ESE's works engine tuner

[sispeed]

I also raced there in GP250 S1 with my modified Yamaha RD. Was very impressed by laptimes of the freetech class.
Thought to my self why are they so fast and I am so slow My best laptime was 2:16,1

Regards Siggi

[katinas]

Hartog's riding style was indeed very different. Mike Sinclair in his book mentions that they could use very hard brake pads on Will's bike as, coming from an agricultural background, he had exceptional hand strength. To the point where he bent brake levers. They put a wide 16in front on his RG to get the most out of his braking ability.
Apparently when Sheene tried Wil's bike he couldn't get on with the high lever pressures needed.

Thanks, very interesting story.

I am very surprised when found this photo, that shows how Honda was keen about carbon comstar wheels, even after some Spencer's era problems. One of many changes that E. Lawson tried in 1989 was comstar "2nd version" front carbon wheel and AP brake discs. Carbon 3.75x16 =2.5kg, magnesium=2.6kg, but 17in version carbon= 2.83kg magnesium=2.81kg.

[wax]

I was looking at a 250 for a project im looking at doing
I find it interesting that the 125 is a square engine ( 54 x 54) but the new 250 mx bikes are longer stroke.
What gives is this to make more torque, is this a mx thing. On a circuit style engine would you still want a square engine ??

[husaberg]

Thanks, very interesting story.

I am very surprised when found this photo, that shows how Honda was keen about carbon comstar wheels, even after some Spencer's era problems. One of many changes that E. Lawson tried in 1989 was comstar "2nd version" front carbon wheel and AP brake discs. Carbon 3.75x16 =2.5kg, magnesium=2.6kg, but 17in version carbon= 2.83kg magnesium=2.81kg.

Even further back back Spencer on the threes ran a carbon wheel as did the NR500 before that only they had one explode pitching him off which is never a good look. the NR also had small wide wheels and slipper clutches and all sorts of common place stuff now.
Even with Erv fettling and chopping and changing the frame Lawson rode the 89 bike with the steering damper wound onto full.

[wobbly]

Wax, the 72 stroke that every 250MX uses is a best compromise between rpm capability and power band width.
Going shorter allows higher revs , and also higher power ,but comes with a corresponding reduction in usable band width.
The 250 MX bikes dont need any more outright power , except for the very , very few super expert riders , and that is easy enough to achieve.
The Honda 500V twin was close to 68 square as that is the best compromise for outright power capability and extended overev rpm.
The factory version was reported as 140Hp at the sprocket, and reved to 10500 all day, but exploded very quickly when taken to 11,000.
Its relatively heavy , high inertia flywheels , created havoc with speedshifting and the factory specifically highlighted in the manual not to fit one as
the gearbox would self destruct real fast due to the ignition cut cut not slowing the crank enough.

[wax]

Wax, the 72 stroke that every 250MX uses is a best compromise between rpm capability and power band width.
Going shorter allows higher revs , and also higher power ,but comes with a corresponding reduction in usable band width.
The 250 MX bikes dont need any more outright power , except for the very , very few super expert riders , and that is easy enough to achieve.
The Honda 500V twin was close to 68 square as that is the best compromise for outright power capability and extended overev rpm.
The factory version was reported as 140Hp at the sprocket, and reved to 10500 all day, but exploded very quickly when taken to 11,000.
Its relatively heavy , high inertia flywheels , created havoc with speedshifting and the factory specifically highlighted in the manual not to fit one as
the gearbox would self destruct real fast due to the ignition cut cut not slowing the crank enough.

Thanks Wobbly so it would stand to reason then that an engine converted to run in a kart would be better off as a square bore as you can deal with the peaky power more ??

[wobbly]

Dealing with a 250 in a kart is not easy in sprint racing due to the huge torque off corners.
The fastest here is a modified 125KZ engine on one side and a 100cc reed direct drive on the other.
In road racing the big issue is that all of the modern MX engines are long stroke so favor torque over high rpm power, but when tuned
the issue then becomes the huge gap to 5th gear ( no 6 speeds any more ).
Thus they are tuned to rev past 11,000 so they drop back near the torque peak, and will still accelerate.
Older YZ250 had 68 square , but old fashioned port layout that would take a huge effort to update.

