4t tuning thread

**kel** · 28th March 2012, 20:33

Originally Posted by richban

How long was the exhaust header?

That was the secret bit, its quite a bit longer than you'd expect. Bike will have the standard short 2 stage header with a nice quite muffler fitted for Easter.

**richban** · 28th March 2012, 20:49

Originally Posted by kel

That was the secret bit, its quite a bit longer than you'd expect. Bike will have the standard short 2 stage header with a nice quite muffler fitted for Easter.

Ahhhh yes the megaphone. Haven't seen one on a moto3 bike yet. Back to the airbox thing. Before Taupo I had a bit of a desater with an needle that was almost worn through at the clip. I epoxyed it onto place and then noticed it had a couple of weid holes in the power. I had cleaned and serviced the carb and check everything. It was running pretty much open. I figured it was time to build a proper air box. 1 hour later fitted to the bike with longer intake she ran crisp and clean. The length could be out for sure but the main thing I noticed it the consistency of the engines power delivery. It just did not miss a beat. It used to.

**Bert** · 27th May 2012, 08:45

interesting article:
http://motortecmagazine.net/article.asp?AID=1&AP=1

Far to many strokes for my liking; but horses for courses.

**Bert** · 31st August 2013, 10:46

Originally Posted by Bert

interesting article:
http://motortecmagazine.net/article.asp?AID=1&AP=1

Far to many strokes for my liking; but horses for courses.

Hummmm

Anyway, since I've taken a backwards step and made a tempory move to quad stroke; I thought this tread should be bumped.

What's been happening in Palmy (GPR headquarters)??

5 freshly finished GPR tuned FXR engines Have been completed
(including one very lucky welly rider).
We have managed get from 14.7hp to ~21hp. Piston, pipe, cams & carb and head mods.

Currently there is a stock fxr sitting on the dyno and are going to test out some simple bolt on mods to see what can be made easily. Pipe, carb, timing, fuel etc
The idea here is to get a simple set of mods for newbies to follow. ~18Hp is the aim which isn't bad to start with.

Too share the love we will post up our findings. And try and do some YouTube stuff show and tell.

Side notes to get things started:
1. Challenge fuel vs BP 98 (0.5 Hp gain on back to back test on full worked GPR engine)... Something to think about here (is it safe)...
2. Cam chains. Old stretched chains can move timing by up to 10 degrees. Might be why engines feel the best before they shit themselves.
They are cheap so replace them regularly to save heartache. Check and record your cam durations (opening etc). If they drift do something.
3. Clean your chains. The frictional losses on the dyno are surprising. >1Hp loss.
Make sure you get everything lined up correctly (and clean& oiled). don't over chain your bike (buckets don't need anything more than a 420, 415 DID race chain is good for 50+ hp, so think about your 520 chains and how much weight and friction you could loose).

More later when I've got time.

**TZ350** · 31st August 2013, 13:09

Really interesting, thanks Bert.

A way of varying the inlet tract length and picking up a couple of thousand rpm at the lower end.

Originally Posted by TZ350

Attachment 254019 Attachment 254020 Attachment 254023

What really surprised me was the inlet with the hole closed was crap up top but with the hole open it had the tuned length (to the hole) of the carb but made better power up top than the carb did. I would have thought the plumbing of the long inlet would have been more restrictive to air flow than the naked carb and made less power.

From experiments I did with Kel and Gigglebuttons bikes I think a 4T could gain a lot from varying the inlet and exhaust header length as required by just 100mm for the inlet and 50mm in the exhaust.