tuning a '91 gsf400 engine for track - what mods are best?

[gsxr400 racer]

[El Dopa]

So the red line is with flatsides?

[gsxr400 racer]

yes sir

[gsxr400 racer]

yes sir=

[Bartjan]

and what is the difference in the carbs?

picture of radial valves.

as you can see the valves are pointed to the center.

when the valves open there is more room to allow better flow (more distance to the cilinderwall), also the combustion chamber is a better shape so the combustion will be (slightly) faster.

the valves are exactly the same but the rocker arms need some special construction.

alot of 1 cilinder cross motors have these and so does the mv agusta f4

[Banditmax]

i actually meant radial valve seats not radially arranged valves. So the are alot smoother than 5 anlge or 3 angle ones.

[gsxr400 racer]

accelerator pump for taking off thats all you need to know race carbs the berries

[Bartjan]

i actually meant radial valve seats not radially arranged valves. So the are alot smoother than 5 anlge or 3 angle ones.

  miscommunication

i agree with making the valve seats "round", other things to do are:
- "edging" the combustion chamber, which means rounding all other edges, to speed up the combustion process
- setting the squish/quench clearance correct, the smaller the better (hp wise) but they shouldnt touch the head ofcourse (if your planning on using titanium conrods it can go smaller cos they strech less at high rpm)
- raise the compression ratio

btw are you gonna use race-fuel?

[gsxr400 racer]

- setting the squish/quench clearance correct, the smaller the better (hp wise) but they shouldnt touch the head of course (if your planning on using titanium con-rods it can go smaller cos they stretch less at high rpm)

This is a bad misconception as there is a limit and a rule of thumb and if you go beyond it you loose HP, I used to be 2mm beyond what the norm is and it really was not beneficial your pistons burn real clean on the edges but you also run into predetination issues this becomes worse when you start milling stuff off of 2 strokes. 30 thousandths has become my bench mark for alot over the years i have found if i go more than that i start to go backwards for example ( 30 piston to head, 30 intake and exhaust to piston ) Now others may go more but this is what i like and i am just a lowly engine builder not a expert by any means

[gsxr400 racer]

also i believe when you mess with squish is when the heat starts coming into factor hence the gsxr 1100 radiator im messing with

[El Dopa]

OK, all the stuff about porting/polishing/changing the shape of the combustion chamber is way, way, way out of my league.

Plus which, would I be correct in thinking that most of that stuff is the cherry on the cake - the stuff you think about once you've done your major mods?

So the main mods I'm thinking of are one or a combination of:

1) Flatsides
2) 442cc kit
3) gsx400 crank

(assuming I can source/afford all these....)

The overbore with the bigger crank should give near enough 500cc, right?

Any problem using the overbore kit with the bigger crank? Jay?

Also, dumb question about flatside carbs - do you need to rebuild them with e.g. a Factory Pro kit, or are they 'good to go' as is?

[gsxr400 racer]

im happy with the 442 and flatslides but with a crank has to be amazing yes they will work with the crank there is enough room
no need for factory pro once you have race carbs and they have 4 orings versus how many in the b4 carbs?

[El Dopa]

Thanks Jay, you're a blimmin' goldmine of information.

[Thief400]

whats the difference with the normal carbs?

Ps. Banditmax do you know what radial valves are? difference with normal valves is that they open directed to the middle of the combustion chamber, so if you want radial valves there is need for more difficult rocker-arm-construction. since normal valves open in 1 direction instead of 2

     

[bsodders]

Old post I know but, is the GSXR 400 crank different than the Bandit.  I'm sporting a 76a and I'm trying to source big bore parts.  Strangely I've found the crank but no rods or pistons.  Any ideas?


Thanks