Topic: Exhaust tuning

[scottly]

It wouldn't be too difficult to slot the cam sprocket, but I would like to optimize the exhaust first, so I can weld up a permanent system. One thing I do have to say in favor of the FT motor is that it has survived well over 100 dyno pulls, as well as logging over 13,000 street miles without a whimper.    

[scottly]

I did a test with an "expansion chamber" of over twice the volume of the previous intermediate pipes, and found both a drop in torque and HP below 6k RPM. I'm going to weld up a compromise of the best systems, and call it done. TG, at this point I have to believe the restriction is now the head.
 

[ivanhoew]

scott , just as a mater of interest ,i notice the graphs have smoothing
5 on them , is it possible there is detail missing because of over smoothing ? i found with a dynocom dyno , the curves only showed detail with smoothing on no1.


robert.

[scottly]

Hey Robert, on your suggestion I viewed the graphs with different smoothing levels from 0 to 5, but didn't find any glaring details. Every graph I viewed did show higher peak HP and TQ with level 0, but it was even across the board for all graphs.   

[Kemp]

Hi Scotty - re Hindle CB750 SOHC Stainless Steel Exhaust. He was using F3 head I believe as the engine was a 1978. The barrel and head received some major attention as it was a set of the inexpensive 836 pistons out of Japan that were used and a fair amount of work was needed to get them to work in the 78 motor. In the end, piston to valve was too close and once it started to rev on its first run, bang! It was a long time ago, the first ever run with the CB750 Hindle pipe so I could be off on the 73hp at 7800. I'll see if they still have the dyno graph. Hindle has the latest software now on the dyno and my CB650 was the first of our pipes to run with it. They are having some issues on exporting dyno runs by email with the new software but I should be able to get them in some format that I can publish. The damaged motor is being rebuilt, new valve seats being made plus some porting this time. I don't have an eta yet but it will be run.

[scottly]

To "export" a dyno graph, I print it out from the dyno PC, and then scan the print at home.