Hi I'm not really new but I'm not on alot but I want some opinions on what I am about to do. I have an 85 first gen. and am preparing to j-bridge port it. What do you guys think would it help or hurt me.

 

Well it will NOT be streetable. Only track. Now way it will ever pass emissions. You'll need a big piped full exhaust system, maybe a better tranny and rear end. Super clutch. BIG carburetor. Not to mention all the mods needed to go into the super high redline of a J Bridge. If I were you I would stick to a streetport. A good 180 - 200 HP. If you want more hp than that go turbo.

Then you can drive it on the street whenever you want.

If you want a race only track car, then a j bridge is friggin awesome, I dream of having a setup like that, but no way it will work on the street.

 

If this is your daily driver, stick to a street port. Yes you can technically physically drive a bridgeport on the street but it will have to be loud, will not like part throttle load levels, will suck down gas like crazy, and will not even get close to ever passing an emissions test ever again. There are people that drive bridges on the street and then downplay the huge list of inconveniences that they have over other types but at full throttle you'd have a blast. If you want a nice power upgrade, do all the bolt ons and a streetport. If you want the power of a bridgeport but none of the hassles and sacrifices of one, add forced induction.

 

You need to provide a heck of a lot more information than that if you want a good answer.

It's like sending a letter to a group of doctors simply saying "will x drug help me or not?" and not providing any symptoms or allowing diagnosis. In the right circumstances "x drug" could save your life, and in others it could kill you.

What do you want the car to be used for? Is it track only, or weekend warrier? If it's track, is it Autocross, 1/4mile or another class like pro7? What other mods have you done to the car? Do you have the budget to do more than just buy a rebuild kit and die grinder?

As an example, I'll be building a rock-solid 12a in the near future to replace my tired old engine. For the stuff I need to rebuild the engine engine along with the front-end things like oil pump and water pump, it'll be about $2k *before* the cost of porting, or even resurfacing the side housings!

Info, info!

Jon

 

Based on my 1st hand experience owning a 12a J-Bridge, I 100% agree with this.

 

the most id say is half bridge. where about are ya in gainesville. Im at the tip of gwinnett by hamilton mill

 

well i know what a bridge port looks like same with a small street and huge street but i'm wondering what a J Port looks like, cause if it revs high i'll be mightly interested


Prôdigy

 

On a j-port you cut the inner o-ring so that the small port on the side can be make as big as possible,if not sealed right coolant could leak into the rotor housing!!!!!!!
Best apex seals to use with this port is carbon seals(one piece)=full j-bridge port
Start making good power from 3500-upwarts,depents were you want to shift!!!
My old j-ported 13b kicked ***,20 16v,v8,v6 etc,could not touched it from robot to robot!
Do it you will not regret it,maybe feul wise =very thirsty(want speed you must pay!)

 

inertresting anyone got any pics of it? i learn best by being shown, so if any one has a pic or two it would be greatly appricated......


Prôdigy

 

I used a J-Bridge on my 7 for about 500 miles, then I bought a new 12A street ported it and swapped my hardware. You cant really use the powerband it allows unless you are at redline CONSTANTLY, from idle-8500 rpms you will have VERY little power. Go with a street port, I havent seen any huge gains from a bridge or a half bridge. A mild street port will give you the low down power you will want for a DD or a stoplight car. if your on the interstate and your street port is big enough (the RB template is plenty) you will still have top end. Although I have a power fall off at around 6500-7000 (I think) But what do you want more, maybe MAYBE 10 extra HP and a power band above lets say 7500 (which in street use you will RARELY reach) or 10 less but an extremely usable porwerband and not to mention a more reliable longer lasting engine. (+ better fuel economy)

J-ports and P-ports are best for track racing where you never slow down below redline. for a DD you will be starting at a stand still. whereas in track racing competion occurs during constant high speed operation.

Get a street port buddy, and also either have a machine shop weight and balance your flywheel or (dont know if anyone sells them anymore) buy a weighted flywheel. Lighter fltwheels are also best used in track racing when less rotational mass is beneficial to allowing the engine to reach higher rpm faster, and it makes it easier for the engine to maintain high rpm operation. A heavier flywheel will eat some HP to use, but it will return what is lost in torque. And if some of you disbelieve me, from a standing start I can pull on a 1982 Camaro Berlinneta with a 350 GM crate swap, Now that pull is only in the first 50 or so feet. after that i cant exactly take him, but its very impressive for a 12A to do all motor.

A heavier flywheel has more momentum, basically, auto-x and any kind og racing=light 1/4mile stop light drags, acceleration on the interstate=heavier
Torque is needed more for this kind of thing, and you will notice the improvement in torque, and you will NOT notice the marginal loss in HP. A light flywheel will adversly affect acceleration from a stop as it does not create enough momentum to help the car accelerate. A heavier flywheel will damage your engine faster in an auto-x car as it will make the engine work harder to turn it, just as a light flywheel would damage your engine if you constantly rev to the atmosphere to move your car.

Light flywheel = More HP Less Torque
Heavier flywheel = Less Torque More HP

Wow, I got a little off-topic, sorry. But this is useful info, so I'll just leave it. Besides I hate typing for no reason....

 

Can someone show me how the coolant seal is blocked?

