Racing Exhaust full system

[Dangerboy]

Hi Everyone!

I'm new here, first post besides my intro.

So, I'm a racer. I used to race pro AMA/CSBK (Canada) and now I've decided to race a 2004 ZZ-R250 as my kids are getting into the sport and the 250 can be used with both the mini club (amra.ca) and the big bike clubs around here, such as the CMRA and EMRA.

Anyway, the ZZ-R250 (EX250H) wasn't available in the USA as far as I can tell and yet I think it is still considered "pregen" by your naming conventions?

I'm trying to find the lightest 2-1 exhaust system I can get for it that also can provide gains but the HP is less of an issue than the weight. To say I'm putting this machine on a diet is probably an understatement and I'll start a thread on that too. (Any suggestions where such a thread would be best posted would be helpful)

Anyway, at this point I'm curious what systems out there have been tried and found to work well for this frame/engine combination in particular. I just spoke with Hindle (Canada) and they can't say if the system they have will work on the pregen or not because they only developed the system for the '08-'12 250R and they don't know how that may differ from the ZZ-R layout. I think the engines as far as the cylinder head and oilpan as it relates for clearance for an exhaust would be identical, but I'm hoping someone here can confirm this.

If anyone has experience that would be great, I would love to find an old Muzzy system as I ran Muzzy on my ZX-6D (which looks almost identical to the ZZ-R 250) and they were great pipes in their day.

I would prefer a Titanium system as I ran a beautiful Akrapovic full system on my superbikes but it doesn't seem they really did anything for the 250 Ninjas, unfortunately.

I've read through all the threads I could find on this on this and other forums but many of them have suggestions for systems that are no longer available or in production (Muzzy, Area P, etc)

Thoughts?

[Dangerboy]

Okay, well forgive my ignorance with this specific bike and all the changes that have been made to it over the years. I've been trying to get up to speed on the ZZ-R.

The summary of what I've learned so far: It seems the "Pregen" versions of the 250 are the engines that do not have "shim under bucket" valve drivetrains. The heads are sufficiently different that a newer header will not work well even if it can be made to fit.

As I've been reviewing all the various offerings I can find online that pre-gen systems are no longer being produced.

Does anyone on this forum have a Muzzy 2-1 pregen header that would be willing to take a few measurements for me? I may get something whipped up in Titanium if I'm going to the trouble to get one made.

[Mohawk]

The pregen + ZZR used standard style exhaust flange headers, with split collet clamps & are larger bore than the newgen & EX300 which use an internal pipe extension that slots into the head & a flat flange plate to tighten it to the head. So whilst the ports are roughly in the same place they won't fit each other.

Best bet for a light system, would be to get a single skin stainless system, but if cost is an issue as its a race bike, then mild steel system should do. Ti would be best bust expensive. I upgraded my ZZR with KR1-S front & rear suspension parts & wheels & used a Honda VTR250 rear wheel to maintain the 17" rear & spoke look (the KR1 rear is 18").

The EX250's slipper cam adjusters are the best, the BMW S1000RR & some other new bikes use the same system, although they use shims for adjustment. Shims were quite rare in bikes in 1980 when this engine was designed. It was the most powerful bike engine per CC for over a decade !

[Dangerboy]

Thanks for your reply and information.

I'm curious if anyone that has a Muzzy system could tell me if the ID of the tubing coming out of the head does indeed match the OEM header ID.

I've read the best was the Muzzy system and it didn't even really offer much gains to the stock header with slip ons, what it offered most was a weight reduction. That Muzzy system is really hard to find now.

If needed I will produce my own to suit the extensive rear changes I'm making to the bike, my Akrapovic Titanium twin pipe setup that was on my '07 ZX10R was very light and very quiet which was helpful at tracks with strict lower noise limits.

The engine design is unfortunately heavy and difficult to make lighter. I have the engine partially apart and the shifter mechanism is crazy!

After reading through some of the long WERA 250 Production threads it seems I've showed up much too late to the party! Based on everything I've weighed so far I think I can get my racebike near 200lbs. With a little attention to the engine if I can get 40HP with the improved suspension and reduced unsprung and rotating mass I think it'll be a fun bike to race.

[maverick9611]

i have a tyga full system for gen 2 (08-12)
unknown if it will fit.

[Dangerboy]

Thanks for your post.

Well I have learned a bit more about this engine and how it has changed over the years and that exhaust will not work unfortunately.

It has to be from a 2007 or older EX250, "Ninja 250R", "ZZR250" and I think GPX250 over in europe, but I'm not sure on that one.

[Mohawk]

Can you re-engine the bike ? The newer 250 &/or 300 engine will fit. I'm updating my ZZR with a 300 engine fitted with 64mm bored newgen 250 cylinders running ZZR600 pistons for 315cc with 12:1 compression ratio. The 300 head has larger intake valves & the larger bore helps them flow better. Should be good for mid 40's hp, compared to 26rwhp now.

[Dangerboy]

Hi thanks for your reply on this.

First, no legally for the class I cannot swap in another engine. The rules let me modify the stock cases and heads quite a bit though, so I think I still have options.

