Upgrade from standard USA cam to........

[Edwin]

Hello everyone,

 

I'm in the process of rebuilding my engine and have taken everything out and was wondering if upgrading the camshaft is worth the investment.

 

It's a 1970 carb model. The cam that came out is part number 307621 (TR250 and early TR6). A friend of mine has a brand new Kent TH12-6 cam which according to Kent has a torque band of 1500-6500 rpm. I'm not looking for a performance car but a bit more power at low revs would be very welcome and the Kent cam seems to give just that.

The car is running on 2 SU HS6 carbs with K&N filters and according to the head thickness (3.46") and standard bore size the compression ratio is about 8.75:1

 

So.....

1. Is the existing USA cam a good enough performer or would the Kent TH12-6 be much better?

2. Kent advises to use new uprated valve springs. Is that really necessary and why? Having an early head it can only have single springs.

3. Is there another cam that you would advise me to use that gives more torque at low revs and can be installed without other modifications?

 

Any comments more than welcome.

 

Cheers.

Edwin.

[jake_a]

I'll be interested in replies to this too.

[rpurchon]

3. Is there another cam that you would advise me to use that gives more torque at low revs and can be installed without other modifications?

 

Any comments more than welcome.

 

Cheers.

Edwin.

 

no, that is the best cam for bottom end torque.

if you want to get more mid to top end power fit a cr cam.

dont bother with double valve springs you will only wear the cam out.

richard

[Edwin]

Hey Richard,

 

And by this being the best cam I'm assuming you mean the Kent TH12-6 and not my existing CC cam?.... I think I'm giving it a try, he's asking about £ 150,- for it.

 

Next week I'm taking the block to a specialist to see if it needs a rebore or not. Hoping not so I can use the new set of pistons.

 

Cheers,

Edwin

[rpurchon]

Hey Richard,

 

And by this being the best cam I'm assuming you mean the Kent TH12-6 and not my existing CC cam?.... I think I'm giving it a try, he's asking about £ 150,- for it.

 

Next week I'm taking the block to a specialist to see if it needs a rebore or not. Hoping not so I can use the new set of pistons.

 

Cheers,

Edwin

 

i have a put my cc one in my car. after my cr lost a lobe after fitting double valve springs.

no i mean the cc cam is best for low down torque from 1000revs. it starts to run out of steam above 4000 revs

the other can not produce torque from 1500 to 6500.

its either low down power or high end power with a cam shaft, and if its quoted to produce power up to 6500 revs

which you will never use in a road car, it going to be more at the top end .

richard

[Edwin]

i have a put my cc one in my car. after my cr lost a lobe after fitting double valve springs.

no i mean the cc cam is best for low down torque from 1000revs. it starts to run out of steam above 4000 revs

the other can not produce torque from 1500 to 6500.

its either low down power or high end power with a cam shaft, and if its quoted to produce power up to 6500 revs

which you will never use in a road car, it going to be more at the top end .

richard

 

Oh... that was a bit of an unexpected answer.... shows how much I know about camshafts

 

If that's the case I'll stick with my CC cam, It's still looking perfect and all the lobes have the same measurements and no scratch marks or whatsoever. A bit strange though that the current owner of the cam is very sure that it will give more low down power than my CC cam...

 

Thanks,

Edwin.

[Tom Fremont]

Hi Edwin,

 

I've had '250s for 34 years, 18 of which were in stock form. Now that I know it can be done reliably, I will always upgrade the Federal spec to 150 BHP or a bit more - the car is transformed and driving is much more entertaining. Without going to extremes the engine will last as long as the Federal spec ones. I've got ~90,000 miles on the last rebuild in my current driver with that much HP available, and it shows no sign of fatigue.

 

There's nothing wrong with keeping in original stock form and others will have more confidence in its reliability than a modified one.

[Canadian TR]

Hello Edwin,

I have just rebuilt my 1970 engine, it's 0.040" oversize with 9.5 CR. The cylinder head is ported but not gas flowed. I had been running with the original cam but have now installed a Goodparts GP2 cam, I am also running with HS6 carbs. The engine is due to go on a dyno this afternoon so I will have some hp and torque figures. All things going well I will be driving at the weekend. I can let you know the results.

 

Andy

[Edwin]

Hello Edwin,

I have just rebuilt my 1970 engine, it's 0.040" oversize with 9.5 CR. The cylinder head is ported but not gas flowed. I had been running with the original cam but have now installed a Goodparts GP2 cam, I am also running with HS6 carbs. The engine is due to go on a dyno this afternoon so I will have some hp and torque figures. All things going well I will be driving at the weekend. I can let you know the results.

 

Andy

 

Hi Andy,

 

I'm indeed very interested in the results of the dyno test but maybe even more so in the difference of the overall driving experience between the two cams.... so when you have the results... let me know.

 

I just completed the disassembly of the engine and am taking it to a Triumph specialist this thursday to see what needs to be done...

 

Cheers,

Edwin

[Canadian TR]

Hello Edwin,

Well as usual things took a little longer than expected not helped by torrential rain followed by -13C and now snow. Anyway the car is running and has been on a few runs. The engine was run in while on the dyno but I am still being a little conservative with it.

It is a lot faster than previous and now pulls all the way past 5000rpm whereas it started gasping for air just above 4000rpm previously. Torque is great but comes in a bit higher than before.I am still running with the original single pipe exhaust system which I think is probably holding the engine back at the moment, I intend to change to a standard two pipe system or maybe splash out for a Pheonix system next year. The dyno test was also carried out with the single pipe manifold.

The air fuel ratio varied greatly on the dyno,it was below 11/1 at idle and 13.5/1 on load. I may install a wide band O2 sensor with the exhaust and try different needles next year.

Overall very happy with the results, I had hoped for around 140hp so the 150hp shown on the Dyno was a bonus. With new exhaust I believe it will just get better.

Dyno results are attached and below is the engine specs:

 

Cylinder head; Later wide port, 9.5 CR.

Inlet Manifold; Standard, port matched and some gas flowing.

Exh Manifold; Original single pipe, port matched.

Engine; Bored 0.040" and all parts balanced.

Flywheel; Original flywheel lightened by 5lbs.

Damper; Rebuilt by Damper Doctor in California.

Camshaft; Goodparts GP2

Carbs; HS6 with BAG needles

Distributor; Original,rebushed and NOS original tension advance springs.

 

Hope this helps in your descisions.

 

Andy

[Canadian TR]

Sorry I'll try again.

Dyno Results.pdf

Dyno Results.pdf