ESE's works engine tuner

[andreas]

Very interesting Wobbly. Yes pumper carbs are mostly out of my scope.

[andreas]

Andreas test it like this save you lot of work you can make changes quicker

I don't really follow how you mean?

[F5 Dave]

He means i believe as a straightish pipe hanging out and then make snake like when you are happy.

[dutchpower]

He means i believe as a straightish pipe hanging out and then make snake like when you are happy.

Yes

[andreas]

Ok, I see. It isn't going on a dyno, and elongate/shorten belly/header is not so hard.

[dutchpower]

Ok, I see. It isn't going on a dyno, and elongate/shorten belly/header is not so hard.

Oke Andreas

[wobbly]

Once again Frits is on the money.
My empirically derived idea of exhaust duct exit reduction to 75% of the effective Exhaust Port area works very well as a guide to the size to be looking for.
Frits has always maintained the exit area should be tied to the Blowdown capability.
Here we have a case of the Blowdown , that is optimized to achieve a relatively modest 13 Bar bmep , achieves Mach 0.8 at the pinch point with a 71% area reduction.
Smaller looses power as does a larger exit diameter.
It seems the only way to optimize this factor is by tracking the Mach number to achieve 0.8.

[Tim Ey]

Once again Frits is on the money.
My empirically derived idea of exhaust duct exit reduction to 75% of the effective Exhaust Port area works very well as a guide to the size to be looking for.
Frits has always maintained the exit area should be tied to the Blowdown capability.
Here we have a case of the Blowdown , that is optimized to achieve a relatively modest 13 Bar bmep , achieves Mach 0.8 at the pinch point with a 71% area reduction.
Smaller looses power as does a larger exit diameter.
It seems the only way to optimize this factor is by tracking the Mach number to achieve 0.8.

Hi Wob,
bore is apparently 59mm, may you tell us the stroke?

Regards
Tim

[porttiming124]

Hi Wob,
bore is apparently 59mm, may you tell us the stroke?

Regards
Tim

Tim here is a small calculation to find the bore .

51.8/71.9*100 = 72 mm

[wobbly]

Yep , she's a big bore dragster.
72 B X 63 S - Rod 130 = 256,5cc
So the power is limited by the huge oversquare ratio compromising STA but also it can't be rev'd hard due to the heavy piston even though the stroke should easily go to 11000.

[Tim Ey]

Tim here is a small calculation to find the bore .

51.8/71.9*100 = 72 mm

Ouch. Wrong window. I did the very same calculation with the Effective Port Diameter

Yep , she's a big bore dragster.
72 B X 63 S - Rod 130 = 256,5cc
So the power is limited by the huge oversquare ratio compromising STA but also it can't be rev'd hard due to the heavy piston even though the stroke should easily go to 11000.

I would agree: the exhaust window area is right on the money.
Regarding the 75% rule in general, I tend to disagree:
The Flange will be allright when:
Flange-Area = .75 x BigEnoughExhaustWindow-Area

but the Flange will be too small when:
Flange-Area = .75 x NotEnoughExhaustWindow-Area

In that case, using a Flange-Area that is too big (>75%) can compensate for an exhaust port that does not supply enough area for the desired power.

[wobbly]

Now I disagree , as the proven 75% exit area works perfectly on a TM or an Aprilia , if you then have an Exhaust port that makes sub optimal power by not having sufficient Blowdown area -
then as the above example shows , a smaller exit % of 71% in this case works way better.
That is , as Frits has said , the exit area is a function of the Blowdown capability , and that is what sets the bmep achievable - low bmep = low exit flow = smaller area needed to hit 0.8 Mach.

[andreas]

Kawasaki Mach4 for sure.

[dutchpower]

Kawasaki Mach4 for sure.

Did you test the pipe Andrea

[andreas]

Did you test the pipe Andrea

Not tested, it wasn't finished before I opted for thicker walls.