Hello everyone, I was wondering what the difference is between each of the different porting between these 3 listed. I'm trying to decide how to rebuild my engine and which port I will go with. I used the search but i was unable to find anything. If there is already a thread i would be really grateful if someone could point me to the direction. Thank you.

 

It all depends on your application:

If you drive your car on the street, you use a street port.

If you your car is a race only car, you use the maximum porting the rules allow. If porting is not restricted by your race sanctioning body rule book, then you run a peripheral port. If they don't allow a peripheral port, then you run a bridge port. These racing ports are not streetable for daily street driving, because 90% of street driving is done at low rpms, below 3500 rpm. These racing ports don't produce torque below 5000 rpm.

 

Except when they do.

I would not say a bridge or peripheral port is for everyone, but they certainly can be driven on the street. You're not going to coast at low RPM in gear, though - they don't CRUISE. You have to be accelerating, decelerating, or in neutral.

They also are not tolerant - at ALL - of exhaust systems that are not free flowing. That said I have found that the RB long primary exhaust system is EXCELLENT for a bridge port engine. It is very quiet and still free flowing enough for a bridge to be livable.

Except for a very brief stint with a large street port 6 port, I have been exclusively running bridge port on the street since 2010, when I took my street port T2 N/A engine and half-bridged it. Instant gain in low end and midrange torque. Went to the street port 6 port and immediately hated how "soft" it felt. Then I messed around with half bridge 6 port engines until I finally said screw it and made my full bridge 4 port, which has the same drivability as a half bridge but WAY more midrange power, and the powerband just keeps going.

BUT it's not an engine where, say, you can drive at 35mph in gear, unless you have a very heavy flywheel to keep it from bucking the drivetrain apart from all of the bokbokbokbokbokbok because the engine isn't loaded enough to run smoothly.

Half bridge GSL-SE engine with new RB exhaust system. All you hear is my 3-link rattling and the gear noise from the trans/diff. And look at how little low end torque there is, driving up that hill in 5th gear at 30mph But notice - never coast in gear. This engine also had the heavy GSL-SE flywheel, my full bridge has a 9lb aluminum flywheel.


Drivability on the full bridge is the same, I don't have any street driving videos of it except for the one where I was limping home with a broken axle, or the drive home from Tulsa (1000mi each way to compete at Nationals) where all you hear is Kleptones and maybe a little engine whrrrr underneath Break On Misirlou.

 

Actually, going back, I could argue that a bridge ported rotary is an altogether more pleasant driving experience than a Dodge Neon

Full bridge RX-7 coming home from Nationals:


Turbocharged Neon coming home from Nationals (friend's car, mine was riding his trailer - broke in competition, still placed 2nd and 3rd in one of the biggest classes of event)


If you squint your ears, you can almost hear the radio playing that same song. I said damn the law, and wore earplugs and earmuffs for the drive home.

 

Here you go Engine Porting & Polishing

 

i wasn't going to post, just because you need to be out of the box to get a PP or BP to be friendly on the street. all the tuning info out there is for a dedicated race car, so its not really applicable to a street car.

ive done two PP's now, and there is a 3rd on the way, end of 2016.

the second P port (Fungus mungus's car), is running the RB exhaust and a stock flywheel, and driving it you'd almost never know it was ported. i think the flywheel made a huge difference, it does part throttle just fine.

the exhaust is ok too, its streetable, and i'm sure he's loosing a few hp at 8500rpm, but i'm not sure we care, its a street/auto-x car. i didn't drive this one with the stock engine, but i did drive my P port back to back with a CSP 1st gen, and the P port makes more power by 2500rpm than the CSP car did anywhere

and like pj's car, its streetable, but i'm not sure you'd want to daily it, its not the engine, its the tire noise, and suspension links, and the fact that its a teeny little 30 year old car to begin with

P port #3 is going to be a 20B, i predict it won't really be streetable, by the time you put enough load on the engine to make it happy, you're going to be going quite fast.

 

Yep, the tuning knowledge that one can easily find has you doing things like locked ignition timing (or - worse - on electronic cars, idle timing in the 30-40 degree range) which is the exact opposite of what you'd want. It's been a long time since I've messed with it but I'm pretty sure that my timing is stock 12A leading timing - 0 at idle and 20 max. Need low advance at low RPM in order to get good drivability. Hurts manifold vacuum but that is where EFI makes it painless.

I remember tuning at the drag strip and peak timing between 18 and 24 degrees made no difference and more timing made slower MPH, so I set it to whatever made highway drivability the most pleasant... which is why I am thinking it is around 20 degrees + vacuum advance. More timing meant more likely to buck which can be covered up with more fuel, which would hurt fuel economy and more importantly make the oil get diluted faster, so less timing means can run leaner mixtures and still cruise happy.

