4 Stroke Big Bore Pipe Complicated Question

[Matt85'350x]

After doing some searching on this I haven't come with a consistent answer. What is the negative affect if any of putting a big bore pipe on a stock engine? I'm looking at these pipes that NOS_350X sells and am wondering what putting that on a stock 400ex engine would do? I've got my ongoing build consisting of a 400ex in a 350x chassis and the stock 350x pipe seems to fit fine. So in theory the pipe that he makes for the 350x should fit as well. The problem is that the stock pipe I'm using is not mine so I can't just run with it. I also don't want to pay the ebay prices I'm seeing for an old nasty stock pipe. Definitely not interested in a DG or Cobra either. So I found these pipes and they look nice but I don't want to have him build it for a stock engine and then later on I big bore my engine and have to buy another one. So my question is what kind of result should I expect to see from running a pipe that is meant for a big bore on a stock engine?

[RIDE-RED 250r]

Well thinking out loud with you here... What about a good aftermarket 400ex pipe, like FMF for example?? I know they are a little bigger diameter than stock 400ex pipe, which is sure to be larger than a stock 350x pipe and maybe a biut bigger than DG or Cobra pipes for the 350x. I don't see why it would run bad on your stock 400 engine or why it wouldn't work with a 440 kit if ghat's what you are looking at. Any chance you might be able to make a good aftermarket 400ex pipe work??

A little food for thought: My brother in law has a 400ex with a 416 Wiseco big bore piston kit, some sort of aftermarket cam and a full FMF exhaust. That quad was very noticeably more snotty than my bone stock 400ex I had at one time. I couldn't believe the difference.

I assume you are thinking of some sort of 440 kit in the future??

[Matt85'350x]

Yes 440 in the future. The problem is the 400ex pipe won't work without modification. So if I'm going to pay someone to make a pipe work why not get a really nice pipe to begin with. That's my curtent thought process

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[RIDE-RED 250r]

Makes sense. I am not a 4-stroke expert, but I don't see how it would hurt to run a "big bore" pipe on a stock displacement thumper. Of course you will want to check your jetting because it will likely need adjustment.

[Matt85'350x]

Thanks, that's what I was thinking too but I don't know much so I'd like to get confirmation.

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[Matt85'350x]

Anyone else have input on this?

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[350for350]

I'd say you're going to be fine as long as you rejet like Ride-Red said. I don't see the difference between that and putting an aftermarket pipe on a stock 350x. Technically, you already have a big bore 350x with a 400ex engine on it. As long as you're doing it, you may want to go ahead and free up the intake too so you can take advantage of your new exhaust. Not that it won't run good with just the exhaust, but I assume that you'd do something to the intake with a 440 kit, so I'm just thinking do it now.

[Matt85'350x]

Haven't done much engine work before, what do you mean or suggest by intake work?

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[jays375]

That pipe really only performs on a big bore.

[knappyfeet]

So I found these pipes and they look nice but I don't want to have him build it for a stock engine and then later on I big bore my engine and have to buy another one. So my question is what kind of result should I expect to see from running a pipe that is meant for a big bore on a stock engine?

Well if this is the criteria then it would make sense to purchase the exhaust intended for a big bore setup.

It's effect on a stock engine? Depends....... but in your case simple jetting (if it's even needed) could be used.

Keep in mind a properly constructed exhaust system needs to deal with scavaging and resonance and torque and engine temperament. Stock systems designed by manufactures needs to comply with federal emissions and sound levels....all the while maintaining a good balance of engine temperament and performance. Right off the bat.....one can make an argument that larger diameter collectors and exhaust can be detrimental for torque but improve higher rpm hp numbers. Great if you live at red line or there nearbouts but for reliable..leisure performance ,aybe not so much.

But at the end of the day it may not matter one ioda in your case.

[RIDE-RED 250r]

I guess what might be helpful in determining if the big bore pipe will be a detriment is to see if you can find some ID specs on quality aftermarket pipes for the 400ex and the NOS350x pipe. I know there is more to it than simply the ID of the pipe, but my guess is that it's the bigger player given two complete systems that are overall similar in length and running the same silencer. If the NOS pipe is alot larger than say an FMF pipe then you might be better off to wait??

I'm not claiming to know this for sure, just throwing it out there for consideration.

[350for350]

What I meant by "intake Work" was this. Are you still running the stock air box? Is the lid on or off? Either an open filter or running with out the airbox lid will let more air flow through the engine.

[Matt85'350x]

Right now I'm running no lid. I think I'm going to try this pipe, might need a month to get the funds together though. They're a top dollar deal for sure.

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[NeverLift]

I don't know if you've seen this but HMF made one for keister. I would call them and ask the affect of running this on a 400ex motor. I have a FCR41mm that I took of my 440EX before I sold it. It had a noticeable gain over the stock carb but it has no choke so it sucked to start in the winter. If you wanted to upgrade the intake as mentioned above i'd let it go for cheap.

Post113
http://www.3wheelerworld.com/showthread.php/149434-Keister-s-400X-build-VIDEO-Page-8/page3

[Matt85'350x]

I don't know if you've seen this but HMF made one for keister. I would call them and ask the affect of running this on a 400ex motor. I have a FCR41mm that I took of my 440EX before I sold it. It had a noticeable gain over the stock carb but it has no choke so it sucked to start in the winter. If you wanted to upgrade the intake as mentioned above i'd let it go for cheap.

Post113
http://www.3wheelerworld.com/showthread.php/149434-Keister-s-400X-build-VIDEO-Page-8/page3

I did consider that pipe but when I did some searching I didn't see where exactly he got it done. I'll have to send him a PM. And yeah I'm interested in the carb-what were you thinking on the price? Did it fit on the stock carb boot?

[NeverLift]

$100 including shipping. It took a little muscle but yes I ran it with a stock carb boot. Again I'll caution you if you ride in the winter you might not want this carb. In the winter i would put the stock one back on. I'll get it out and take some pictures of it tonight. He went directly to HMF and the built it for him. I had an HMF on my Cannondale and installed a few on street bike and always liked them.

[Matt85'350x]

$100 including shipping. It took a little muscle but yes I ran it with a stock carb boot. Again I'll caution you if you ride in the winter you might not want this carb. In the winter i would put the stock one back on. I'll get it out and take some pictures of it tonight. He went directly to HMF and the built it for him. I had an HMF on my Cannondale and installed a few on street bike and always liked them.
Sounds like a good deal. But yeah you're right that no choke thing seems like a bad idea. Is there no way to put one in? I think I'll pass but I do appreciate the offer

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