Starting with a Standalone
 

Apparently, the stock ECU is just too safe and conservative. Mazda gave it a large margin for error. But a standalone can be customized to meet your needs and maximize your setup.
It seems even if everything is kept stock, a standalone could find extra horsepower.
I would like to get an idea of how much horsepower Mazda left behind on a totally stock setup. What can I gain with a well tuned standalone on a healthy stock S4?
I haven't ever dyno'd it, so I have no idea what this 24 year old rotary engine could pump out on the stock ECU. So let's start there.

I'd wager to say a touch of porting, good intake and exhaust mods, and ridding the engine bay of that garbage rats' nest of vacuum lines would pull an extra 30hp with a proper tune on good fuel.

Why don't you tear down that 24 year old engine and clean out the carbon buildup and check the side seal clearance among others. A healthy engine will outperform and out live a tired old engine with a programmable ems. If you can handle installing a custom ems you can probably learn how to rebuild the engine.

well to give some idea, the SCCA ITS class rules spec out a STOCK engine, and intake manifold.

this limits you to exhaust, air filter (the AFM has to stay) and the ecu. they do between 165-175RWHP.

the peak hp difference between the stocker and a tuned one is only like 10hp, but we found that the power band was way broader with the standalone.

for example, the peak power on the stock ecu was 6500rpms, with the standalone it still peaked @6500, but we got it to be within a couple hp of peak for something like 1000rpms, from maybe 6200-7200.

and we were up in the 4000-6000rpm range by quite a bit too.

Depending on where you plan on ending up, starting with an ECU might be a good thing. I personally would take a slightly different appraoch by freshening the engine, but can understand why you might wait on this until you make decisions regarding porting, headers, fuel, etc.

The S4 made 146 hp and 138 lb/ft when new. I'm guessing I dropped 10horses and 20 torq by now. So lets say I'm at 135 hp.

By porting, I take it you mean mild street port for primary intake; nothing more?
Define good intake...CAI with stock EFI...or custom intake manifold with carb'd throttle body
I got a RB cat-back and hi-flo cat, but still using the stock manifold. A header is on my to-do list.
Does removing that rats' nest make power? How much...5hp?

You give me too much credit. Bolting on a cat-back and replacing struts is as far as I go. I can buy a basic EMS and pay someone to install it and tune it. That would be cheaper than being without a car for a week while I pay someone to rebuild my engine. And it still only has a stock tune.

I think my butt-dyno would appreciate that longer powerband

Yeah, learn to tune on an old engine. If it blows up, rebuild it. Also, it spreads out the project cost over time.

So it sounds like a standalone can gain me 10hp over the stock ECU. And the stock ECU will never maximize my other power mods down the road.

Im tempted to try this as well, Ive got my T2 hibernating... Could pull the haltech out of it lol

removing the rats nest by itself wont gain any power at all, unless something was very broken to start with.

your butt will appreciate the bigger power band, its really obvious

if you're not one to install a traditional standalone, you might wanna look at the rtek, its a stock ecu so it plugs in and everything works, and you tune that.

tuning an NA is fun, and its a great way to learn how to tune, because they are pretty bulletproof

+1
it's akin to learning to swim. start at the shallow end. :)

Considering porting, I refer to the TB mod as well as cleaning up runners in the intake manifold. Stock ports make good power as it is, and they are something that can be replicated with every engine build because they're, well, stock. As for an intake, yes, a good CAI and a good cleaning/rebuild of the AFM are where I'd go first. Depending on the stand-alone you want to use, you'll more than likely be able to rid yourself the headache of the AFM entirely, which is a huge bonus for opening up power.

A header is on my list as well, but for now I'm in the same boat as you, with the stock manifold, the stock pre-cats, an aftermarket main cat, and a 2.5" cat-back dual to Magnaflows. Next setup until a header is purchased is a 3" Flowmaster 40-series with straight piping to a single-exit rear. Pulling all 3 cats will yield some top-end power.

Removing the rats' nest doesn't make or lose any power, just cleans things up a good bit. The only plastic lines I want to see on any of my engines go to the S4 OMP system.