 

I have just completed a injected 13bpp with modified rx8 rotating assembly . it's a street used Repu so used 43mm ports. this was to replace a customers full cut bridgeport. makes more tourqe everywhere. while running it in I actually had to look down see what gear I was in as it drove so smooth part throttle . no bucking. anyways when it was fresh I zeroed timing but left the bridgeport timing table in there thinking it would be close. well I had to pull 6 degrees out of cranking timing to get it to fire up nicely. bridgeport wanted 14 pp 8 degrees.anyways we redid exhaust managed to get it flowing better then old setup and seem to have managed doing it with out to much of a noise increase. all around though far far superior to the bridgeport. Oh and it idles happy as @ 1700 rpm dropping to 1550rpm with fan on. I was able to get it all the way down to 1300rpm but wasn't the happiest lol.

 

Took a peek on your recommendations on porting....

A smaller P-port can be very streetable if sized and tuned correctly, I've had many combinations when I use to swap new combos overnight and go to the track, I also like the standard bridgeport way better than any street port, they have better mid-range-top end power, exhaust, tuning, porting flow, gearing factors in the final result in the real world,

I've out ran bridgeports and p-ports with a street port engines during competition. lets not forget the stock porting turbo cars that make high hp but that's another subject, anything will work if set up correctly.

 

^ It is a general guideline. There is always someone that will come onto one of these threads and claim to DD a PP. Of course it "can" be done, however I do not consider a car with a 1700+ rpm idle a DD. These types of cars are purpose built and the engines are on the expensive end of the spectrum.

I could also DD drive my S/P 20B FD, which actually has a very nice 850 rpm idle and incredible cruising ability, but I am not going to, simply because I own other cars that are suited to daily driving. Not to mention driving in the rain or snow is just dangerous, making it not a DD in most of Spring, all of Winter and a good portion of Fall (so much for it being a DD)

 

i agree, i had to go out of the box to tune mine, and more importantly, you could DD it, but i don't think you'd want to. BTW mine idles around 900rpm.

 

Yah, i can get mine to idle at 700-800 or so, which is hilarious because I could never get a streetport or even a stockport to idle that low. But the charging system doesn't start doing anything until 1200ish or so, and I don't have any kind of cold idle-up, so I set the idle to work sort of OK when cold and it idles maybe 1400-1600 hot and I can knock that down to 1200 by turning the fans on, so i used the fans as a crude idle control when in traffic.

 

Peejay already hit on it. To make a bridge engine run smoothly at low loads, you set ignition timing to retard dramatically based on throttle position so that manifold vacuum never goes high. This decreases the amount of egr to the point that it will run smooth.

 

i did a test on mine, and the test failed, but i learned something else. any carb has an idle hole, and a transition hole or two, or three. anyways i noticed with my PP that when its running at 1000rpm, its actually at the 1st transition hole, and not the idle hole.

this makes the idle mixture screws not really work, as you're not using that port anymore, but it also takes 1 hole away from the transition to the main circuit (on a 48 IDA, YMMV), this is perhaps a contributor to the lean stumble everyone gets around 3000rpm with the webers.

i decided to try and get mine to idle on the idle hole. weber has two options, they have a throttle plate with a different taper, so it can be open slightly more and get the idle hole, and the second option is to drill a hole in the throttle plate.

so i decided to try drilling a hole, and i started small, 0.005 maybe, and worked my way up.

to my surprise the idle speed adjustment (its actually not, its a throttle stop, not supposed to be adjusted), didn't change but drivability did; it got way better.

in fact it got better the bigger i made the hole, to the point where the carb stopped working because there was no vacuum anymore.

i filled in the holes and redrilled a smaller one, i forget what i ended up with, but even with huge ports, locked timing, etc it runs like an FC with a tps thats off a little, it can be jerky in the parking lot, but outside of that runs like a stock car, except it makes power.

i also left the holes a little small, because it stopped brapping at idle, and part of the reason i have a PP is the brap brap idle, so i put it back. it still goes in and out of the normal idle, to the extent that i spent some time before sevenstock making it idle with a more consistent brap. if you showed up with a P port that idled like a stock port, i think you'd get tossed out

i'm still idling on the 1st transition hole, this requires that the idle jet be more correct, as it has a bigger influence on idle mixture than it should. i've also found that the P port, with a reasonable E tube, can have the hesitation at the mains transition like everyone else, but that the mains can come on so fast its actually too rich. this is at least easy to tune out, you just have to try different air correctors until it works.