Questions: Full Bridge vs. Large Streeport
10-07-06, 12:55 PM
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Questions: Full Bridge vs. Large Streeport
I read that there is no torque down low in a bridgeport, but i'm tryiing to guage on what basis. So anyone that drives a bridgeport is the torque down low just like a stock 12a or worse, stock 13b, almost like a street port, etc...
Another question is how much louder is a full bridge port vs. a large street port?
thanks for your input
Another question is how much louder is a full bridge port vs. a large street port?
thanks for your input
10-10-06, 08:53 PM
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i heard of something called a half bridge......im looking into it pretty hard and read that its a "streetable" bridge port.........stronger than any street port job but not as harsh on gas and low end torque as a full bridge..."but that dose not mean that it is not effected".......the cool things is that you still get that bad *** "brap brap" sound....that sound is better than any cammed out engine in my opinion...but anyway i know it cant be anything new but just dosnt sound like its popular in the states....ive only heard about it from australian rotary owners.......check it out.
10-10-06, 10:31 PM
#6
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Originally Posted by 2wankel
I read that there is no torque down low in a bridgeport, but i'm tryiing to guage on what basis. So anyone that drives a bridgeport is the torque down low just like a stock 12a or worse, stock 13b, almost like a street port, etc...
Another question is how much louder is a full bridge port vs. a large street port?
thanks for your input
Another question is how much louder is a full bridge port vs. a large street port?
thanks for your input
Point B: My 12A P-port made my stockport feel like a slug, any RPM above 2000.
What does THAT tell you?
Without going too in depth, bridge/peripheral engines increase torque output EVERYWHERE because of the increased intake port timing (increases VE) but still reasonable port closing time (keeps powerband down).
Now, the downside: The engines are less driveable. While they make KILLER power at full throttle, part throttle is not so good, and they aren't smooth. The "the engines have no low end torque" is usually said by people who haven't tried stomping the go-pedal at low RPM, but only soft pedal it. Do that and the engines feel soggy and generally uphappy about their lives.
How often do you use WOT on the street? Never. That's why street ports are called STREET ports, because you can do things like drive smoothly in traffic.
As far as noise... I couldn't tell a difference exhaust-wise. You do need a very free flowing exhaust the worse your idle vacuum is, which tends to be loud. On the other hand, a stock port or street port will also greatly benefit from that very same exhaust, and it will be just as loud (or quiet), so what's the difference?
10-10-06, 10:35 PM
#7
Full bridge = Eyebrow on both primary and secondary ports.
Half bridge= Eyebrow only on the secondary ports.
Full bridge biggest advantage is more power in the upper rpm's due to more intake timing and port area. In plain english that means the engine is able to ingest more air as the rotor sweeps over the intake port. The more air you compress and ignite, the more power you will make. This is best for and all out race car.
Full bridge biggest disadvantage is less low end torque. This happens because with the eyebrows on both ports (which creates all that timing), more of your fuel/air mixture will be drawn out the exhaust port due to overlap in the lower rpm's leaving less fuel air to explode on the power stroke. Less fuel air to explode means less power and torque. However this is opposite as the rpm's increase. Also with your fuel/air burning in the exhaust, you will have terrible emissions.
Half bridge biggest advantage is you will still keep the low end while still increasing the top end. To understand this you have to understand the way the stock throttle body is engineered. The stock TB has a mechanical delay that allows the primary ports to open 1st and the secondaries open later. At partial throttle, all the air flow is directed though the primary ports. The secondaries are completely close off. Mazda engineered the TB this way as to keep the intake air velocity high through the primaries. With higher air velocity in the lower rpm's, the engine is able to ingest more air down low to properly fill the combustion chamber. Remember the more air you can cram in their the more power potential you will have which will also increase your low end torque. This is why a half bridge retains it's low end because the primary ports dont have any overlap from the bridge/eyebrow. You will also have cleaner emissions with the half bridge.
Half bridge biggest disadvantage is slightly less power potential.
Half bridge= Eyebrow only on the secondary ports.
Full bridge biggest advantage is more power in the upper rpm's due to more intake timing and port area. In plain english that means the engine is able to ingest more air as the rotor sweeps over the intake port. The more air you compress and ignite, the more power you will make. This is best for and all out race car.
