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Choice of camshaft for 2lt Straight 6 Mark 1 engine.


Algy
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I am rebuilding a 2ltr Mk1 Vitesse engine and the original cam is very badly worn. As this is the engine from a special built  in 1967 and the engine had been breathed on, I assume the cam would have as well.

To give you an idea of the mods that I have found: The inlet manifold is matched to the carb’s and head, the pistons and conrods show signs of balancing, the combustion chambers and ports have been worked.

My question is what cam would you recommend, that is available?

Somebody suggested a Mk2 cam, which to me sounds plausible; however, I am wondering if there is better or if the Mk2 cam would give any improvement over standard.

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mk2 cam is a very capable all-rounder, but if the head is heavily skimmed to give a very high CR, you may need something hotter to bring the dynamic CR down.

No such thing as a "best" cam (unless you have VVT!!!!) choice is made on what power you want to achieve and the power/torque spread and where it comes in. If you want max power it will be dreadful to drive under 2-3000 rpm. 

Newman cams are very knowledgeable, so worth speaking to. Chris Witor too. But I suspect they will want an idea of the CR. Plus what carbs it is using and exhaust manifold.

(in fact if using the std cast manifold you will be pretty restricted, likewise the std strombergs. The carb needle will give an indication too, is it std or richer?)

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The engine currently has a very rusty tubular 6-2-1 exhaust manifold, that needs to be replaced / repaired, the head combustion chambers are all matched and have been dressed back around the valves and inside the ports (although not as much as Vizard might have gone) and the head must have been skimmed to as the chambers have a volume of 33.5cc, which would put the CR just under to 10:1 originally but will be closer to this with the +0.020” re-bore (due to bore pitting). The valves are standard size and I will be having the head converted to unleaded as the valve seats are corroded and the engine is having a full rebuild so it makes sense to me to do this now.

I not been able to drive the car as it had a crash in 1975 and the then owner stripped everything and then found he was not capable of doing the work, the car then migrated out of his garage and was left to decay, until another chap bought it then quickly realised it was beyond hi and sold it to me. Luckily it came with a fair bit of the cars early history and the fact the engine was replaced with a tuned 2ltr engine (originally a 1600 straight 6) in 1967. Unfortunately the state of tune in not detailed. The carburettors appear to be standard other than the fact they are matched to the inlet manifold, however they had been stripped and some parts are missing (like needles and jets) so I plan on having them fully rebuilt and jetted once the final engine build if completed.

I would like the engine to be driveable, ie not a race engine, but would like to get it in the realm of how it might have been before it was crashed. I am assuming it would be in the format that I would term stage 1 or low end stage 2 tune.

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if an ex 1600 mk1 it will have the small cam followers so dont go mad with lobe loading or it will soon reduce the cam lobes to lumps

and if its still got 3/8 head studs on a CR of 10+ expect the head washers to be distorted , this is bad enough on a std  mk1 engine  let alone souped up a bit

did  it have the steel shim 1600 head gasket or a compostie ??  2ltr version , as this also affects CR .

 

pete

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Algy,

Worthwhile (IMHO) doing the CR calcs again, if you have had a rebore, especially with the CR near 10:1- you don't wnat it much higher, unless you're willing to run alwyas on Shell V-power or equivalent, 98/9 octane.    You've done the chamber volumes (are they equal?) so it's just the arithmetic.   If that fazes you may I humbly recommend my article http://sideways-technologies.co.uk/forums/index.php?/topic/7551-how-to-raise-the-compression-ratio-safely-and-effectively/ ?

A 6-2-1 exhaust is little better than the OE anchor, but is easier to fit than the 6-3-1s, which are very tight, but worth it for the extractor effect, which will raise power in mid-range.   

If you plan to have the standard valve seats 'unleaded', that's exhausts alone, but consider getteing a set of the bigger, later valves (Witor) and fitting those by recutting the inlets as well.

A Mk2 camshaft is a good choice (24-64), unless you can find a TR5 one, 35-65.  Whatever you get, don't gio for more than about .288 of lift, no point as Triumphs shroud the valves too much.

JOhn

 

 

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Thanks John.

