Jump to content
AndyK

Upgrading from 125 to 150 BHP

Recommended Posts

Currently doing full refurbish of my  CR TR6. Reading Roger Williams book he suggests that you can increase the power of the CR model from 125BHP to the CP level of 150BHP by putting in a CP metering unit and cam shaft. I need the MU refurbished anyway and the engine overhauled so wondering it it is worth trying this simple upgrade. Just wondering if anyone else has done this and any pitfalls/problems that might be encountered. Thanks. Andy

Share this post


Link to post
Share on other sites

Andy,

sorry, that is not how it works....

https://www.tr-register.co.uk/forums/index.php?/topic/19308-150bhp-v-125bhp/

Andreas (TriumphV8) mentions it....CR Ratio, Valves and TB Size...

Jochem

Share this post


Link to post
Share on other sites

125 cannot be directly compared with 150.  The value of  150 was obtained by measuring the power when the engine was not powering a fan, water pump, alternator or fan belt. Those parasitic losses when added to 125 give around 137, which can be compared with 150.   Those extra 12 hp can be won by reverting to the earlier design, but it is a lot of hassle for a small gain.

Peter

Share this post


Link to post
Share on other sites
6 minutes ago, Peter Cobbold said:

125 cannot be directly compared with 150.  The value of  150 was obtained by measuring the power when the engine was not powering a fan, water pump, alternator or fan belt. Those parasitic losses when added to 125 give around 137, which can be compared with 150.   Those extra 12 hp can be won by reverting to the earlier design, but it is a lot of hassle for a small gain.

Peter

I did this and Peter is quite right and when I rebuilt my engine after 44 years I made a second attempt but did much more. On the first attempt I fitted a SAH gas flowed head, an original early PI cam and an extractor manifold and early  inlet manifolds which are different in shape (ports) to the later CR type but was disappointed with the performance increase. Yes it did rev better but not that much better. On the second attempt: The whole engine was stripped down, re-bored, reground crank, , fly wheel lighten, whole assembly balanced, Newman cam and followers, I was told to keep away from re-ground cams, Con-rods lighten, new small ends and all weight adjusted including the pistons. The cyl- head was reworked  to BL booklet 'Triumph Competition Preparation Manual' and Chris Whitor spec . On the first drive up the road the difference was unbelievable and it was not run in? Bottom end torque and rev range increased! Really pulls from 1500 RPM.

Bruce

Share this post


Link to post
Share on other sites

Thanks - sounds like on balance not worth the additional hassle. I probably have enough other things to worry about before thinking about this!!

Share this post


Link to post
Share on other sites

I have a 150bhp 1970 CP car. I've driven a couple of CR cars when looking for mine.

The CP might only have an extra 13bhp but I can tell you it goes much harder than the CR. Whether the revised bhp measurements are out or its the increased torque I can't say but a CP goes much better than a CR.

Share this post


Link to post
Share on other sites

Hi Andy,

Despite the actual small difference in actual BHP between the two, the CP early cars do feel quite a bit different on the road with regards to power and torque. I have owned both a standard CR & CP models, both set-up properly.  If you're involved in an engine build anyway, it is an ideal time to upgrade, and not much additional cost in the grand scheme of things to make these changes at this time. However, when you start tuning/improving, it can be difficult to know where to stop !

 

Share this post


Link to post
Share on other sites
3 hours ago, John McCormack said:

I have a 150bhp 1970 CP car. I've driven a couple of CR cars when looking for mine.

The CP might only have an extra 13bhp but I can tell you it goes much harder than the CR. Whether the revised bhp measurements are out or its the increased torque I can't say but a CP goes much better than a CR.

+1

Share this post


Link to post
Share on other sites

Agreed Mike, in my experience the standard CR is quite breathless and doesn't rev easily. Easily remedied nowadays however in period the road test figure differences between the two were markedly different.

Share this post


Link to post
Share on other sites

This is especially true for the later US cars which were progressively detuned. By 1974 the compression ratio was down to 7.5:1 and needs around .25 Inch milled off to get back to around 9.6:1. That simple machining and a PI cam will really wake these engines up and will not add a lot of cost to the next engine rebuild.

Stan

Share this post


Link to post
Share on other sites

The CP cam will deliver lower fuel economy than the CR; my guess is ~ 4 MPG overall. Duration is the reason; the more of this the lower the MPG.

Headwork and exhaust system can add several HP; with CP cam mine gained a second in the 1/4 mile over unmodified head with 295 degree duration cam.

I've been enjoying TR nirvana with my CP cam on Webers since 2000. To my thinking the CR cam doesn't take advantage of the 6 throttles provided.

 

Cheers,

Tom

Share this post


Link to post
Share on other sites

My first experience with a TR6 was an early probably CP version from a friend, around 1985. What a car! This inspired me to buy and restore one myself, around 1990. It was a US-car with twin Strombergs and OD. It was in perfect condition, little parts required replacement then, and it was absolutely rust-free. But the lack of power, compared to the PI I had driven before was disappointing for me. There was no TR forum then, so I tried to invent my own wheel, and installed 2xSU. It made little or no difference.

Had we had internet and this great forum then, it would have been easy:)

 

Cheers,

Waldi

Share this post


Link to post
Share on other sites

Many years ago when I was running my TR6 I had a 132 saloon cam fitted. It started out as a USA spec TR6 but I fitted the PI bits from a PI saloon I bought for the purpose.

IIRC (and I probably don't), peak torque figures were all similar but occurred at 2500rpm for the 125, 3000rpm for the 132 and 3500rpm for the 150. The extra power comes from the torque occurring at higher rpm. When a convoy run of 6's all floored the throttle at the same time the rapidity of acceleration depended on the cam fitted (unless someone disengaged overdrive of course).

Starting at 50mph/2000rpm the 125s would be noticeably quicker than the 150s, but if starting from 70ish the 150s would leave the 125s as they would be nearer peak torque and the 125s would be fading. The 132 was somewhere in the middle, but probably nearer the 150s than the 125s (or I could just have been better at setting it up.)

Drop a couple of gears and he who has the fastest cam wins!

Neil

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...

×
×
  • Create New...

Important Information

Please familiarise yourself with our Terms and Conditions. By using this site, you agree to the following: Terms of Use.