Full bridge biggest disadvantage is less low end torque. This happens because with the eyebrows on both ports (which creates all that timing), more of your fuel/air mixture will be drawn out the exhaust port due to overlap in the lower rpm's leaving less fuel air to explode on the power stroke. Less fuel air to explode means less power and torque. However this is opposite as the rpm's increase. Also with your fuel/air burning in the exhaust, you will have terrible emissions.
Half bridge biggest advantage is you will still keep the low end while still increasing the top end. To understand this you have to understand the way the stock throttle body is engineered. The stock TB has a mechanical delay that allows the primary ports to open 1st and the secondaries open later. At partial throttle, all the air flow is directed though the primary ports. The secondaries are completely close off. Mazda engineered the TB this way as to keep the intake air velocity high through the primaries. With higher air velocity in the lower rpm's, the engine is able to ingest more air down low to properly fill the combustion chamber. Remember the more air you can cram in their the more power potential you will have which will also increase your low end torque. This is why a half bridge retains it's low end because the primary ports dont have any overlap from the bridge/eyebrow. You will also have cleaner emissions with the half bridge.
Half bridge biggest disadvantage is slightly less power potential.
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10-10-06, 10:39 PM
#8
Originally Posted by peejay
The "the engines have no low end torque" is usually said by people who haven't tried stomping the go-pedal at low RPM, but only soft pedal it. Do that and the engines feel soggy and generally uphappy about their lives.
Quick question, how drivable would either of your engines be on the highway with cruise control engaged? I would imagine terrible since the cruise would be at partial throttle.
10-11-06, 05:13 AM
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my six port is already street ported. would i be able to upgrade my port job and go half bridge or do i have to get a whole new engine....i am running a 600cfm carb but want to buy the throttle body kit from www.tweakit.net, how powerful would a half bridge be with a stand alone ECU and what kinda injectors would go good with the application....sorry if im getting off topic but this thread is the only one tha has the most info on this subject.
10-11-06, 11:50 AM
#10
Originally Posted by t-von
Full bridge biggest disadvantage is less low-end torque. This happens because with the eyebrows on both ports (which creates all that timing), more of your fuel/air mixture will be drawn out the exhaust port due to overlap in the lower rpm's leaving less fuel air to explode on the power stroke. Less fuel air to explode means less power and torque. However this is opposite as the rpm's increase. Also with your fuel/air burning in the exhaust, you will have terrible emissions.
Not quite. The lumpy idle, poor low load/low RPM cruising, and poor torque at low rpm are NOT a result of the air/fuel charge going out the exhaust.
Its a couple things, mainly exhaust dilution. High over lap engines have poor vacuum and poor air/fuel charge velocity at low RPM, so you get exhaust dilution, were the two ports (intake and exhaust) are open at the same time, you get exhaust creeping into the combustion chamber during the intake stroke (NOT vise versa {vacuum in the intake, pressure in the exhaust, what’s going were?}). Your combustion chamber now has already burnt gas in it as apposed to a full fresh air and fuel charge (exhaust dilution), so getting this mixture to fire is difficult and not only has less bang when it does fire (due to some of it being diluted), but a lot of the time doesn't even fire off (miss fire). The result is less torque due to low fresh charge and not firing every go around, hence the lump idle and poor power at low RPMs. The poor fuel mileage is because low velocity and what was already mentioned. You wet the intake runners and combustion chamber with fuel because it doesn't stay suspended and sticks to the runner walls and combustion chamber surfaces (IE, rotor face, rotor housing walls), so in order to get it to fire off, you add more fuel. Another factor is late closing of the intake ports. Even street ports have this phenomenon, were incoming charge does not have enough velocity to have enough inertia to keep going into the combustion chamber. Your port closes AFTER top dead center, so you get reversion, were part of your intake charge gets squished back out the intake port. Now at high RPM's when you get enough intake charge velocity, this is when your air charge has enough speed and inertia to over come the exhaust dilution and keep its fuel suspended in it and continue filling the chamber after TDC. At higher RPM, you start to exhaust scavenge (granted you have a proper exhaust system). This is when a negative pressure wave actually pulls some air out of the combustion chamber right at the beginning of the intake stroke. This does NOT however pull fresh air out, but pulls the stale already burnt left over exhaust still in the combustion chamber. While this old stale burnt stuff evacuates out the exhaust port, fresh air is pulled into the combustion to replace the old crap going out. It is possible to have such great scavenging that some fresh air gets pulled out the exhaust, but highly unlikely enough to effect power. Further along during the intake stroke, the exhaust port is closed and things are starting to compress already because you past top dead center, but wait, the intake is still open (late close timing of the intake port). Well, at this RPM your intake air charge has enough velocity and inertia to over come the squishing of the shrinking combustion chamber and continue filling it.
