Well it’s getting about that time. I got my rebuild kit, all my engine parts are ready. Time to rebuild my engine.

“But wait lespaul” you say “your plates have STOCK PORTS! Don’t you know that Porting is what everyone does to their engine?”

Yep. I do. So that’s why I’m asking. I got an 86 GXL that’s being built N/A as a street/track car (relevant). Right now my setup stands

-6 port S4 irons (lapped and nitrided)
-new S5 TII rotor housings (stock TII exhaust ports)
-S5 rotors
-new RX8 e shaft and stationary gears

-Racing Beat Holley 6 port carburetor and intake setup

every seal is being renewed

Thing is, I was 100% ready to take this engine to get ported at Defined Autoworks. Thinking aggressive street port and exhaust port. Until I saw a thread pertaining as to why people use 4 port irons when building N/A engines. In this thread the simple answer seemed to be that 6 ports are utterly un-portable for N/A applications and if you’re running them without the 5/6 actuators, stock ports are going to be horrifically sluggish, boggy, and just incredibly unpleasant to drive, and any porting raises the power band so high above 9k that you might as well just peripheral port it, spend $1000 clearancing the rotors, and make it a dedicated track pig.

So now I’m stuck. Do I port this engine and hope I can make it (somewhat) streetable? Do I run stock ports and stay happy with the (roughly) 200bhp Racing Beat estimated? My main worry is my local rotary machinist basically told me you can’t port 6 ports unless you go full bridge, and even that’s not justifiable. Only PP is a worthwhile port job. I was hoping with a street port exhaust port, higher comp rotors, and the Holley kit I could JUST tickle 200whp.

I can sink maybe another grand into this engine. I’m already well past $10k not including purchase of the vehicle, if I have to pull out another $1500-2000 on top of that to machine the rotors to allow it to reach peak power and RPMs I might have to hit the brakes on the project.

what’s opinion around here? I know a few guys have built N/A cars.

 

I can only speak about my limited experience with my street port that's currently still using the stock intake manifolds and ECU. I would say they are wrong if you don't get too aggressive on the aux ports. It sounds like they are talking about what happens when you combine the secondary and aux port into one big port. I used Pineapple Racing templates but Mazdatrix's look similar from the pictures. It opened the primaries up a good amount, opened the secondaries up a little and I didn't really touch the aux( 5th & 6th ports) at all. I street ported TII rotor housings. Bear in mind my 5th and 6th(aux ) port sleeves and rods are removed and the VDI set to it's high rpm position since I have no air pump. Aux ports were wired open before. Not much change on the low end. Maybe a little less. Power comes on between 5 and 6k and pulls all the way to the 8500rpm rev limit. Stock port fell on its face between 7000 and 7500 rpm. I have no problems driving it on the street but I typically shift between 4000 to 4500rpm. I'll admit if I was shifting below 3000 it would feel pretty slow. IMO I think the 4.3 gears help offset the wired 6 port penalty. Here's what Mazdatrix says about porting the 6 port 84-92 6-Port Intake Porting | Mazdatrix
Also here are some picture of the Pineapple templates overlaid over the housing. and my Exhaust port.

 

If your local rotary mechanic truly said "you can't port 6 port unless you go full bridge", then full stop, never deal with them again. Hopefully they were joking as that is a truly stupid thing to say.

Noticed you are going to run a carburetor? What is your goal for this car truly though? How much time on the track vs. the street? What happened to the EFI system?

Honestly, by converting to carb you are destroying a significant amount of drivability anyway, so be less concerned about negative effects of porting. That said, a mild port as shown by the poster above won't effect drivability in the least and result in about a 15% - 20% power increase if well set up.

By eliminating the aux port actuator system, you are already decreasing low end torque by about 40% without any benefits in the high end.

If the engine is apart, I'd say port it using one of the common (ie. Mazdatrix) 6 port street templates.

 

Are the Holley kits really that bad? I wouldn’t think they’d sell them or use them if they were. And isn’t the only way to use the aux ports to run all stock ECU and all that?

It’s going to see much more street use than track use, and the track use is only going to be at open track days, not looking for competitive, just a little more power, and Racing Beat quotes roughly 200bhp off stock ports with that setup. The EFI plan fizzled out based entirely on A) money and B) No rotary tuners in the area, and I’m by far not smart enough to be able to set something like that up, I’ve got experience with carburetors, I can see the EFI standalone route being nothing but mistakes and headaches and thousands and thousands of dollars into an engine that’s already damn close to $6-7k in parts.

