i gotta rebuild my motor so i was thinkin of doin a bridgeport on my s4 na i wanna make some power with the na i kno not big number but i just wanna have fun and be able to DD her so what you guys think i should do well an idea

 

But just remember, you're comparing a lightly modded TII to a car with a full turbo upgrade, regardless of the bridgeport. Put a GT35R (or similar sized turbo) on a stock or street ported car and you have a 400HP RX-7 that will pull harder than almost everything else on the road.

Not saying anything against bridgeports, just keeping perspective.

Short answer is no. If you bridgeport that engine then you are now in for a host of other upgrades to make the best of those ports. These include: new intake manifold (custom or off the shelf ITBs), full exhaust with minimal restriction (loud!) and a standalone EMS to tune it. Also since a bridgeported 6 port NA engine will need to spin to over 8000 RPM to make peak power, you'll want to balance the rotating assembly and move to a lightweight flywheel.

So, you probably don't want to bridgeport it. Go with a nice mild to medium street port (not those ridiculous things that NA owners often flaunt which do nothing but move the power band up and maybe make 10 more HP peak than a reasonable port, but make the car slower everywhere else) and you'll be happy.

 

so if i do go street port what else do i need to do like i said its a dd but i wanna have some power with the na untill im ready to do a full turbo swap.. i have rb headers waiting on rb presilencer and my catback is a JIC exhaust ..thanks aaron for the info

 

i would like to know a good combo for the streetport to help make some extra ponys also since its gonna be my first rebuild any idea whats the best close up kit and seal to get from ..thanks

 

In your opinion, do you think a full 3" Racing Beat exhaust is too restrictive for a HBP? I did a straight trade with a buddy of mine for his RB exhaust with my 3.5" JIC Spec 90 and not only is it enjoyably quiet, the performance is almost identical (slightly laggier).

 

im guessin im going turboII

 

Was just reading through the thread and came across this from 2010 . I have to say I can't see the logic in the answer given back then . The primary ports would certainly flow enough to supply a little eyebrow port and the eyebrow does not need to add to the flow demand once the main port is open.
I actually think it would work better on 6 port engines in particular as the timing can be much later yet still offer a decent duration and overlap . Not so good for people wanting the brap brap but offering the same benefits without the driveability issues.
Has anyone tried it ?

 

OK, so to be clear, obviously the eyebrow ports on the primaries would add some flow. And you'd get all the overlap so you'd have that bridgeport idle, the poor fuel economy, the difficulty in tuning, and some scavenging up top.

But in doing so, you're making an eyebrow port smaller than you can on the secondaries. So you are leaving a lot of flow on the table, yet ending up with the same negatives as a half bridge on the secondaries. Also the primaries have less room for porting in general (unless you have those coveted RX-5 Cosmo irons, which I have been trying to sell a set of basically news ones for 6 years), and the stock manifold has primary runners 50% the size of the secondary runners.

6 port bridgeported engines can work just with the issues discussed above. Use a 4 port bridgeport template. Problem is that you are dealing with so much port timing at that point that you've built a high RPM engine. Note here I'm NOT talking about aux port only bridges. I'm talking about a secondary bridge which is going to extend slightly into the aux port (done it, worked basically well on a turbo car).

If you are going to make big power in a bridged NA car then you want 4 port irons for the best powerband. If you want stratospheric high RPMs, then 6 port irons. Or you could cut the crap and go peripheral port as bridgeports have always been a compromise port for racing classes where peripheral porting was not allowed.

It's important to remember with bridgeports that you can't cheat the port. No matter what you do with the eyebrow, you're adding the overlap. So really, the difference in negative characteristics are pretty slim between a half bridge and full bridge so fire up your Dremel, get some one piece seals, and full bridge the thing because the differences in flow are dramatic as you're adding basically twice the port area you would only performing a half bridge.

 

Thanks for the answer Aaron .
Looking at a mockup assembly , i'm thinking that if the bridge opens at the point where the rotor starts to move away from the housing (which is quite late compared to many bridgeport designs I've seen) , the pressure adjacent to the bridge will be lower than elsewhere in the chamber so the tendency for exhaust gases to enter the intake tract is less than with designs that open earlier. Doing the primaries only allows you to put in a port that is almost as big as a secondary one but with better timing that should help make the engine much more civilised - IMO.
And sure , it might not achieve the ultimate potential of a bridgeport. But if you got ,say, 75% of the gains and eliminated 90% of the negative ....would people be interested in that compromise ?

 

i think what aaron means by you can't cheat the port.. the part that can be ported is at the same timing on either side of the rotor. so if you add the brow to the primary it will be at the same opening, as if you had put the port on the secondary side.. basicly if you have a brow you have x amount of overlap, no matter if you do the primarys or the secondarys .. so you might as well do both..

if you're seeing if from a different angle let us know, i know you're a smart guy brettus, what are you getting at. something todo with rx8 ports??

 

Busted ... lol . But not being a 7 guy I am only going off pics I've seen on the net . To me it looks like (on a 6 port engine anyway) the primaries are actually much higher on the plates than the secondaries ...just like on a Renesis. When bridgeporting ...this changes where the bridgeports open dramatically .

 

i think the only way to make a later opening bridge would be to make it thinner, which would make flow worse.. im into p ports myself. trying to close them off as close to the housing under 4k rpm and use stock ports for idle and cruise. ive been shunned for the idea already.