BTW, the missfireing unburnt fuel and the poor combustion (remember diluted intake charge) are the main factors for the poor emmissions associated with high over lap engines.
theres more I'm leaving out, just trying to clarify some things and hopefully didn't confuse further.
~Mike..........
Last edited by RacerXtreme7; 10-11-06 at 12:16 PM.
10-11-06, 06:50 PM
#11
Old [Sch|F]ool
Originally Posted by t-von
Quick question, how drivable would either of your engines be on the highway with cruise control engaged? I would imagine terrible since the cruise would be at partial throttle.
With stock FB gearing, it didn't stop bucking until about an 80mph cruise.
Steady speed in traffic meant throwing it in 5th and using heavy throttle, then coasting with the clutch down. Even at 60mph.
I bet it'd be undriveable with the 4.78's at any speed, since they don't load the engine down enough.
The stockport drives like, well, stock.
It's amazing how much torque the engines will make if you uncork the intake and exhaust, remove the power sucking clutch fan, and give them decent ignition timing. It has a little bit of a blurble at one point in the throttle tip-in, which I suspect is the vacuum advance coming in and out as the throttle plate hovers just over the vacuum port. Big effing deal, it's still way more driveable than a completely stock car, which feels like a slug swimming in molasses.I am told EFI makes things better for the P-port. That's too rich for my blood, so I have a stockport. Although if I ever get a decent 12A core engine, i want to build an extreme-early-opening street port, say closing time of only 50ADTC but the opening so early that the corner seals barely stay in, plus hignly beveled rotors.
Last edited by peejay; 10-11-06 at 06:53 PM.
10-12-06, 09:06 AM
#13
not exactly ... he said he was "told" EFI makes it better. at any rate, better is relative.
i know it's far from a 13B, but if you look up City Performance in Australia, they have some video clips of their Peripheral port 20B EFI Turbo FD and you can listen to it for yourself.
hope that helps some.
i know it's far from a 13B, but if you look up City Performance in Australia, they have some video clips of their Peripheral port 20B EFI Turbo FD and you can listen to it for yourself.
hope that helps some.
10-12-06, 08:32 PM
#14
Old [Sch|F]ool
Lots of video clips at Anniversary Racing Factory. They have a naturally aspirated, fuel injected peripheral port FD that "stars" in at least two of them. The thing seems like it drives like a stocker except at sub-3k off-throttle (cruises okay!) and when it's brapping the whole car isn't jerking. Seems like a winner to me.
Also note that they shift it at 8k.
They also have a N/A FC, peripheral port, with a Weber IDA. That car seems more like my P-port experiences. Lots of brap, barely runs except at WOT. Watching the videos allmost makes my eyes water from memories of all of the unburned HC's that flowed through my engine unscathed...
Also note that they shift it at 8k.
They also have a N/A FC, peripheral port, with a Weber IDA. That car seems more like my P-port experiences. Lots of brap, barely runs except at WOT. Watching the videos allmost makes my eyes water from memories of all of the unburned HC's that flowed through my engine unscathed...
10-15-06, 01:04 AM
#17
Originally Posted by RacerXtreme7
Not quite. The lumpy idle, poor low load/low RPM cruising, and poor torque at low rpm are NOT a result of the air/fuel charge going out the exhaust.
