Full Exhaust vs Slip-on

[TrxTex]

How much difference does it really make? I'm looking at getting the Yoshi Comp series full or slip-on....havent decided if it will really be worth it to get the full. I've heard that if you dont have a lot of motor work done then it is fairly pointless to get the full...

I know you guys have your opinions...let me have them.

Thanks....ASAP by the way....I hope to order today.

I'm picking up my 450r this friday and I want parts here by then.

[sparky450AR]

The trx motor is choked down. If you want maximum power the full exhaust is the only way to go. Ussually on the dynos, when the header is added it adds atleast a third of the power. Look at some of HMF's dynos.

HMF Slip on(look at theHP and torque numbers):


http://www.hmfengineering.com/honda450r.jpg



HMF full system(now look at the torque and HP numbers):

http://www.hmfengineering.com/honda450rfs.jpg

[TrxTex]

From what I've read along with your info...it looks like you can unleash quite a bit more power with the full exhaust. I ordered the full Yoshi Comp...

Thanks!

[sparky450AR]

Originally posted by TrxTex
From what I've read along with your info...it looks like you can unleash quite a bit more power with the full exhaust. I ordered the full Yoshi Comp...

Thanks!

You wont be sorry, the Yoshi's are very nice setup.

When you get it make sure you post pics, and a write up.

[86atc250r]

The problem with those dyno runs is that they're not comparable. They pulled off the airbox lid for the run with the full exhaust --- so you now don't know if the bulk of the gains came from opening up the intake side or not....

[sparky450AR]

Originally posted by 86atc250r
The problem with those dyno runs is that they're not comparable. They pulled off the airbox lid for the run with the full exhaust --- so you now don't know if the bulk of the gains came from opening up the intake side or not....

yes, but if you ever were too take off your airbox lid, im sure a larger diameter header would help with air flow.

[Manny55]

Taking off the air lid is a most. It performs so much better with an open air lid. It can finally breath with the air lid off. Before i didnt have the air lid of when i went to check the filter if it was dirty there is like no dirt inside the air box or anything like that, thats how restrictive it is.

[86atc250r]

yes, but if you ever were too take off your airbox lid, im sure a larger diameter header would help with air flow.

That's not the point though - The same thing would occur if you were to remove the lid and run a slip on.

I think those dyno's are a bit misleading.

What those dyno's say to me is the header didn't make much of a difference, so to make the run look better, they removed the lid & rejetted.

May or may not be true, but that's what it says to me when they do something like that.

The way they performed that test actually turned me off their header setup since they weren't confident enough to make an apples to apples comparison.

[sparky450AR]

Originally posted by 86atc250r
That's not the point though - The same thing would occur if you were to remove the lid and run a slip on.

I think those dyno's are a bit misleading.

What those dyno's say to me is the header didn't make much of a difference, so to make the run look better, they removed the lid & rejetted.

May or may not be true, but that's what it says to me when they do something like that.

The way they performed that test actually turned me off their header setup since they weren't confident enough to make an apples to apples comparison.

Me too, but do you think removing the airbox lid will gain 3 horse? While still having the same restrictive header? I just never understood how the slip on could do much, I do realize it is a lot less restrictive than stock, but it seems like you would have to increase header size to get the full advantage. I know with cars, headers are what makes a lot of the difference.

[86atc250r]

You've got it somewhat backwards. The stock header is not restrictive. The stock silencer is - but the header is not.

In a stock silencer, the exhaust has to change directions 180° at least twice and then has to travel thru a screen spark arrestor, then a pea shooter baffle that's less than half the diameter of the rest of the pipe. Each time it changes directions, it's also going thru small & restrictive passages.

The stock airbox is FAR more restrictive than the stock header would be even if 1/2 filled with carbon buildup.

Will it make 3hp difference? Who knows - we sure don't by looking at those un-comparable dyno runs.

When you talk cars, you're talking about a completely different subject all together.

Headers on a car typically replace heavy and restrictive exhaust manifolds. Equal length header tube design to take advantage of multiple cylinders, tuned runner length, smoother contours, much higher flow all contribute to much greater results.

Compare changing the stock header on the 450R to changing from one aftermarket header to another of slightly larger diameter on a car - there will be a small difference, but nothing huge & you may actually hurt power in the bottom end to help power in the top.

Larger diameter header tubes lower back pressure at higher RPMs - but reduce velocity at lower RPMs, which reduces scavenging & efficiency at the lower Rs.

That's not the only part of the picture, but don't expect any kind of huge gain by just changing a header pipe on a 450R, especially if the engine is relatively stock. There's more power to be found in replacing the silencer - from there you will only see small difference in exhausts.

[sparky450AR]

Originally posted by 86atc250r
You've got it somewhat backwards. The stock header is not restrictive. The stock silencer is - but the header is not.

