super6al Posted June 28, 2021 Report Share Posted June 28, 2021 Hello Everyone I have a '74 CR series with std 125hp cam/MU setup. For months now I've compromised throttle balance & rough idle due to wear in the linkage & throttle spindles. So finally I've stripped the manifolds & attempted a home repair until a refurbished set becomes available & I can bring myself to spend the £000's required. I've fitted new linkage, pivot bushes,aligned everything up & soldered up the brass spindles in the worn areas. I've honed them by hand to fit the throttle casings. Its not ideal but the butterfly operation is now way better than it was, I haven't access to brazing equipment so just used hard solder. I guess these will wear pretty quickly(?) but I figure it will do as a trial & eventually will replace or get them brazed properly. One thing I've noticed is the CR manifold has 'D' shaped ports that don't match up with the 'O' shaped inlet ports. My experience with Minis cylinder heads tell me this will have a detrimental effect on air flow & I'm considering matching these up. Has anyone done this before on a CR car? Reading on the web has thrown up a couple of theories - one is the this shape mismatch was intentional to create a 'swirl effect' to improve fuel economy & the other is its a consequence of improving access to the top manifold nut. I'm pretty certain Triumph wouldn't do such a change without understanding the effect on performance. Alan Quote Link to post Share on other sites
jerrytr5 Posted June 29, 2021 Report Share Posted June 29, 2021 'D' shaped ? Got a picture? I've only seen round ones. Jerry Quote Link to post Share on other sites
super6al Posted June 29, 2021 Author Report Share Posted June 29, 2021 Hi Jerry Will post photo tomorrow. Its an odd set up to my mind. Going off topic, I'm thinking the CR series must have cost Triumph a fortune given the low numbers of home market PI. Even lumping in 2500 saloon PI numbers there surely can't have been enough sales (forecast or actual) to pay for the tooling costs for new throttle body castings,changes to the MU, valve sizes & camshaft. Let alone all the other changes & development work required. All that to make the car slower & probably less marketable. What were they thinking? Given one eye must have already have been on the 2500TC/S saloon it would have made sense to ditch PI & consolidate twin carb fitment to all home & overseas markets. I can only assume there was some contract with Lucas that committed to a minimum take up of PI. Indicative of British Motor Industry thinking at the time & sad really. On the plus side at least we can enjoy the character of driving with PI. Alan Quote Link to post Share on other sites
super6al Posted June 30, 2021 Author Report Share Posted June 30, 2021 Hi These are the CR 'D' shape inlet manifold. You can just make out the outline where they mate with the circular cylinder head inlet. Alan Quote Link to post Share on other sites
jerrytr5 Posted June 30, 2021 Report Share Posted June 30, 2021 Well I never, you speaketh the truth. Maybe I've only seen CP ones. I'm sure there will be an expert along in a minute to tell us all. Jerry Quote Link to post Share on other sites
super6al Posted June 30, 2021 Author Report Share Posted June 30, 2021 Cant see how its good for air flow myself & its nigh on impossible to align the rounded part with the inlet port as the bottom hole in the picture is dowelled to the head (top hole is for stud), so theres not much float. From what I've read the access to the top nut was improved so it could be this meant they had to compromise with a smaller inlet of this shape. I don't know what the access is like for CP top nut but its still tight for the CR. Quote Link to post Share on other sites
JochemsTR Posted June 30, 2021 Report Share Posted June 30, 2021 (edited) Alan, I had CR bodies with the "D" machined to an "O". Got my hands on another CR and did the machining just for fun. There is some material to work with. But the setup requires lots of time and I did not have any need for CR bodies so I did not spend more time on it. Jochem Edited June 30, 2021 by JochemsTR Quote Link to post Share on other sites
super6al Posted June 30, 2021 Author Report Share Posted June 30, 2021 Thanks for the info Jochem I see your on EFI so I guess you didn't get the chance to see if there was any change (good or bad) with the machined 'O' shape.? Quote Link to post Share on other sites
JochemsTR Posted July 1, 2021 Report Share Posted July 1, 2021 The CR and CP difference is not only the manifold shape but also the metering unit and C.R. Therefore, you need to address all three of them in order to achive original spec CP performance. Since the CP "O" Shape allows for more air flow, unrestricted, in combination with a higher compression ratio the metering unit requires a more rich configuration. But I have not done any detailed testing or flow analysis between both shapes. Quote Link to post Share on other sites
astontr6 Posted July 1, 2021 Report Share Posted July 1, 2021 On 6/28/2021 at 6:16 PM, super6al said: Hello Everyone I have a '74 CR series with std 125hp cam/MU setup. For months now I've compromised throttle balance & rough idle due to wear in the linkage & throttle spindles. So finally I've stripped the manifolds & attempted a home repair until a refurbished set becomes available & I can bring myself to spend the £000's required. I've fitted new linkage, pivot bushes,aligned everything up & soldered up the brass spindles in the worn areas. I've honed them by hand to fit the throttle casings. Its not ideal but the butterfly operation is now way better than it was, I haven't access to brazing equipment so just used hard solder. I guess these will wear pretty quickly(?) but I figure it will do as a trial & eventually will replace or get them brazed properly. One thing I've noticed is the CR manifold has 'D' shaped ports that don't match up with the 'O' shaped inlet ports. My experience with Minis cylinder heads tell me this will have a detrimental effect on air flow & I'm considering matching these up. Has anyone done this before on a CR car? Reading on the web has thrown up a couple of theories - one is the this shape mismatch was intentional to create a 'swirl effect' to improve fuel economy & the other is its a consequence of improving access to the top manifold nut. I'm pretty certain Triumph wouldn't do such a change without understanding the effect on performance. Alan Years ago in the late 1970's the master tuner of Triumph cars S.A.H. who were also ST approved by B.L. used to replace the D shape manifolds with the original round type when tuning the 125 Din post 1972 models of TRs as you stated it restricts flow. This was done to my car by them! Bruce. Quote Link to post Share on other sites
super6al Posted July 1, 2021 Author Report Share Posted July 1, 2021 Thanks Bruce & Jochem you confirmed my thoughts. Ive fitted them back on as they are, so it will be a job for the future. Its running much better (not perfect) and will now pull from standstill without bogging down. Incidentally I thought the CP & CR had the same compression ratio (the USA variant being low compression), the performance differences being the camshaft, MU, distributor, manifolds & a smaller exhaust valve. Alan Quote Link to post Share on other sites
JochemsTR Posted July 2, 2021 Report Share Posted July 2, 2021 Alan, my bad....I looked in my documentation and CP and CR DO have the same C.R. So even without this, the performance differences are noticeable. Quote Link to post Share on other sites
astontr6 Posted July 10, 2021 Report Share Posted July 10, 2021 On 7/1/2021 at 10:26 PM, super6al said: Thanks Bruce & Jochem you confirmed my thoughts. Ive fitted them back on as they are, so it will be a job for the future. Its running much better (not perfect) and will now pull from standstill without bogging down. Incidentally I thought the CP & CR had the same compression ratio (the USA variant being low compression), the performance differences being the camshaft, MU, distributor, manifolds & a smaller exhaust valve. Alan The issue was always the original cam shaft. Many people did not like the so called rough tick over and there were new rules coming in on pollution i.e. no more 100 octane high lead content fuel, caused the detuning! I went down the route of SAH modified cylinder head with larger inlet valves, SAH 357 cam, this cam is more powerful than the original BL one, SAH exhaust header and exhaust system. These mods do produce a genuine150 bhp+ car with more bottom end torque. Bruce. Quote Link to post Share on other sites
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