Cardinell

I've recently picked up spare S4 NA motor that I've decided to build. I think I have a pretty clear direction that I want to go, but I wanted to get some opinions before I dive head first into it and not liking how it turns out.

1) I definitely want to bridge port it. But, I'd rather not lose TOO much low end torque. I've heard mixed opinions on just bridging the 5/6 ports, and just leaving the 1-4 ports as a street port. Does this yeild any significant top end power over your standard aggressive street port?

2) I'm aware that the stock LIM is very restrictive when it comes to airflow, which is very important when it comes to NA cars and making power. I would like to retain the functionality of the 5/6 ports, but also allow for better airflow. It looks like EFI hardware sells a LIM for 6 port motors, and allows for an ITB setup, but it's unclear if this retains the port functionality. Does anyone know a workaround for this?

3) Is 300 rwhp an attainable goal for a bridgeport NA motor? If so, would a half bridge, or just a 5/6 port bridge get me there?


Any other anecdotes anyone would like to add would be very much appreciated. I would like to go into this build with as much insight as possible

fidelity101

iTrader: (11)

200 yes 300 no
also depends on your intake and I wouldn't see anything above 200-210whp on OEM intake manifolds.

dont just port the aux ports, just bridge the secondaries leave the aux ports as is or streetport those.

or carb it otherwise you really need a standalone to get that power levels the stock ECU is garbage and SAFC is too outdated and also garbage.

Dak

Racing Beat used to make a Weber manifold that bolted to the 6-port LIM. There are ITB's out there that would work with it. It would leave the 5th & 6th ports functional. It's no longer on their site but maybe you could keep your eye out for a used one.

Edit to add: Here's a link to and old for sale add so you know what you're looking for.
13b 6 Port LIM with Racingbeat Sidedraft Upper Intake Manifold - RX7Club.com - Mazda RX7 Forum

Cardinell

Understood. The plan is to go full standalone with a haltech 750 or 1500, so I'm not really worried about how it would run with a stock ECU.

The question then becomes: what type of timing do I want to run? I've seen wildly varying opinions on this. Split vs no split, 20 degrees down to the stock 5 degrees.

For the aux ports, would I notice any significant HP gain from using RB sleeves?

Cardinell

There are UIM options that I'm aware of, my question comes into play with the LIM. From what I understand, it's very restrictive from factory. EFI hardware makes a LIM for 6 port engines, but it's very difficult to tell if it retains the 5/6 actuators, or if it's intended to be used with the sleeves removed/always open

j9fd3s

iTrader: (3)

with an NA, its really straightforward. ideally on a dyno, but you can use the datalog (rpm vs time), or even a stopwatch.

you'd start with something like 18 degrees, and then 20, 22, etc. with a dyno you can lay the charts on top of each other and it'll show you the curve you want.

Adrian had a couple of dyno's playing with timing, and spoiler alert, the timing you'd run isn't much different than stock https://www.rx7club.com/1st-generati...risons-823229/

diabolical1

iTrader: (3)

do not bridge the auxiliaries. if you're going bridge, do the primaries and secondaries, then call it a day.

i've never seen any aftermarket manifold retain the auxiliary actuators. i don't think the EFI Hardware parts are any different. i suppose confirmation would be a matter of a phone call or email though.

Cardinell

Roger that. And what about timing split? Any advantages or disadvantages to running 0?

Cardinell

Understood. Are there any disadvantages to bridging the aux ports? Or is it just not worth the time, because of negligible HP gains?

I've reached out to EFI hardware on this via email and haven't heard back. They're in Australia so a phone call isn't the most viable option there 😬

diabolical1

iTrader: (3)

well, here's the deal, i remember reading something compelling on the subject many years ago. the problem is it was many years ago and i haven't much kept bridges (much less bridged 6-ports) on the mind. my rotary fantasies revolve around peripherals and semi-peripherals. so i am unable to re-articulate the whole thing for now (and i can't remember the source). what i think i do remember is it had something to do with the bridges not liking how long a 6-port keeps the intake open.

that said, if you dig up some of Rotarygod's old posts, maybe you might find something useful. i remember him speaking on the subject quite a bit in many threads.

Cardinell

Gotcha. I've seen conflicting opinions on this topic, so I guess a bit more research on my end is necessary

That being said, I've got another porting question that maybe you'll be more familiar with. Exhaust porting.

From what I understand, if you want more HP from an NA car, you extend the exhaust port up, towards the intake. For turbo cars, the opposite. Is there any truth to thisto
Also, I've seen certain bridges brap, and others not do it. Is there some secret sauce that lends itself to the lumpy idle?

diabolical1

iTrader: (3)

for exhaust ports, that is the general consensus. just keep in mind there needs to be balance and, therefore, some compromises. wherever you get your bridge templates from, you should probably get your exhausts from there as well, and use whatever template they recommend.

i, myself, have never seen a bridge not brap, but i have heard of people doing it. i don't know, but i suppose you could achieve that a few ways. first, maybe go for a fairly mild (small) bridge and less overlap with the exhaust porting. second, maybe play around with the intake and exhaust tracts. third (and to a lesser extent) play around with idle mixtures. those are what i would imagine could decrease the brap.

j9fd3s

iTrader: (3)

so i had thought that bridging a 6 port just doesn't work that well, and then my buddy told me about this car in Japan where the shop imported the irons from the US, bridge ported all of them (so 9 port openings). they used a T88 turbo, and the T2 intakes, for like 600hp. a couple years later i ran across the ad for the shop that featured this car, and sent the pic to my buddy, and then the guy who owned the shop posted the dyno sheet!

the other thing that is worth a watch is this little series
for some reason the 6 port has good flow, but makes less power, if you can figure out why, it should do better than a 4 port...