In a stock silencer, the exhaust has to change directions 180° at least twice and then has to travel thru a screen spark arrestor, then a pea shooter baffle that's less than half the diameter of the rest of the pipe. Each time it changes directions, it's also going thru small & restrictive passages.

The stock airbox is FAR more restrictive than the stock header would be even if 1/2 filled with carbon buildup.

Will it make 3hp difference? Who knows - we sure don't by looking at those un-comparable dyno runs.

When you talk cars, you're talking about a completely different subject all together.

Headers on a car typically replace heavy and restrictive exhaust manifolds. Equal length header tube design to take advantage of multiple cylinders, tuned runner length, smoother contours, much higher flow all contribute to much greater results.

Compare changing the stock header on the 450R to changing from one aftermarket header to another of slightly larger diameter on a car - there will be a small difference, but nothing huge & you may actually hurt power in the bottom end to help power in the top.

Larger diameter header tubes lower back pressure at higher RPMs - but reduce velocity at lower RPMs, which reduces scavenging & efficiency at the lower Rs.

That's not the only part of the picture, but don't expect any kind of huge gain by just changing a header pipe on a 450R, especially if the engine is relatively stock. There's more power to be found in replacing the silencer - from there you will only see small difference in exhausts.

I understand what you are saying....all i was saying is if you want full advantage in torque and HP go with the full system. But a less restrictive slip-on would do the same thing a less restrictive header would do, lose bottom end. I still dont have it all figured out, obviously. How can a slip on be less restrictive, yet still create backpressure?

[86atc250r]

Actually, a slip on will increase bottom end.

One thing most people don't understand is backpressure does not help bottom end. Velocity helps bottom end - because the velocity of the exhaust gases improves cylinder scavenging. Backpressure kills velocity, hence, backpressure hurts power.

Backpressure at higher RPMs is a side effect of smaller header tubes that keep velocity high at lower RPMs - this is apparrently the reason people have it in their heads that "backpressure" increases bottom end power.

If you have a restrictive silencer - it hurts power everywhere. This is because there are restrictions to the exhaust flow at all RPMs due to the changes in exhaust flow direction and small pathways between chambers in the silencer body.

Stock silencers are made with one goal in mind & it's not low end power - it's to keep the quad quiet.

[sparky450AR]

Originally posted by 86atc250r
Actually, a slip on will increase bottom end.

One thing most people don't understand is backpressure does not help bottom end. Velocity helps bottom end - because the velocity of the exhaust gases improves cylinder scavenging. Backpressure kills velocity, hence, backpressure hurts power.

Backpressure at higher RPMs is a side effect of smaller header tubes that keep velocity high at lower RPMs - this is apparrently the reason people have it in their heads that "backpressure" increases bottom end power.

If you have a restrictive silencer - it hurts power everywhere. This is because there are restrictions to the exhaust flow at all RPMs due to the changes in exhaust flow direction and small pathways between chambers in the silencer body.

Stock silencers are made with one goal in mind & it's not low end power - it's to keep the quad quiet.


Thank you! Now i understand! One question though, how do smaller header tubes keep velocity high in lower RPM's. Woudnt larger header tubes always keep velocity high? Is this why they "step" the headers? Stepping the headers would allow for good bottom end because you said smaller header tubes keep velocity up. But as the steps get bigger, this allows for a good top end. Correct?

[TrxTex]

Ok....now yall are cracking me up. I think you both make good points. Either way I have the full exhaust on the way and I appreciate the input.

:D

[sparky450AR]

Originally posted by TrxTex
Ok....now yall are cracking me up. I think you both make good points. Either way I have the full exhaust on the way and I appreciate the input.

:D

lol, all i know is what those dynoes tell me. I wish there was a book "exhaust advertisements for Dummies":p

[450 Racer R]

I just picked up my R this weekend... would it be helpful to remove the spark arrestor? It shouldn't hurt anything

[sparky450AR]

Originally posted by 450 Racer R
I just picked up my R this weekend... would it be helpful to remove the spark arrestor? It shouldn't hurt anything

It wont hurt anything, but it sounds bad. I would just remove the airbox lid, and rejet.

[jmoney45]

Originally posted by 450 Racer R
I just picked up my R this weekend... would it be helpful to remove the spark arrestor? It shouldn't hurt anything

I bought this off ebay:
Click Here (http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=2474216049)

It's an insert that is just like the hrc insert. Sounds good and gives a boost in power. I just got the hrc kit and I put in the hrc exhaust insert, so I'll sell this to ya if you want. I paid $34 but I'd take $30 shipped for it. Let me know.

[450 Racer R]

no thanks. I'm just gonna remove the spark arrestor for now and go with an exhaust in a week or two. I was just looking for a nastier sounding exhaust note cause where I ride everyone has an exhaust