Plugging pipe

[wydeglyde]

I read with great interest your letter in American Iron regarding the effects of pipes. I have looked through several dyno charts and have some questions. My bike is an 05 FLTRI with 95", Woods 6HG cams, SERT, (approx 9.5:1 compression, cranking pressure is about 175 psi each cylinder), and S&S SPO slipons. I am experiencing a nasty dip at 2800 rpm which doesn't recover until a little over 3200. The bike doesn't want to pull through these rpm and vuibration increases. Once past there it pulls pretty good.

I noticed in the comparison area you plugged the left pipe. Where was the plug placed, what was it made of? I believe it had a 5/16" opening? It really seemed to straighten out a similar dip in torque.

Would this work with the S&S SPO's? I see you don't have a lot of dyno's for these pipes.

I also noticed the D&D Boarzilla pipe seemed to maintain torque very well through the same area. Do you think that pipe could work with my setup?

Thanks for you advice you can give. I have been fighting with this issue for over a year and the shop and I can't seem to agree on the solution.

[Mike]

We were experimenting with plugging the left side head pipe on stock systems to mostly try and cure decel pop, which it did, but we do also pick up a little torque with little or no hp loss. DO NOT do this with true duals systems, you'll damage the motor. The plug was placed at the end of the pipe where the muffler slips on. Others have placed it higher up where the left cross over pipe fits to the right side down pipe at the rear head. We use a block freeze plug purchased at the local auto shop. We did notice an increase in heat (logical) in the rear pipe when doing this mod. The new mapping on later bikes has reduced decel pop to the point that we've kind of gotten away from this mod, mostly for the heat reasons.

We do not have a lot of data for the SPO's, not real popular due to the cosmetics and the lazy torque dip around 4k rpm (a W shaped tq curve). I'm surprised yours dips at 2.8k, typically it's fairly strong through that area. Part of the problem may also be that compression is a bit low for the 6H cams. They really like at least 10.0 and we recommend 10.5 with them for a cranking pressure of around 210lbs (Bob Wood will recommend even higher numbers).

I'm a big fan of the D&D exh because they place the torque dip low enough in the rpm band (typ about 2k) that it's no longer really an issue. On a 95ci motor I would recommend the Fatcat system, the Boarzilla will have too much volume to carry the exh well for scavenging and back prressure will be too low (great pipe for 110ci+).
Mike

[wydeglyde]

Thanks Mike! I have long suspected that compression was too low for those cams. I have read a few people state that 10:1 is very reliable with the TC and detonation is easily controllable, how about at 10.5:1? Thanks in advance.

[Mike]

Just depends on the cam choice. The higher the compression, the more cam timing you can have to reduce risk of detonation. 10.5 and even 11 is becoming more and more common with the better chamber shapes and electronics we have today.
Mike