Thanks Racegass. it is obvious that the TBR slipon is compatible as there is no gasket involved and the clamp is not deforming the PowerBomb's slip-joint-bell in order to get a seal on the TBR nipple..

 

But the Two Brothers canister does not have the 02 sensor for the 2018 EFI, right?

KLXster, how do you know the bike is making less power due to the restriction at this junction?

I'm just looking for an excuse not to have to undo all that exhaust wrap to put the stock header back on

 

The 2 Bros will have the 02 bung. When I spoke to them about a month ago they were getting ready to go into production and said it would be a few weeks before they were ready to ship. The only place online you could find them listed was on their website because they weren't available yet.

 

One of you guys is going to have to verify the nipple size on the Yoshi . It is either identical in dimension to the stock slipon or it isn't - It either slides into the Powerbomb tightly without any "gasket" or it doesn't - it either slides into the stock header tightly without any gasket or it doesn't.. It is that simple..

I know of the power loss because, early on, when I didn't know better, I managed to seal a DGR slipon into the bell of a Megabomb - and dyno test it.. The resulting chart is posted in here, somewhere, in a very old post or thread.. The losses were profound and I remember the anger of having spent about $300 on the Megabomb only to end up with less power than the stock header chart I already had..

If the Yoshi nipple size is verified as not compatible with the larger diameter performance headers, the below applies:

You will need to reinstall your stock header & sell the Powerbomb OR sell the Yoshi & buy an FMF or other compatible slipon..The Yoshi/stock header will offer you more low -midrange power, the Powerbomb+PC4 or Q4 will offer you more upper mid - top end power - I say offer because full benefit of each is not realized until you run the airbox lidless and a tuner is used to get the fueling correct.. So that fact is your excuse. If you are not running a tuner with corrected fueling, on a lidless airbox, there can be no significant gains in power regardless of the exhaust system.. The only other option that may produce a noticeable power increase is a midrange boost by running the lid without a snorkel, with a tuner and corrected fueling, along with the Yoshi and the stock header.

Other info:
Anyone running the stock airbox without a tuner can forget about performance increases - you are doing exhaust components just for the "new sound" whether you know it or not. Without a tuner, the snorkel should not be removed. The increase in airflow is significant enough to require a tuner to correct the fueling of open loop operations. Otherwise, fueling at high throttle settings is unknown and could be quit lean - especially with performance exhaust components installed - defeating any performance offered from the money spent..

It is quite likely that the first purchase, for the performance minded, should be a tuner. It is quite common that re-tuning a stock bike with a performance fueling curve provides a significant and noticeable power increase over the stock EPA certified fueling curve. The "nuts and bolts" of this are that the closed loop operations (usually below about 60% throttle) are quite lean in order to pass EPA. Once a tuner is used to replace this area of operations with performance fueling, a significant increase in performance is realized.. a tuner supplying a performance fueling curve on a stock bike will only increase top end performance if the stock open loop fueling is not optimal. Someone is going to have to start dyno testing and performance tuning an '18 ..

 

Ok, finished with the above post.. If need be, read it over several sessions.. It can save you guys a lot of money and time whether you are looking for performance or not..

 

Wow! Thanks for the great summary of your findings!

One question.

"it (The Yoshimura slip on) either slides into the stock header tightly without any gasket or it doesn't.. It is that simple.."

The Yoshimura slip on ships with the same gasket as the stock exhaust so why would they ship it with a that if they did not intend you to use it?

http://www.yoshimura-rd.com/images/14301BC350.pdf

 

Hey, if you want to declare the Yoshi incompatible, go for it.. You say it comes with a stock-like gasket - which is not shown in the instructions.. This would certainly indicate the Yoshi carries a "stock-like" nipple that is not compatible with performance headers.

It is a sad fact that some KLX250 slipons are made to work with either the stock header or a performance header, and some are made to work only with the stock header via a small nipple and a big exhaust gasket (like the stock setup uses)..

I would rather have a picture of the stock nipple next to the Yoshi's - showing proof that they are the same size, or a set of measurements on both showing that they are the same - before I declare it incompatible..

Perhaps I should talk to Deej about having the exhaust fitment/option thread stickied so that others can more easily find this information..

 

My exhaust fitment thread is now stickied - at the top of the forum.. Hopefully it'll help members...

 

OK. I just removed the Powerbomb and put the stock header back on. Here is the measurement of the nipple of the Yoshimura. 31.8mm or 1.25in. I hope this answers your question.

Now to go wash off all this fiberglass from the exhaust wrap....