Hello,
I'm gonna do a DIY port job on my 87 zilla with a roary tool kit (cheap version of a dremel) and I want to know is there any tips or guidelines.

 

Join the forum at Macdizzy.com. There is more Zilla engine info over there than anywhere else.

 

Ditto that one... you need to get the specs that Dr. Q recommended for MOREPOWERTHANU... (Those specs ROCK!, and my Motor really runs hard in comparison to a stocker)

I hate to send anyone over there, because it became a $pay$ site, and I don't agree with that... hence why I've not been there in a long long time.... but there is some good info over there... Not sure how much new stuff there is.

There's a great deal to pay attention to when considering a port job.... it's not just a matter of going in there and making things bigger better smoother rougher or whatever...

There are critical dimensions to consider. Also, a cheap dremmel is not the correct tool for the job. The spots are hard to get into, and even harder to do a good job with. (I use a 90 degree tool to gain access to the transfer ports)
Also a dremmel runs at high speeds... when you try and cut aluminum at high speeds, it gets hot and hardens, thus making it harder to do a good job making a nice smooth cut.

I'd recommend doing a LOT of homework before chopping on your cylinder.. there's a lot of science involved....

Good luck,

 

Yah, I agree with duneaddict. Porting and polishing is not something you wanna just go give it a shot at. Its something that takes knowhow because you can really screw things up. You have to know about port timing and all that sort of thing. If i was you i would let somebody who knows what they are doing take care of that.

 

When I say a cheap version I ment a immitation. The machine goes from 8000rpm to 35000rpm and it has a flexible shaft to get into corners. I've been doing some homework and I've asked a machine guy who used to polish ports in go-carts. I understand bigger is not necciseraly better and i know not to go too big a rings may get caught. I was thinking of a mild port like a few mm all round. But I will do more research before I start. I wish I could find someone here but I can't and zillas are pretty much rare here. Thanks for the input keep it up.

 

I'd just polish the ports and reshape any obstacle or anything that would cause turbulence...
I think this would help the zilla alot but a serious porting should be done by a professionnal, don't you think ?

JMHO

I found something that may interest you..


CYLINDER PORTING

The cylinder ports are designed to produce a certain power characteristic over a fairly narrow rpm band. Porting or tuning is a metal machining process performed to the cylinder ports (exhaust & transfers) that alters the timing, area size, and angles of the ports in order to adjust the power band to better suit the rider's demands. For example, a veteran trail rider riding an RM250 in the Rocky mountain region of the USA will need to adjust the power band for more low end power because of the steep hill climbs and the lower air density of higher altitudes. The only way to determine what changes will be needed to the engine is by measuring and calculating the stock engine's specifications. The most critical measurement is termed port-time-area. This term is a calculation of a port's size area and timing in relation to the displacement of the engine and the rpm. Experienced tuners know what the port-time-area values of the exhaust and transfer ports should be for an engine used for a particular purpose. In general, if a tuner wants to adjust the engine's power band for more low to mid range he would do the following things. Turn down the cylinder base on a lathe to increase the effective stroke (distance from TDC to exhaust port opening). This also retards the exhaust port timing and shortens the duration and increases the compression ratio. Next the transfer ports should be narrowed and re-angled with epoxy to reduce the port-time-area for an rpm peak of 7,000 rpm. The rear transfer ports need to be re-angled so they oppose each other rather than pointing forward to the exhaust port. This changes the loop scavenging flow pattern of the transfer ports to improve scavenging efficiency at low to mid rpm (2,000 to 5,000 rpm). An expert rider racing mx in England would want to adjust the power band of an RM250 for more mid to top end power. The cylinder would need to be tuned radically different than for trail riding.

Here is an example. The exhaust port would have to be raised and widened to change the port-time-area peak for a higher rpm (9,000 rpm). For either of these cylinder modifications to be effective, other engine components would also need to be changed to get the desired tuning effect.

 

yeah maybe just a polish and a bit of a clean up. The guy I talked to recond that a polish can add upto 7mph to his top speed in go-carts. Could that be true?

 

thats impressive for a small displacement engine

 

sometimes there is major turbulence in ports due to the casting of the cylinder. and by major I mean MAJOR. Last week when I removed the head of my zilla I looked into ports and there was an excedent of aluminium obstructing about 1/20 of the hole !!!
You know, a kind of thin little plate formed by the mould..


7 mph its very realistic, even for a cart. It improves top end allowing to rev highter.
but you can gain much more than 7mph on your zilla with a polish, particulary with the pipe and k&n

 

The 90 degree tool Duneaddict is talking about is a Falcon or Foredom tool. I also use them in porting. The motor is designed to handle a hard load and keep the rpms steady. You can set it to turn at a few hundred rpms and cut nicely and evenly without balling up the aluminum. I dont knock someone who wants to do a job themselves, but I have to advise you to please be very careful. You are dealing with the one year jug that is totally different than all the others and are hard and expensive to find. The other is that the Zilla jug does not have an exhaust port design like other cylinders. Blending the aluminum to the cast iron everywhere is a must. Also anything you can see that would be an obstruction of air flow. The motor is an air pump and has to be efficient to be productive. If you get into the transfer port windows DO NOT do any griding that will change any angles on how the charge will exit. other than that polish the exhaust port area as smooth as glass if you can get it that way and leave all intake areas with a 40-60 grit finish to keep fuel in suspension. Hope that helps,Bubba