Its a couple things, mainly exhaust dilution. High over lap engines have poor vacuum and poor air/fuel charge velocity at low RPM, so you get exhaust dilution, were the two ports (intake and exhaust) are open at the same time, you get exhaust creeping into the combustion chamber during the intake stroke (NOT vise versa {vacuum in the intake, pressure in the exhaust, what’s going were?}). Your combustion chamber now has already burnt gas in it as apposed to a full fresh air and fuel charge (exhaust dilution), so getting this mixture to fire is difficult and not only has less bang when it does fire (due to some of it being diluted), but a lot of the time doesn't even fire off (miss fire). The result is less torque due to low fresh charge and not firing every go around, hence the lump idle and poor power at low RPMs. The poor fuel mileage is because low velocity and what was already mentioned. You wet the intake runners and combustion chamber with fuel because it doesn't stay suspended and sticks to the runner walls and combustion chamber surfaces (IE, rotor face, rotor housing walls), so in order to get it to fire off, you add more fuel. Another factor is late closing of the intake ports. Even street ports have this phenomenon, were incoming charge does not have enough velocity to have enough inertia to keep going into the combustion chamber. Your port closes AFTER top dead center, so you get reversion, were part of your intake charge gets squished back out the intake port. Now at high RPM's when you get enough intake charge velocity, this is when your air charge has enough speed and inertia to over come the exhaust dilution and keep its fuel suspended in it and continue filling the chamber after TDC. At higher RPM, you start to exhaust scavenge (granted you have a proper exhaust system). This is when a negative pressure wave actually pulls some air out of the combustion chamber right at the beginning of the intake stroke. This does NOT however pull fresh air out, but pulls the stale already burnt left over exhaust still in the combustion chamber. While this old stale burnt stuff evacuates out the exhaust port, fresh air is pulled into the combustion to replace the old crap going out. It is possible to have such great scavenging that some fresh air gets pulled out the exhaust, but highly unlikely enough to effect power. Further along during the intake stroke, the exhaust port is closed and things are starting to compress already because you past top dead center, but wait, the intake is still open (late close timing of the intake port). Well, at this RPM your intake air charge has enough velocity and inertia to over come the squishing of the shrinking combustion chamber and continue filling it.
BTW, the missfireing unburnt fuel and the poor combustion (remember diluted intake charge) are the main factors for the poor emmissions associated with high over lap engines.
theres more I'm leaving out, just trying to clarify some things and hopefully didn't confuse further.
~Mike..........
Its a couple things, mainly exhaust dilution. High over lap engines have poor vacuum and poor air/fuel charge velocity at low RPM, so you get exhaust dilution, were the two ports (intake and exhaust) are open at the same time, you get exhaust creeping into the combustion chamber during the intake stroke (NOT vise versa {vacuum in the intake, pressure in the exhaust, what’s going were?}). Your combustion chamber now has already burnt gas in it as apposed to a full fresh air and fuel charge (exhaust dilution), so getting this mixture to fire is difficult and not only has less bang when it does fire (due to some of it being diluted), but a lot of the time doesn't even fire off (miss fire). The result is less torque due to low fresh charge and not firing every go around, hence the lump idle and poor power at low RPMs. The poor fuel mileage is because low velocity and what was already mentioned. You wet the intake runners and combustion chamber with fuel because it doesn't stay suspended and sticks to the runner walls and combustion chamber surfaces (IE, rotor face, rotor housing walls), so in order to get it to fire off, you add more fuel. Another factor is late closing of the intake ports. Even street ports have this phenomenon, were incoming charge does not have enough velocity to have enough inertia to keep going into the combustion chamber. Your port closes AFTER top dead center, so you get reversion, were part of your intake charge gets squished back out the intake port. Now at high RPM's when you get enough intake charge velocity, this is when your air charge has enough speed and inertia to over come the exhaust dilution and keep its fuel suspended in it and continue filling the chamber after TDC. At higher RPM, you start to exhaust scavenge (granted you have a proper exhaust system). This is when a negative pressure wave actually pulls some air out of the combustion chamber right at the beginning of the intake stroke. This does NOT however pull fresh air out, but pulls the stale already burnt left over exhaust still in the combustion chamber. While this old stale burnt stuff evacuates out the exhaust port, fresh air is pulled into the combustion to replace the old crap going out. It is possible to have such great scavenging that some fresh air gets pulled out the exhaust, but highly unlikely enough to effect power. Further along during the intake stroke, the exhaust port is closed and things are starting to compress already because you past top dead center, but wait, the intake is still open (late close timing of the intake port). Well, at this RPM your intake air charge has enough velocity and inertia to over come the squishing of the shrinking combustion chamber and continue filling it.
