TR7 Sprint Conversion

History

In 1973, the Triumph Dolomite Sprint was born. It's cast iron block consisted of the old 1850cc casting having thicker liners fitted, then rebored to 1998cc. In other words, later 1850cc engines could become 1998cc with a rebore and new pistons - sound familiar TR7 people?

The clever part of the Sprint engine was that the new 16 valve head only needed one camshaft - this won it a British design award. The camshaft acts directly onto the inlet valves, but uses long fingered rockers to open the exhaust valves. To do this, each cam lobe is used to open both inlet and exhausts. There is a downside caused by this interaction in that 'manic' cam profiles (specifically overlaps) cannot be used.

The TR7 engine was, in effect, a Sprint engine with the 1850's 8 valve head.

In all, there were about 22,000 Sprint engines made, the last being sold in 1980.

Sprint FAQ?

BL designed the TR7 Sprint (non-US markets only) but due to a long strike at Speke, only 100 were made and sold. The car effectively died with the factory - Speke closed and the TR7 moved to Canley.

Question: why was the Sprint never destined for the US
Answer: the 8 valve head had integral ports for exhaust recycling, the Sprint had no room for this emission control device.

Question: was the Sprint used elsewhere?
Answer: I like to think that it could have been used in the Triumph Stag (think of 2 TR7 engine siamesed together to make a 3000cc V8). This engine could have gone to 4 litres and had 32 valves... mmm, nice!

Question: Why not just fit a V8.
Answer: The Sprint conversion is alot simpler and, if the engine is tuned, can give 150bhp which is only 5bhp lower than that of the standard Rover SD1. The Dolomite Sprint race/rally engines reached 200bhp.

TR7 Sprint installation details

Find your engine

In the US, you could spend money on the Rimmers option, or you could buy the parts to convert your old TR7 engine. This is what I did, so read on for further details.

You could also try The Dolomite Homepage for more information.

Converting a standard TR7 engine to Sprint specifications

• A cast iron exhaust manifold, similar to the TR7 in size, although completely incompatible.
• A new water transfer housing fitted to the rear of the head, specifically for the TR7 heater hoses and system.

Purchase the following preferably secondhand:

• A 'complete' 16 valve head for about 100 pounds sterling
• New head bolts and studs (reuse old ones if money a problem)
• An inlet manifold/carbs and air box for about 30 pounds sterling
• An exhaust manifold for 200 pounds (this is a new 4 branch - the Dolomite version is unuseable)
• +20 thou Sprint pistons (you can use the old TR7 items, and machine new valve cutouts - downside is low compression)
• Sprint timing cover, gears, chain and tensioner (100 pound sterling)
• Sprint crankshaft pulley (10 pounds sterling)

Do the following:

• Strip old TR7 engine
• Balance rotating parts
• Fit fast road cam and shim up accordingly - shims from Triumphtune
• Fit uprated valve springs from Triumphtune
• Dowel the cam to it's sprocket - otherwise the connection will break!
• Rebore engine to fit new pistons
• Rebuild engine
• Fit inlet manifold and carbs (can use old TR7 SUs)
• Modify TR7 linkage to fit Sprint carbs (actually convert Sprint link bar to TR7 standards - a bit of brazing)
• Modify Sprint airbox to take hot air sensor and TR7 outer cover and it's air flap
• Use Sprint heater hose system if the TR7 transfer housing unavailable
• Refit engine using TR7 mounts
• Fit exhaust manifold to existing system

All done, and all the car 'sees' that is different is the exhaust downpipe. Simple n'est pas?

Errors and omissions excepted!