[katinas]

Even further back back Spencer on the threes ran a carbon wheel as did the NR500 before that only they had one explode pitching him off which is never a good look. the NR also had small wide wheels and slipper clutches and all sorts of common place stuff now.
Even with Erv fettling and chopping and changing the frame Lawson rode the 89 bike with the steering damper wound onto full.

They have very radical steering geometry in 89: most marginal version, rake- 20.58, trail-74.6mm, wheelbase-1358mm, but engine changed for torque, maybe first time not for peak: 165 hp -12000rpm. (163 hp 12500rpm 88') Looks like HRC experimenting very hard between 88-90, twin-crank 500, fuel injected NSR 250.
For chassis Honda chose strong 7000 Zn series good welding properties (very small or zero Cu) 7003 T4 alloy. Welding zone strength, after temper, remains 90 percents of main structure.
I'm not sure, but looks like 7003 alloy was used for NS 250/400, as I cut rear frame (prepare bike for racing) and put some pieces in lathe, after some cuttings welding zone looks same like main material, feels really like 7000 and stronger than RGV 250. Maybe for RGV, Suzuki used 6000 series alloy, but I'm not sure.

[mclarengp]

Hey guys
Great thread I’m only at the start but making my way through and hopefully have my gp singing with some of the great ideas!!! I’ll be racing against the old mc22 which I previously raced and I’ll probably get lapped hahahahaha I’ve link a few imagines of bike so far , will also be getting it logged booked to race classic and keeping original forks and will have to get tricky with internals

[TZ350]

.
Great, I love those GP's ....

The team GP's would flap all about the place when pressed hard so we beefed up the frames with all sorts of bracing but found that the more we "improved" the frame the handling got worse. never figured that out. The GT185 forks with gold valves and bracing were an improvement and so were a good set of inexpensive medium weight rear shocks.

We ran a RG250 chamber at first and that was quite good and a great place to start then later ran a Honda NF4 RS125 chamber which worked very well and was quite easy to fit.

[Matt@TYGA]

The Honda 500V twin was close to 68 square as that is the best compromise for outright power capability and extended overev rpm.
The factory version was reported as 140Hp at the sprocket, and reved to 10500 all day, but exploded very quickly when taken to 11,000.
Its relatively heavy , high inertia flywheels , created havoc with speedshifting and the factory specifically highlighted in the manual not to fit one as
the gearbox would self destruct real fast due to the ignition cut cut not slowing the crank enough.

Had the pleasure of riding two NSR500V's at Donington. The first a 2001 spec with kit parts. Made just shy of 140 at the wheel I believe and was an absolute missile. Surprisingly (thankfully?) not as difficult to ride as I thought it would be. Revved to around 11,500 and occasionally 12k and seemed happy to do it. Twas frightfully rapid. The next one was a '98 version. Around 130 ish ponies, wrapped in a TSR chassis (TSR AC50). Wasn't quite as fast and was hooking gears at around 10,500rpm, but it was beautiful in the handling department. Same day was also granted a couple of laps on an RS500 triple. That was a shock to the system! Not sure exact year/model, but guess late 80's. Handling?....interesting....brakes?....what brakes?....engine?....was jetted way to rich but cleared up around 8k and was clicking cogs at 10k.

Trying to keep two wheel on the ground on a 500 is no easy task

https://www.youtube.com/watch?v=ooqeQ2Jmgt0&t=64s

[SwePatrick]

My weldproject as arrived from nicasilplating.
This is my downstroked kx250 engine, from 72mm down to 61mm
My other cylinder has dynoed 68hp at 13100rpm on the rear wheel, i´m hoping for stepping above 70hp with this one.
If not? i will blend in some nitro in the fuel.

[TZ350]

.
Nitro ....... ... love it.

[peewee]

looks like nice work Patrick. I was testing mine alittle more today with the 30%. I made the needle 1 turn richer from last time but it still has alittle zing when clearing the crankcase. maybe it needs 1 more turn rich but really its not a big problem I guess.

[F5 Dave]

My weldproject as arrived from nicasilplating.
This is my downstroked kx250 engine, from 72mm down to 61mm
My other cylinder has dynoed 68hp at 13100rpm on the rear wheel, i´m hoping for stepping above 70hp with this one.
If not? i will blend in some nitro in the fuel.

I was assuming you'd be blending more vodka into your beverage.