I was setting free a south bound butt nugget. and checking out an RX-7 Magazine. and I found this

looks like they port matched the side of the rotor.







what do you guys think of this? worth it or not

 

Maybe it was for lowering the compression?

 

Port matching the rotor?

Damn, that was MY idea, at least I thought....

By my calculations, C/R only drops by a couple tenths of a point if you do that. (say, from 9.4 to 9.2 :1) And, the placement of the increased volume wouldn't do anything to help combustion. So yeah, it's there to trick a little more intake port timing out of the intake ports without going bridge yet.

 

Looks like that would be an attempt to make the port open earlier and close later.

 

to solve that over here we run lpg and run 9.7:1 compresion rotors

 

solve what? being unable to make the port open earlier because the corner seal needs that space?

 

Peejay, I'm confused.
"And, the placement of the increased volume wouldn't do anything to help combustion"

Do you think it would pull in that much more juice through that little chamfer? Is it worth it? (echo in here?)

Edit: Also, (asking you because I guess you've pondered this) what kind of dimmensions are on your proposed rotor port/chamfer? Or is that top secret info.

 

What I mean is, it's increased crevice volume away from the main combustion area. One more place for air and fuel to be tucked away and not get burned.

The better port timing would make up for that, though.

 

Ahhhh, I have been enlightened.
Maybe next time I have some $400 rotors laying around I'll try that.

 

....and don't forget to polish the rotor sides as well.

 

? U mean by rotor side u mean the Squash Chamber? or do you mean the all the rotor faces?

 

The above mod works great in boosted applications but lowers power on naturally aspirated situations.
From what I've experienced it seems the added timing does not compensate for the lost in compression.
It works great in a boosted enviroment though!

crispeed
87 Rx-7 TII
9.204@150.47mph
2600lbs
un-tubbed

 

its one way of getting a bit of extra port duration i suppose

 

i think it will have a small affect on compresion, port will be open a little longer and i think it will shorten the life of the side seal a little

 

ok, here's my numbers.

first i calculated the clearance volume for a 9.4:1 12A. A 12A is 573cc (1146 / 2) cc per chamber. this worked out to a 68.214cc clearance volume, assuming exactly a 9.4:1 compression ratio. (68.214 plus 573 is 641.214 total volume at BDC, divided by 68.214 (volume at TDC) is 9.4 - 9.4:1 compression)

then i roughly guesstimated the size of the "notch" to be a 5mm by 5mm triangle, 50mm long. Since there are two of them, one on each side, then this means the total volume increase is approximated by a box 5x5x50mm, which is 1250mm^2 or 1.25cc.

Addid 1.25cc to the original clearance volume gives us a 69.464cc volume. 573 + 69.464 is 642.464, divided by 69.464 makes for 9.25:1 compression ratio.

The notches would probably be smaller in size, in actuality. (I just pulled 5mm out of my ***, I doubt there's that much room between the rotor face and the side seal) Also, if you're playing with 13Bs, the larger displacement means the clearance volume is necessarily larger to make a similar C/R, so an addition of (roughly) 1.25cc of volume will have even less of an effect.

The effect on compression is very small...

 

Can't beat numbers. So the next question, is there any excessive overlap with this setup? I guess if there were, it would be a good thing anyway.

I'm starting to like this idea alot. How bout ported rotors with a bridge port? Too much? Just throwin out some ideas.

 

the overlap would be less than with a bridge port but more than you could normally go with a street port.

i don't see an benefit w/ a bridge port, seeing as a bridge port is more opened/closed by the apex seal than by the side of the rotor, in which respect it's a lot like a peripheral port.

 

how about you bridge port the rotors!!! hahahaha

j/k

 

I've got a set of ported apex seals if you want to try them... they're 3mm most of the time