My plan is to stay 100% stock [internally] until I purchase a Haltech SprintRE, then grab a set of 1600s and a Holset and go boost on the 6-port.

cludwig posted a 180hp dyno with the stock afm, its not a huge restriction. could he have made 182 without it? probably. this is on stock ports too, ITS car

the stock cats are a restriction. on my FC i measured the exhaust backpressure, and once you do that its pretty obvious what you need to do and that there isn't much more power to be made over 4500rpms without making the exhaust flow more

I really need to look that up. Do you have a link or anything for me off-hand?

I think going with 3" might initially be a bit too-large for my car, but the drop in low-end shouldn't really bother me, as a majority of the time it'll be seeing 5k+ anyway. I'm hoping having the Flowmaster in there will keep enough backpressure in without choking things out up top.

https://www.rx7club.com/naturally-aspirated-performance-forum-220/s5-na-stock-port-dyno-830392/

if he's nice maybe he'd put up the chart again.

Beautiful, thanks for the link. I had figured it was an S5 6-port, don't think anybody has cracked the 170s on a stock-port S4.

Unfortunately, the engine in that thread turned out to be ported. We didn't build the engine, and felt the numbers were too good to be true, and they were. The owner assured us that it was a stock port engine, because that's what the guy he bought the car from had told him. At any rate, the numbers below are true Dyno Dynamics numbers. We've done back to back testing with a Dynojet and found a 15% difference. With that in mind, 200+ on a Dynojet with a street ported 6-port is fairly stout.

For 2010 we built this customer a legal, stock port engine and it put down 165 on the Dyno Dynamics if memory serves me correctly. Keep in mind, to make power at this level exhaust tuning is crucial and the end result is a car that is horrendously loud. Quieting the car to make it streetable will do the power output no favors.


http://www.lms-efi.com/haltech/dyno2.jpg

So that's the tradeoff, eh?
Either a streetable exhaust with restricted power.
Or maximum power from an exhaust that is race-ready, but unstreetable.

Hey C. Ludwig...
Is that a S4 engine with S4 AFM but S5 intake manifold, with a HALTECH tune?
How much does the HALTECH help and how much does the VDI help?

That particular car uses S5 irons, S5 rotating assembly, S5 intake, S4 AFM. The VDI is locked in the high rpm position, 6-port sleeves are removed.

Since this is a purpose built race car, there is no interest in using the VDI or 6PI to help boost low rpm operation. The engine lives above 5k, so we really only worry about that area of the power curve. Removing the 6PI sleeves all together helps boost high rpm power. We lock the VDI for simplicity sake.

The best we'd done with the stock ECU was about 152 on the Dyno Dynamics. That was with fuel optimized as best we could with various tricks and timing optimized as best as possible by moving the CAS. With the programmable ECU we can do a couple things we couldn't do before and we can optimize fuel across the entire rev range instead of making gross adjustments. The result is an engine that works better at all operating situations along with more top end power.

Welcome to naturally aspirated rotaries.

If it's any consolation, ported engines lose power faster than stock ported engines. It's possible to have a ported engine that is both louder and less powerful than a stock engine/exhaust.

Just how aggressive was the porting on that engine? Mild street port I assume?

I am glad I don't have to adhere to any engine spec regulations [simple daily / drift missile here], but it is nice to see the "limits" of a stock 6-port engine.

It was mild. The secondary ports were not touched. The primaries were opened up some on the closing line.

What do you mean?

check out the graph.

That's a bingo.

Notice that while both engines show definite benefits for reduction in backpressure, the side port engine is nowhere near as finicky about exhaust pressure as is the peripheral port engine. And at 400mm-Hg the lines cross. 400mm-Hg is not even one PSI.

There's a reason why Mazda chose the port timings that they did. Smooth idle for good emissions, and relative indifference to exhaust backpressure.

Personally, I'd like to see a graph with side exhaust ports. I remember reading that much of the power advantage for the RX-8 was that the OEM exhaust could be a lot more free flowing, since the engine itself produced a lot less noise. Thus, my curiosity on how sensitive it is to exhaust pressure in the first place.

- Pete (where does he get those wonderful graphs?)

the rx8 SAE paper says something about that