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Large diameter header for stock (400) engine?

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Is there any advantage to an oversized header on a stock engine? If not, when do these help out, just with big bore kits or with a cam? I found a Big Gun large diameter header for sale at a decent price and was wondering if it's worth grabbing or not. I would most likely run it with a stock can and an open 96-97 SA.

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I use the big gun headers,they are for low and mid range,on my big bore motors they work well.On your stock xr4 just grind the header welds,stock header is great for your use.

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A couple of months ago I was trying to find out this same information myself. My search took me to an article about the TRX400, which is basically the identical motor for a quad. The article stated that the larger head pipe is not an advantage to a stock motor at all, and can in fact take away bottom end power which is what most of us like so much about the XR400. They found that with a 426 and a cam upgrade the larger head pipe came into play, but not before.

I can't remember where the article was exactly, but I copied and pasted the info to a Word file I keep for little bits of info I find interesting about XR400 mods. I think the source was quoted from Duncan Racing or Curtis Sparks racing. Both are businesses that have spent a lot of time developing this motor in quads for racing, so I considered it a reliable source that had done their research.

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Good info guys. Much appreciated. I don't wanna lose any snap on the bottom but I would like more mid range punch. Already have the 96-97 SA, UNI filter and pumper carb on the ole girl. 426 or 440 was next (depends how much I get back from Uncle Sam :smirk: ) on my list. Most likely will skip the oversize header for now. Hopefully I can find one at a good price later this year.

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The large header on our big bores(280-300-426-440) makes tractor like bottom end.We have a 280 with a custom over size header(much larger than anything you could buy.Also my 440 large custom header.Both seem to have more low end than all of our big bores.Just dont over cam your xr for trail riding..

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I ground out the joint weld on the header pipe on my XR400 together with a K&N air filter, rejetted standard carb with the A16A needle, Precision Concepts choke plate & an alloy silencer from DEP here in the UK. This has made for a very broad spread of power that friends with XR400s have found surprisingly differant to their machines. Since those comparison rides they've sought to modify their bikes in the same way as I have.

Besides which, I like the way that the standard downpipe flows visually & the heat guard fits. It also cleans up nicely as the stainless steel seems to be of a reasonable quality.

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The large header on our big bores(280-300-426-440) makes tractor like bottom end.We have a 280 with a custom over size header(much larger than anything you could buy.Also my 440 large custom header.Both seem to have more low end than all of our big bores.Just dont over cam your xr for trail riding..

I was thinking about a 426 + cam or,, a 440 bolt on kit and keep the stock cam for best low end. The 440 sounds better every time I think about it.

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I was thinking about a 426 + cam or,, a 440 bolt on kit and keep the stock cam for best low end. The 440 sounds better every time I think about it.

The stock cam is also recommended for the 440 for longevity reasons. You'll read of people saying it's already almost too much for the rest of the XR mechanicals. A hi perf cam might turn it into a ticking time bomb. But mine with the stock cam has been fantastic, going on 6 years now. Just take care of it.

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Good info TR42. I want more grunt out of her, I have the EXC for warp speed outings. I want the big torque so I can use the taller gearing (16/45) even off road. Run 3rd gear from 10mph to 40mph type of power and not worry about shifting. Basically, a lazy mans bike that still has some bite when you want it.

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We use the web stage 1 cam in our 440s.Zero problems lots of low end tractor like.Almost too much low end.Rememer guys you need the right header,muffler,airbox mods.

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I put the cylinder works DRZ400 big bore kit on my 2009 DRZ400SM because she was able to get to 84mph really surprisingly easy with 15/44 gearing, I felt like there would be more to get out of her with a big bore. I had the Yosh RS-2 exhaust and the TT FCRMX kit and that thing just railed but when I added the big bore, it had a lot more torque. The crazy thing is that the RPMs slowed down just a bit it felt like. Kinda like it was laboring to rev. Still worth the money to me.

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I have been a XR400 owner since 1998 till today. It has undergone 2 top end overhauls, one set of clutch pack, countless oil, spark plug changes. Uses K&N air filter, Pro Com CDI, Mikuni Tm36-50 carb, #35 and #130 with White Bros Megalloy pipes from header to muffler. The most recent overhaul, I changed out to a 440 kit with an angle cut job done to the valve seats, changed out cam gear, bearing, tensioner and chain. It is a daily rider and occasional trail machine. I seriously lost track of how many hours I have been riding it. I had the over sized header since it was stock bore and upon increasing to a 440 recently, It's a immaculate match. Wheelie pops are happening often at 3rd gear in the trails and I dare say I will ride this XR400 easily for another 10 more years to come. Have fun, ride safe.

Edited by lesteryeong

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I have been a XR400 owner since 1998 till today. It has undergone 2 top end overhauls, one set of clutch pack, countless oil, spark plug changes. Uses K&N air filter, Pro Com CDI, Mikuni Tm36-50 carb, #35 and #130 with White Bros Megalloy pipes from header to muffler. The most recent overhaul, I changed out to a 440 kit with an angle cut job done to the valve seats, changed out cam gear, bearing, tensioner and chain. It is a daily rider and occasional trail machine. I seriously lost track of how many hours I have been riding it. I had the over sized header since it was stock bore and upon increasing to a 440 recently, It's a immaculate match. Wheelie pops are happening often at 3rd gear in the trails and I dare say I will ride this XR400 easily for another 10 more years to come. Have fun, ride safe.

Good info, thanks! :smirk:

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Mikuni Tm36-50 carb, #35 and #130 with White Bros Megalloy pipes from header to muffler

Is that a 35 pilot jet in the Mikuni? I'm at sea level and just changed from 15 to 17.5, nice improvement, but I haven't heard anyone using larger pilots, isn't 35 extremely large?

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Is that a 35 pilot jet in the Mikuni? I'm at sea level and just changed from 15 to 17.5, nice improvement, but I haven't heard anyone using larger pilots, isn't 35 extremely large?

Same thing I was thinking. I have read on here about someone using up to a 25 pilot but a 35 seems huge. I'm at sea level here in Michigan as well, maybe I'll give the 17.5 a try. I know when I switched to the 96-97 exhaust it ran hot instantly. All I did though was richen the fuel screw and made the pump come on a touch sooner and that seemed to resolve the issue for me. I ended up with the screw at 2.25 turns out and the pump actuation screw 1.5 turns out from bottomed.

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