bottom end with CD carbs due to reversion.

I note you say your engine has flat top pistons. This makes it a very early Mk3 or possibly a transplant from a Mk2. Can you find a part number on your old cam?

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

As regards the endfloat, I’d be very happy to see that number on an engine that has been run. However, a bit less happy on an engine in build because experience suggests that you usually gain a 2 - 3 thou more during the bedding process. I like to see 5 - 8 thou. 10 is a bit of an awkward number as even a 5 thou oversized washer risks making things a bit tight. I have been known to use a used washer (the front-side ones are usually in good shape) to gain the odd thou.

If any of the washers you have are more brassy coloured, use it on the harder working flywheel side.

If your ocd is fierce then there is this

http://www.customthrustwashers.com/

posting as a satisfied customer 

 

Thanks nick! 

Ya I'm going to shim it up to around 5 or 6 thous. I'm hoping standard washers will be good. Should. Lol.

I've chatted with tony lyndsey-dean alot on the cam, not sure you know him or not. He is based in u.k does race cars etc has a shop as well, does parts. He has told me that the cam is a tr6 pi injection cam, will drop in and use my push rods. So thats good. Basically what you have talked about. I actually dont mind the lower end torque to the top end. I do more spirited back road driving. I've never taken the car on a hwy dont think I will, rear end and trans gearing make it scream. Lol. I've hit 5k rpm once. Lol. 

Also going to run the dual chain setup which will be better as well. 

My car is a 73 mk3. Original engine. With flat top pistons, u.s car. Read somewhere that said the u.s versions came with the flat top?? I have no idea. 

I was told there was no reason why I couldn't get 120hp to 125hp put of it with the cam, ignition,  carb jetting. 

I am hoping 115hp. It would make the car very fun. Lol. 

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TLD is well know in UK Triumph circles.  Has been in the game since the late 70s that I know of (Kingston Sports Cars), maybe longer.

He certainly talks a good one and he does definitely build good diffs and gearboxes.  You'll find opinion a little more varied on his engine tuning views.

I say again - there are two TR6 PI injection cams.  The early "CP" one has 35/65 timing and .250" lift.  You do not want that with CD carbs.  The later "CR" one has 18/58 timing (same as GT6 mk3, 2000, 2500) but with .240" lift.  I assume this is the one he is steering you towards?

Would not be my choice.  If sticking to standard Triumph profiles I would choose the 308778 as used on Mk2 Vitesse, Mk2 GT6 (and maybe early Mk3) and also the earlier 2.5PI saloons. 25/65 timing (270º duration) and .232 lift.  Or the Witor one with more lift on the inlet.

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2 hours ago, Nick Jones said:

Would not be my choice.  If sticking to standard Triumph profiles I would choose the 308778 as used on Mk2 Vitesse, Mk2 GT6 (and maybe early Mk3) and also the earlier 2.5PI saloons. 25/65 timing (270º duration) and .232 lift.  Or the Witor one with more lift on the inlet.

Hello All

              I would go for the 308778 or Witor one (I fitted one to the brother in laws TR6 with SU's) and it worked well and even better when I fitted Megajolt for him(Then the Pratt went and sold it!!!!!!!!!!!!)

I have just fitted a Witor one in my Vitesse engine but with extra lift on both lobes!

I also ran the 25/65/65/25 profile in my 1500 Spitfire and it worked well.

I fitted a Newman PH2 to the new 1500 engine but it does run Micro squirt EFI so is ok not sure how it would be with carbs.

The 18/58 is an emissions cam to satisfy the US market I think?

Roger

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So decided on the mk2 cam instead of the injection cam.  Just easier for me not messing with carbs and other issues that may occur or show up with the ip cam. 

Beside with the mk2 cam it seems I'll gain quite abit more anyway over the stock cam even if it were new. 

Then I can later on tune the carbs etc.. the engine I'll take to my buddy's shop and set it on his stand to be broke in as well. So he will fiddle with that then. 

Hopefully soon I can get these here, just waiting one full price for it all shipped here. 

Thanks for the help, much appreciated!!!

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