Setting up the engine with a performance cam

How do you improve the performance of your beastie?
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Gary H
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Setting up the engine with a performance cam

#1 Post by Gary H » Mon Nov 16, 2020 12:08 am

Hi guys
I recently fitted a newly acquired cam into my 2500s engine and I've not been able to set it up.
It's has a 320 degree duration and a valve lift 1.52.....
I spent a while struggling to get it to run half smoothly and went through the usual checks of setting the rockers and the distributed timing.
When I set the rockers to 0.010 while cold (as per the triumph operation manual) and then started the car, it ran like it had very little compression, a test confirmed I was down on pressure so I backed the rockers off until I had maximum compression, unfortunately I can't remember the exact pressures but they were all up at around 160psi I think anyway.
I have recently set the dizzy timing at 10 degrees BTDC (again as per the big blue book)

It's still not right, can anyone shed any light on what I'm doing wrong?
I didn't realise till now just how wild a cam it is so I'm after any hints or tips from those in the know.

Thanks
The Mutant PAU 856R 2500s with a twist
2500s estate causes a scene and
the next headache is ready and waiting..
GAR 317C mk1 2000 'son of bomb'

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Alec
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Re: Setting up the engine with a performance cam

#2 Post by Alec » Mon Nov 16, 2020 12:55 pm

Hello Gary,

I have a Newman cam, not quite as extreme as yours at 300\280 duration (asymetric). The valve clearances specified are 14 thou inlet 16 thou exhaust. This difference to Triumph's cams is usual I think with aftermarket cams. You may also have to get a different distributor depending on which specification you have?

Have you done any other modifications to the engine to make use of that cam?

Alec
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MK1.5 2.5 P.I.
Jaguar MK 2 (Long term restoration.)
Hymer 564 Motorhome.

Gary H
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Re: Setting up the engine with a performance cam

#3 Post by Gary H » Mon Nov 16, 2020 6:38 pm

Hi Alec
This cam is a holbay/ Carlow engineering cam.
What I’ve done so far is port-matched the cylinder head to the exhaust manifold which is a TR6 twin outlet manifold coupled to twin SS straight through exhausts.
Other then that and the cam there’s no other mods to it.

What sort of distributor would you suggest?
Any info is greatly appreciated 👍🏻
The Mutant PAU 856R 2500s with a twist
2500s estate causes a scene and
the next headache is ready and waiting..
GAR 317C mk1 2000 'son of bomb'

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Alec
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Re: Setting up the engine with a performance cam

#4 Post by Alec » Tue Nov 17, 2020 9:52 am

Hello Gary,

once you modify the engine it is a bit of guess work as to what distributor you need. There is a difference between injection distributors and carburettor distributors, with from memory, less total advance with injection engines.
I think you will need to go for a higher compression ratio as well, is the 'S' on 13/4" S.U.'s ? Anything smaller would limit the cam's potential I would say?
Can Carlow Engineering offer any advice? (If they are still going?)

Alec
0465

MK1.5 2.5 P.I.
Jaguar MK 2 (Long term restoration.)
Hymer 564 Motorhome.

Gary H
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Re: Setting up the engine with a performance cam

#5 Post by Gary H » Tue Nov 17, 2020 3:15 pm

I had a quick look into Holbay/ Carlow engineering with very little found so I’ll have a more comprehensive search later on.

It’s running it’s standard SU carbs atm. There was a plan for an engine swap from a non triumph donor but that wouldn’t happen until the end of next summer at the earliest. I’d just like the damn thing to run a bit better is all.
The Mutant PAU 856R 2500s with a twist
2500s estate causes a scene and
the next headache is ready and waiting..
GAR 317C mk1 2000 'son of bomb'

Mike Stevens
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Re: Setting up the engine with a performance cam

#6 Post by Mike Stevens » Wed Nov 25, 2020 10:43 pm

The standard 'S' CAM was matched to the long inlet manifold. The long inlet manifold combined with a long overlap CAM will cause the inlet charge to go back and forth through the carbs at tick-over, each time drawing in more petrol. This means that setting the idle mixture will be very difficult and it will always be 'lumpy' at idle. Almost certainly the carb needles will need changing. CW may be able to help with this. As the revs rise, the engine note should smooth out.

Alec has mentioned the very low CR on the 'S' head and this would benefit from being raised.

The CAM manufacturer should supply timing information and valve clearances. If it is an asymmetrical CAM that would require different valve timings. The valve timing for a non-standard CAM can really only be set properly with a timing disc on the front engine pulley with bits of bent wire bent acting as pointers. Also a dial gauge will help.

An interesting project though. I have an SAH 357 CAM in an old PI engine (actually a CP TR6 engine) which ran very well on injection especially with a bunch of bananas exhaust manifold and straight through exhaust. Prior to that I ran the same engine (with the standard early TR6 CAM) in a Mk1 2000 with twin 1.5" Strombergs on a short inlet manifold. That was also very lumpy at idle but flew away from the lights! Mind you, the 4.1 diff probably help that a bit.

Good luck!
Cheers,
Mike.
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