Years ago I swapped pistons around between Kawasaki ZX-6R's and based on what I can tell here throwing in specifically ZX6E model pistons with wrist pins is the best option as those pistons are higher compression (12:1 with the 6E) and the wrist pins I think are tapered? I think keeping the stock EX250 cylinders is preferable anyway as they have the iron sleeves and the ZX6E pistons and rings were designed to run in iron sleeves as well. Machining out some of that iron will reduce the weight which is nice. I don't mind keeping the head from the pregen too, I like the rocker design and look forward to seeing what I can do with it. I can replace or modify the cam, and I can increase the valve sizes.

I'll scan the OEM pistons, porting, heads, valves and everything to determine what the compression volume and clearances look like stock vs with the new pistons, as well as compare some other 600 chambers like the semi hemi heads used on the later 6R's. I have some high speed DMG 5 axis mills here so porting and custom milling of these parts is not only permitted by the rules, but easy for me to do and replicate again in the future. I think I read the ZX6E heads run different valve angles than the ex250 does, so milling the valve reliefs in the pistons will probably be necessary.

If I drop in the crank and counterbalancer from a 300 (Legal) then I should be around 315cc and I'm hoping with at least 12:1 compression, boring out the carbs a little, installing the Yoshimura MJN kit in the carbs, ceramic coating of the pistons, valve faces and combustion chambers and exhaust ports + exhaust header, some porting and cams we can get a little over 50HP out of it. I think this is reasonable as the 300 has been tuned to produce this, but we'll see. I'm running total loss ignition so when I remake the flywheel cover I'll make the pickup point adjustable to allow for a bit more advance so I can just reuse the stock ECU for now and adjust on the dyno. I think with higher compression and ceramics I probably will not need too much more advance but we'll see.

I think I have located a race exhaust to start with for now. I just was at a track night (Minis, Kart track) this evening and there was a rider there with a "stock-ish" (Claimed) Ninja 400 that was really quite quick. There is no way that bike will be ever able to be as light as this bike will be by the time I'm finished (Mind you I personally probably have 60 lbs more weight than that rider) I'm hoping this can achieve similar acceleration, the GP wheels certainly will not hurt.

The TZ fork is too short to work with the chassis so I'm likely going to find a WP inverted fork off a RC390 and throw a better cartridge in it or find a set of ZX4RR forks, any suggestions on other forks I may have not considered are welcome, I would prefer an open cartridge fully adjustable fork. I may consider modifying some 85cc Dirtbike cartridge inverted forks and machining custom bottoms for them and running them.

[Mohawk]

I have a set of Pregen cylinders that I had the liners replaced with ZZR600 ones & bored to 66mm & a set of modified pistons to suit. Needs a little milling between the liners so it will fit in the case mouth. IIRC that gives 285cc + 12.5:1 compression. Can ship to Canada if you are interested, as I'm now going to use a 300 engine.

[Dangerboy]

Very interesting!

Yesterday I was already thinking about putting ZZR liners in the 250 block instead of boring so if you already have cylinders prepped for that, excellent! Now this makes me wonder, why not put ZX6R/636 pistons in those liners bored out now there is a little more meat that can be cut? Replacing liners is a legal mod and if I made some nikasil liners instead that would work too.

I found some custom high compression JE 2mm over ZZR pistons that could work too, they come with a ZZR cylinder assy so I could always press those liners out to use in this block. Did you just have to press out the liner, bore and press in another? I've never had to swap liners in those blocks before.

Thanks for your input so far. Any reason you decided to go to the 300?

Edit: I read closer that you already DID bore the ZZR600 liners out to 6R pistons. I guess we are already on the same page! Those O-rings in the block must not have much material left behind them in the middle! I ran 6R pistons in a ZX6D and they worked great.

[Dangerboy]

I just read the "Hulk and Batman" thread regarding the liner and piston efforts that have been made on this in the past. What a great thread!

Too bad there are no dyno numbers on the results of all those efforts. I will try to get some but at this point my bike came so badly damaged that I would have to go find a stock exhaust to run the bike as a baseline on the dyno here.

I can confirm I have the race exhaust I need for this project now so I'll try to either find a stock exhaust or an entire spare parts bike so I can get some reasonable data to compare against. What would be best would be same dyno, same day measurements with parts being quickly swapped to compare simple things like velocity stack lengths, MJN vs normal jet kit and exhausts, and then multiple engines/bikes to compare modified engines to each other and OEM.

[Mohawk]

Mine is a road bike & I got stuck with the need to mill the liners to fit the crankcase just when Covid arrived. Then before the world was back to normal I found a complete 300 engine with injectors & wiring harness from a stolen/crashed/recovered bike, so decided to go that route as I also own a Versys-X 300, which I'm doing a similar Big Bore on. If when I get those finished, I may still do the 250-285 Big Bore.

Have a search & check with Ducati-Man on here for 32mm carbs, GPZ & GPX 250 had 32mm units, before Ninja/ZZR 250 switched to 30mm ones.

[Dangerboy]

Interesting, I have to use the stock carb bodies as per the rules so I will just mill out my existing units as needed. It would be nice to have the larger carbs to capture profile data off them in the event my slides size become an issue.