Cardinell

Super interesting.

I suppose in theory just bridging the aux ports would give you the top end benefits of the bridge, while keeping the low end torque of a street port. Yet for some reason, a lot of people are up in arms about NOT doing that, because of whatever reason... Maybe the power gains at high rpm are negligible?

My suspicion was that when people bridge the aux ports, they don't modify the port sleeves so that when they open, they open under the bridge as well. I don't believe the opening in the stock sleeves extends that far back

Dak

It's my understanding the LIM flows decent other than the AUX port rods being in the way of all the air going to the end ports. It's the TII that is restrictive due to the tight bends needed to clear the turbo. That said there is some debate about that.

From the pics I've seen in the N/A section people are modifying the sleeves. I think it is more what diabolical1 alluded too. It's the port timing. From what is said on here the aux ports close so late they are already struggling to fill the chamber so adding a bridge really doesn't help much. I think someone said it's due to velocity and there isn't much of it in those ports and that's what's needed to fill the chamber at high rpm. Unfortunately there just isn't a lot of info out there of people doing this. Alot of talk about it but not many posts with dyno charts of the results. Of the few that can be found the results are dismal with no more power being made than a street ported 6 port. Sorry to be negative Nancy. Maybe you can find the magic sauce others have failed to. Here's a thread Half bridge 6 port - Page 3 - RX7Club.com - Mazda RX7 Forum I found from this section Naturally Aspirated Performance Forum - RX7Club.com - Mazda RX7 Forum Unfortunately he never came back with the results of when he leaned it out as he was running rich on those dyno runs.

diabolical1

iTrader: (3)

... and for the sake of clarity, what i said about the port timing was limited to when people are running their bridges N/A. when you go turbo, obviously chamber filling becomes far less of an issue, so you can get numbers. i'm not convinced they compare tit for tat versus an actual turbo block (same turbo, compression, etc.), but that's conjecture on my part. with that said (and in the same breath), i look at something like Aaron Cake's engine (TiNA) as a total success.

for the sleeves, i think the average person that ports their auxiliaries would probably modify the sleeves, too. i have seen photos of a few, so for what that's worth, i tend to think whatever results you see out there are from people that modified their sleeves.

also, just curious why you're looking all the way to EFI Hardware for the manifold when you can get one from RB. i think by the time you figure out exchange rates, they cost about the same, but i can't imagine the shipping from Australia would be comparable to CA. again, just curious ....

Cardinell

I figured as much, lol. I'm just trying to make as much NA power as I can and get that dialed in before I go throwing boost at it
As for modifying the port sleeves, you just extend the opening back towards the water jacket side, correct?

As for the EFI hardware vs RB manifold, from what I've seen, RB's manifold doesn't allow for an ITB setup, which I would eventually like to go to. It looks like it was designed for a carb

Dak

The RB is for IDA carbs so any IDA style TB meant to replace IDA carbs should work. It also looks like the EFI hardware is for IDA as well so you're using the same style throttle body with either one.

diabolical1

iTrader: (3)

i can confirm that the RB manifold will work with an IDA-style throttle body. i have one with a TWM bolted to it. my only gripe with it, and it would probably be the same gripe with any other aftermarket manifold, is that it didn't come with a provision (or even a dedicate boss) for a brake booster. so you'll have to have the worked out on your own. outside of that, it's a nice piece.

Cardinell

How is the low end torque with the RB manifold? Does it feels sluggish at all, or like a stock 6 port should?

diabolical1

iTrader: (3)

lol. unfortunately, i can't answer any of that because the car hasn't run yet. i'm still working on it. also, i'm running a T2 block (built with a set of 9.4s), so mine is not 6-port.

Cardinell

Ah gotcha

Does anyone know if it makes sense to get hardened stat gears and multi-window bearings? Or will the stock components hold up? My goal for redline is 7500 or 8k rpm

WondrousBread

Rx8 front & rear gears are a drop-in swap, and already include the multi-window bearings. They are both factory hardened. While you're in there, the Rx8 e-shaft is marginally lighter as well (~.6lbs).

I asked Rob at Pineapple Racing, and the only mod required is that the rear Rx8 gear does not include an o-ring groove, so you need to apply a bit of RTV there when building the engine to prevent an oil leak.

He also told me that the Rx8 shaft can be used with Rx7 rotating assembly without balancing, but since you want to run at high rpm anyways, it's probably a good idea.

Cardinell

Oh that's awesome. Rx8 stuff is relatively cheap and easy to find used, which works out perfectly

Any idea how much RTV is needed? Just a skim, or do I need a pretty good bead?

WondrousBread

I think just a skim. These parts have a very close tolerance. You could email Rob directly to ask though. He also seems to have the best prices on the gears + eshaft, so if that's the way you decide to go then I suggest buying from Pineapple.

I didn't end up purchasing because I found a whole shortblock, but he was very helpful.