The cheater MX85 argument. I might be changing my mind.

[koba]

I have finally caught up!

I'm loving the constructive debate here, it is good to see the ideas being thrown about amongst a bunch of good mate who race together regularly. We do have to be mindful that the South Island contingent is underrepresented in this though.


As an interesting point for price context, I run a MB 100, it was on the standard bore when I purchased the entire bike for $400.

About 4? years later, (Overdue somewhat) I've just gone out to the first oversize.

To buy a new MB piston and rod kit, both TKRJ replacement parts, was a total for around $220. (Bad memory)
To pay someone to do the rebore was $131.10.

Rod kit, rebore and piston $351.10.

That really ain't too bad!

[Sketchy_Racer]

Wash your mouth out with battery acid you heathen, there were a lot of FXR riding poofters finishing behind me at BOB

How many also finished in front

Where HP is still being built out back in the shed Attachment 297190 not brought. Attachment 297189

Whilst this is true, we really cant start comparing it to "buying" HP. Lets be honest there are now 4 bucket purposed dynos that I can think of off the top of my head and I would hate to think how much money has been accumulatively spent over the years with engine development "on the cheap"

Just a new die grinder here, a new cylinder here, how about this new carb, what about this ignition system here.... It all adds up very very fast to the point that the "$300" old school 2T motor has now cost thousands to build even if tools etc are a recoverable cost. But building a even mid level bike in the shed with a file and a die grinder are long gone in buckets.

Most of the posters on here are posting as though the only bucket racing happens on kart tracks and are formulating their want lists based on their personal needs.
How would these engines go on a full track like ruapuna or a street race like greymouth or methven ?
I suspect the uptake would be fairly low, with FXRs you can buy an engine , buy the amount of tuning you can afford, get reasonable advice from any number of clever people
with 2 strokes its much more cloak and daggerand the clever people probably wont be interested in rebuilding stock engines.
For just a few thousand dollars more you can have a water cooled 100 with 10 or 12 more hp but uglier gear ratios.

Interesting comments earlier in the thread about aircooled 2Ts being too dangerous (in aus?) this sounds like its in line with some of recent history with the big hp gp125s and kes up north, would they finish a race at ruapuna?

I dont think having 85's would do any harm but they arent the magic bullet either

A few weeks ago I watched a srteetstock 150/ bucket race at ruapuna Matt and Al Hoogie were ahead of the rest of the field including the RG150's and KR150's by 3/4 the length of the front straight they were riding FXR and CBR respectivly, so the death notices of the diesel brigade may be premature

They would be quite a bit slower than a 4T with less power and more curve. It's all about average HP though the rev range of the gear box. Example being is my 85 vs Kyles FXR. The FXR is 13hp and the 85 is 16HP on the same dyno on the same night so it's apples for apples. Which one should be faster? Well it would seem intuitive that the 85 would have the advantage on the track here with it's considerable % of HP over the FXR. The reality is that on the track it is neck and neck. This is becuase the FXR makes 13HP from 5k rpm to 12k rpm so in any gear at any time he has nearly 13hp to use. The 85 on the other hand starts at the bottom of the gear at 10HP hits a peak of 16HP then drops to 8HP before hitting the next gear. This makes it super exciting to ride but ultimately not fast at all.

This is certainly not a case of death to the 4T at all! I want to emphasise this as the sole purpose and my own personal agenda to the 85s are that I really want a "modern" 2T with good reliability for the stock HP output and easily avaliable parts that are nice and cheap. I'm not arguing that you cant get good cheap parts for some of the other older bikes but if they ruin a crank, they certainly wont have one in the post the next day.

I have finally caught up!

I'm loving the constructive debate here, it is good to see the ideas being thrown about amongst a bunch of good mate who race together regularly. We do have to be mindful that the South Island contingent is underrepresented in this though.


As an interesting point for price context, I run a MB 100, it was on the standard bore when I purchased the entire bike for $400.

About 4? years later, (Overdue somewhat) I've just gone out to the first oversize.

To buy a new MB piston and rod kit, both TKRJ replacement parts, was a total for around $220. (Bad memory)
To pay someone to do the rebore was $131.10.

Rod kit, rebore and piston $351.10.

That really ain't too bad!

Yep its been a good convo which is nice for a change on a forum especially when it comes to a controversial subject such as this.

That's a good price for the MB stuff for sure!

[F5 Dave]

. .
Most of the posters on here are posting as though the only bucket racing happens on kart tracks and are formulating their want lists based on their personal needs.
How would these engines go on a full track like ruapuna or a street race like greymouth or methven ?

