DRX2 50 rod and stroke

[Airchunk]

Does anybody know the lenght on centers of the DRX2 50 rod ?

Also what is the stroke ?

I know the bore is 40mm.

Thanks!

[#404's Dad]

Stroke I believe is 39.2 mm, Rod length I have no idea, Sorry.

[Airchunk]

OK cool !
That gives us 49.2cc

Now we need the rod length on centers to work out the exh port timing !

[neveready]

80mm

[Airchunk]

Ok thanks,
that makes the exhaust timing 95.43 deg ATDC
and the transfers 109.28 Deg ATDC

Now for some machining !

[neveready]

You also need to know ABDC on both to figure your total duration. and the width for your total port time area. There is alot more to porting than just some machining especially in a 50cc cylinder. You can really slow one down if not done perfectly.

[Airchunk]

Yep , you have got that right .

I have been porting cylinders since 1986 . Full time since 1994. Didn't feel like splitting the cases and pressing apart the rod to measure on centers , or laying out the cash for a new on to measure .

[hotquads1]

Originally posted by Airchunk
Ok thanks,
that makes the exhaust timing 95.43 deg ATDC
and the transfers 109.28 Deg ATDC

Now for some machining !

. these numbers don't look familiar , how did you determine them ? are you using software ? is this a l/c or air cooled cyl ? your #'s would reflect ex dur of approx 169 degrees which is not similar the DRR cylinders I have seen. also your #'s seem to estimate about 15 degrees between the ex roof and the transfer roofs, which is odd.
marc

[Airchunk]

hotquads1,
You have got it man . It does look weird . Yes I do use software . It is a liquid cooled cylinder and head .

This engine was built by someone that suposedly specializes in the DRR's .

I have had pretty much a motocross bike background , although I have built many an LT or trx 250R.

My kids are racing bikes now and have friends racing quads .

So I stumbled upon this job. It is so heart breaking to see the little guys held back from engine performance , more less that Dad sheled out some hard earned $$$ for this .

I am going to try and straighten it out .

Thanks for the help guys !

I am going to crunch some #'s

.

[bulldogfallon]

50s are very easy to make slower....Things that work on the bigger units do not work on the 50s

Keep us posted on the reults


You can usually get more out the 50s by tuning the carb and CVT

[Airchunk]

Ok , I went back and double checked all my measurements.


The transfers are definetly high and the exh is definetly low .

This is a strange set up . I am surprised this little quad ran as good as it did .

There were definately no grinder marks ( from the porting tool ) on the transfer or exh port. The prevoius engine builder stuffed the cases a little , and ground in some boyesen ports like we do on a KX60 , down on the intake side of the cylinder skirt . Other Than that it was stock .

The only other thing that could have been changed ( from stock )is the step in the cylinder head .

What is the stock step in the cylinder head?
This one had no step in the head (to the squish band)

Squish clearance was 1.22mm

[Airchunk]

Well , the mods worked great . We were able to out run a guy, this last weekend , that we have been chasing all year long . He always seemed to out power us --- Not anymore !!!!

[hotquads1]

priceless !

[spider525]

airchuck what did u end up doing to make it work if u dont mind me asking