Dry Lakes Racers Australia

Stayt`ie wrote:mate, never underestimate the information gathered from a dyno, sure, thay all read different, but,, always use the same dyno and work with what it tells ya,, sometimes changes to your machine "feel" right, dyno readings will confirm, ,, for example, i made a new exhaust system and ran it at the drags, thought it was better by the sound and feel , ran it up on the dyno, had made horsepower where i didnt want it, and overall had lost heaps up in the rev range,, i binned that pipe, , but without the dyno readings i would have kept using it, mistakingly thinking it was better, ,,,

Spot on, and the Seat of the Pants Dyno can be even more deceptive with a 2 Stroke.

If the changes you make lead to a narrowing of the powerband, it simply feel like more power and it usually isn't.

You simply have less power off pipe and a sudden rush of power when you come on pipe, but it does not mean you have gained power.

Get a baseline curve and go from there.

Pete

Here's a chart from my simulation software.



The porting here is pretty wild and it's on methanol to boot. I'm not sure 35.5HP is really possible (ie sustainable) with this engine without it being a grenade. The real issue here is whether or not the power curve as shown here ends up being anywhere close to reality. The torque is rising from 8,500RPM and redline is 13,500RPM. For the type of run it'll do on the salt, that power curve should be pretty good. It's not like it needs to launch out of corners. For the top three gears, it never drops below peak torque at 11,000RPM.

I think what I'll end up doing is not porting it quite so wild at first and see what the dyno says.

Chris

What Exhaust Pipe design are you going to use?

Pete

A custom expansion chamber of my own design.

It's taken a couple of years iterating through the sim to get it right although until I get it running on a dyno, I won't know how "right" it is.