 

its not so much a shunning, its just that once you've tried a P port, you realize that with a couple of tweaks the side ports are just pointless.

my P port idles right at 900rpm, hot or cold*, low speed/ low throttle is about like an FC with a tps thats a little off. if i put a heavier flywheel on it, this would get better.

power is instant. it makes more power @3000 rpm than my friends CSP car (both 1st gen 12A's), does anywhere.

and it gets better mileage on the race track than my friends IT prepped FC.

i have even gotten it to idle without the brap brap, although its boring, so i put it back.

this is even with a carb and a locked distributor too, adding an ignition curve and EFI would make it even better.

the breakthrough was to lower intake manifold vacuum, less intake vacuum = less exhaust getting sucked up = much improved drivability

so i don't see why you'd bother with the side ports at all, the brap brap idle is the fun part, and the P port drives fine once you tune it.

trust me you once you go full PP you'll wonder why anyone bothers with side ports at all.

*its California cold not Canada cold

 

Has anyone noticed the difference between Xtreme Rotaries bridge templates?
http://www.xtremeautoparts.com.au/sh...490_detail.jpg
http://www.xtremeautoparts.com.au/sh...078_detail.jpg


If, my brief convo with Brettus on this topic a few days ago is any indication of what he's refering to I think it's this:
Starting the bridge later means less overlap. For a renesis (Zero overlap) I believe adding some overlap will work wonders. The backpressure seen in turbo setups is really a killer. What brettus is attempting to do is add the overlap needed to release some backpressure and free up some power.

 

buddy, im gonna listen to ya. you've convinced me.

 

The advantage of a bridge port is the ability to flow air into the chamber before TDC. Once the main port opens, until you get into massive J-port range, the eyebrow's influence to flow is negligible. Maybe it helps reduce pressure before the short turn radius, which should help the airflow turn into the chamber, but it isn't significantly contributing to bulk flow.

 

Those templates are what got me thinking about just doing the primaries . IMO going lower than that does next to nothing on a turbo car apart from mess up the drive-ability.

Not at all . I'm thinking that opening them late will avoid much of the exhaust reversion at cruise/idle and when under boost at high rpm - but offer a significant bump in torque in the mid range where boost pressure is higher than turbine backpressure.

 

The port just needs to be higher on the plates to open later ....... just like on those templates fkuwin posted (bottom link).

 

well imma have to spin a rotor on a housing to confirm that works.. gimme 5.
i say nah, im looking at a 6 port motor, and moving the rotor on a sideplate without the housing i can see the intake would be less port area be be about the same port time, not much different as far as when the port opens. bridge dumb, go p.

 

He's right. Bridge opening is influenced by when the apex seal crosses it.

I have experimented with late opening bridges, and what I found is that it is pointless. The trick is this: The rotor is right there blocking the port from getting very much flow. Any real flow going through the port AT THE OPENING POINT (which is like 70-110BTDC) is going to have a big fat fistful of rotor in its face. The port doesn't really begin to actually get opened until much closer to TDC as the rotor face swings out of the way. At that point it doesn't matter if the port is "late opening" or not. So it is best to just make the eyebrow the full height of the port so that the port flows evenly across its height so you don't generate any weird vortices in the port from it pulling just off of the top. Or blowing back just into the top, if you're at part throttle with a streetable exhaust.

Don't just listen to me, if you have a rotor and an E-shaft and an end housing and rotor housing, mock it up and play around with it. It's amazing what you can see just by looking

Real world, I tried late opening and the drivability was the same as a full height eyebrow, it just made a lot less power. Less power than when the engine was a street port. (This was a 6 port engine, the eyebrows started halfway up the std ports and were relieved to a mm from the coolant seal groove) I pulled it apart again and did it right and was much happier.

 

^ your experimentation was on a N/A motor right?

 

Great info peejay , exactly what I was looking for . Just to clarify , did you try this on an N/A engine or turbo ?

Also : i do believe that care should be taken so that the port doesn't open before the rotor starts to block it off ,as exhuast gas will then have a free passage to the intake .

 

All nonturbo.

The exhaust will always have free passage to the intake on a bridge port. That is why they are so intolerant of any restriction in the exhaust, and they run poorly at low loads besides.

But when manifold pressure goes up and a properly tuned exhaust scavenges the chamber, that is when the magic happens.

 

this is what i was trying to explain to scrappy_brap... that he needs to ditch the s4 turbo intake for s4 N/a lower mated to a short header to common plenum with a single TB like Ulimate_jays setup... but his pp port.
and then to ditch the racing beat header for a proper flowing one designed closer like defines.. but he says hes going turbo so it its kinda pointless to do all that if he is gonna go turbo, but it also pointless to try to tune is N/a with half turbo parts, its always going to run terrible at any kinda part throttle because of the choke of flow.

 

I don't quite follow what you are saying as to the proper intake setup for a full bridge. I have a full bridge engine in my car right now that started as a 4-port keg but swapped in s5 na rotors. Since it was originally an s5 t2 I am still using the t2 intake and TB but port matched at all junctions. I currently have the Racing Beat true dual full exhaust because that's what I had on my car before swapping in this engine and I plan to order a collected long header from defined autoworks because I know I'm not getting the most out of my setup because of the exhaust. Should I also be looking at using an s4 na intake setup or was that only because scrappy_brap was still using a 6-port keg? I am also running Apexi PowerFC if that matters. I have my old s4 na long block sitting on an engine stand so I could use that intake if needed...

Manifold vacuum does not seem to be very high with my setup currently though because my brakes seemed a little weak right after swapping in the bridgey so I had to install a vacuum resevoir after the intake but before the booster to get decent pedal feel back. Loving this coversation though. Below is a link to a thread from whom I bought this whole engine setup from showing the engine internals before it was assembled if anyone is interested.

https://www.rx7club.com/naturally-as...d-t2-n-951173/