Just wondering what modifications should i do for 3mb cylinderhead? Because big bore kit isn´t option, carburator is not worth it, exhaust is expensive and electrics are expensive. I know this stuff, but what cr should i run and squish cap? Also piston is 2mm larger than stock. Also is there any tuning heads for dt 125r?
Darty last edited by
@jonne123 Just leave it alone then?
Calum last edited by Calum
My recommendation would be to start simple.
I think the stock carb is more than capable for light modifications.
The first thing I'd grab is an aftermarket exhaust. A DEP system is a nice upgrade from stock. The main difference to the DEP is the weight savings.
Probably look next into some carbon fibre reeds, but it's questionable if there is actually any real-world difference to the OEM ones as they're already pretty good.
I'd definitely recommend an aftermarket ignition system. That was above all else the biggest jump in performance.
With regards to cylinder head modifications, I'd say it's meaningless if you can't adjust the ignition timing, so an aftermarket programmable ignition system is a must.
As you increase the CR and/or adjust the squish band, you're going to introduce some elements of knock. This can be controlled via various mechanisms
- Spark Plug Heat
- Combustion chamber heat (So increase cooling)
- Retarding ignition
- Higher octane fuel
Some of these you're limited in doing, but adjusting ignition is controllable. I try run my bikes/cars on Shell V Power as they're all modified and I want to reduce knock.
Modifying the head should be done alongside your supporting mods, as well as supplying the barrel and piston that is going to be used.
A very simple way of increasing CR would be to use a thinner base gasket.
This can be achieved by merely making your own gaskets out of some high quality, albeit thinner, gasket paper.
Again, if you don't know what you're doing, then I'd recommend just starting simple, one modification at a time.
An exhaust is a great/simple modification to get a few more ponies.
Yeah i already have carbon reeds and giannelli exhaust. I just wondered if i can get little more performance. Because its not worth it to spend lots of money on dt because the value wont increase as much and because there is better bikes for less money. I think i willl leave it as same.
Id say just start with measuring everything, and then start and get everything to the manufacturers specification. Maybe someone in the past added thicker base gaskets so your a couple 0.1mm+- over recommended measurements from yamaha. Just get everything back to standards so you have a good place to go from if you want to continue modifying, but you will probably be happy leaving it as is after that tbh.
Im no dtr cylinder head genius but i know that the 3mb is the unrestricted head compared to the 3bn, idk how the 3mb compares to the 4fu or 3mbP however
Might also be possible to just move the stator and pick up assembly as a budget way of changing ignition timing. Im not 100% sure now and you should do your own calculations tbh but when i measured it myself the number i got (I think) is every 0.7mm of rotation of stator is equal to 1 degree of timing. you would just have to slot the screw holes using a dremel or round file.
Glynn123 last edited by
For reference I’m running about 1mm squish on my engine with programmable ignition, I was melting the tip of the standard range spark plug after a top gear hoon but I think I was a fair bit further advanced than standard on the top end, I’d maybe stick to 1.2-1.3mm, I’m sure that’s the standard figure but my Frankenstein engine with different barrel and head measured something crazy like 1.8mm as it was! So it’s worth checking..
also to note for the future, you don’t want to go any less than about 0.8mm squish on these engines as the Conrod stretch at high rpm will smack the head.