125bhp v 150bhp

[Guest nick lawn]

Can anyone please give me any idea of just how marked the diference in performance is between early 150 bhp models and later 125bhp versions.  Are there any other significant advantages/disadvantages?  How easy is it to upgrade performance of later models?

 

Oh yes one other thing!  How easy is it to retrofit overdrive?

 

Thanks.

[Guest ron]

Nick

To retrofit, an OD is a 'relatively' easy job if you can rebuild gearboxes, the simpler one to source and fit is the later J type, you need the OD unit complete with adapter, a new mainshaft for the gearbox and the wiring ,switches etc. If you have an earlier car that would have had an A-type OD you either need to source the OD & mainshaft or convert it to a J-type box & OD which involves chassis mounting mods. The prop shaft does not need modified to fit an OD.

The cheapest source of J-type OD's are Dolly sprints but you need to do a slight mod to the output flange.

If money is no object most of the TR specialist will supply a rebuilt gearbox & OD unit.

If you need any more info email me.

Ron

[Peter Douglas Winn]

Nick

Be careful about your BHP values. If you look back in the forum you will find many explanations about the different was of measuring BHP at the end of the engine or at the flywheel or,or. The experts all think that the difference between the 2 types is not so large as one would think. 150 BHP was a nett value.

[Guest Neil Russell]

The difference on the road is hardly noticable. I cannot remember which way round, but one car was measured with the SAE standard and one with DIN. in real terms the difference is something like 9-10hp. unless you are really screwing on you will never notice the difference.

 

Neil.

[Peter Douglas Winn]

Neil

150 was SAE which was a bare engine with nothing. The DIN norm requires certain parts to be mounted. This of course take HP that's why the real difference is so small.

[Guest andythompson]

Regardless of official figures, the "150" cam gives better torque, hardly wears compared to the much shorter duration 125 cam (which can be a horror for chopping off lobes.. especially is the tappets are run too loose).

 

Also.. if you fit a serious set of extractors (6-3-1) on a "150"  car, the long duration cam really starts to work at higher revs giving a easy 20 even 25 bhp increase....

 

The 125 bhp cam is probably bested suited to an automatic 2500PI saloon.... nice even tickover and all that sort of stuff

[Guest lukewarm]

Just out of interest what's the actual (ie mechanical) difference between the standard '150' and standard '125' models? Is it just cam, or were there other changes too?

[Peter Douglas Winn]

Well immediately comes to mind. Throttle linkage (grotty), Distributor, metering unit, Air intake manifold. Tank is smaller, dashboard different etc.

[Guest lukewarm]

Thanks Peter...

 

...but I guess the thrust of my question was directly related to the power output... and none of these things sounds like they'd have too much effect...? Please feel free to contradict - I never got far past Mechanics 101!

 

I guess I could paraphrase and ask "If I changed the cam of a '125' for a '150' cam, would expect the power output to become similar to that of a '150'?"

 

Cheers,

[Guest Neil Russell]

the mechanical bits strapped to the engine which are different and matter re power output are basically:

 

Cam, longer duration

metering unit, CR series can be re-calibrated though.

Distributor

throttle linkages. The CR series don't allow fitment of an extractor manifold and are notoriously poor, often not allowing full throttle operation.

 

Neil.

 

PS. The answer to the question you have not asked yet is YES. The CR engine can be modified to give the same as the earlier cars output.

[TIMS]

Guys  As I have discussed in an earler thread I am in for a bottom end rebuild in the next few months (see Big End, mains or something else).

 

I have what I believe to be a 125BHP engine with an unleaded head and new MU set up by Malcolm at Prestige earler this year to suit the car.

 

So Neil, I'm asking the question, On a rebuild what will I need to do to bring the 125 engine to 150 spec?.  

 

I propose to do things over time, cash constraints as ever, but want to do whatever is needed to the bottom end whilst it is out.  Changes to the top end and bolt on's (manifolds, distributor ect) can be done, unless necessary to get the egine running, as funds permit.

[Richard Crawley]

I propose to do things over time, cash constraints as ever, but want to do whatever is needed to the bottom end whilst it is out.

Tim

Others will no doubt confirm but as far as I am aware the 125 & 150 engines are identical at the bottom end. The cam is obviously different & will need changing, this can be done with the engine in the car but the followers can be a pig to extract with the engine the right way up!

[john.r.davies]

All,

Not sure if this helps, but my Silverback race car has a 2500 saloon engine with larger valves, ported head, '150' cam and a 6-3-1 tubular manifold.  For comparison, Dennis Vessey got 125bhp at the wheels on his rollers, est. 140 at flywheeel.

But with 13" wheels, boy do I need an overdrive!

John

PS An 'overhead' throttle linkage from Malcolm JOnes @ Prestige avoids conflict with the exhaust manifold.