 

I don't know that it's because they're that bad just that at this point in time fuel injection is so much better. These carb kit's were designed before standalone ecu's came to be what they are now and as accessable to the everyday consumer not just the big race teams. I don't know when that Holley kit was designed but it was in the first RB catalog I got in the mid '90s. To me unless you're racing in a class that doesn't allow fuel injection there is no reason to convert to a carb. You're going backwards in technology and limiting reaching your engine's full potential. If you like/want the holley manifold there are 4150 style throttle bodies that will bolt right on. Here is an article that compares carb vs. efi. 004 020-029 CARB. VS FUEL_qx1 (borlainduction.com)
Looks like RB doesn't sell them anymore but the upper manifold they use in the article that bolts to the sock lower would allow the use of the aux ports if your standalone had enough spare outputs to control them.

 

There's nothing wrong with the Holley kits per say, except that they are a carburetor kit.

You're removing an electronically controlled fuel injection system (though, a very crude one) that is capable of adjusting to almost all operating conditions and replacing it with a semi-controlled fuel leak into the manifold (carburetor).

What are you going to do for ignition? Typically this means either maintaining the EFI system (now missing some of it's important inputs like AFM) or converting to a distributor. Dizzy is another downgrade. Not only the extra maintenance required, but the lower ignition output. Mazda does pretty well with ignition control on the EFI L-Jetronic trying to optimize timing and split about as well as they knew how to in the era.

Those Holley conversion intakes are really meant for dedicated track/off road cars that are modded beyond what the stock EFI system can cope with, or racing classes which spec a carburetor. Or primarily, putting the newer 13B engines into older vehicles which were carbureted.

Edit...Should have mentioned that in S4, the aux ports are actuated by exhaust backpressure using pneumatic actuators. No ECU control at all. If you are running a different exhaust which will most certainly be the case, there are various methods to control the ports (ie. RPM switch connected to a small air pump, welding a pressure tube into the exhaust, converting them to electric actuators, etc.).

 

So survey says I should push the car back another couple years in order to build an EFI system...

probably end up using a stock intake manifold and throttle body then right?

why would you have to use the standalone to control the aux ports? Aren’t they pressure operated? On that note, wouldn’t the cavities fill with fuel until the ports opened and then it would run rich? Or can you program the ECU to like, not run fuel to the secondaries until...?

Like I said earlier, half the reason I’m going carb is because I am not smart. I’m a dirty *** broke *** mechanic who does decent work on older cars and can usually limp my way through diagnosis on modern computer systems with codes and scan tools. The thought of PROGRAMMING an entire ECU and picking the right range sensors and making sure everything works with everything makes my head spin just thinking about it. I’m mechanically inclined, electronically, not so much haha

edit: just saw your bit about the actuators, I got the Racing Beat true dual cat back with the back pressure tube and it worked great until the iron cracked.

 

Was the car running before you tore it down for the rebuild? If so I don't see why you would have to push the build back another couple years. Do the mild street port and put it back together using all the stock stuff( manifolds, ecu, etc). The stock ecu will run it but you won't get all the power out of it you would with a standalone. At least the S5 ecu will. I

As to the aux ports I forgot you have a S4 I was thinking S5 where the pressure comes from the air pump and the ecu controls solenoids to turn them on/ off.
I never gave it much thought but since the secondaries are open the fuel/ air mix goes through them. Also I think the secondary injectors are staged so they don't inject fuel until a certain RPM. Maybe someone else can clarify.

As to your concerns about going standalone. I can't help much there as I've not went down that road and only know what I've read on here. I'm currently trying to select which one so give me a few months and I may have some input on how hard it is to do on your own as there are no rotary tuners in my area either. I'm more worried about learning to tune than the install. I think most of the stock sensors can be used. You just have to teach the ecu to use them. Someone else may have to clarify that's been down that road.

 

I had a similar question awhile back before I found a good compression shortblock and just tossed that into the car. I had settled on basically the plan that Dak mentioned (in fact, most of the participants in the thread I had posted are in this thread too).