 

All things being equal, a bridge will give you far more than 10hp over an extended port.

Bullcrap. A heavier flywheel will not give you more torque/horsepower. What it does do is store momentum. This is helpful when taking off as it helps overcome the vehicles inertia whithout the need for increased throttle input and/or slipping of the clutch.

It also slows down the rate at which the revs rise or fall when opening or closing the throttle. This means smoother operation but less engine braking and slower acceleration.

A lightened flywheel will always help you accelerate faster.

 

I'm in Hall County around the chestatee area

 

LMAO!

 

The engine that i am porting now is just an expiremental project but by april the plans are for another engine to be turbo-charged with a T-60 greddy turbo.

 

I highly doubt the ports actually increase you power that much, what they allow is your bolt on performance parts to breath better, that would be the only reason you would see any larger of a gain than MAYBE 10 HP, And it is a proven fact, look it up. The flywheels stored momentum and larger inertia accelerates your vehicle faster, at a LOWER RPM than a lighter flywheel would require. Realistically a flywheel does not add power. A light flywheel will subtract torque as it has less inertia, A heavy flywheel will subtract horsepower but at higher rpm it will put more stress on the drivetrain.
I am sorry as I misspoke, It is a fact that your flywheel weight actually has very little to do with power/E.T.'s A lightened flywheel requires you to rev higher to build equal inertia as a heavier flywheel would build that inertia at a lower RPM. So yes I was wrong on that point, But if you would like me to cite a few sources I could, because a flywheel is not a power adder.

 

I bet if I raced an Rx-7 with the same supporting mods as me, and the other 7 had a J-port or even a P-port and a lightened flywheel, I bet I would eat it alive in a 1/4 mile or a stoplight drag. I will reach my powerband at a MUCH lower RPM and since I will get into my powerband first, Now in auto-x the other 7 will have the advantage as it will have more power than me, at low rpm a J or P-port makes little power. and a lightened flywheel doesnt help much.... But thats not what they are designed to do so it wouldnt be a fair race.

 

Alight flywheel makes a very noticable difference over a heavier one. The car most certainly will accelerate faster with one. It is easier to launch a car from a stop with a heavier one but that's the only advantage performance wise. Drag racing sucks anyways so who really cares? Go faster everywhere else. Yes I have a light flywheel. I've had a few of them on different cars. They are always faster.

A bridge or peripheral port is a more powreful engine. Yes more than 10 hp over a streetport. This assumes you are running everything else properly with it. There is more to them that just making your bolt on's do more. Alot of conventional bolt on mods don't work that well with those engines as they are very finicky. The more extremem porting styles do make more lowe end power but at full throttle not part throttle. That is where everyeone gets confused. In a race you are at full throttle so it would easily hit it's powerband. I hate to say it but a streetported engine with a stock flywheel will absolutely get it's *** kicked by a bridge or peripheral port engine with a light flywheel. It wouldn't even be close. How many bus lengths do you want? With the same mods isn't very fair though as the same mods may not work well between both porting styles. Reality isn't like video games. The same mods don't apply to every scenario. What works best with one style may not work at all with another. If both were setup properly for their styles you may as well not turn your car on.

 

Check out my beveled rotors thread.

Port timing is about like a partial bridge, but with almost no low end loss.
It will work well on an NA with header & intake mods.

https://www.rx7club.com/forum/showth...beveled+rotors

 

It's common for n/a bridgeports/peripherals to run 11's and 12's in the 1/4. Show me a streetport that can do that. lol

The bolt ons are there to compliment the porting not the other way around. That's why they are often called supporting mods.

Bridgeports are able to flow far more air due to the fact they have longer port timing and more area. The overlap period also helps draw the intake charge in but the only downside is exhaust gas dilution of the intake charge at low rpm.

As for the flyhweel, it's simple. A lighter flwyheel requires less effort to turn meaning more horsepower to the driven wheels. And don't say it adds torque. The two are directly related.

 

This is a bridgeport dyno sheet. On a Dynojet that would be well over 230rwhp. It has a nice flat power band over half of it's operating range. Assuming it made peak power at a conservative 9000rpm that's a power band from around 4500rpm. I'd love to see a streetport with a spread of power like that.

 

You do realize you just said a J-port only kicks in at 8500 rpms, right?

Got a more realistic powerband figure?

 

Could you go into the specifics of this setup? 12A/13B, carb/FI, type and size of exhaust system and how the primaries and secondaries were ported? I'm running a 12A-1/2bp-1/2sp with a Mikuni 44 and I know it is missing something. I need to redo the exhaust and open it up, the over the axle pipe is still stock and is holding the true potential back. I've been thinking about going with a full 3" system from the RP pre-silencer and headers back. I have more than enough fuel, just don't know if I have enough carb, even though it is running a bit rich, and I know the exhaust is inadequate. Exhaust ports may have been opened up too high, but they are big.

 

It's a 13B. Dyno was with a 51mm IDA and very free flowing exhaust system.

I'm not sure on the exact port specs but it was built for Improved Production which means the eyebrow cant go past the water seal line. That goes to show that it's all about attention to detail and shaping of the runners rather than all out port area. Some of the leading IPRA guys are making well over 350hp at the crank with injection.