There are so many limiting factors working against making 38 hp more on an automatic car. It is always easier to make more power higher in the rpm range but the 4 port engine doesn't rev near as high as the 6 port engine. That is a big holdback. Making 38 more power at 7500 rpm is much harder than making 38 hp more at 9000 rpm. A retuned computer, intake, exhaust will probably get you close but you are really going to be pushing the limits. You would probably like the car alot more if it had more midrange power. You alo need to be careful on an auto that you don't change the way the transmission shifts. The Camaros would mess up if anything was done different to the mass air flow sensor of the throttlebody. A retuned computer needs to take into account the added power and where it is in relation to when to shift. Even if you get some more power out of that engine, it won't feel anything like the 6 speed engine.

Just for knowledge sake here is some info as to just how different both engines really are. Just thought some people would find this interesting. The 4 port engine has everything that makes it a more efficient midrange engine which is right where you need it for an automatic. Here's the difference in intake runner length:

6 speed
primary runners 19.8" (long)
primary runners 13.5" (short)
secondaries 20.4" (long)
secondaries 14.2" (short)
Auxillary 17.3" fixed


Automatic
primary runners 27.4" (long)
primary runners 14.5" (short)
secondaries 29.1" (long)
secondaries 16.5" (short)
Auxillary none


The long and short runners are the effective lengths before and after the VDI valve opens on the intake manifold. That is how it affects the powerband. The engine only "sees" the length up to that point. Note that the primary and secondary runners are siamesed before the VDI valve so there is a useful interaction over a much wider powerband when the valve is open. The above numbers only apply if you disregard the siamesed section and just measured from intake port to the first intake split in the manifold. The auxillary numbers are only the length to where both sides join each other. Before this number is irrelevant.

As you can see the runners are much longer on the auto which gives better low end power. An easy way to get more total power would be to shorten the runners on the intake manifold but now you will lose low to mid range power. The auto needs this range. The auto also has less total intake runner area than the 6 speed which will max out its potential much faster. After the air intake velocity reaches .6 mach in speed in the manifold, power will start to fall back off. The total area of the runners is a limiting feature. The port timing is also much less. Even the individual ports between the engines are different. Here"s another comparison.

Port timing: 6 speed
IN: OPEN: Primary port ATDC 3
Secondary port ATDC 12
Auxillary port ATDC 38

CLOSE: Primary port ABDC 65
Secondary port ABDC 36
Auxillary port ABDC 80

EX: OPEN: BBDC 50
CLOSE: BTDC 3


Port timing:auto
IN: OPEN: Primary port ATDC 3
Secondary port ATDC 12
Auxillary port ATDC -

CLOSE: Primary port ABDC 60
Secondary port ABDC 45
Auxillary port ABDC -

EX: OPEN: BBDC 40
CLOSE: BTDC 3



The port timing isn't even close. The primary and secondary intake ports aren't even similar. They aren't even close to the old 13B 6 ports. The exhaust ports are smaller on the auto. There are alot of things going against it in the power department. There is one more thing that is holding the auto back and that is the intake tube to the airbox. The auto only has 1 while the 6 speed has 2 of different lengths for tuning sake. The only one that the auto has is longer than the long tube on the 6 speed. This will again tune lower down.

Mazda worked pretty hard to get more average power out of the 4 port engine but the big sacrifice is top end power. All of these factors add up to make improving this engine in terms of ultimate power much more challenging.

Wow rotarygod thankyou very much for all that analysis! Anyway I think the auto alreadyhas terrible low to mid power. You really feelnothing until you pass 4000 RPM. Its very strong between 5000 and 7000 likeyou said though. I couldntimagine the low end power being any lower than where it is now. If onlythere were a feasible way to strengthen the low end!!

Butat any rate what you are telling me seems to be pointingto the idea that the automatic Rx8 has very limited mod potential unless something extreme and obvious is applied to the engine like a turbocharger. Unfortunately I seriously doubt Id be willing to make that typeof investment even though Ive read that turbo is supposed to work better w/4 port than 6 port rotaries.

It's funny how you aren't happy with the midrange power of the auto because the 4 port engine makes more power than the 6 port engine up to about 7000 rpm. If you had the 6 port engine in your car with the same redline it does now, you'd really hate it. An ecu update would probably be the best bang for the buck but finding one tuned around the 4 port engine will be tough unless it is programmable. Any ecu for this engine should be designed around more low to mid punch. You really need a positive displacement supercharger but obviously the price is out of the question.

Another thing to consider is that if any headers come out on the market that do show a gain, they will be designed for the 6 port engine and therefore have the most benefit at a range out of your engine's powerband. My header design that I have been planning uses 24" primaries for the outer 2 ports and a 32" runner for the center runner. This is assuming it will be for the 6 port engine and I can fit it in the car. I think I can get it to go. The 4 port engine is a little different with the outer runners being at a length of 32" and the center port runner at 42". That I can't fit in the car! At least not with the cat in its current location. See the design differences. The 6 port engine header is assuming not only a higher rpm peak but also a different exhaust port timing. These numbers should be close to actual but only dyno trial and error can confirm it. Anything you decide to purchase should be solely designed for the auto car and not the manual. Unfortunately it will be hard to find upgrades designed for yours since the amount sold is drastically less than the standards and a majority of the performance oriented people will have the standard.

The thing about the turbo on the 4 port engines is that they are far less complicated. I have seen some fantastic 6 port turbo RX-7's. When it comes to a turbo car, you can design the intake timing with a lot less port timing and install a longer intake manifold. This will help give the car good low end power and drivability. The top end is taken care of even though everything is tuned against it because the turbo can continue to force air in to the engine even after the intake manifold is out of its peak range. It is possible to have a turbo engine with a power peak far higher or lower in the powerband than the manifold and port timing were designed for. If someone were to use a properly tuned length manifold with a more aggressive port job, we'd have some really powerful engines that have less low end and aren't as driveable on the street in terms of fuel economy and emissions. A manufacturer wants max average horsepower but with reasonable expectations. You will never see a 1.3l rotary with 500 hp from the factory. It can be done but isn't reliable. While they could do a good 6 port engine with a turbo, the cost and expense of adding another component to an already complicated package is just too great. Also consider that while it may sound like a good idea to keep an intake runner/port on demand, the lower intake area will result in less total air going through the engine and greater turbo lag times. If you just had all the ports open at once, initial power may come on slower but once the turbo spooled, power would be greater everywhere up to the point that they would have all been open anyways. When it comes to forced induction, you are pretty much relying on the turbo/supercharger for your power production. They just like to keep it simple and who am I to argue.

AT fluid cooler?
 

I too thought the second slot for a cooler would be used for the AT fluid. As Mazda didn't do it, they apparently think that people who don't clutch/shift for themselves and settle for a lower power engine will not drive hard.
The AT is a modified version of an existing Mazda unit, so it probqbly was designed to operate without a separate cooler (I know, the previous engine would not rev to 7,500).

Very good thread this. Lots of good, honest information.

I think the CAI on the RX-8 is "best-of-breed" status.

And yes, ram air is a bit of a misnomer, especially on a MAF'ed engine. You need a gentle smooth flow of air over the MAF sensor to get a reliable reading. Most benefits of "ram-air" intakes on cars comes from the fact cooler air is getting to the engine. I have a performance/racing engine text book that a forward facing intake will give only 0.5 PSI "boost" at 100 MPH. That is not going to do much getting out of the hole, hey? What engines love is cool, calm, dry air.

Cheers,
Hymee.