Cams

[Mad Mart]

Just a quicky. Is the L1 equivalent (or near enough) to the STR139 or STR91? I can't remember.

[Dolly-Nut]

I'm not aware of what the L1 is but does this help?
http://www.triumphowners.com/uploaded/3 ... sprint.jpg
If not some useful information there anyway...

[TahitiSPRINT]

Just a quicky. Is the L1 equivalent (or near enough) to the STR139 or STR91? I can't remember

Hi Mart, the L1 cam was originally designed for the twin-cam Lotus/Ford/Cosworth engine, so the cam lobe design may not be optimized for the SOHC Dolomite Sprint engine.

These are the figures (as found on a Lotus Elan website):

L1 Camshaft
Valve timing 46/78 - 70/50. Duration 304 deg. Lift @ valve .410" (10.41mm)

Installation data:
Valve clearances (Cold) inlet .007" (0.18 mm)
Ex .008" (0.20mm)

Inlet valve fully open 106 deg. ATDC

These figures come very, very close to the Kent DMS2 cam
Timing is in-between the STR91 and STR139, but that doesn’t mean the performance will be better than STR91, due to design. If it’s for your trackday Sprint, I think STR91 would be your best bet.

Some (unorthodox?) info on Triumph cams and (de-)tuning in general:

Cylinder head work

Camshaft technology

Triumph modified head’s


Happy reading

[soe8m]

Ronald, that man did also claim that the russian women were the prettiest in the world?

Jeroen

[TahitiSPRINT]

So you mean every word he says is true?!?

[soe8m]

Do they have a lot of red hair green eyes combi's in russia???????????

Jeroen

[hsdolly]

On the HS Chevette engine we use this cam for the inlet at 103 degrees ATDC max. We use the GT2 for exhaust at 108 degrees BTDC max open. I have never checked on these cams to see if the grind is possible to get the Dolly inlet and exhaust durations correct. GT3 and GT4 are available for 16 valve lobes too. The other Achilles heel is being cam chain driven of course - this makes infinite quick timing variation difficult to achieve - I have not looked lately but I wonder if anyone developed a wheel in wheel cam drive sprocket. We use these on Lotus/HS engines and they basically allow infinitely small adjustments to occur, changing timing by fractions of a degree if required - but they are external to the engine of course.

It depends what you are trying to achieve - often one set up gives you tractable torque when you need it (usually a lower revs too), whereas the opposite way to go is for maxed out BHP curve at higher rpm - the former is best for what we get up to - rallying, the latter circuit work. In our experience it is worth flow benching the head too for airflow - of course this is only truly worthwhile if you are going to use balanced length extractors and probably very short inlets. The TR7 inlets work for this quite well, using a mini submarine set up too. The STR larger air box set up should help too - the inlet pipes are larger. If you want to squeeze a few more bhp then go dry sump of course - I have one of the dry sump dolomite engines - quite a simple enough conversion really. I have posted on here years ago too that if the engine is lifted up nearer to the vertical a few more bhp can be squeezed too - but you end up needing a specially adapted bell housing and inlet manifolds - on a Chevette these are 35 degrees.