Questions: Full Bridge vs. Large Streeport
10-26-06, 01:27 PM
#26
I am a major disciple of the 'every little bit helps' school of thought. I probably have 15 2-5hp modifications done to my car. add that up and see what you get. Little things like polishing the inside of a manifold or buying mandrel bends instead of squeeze bends really add up after a while.
as for turbo/port choice, the thing you need to keep in mind is that a bigger turbo has more lag, and more port overlap also has more 'lag' due to overlap. As racerextreme explained above, the lack of low end torque on an engine with lots of overlap is due to the pressure differental across the ports. since a bigger turbo takes mroe energy to spool than a smaller turbo, this will cause a higher pressure in the exhaust manifold, which makes the lag due to overlap even worse.
Once the turbo begins to spool, the intake pressure rises, so the problem is reduced drastically.
So what you want to do is to consider the powerband you ultimately want to have and then compromise between turbo size and port timing to achieve it. The bigger the turbo, the less timing you will have to have to get the same low range powerband, or vice versa. If you can live with a powerband that only really starts at 3k rpm, then you can have plenty of both, its really all just personal preference.
So how do you chose between big turbo or big ports?
Part of it is just personal preference, but there are a few real things to consider.
A. Port size is limited by the geometry of the engine, so you can only go so big before you either hit stuff, or are out of the effective timing range.
B. Big turbos are expensive, big ports are free (kinda).
C. Turbos lower BSFC (brake specific fuel consumption) by recycling some of the wasted heat, while porting raises it due less complete combustion. (lower is better, and note that this is also affected by the afrs that you run at boost)
D. The thing I personally consider to be the most important factor is this: Turbos are only partially efficent, and are driven by the combustion of the engine. So if you take a NA engine and add a turbocharger which increases the power output by 50%, you actually have to combust something like 60 or 70% more fuel. This means higher combustion pressures and temperatures and more stress on internal parts. On the other hand, if you open the ports up, all you are really doing is increaseing the flow through the system, so there is less increased stress on the engine internals for each extra hp made compared to forced induction. There are a few things that do add stress from porting, because you are still making more power, and also the timing adjustments change the internal stresses some too, but it is much less comparatively.
Sorry I am not quite as eloquent as racerextreme7, but hopefully some of that is useful, and im pretty sure most of it is correct.
pat
as for turbo/port choice, the thing you need to keep in mind is that a bigger turbo has more lag, and more port overlap also has more 'lag' due to overlap. As racerextreme explained above, the lack of low end torque on an engine with lots of overlap is due to the pressure differental across the ports. since a bigger turbo takes mroe energy to spool than a smaller turbo, this will cause a higher pressure in the exhaust manifold, which makes the lag due to overlap even worse.
Once the turbo begins to spool, the intake pressure rises, so the problem is reduced drastically.
So what you want to do is to consider the powerband you ultimately want to have and then compromise between turbo size and port timing to achieve it. The bigger the turbo, the less timing you will have to have to get the same low range powerband, or vice versa. If you can live with a powerband that only really starts at 3k rpm, then you can have plenty of both, its really all just personal preference.
So how do you chose between big turbo or big ports?
Part of it is just personal preference, but there are a few real things to consider.
A. Port size is limited by the geometry of the engine, so you can only go so big before you either hit stuff, or are out of the effective timing range.
B. Big turbos are expensive, big ports are free (kinda).
C. Turbos lower BSFC (brake specific fuel consumption) by recycling some of the wasted heat, while porting raises it due less complete combustion. (lower is better, and note that this is also affected by the afrs that you run at boost)
D. The thing I personally consider to be the most important factor is this: Turbos are only partially efficent, and are driven by the combustion of the engine. So if you take a NA engine and add a turbocharger which increases the power output by 50%, you actually have to combust something like 60 or 70% more fuel. This means higher combustion pressures and temperatures and more stress on internal parts. On the other hand, if you open the ports up, all you are really doing is increaseing the flow through the system, so there is less increased stress on the engine internals for each extra hp made compared to forced induction. There are a few things that do add stress from porting, because you are still making more power, and also the timing adjustments change the internal stresses some too, but it is much less comparatively.
Sorry I am not quite as eloquent as racerextreme7, but hopefully some of that is useful, and im pretty sure most of it is correct.
pat
10-26-06, 01:41 PM
#27
Full Member
Join Date: Nov 2003
Location: Essex, UK
Posts: 79
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by patman
I am a major disciple of the 'every little bit helps' school of thought. I probably have 15 2-5hp modifications done to my car. add that up and see what you get. Little things like polishing the inside of a manifold or buying mandrel bends instead of squeeze bends really add up after a while.
as for turbo/port choice, the thing you need to keep in mind is that a bigger turbo has more lag, and more port overlap also has more 'lag' due to overlap. As racerextreme explained above, the lack of low end torque on an engine with lots of overlap is due to the pressure differental across the ports. since a bigger turbo takes mroe energy to spool than a smaller turbo, this will cause a higher pressure in the exhaust manifold, which makes the lag due to overlap even worse.