. .

actually good point. The answer is that taller gearing will have a bigger detrimental effect on peaky bikes. Flat curves make high top speed easier too.

[Grumph]

actually good point. The answer is that taller gearing will have a bigger detrimental effect on peaky bikes. Flat curves make high top speed easier too.

correct - but this is the one area where Husa has a point....The close ratio boxes in the 80/85's will have a bigger influence on the long tracks. From experience with post classic singles, when we went close ratio we gained about 20kph top speed due to the better through the gears acceleration - and the smaller gap 4th to top.

And koba - yes, good MB parts prices - but by ChCh standards the bore job is very expensive....

[husaberg]

correct - but this is the one area where Husa has a point....The close ratio boxes in the 80/85's will have a bigger influence on the long tracks. From experience with post classic singles, when we went close ratio we gained about 20kph top speed due to the better through the gears acceleration - and the smaller gap 4th to top.

And koba - yes, good MB parts prices - but by ChCh standards the bore job is very expensive....

The "one area" Greg what about the parts parody, no competition rods and bearings for Current f4 and 5 but open slather for MX85's.
The MX85 are designed from scratch to be a competition bike. It is there sole reason for existance.
The other bikes (which are eligible) are not, So then if the rules are to be changed is 15cc enough............
Lastly I don't think it is fair to use the Grey 80 as a example of what an MX85 is capable of, No offence but is the Grey 80 case reed with a power valve and a CR gearbox? Or is it a modified road bike engine.

Sketchy said about the power range on the 85, Seriously a stepper Pj and a decent pipe and an adjustable ignition and some minor work will fix those issues easily. Does anyone disagree with that?

[F5 Dave]

Mb50 gearbox is pretty good in the 100 and so is the kawi KE gearbox.

[F5 Dave]

My MB100 is case reed with what was probably very similar to a CR80 gearbox. No PV though.

[kel]

Mb50 gearbox is pretty good in the 100 and so is the kawi KE gearbox.

Yes best part of the motor. I have had my cranks (more than one) machined so can run RGV250 big end bearings (easy when you spend the time and money) so not only do I have a great gearbox but also a fancy flat cage big end bearing. I have phenolic main bearings, a selection of conrods from 100mm to 110mm, straight cut primarys and rotary valve induction as well. Not a bad setup for a non comp motor but it sure isnt in reach of everyone as I havent seen a single KE motor for sale in more than 2 years! Has anyone mentioned that I have almost 50% capacity advantage over the MX85's?

And for Husa. Aprilia works racer cylinder cores (at how many thousand?) for making supposed non competition cylinders, paying Wobbly god knows how much for engine work and design etc etc yet he doubts his wallet and 17.7% capacity advantage so much that he's worried about MX85's

MX85's vs non comp 100's vs 150 4 strokes. Looks to me that a well designed 100cc water cooled 2 stroke should still have a sizeable advantage.

Now where did I leave that kit Derbi 50mm cylinder thats being grafted on to the spare KE bottom end? 32hp anyone

[Sketchy_Racer]

correct - but this is the one area where Husa has a point....The close ratio boxes in the 80/85's will have a bigger influence on the long tracks. From experience with post classic singles, when we went close ratio we gained about 20kph top speed due to the better through the gears acceleration - and the smaller gap 4th to top.

And koba - yes, good MB parts prices - but by ChCh standards the bore job is very expensive....

The 85 close ratio box is still not close enough on the tarmac with the stock power curve, It uses quite a bit of clutch to have a chance at keeping it in the power. Longer gearing for faster tracks would make it worse.

The "one area" Greg what about the parts parody, no competition rods and bearings for Current f4 and 5 but open slather for MX85's.
The MX85 are designed from scratch to be a competition bike. It is there sole reason for existance.
The other bikes (which are eligible) are not, So then if the rules are to be changed is 15cc enough............
Lastly I don't think it is fair to use the Grey 80 as a example of what an MX85 is capable of, No offence but is the Grey 80 case reed with a power valve and a CR gearbox? Or is it a modified road bike engine.

Sketchy said about the power range on the 85, Seriously a stepper Pj and a decent pipe and an adjustable ignition and some minor work will fix those issues easily. Does anyone disagree with that?

