benjaminkarlson

Hi everyone!
So about 3 months i bought 2 S4 NA FC's of wich one could drive and the other already had the engine pulled out (owner said that his 2 daughters had driven it to germany and back, and aparently didnt know how to change gear, and ever since, it had been running oddly hot at times). They had both been standing still for quite some time, since the previous owner had become ill and was therefore no longer able to look after them. Anyway, I got them both for peanuts, and I drove around in the one that could drive for about 100km until it started to loose compression, started boiling and oil seemed to have escaped into the coolant water

So i decided that since the two engines are identical, i would mix and match the best parts from the two engines. So about 3 weeks ago, i pulled both engines apart, and found the best parts...Anyway, I am thinking that since I am already in there i might as well so some mods. I am probably going to do streetports on the primary and secondary ports, but i was thinking of maybe doing a bridge on the aux (see pics). Now i know that a lot of people are anti bridged NA's but keep in mind that I have the eurospec LIM, that has the TBish actuators. I also know that on an NA setup smooth flow is the key, and therefore a bridgeport is not prefered. I also understand that porting alone wont make power, and I am prepared to make a full custom exhaust and intake with the correct lengths and so on. Also I am going to install a megasquirt and clear up the engine bay and keep it simple, I.E. removing the emissions. Hoping for around 200hp when I'm done, which is mighty fine for my spirited street driving
Please share opinions and knowledge

PS: I am thinking that i might turbo it later, where a bridge would be more at home...

cBigganz

I would suggest only bridging the primary ports and not touching the secondaries what so ever. They already offer similar port timing to a pport engine and are significantly bigger than other stock ports. Adding the bridge you have drawn will cut into your compression stroke and rob power.

Here's a comparison of stock ports:
http://www.turborx7.com/porttiming.htm


I'm currently rewiring my 6port and installing a haltech and gt4088. I haven't ported anything as I wanted to see what the stock 6 ports are capable of. Once I decide to port I'll likely only do a half bridge on the primaries. The biggest gains you would see would probably come from exhaust porting. There are lots of good templates out there depending on induction type.

jjwalker

I would go ahead and port the stock ports how you have them marked, but I would put the bridge on the primary, and not the secondary port.

If anything, since you are rebuilding an engine and dont have it back together, I would do a massive port but no bridge on an s5 4 port engine. What I mean is, get the 4 port irons and holy mother port that. The 6 port irons can never EVER touch a good and solid gigantic 4 port housing.

benjaminkarlson

I will be porting the exhaust, probably with the epa2 from pineapple and I will put a diffuser-less sleeve in. Probably also going to do pineapple streetports, but i was just thinking that since the aux would open at 3800RPM or what not, and a bridge is for higher RPM's (correct me if im wrong), therefore it would be best for low end torque to keep the bridge on the aux. I'm gonna try and do the math on the port timing and intake runner lengths.

I think i see what you are saying with the bridge cutting into the compression stroke, I've looked at some crank angle charts, and it would open at TDC or thereabout?

thanks for actualy giving some feedback and not just go "bridged NA's dont work"

benjaminkarlson

That seems to be the answer that most people give, with good reason, but i dont really have the money for new irons, since I am currently a student :/ I do get what you are saying, but the turbo would probably first be in a couple of years or so.

Wouldnt a bridge on the primary affect low end torque and streetability?

jjwalker

Either go big or go home. Bridge porting with screw your idle up. If you want streetability, then you just need to street port the motor.

j9fd3s

iTrader: (3)

the problem with bridging a 6 port is not just the actuators, but its also the port timing.

the stock 6 ports close @80 degrees, the racing engines from the 80's closed @75 degrees, which is actually EARLIER, and it wasn't until the revision in about 1990 that the race engines closed @80.

so the problem with the bridge on the aux port is that the port timing is already more than you'd want, and the bridge just makes it worse.

you are better off by using the bridge to open the intakes earlier, which would have you port on the other ports.

jjwalker

^ this!

benjaminkarlson

If I do the port as in this picture, wouldnt it then open earlier (TDC)? and still close at 80deg like standard?

benjaminkarlson

Just realized i just broke physics, I cant do that since the corner seal would fall out.... silly me

benjaminkarlson

wait... no it wont....

arghx

iTrader: (3)

Here's the problem. With a 6 port you're running into something that Mazda already optimized for the most part. The biggest thing that adds n/a power at high speed, even on piston engines, is the intake closing timing. It's the big limiting factor besides things like displacement. As j9fd3s already pointed out, the closing timing is already maxed out on the front and rear irons.