Once the turbo begins to spool, the intake pressure rises, so the problem is reduced drastically.
So what you want to do is to consider the powerband you ultimately want to have and then compromise between turbo size and port timing to achieve it. The bigger the turbo, the less timing you will have to have to get the same low range powerband, or vice versa. If you can live with a powerband that only really starts at 3k rpm, then you can have plenty of both, its really all just personal preference.
So how do you chose between big turbo or big ports?
Part of it is just personal preference, but there are a few real things to consider.
A. Port size is limited by the geometry of the engine, so you can only go so big before you either hit stuff, or are out of the effective timing range.
B. Big turbos are expensive, big ports are free (kinda).
C. Turbos lower BSFC (brake specific fuel consumption) by recycling some of the wasted heat, while porting raises it due less complete combustion. (lower is better, and note that this is also affected by the afrs that you run at boost)
D. The thing I personally consider to be the most important factor is this: Turbos are only partially efficent, and are driven by the combustion of the engine. So if you take a NA engine and add a turbocharger which increases the power output by 50%, you actually have to combust something like 60 or 70% more fuel. This means higher combustion pressures and temperatures and more stress on internal parts. On the other hand, if you open the ports up, all you are really doing is increaseing the flow through the system, so there is less increased stress on the engine internals for each extra hp made compared to forced induction. There are a few things that do add stress from porting, because you are still making more power, and also the timing adjustments change the internal stresses some too, but it is much less comparatively.
Sorry I am not quite as eloquent as racerextreme7, but hopefully some of that is useful, and im pretty sure most of it is correct.
pat
as for turbo/port choice, the thing you need to keep in mind is that a bigger turbo has more lag, and more port overlap also has more 'lag' due to overlap. As racerextreme explained above, the lack of low end torque on an engine with lots of overlap is due to the pressure differental across the ports. since a bigger turbo takes mroe energy to spool than a smaller turbo, this will cause a higher pressure in the exhaust manifold, which makes the lag due to overlap even worse.
Once the turbo begins to spool, the intake pressure rises, so the problem is reduced drastically.
So what you want to do is to consider the powerband you ultimately want to have and then compromise between turbo size and port timing to achieve it. The bigger the turbo, the less timing you will have to have to get the same low range powerband, or vice versa. If you can live with a powerband that only really starts at 3k rpm, then you can have plenty of both, its really all just personal preference.
So how do you chose between big turbo or big ports?
Part of it is just personal preference, but there are a few real things to consider.
A. Port size is limited by the geometry of the engine, so you can only go so big before you either hit stuff, or are out of the effective timing range.
B. Big turbos are expensive, big ports are free (kinda).
C. Turbos lower BSFC (brake specific fuel consumption) by recycling some of the wasted heat, while porting raises it due less complete combustion. (lower is better, and note that this is also affected by the afrs that you run at boost)
D. The thing I personally consider to be the most important factor is this: Turbos are only partially efficent, and are driven by the combustion of the engine. So if you take a NA engine and add a turbocharger which increases the power output by 50%, you actually have to combust something like 60 or 70% more fuel. This means higher combustion pressures and temperatures and more stress on internal parts. On the other hand, if you open the ports up, all you are really doing is increaseing the flow through the system, so there is less increased stress on the engine internals for each extra hp made compared to forced induction. There are a few things that do add stress from porting, because you are still making more power, and also the timing adjustments change the internal stresses some too, but it is much less comparatively.
Sorry I am not quite as eloquent as racerextreme7, but hopefully some of that is useful, and im pretty sure most of it is correct.
pat
Glad someone else likes the 'every little helps' mantra Your making me tempted to go for the half bridge, and I like that. I'll be sticking with the stock turbos for quite a bit but like I say hoping to push them to their max. From what ive read with big ports and small ish turbo powerband is likely to be high in the rev range, which suits me fine, and when the turbos finally give up the ghost (which theyre bound too!) i'll have the ports for a nice big single
10-26-06, 01:59 PM
#28
The General RE
If you want to turbo a bridgeport you will need to be careful not to choke it. Basically once the wastegate starts to open the backpressure climbs, but the intake pressure won't. It won't be long after this point that the engine's torque will fall off. You will need to either run more boost, less RPM or get a larger A/R turbine housing. If you have stock twins eliminating the sequential setup should help a bit too.