Yes all at the same volume as measured with an accurate pipette. Without the head gasket to measure the thickness I am just going from the chamber volume for the calculation. I must say I would prefer to be at the 9.5:1 ratio and as I have a spare vitesse 2ltr Mk1 head, was considering relieving the head around the valves (in the same way as this head has been done) and having it lightly skimmed to get back to 9.5:1.

I had also thought, if I was to do that to the replacement head, that I could go for larger inlet valves at the same time.

I would still have the original head, should I ever sell the car.

I can hear you ask why worry when it is a special? Well it is a special –special, it is one of six commissioned by Bond, so trying to keep it as original as possible.

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For road use and with the present fuel available the best cam when running on carbs is the Mk2 308778 cam. The TR5 cam has too much over lap for carbs and ends up with most of the fuel down the exhaust pipe! The TR5 cam is good on injection where the fuel is shot in at the right time. Forget about wild cams for road use as they can be a nightmare when stuck in traffic. However, if you are going to use the car on the track then that is a different story.

Dave 

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Agree, the mk2vitesse cam is a really good all-rounder.

I believe you can drill and retap teh block to accept the mk2 head studs? would be more reliable long term.

If getting valve seats done, make sure they do a 3 angle cut. Very cheap to be done and really helps matters.

I think a call to Chris Witor would be time well spent. He will be able to sell you everything you need! Plus he tends to sell stuff that actually works and well made.

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algy,

"was considering relieving the head around the valves"  By undermining the rim of the chamber?   I acqquired such a head, thinking WoW! that's a good idea, to unshroud the valves.     It was a disaster, the head gasket fauiled, repeatedly.   I think the edge of the chamber was made flexible by the undermining.

I use 3.5mls as the gasket volume.   It's invariant for all 2-2.5L engines!

If you follow Clive's good advice to drill the block for the bigger studs, then ensure that they are counterdrilled enough to take out the first turn of thread.  This will ensure that the stud going in will not bulge the head face around it and prevent proper seating of the gasket and head.

JohnShow Reply

 

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As I said before I a trying to keep the car as close to the original spec as possible. This is not a new special being made from an old car it is an old special that was built from scratch for Bond and subsequently modified by Bond before being registered in 1967.

If it were a modified car, I would have no hesitation in just changing the engine, possibly to a later Mk2 2ltr (I have one) and the head ports are better designed to start with, but to modify the block would not be reversible. It is also not just as easy as drilling out and tapping; you need to counter bore slightly as well and drill the head.

I am very happy to modify my spare Mk1 head, as that is reversible.

The original head is a close match to David Vizard’s recommended modifications for fast road, from what I can see, the valve seats are cut with three angles and the valve heads have been rounded. That said four exhaust valve seats have been without valves and although the head face has been protected by grease the seats have been exposed and rusted (hence the thinking to convert to unleaded).

From the advice given so far, I think I will go with the Mk2 cam and lightly modify my spare head to unleaded and larger inlet with three angle seat and light porting. The bottom end will be check balanced and built with new shells as the crank is in good order. Hopefully that will give me an engine that would be close to the original spec / performance and flexibility to drive in modern traffic.

Thanks to all for the advice so far.

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1 hour ago, Pete Lewis said:

algy  why not link to your linkedin photos  ??

 

Pete

Not a great one for taking photos. I only ever bother if I think it would be of use to my learners or if I think it might help someone else. Don’t think many would be interested in the rebuild of an obscure car, there would be more interest, in the work I do for my customers but that is not for me to post.

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Algy.

I disagree, I think you will find that Forum users are always interested in a variety of threads especially when supported by photographs - one picture speaks a thousand words etc. 

In addition this Forum has excellent photo / document uploading access.

Regards.

Richard.

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Thanks for all the advice, have opted for a Mk2 cam. Just now whether to use the stage 2 head as adverised in the club shop or just match my spare head and fit hard seats.

Can anyone tell me what the stage 2 head spec is as there is no info on the shop page!

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Again, speak to Mr Witor, or explore his website. The inlet mkanifold on a MK1 is somewhat imbalanced, not sure if that has been attended to on yours, but info on the web somewhere.

The whole "stage 2" stuff is just a label that is meaningless. It probably means a bit of porting and so on, I doubt if it includes bigger valves. But the Witor info should give some pointers to what is worth pursuing. 

 

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