13B RX-7 intake ports (aka are my housings junk?)

sburkett

sburkett

Well-known member
Hi all,

I am way down on power. I had reason to suspect my porting (by a big name shop) was less than ideal, and tore down tonight thinking I could open things up a bit. But I think after seeing this maybe part of the problem is too much porting.

Without giving away any speed secrets can someone give me a hint as to whether this port is so oversized that I need to start over? Intake closing is about 115 degrees ABDC of the intake stroke. Seems to me that is too long to stay open, but I don't know all the latest tricks.

So, junk the end plates and start over, or does this look okay (if not 100% ideal).

Any and all input appreciated!
Steven
 
I'm assuming you did a compression test before you pulled it apart and everything was ok?

I'm assuming you have a 13B non-turbo from a second gen. If so here is an image of a "large" porting template for that endplate. It doesn't look too far off, but it may be too big on the top port.
 
Steve, the real issue usually is the center housing. That end plate is a little big maybe but that's not the reason for you being down on power. Call me if you want to chat.
 
Thanks all - compression is okay and nothing really "wrong" with the engine, just not making the power that it should.

I'm glad to hear those end plates aren't junk because I'm probably stuck with this engine for the rest of the season.

The center and exhaust ports are relatively anemic. I'll see if I can squeeze out a couple of horsepower there.

Jesse, I'll be in touch, probably an off-season project unless you want to work a trade on a nice PBS box. :)

Thanks again!
Steven
 
We spent MANY dyno runs on my engines. We found that going brarely higher than stock on the top of the top port was best. The engines where we had gone not even half as tall as yours made less power the higher we went.

That port top is intake closing and the stock location is about as much port timing as these engines want. My engines were still making good power at 10,000 rpm with the 42 mm chokes.

Btw, I took a set of those "too big" ports (still WAY smaller than yours) and put the engine in my NASA car (where they have no choke limits) and dynoed it with a 58mm Berg IDA with 50mm (!) chokes and it REALLY worked -- made 251hp at the wheels.
 
Thanks Dave I really appreciate that info! I also discovered tonight that the center ports were a bit too big... as in they chewed on the leading end of the side seals. So it sounds like time to start over.
 
The height, angle, and radius of the top of the port is EXTREMELY critical to keep from damaging the ends of the side seals.
 
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