S4 NA RX7 needs more powars....

I want to get about 10 to 20 more HP out of my S4 NA rx7. How do I do that?

I do NOT want to take the engine apart.

I have a OBX header that terminates in a borla dual exhaust.

I have the "6th" ports wired open.

I have no A/C or Power steering or air pump.

All emmissions removed.

I am currently running stock timing off the stock ECU with stock injectors and stock coils.

The keg itself is an S5 with all S4 accessories.

Any help is appreciated.

You pretty much have to take the engine apart and port it.

You might try a better header, but you're not going to gain that much power. Unless the actuators don't work, I'm also not sure that wiring open the 6th ports is going to help with top end power, they should be open at that point anyway.

You might also be getting a little more power from an aftermarket ECU, but the cost/benefit equation for that is pretty bad.

So, you have to take the engine apart and port it/have it ported properly, then look at the ECU etc afterwards.

Is porting the throttle body worth anything?

What about gasket matching the intake?

Isnt there funny little things in the exhuast ports that can be removed?

I would like to do ALL the little things that are known to increase HP before I split the engine apart

I'm not sure the scoops in the exhaust really do much, but I would remove them anyway. Any restriction is bad.

BoxheadTim wrote: You might also be getting a little more power from an aftermarket ECU, but the cost/benefit equation for that is pretty bad.

I completely disagree with this statement, sorry mate :) On my S4, when I replaced the stock ECU with a Megasquirt, it completely changed the car. They run quite a bit rich from the factory, which was needed to keep the 80s cats cool enough to not disintegrate (at least within the 100k that the government required them to last). If you put a standalone on there, especially one with emmissions removed and breathing mods, you'll probably pick that up pretty easily, and you'll have way more power throughout the band.

The downside is cost, though, Tim's right about that. You'll be all-in at least $800 by the time you build a megasquirt, wire up a full-range Throttle Position Sensor, redo your intake to get rid of the AFM, get a wide-band O2 sensor and then get it tuned on a dyno.

But it will feel like a completely different car.

The problem with a lot of your list (port matching, things like that) is that you're banking on 1990s-2000s era computers, which were smart enough to deal with it. Your S4 was built between 1986-1988, which means it's using a computer designed in at best 1982.

The stockers can't actually compensate correctly based on any mods, they have a fixed map that they start with and under open loop (which is VERY, VERY narrow with a narrowband O2), it can trim it +-10%. That's it.

If I recall correctly, the Rx-7 community found that although most mods will give give you an overall gain, they end up hurting a lot of "under the curve" area and trade it for peak performance, which sounds and feels a bit more alive, but doesn't really help much. It's been a while since I looked at those dyno carts, though, so my memory may be rusty.

In reply to WonkoTheSane:

I already have a wideband 02 sensor.

So, an Rtek would NOT be the easy way to go here? I have already redone my wiring harness.

Can you be more specific on HOW to go about setting a up a standalone for the RX7?

Thanks!

Rob R.

P.S. this is for a track car ONLY. Max power between 4 to 7.5K is all I am looking for.

Rtek would probably do it, I haven't looked at them in quite a while and I've never used one.

One of the things I really liked my about the MS direction is the ability for it to tune itself, which is quite handy. You fill in the map and hit "auto" and it'll just keep adjusting the fuel trim in that range until it gets what you asked for.

Generally with this stuff I recommend asking the guy doing the tuning who he likes to work with and seeing if that'll fit in the budget.

Anybody know a decent RX7 tuner in the pittsburgh area?

Thanks!

Rob R.

LSJuan?

FYI - some good threads on NA rotary tuning here: http://www.rx7club.com/naturally-aspirated-performance-forum-220/

wvumtnbkr wrote: Anybody know a decent RX7 tuner in the pittsburgh area? Thanks! Rob R.

Define "area" :)

Here is a good one "near" pittsburg but they are in OH: http://www.definedautoworks.com/

Five things: 1) the S4 'flap door' air flow meter is restrictive. It can easily be swapped for the S5 'inline' or 'torpedo' AFM.

2) The S4 intake is also restrictive. The S5 is much freer flowing and is a bolt on swap. It has a 'short runner' valve which can be wired to provide short or long runners. They are easy to tell apart; the S4 has a finned dynamic chamber, the S5's is not. S5 intake:

S4 intake:

3) The stock 6 port valve is a cheap design, there are 'ported' versions available which do make a noticeable HP boost. If you aren't using them, then swap a set in when you swap the intakes. Do this even if you are wiring them open, removing the stock valves makes turbulence and reversion worse not better..http://atkinsrotary.com/store/84-92-Rx7-Atkins-Designed-Six-Port-Actuator-Valve-Kit-ARE113.html

4) There is a guy on RX7Club (SonicRaT) who is building real time tunable piggybacks for the stock ECU's. http://www.rx7club.com/2nd-generation-specific-1986-1992-17/stock-ecu-real-time-tuning-datalogging-1065541/

5) The exhaust on an NA works best with a primary length between 24 and 27 inches. If the Borla is a dual all the way back, it may actually be costing you power. I'm assuming the OBX header is dual outlet, if so then continue the primary tube length to the 24-27" area, then bring them together in a single 2 1/2" tube. The total exhaust length will move power around a bit, the accepted best compromise is around 96" overall, this will mean side exit exhaust.

wvumtnbkr wrote: I want to get about 10 to 20 more HP out of my S4 NA rx7. How do I do that? I do NOT want to take the engine apart. I have a OBX header that terminates in a borla dual exhaust. I have the "6th" ports wired open. I have no A/C or Power steering or air pump. All emmissions removed. I am currently running stock timing off the stock ECU with stock injectors and stock coils. The keg itself is an S5 with all S4 accessories. Any help is appreciated.

