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MKIII camshaft  for spitfire 1500 ?


popeye

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Hello everybody,
Here is the situation, I have to change my very tired camshaft of my spitfire 1500. All the lobes are completly full of nicks (the camshaft has run more than 240 000km), as the cam followers.
After an inspection, I suppose I will have to change the pistons rings too.
I have seen on the Canley Classics website a large bearings camshaft with the MKIII profile.
Here is my questions:
Is there a benefit to fit this camshaft in my 1500 engine instead of the factory 18/58-18/18?
The advance curve of the distributor might need some modifications to suit the MKIII profile, am I wrong ?
What will be the "behaviour" of the engine with the MKIII camshaft ? If someone has ever tried this fitting I will be very happy to know his opinion.
My knowledge concerning the camshafts is very poor : so, all advices are welcome and Manyn thanks by advance for all your help.
PS: I am an overseas spitfire enthusiast, so I apologize for my poor english.


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Triumph engines always benefit from longer duration cams almost regardless of the lift, due to the small valves.
The Spitfire 1500 cam is a lemon and is the same profile as the later GT6, TR6 and 2.5pi. Lacklustre.
Anyone will tell you the engines they made before 1971 were far more exciting, so if you fit the early 2.5pi/GT6 cam (which is exactly what the Spitfire 11/111 on is), or a profile from the TR5, then you get a big boost in torque, and power band. ;D

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Watch if the figure quoted is valve lift or cam lift. The rockers have a 1:1.5 ratio so if cam lift = 0.24" (6.1mm), valve lift = 0.36" (9.1mm) (minus the valve clearance) Lets hope I've got the figures right this time!

Do you have a flowed head? If not, don't go mad on the camshaft or you'll not get the benefit & you'll lose low end torque.

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I went for a mk3 profile cam for my 1500. Basically it didnt require any mods to the distributor curve and I just fitted it as per standard. It seems to gives a better torque and power spread than the standard cam (although obviously I was doing other work as well so I cant be 100% sure it was due entirely to the cam).

I'm the kind of person that cant stop messing with things so next time I'll probably go for the fast road cam which will work better with the ported head I have waiting to fit! I think the mk3 profile is a good replacement for standard but if you're building an engine up an intend to mod it then you'd probably be better off going for a fast road cam in the first place!

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I had a look at the Piper documents: the figure quoted are the valve lift.
I am quite worried with such cams: I am afraid they "kill" my old engine.

In fact, I done a small work some years ago on the cylinder head: matched the exhaust and inlet ports with the manifolds ; remove the castings and smooth the ports. The combustion chamber are standard. The car is fitted with a 4-2-1 exhaust system ended by twn exhaust pipes. I use a Mangoletsi inlet manifold (which is supposed to allow a better flow) for a pair of HS4 (AAT needles and yellow springs).The bottom end is standard too: I have never balanced it or tuftride hardening it. I know it is very recommended...but unfortunatly,I have no room to remove the engine off the car and dismantle the engine in a view of a genuine rebuilt as it should be done.

That is the reason why I will go for a standard camshaft or the MKIII profile. My problem is I don't know which one to choose.
In a first time Iwas thinking like you CharlieB  when you said: "unless the lift of the MkIII profile has been increased I would say there would be no benefit".
Now with the comment of GTEVO and WILLCOLUMBINE: I really don't know which one to choose.

William, may you tell me more about the car after the fitting of the MKIII camshaft ? what kind of extra work have you done ?

Once again: many thanks for your help

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Sorry hadn't noticed the progression of this thread. Just to confirm I just took a large bearing MKIII cam from stock and measured the lift, it is indeed 0.23. See we can do that here because we have some digital calipers, and someone who knows how to use them!

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