ESE's works engine tuner

[Roflhat]

New to the forum, from Scotland!
I'm building a GP100 to take to Bonneville, only going for production records so no big changes. Basically the bike has to appear standard and have the standard venturi size. Other than that you can get away with changing internal parts. Currently I've got a sort of expansion chamber welded into the standard exhaust, barrel ported, rotary valve cut to gp125 spec, standard carb bellmouthed instead of the standard shape. Got a thin spacer under the barrel, barrel skimmed and o ringed.

Went from 9.6rwhp to around 13.6, have done a couple mods since but would love to get more out of it

[F5 Dave]

And the reason you didn't start with a TM100, or even KX100 is?

[TZ350]

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Welcome Roflhat. Great to see you here. I am looking forward to following your project. Great to see its a Suzuki GP100. Team ESE's favorite bike.

[TZ350]

I'm building a GP100 to take to Bonneville, only going for production records so no big changes. Went from 9.6rwhp to around 13.6, have done a couple mods since but would love to get more out of it.

From our experience with original air cooled GP100's. 18 rwhp is realistic and 22 is about tops.

It will be interesting to see whats possible with the class restrictions you have.

[Grumph]

With those class restrictions, IMO the most cost effective add-on power is a NO2 bottle hidden in the frame.....

[Roflhat]

And the reason you didn't start with a TM100, or even KX100 is?

Not too late to change, basically went for the fastest production 100cc bike in 1980 (class is for classic which is pre 1981).

18rwhp I'd be very happy with. I took it down to Mick Abbey for tuning last year, that's him in the photo with the exhaust. Big improvement after that but his knowledge isn't specific to GP100 or as in depth as the info in this thread.

How much of your GP125 recipe would be applicable to the GP100 given the exhaust + carb restrictions I've got?

GP125 18+ rwhp: skim the barrel 1.5mm and “o” ring it, thin alloy spacer plate under the barrel and Suzuki RG250 pipe. Ex opens 86 deg ATDC and Trans opens 114 ATDC, std head , inlet timing 145/55 and carb mj 95.

GP125 20+ rwhp: skim the barrel 1.5mm and “o” ring it, thin alloy Spacer plate under the barrel and Suzuki RG250 pipe modified to RM125 specs, KX80 ignition. Raise the exhaust to open 83 deg ATDC, and widen to 70% of the bore, cut 30 deg from the closing point of the rotary disk, so inlet opens 145 BTDC and closes 85 ATDC. Set the mj 105 and ignition timing, 26-28 BTDC using a dyno.

[TZ350]

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Once we opened up the "B" and "C" transfers we started to make some real power with the GP's.

Looks crude but was very effective.



Porting the cases to match the cylinder we broke through in some places. We learnt to glue the cases with JB Weld before porting them.

We never had any problems with the glue coming away and leaking.

[TZ350]

How much of your GP125 recipe would be applicable to the GP100 given the exhaust + carb restrictions I've got?

Pretty much every thing. All the port and inlet timings. Maybe not the Honda RS125 chamber although we do use it with the 110cc engines.
The GP125 looks exactly like the 100 one except it is 24mm not 22. I would use the GP125 rotary valve cover, disk and carb if you can. Carb size is not that important, we have had 30rwhp out of a GP125 with a 24mm carb.

Exhaust opens 80deg ATDC for 200deg Duration 70% bore width. Transfers open 116deg ATDC for 128deg Duration. Inlet port opens 145 BTDC closes 80 ATDC.

[Tim Ey]

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We learnt to glue the cases with JB Weld before porting them.

There is an alternative.



I am selling these mostly to Vespa tuners.
21€ including shipping Worldwide.

If anyone needs it write me an email
mail [at] overrev.de

I hope this add is ok with all of you - otherwise let me know & I will delete it.

Regards
Tim

[Roflhat]

Thanks very much for the info, photos will be especially useful. What's the advantage with kx80 ignition? I've got an electronic ignition kit from malaysia somewhere on there currently

Have to use the standard carb, 22mm for the rules unfortunately

[F5 Dave]

Ahh, didn't realise the year limit.

[TZ350]

What's the advantage with kx80 ignition? Have to use the standard carb, 22mm for the rules unfortunately

Would not worry to much about the 22mm carb. Plenty enough air will flow through it. Only draw back is a little loss of over rev capability, not a big deal for Bonneville.

KX80 ignitions are fixed advance, we used to run them and they will work but lack the ability to be correct for "low end drive" "max power" "over rev". Un like a digital ignition the KX80 has no curve so it is compromised as you cant bend the ignition curve to get the best of everything. Maybe ok for Bonneville??

We use Ignitec DCCDI Race1 or Race2 Ignitions. No more top end power than the KX80 but a much better power curve and ride able bike. The Ignitec DCCDI can be powered by a 12-14Volt battery and gives a good CDI spark.

On our later bikes we used the center from a GP's flywheel to modify a Chinese after market ignition unit which was re wound by hand for 12Volts. These bikes had a Voltage rectifier regulator and capacitor to power the Ignitec. No battery. We call them push and goes.

How to make a decent light weight racing 12 Volt generator stator for the Suzuki GP/TF/TS RG50 from a Lifan after market magneto kit. We have spun these to 14,000 rpm plus on the dyno and they have proved reliable on the track.

[Roflhat]

Excellent, buying a barrel or maybe 2 in case I mess it up. Already got a spare set of cases and a pile of bits, will probably take my complete engine out and just build another one to your specs
Will any year KX80 ignition work? Not so many of those bikes up here, will probably have to buy from abroad.
www.ebay.co.uk/itm/224691973171 - some great photos of this one

[Condyn]

We do similar with our snowmobile race ignitions. Press out the rivets and weld the desired mag onto the hub.

[TZ350]

Excellent, buying a barrel or maybe 2 in case I mess it up. Already got a spare set of cases and a pile of bits, will probably take my complete engine out and just build another one.

You can never have to many spares....

I was able to triple exhaust port a cylinder. Worked great, then ruined it by trying to improve it. A lot of hand work with long drills and porting tools. But it is possible to do and keep the cylinder looking standard from the outside.

Will any year KX80 ignition work? Not so many of those bikes up here, will probably have to buy from abroad.
www.ebay.co.uk/itm/224691973171 - some great photos of this one

Yes, but the later ones like the ebay picture may have a heavy retard to protect the KX engine. There is also a little bit of machining to the stater plate required to fit the GP100 mount and to clear the main bearing boss.