LeeU

My Feedback: (5)

I am working on an adapter for my 2000 Rossi .45 and the Performance Specialties Ultra Thrust muffler. My question is how much of a differance does it make to port match the muffler to the motor, I know it makes a lot of differance in full scale motors. The Rossi 2000 27R .45 has exaust dim. as follows (.8175" w x .300" h) and the Ultra Thrust muffler has an exaust inlet of ( .7090"w x .3375"h) there is enough meat on the muffler to port match. Also th stock Rossi muffler has an exit hole of .3460" and the diam. of the exspansion portion of the muffler is 1.5490" compared to the Ultra Thrust mufflers .250" exit hole with an exspansion diam. 1.5605", the big differance is the stright portion of the Ultra Thrust muffler is 1.00" longer. Both mufflers have the same lenght of 8.00". The Stock 2000 muffler weights 3.46 oz compared to the Ultra Thrust muffler weight of 4.52 oz with the alum. adapters. Just for kicks my Rossi weighed 15.08 oz. If any one wants the drawings of the adapter down load the AutoCAD viewer from Autodesk (if you don't have AutoCAD) and I will email a copy to any one that wants it.Lee

w8ye

My Feedback: (16)

I have a Super Tigre 61 that I bought used and the muffler stack had a 2mm screw threaded halfway through the stack up close to the motor. I could gain 200 rpm by taking the screw out. I also gained another 100 by matching and blending the square portion into the round portion. (This stack was a poorly made one from Super Tigre. My others were made much better.) My point is that up close to the engine the flow should be smooth.

However in a tuned situation you can get into a total chamber volume problem. So be careful.

Good luck

Jim

JasonF

My Feedback: (2)

This is a very interesting question and one that I have asked myself. On helicopters in particular nearly all of the aftermarket expensive mufflers are not even close on the port matching. You would think if it would add power they would go ahead and do it. I once emailed an engine expert (forget his name at the moment) and he told me matching the ports would cause a run away lean condition in the midrange whereas if you left it as is it would be nice and rich. Something to consider.

Jason

LeeU

My Feedback: (5)

Performance Specialties does not have a muffler that is specifically for a Rossi, the one I got does match my OS FX .46 bolt pattern but the measurments for my exaust port on the OS does not match. The OS exaust port is (1.143" X .272") compared to the Ultra Thrust muffler (.7090" X .3375") so you may be right. And since I will use this for my new aerobatic Hot Hots I will be in the midrange a lot. Lee

ChuckAuger

My Feedback: (12)

I put an UT for OS 46 on the Irvine 53..and had the same mis-match as you. I Dremeled the muffler just a tad on either end of the port so it would match. Just hated the thought of a ledge right in the exhaust port. Didn't tach it before I did it, so I don't know how much, if any, it helped. FWIW

Oh yeah..my mid-range is just dandy...but we are talking 2 different brands of engine/carb. The amount I removed was probably .125 either end of the port.

LeeU

My Feedback: (5)

ChuckAuger, that was the problem I had, was that lip on the inside bothers me too. Lee

Taildrager-inactive

My Feedback: (11)

Anything you can do to make the air fuel mix -exhaust flow smoothly makes more power.

gubbs3

My Feedback: (1)

I don't know what the RPM gain would be but I did do that mod in a R/C car. There was a noticiable gain in top end speed. I didn't notice any increase in noise. I would say do it. Even if it is just a 100 RPM increase.

"It doesn't matter if you win(gain) by an inch(1 RPM) or a mile(1000 RPM) , winning is winning."

Steve Collins

My Feedback: (8)

LEE U,

Your best source for advice on this matter is Performance Specialties. Give Dave Shadel a call and discuss it with him. He is the expert and can tell you what sort of pros/cons you can expect.

ChuckAuger

My Feedback: (12)

About this when I did mine..he volunteered the info about matching the port as soon as I mentioned the mis-match...FWIW