Building a High Performance Triumph Six Cylinder

To build a Triumph six cylinder with improved performance, start with a good general bottom end rebuild.  Bore cylinders as needed.  I do not suggest boring further than needed just for the few extra CC’s of displacement.  Standard cast pistons will work fine for street engine running premium pump gas.  Recondition crank as needed.  I always balance crank, flywheel, clutch, rods and pistons.

Decking the block is optional unless it needs to be skimmed to flatten.  From the factory the pistons are usually recessed about .010″ to .012″ below the deck at TDC.  It does help performance if the pistons are exactly flush at TDC (zero deck) but you do not want them protruding above the deck.  It gets a little time consuming to determine exactly how much to cut off the block to reach zero deck.  To get it exact it is best to do all other machine work first then temporarily install the crank, rods and pistons without rings and accurately measure how far the center of each piston is below the deck of the block (deck height).  Then disassemble and cut the recession amount off the deck.  The 1972 and later blocks have a groove cut into the deck around each cylinder so if you deck the block you have to re-cut the grooves to the right depth.

The TR6 engine does not have cam bearings.  The cam rides right in the block, cast iron to cast iron.  This works fine at the mild performance level of the stock engine but as we increase valve lift and valve spring pressure to handle the higher lift, pressure on the cam is increased and at some level, we become concerned about the lack of cam bearings.  Many customers are running our GP2 cam with 1.55:1 rockers without cam bearings but for anything beyond that I strongly suggest boring the block and installing bearings.

Most of the performance increase will come from the camshaft and compression increase.  Other upgrades can build on that base for further increase in performance. Choice of our GP2 or GP3 cam will depend on your performance goals.  The GP2 will provide great low end and midrange torque.  The GP3 will have a little less torque at the low rpm, about equal around 4000 and more power from there on up.  In back to back dyno tests on my engine the GP2 had 157 flywheel hp at 5500 rpm and the GP3 had 171 at 6000.  The test engine had 10.8:1 compression, 1.65:1 roller rockers, triple Strombergs and exhaust header.  Back then I was able to get away with 10.8:1 compression on 93 octane pump gas but with today’s gas I suggest not going over 10:1.  Most folks go with about 9.75:1 to be safe.

Good head preparation also contributes to performance.  Porting and combustion chamber shaping can significantly improve flow but can be very time consuming so it can be expensive if you are paying someone to do it.  To increase compression you just machine material off the face of the head.  Our compression ratio chart shows approximate head thickness for various compression ratios.  Of course if the combustion chambers are reshaped, adjustments will have to be made for the increase in combustion chamber volume.  I suggest using bronze valve guides with Viton seals.  The standard intake and exhaust valves will work.  For optimum flow you can use the oversized “flow optimized” valves.  I always recommend having hard exhaust valve seats installed.  Without hard seats the extreme heat of the exhaust will cause pitting of the cast iron seats.  With either cam you will need our high lift valve spring set.  For proper centering of the springs around the guide to avoid the spring hitting the seal I suggest using our valve spring seats.  Our titanium valve retainers and hard valve locks are a nice upgrade over the OE retainers.  Shorter push rods will be needed due to the reduced head thickness.  At about 9.75:1 our .120″ shorter than stock tubular push rods will work best.

When rebuilding a TR6 engine you usually find that the rocker shaft is worn and the ID of the rocker arms are galled and worn.  Our roller rocker assembly is a great upgrade in reliability and performance.  The original rocker ratio is about 1.45:1.  Increasing the rocker ratio improves performance by increasing valve lift and valve speed.  We make the roller rocker assemblies in 1.55:1 and 1.65:1 ratio.  Performance gain can be up to about 5% with 1.55:1 and 10% with 1.65:1.  Additionally, roller rockers reduce valve stem wear by reducing side load on the valve.

Other items to consider for increasing performance are our lightweight steel flywheel to allow the engine to rev quicker and our ATI Superdamper kit to reduce power robbing harmonic vibrations in the crankshaft.

External items that can be added at the same time as the rebuild or added later include our 6-3-1 exhaust header and triple carb intake.