Supertrapp 2-1...........how many discs???

[maineultraclassic]

I just installed the Supertrapp 2-1 on my bike, and now I'd like to know how many discs to run with the closed endcap.

95" 1550 flattops
Andrews 26G cams
Big Boyz Ported/Polished heads
9.5-1 compression
Ness Big Sucker
PCIIIusb

I want good low end torque, but at the same time I want the best power all-around possible.

Thanks,

Steve

[Mike]

We have found that 12-14 gives best all around performance with most engine combo's. Larger cubic inch motors may be happier with 2-4 more (but the 1-3/4 primary runners will limit these anyway). As you go down on the count (as low as 8), the torque tends to develope a W shape, softening in the 3-4k range with some improvement from 2-4. As you go up on the count the 2-4 area starts to suffer but the 4+ will pick up resulting in more high end hp. These affects are more prevailant as overlap and duration is added to the cam timing. FYI, we do see an improved torque curve with the closed end cap vs. the open even when used with a large number of discs (24).
Thanks, Mike

[maineultraclassic]

I prefer to run the Closed endcap to keep the noise level down.

I have 20 discs on there right now to see how it felt. At wide open throttle it felt a little weak, not sure why.

Would less discs make it feel stronger all around? Or would 2-4 more discs make it feel better?

Many have said that the open end cap is the way to go, but I want to keep the noise down.

What have you used with the closed endcap?

Steve

[Mike]

We've gone as high as 24 with the closed end cap. As mentioned earlier, we get a better torque curve with the same hp when using the closed end cap vs. the open. Theory has it that the closed end cap helps reflect back the reversion and acustical waves in a positive way. Less disc equals more back pressure and typically more torque from 2-4k. More disc equals less back pressure and more hp at higher rpms (4-6k) but with a corresponding loss of torque in the low rpms (2-4k). Too low a disc count torque starts to dip from 4-5k, that W shape I mentioned earlier, but without a good top end recovery. Best "seat of the pants" will be 12 disc and with really good noise control. We normally tune by removing discs until we see a greater hp loss than torque gain. when both start to suffer or when the 4-5k area starts to dip. All based on the customers preferences also.
Thanks, Mike

[maineultraclassic]

I want to make sure it's "open" enough to move the air...........with the ported heads and the cams, it's breathing good.

So it's a fine line in tuning............too many discs and the HP goes up but Torque does down, too few discs and the Torque goes up but the HP goes down.

From other people I've talked to online, with similar builds they are using 18 and 20 discs with great results.

It almost seems like it needs about 2-4 more discs when going WOT, but the bottom end feels good as is.

Steve

[Mike]

I believe the guys using 18-20 are going for best dyno numbers, not neccessarily best torque curve shape. Proper thing to do is start with 20 on the dyno then start going down to see what affect this has on your specific bike and combo. The best count for your riding preferences can be decided upon and the EFI mapping done with that.
Thanks, Mike

[maineultraclassic]

I have my plugs out right now, and they are showing a lean condition.

I had thought my map I was using was going to put me rich, but I was wrong.

If I remove discs, will that cause the lean condition to go away?

Or should I go into the map and add 5 to each cell?

Steve

[Mike]

We want to be cautious when reading plugs as the reading can change based on load, rpm and other conditions. The TC motor is a "lean burn" chamber design and so the plugs should appear fairly clean. If you are not experiancing detonation (pinging) or elevated engine/oil temps you may not be too lean. However, better to be safe than sorry so we always err to the rich side when in doubt. Removing discs may richen the mixture but only in higher rpm or high load situations, part throttle light load should not be affected much. Better to go to the AFR table and REDUCE those cells which influence the area in which the plug reading was taken (map, tp and rpm), by 5 or more. This will richen both cylinders the same amount.
Thanks, Mike