Anyhow, this thread is what I wanted to point out. ~185rwhp from a 6 port street port. Keep in mind that this person was still using stock ecu with an SAFC, so they still didn't have timing control. The OP also says that he was running out of fuel (some quirk of the AFC maybe?) because duty cycle wouldn't cross 65% at higher rpm. With a standalone I think 200rwhp may be reasonable.

This means that your target is within sight.

And as for your builder's comments about porting a 6 port not being worth it, I think that isn't quite true. A street ported 6 port seems to do well compared to an unported 6 port.

Now when compared to a ported 4 port they always seem to make less due to the shape and port area. But this doesn't mean that porting it isn't worthwhile, only that if you want even more power you need the 4 port irons. The reputation of 6 port unportability probably comes from people doing bad port jobs or hogging them out into one big port and then being surprised when it makes terrible power down low.

As these parts become rarer and more expensive, we are seeing a shift in what is considered "worthwhile". Compare the cost of 6 port irons to 4 port irons. Is the $1000 difference worth the HP on a street car? Probably not. Many of the old posts about what was worthwhile were written when these cars and parts were cheap and plentiful.

 

if you wanna go carb go carb. the stock manifolds with working actuators can make the thing feel like a V8, you can really make good power from ~2500rpm all the way to about 6500, which is nice on the street, but kind of limits hp (the S5 revs a little higher) the holley will loose a bunch of low end, because no actuators, but while the stock stuff makes peak power around 6500, the holley could be higher

and you know what, the intake unbolts easily, so you could try one or the other or both

 

Alright. After a lot of thinking, plan is to port the engine, aggressive street, put it back in on stock everything, and go back to my original plan of building the chassis before the motor. I just had this reasoning that since my engine was now popped i should build the engine first, but i suppose youre right, i can run stock until i get the chassis situated, and then start worrying about the power. My original plan was to go ITBs on a Haltech, but it just seemed like a lot of headache.

No way to retain the aux ports with ITBs though right? I cant say ive seen any intakes that retain them, unless you use a sidedraft dellorto manifold, which idk if anyone even makes TBs for those. Stock manifold and TB is probably the best route right? That way you retain the primary/secondary injector setup, aux ports, etc...

Is there a preferred upper/lower intake combo that flows the best? And at least isnt prohibitively expensive (looking at you 13B-RE). I think i remember hearing that a ported and smoothed S4 intake will flow better than an S5 or and FD or what have you...

Also how bad is porting? Id be nervous as **** about doing it myself because i got brand new housings and $1000 renitrided and lapped irons, but the $1000 to have it done is scary too. Is it fairly idiot proof with a template and the right tools or could i end up in a lot of trouble...?

 

they do, i think its the same as a DCOE?

 

You can certainly realize gains with little to no drawbacks by porting a 6 port engine intelligently. The aux plates don't really need much other than cleaning up casting, cleaning up the hard edges/short turn radius and smoothing and the primaries can certainly be made larger though no reason to go nutty. That said, 4 ports can be made to flow more/make more power than a 6 port at all but the most high RPM applications in an NA setup.

 

They aren't listed on their website anymore but Racing Beat used to sell one for a Dellorto side draft that bolted to the stock lower. Description said it also worked with Weber 40, 45, 48, 50,and 55 DCOE carbs.
https://web.archive.org/web/20191010...to-Intake.html

Borla makes some throttle bodies
https://www.borlainduction.com/2900-series.html

 

Thanks. Is there any reason to situate that whole setup right away, or would it be logical to run with stock intake and throttle body on standalone and switch over to Borla TBs later on? Would I have to recode the whole ECU?

 

like you're hinting at, installing and tuning the aftermarket EFI is a big job. its nice to start with the stock intake and fuel setup, just because its there and it works, its one less thing to worry about.
to go from a stock intake to some borla TB intake, you would have to change stuff in the ecu, but not the whole thing. mostly the fuel map, and you might need to tweak the timing a bit.

if you can tune a carb, you can do efi too, the principals are the same, the engine wants the same thing. the big difference is that you need to learn the software, but after you do you don't need to mail order the jets to make changes....

 

One of the benefits about where i work is we do tons of carb rebuilds, so we have a filing cabinet and each drawer is full of every possible variable for almost every possible carb. Pretty nice lol. When I was tuning my Carter AFBs for my dual quad 455, It was a god send to just be able to go to the carter drawer, grab the case of jets, and get to work.

 

yeah that is cool, and if you have a Holley drawer that would make a Holley a pretty simple choice!