Install a wideband as a diagnostic gauge. Then install an adjustable fuel pressure regulator. The stock computer can run really really rich at WOT, I've heard 10:1. You'll want to knock that down to the 13.0-13.5 range. I've "heard" of IT guys running fuel pressure as low as 25psi in order to make best power.

Curmudgeon wrote: Five things: 1) the S4 'flap door' air flow meter is restrictive. It can easily be swapped for the S5 'inline' or 'torpedo' AFM.

It's not a restriction at the power levels you will see with a stock port engine. People have removed them while going to a standalone and found no change in power.

2) The S4 intake is also restrictive. The S5 is much freer flowing and is a bolt on swap. It has a 'short runner' valve which can be wired to provide short or long runners. They are easy to tell apart; the S4 has a finned dynamic chamber, the S5's is not. S5 intake:

The S5 intake is a lot LESS freer flowing. It has a lot more surface area and a lot more tight bends, both of which hurt airflow. I firmly believe that the S4 N/A intake manifold is the best one Mazda put on an EFI rotary. The S5 has all the fancy variable runner stuff for a broad powerband, just perfect for a heavy automatic convertible, but the S4 manifold make more ultimate power.

Yeah, I'm the guy who port-matched one to put on a Turbo II engine. Saw HUGE gains there, too.

Mind you, I have three S5 N/A intake manifolds, so it is in my best interest to say they are awesome so I can get top dollar for them But in reality the S4 manifold is better from a power standpoint.

Knurled wrote: Install a wideband as a diagnostic gauge. Then install an adjustable fuel pressure regulator. The stock computer can run really really rich at WOT, I've heard 10:1. You'll want to knock that down to the 13.0-13.5 range. I've "heard" of IT guys running fuel pressure as low as 25psi in order to make best power.

This is a good and cheap hack.. Any idea how much HP they've picked up with it?

When I originally built my MS (v2.2 MS1!) about 12 years ago(!!! I'm old now!), a wideband O2 was more expensive than building the MS and taking the car to a dyno :) Innovate hadn't come out with their sub $400 unit yet, so that seemed like the way to get good fuel control.

I probably would have done this instead. Oh, wait, no, I was fixing other electrical gremlins, too..

No idea for hard numbers, especially since it's hard to know where he's starting from. But I witnessed a friend's car drop a half second in the quarter mile when he pulled a bunch of fuel out with one of those stereo equalizer style piggyback controllers.

I think Summit has an AEM gauge/controller/sensor for $160 now.

Okay, here we go!

I do have a wideband. I will install and verify the AFRs under load (on a dyno - car isnt street legal)

I can not change the intake (too many points in chump).

I CAN gasket match the intake manifolds.

I CAN remove the diffusers from the exhaust ports (anybody have a write up on how to do it? Can I do this with the engine in the car?)

How lean is too lean?

What timing should I run and what are the negatives of too much timing?

Thanks!

Rob R.

P.S. I am going to try to get a baseline dyno reading this week.

Grab a fuel pressure regulator before you go to the dyno. For the range you're looking at working in, there's no sense not to play with it a bit on the dyno.

I generally looked for 12.5-13 or so at full load, but I felt that was pretty conservative considering I started in the 10.5 range (like Knurled talked about above). I don't know how cozy I'd feel @ 13.5:1, but I'd also trust a tuner who knew what the hell they were doing as opposed to myself. I was mostly worried about keeping heat under control..

Along those lines, I've always ran @ 2* over stock advance, and never had a problem, but I haven't tried endurance racing it either.. I'd see what you come up with on the dyno. It's hard to say what you'll experience in real life, when everything gets heatsoaked...

I've run lean enough that the spark plugs melted but the engine was fine. In the realm of mild ported non turbo rotaries, you can't hurt the engines with air/fuel ratio.

I've heard of people making best power as lean as 14.2:1. I am assuming that is normalized for gasoline's 14.7 stoich since E10 is stoich at 14.2:1.

Personally I like to see 12-12.5:1, but I have a badass ignition system, and I might have one minute long runs 5-6 minutes apart, so I like trading off some power for some more in-chamber cooling. Plus it seems like the more power I make, I just spend more time not at WOT

I've noticed gains leaning it out to 13.5:1 or so. OTOH I have also noticed no difference running peak timing anywhere from 18 degrees to 26 degrees, other people have noticed big differences, and also no differences across the spectrum from 11:1 to 14:1, so everyone's different I suppose.

Going to the dyno tomorrow for a baseline.

How much timing can I add and be stock reliable?

Thanks!

Nitrous?

You won't really hurt it, although don't be surprised if you find that you don't gain anything with more timing.

Just got back from the dyno. 144 at the wheels. Stock timing and running 14:1 AFR.

Gonna bump up pressure and go back soon! Then I will mess with timing too.