BTW, the missfireing unburnt fuel and the poor combustion (remember diluted intake charge) are the main factors for the poor emmissions associated with high over lap engines.
theres more I'm leaving out, just trying to clarify some things and hopefully didn't confuse further.
~Mike..........
Not confusing at all, great explanation.
10-23-06, 06:24 PM
#20
Old [Sch|F]ool
Originally Posted by My5ABaby
You haven't driven a decent 13B then.
You haven't experienced my 12A. Everyone who drives it says something like "my god this thing has torque".
This weekend I was beating up on cars with twice the power. Once I'm in 2nd gear, I never have to downshift, unless I do something really stupid. Awesome power from 3k to 8k. Downshifting just wastes time...
10-25-06, 09:41 PM
#21
The General RE
A few years back I put a turbo on my J-bridge after running it NA for years . The difference was increadible. The idle had to come up a little. But when it was idling it was just about the coolest sounding engine I had heard. The Brapps would send the turbo spinning. The turbo whistled to the pulse of the engine. The best thing after adding the turbo was that the engine actually got low speed torque. Basically as soon as there was 1psi the exhaust reversion problem was gone. Instead of torque at 5K it was more like 2K. The engine also got quieter, but not actually quiet. With the 1.3AR it reved all the way out with 10psi. One day it all came to an end due to a ping on an odd transion from cruise. Blow thru carb problem. I have EFI now, but I am a little hesitant to build another BridgePort. I am thinking about doing a small one because I miss the sound of it.
10-26-06, 02:56 AM
#23
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Originally Posted by eriksseven
RacerXtreme... Wonderful post. Thanks for taking the time to teach.
I was wondering about porting on a FD with stock twins (at around 15-17psi), do you get to a point where you cant make enough puff to exploit the benefits of the larger ports?
I was thinking of going half bridge, car is a weekend toy so streetablity is not a major concern but dont want to make it totally undriveable, from the explanations given seems like a fair compromise? That is if the twins can make use of it or on the flip side there is no detrimental effect. I may eventually switch to BNR's or single one day so im bearing that in mind too
10-26-06, 08:01 AM
#24
you will always make more power with a bigger port, even on stock turbos, but you probably will not flow enough to reach the full potential of your block until you upgrade.
Porting changes two things- port area and port timing. more port area means you can flow more charge per given amount of time. more timing means you have more port open time to flow the charge. both things increase the flow efficiency of your engine, which means you will make more power at any given intake pressure. you will also require a higher volumetric flowrate, so smaller stock turbos will have trouble keeping up.
what most people do is do a rebuild at one time, and then a turbo upgrade at different times just to help with expenses. generally you want to do the rebuild and porting first because the freshened engine will be more capable of dealing with the higher stresses from the extra power once you get a turbo, and also because you can choose a slightly bigger turbo and retain streetability if you are running it on an already ported engine.
pat
Porting changes two things- port area and port timing. more port area means you can flow more charge per given amount of time. more timing means you have more port open time to flow the charge. both things increase the flow efficiency of your engine, which means you will make more power at any given intake pressure. you will also require a higher volumetric flowrate, so smaller stock turbos will have trouble keeping up.
what most people do is do a rebuild at one time, and then a turbo upgrade at different times just to help with expenses. generally you want to do the rebuild and porting first because the freshened engine will be more capable of dealing with the higher stresses from the extra power once you get a turbo, and also because you can choose a slightly bigger turbo and retain streetability if you are running it on an already ported engine.
pat
10-26-06, 10:50 AM
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Thanks for the info Pat, so although I wont be utilising all the potential of the half bridge, there will still be a gain, with potential for more if I ever do a turbo swap. And also more cost effective than having the engine out twice to do porting!
Im also planning a pre-turbo WI set-up which im hoping will give the Volumetric efficiency a sizeable hike, not to single turbo level obviously, but as tescos say, 'every little helps'
2 things I dont wont to do are...get a smaller port done and wish id gone larger...get a port that ruins my power/ride (bearing in mind I can live without perfect streetability)
Im also planning a pre-turbo WI set-up which im hoping will give the Volumetric efficiency a sizeable hike, not to single turbo level obviously, but as tescos say, 'every little helps'
2 things I dont wont to do are...get a smaller port done and wish id gone larger...get a port that ruins my power/ride (bearing in mind I can live without perfect streetability)