So I think you might be putting a little to much emphasis on the level of the 85 engines tune. They are built as a good engine but certainly claiming them as race engines is marginal. As for some numbers, lets say that getting 30HP out of a 100cc (300HP per litre) engine is certainly achievable and if we applied the percentage offset of the capacity which is 15% then the 85cc would be capable of 25.5HP at the same HP per litre. Even at 330 HP per litre (same as good RS125) they would still only make 28.05HP and lets be honest, no one will get 330HP per litre without some serious time and effort. It would be easier to do a 100cc non competition to 300HP per litre. And to really top it off even if someone got 28HP out of one of these it would still get wasted by a FXR150 with 24HP and a nice flat torque curve.

Your argument is a little flawed in claiming that they are race engines but then suggesting that by adding some simple parts would instantly make them a lot better. If this was the case and it really was large change in the engine performance dont you think that the manufactures would have done it in the first place if the really were "race engines"

At the end of the day if you define them as competition engines or not, they are motors that were built for little johnny. They are most certainly not close to GP engines.

Mb50 gearbox is pretty good in the 100 and so is the kawi KE gearbox.

The MB50 gear box is as good as the RM85 box. Maybe better as the 85 first gear is a little tall to get it off the line I have found

[Drew]

The "one area" Greg what about the parts parody, no competition rods and bearings for Current f4 and 5 but open slather for MX85's.
The MX85 are designed from scratch to be a competition bike. It is there sole reason for existance.
The other bikes (which are eligible) are not, So then if the rules are to be changed is 15cc enough............
Lastly I don't think it is fair to use the Grey 80 as a example of what an MX85 is capable of, No offence but is the Grey 80 case reed with a power valve and a CR gearbox? Or is it a modified road bike engine.

Sketchy said about the power range on the 85, Seriously a stepper Pj and a decent pipe and an adjustable ignition and some minor work will fix those issues easily. Does anyone disagree with that?

Which is the point of the conversation. "Should they be permitted into the rules?"

[kel]

And to really top it off even if someone got 28HP

I have no doubt that 28hp is achieveable. I hate it when I do this but; Husa is right about the PJ carb, porting, programmable ignition and pipe, throw in some serious set up and dyno time and 28hp will come.
The top 100cc non comp 2 stroke all ready makes 30hp. The best 4 strokes all ready make 28hp. I see no problem with a 85MX tuned to 28hp.

[husaberg]

The 85 close ratio box is still not close enough on the tarmac with the stock power curve, It uses quite a bit of clutch to have a chance at keeping it in the power. Longer gearing for faster tracks would make it worse.



So I think you might be putting a little to much emphasis on the level of the 85 engines tune. They are built as a good engine but certainly claiming them as race engines is marginal. As for some numbers, lets say that getting 30HP out of a 100cc (300HP per litre) engine is certainly achievable and if we applied the percentage offset of the capacity which is 15% then the 85cc would be capable of 25.5HP at the same HP per litre. Even at 330 HP per litre (same as good RS125) they would still only make 28.05HP and lets be honest, no one will get 330HP per litre without some serious time and effort. It would be easier to do a 100cc non competition to 300HP per litre. And to really top it off even if someone got 28HP out of one of these it would still get wasted by a FXR150 with 24HP and a nice flat torque curve.

Your argument is a little flawed in claiming that they are race engines but then suggesting that by adding some simple parts would instantly make them a lot better. If this was the case and it really was large change in the engine performance dont you think that the manufactures would have done it in the first place if the really were "race engines"

At the end of the day if you define them as competition engines or not, they are motors that were built for little johnny. They are most certainly not close to GP engines.



The MB50 gear box is as good as the RM85 box. Maybe better as the 85 first gear is a little tall to get it off the line I have found

The Mx 85 are race engines built to race i don't think anyone can honesty disagree with this.
The MX85 are of course designed with some compromises such as longevity factors and ultimately cost.
The MX bikes do in most cases in std spec as delivered have a power spread that is narrower than a highly developed bike such as Mikes MB100.
This is due to a number of factors one being the surface they race on allows the engines to get back into the power band by breaking traction.

But this is able to be rectified. which is something that needs to be coinsidered. As I pointed out in my last post.
The way it is able to be achieved is clearly detailed in the ESE thread.
While they are not GP engines as you stated, they are miles in advance in design and construction to the legal bikes available.
While the 85's until KTM started getting serious admittedly stagnated but the new ones are to all intents and purposes pretty much a GP engine. KTM85 (Very close in design to the last 2 stroke gp engines.)

As for the Gearbox compare the ratios of both the MB50 and the Cr80's the results are Night and day then compare them to the other 2 strokes you will get a worse result.
That said Mb spread of ratios is just the best of a bad bunch
When I can be bothered I will post the ratios.

