fj1289 wrote:
1349 cc big bore in XJR siamesed cylinder. (Plan to use Ross pistons - full skirt design and smoother piston top than other FJ/XJR pistons available - no “ridge” between the valve cut outs)
That all sounds fine but when possible, the MOST important nitrous specific piston feature is a taller crown (at the perimeter NOT the center), so there is more land between the rings. If possible, raising the cylinder block (by fitting a spacer underneath) or sourcing a taller block, is the best way to accommodate that feature.
The second most important feature is the compression ratio, which benefits from being lower than would otherwise be the case.
.0022” top ring gap
.0020” second ring gap
I can't give you actual figures but the guide is as follows;
1) Bigger than stock is essential
2) Too big is better than too little
3) Too much will have negligible negative effect
(Base gaskets stacked to put the piston .04-.05” in the hole. Head gasket is .040” - to give .090” quench — or lack of!) I think we previously set the piston even with the deck — will have to check with my engine builder/sponsor
With that being the case, you could fit a taller piston, as a stronger ring pack is more important than having no squish.
Cylinder head
Stock sized intake valves
Stock sized exhaust valves (1mm oversized exhaust valves for this year)
Mild performance camshafts (slightly larger exhaust cam for this year)
Stock style shim over bucket valve train
Minor port cleanup
Combustion chambers opened up to bore size - unshroud valves and decrease compression
Wise improvements
4-1 exhaust with open megaphone
C-16 race fuel (strongly considering Ignite 114 ethanol based race fuel based on Ransom Holbrook’s suggestions)
Ransom obviously knows how to get the job done, so following his advice is a must.
Fuel injection conversion utilizing Yamaha FJR throttle bodies (with Subaru WRX injectors) and Megasquirt MS3X ECU.
I’m running a dry nitrous setup utilizing WON bottle valve, 250 pulsoid, Y blocks, and discharge tubes.
Please post some pics of the installation, especially showing the Y-Blocks and pipework.
The MS3X progressively controls the nitrous based on rear wheel speed (VSS sensor fitted to rear wheel) with 10 set points. The PWM frequency is adjustable (need to see what freqs are selectable on the pull down menu). I run the PWM output through a solid state relay to the pulsoid.
We’ve slowly evolved to this setup over the course of a few years as we address different short falls and make incremental improvements on previous successes, build on our own knowledge, and receive valued advice from trusted sources.
Thanks for any and all input!! (And hope this is not too much info to begin.... !)
No problem.
