Upgrading the TR250 Engine

[Dave Ashworth]

Dear All,

Can anyone help me to understand the procedures and modifications necessary for upgrading the TR250 engine to TR5 spec or slightly above that level of performance? Is this easily attainable or am I better off sourcing a different engine?

Thank you for your wisdom.

Dave.

[tr graham]

Dave

a polished and ported PI head and a fast road cam , you can go Pi or triple carbs

graham

[TriumphV8]

Hi Dave,

first the engine must be in perfect good condition to invisage such a tuning.

 

The difference between TR250 ans TR5PI is the cam from 256 degrees to 280

a different exhaust manifold from 1 branch to 2 branch and a higher CR and a different

inlet manifold with fuel injection.

 

All can be swapped quite easily but what remains is the fuel supply in the trunk and a high pressure fuel line to the front.

 

Complete sets with metering unit, pipes, manifold and collector and air filter together with pressure regulator, filter and pump in the trunk became quite expensive during the last years. To avoid trouble I would buy a remanfactured set from people like Neil Ferguson.

[MJF]

I think the TR250 (and early US TR6) heads had a narrower inlet port spacing, so as Graham said, if you still have the original TR250 head fitted you will need to change this to convert to PI

Martin.

[TriumphV8]

Oh yes, some heads are different and the ignition advance is different....

[Dazzer]

The Kas Kastner tuning manuals cover the TR250 and from memory with an S2 cam (There is a comparable Newman cam) comp ratio 10:1 and opening up on the inlet manifold and keeping the 175 Strombergs it will deliver 170 bhp. I used Kastners manual in a similar manner on a 2500S in my rally saloon and the torque and usuable power is very impressive. I use 175 Strombergs from a TR4 on a short manifold on mine. So yes no need for a different head or anything on your TR250, source one of Kas Kastners pamphlet tuning guides and just follow the steps that were very succesful for him in the day.

Hope this helps

Darren

[Tom Fremont]

With my first '250 I took the original head and milled off 1/16", fitted a Kent TH2 cam and triple DCOEs. Everything else was stock ( AC fuel pump, bottom end, exhaust ). When a TRF rebuild group guy rode in it he said it was more impressive than the TRF mascot TR5 belonging to Charles Runyan ( RIP ). 

The TR250 cam has 240 degrees duration ( not 256 ). The CP cam has 280, and I've since switched to this with wide port reworked head and tubular exhaust manifold. It's at least 1/2 second quicker in the 1/4 mile than an original TR5 ( with an amateur at the wheel - myself! ). This recipe is still going very strong after 90,000 miles and has crossed the Continental Divide at 11,150 ft. without any issues whatsoever ( try that with a LUCAS P.I. ).

Kastner was able to get 167 BHP using twin Strombergs but had to go to 12:1 c/r, extreme cam and 6000 rpm to get there, with open velocity stacks. Longevity wasn't a priority!

If you want longevity with these engines I suggest settling for 1 HP / cubic inch, and due to the poor breathing characteristics long duration cams are necessary, and high lift ones risky ( S2 is probably pushing it a bit ). That leaves the CP cam which is gentle on the valve train, and (6) throttles. We can choose between LUCAS P.I. ( out of production, problematic at altitude ), EFI ( modern technology, one-of-a-kind on a TR application mostly ) and Weber DCOEs ( still in production, much expertise on TRs, vintage cachet and unsurpassed reliability ). 

Cheers,

Tom  

Edited January 7, 2019 by Tom Fremont

[Dave Ashworth]

Dear All,

Thank you for this variety of wisdom to explore and play with.

I have a traditional TR5 which is very reliable but have decided to go with triple carbs on the 250. I do actually have a spare original TR5 engine to hand too, but I want to see what I can do with the original 250 engine that came with the car to keep the numbers matching whilst honouring the heritage of this 250 being a carb car.

Thank you so much for your input which I will study carefully and apply gently.

 

Cheers.

Dave.

[Jon R]

I have a GT6 Mk2 head that I am currently getting ready to fit on my TR250.

Engine has been blue printed. Head has Standard valves not skimmed (Its 9.5:1 standard I believe)

Ive heard that this head with a Kent cam offers similar performance to the 2500 PI head but with slightly less top rpm hp but an earlier torque characteristic.

Will be fitting SU HS6 or the standard Stroms, with 1" inlet stacks. Either Ive always found straight forward to keep on song and fettle, SUs marginally easier.

Does any one have any experience with this set up ?

Cheers

Jon R (Oxford)