Adding opening timing doesn't get you a whole lot except some cool sounding overlap. Adding more port area is easier with a big 4 port. Changing runner lengths has already been done--by Mazda, on the s5 engines with the VDI system.

You can take out the exhaust diffuser, but IMO it makes the engines sound a lot worse and benefits are minimal. It makes you want to put something restrictive in the exhaust so it sounds better. Opening the exhaust earlier will help with some top end by relieving exhaust pressure and giving more time to evacuate the cylinder, if runner lengths are tuned right.

IMO porting a 6 port on the intake side really is a lot of trouble for little benefit. I would clean them out a bit with a grinder, then focus on other aspects of the engine. Run a 6 port/VDI system, lean out the tune because you don't care about emissions, change the header, that kind of thing.

j9fd3s

iTrader: (3)

i think i would open the 4th and 5th ports a little earlier, makes them a little bigger, maybe port the primary to FD or Cosmo spec, and call it good. one of the big gains with the Rx8, was to make the intake ports bigger, but they open earlier, and close at, you guessed it 80 degrees.

and then work on the intake/exhaust/tune. there is quite a bit of power locked up in the exhaust, heat management, the ecu tune.

i looked at my S5 intakes and the casting and port matches look pretty good, but there is probably still room for improvement

benjaminkarlson

^ 4th and 5th? I'm guessing that you mean 3th and 4th right? 5th would be only one of the auxilliaries But thanks, I'm probably just going to streetport it (which is pretty much what you are saying ) and them tweek intake and exhaust and get a nice tune

j9fd3s

iTrader: (3)

or quit f-ing around and go P port..

benjaminkarlson

If only it were streetable and would pas the MOT

Aaron Cake

iTrader: (1)

News flash, bridgeporting the aux port won't pass MOT either.

I have a LOT of experience with this type of port and overall, don't recommend it except in very specific circumstances. You're going to get all the downsides of the Bridgeport but none of the advantages in an NA application. Now in a big turbo application, you're going to have the advantage of the overlap spooling the turbo like any Bridgeport would. Tuning is much like an extended street port under load, and easier under part throttle because the overlap isn't quite as severe leading to a more stable vacuum signal. But vacuum resolution is still reduced to about 15", only seeing higher vacuum on overrun and flying to atmospheric at any amount of moderate throttle.

Oh, and like any bridegeport the fuel economy sucks. The idle is rather unique though. More of a burbling "brap" than a typical bridgeport hard "brap brap brap....brap brap brap". Easier to quiet down.

j9fd3s

iTrader: (3)

https://www.rx7club.com/build-thread.../#post11778999

this one passed the MOT, and its pretty wild...

this one too,
if you look he's got a bunch of videos just driving around.

benjaminkarlson

Thanks for the input Aaron, I am propably just going to leave the secondaries untouched, but smoothed, and then port the primaries. This way i can do a bridge on the secondaries if I some day decide (more like have the time and money ) to turbo it


It may pass the MOT in that country, but it undoubtedly wouldnt in denmark The country where it is illegal to fit a 4 point harness due to "safety" reasons... Having said that I'm not even sure i will be able to pass the emissions test without the airpump system so I will see how this goes, if all goes wrong i will have to register it as a race car, which means it cant be used as a daily driver

luckily for me, the local MOT people wont know how an rx7 is even supposed to sound or look like, since rotaries (and any other exotic cars for that matter) are extremely rare here due to the 180% import tax on vehicles...

j9fd3s

iTrader: (3)

THAT country is Belgium, can't be too different....

oh and if you think your test is bad, in California we have a visual AND tailpipe emissions test, and for the visual, EVERY piece of emissions equipment has to be there, and then the tail pipe part is more strict than when the car was new.