I began porting my first set of rotor housings today. I went for a D shape for a broader, less peaky powerband because it's destined to go into an REPU. They need a little finishing work. I'll see if I can post some pics tomorrow.



I'll also take Ito's advice and smooth the intake ports. They're really rough from a mildport done earlier this year. I'll make them smooth but not glass-like.



Is the port's smoothness a factor if using a carb? The engine will get broken-in with a stock 13B carb (Hitachi) that's been jetted for a streetport (I think). Then it'll get a dellorto 48 DHLA.



Speaking of porting, I used a dremel and some hand files to port the exhaust ports. I used dowel pins and aligned the pre-GSL-SE (old style 4 port) 13B housings to a T2 housing to match port timing to it. The port opening is the same, interestingly enough. The closing is much later on the T2. I extended the round part of the D a little higher than the top of the T2 port. The begining of the D starts at the old port for a nice round (slow) port closing.



Do you think I should extend the outer edges of the ports at least up to where the T2 closing is? If I did, it would look less like a D and more like a rectangle with a rounded upper edge. Infact, this engine's old overheated rotorhousings were done this way. Since this engine is ultimately going into an REPU, it needs half decent low-end. It'll be NA untill I can afford a supercharger. It'll use the heavy stock 33LBS flywheel, if that makes any difference (easier to tow with I guess).



Do you guys have any pointers or tips?

 

I would say port them with the same exact timing because it could cause differences in cylinder power output and end up damaging your engine under load.

 

I'm trying to make them look as identical as possible. If I have time, I'll start on the other set of housings. They're the '74-'75 style with small sleeves. I think I'll remove them since they're the only housings where you can get away with it.

 

How would it damage the engine if there was a little power difference? I think it would not. Heck, most people's engines have different power amounts comming from each rotor/cylinder. With lower compression, the power is lowered. There are a lot of cars with different compression within each of the cylinders.

 

My thoughts exactly. Infact, this engine's old overheated rotorhousings had different closing exhaust port heights. I may set up the CCD camera later and snap a few pics.

 

Here is one of the D shaped ports. It looks a little crooked, but that's because of the angle and fish-eye effect of the camera. You can see the other rotor housing's leading plug hole through the port.

 

There's both of them. They just need a little finishing work.

 

Here are the old overheated rotorhousings. The PO ported them really tall. Maybe a little too tall for such mild intake ports. It's too bad the engine overheated before it was fully broken-in.

 

A '74-'75 housing on the left with a D line drawn on it. On the right is a T2 housing. The bottom horizontal line is the closing of the T2 port. The upper line represents the top of the D.



Not much of a difference for the T2 port, but a big difference on the older ports.

 

Why the "D" shape on them Jeff?

Why did you choose to opem the exhaust ports at considering you wanted low end torque?

These are generally speaking more benifcial for more top end.