4 into 1 on an XJ650RJ

I am in the process of changing out my stock 4 into 2 exhaust for a MAC 4 into 1 and for the time being keeping the stock air box but possibly changing over to a K and N air filter. I've seen that quite a few people have made this mod and I was just wondering if it requires re-jetting. If any one has information on this mod please post.
Thanks
JDog650
82 XJ650RJ

 

Hey,

Just wondering why you are making this mod?

I would have thought that the 4 in to 2 would have better flow of gasses and therefore better performance.

Personally I think the 4 in to 2's look better too.

Oh and shouldn't require re-jetting but that's an option you could look at if it's running badly after the change

 

if i am not mistaken, the 4to1 SHOULD not require re-jetting. though with this kind of mod it would be advisable to do so. The K'N filter modification WILL MOST DEFINATELY require a re-jetting. Usually if you adjust the exhaust, most people change the intake at the same time. But, if you think about it, the 4to1 restricts exhaust flow, the K'N gives plenty more air- therefore you are tweeking two very important variables without changing how your motor responds to it (jets). Hope this helps!

PS: the stock yamaha was setup to run at peak performance the way it is

 

I guess I just love the look, not that the look should matter. Thanks for the info anyway. This site has been fantatic for everythig I'm doing to the beast.
Thank you ALL

 

Actually if done properly a 4-1 can easily outflow a 4-2 exhaust.

 

I was actually thinking about wrapping it to increase the exhaust heat and help with the flow of gasses

 

wrapping your exhaust isn't going to help with the flow of gasses.

 

I beg to differ.

If you retain the heat within the exhaust, it (the exhaust) will be less dense. Any mass of of air that is less dense, will effectively flow through the same size of passage faster than that of a cooler more dense air mass.

And believe it or not; wrapping or ceramic coating the inside of your exhaust ( or both) aid in retaining the heat of the exhaust.

 

wink1018--please explain how Nitrous Oxide increases flow in the intake by about double. If hotter flows better.
the lower the temp, the greater the density, the larger effective flow.
and where are the badly needed 1/4 mile #'s to back up the header wrap theory?

 

TimetoRide... NO2 increases the amount available oxygen in the atmosphere of the intake charge, effectively supercharging the mixture. This is why it is advised to increase the fuel mixture when using nitrous. Wrapping the exhaust with header wrap will increase exhaust flow as it retains the heat and allows the exhaust to flow faster. Now on the 4:1 pipe situation. A well designed 4:1 pipe will make more power in whatever power band it is designed for. The Mac system is a decent stock alternative but does not provide as good of scavenging as the Kerker or Jardine systems. FWIW, I had a Mac system on my 1982 Seca 650 when I purchased it. I replaced it with a Kerker, which flowed much better, but needed jetting to get it right. I replaced that with a stock system and got much better bottom end with a loss on the midrange and top end. Same with a Jardine canister system. Lots of noise but a small gain in upper end power. The best system out there for the Seca is stock. If you are racing, the Kerker will make a lot more top end but you have to rev it to get it. cruzerjd

 

I'm not sure where I even mentioned anything about adding Nitrous to anything. Nor it's results. I only commented on the effects of wrapping the exhaust vs flow of the exhaust.

Besides, talking exhaust vs intake flow/density is just like comparing night and day.


However Cruzerjd has the basic points of how Nitrous works.

 

I have the MAC 4-1 installed on my 750. The quality is ok, not great, but for the price it is a good buy. I also have the K&N stock replacement filter and it does run on the lean side. I have installed a Dynojet kit for it. Dynojet recommends using their 124 main for K&N stock filter replacement and aftermarket exhaust. I have discovered that the main is a slightly too large, and used their 120 main instead. I also moved the needle to the number 4 position and it runs great so far. Hope this helps.

 

From a practical point of view when choosing a 4-1 try to see if you still have access to your sump plug and oil filter without having to undo your exhaust system.The 4-1 on my 81 seca no worries but on my current one an 83 I have to remove the headers to change the filter just complicates what should be the simplest job.

 

Changing out the exhaust only will never require re-jetting of the carbs. The exhaust will only remove the waste in the cylinder. Rejetting is only needed when the intake side of the equation is changed. Going to a high flow intake system will require rejetting, but just changing the exhaust won't. BTW, rejetting is not needed as much on the older bikes since they weren't lean jetted from the factory. Newer bikes are jetted to run very lean in order to meet all the EPA crap. The older bikes didn't have that problem, so they already run (usually) to the rich side.

Hope this helps.

Dave
Ace of Clubs

 

bluzglide, i beg to differ. A replacement exhaust like the Mac may not require a rejet as it flows about the same as stock. A Kerker or Jardine may need jetting as they flow more efficiently than stock. I installed a Kerker on my '82 and needed to rejet. It would stumble and surge in the midrange and topend was way to lean. The Jardine exhaust was the same toa lesser degree. The '80's bikes were lean tuned from the factory for "emission purposes". It all depends on the exhaust. If i recall correctly, the mac does not call for a rejet but Jardine does. Just my .02 worth, cruzerjd

 

Hey guys you are both right. The exhaust change may require rejeting if it is the restrictive link in the air pump {motor}. If the intake is the restrictive link then changing the exhaust it self may not cause higher air flow.