Improving Performance On A Xu9j4 On Bike Carbs And Megajolt

[unariciflocos 49 1 Cars]

The first dyno was installed here so I finally had a chance to have the power of my car measured. It came to approximately what I was expecting considering I never properly tuned the carbs and I just threw a Zetec map in the Megajolt, but I can't help think that it can do better. This is my dyno chart and this is the ignition map I was running when it was measured.

 

The dyno place just do standard remaps and dyno runs and they don't have anyone qualified to do a custom map, so I'll have to get some hours booked on the dyno and try and map the thing myself.

 

I found a good guide to setting up the carbs here, but I don't know what to do with the ignition map and I am looking for a few pointers. Below is the map that was running at the time it was measured, I tried giving it a bit more advance through the range, but I don't know how much is too much and how advance should increase with revs or how maximum effieciency is achieved.

 

My spec is standard 1.9 158 hp alloy block Mi16 running Mikuni carbs with 40 mm chokes, Megajolt V4 mappable ignition controller with vacuum load sensing, std exhaust manifold and a straight 54 mm exhaust with just a mid silencer. The inlet length is 32 cm from carb mouth to valve and I'm not using trumpets or a filter yet.

 

I'm looking for any kind of advice to increase the performance of the current setup, inlet length, air filter, exhaust, ignition map, ANY advice is welcome. I know most of this is sensitive information because this may be your trade, but I'm in a country where everybody is absolutely clueless about performance tuning, so you guys are my only hope.

Edited May 11, 2009 by unariciflocos

[wracing 19]

trumpets are a must, so you reduce your costs match the track length of a standard manifold. and as far as advance is concerned advance it till the onset of knock then retard a degree until stable (if tuning for max power) remember that you cant change to a lower fuel quality as this will knock if to advanced

[unariciflocos 49 1 Cars]

I am running 100 RON fuel atm, but i have the option to chose between two maps, so running on regular won't be a problem with a secondary, more civilized map.

 

But how will I know when knocking occurs?

 

What about the exhaust? Is it the right size or should I go for a smaller or larger diameter exhaust to get more torque?

[unariciflocos 49 1 Cars]

I've been looking over dyno charts of other Mi16s and mine seems to be really down on torque

 

I am going to change try changing the carbs and change the inlet length. What would be the ideal inlet length (valve to carb mouth) and what length trumpets should I use?

 

(sorry for the consecutive posts but I can't edit my old one)

[Rippthrough 98]

Exhaust is about bang on imo, but yes, the trumpets should bring the mid-range right up.

I used this map to get an Mi16 running up and down the yard/lane a while back, but it never went on a dyno or serious road use, so treat it with caution, I was just playing with the Megajolt before I bolted it to a VW engine:

 

Edited May 12, 2009 by Rippthrough

[wracing 19]

knock detection is fun you can either by your self a knock sensor and conditioner, or do what i did flatten some micro bore heat tube bolt it to the block between 2and 3 cylinders 70mm down from the head put some rubber tube on the end. Long enough to reach your ear find an old stethoscope attach the rubber tube to the ear piece, crimp the tube to adjust volume you will know about it when you hear knock, and it’s like a car crash!

 

I got that tip from the net somewhere works great!!!

 

Add trumpets to increase to total length of the inlet tract. I guess total inlet length should be 300mm ish(head to trumpet tip). Depending on peak rpm is how far the carbs should be from the head. Higher velocity means the air is of a higher theoretical viscosity thus longer fuel mixing time required as you increase rpm.

 

Only play with one variable at a time 2.5" is good for a mild tune mi