10-26-06, 02:16 PM
#29
Full Member
Join Date: Nov 2003
Location: Essex, UK
Posts: 79
Likes: 0
Received 0 Likes
on
0 Posts
ah I see,
this distracts from the thread a bit, but what is it about the non-sequential conversion that makes them flow more? I can understand under the transition point, as youve got 2 tubbies instead of 1, but what difference does it make in high rpm when both turbos will be flowing regardless? Is it just removing all the gubbins that controls 2nd turbo that increases the air flow a bit?
So on the stock twins, I could end up losing torque earlier on in the rev range compared to stock ports, but should have better flow/power before that point, and where that point is depends on how much boost I can make (if can make enough will be gains all the way)...I think?!
this distracts from the thread a bit, but what is it about the non-sequential conversion that makes them flow more? I can understand under the transition point, as youve got 2 tubbies instead of 1, but what difference does it make in high rpm when both turbos will be flowing regardless? Is it just removing all the gubbins that controls 2nd turbo that increases the air flow a bit?
So on the stock twins, I could end up losing torque earlier on in the rev range compared to stock ports, but should have better flow/power before that point, and where that point is depends on how much boost I can make (if can make enough will be gains all the way)...I think?!
10-26-06, 07:14 PM
#30
Originally Posted by 13BT_RX3
If you want to turbo a bridgeport you will need to be careful not to choke it. Basically once the wastegate starts to open the backpressure climbs, but the intake pressure won't. It won't be long after this point that the engine's torque will fall off. You will need to either run more boost, less RPM or get a larger A/R turbine housing. If you have stock twins eliminating the sequential setup should help a bit too.
if the wastegate is open, backpressure should not be climbing, there is nothing to keep it from simply venting to the atmosphere. I suppose there would be a tiny bit of restriction at the wastegate dump, but i wouldnt imagine it would account for the several psi difference between the inlet pressure and atmospheric.
please explain.
10-26-06, 07:30 PM
#31
Old [Sch|F]ool
Originally Posted by patman
i find this hard to believe.
if the wastegate is open, backpressure should not be climbing, there is nothing to keep it from simply venting to the atmosphere. I suppose there would be a tiny bit of restriction at the wastegate dump, but i wouldnt imagine it would account for the several psi difference between the inlet pressure and atmospheric.
please explain.
if the wastegate is open, backpressure should not be climbing, there is nothing to keep it from simply venting to the atmosphere. I suppose there would be a tiny bit of restriction at the wastegate dump, but i wouldnt imagine it would account for the several psi difference between the inlet pressure and atmospheric.
please explain.
It would depend on how much exhaust manifold pressure (really, pressure drop across the turbine) was required to keep the turbo spinning. If it's a shitty turbo that requires a lot of power to make top end boost, then backpressure WILL climb, out of necessity. The wastegate only vents off what exhaust pressure is not needed to maintain intake pressure.
10-26-06, 08:30 PM
#32
The General RE
Originally Posted by peejay
It would depend on how much exhaust manifold pressure (really, pressure drop across the turbine) was required to keep the turbo spinning. If it's a shitty turbo that requires a lot of power to make top end boost, then backpressure WILL climb, out of necessity. The wastegate only vents off what exhaust pressure is not needed to maintain intake pressure.
10-27-06, 07:52 AM
#33
Originally Posted by peejay
Mostly series 4s, but one series 5.
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...
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...
10-29-06, 01:54 AM
#34
The General RE
To get this thread back on track...Displacement aside. Bridge ports are for hard core Mother F...ers and street ports are for upstanding citizens. Bridgeports are Mazda's secret dark Harley Davison side. If you don't have the personality for one you can't get away with driving it on the street. On the race track the bridgeport shines. This is the reason why we are all in this discussion. Bridge porting takes a rotary to a diferent level. But when you go this far you might want to mention the peripheral port.
10-08-07, 10:12 PM
#37
Junior Member
Join Date: May 2007
Location: Pickerington Ohio
Posts: 16
Likes: 0
Received 0 Likes
on
0 Posts
Iam running a half bridge port and i love it. The only bad thing is is that it has no low end power. Of course iam running a garret TO4R and it doesnt hit boost till 4 grand, but once it opens up MY GOD DOES IT KICK ***. ITs not to bad to drive on the street as long has you dont mind people yelling at you to shut off your car. I looked in to getting the full bridge but i couldnt see getting it for the street. IT just seemed to radical not good for just driving.
Thread
Thread Starter
Forum
Replies
Last Post
Jeff20B
1st Generation Specific (1979-1985)
73
09-16-18 07:16 PM
rx8volks
Canadian Forum
0
09-01-15 11:02 PM
