Author Topic: tuning a '91 gsf400 engine for track - what mods are best? (Read 15483 times)

El Dopa · « **on:** July 08, 2007, 06:25:31 AM »

I have just shaken hands on a deal to buy a 'parts' bike - a '91 Bandit 400. Hopefully i'll be picking it up next weekend.

I'm inclined to drop the engine and carbs out and tune the bejeebus out of them for use on the track.

My headers/cans are already upgraded. I'm upgrading my suspension as part of the overall project.

So what's a good place to start on the engine?

I'm thinking:

Rebuild the carbs with something from Factory Pro, probably a race kit.

Replace the airbox with pods.

Possibly one of Jay's bore-out kits.

What other suggestions does anyone have?

Banditmax · « **Reply #1 on:** July 08, 2007, 07:48:04 AM »

Bigger valves in new radial seats ported and polished. long stroke crank with 460cc kit from jay giving you a 500. Some keihin fcr flatslides. That'll be fast when sorted.

Bartjan · « **Reply #2 on:** July 08, 2007, 08:42:48 AM »

what will radial seat do when the valves arent radial?

polishing the ports is a bad idea, cos the mixture get mixed worse compared to no polishing and you lose some power although its slightly better on the flowbench.

getting hold of the longer crankshaft takes alot of searching i think

Banditmax · « **Reply #3 on:** July 08, 2007, 10:00:43 AM »

well get radial valves too then.

gsxr400 racer · « **Reply #4 on:** July 08, 2007, 12:12:44 PM »

really no room due to angle, for bigger valves tried that route was going to be 1200.00 for valves and i wont even say what they wanted to charge for custom ti valves about the only custom thing i was going to do was have corrillo rods made for 800.00 that was the only company i found that would make them that small but my lightened stock rods are holding up OK with the big bore.

El Dopa · « **Reply #5 on:** July 08, 2007, 05:47:03 PM »

OK, so putting the valve and the crank in the 'too hard' basket for the moment,

1) what exactly are flatside carbs?

2) Where do I get a set that fits the bandit?

gsxr400 racer · « **Reply #6 on:** July 08, 2007, 07:45:42 PM »

http://www.okshon.com/v.cgi?YYurl=http://page13.auctions.yahoo.co.jp/jp/auction/r37615971

those are smaller than what i have but will work great for the road. I have 33 here is a pic of soem tmr a little diff than fcr but i can find the pic of my bike with the fcrs on.

they do make adapter for both to mount pod filters

gsxr400 racer · « **Reply #7 on:** July 08, 2007, 07:50:58 PM »

there are a number that fit JC bought my old RS round slide race carbs (haven't heard much from him) with the big bore i think i could go bigger carbwise than 33 as soon as i stuck them on with the big bore they where really crisp like like i needed bigger carbs mine came from a Yamaha xjr 400 thats what they where bought for originally by a guy in japan for they went right on my bike no problem or spacing issues.

El Dopa · « **Reply #8 on:** July 08, 2007, 10:51:07 PM »

Like these?

http://cgi.ebay.com/ebaymotors/keihin-flatslide-33mm-carborators_W0QQcmdZViewItemQQcategoryZ133200QQihZ002QQitemZ120139777264QQrdZ1

El Dopa · « **Reply #9 on:** July 08, 2007, 10:53:22 PM »

Or these?

http://cgi.ebay.com/ebaymotors/zx7-zx9-keihin-fcr-carbs-flat-slides-BRAND-NEW_W0QQcmdZViewItemQQcategoryZ35587QQihZ007QQitemZ170129056424QQrdZ1

El Dopa · « **Reply #10 on:** July 08, 2007, 10:57:56 PM »

Or these?

http://cgi.ebay.com/ebaymotors/keihin-41mm-fcr-flatslide-GSXR-CBR-ZX_W0QQitemZ120139842049QQihZ002QQcategoryZ35580QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

gsxr400 racer · « **Reply #11 on:** July 08, 2007, 11:36:28 PM »

it may be worth a shot on the top ones for the f2 thats a good deal and the spacing might be real close

http://cgi.ebay.com/ebaymotors/keihin-flatslide-33mm-carborators_W0QQcmdZViewItemQQcategoryZ133200QQihZ002QQitemZ120139777264QQrdZ1

just have to make sure you dont buy down draft carbs as they are angled to much

Bartjan · « **Reply #12 on:** July 09, 2007, 06:03:32 AM »

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

Banditmax · « **Reply #13 on:** July 09, 2007, 06:39:08 AM »

ill keep quiet

gsxr400 racer · « **Reply #14 on:** July 09, 2007, 08:53:52 AM »

Quote from: "Bartjan"

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

never heard of that one, would like to see some research or documentation on that one "radial valves"

carbs i have a a dyno print out to show the performance gains on a 400 with them.