dyno results

[bmbm40]

So I was looking at the Dyno results #3A and #3B and the torque increased from 120 @ 3950 rpm to 140 @ 2500 rpm.
The increased torque is good but having it at 2500 vs 3950 rpm is even better. The exhaust valve is a bit larger and the compression ratio is a half point higher in #3B which doesn't seem to drastic so the major contributing factor must be the direct mount 2v. If you have different insight I would like to know. Thanks.

 

[xctasy]

Certainly is. The standard log hole is too small, and the 2-bbl needs more than a 1.83" single hole to accomodate two 1.6875" spaced carb barrels.

When sufficent spacing is placed between each barrel, and enough of a clear shot to the port runners, there is no longer a 180 degree short turn radius. Its that which really riuns the i take cfm figures, the need for the air fuel mix to bend so drastically.

Intake hole area alone is most of the solution. The first heads saw about 105 cfm tops with the 1.3" hole, but opening it out helps a huge amount. With the later heads, you got about 1.75" of opening. But with 2-bbls, 1.83" minimum is needed, or better still, the whole of a Weber 38, 32/36 or Holley 5200 carb adaptor, which would be a huge 2.25 " diameter.

The rest is de dagging the sharp bends. That could make a bland 127 cfm D8 to E0 head see closer to 145 cfm, close to what an alloy cross flow or 2V iron head does right out of the box.

There is plenty of flow to be found if you do your homework!

 

[bmbm40]

Thanks for the quick reply xctasy. I reread my post and not sure if I explained my question well so just to be sure-I like the fact that the peak torque is at a much lower rpm. Having max torque available 1500 rpm lower is good for Bronco driving. Opening up the log is the biggest change so I guess it would follow that is the cause it just seemed to good to be true.

 

[xctasy]

If the port and cam are sized for low end torque, improving the air flow by opening the carb mounting face will help torque without hurting any of the great easy going characteristics of the engine.

When the cross flow head was added to the Aussie I6's, there was no loss in low end torque, and in fact, torque rpm went down to 1800 rpm from 2400 rpm with the 256 degree cams.

In a simialr way, the direct mount is adding flow, but it doesn't result in loosing torque if you do it right.

 

[chad]

I was thinking you could get better low rev tq with 1V (large of course) than a 2V carb, all other specs equal...