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TTP 904s Sports Big Bore Kit

TTP 904s Sports Big Bore Kit
  • Description
  • Reviews

There are very few modifications you can perform on an engine that will improve power and torque right through the rev range, but TTP's 904s big bore kit is one of those modifications. Increasing cubic capacity and compression ratio give improved performance from idle to the rev limit, with no downside.

In use the extra top end horsepower is excellent for acceleration and top speed, but the revelation is the extra torque through out the rev range. It makes riding a Triumph twin far more exiting as when you open the throttle, the engine just pulls and pulls to the red line.

Designed by TTP, the 904s kit includes race quality pistons, a custom 904 MLS steel head gasket together with OEM cylinders which are bored, Nikasil plated and then powder coated externally to give a virtually new set of barrels.

Available for the air cooled Bonneville, Thruxton, Scrambler, America and Speedmaster from 2001-2016.

Kit Features:
  • 12:1 compression ratio.
  • Larger valve pockets for +2mm valves.
  • Tight quench to improve tubulence & combustion burn.
  • Anti-friction coating on the piston skirts.
  • Pistons hand balanced to within 0.1gms of each other.
  • Nikasil plated barrels give tighter cylinder/piston clearance.
  • Hand gapped piston rings.
  • Custom 904 MLS steel head gasket.
  • Optional OEM gasket kit.

Core must have no broken fins and no scratches on the bore or mating surfaces.
Shipping details will be on your emailed order receipt.

3 Product Reviews - Average rating 5 / 5 (Show All)

Click to review this product

904 big bore kit w/ performance cams

- 09th July 2019

I’m about 500 miles...or 800km for those using that other system...into TTPs 904 BB kit & their performance cams, fitted with D&D full exhaust and stage 2 mods rocking K&N intake pod filters, installed on a 2010 thruxton 900...the hype is real folks, the power gains are no joke!!

I have yet to really push it but oh my the top end is SO money. Low end on thruxtons already rocked(s), so add additional 30-35% more power and add that up.

As far as the install...I did it myself, with only oil changes and brake pad replacement experience prior. The learning curve was steep, bloody vertical at times, but with triumphs maintenance manual, various triumphrat post reads, a few YouTube videos and an extra clutch lifter plate later, TTPs 904 BB kit was successfully installed. Was never overwhelmed during but took 2-3x as long as expected.


TTP were there from start to finish. Quick and thorough email replies, addressing any question. Oh ya, even their packaging rocks!!

Is that enough to convince you to buy TTPs 904 BB kit? GET SOME!!

Click to review this product

The later barrels have machined and polished edges which
after processing need to have the powder coat removed
and the fin edges polished back to a shine.

Like for like core exchange only.

Early Barrels  Late Barrels
Early Barrels                    Late Barrels
The Stage 2 Power Induction Kit comes complete with
fitting kit, DNA Performance pod filters, installation
instructions and the required jetting or EFI tune for
the 904s kit.

Carb Stage 2 Kit            EFI Stage 2 Kit
Carb Stage 2 Kit          EFI Stage 2 Kit
This gasket kit includes all of the OEM gaskets
required when installing the big bore kit.
(except head gasket which comes with 904s kit)

904s Gasket Set
904s Gasket Set
With a 904s Big Bore Kit installed,
the standard clutch springs are
pushed to their limit, so we offer
the Barnet Green clutch springs
along with a Triumph clutch case
gasket as an upgrade.

Barnet Green Clutch Springs
Barnet Green Clutch Springs
The Safe Start is a good preventative measure for
a standard engine, with the 904s Big Bore Kit
installed giving an increased compression ratio,
the Safe Start will give protection from the only
engine structural weakness of the air cooled
Triumph twins.

NB: If you're upgrading to the green clutch springs,
why not install the Safe Start while the clutch cover
is off, for complete peace of mind.

TTP Safe Start
TTP Safe Start
Installation of the 904s Big Bore Kit at our
workshop in Bournemouth, Dorset, England.
List Price: £922.00
   Discount on this product.
Price: £830.00 (£996.00 Inc. VAT)
€919.58 EUR (+VAT)    $1,032.08 USD    $1,467.21 AUD