Club Triumph

Hi,
I hope you don't mind me joining your forum as a guest.

I have a 1971 TVR 2500 with the US detuned TR6 engine (engine number CC751..). I believe this has a 8.5:1 compression ratio.

I was wondering what the main differences are between this and the 2500TC or 2500S engines. Mine is running (badly) on HS6 SUs with K&N filters.

What spark plugs are recommended for this engine? Mine currently has NGK BPR6ES plugs that probably need changing.

The NGK site recommends BP5.. plugs for the 2500 saloon and BP6 plugs for the TR6. I can't find the difference between the two plugs. Does anyone know.

I'd be interested in your thoughts.

Best regards,

Chris

Chris,

BP5 is a hotter plug than BP6 which is to say that it will be better at burning off carbon deposits from its electrodes/insulator (and thus less prone to fouling) but more prone to causing pinking in higher performance engines.

Not all US spec engines are the same.  Some had even less than 8.5:1 CR I think.  All had very mild cams.

The bottom end of all of the 2.5 6 cylinders engines re. crank/rods/pistons are basically the same (excepting earlier versions of the higher performance engines used in TR5, MK1 PI saloon and very early TR6, which had some crank variations).  The differences lie in the head and cam.  It is therefore relatively straightforward to upgrade.  How far to go will depend on what you plan to use your car for.

Cheers

Nick

Nick,

Many thanks for your reply. The plugs in mine are prone to quite a lot of carbon build up. Over the last week or two, with the colder weather, I've noticed the engine won't run smoothly until I've been driving for ten minutes or so. I think some hotter BP5 plugs are in order. Got to be worth a try.

Thanks again,

Chris

Hi Chris,
             your rough running of the engine in the first few minutes may not be the fault of the plugs.
The HS6 carbs are very simple and work very well. Are they in good condition?
After a good number of miles the butterfly spindles wear and let air in weakening the mix. Even with the choke out it may not be getting the full fuel mix it needs.
Once warm the air leaks tend to noticeless.

Roger

Hi Roger,

Thanks for your reply. I've only given the carbs a superficial check for air leaks so far. I've used a carb balancer to check the air flow. The readings on each carb are steady.

On my previous car - an MG Midget, the spindles were worn. This led to a lumpy tickover and erratic readings with the carb balancer. Synchronising them was somewhat hit an miss. New spindles and throttle discs worked wonders for the tickover (and readings on the balancer) but made no noticeable difference when driving the car.

I hope I'll get a chance to get the carbs off and have a good look possibly over Christmas.

Until then, I think a new set of plugs is worth a try. The car had been standing for six or seven years (started regularly though) before I bought it. I think it deserves some new bits. BP5 plugs are probably worth a go. The engine in mine is a low compression, low output - about 104 or 106 bhp I think. Must be worth trying the plugs recommended for the 6 cylinder saloons.

Thanks again for your reply.

Best regards,

Chris