Gilgamesh

I see this thread.

Then I see Banzai's dyno gallery has an S5 RX7 ITS car which no porting is allowed, not even port matching.
Banzai Racing (Keefer 13B RX-7 Engine Installation)

fidelity101

iTrader: (11)

My engine is more like 100psi compression on the faces, I needed to do a better job on the side seal clearancing. I'm sure this ITS car has had hours on the dyno and lot of ignition tuning. I had about 1 hr of work into it.

peejay

The S5 manifold has way too much surface area and therefore flow restriction to be a good performance manifold, IMO. Although I shouldn't say this until after I sell off my stock of S5 manifolds, I have 3 of them and will never use 'em. Think $200 a set is a fair price? I need to buy tires

rotarygod

iTrader: (1)

I'm a little late to the party but when I had an S4 for all those years, all I wanted was an S5. Now that I've got an S5, I wish I had the S4 again. The intake is certainly simpler. For the mild porting level of the stock ports and the power band and economy demands of a stock car, the S5 manifold is nice. I'm keeping this car very mild so the S5 manifold will stay. For performance, it limits things. A modified S4 intake can flow a ton of air, and I do mean a ton. It is easy to modify too. An S5 manifold is very hard to modify and even then it's very hard to get any benefit in any location without seriously hurting it in other places.

The real limitation of the 6 port engines is actually the ports though and not the manifolds. The manifolds, even the S5, can flow enough to support 200 rwhp and the S4 far more than that. The biggest issue lies in the port timing of the 6 port motors. The reason that a 4 port motor typically makes more power and has a smoother power band has to do with the fact that the intake ports, primary and secondary, close at the same time. On the 6 port motors, with the auxiliary ports shut, the secondaries close first and then the primaries. The point of the divided intake manifolds is to take advantage of tuning the return wave pulses to help charge the other rotor just before it closes. The problem is that this closing pulse in the engine does affect the other port in the same rotor as well through the rotor housing. When the auxiliary ports are open, now the primaries close first and the outer ports essentially keep moving. It's a mess.

Another neat thing is that the exhaust port size on an n/a is what affects your power peak. It actually flows plenty and if it is going to be opened up, should really only be opened up to what Racing Beat considers a street port exhaust profile. Even a large bridge port can be supported by this. Going larger on the exhaust side only shifts the power band up in the rpm range. If you make a really large exhaust port but don't do much to the intake or manifolds, you'll just have a car that makes lower power everywhere in the rpm range, something that is pretty common. If you make really large intake ports but then use longer, free flowing runners to tune them and keep the exhaust ports mild, you'll make some very nice power everywhere. At this point, dividing the intake manifold into individual rotors that don't cross talk is the best option.

For street cars using the stock manifolds, mild porting (no bridging) is best and definitely do very little to the exhaust ports.

peejay

One interesting thing is that I'm seeing the power lay over like mine never did.

I always removed the sleeves and removed the actuator shafts. The actuator shafts represent a large cross sectional area restriction and ALL air to the end housings has to go past them since the main secondaries are under the aux ports.

dpartinvr4

iTrader: (1)

well I picked up a caged FC shell I'm going to basically mirror this build but I'm adding a GT45 turbo. and I'm naming what I did with the AUX ports the "Drawbridge Port"......a new build thread will be coming soon..... that is all