Centermount pipe

[PR Crippen]

Building my first bike, it's a 330 esr motor not sure how it's ported pretty sure pipe that came with it was for mx/or woods riding, it's regular mount pipe. My question is how does centermount pipe/silencer look compared to regular mount? Does the silencer sit inside frame rails instead of outside? And if my motor is ported for woods/mx how would trx9 pipe change the performance of my motor? I'm switching from 38 a/s with airbox to 39 pwk carb an airbox eliminator. Thanks for any help everyone, I'm way out of my depth with this project.

[Hawaiiysr]

Yes, Center mount pipe mounts inside the frame rails. It is designed for those guys that do not run a air box just like your wanting to do. It also is good because the silencer will no longer hit the rear caliper on hard landings. Personally it think a CM looks cool. Performance should be nearly exactly the same as a regular mount.

TRX9 is a hi rev pipe. So for XC it may not be so great. More of a mid to top pipe. Many of us like the TRX5. I would think that pipe may suit your needs more if you riding XC and MX. And since you have a 330 a TRX5B would be the wiser choice. The diameter of the stinger is bigger then the normal TRX5.

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[PROX370R]

I agree with the Hawaii dude ^^^^

[rk88r]

The 5 is a great pipe. The B has a larger diameter head pipe, I think the stinger is the same.

[hickwheeler]

I thought the purpose of going to the big bore pipes was to get a bigger stinger

[Jerry Hall]

Yes, Center mount pipe mounts inside the frame rails. It is designed for those guys that do not run a air box just like your wanting to do. It also is good because the silencer will no longer hit the rear caliper on hard landings. Personally it think a CM looks cool. Performance should be nearly exactly the same as a regular mount.

TRX9 is a hi rev pipe. So for XC it may not be so great. More of a mid to top pipe. Many of us like the TRX5. I would think that pipe may suit your needs more if you riding XC and MX. And since you have a 330 a TRX5B would be the wiser choice. The diameter of the stinger is bigger then the normal TRX5.

Hold on for more input. The rest of the fellas will pop in with more to say.

The stinger on the  ESR TRX 5 B is the same diameter as the  ESR TRX 5.  The center mount pipe also has the same diameter stinger without the bend.  Most of the 250s that come through our shop for tuning, loose power with the center mount pipes verses the same pipe in the out of frame silencer version. I have seen 250s that are making around 50 hp loose more than 4 hp when going from the out of frame silencer to the center mount silencer on the ESR TRX5 pipes.

A pipe must have the correct amount of restriction to make the most power over the widest RPM range.  A pipe that does not have enough restriction will usually see a slight boost in the low and mid RPM power with less peak power and over-rev power.  A pipe that has slightly too much restriction will make good power over a wide range but will cause excessive piston crown temperatures.  A pipe that is severely over-restricted will not make good power in the usable power range through the over-rev range and will not usually cause piston crown overheating.

The center mount pipes will flow more exhaust through a straight stinger because they do not have the bend in the stinger and there is not a reduction in the stinger's inside diameter where the stinger is crushed in the middle of mandrel bend.  This crushed bend is common place in the out of frame TRX 5 and TRX 9 silencer versions.  

My suggestion is to use the out of frame silencer version if you have a 250 and the center mount version for above average 310s, and mild 330s.  If you have a really hard running 310 (around 55 HP on my dyno) you may need to consider a 1 1/8" inside diameter stinger and silencer.  I would suggest that anything making more than 55 hp to use the 1/1/8" inside diameter stinger and silencer.  Engines that make 70 hp or more may need to reduce the restriction even more than the 1 1/8" id stinger generates.  

The stinger size depends upon the flow characteristics of the stinger and silencer package combined with a engine that is putting out a specific amount of power.  A smaller straight stinger and silencer can have the same flow characteristics as a larger stinger and silencer if the stinger has bends in it or has flow reducing bad junctions or weld boogers.

[wilkin250r]

To help support exactly what Jerry said, there are two-stroke porting and expansion chamber design software programs out there.  They don't take into account every little factor, but they do a good aproximation.

With two-stroke pipe software, you can create artificially high HP numbers using small stinger diameters.  In actual practice this results in overheating, so there is a discrepency between calculations and real-life applications, but the THEORY is still sound, stinger restriction is a very important aspect of pipe design.

Restriction has a variety of factors, the largest being diameter, but length and path are also important aspects, and that's the biggest difference between the in-frame and out-of-frame pipes.  The in-frame pipes have both a shorter length and less restrictive path, making them better for the bigger bores that need that extra flow, and actually worse in many situations for the stock and small-bore engines.

[PR Crippen]

Thanks everyone for ur input and information it's greatly appreciated. Thinking I'm gonna go with trx9 center mount

[The Phantom]

Thanks everyone for ur input and information it's greatly appreciated. Thinking I'm gonna go with trx9 center mount

might have one for sale check your PM