squish?

mgtkr1 · Post by **mgtkr1** » Sun Oct 21, 2007 6:37 pm

im using 26j pistons with std head atm with no problems on optimax pump fuel. over winter i want to have optimum shape/clearance for 50/50 avgas and any advice would be appreciated. a new crank will be used with l/ends etc. also has anyone bothered juggling diffrent base gaskets in order to get diffrent timings etc or do you change the porting itself to get desired timings as i have? the rgv boys use diffrent gaskets in order to have the pston uncoer the transfer ports at BDC and wondered if you lot did the same? my mane focus will be optimising the squish and just a refresh though, any help appreciated, cheers matt

mj43 · Post by **mj43** » Sun Oct 21, 2007 7:04 pm

Matt

there is a spreadsheet http://myweb.tiscali.co.uk/teamsparrow/ ... dsv2_3.xls

Dimensions when you open it are suitable for 50/50 fuel and 26J, 3AK, 3TC and 59W pistons, i.e. 120 dome radius.

Bit of advice - please don't take offence - spend your time and money on suspension, tyres and learning to ride. A good stock motor lightly tuned as I have described elsewhere is good enough to get you in the top 5.
You only need the mega tuned motor to win. A fast motor when you are learning to race will get you lazy - a slow motor makes you work for a living. When you are riding the wheels off the thing and are getiing top 5 finishes then it is time to tune it for a win.....

Only my two pence worth

MJ

the kid · Post by **the kid** » Sun Oct 21, 2007 9:24 pm

That sounds like very good advice MJ . Will remind myself of that when playing with the motor

Cheers

mgtkr1 · Post by **mgtkr1** » Sun Oct 21, 2007 10:00 pm

cheers for the advice mark, ive got a (potentiolly) good suspension setup in the pipeline for march and this will be my main focus, second to improving myself which has to be priority. im just going to concentrate on things that NEED doing until i have the speed to warrant a fast motor. tbh, the motor was super and the way it picked up off a closed throttle suprised me, i was expecting it to be a lot more peaky than it was( all the std kr's i have ridden have had little lower power with an ok top end) but this seemed nearer to yamagamma(tuned 350ypvs) than the std kr. i enjoy fiddling with the motor but as you said the serious power is not neccesery until been near the front. the forks were a big problem and the rear has seen better days so these will be sorted. im also gonna invest in spares that are likely to break in an off as elf got me back on track with a gear lever(need to be more organised). you learn as you go on i guess.

the-elf · Post by **the-elf** » Sun Oct 21, 2007 10:31 pm

Got to agree totally with MJ, Mat, but I'm sure you'll get there pretty quickly though

. This is just a bit of advice from what I learned during my first seasons.
When I started racing I had a mildly tuned engine but decent suspension and then I developed the bike as I raced and improved things as and when I could. In some kinda order I think the most important things are:

Decent rear shock and front forks
Resprung suspension (to match your weight), properly setup and with the ride height sorted
Decent wheels and tyres; try to match tyre sizes as well so if you go to a 120 17" front (if you use different forks) then you really need to have a 160 17" rear to match, which will need an RGV rear wheel as a minimum or better still a 4.5" rear rim (think Dymag and kiss goodbye to £600+

(I did)).
Also play with the riding position with rearsets etc as the standard position is very sit up and beg and it takes a bit of work to get a more modern head down - arse up riding position

Once you've got that far, then think about getting the most from the engine, with say 35mm carbs and a CR gearbox. I think the CR box makes the bike a lot easier to keep in the power and is more rewarding than the 35mm carbs but both will cost a few quid to install and they are both worth doing as and when you can afford to pay for them

. You will though get more bang for your buck (or seconds off you lap times) with decent suspension then you ever get with just a faster motor.

Spend your time fettleing what you've got and improve it over time and be prepared to go down the odd blind alley and never be too proud to amite to a mistake and start again from scratch

I didn't do all this my-self in the order stated but I did what I could, as I could and as funds were availble to do it and from experience the cheaper mods were the ones that got done the quickest and often had a sursprisingly quick (pun intended) return

Like my home made rearsets so I could get a proper riding position or my straight in air ram system (copied from Colin, who you got your 35mm carbs from).

Anyway mate best of luck and if you need anything just give me a shout and I'll try and help. If you can get to a trackday with me sometime then you can take my bike out and see what you think to her.

Mind you that'll have to be after I've got the cylinders re-plated

mgtkr1 · Post by **mgtkr1** » Sun Oct 21, 2007 11:11 pm

appreciate the advice guys, always worth listening to you race veterans! my dosh is going on suspension that works and tyres etc. will also improve on the brakes for march. any engine work(minimal/replacing the odd gasket thats needed etc) will be kept to a minimum and i wont be spending big money engine work. just gonna get the best from what i got and as i can get the squish done for nowt thought it may be worth doing to match the piston shape. from what i learnt at cadwell i would say that the motor was a peach compared to the crucial handling, definitly learnt a big lesson! the foks were atrocious and the rear was like a pogo meaning the power couldnt be exploited as well as it could with a decent chassis setup and more importantly a better pilot! i breckon the probems i encountered come in the order as follows 1. rider 70% 2.forks 25% 3.r/shock 5%.

had a decent pilot been on board it would have been 1.forks 60% 2.rear shock 20% 3.brakes20%

the-elf · Post by **the-elf** » Sun Oct 21, 2007 11:31 pm

Mat,

The standard Kr1S brakes are awesome, your's may need refreshing and some decent fluid but apart from that they shouldn't need anything. If they were good enough for a ZX9R then they are more than good enough for a tiny 250. I've replaced the mater cylinder, fitted new pistons and seals in the calipers and I use Halfords own brand 5 dot 1 fluid and they are ace.

Standard suspension on the other hand was old and crap when the bike was new and dosn't compare well at all to anything more modern than Fred Flitstone's car.

mgtkr1 · Post by **mgtkr1** » Sun Oct 21, 2007 11:43 pm

im mthinking of using kr1s brakes, im currently on kr1 brakes which are probably in need of fresh seal but instead im gonna improve them by replacing them as far better calipers can bew obtained for reasonable money, i have a rrsp m/c atm. maybe not compatible with kr1 calipers? i reckon the 1s calipers are prob the best a 250 has seen and will look into what decent forks are out there so i can have the best of both worlds, prob zxr usd? will be reading some old poists i think! colin sleigh gave me some good pointers aswell and swears by the std calipers but also said the brembo's frtom the prilla were fantastic so depending on what front end i use these 2 are likely candidates so far although ive heard fireblade calipers are also v.good and a straight fit. i should of said i had the not so good kr1 calipers