Potato in tail pipe.

[BASHERCAT]

Did i just stick a potato in my tail pipe.?
Bought a new light weight single can and after chopping it apart I noticed the inside diameter (id)was only 1.800.
By looks thought it was 2.350 but it's necked down way inside there making it 1.800
The inside diameter coming out of my pipes is 1.250

So out of pipes is 1.250 going into can pipes which are 1.375 which dumps into can which is 1.800 and exiting 2.350.

So originally thought was dumping pipe 1.375 into 2.350 pipe but i.m not because inside of can is necked down to 1.800.

So did I just drop $300 to put a potato in my exhaust to decrease a bunch of HP ?????? Not mention the time to hack and whack the can to fit.

You would think the manufacturer did a flow test but I have read many times where a can decreases performance and in this instance now I can see why.
They don't have a picture looking down the tail pipe in the adds so couldn't see this online.

Psi modblaster can 13.70 pounds! Hacked up dyi can 7.4 pounds. Big difference in weight. Always hated removing the psi can because it was so heavy and after my bearing swap out for new ones had enough of it and bought a single can.

Was paying more attention to the girls in math class than the teacher.Does anyone know how to calculate air flow without a machine. Where I ride can't get 2 sleds side by side without killing each other or one catching the other guys roost.Would be simple if could just take both cans out and swap out to see if one was better than the other as far as performance goes.But I can't

Any help would be very much appreciated. Common sense says I made a big mistake only after I cut it apart and looked inside.

 

[winter brew]

There is definatly a science to silencer design. I can't speak for a particular silencer but a lot of them do restrict as part of the design. Correct back pressure to work with the pipe for proper scavenging of the cylinder is part of what either makes or loses power. Too tight and it may build more heat on a long pull....but this is where the silencer builders have hopefully done the testing to not lose power, or to cater to certain altitudes etc...

 

[BASHERCAT]

testing but not with winter brew

Well guess my only option is to run it down a logging rd side by side and see what happens.
But by your profile pic not testing with you.That's the problem I encounter when lining them up.Touch the throttle and skis are off the ground and it's all over the place the first 100 yrds so someones either in the roost our your bumping sleds and high speeds.First one to let off gets a free sandblast job.Well in this case a snow job same effect.

Should of just stayed with psi's matched pipe and cans combo but
finally snapped over how heavy the cans were.

The mountain is around 9 miles from the snow park to be lugging a can around on a whooped out trail.By the snopark is granola bar eaters (snoshoers & skiers) so can't test there without pissing someone off.It's flat ground so doesn't take much hp to go fast. Need to test on a steep and deep climb to see if it'll hold the rpm's.Since we have no powder or snow just frozen concrete guess a day of testing isn't going to hurt me. Throwing my mono head back on so will need to jet again so can get 2 birds with one stone.
Was hoping to do one mod at a time so wouldn't confuse which performance mod worked or didn't work.

Thanks for the info just need to test and see what happens.


Just took my handy dandy piston wash led light and stuck it inside psi's can.It is necked down in there also.They have a thin tube with a bunch of holes sliding into the 1.250 pipe.Probably makes it 1.140 inside there.

Taking any opinions on the subject. Don't be shy I'd appreciate any input.


Think got the wrong domes in running 160 psi probably need to run a splash of race gas with my 92 premium no ethonol.
Starting at 2800 ft and playing around 5000 ft.Hope she don't scatter.


That was old piston wash running hard wide open back to the snopark for 7 miles.Then loading on trailer .3000 ft.

Is it within specs?

 

[Idcatman3]

You can approximate air flow by taking the cylinder volume (900 cubic centimeters) times an assumed volumetric efficiency (say 85%, but that's likely high, I don't have my book at home) time peak RPM (8500) and that will give you volumetric flow. Those numbers come out to not quite 4 cubic feet per second, provided I did my quick math right.

The area of three pipes at 1.25" diameter each is ~3.7 in^2,
1 pipe at 1.8" diameter is just over 2.5 in^2, or ~70% of the total. This is likely intended, as Winterbrew said, for backpressure. Many of the cans that lose power do so because they have too little backpressure.

 

[boone]

Maybe i'm completely out of the ballpark on this, but, I know when calculating water flow for fire department purposes...one 2 1/2" hose will flow more water than two 1 3/4" hoses(depending upon hose length) due to the friction loss of the hose.

Could any of that same logic apply here?

Boone

 

[BBP]

So out of pipes is 1.250 going into can pipes which are 1.375 which dumps into can which is 1.800 and exiting 2.350.

I'm not a pipe builder but I don't think the 1.8" can is going to be restrictive, the pipes don't all fire at the same time. I think that changing the can pipes from 1.25" to 1.375" will change your tune more than anything & overall you will have less backpressure than before.

 

[BASHERCAT]

Messengers

Thanks guys for the input.
IDC3 has the math was hoping someone could do. (smart). Except 998 cc
Boone has the theory I was thinking about just by experience. A bigger hose flows more than 3 smaller ones just from siphoning gas. Didn't know it was from friction.
BBP has a point was also thinking.But thought once the rpm got up there it would catch up with not flowing fast enough.

I know the newer sleds with electronics are very finicky with back pressure issues.
Started it up in garage and weather is warmer than on mountain and raining but seems it's running richer now smoking up my garage like crazy.Could only run it for a few minutes so never got it warmed up.Was late at night and didn't want to wake the neighbors at 10 by opening the garage door.It's running on the very safe side already so just maybe needs warmed up.Then again it's a 2 smoke.

Saturday is almost here and were finally getting a little bit of new snow.Just don't want a major engine failure from a stupidity mistake over 7 lbs.



The weight savings made the 1m handle so much better in balance.
The engine mods with head and can ended up being a disaster.
Fresh powder finally and engine leaned out and detonated badly.Didn't get to play in snow after all that work.Forgot jets on bench and left can on garage floor. So bummed .So potato in tail pipe made a huge change in performance. Just not for the better.But didn't have bigger jets to try and fix failure.What a mess.

 

[Booster]

Hey basher, Idac3 is on the right track but you can toss the can in the trash because its the stinger length proportionate to rpm>cylinder volume that affects power not how the silly can cuts dowm db's.

 

[Thunder101]

Lots of people have ran those MBRP cans ( I myself dont like them) but your deto would have came from the head. You said you had 160 cranking psi. You probably needed 100+ octane.