[Sketchy_Racer]

I have no doubt that 28hp is achieveable. I hate it when I do this but; Husa is right about the PJ carb, porting, programmable ignition and pipe, throw in some serious set up and dyno time and 28hp will come.
The top 100cc non comp 2 stroke all ready makes 30hp. The best 4 strokes all ready make 28hp. I see no problem with a 85MX tuned to 28hp.

Achievable sure, but probable? I would love to see it done. But getting up near GP engine HP per litre outputs is impressive.

28HP out of the 4T's im not sure about, whos got that much? The fastest one I know is Richbans FXR and I not going to lie I'm dubious about the numbers off of a lot of the dynos around.

I watched a FXR with a claimed 20+ HP on one dyno struggle to pull away from one that has 14HP on another dyno.

After all the discussion I am really having a hard time to understand where an constructive argument against the 85s are coming from.

They are just another motor for those who want new and available 2Ts with a maximum tunability as any other bike in the current rules in terms of power (although personally I think they will be slower than the other tuned bikes)

And at the end of the day, If you don't like it don't get one but let the 2T crowd have some new motors!! It's not going to make anyone's bike redundant and the uptake to 85 engines would be minimal but it is an option!

[Sketchy_Racer]

The Mx 85 are race engines built to race i don't think anyone can honesty disagree with this.
The MX85 are of course designed with some compromises such as longevity factors and ultimately cost.
The MX bikes do in most cases in std spec as delivered have a power spread that is narrower than a highly developed bike such as Mikes MB100.
This is due to a number of factors one being the surface they race on allows the engines to get back into the power band by breaking traction.

But this is able to be rectified. which is something that needs to be coinsidered. As I pointed out in my last post.
The way it is able to be achieved is clearly detailed in the ESE thread.
While they are not GP engines as you stated, they are miles in advance in design and construction to the legal bikes available.
While the 85's until KTM started getting serious admittedly stagnated but the new ones are to all intents and purposes pretty much a GP engine. KTM85 (Very close in design to the last 2 stroke gp engines.)

As for the Gearbox compare the ratios of both the MB50 and the Cr80's the results are Night and day then compare them to the other 2 strokes you will get a worse result.
That said Mb spread of ratios is just the best of a bad bunch
When I can be bothered I will post the ratios.

Yes I can't say I disagree with you comments at all, they are based around being used for MX racing and they are certainly quite a bit more advanced than a old MB100 etc. Which is the whole point. I know you are seeing these things as an unfairness towards the non competition engines but that is where the 15% capacity restriction curbs the power output and also will inherently make them harder to ride as the power comes up and the torque curve gets a big spike in it.

I can't comment on the MB50 gearbox on larger tracks, but I can say that on the kart tracks there is literally no advantage what so ever to the RM box VS the MB box. Numbers are numbers but on the track it's a moot point (on kart tracks at least)

At the end of the day these motors are already in buckets, they just have the name DERBI on the side of them instead of Suzuki or Kawasaki etc and I think that it is silly that we restrict ourselves as 2T enthusiast to redundant engines or ones that are a real pain in the ass to get and cost a bomb. 2Ts are not long of this world if the current trend keeps going so get them in an enjoy them before it's too late!

[husaberg]

Yes I can't say I disagree with you comments at all, they are based around being used for MX racing and they are certainly quite a bit more advanced than a old MB100 etc. Which is the whole point. I know you are seeing these things as an unfairness towards the non competition engines but that is where the 15% capacity restriction curbs the power output and also will inherently make them harder to ride as the power comes up and the torque curve gets a big spike in it.

I can't comment on the MB50 gearbox on larger tracks, but I can say that on the kart tracks there is literally no advantage what so ever to the RM box VS the MB box. Numbers are numbers but on the track it's a moot point (on kart tracks at least)

At the end of the day these motors are already in buckets, they just have the name DERBI on the side of them instead of Suzuki or Kawasaki etc and I think that it is silly that we restrict ourselves as 2T enthusiast to redundant engines or ones that are a real pain in the ass to get and cost a bomb. 2Ts are not long of this world if the current trend keeps going so get them in an enjoy them before it's too late!

There is a lot of agreement on the thread but some simple things need to be sorted.
We have a bunch of individuals touting them as an option viable option for non tuners then a group saying they have to be able to be tuned as well.
Which camp are you in?
I will go on the record as saying if they make the 85's legal; (with no restrictions) i will buy kate model KTM85 and biff out my current NSR125 project.
I sincerely believe the parity is on the side of the 85 if there is no restriction on them.
I will of course never actually complete it of course