904 Big Bore Pistons


Two Stroke
We thought we would give you a preview of our 904cc Sports Big Bore Kit pistons for the air cooled twins.

They give a compression ratio of 12:1, have a tight quench, anti-friction coated skirts and have +2mm valve pockets.

The big bore kit should be available in 6-8 weeks.

TTP 904 Pistons.jpg




Two Stroke
Hi All,

thought you may be interested in the first dyno run for our new 904s Sports Big Bore Kit.

On this dyno there are three runs showing, EFI 865 OEM, EFI 865 with TTP Stage 2 Power Induction Kit and 904s with Stage 2 kit.

EFI 865, Stage 2, Short Megas vs Same +904s.png

The bike was an 865 EFI Bonneville fitted with the TTP Stage 2 Power Induction Kit, Tune 12 & short free flowing silencers vs. the same bike with 904s Big Bore Kit installed with 904s Tune 12.

904s St2 vs. 865 St2 - Peak Power +12% (78.76 bhp), Peak Torque +18.1% (61.21 ftlb) & Max Torque Increase +20.5% @ 5,735 rpm.

904s St2 vs. 865 OEM - Peak Power +29.8%. Peak Torque +30.6% & Max Torque Increase 34.3% @ 4,173 rpm.

We're really pleased with the results, not bad for an OEM engine using the 865 cams and 904 big bore. The bike pulls really well through the rev range, which isn't surprising as it has more mid range torque than our carb 904 with Stage 2 kit, 790 cams, less CR and Keihin FCR39's carbs. The carb bike had 4bhp more at the top end due to 790 cams and FCR39's.

Next will be the same EFI configuration, but using the early 790 cams for more top end power........