Exhaust pipe analysis

[dvogtvpe]

Most of you guys probably by now know that I say exhaust pipe diameter and length is critical. playing with a 16 stocker on the dyno today. I cut 3 1/2 inchs off of the pipe and lost 2 ft lbs of torque. so I welded it back on. picked up 2 ft lbs of torque. put a lollipop in the exhaust and started adjusting back pressure and picked up another .5 ft lbs of torque.

[counciltucky]

sorry but I am not formilliar with lollipop, and how that works can you explain? Also could you help me with the length of pipe for improved torque

[fourinchdragslicks]

It is basicly a damper, a washer welded on the end of a stud...you turn the stud in the exhaust to block more or less of the pipe area with the washer. With pipe length, you are "tuning" the exhaust for your target operating conditions... rpm under load... if I remember right it you are using the diameter and length of pipe to optimize scavenging effect under your target conditions.

[dvogtvpe]

your pretty much on as far as exhaust tuning goes. I use a 1/4 in eye bolt and weld a washer to it then round it off a bit. its a little sturdier.
I've never played with one on a 4 cycle , they are more popular with 2 cycles. it was worth the time for a .5 of a ft lb of torque. I would have liked to play with it some more but we had close to 20 runs in 4 hours and I was ready to call it quits for the day.

[Sam Mac]

Everything you do on an engine affects power. Ask me how I know. Pic of one of my engines on the Dyno

[J-Mech]

I'm really surprised that a little back pressure increased torque. Got any ideas why? I've got a theory.....

[OffTime]

Originally Posted by J-Mech

I'm really surprised that a little back pressure increased torque. Got any ideas why? I've got a theory.....

I thought that back pressure would only decrease the scavenging effect as well, therefore decreasing torque. I'm interested in that explanation.

[mickb72]

Originally Posted by J-Mech

I'm really surprised that a little back pressure increased torque. Got any ideas why? I've got a theory.....

Waiting to see what Don has to say about those singles. I know he said 25" earlier. I am building a stock 16 one now and have a pipe i don't like. It's a 3 stage mainly for open rpm motors. It was cheap and delivered. The kid wouldn't call me back, i was gonna change the design, guess I'll be doing some chopping. On my stock 25hp twin puller Jullian at MWSC told me the smaller pipes 11/8" were better. Good for 2 or 3 hp. The two into one pipe. He says those stock twins like the back pressure and they sound great. Mike

[Mike McKown]

Talking about changing pipe diameter to change torque or curve of torque.

Years ago, I used to ride motocross, hare scrambles and enduros. One of the last bikes I rode was a TM 400 Suzuki. 40 hp/220 lbs. No flywheel. The throttle was either on/off, there was no in between. Like a light switch.

The thing had a tuned pipe on it called an expansion chamber. Tuned for wide open throttle.

One day, I hopped across a very large log and didn't quite make it. I bottomed the bike out of the log and the exhaust pipe got mashed about half shut.

The immediate effect was, all of a sudden, the bike became manageable at slower speeds and would now lug along where before, like it said, the throttle was like a light switch. I never fixed the mashed pipe.

[nikster]

This topic is way beyond my comprehension of fabricating

Doo-Hickeys?

NIK,

I guess if one is into pulling/racing a small 12hp., it would be usefull?