[jonlar]

Hi Tim and Luke, the biggest mechanical difference between the CP and CR engines is the cam..   The CP cam has greater overlaps, which results in the inlet valves opening while the exhaust valves are still open, this gives a better gas flow.   It is important for the Metering Unit to be calibrated to the cam., the greater overlap results in lower vacuum being applied to the M/U which with the CR M/U will cause enrichment to the fuel, the vacuum figures are given in the Lucas PI Manual reprinted by the Wheatsheaf Press.    I believe the CP and CR heads are slightly different - better gas flow....?   Having driven saloons with both the early and later engines, the difference is noticeable, the earlier engines feeing torquier, revvier and more willing.   CR engines can easily be tuned to give a lot higher BHP than a standard CP - how long is a piece of string?

[Red 6]

Tim,

 

Hello again.

 

I found the CR head "better" than the CP head when i built my first go faster engine using a CR engine as the starting point.

 

All i did was to change the cam for a fast road cam from Kent together with the followers etc.

 

I fitted a Phoenix 6into1 single pipe exhaust system and a K+N filter which relpaced the standard one (but with several extra holes cut in the origional filter can.

 

The throttle linkage was replaced with a prestige designed one and the metering unit recalibrated on the rolling road during the tuning session.

 

The whole lot was less than £800 and the output ie from the rolling road not the triumph marketing department was about 145bhp but the torque (the bit that counts) was monumental!

And substantially better than my standard "150" bhp TR5.

 

Another time i put a flowed head with the same set up as above but with su carbs and that one blew my first one away

 

Finally one of the best and cheapest mods is to lighten the flywheel, it dosnt add bhp or torque but when you pull away from standstill its like someone fitted 2 extra cylinders!

 

Let us know how the rebulid goes.

[TIMS]

Guys

 

Well I have not got off to a very good start.  I dropped the sump at the weekend and examined two big ends.  Both are pitted and look to have been starved of oil in the past.  The car only did 1,400 miles between MOT's in the 4 years before I purchaed it last November.  I think this must have been mainly Sunday Morning trips to the local golf club or some such.  Anyway, the bad news is that the sheels are marked at .060u/s.  A 60 thou undersize.  Not wanting to go any further undersize I must add the cost of a crankshaft to the rebuild, or has anybody got a spare they would like taking away? (says he optimisticly)

 

It will be interesting to see the condition of the camshaft bearings when the engine comes out.  I have a horrible feeling that the rebuild could be much more extensive than first envisaged.

 

I will keep you informed

 

Regards

 

Tim

[Richard Crawley]

I have a horrible feeling that the rebuild could be much more extensive than first envisaged.

Tim

They always are & it's best not to skimp! Is the crank pitted & marked or is it just the shells? These cranks are pretty robust & if they mic up OK, you can sometimes get away with a good clean up; my standard crank had done over 80K but the tolerances measured up very good so it went straight back in after a light polish.

 

The good news is that as these cranks are strong so there are plenty around & you should be able to pick up a good one without going bankrupt. Get a ‘standard’ or no more than +20 if you can & if you have to have another ‘grind’, get the journals Tuftrided as undersize grinds remove the original surface hardening which makes the crank more susceptible to wear.

 

When you rebuild, fit a spin on oil filter conversion; the modern filters these take prevents the oil from draining away in to the sump & so ensures almost instant oil pressure on start up. If the car is used for short, infrequent journeys, the original filter design starves the engine of oil in those critical couple of seconds after start up & is a recognised cause of wear problems. Tricks to keep the crank/engine in good condition; crank the engine for at least 5 seconds before starting & replace the bearing shells regularly – every 20-30K miles.

[TIMS]

Richard

 

You are preaching to the converted.  The first thing I did on buying the car was to change the oil and filter, a spin adapter was already fitted.  I won't use the car for short journeys and anyway it's a great excuse to take the car out for a spin if all that is really needed is to get it out of the garage for access to something else!  And as for cranking the engine for at least 5 seconds, I thought that this was a built in design factor with starting a PI car from cold?

 

Ah well off on the search for a crank.

 

Tim

[Richard Crawley]

You are preaching to the converted.  And as for cranking the engine for at least 5 seconds, I thought that this was a built in design factor with starting a PI car from cold?

Sorry Tim, it's sometimes difficult to tell with posts!

& yes you are probably right although my car will start fairly quickly on a day-to-day basis, if I follow starting procedure.

 

What I do is leave everything alone, crank the engine for at least 5 seconds to prime the oil & injectors & then choke & jab & it usually fires up straight away; but never on all 6, this takes a few more jabs on the throttle!

[Tom Fremont]

FWIW, a fraction of a turn is all it takes, hot or cold, every time, with my triple Weber set-up.

 

Glad I am of it especially given the pig of a job it is to change the starter with the tubular headers clogging up the works! ::

[unclepete]

At Malvern, on the rolling road test bed, the top power output from a TR6 was 148bhp at the wheels!

Equates to about 185 - 195 at the flywheel.

This was an american import converted to RHD with triple twin CARBS , hotter Cam, Balanced Lump and I think a skimmed gas flowed head.

The guy doing the test said it was out of tune at the top end!!!

The owner said that as 'a new set of jets was £150 he would live with it'!

It seemed that standard TR6's came out at about 105 - 115bhp at the wheels, if they were tuned up properly.

Just shows what you can do?

I didn't ask him how much it cost though.

I didn't put mine on as I didn't think the scale went high(low) enough!

Unc