Rebuild Upcoming, PP or Bridge?
09-19-23, 04:10 PM
#1
Junior Member
Thread Starter
Rebuild Upcoming, PP or Bridge?
Hi all,
I understand this question has been asked a lot and I promise I have been searching around, but I haven't found the specifics I've been looking for.
In December, I'll be rebuilding my engine. It's a stockport 12A in an 85 RX7 and I'm looking to get as much HP out of it as possible while staying N/A (it's a RHD car so turbo placement is an **** and very few people have experience tuning 12A turbos in UK). The two options I'm currently looking at are: Bridgeport the 12A or build a 13b PP using the 12A irons, Racing Beat gslse PP housings and S5 rotating assembly. I understand the first response is going to be "Why not just buy a 13B and work from there?". The answer is, in the UK, S5 engines go for £3k-£4k for a good running block, and for that price I could build a nice BP 12A and have some money left over for extras.
In my mind, the bridgeport is the more economical choice, as I won't need to fully build the engine for high RPMs. Maybe some hardened stat gears and oiling mods, due to it not being a racing application and only occasionally seeing 9,000 RPM on the odd spirited drive. Carbon Apex Seals would be lovely, but I cannot for the life of me find any for the 12A that are produced any more. For the PP, I'd have the rotating assembly balanced and side clearanced so it could withstand up to 10,000 RPM, and carbon seals would still be preferable, but not as necessary thanks to the 13B's 2mm seals being able to take higher RPMs than the 12A's 3mm.
This is just going to be a fun weekend car with the odd track day, so noise and drivability isn't a massive issue. I'm looking to stick to a Weber carb, 48 or 51 IDA depending on the application. I know both will be loud, however, I understand a PP is slightly less tolerant of exhaust backpressure than a BP, so how much louder would it have to be to get some nice power out of it as opposed to the BP? You guys are more experienced than me, so I'd love to hear your opinions on what you'd choose for my situation.
As a sidenote, so far the car has a completely stock drivetrain with a GSL-SE rear end. I know the rear end can take about 300hp max, but this is going to be on street tyres, not launching on sticky drag tyres, so would it hold up alright?
Many thanks
I understand this question has been asked a lot and I promise I have been searching around, but I haven't found the specifics I've been looking for.
In December, I'll be rebuilding my engine. It's a stockport 12A in an 85 RX7 and I'm looking to get as much HP out of it as possible while staying N/A (it's a RHD car so turbo placement is an **** and very few people have experience tuning 12A turbos in UK). The two options I'm currently looking at are: Bridgeport the 12A or build a 13b PP using the 12A irons, Racing Beat gslse PP housings and S5 rotating assembly. I understand the first response is going to be "Why not just buy a 13B and work from there?". The answer is, in the UK, S5 engines go for £3k-£4k for a good running block, and for that price I could build a nice BP 12A and have some money left over for extras.
In my mind, the bridgeport is the more economical choice, as I won't need to fully build the engine for high RPMs. Maybe some hardened stat gears and oiling mods, due to it not being a racing application and only occasionally seeing 9,000 RPM on the odd spirited drive. Carbon Apex Seals would be lovely, but I cannot for the life of me find any for the 12A that are produced any more. For the PP, I'd have the rotating assembly balanced and side clearanced so it could withstand up to 10,000 RPM, and carbon seals would still be preferable, but not as necessary thanks to the 13B's 2mm seals being able to take higher RPMs than the 12A's 3mm.
This is just going to be a fun weekend car with the odd track day, so noise and drivability isn't a massive issue. I'm looking to stick to a Weber carb, 48 or 51 IDA depending on the application. I know both will be loud, however, I understand a PP is slightly less tolerant of exhaust backpressure than a BP, so how much louder would it have to be to get some nice power out of it as opposed to the BP? You guys are more experienced than me, so I'd love to hear your opinions on what you'd choose for my situation.
As a sidenote, so far the car has a completely stock drivetrain with a GSL-SE rear end. I know the rear end can take about 300hp max, but this is going to be on street tyres, not launching on sticky drag tyres, so would it hold up alright?
Many thanks
09-19-23, 04:47 PM
#2
Junior Member
Hi all,
I understand this question has been asked a lot and I promise I have been searching around, but I haven't found the specifics I've been looking for.
In December, I'll be rebuilding my engine. It's a stockport 12A in an 85 RX7 and I'm looking to get as much HP out of it as possible while staying N/A (it's a RHD car so turbo placement is an **** and very few people have experience tuning 12A turbos in UK). The two options I'm currently looking at are: Bridgeport the 12A or build a 13b PP using the 12A irons, Racing Beat gslse PP housings and S5 rotating assembly. I understand the first response is going to be "Why not just buy a 13B and work from there?". The answer is, in the UK, S5 engines go for £3k-£4k for a good running block, and for that price I could build a nice BP 12A and have some money left over for extras.
In my mind, the bridgeport is the more economical choice, as I won't need to fully build the engine for high RPMs. Maybe some hardened stat gears and oiling mods, due to it not being a racing application and only occasionally seeing 9,000 RPM on the odd spirited drive. Carbon Apex Seals would be lovely, but I cannot for the life of me find any for the 12A that are produced any more. For the PP, I'd have the rotating assembly balanced and side clearanced so it could withstand up to 10,000 RPM, and carbon seals would still be preferable, but not as necessary thanks to the 13B's 2mm seals being able to take higher RPMs than the 12A's 3mm.
This is just going to be a fun weekend car with the odd track day, so noise and drivability isn't a massive issue. I'm looking to stick to a Weber carb, 48 or 51 IDA depending on the application. I know both will be loud, however, I understand a PP is slightly less tolerant of exhaust backpressure than a BP, so how much louder would it have to be to get some nice power out of it as opposed to the BP? You guys are more experienced than me, so I'd love to hear your opinions on what you'd choose for my situation.
As a sidenote, so far the car has a completely stock drivetrain with a GSL-SE rear end. I know the rear end can take about 300hp max, but this is going to be on street tyres, not launching on sticky drag tyres, so would it hold up alright?
Many thanks
I understand this question has been asked a lot and I promise I have been searching around, but I haven't found the specifics I've been looking for.
In December, I'll be rebuilding my engine. It's a stockport 12A in an 85 RX7 and I'm looking to get as much HP out of it as possible while staying N/A (it's a RHD car so turbo placement is an **** and very few people have experience tuning 12A turbos in UK). The two options I'm currently looking at are: Bridgeport the 12A or build a 13b PP using the 12A irons, Racing Beat gslse PP housings and S5 rotating assembly. I understand the first response is going to be "Why not just buy a 13B and work from there?". The answer is, in the UK, S5 engines go for £3k-£4k for a good running block, and for that price I could build a nice BP 12A and have some money left over for extras.
In my mind, the bridgeport is the more economical choice, as I won't need to fully build the engine for high RPMs. Maybe some hardened stat gears and oiling mods, due to it not being a racing application and only occasionally seeing 9,000 RPM on the odd spirited drive. Carbon Apex Seals would be lovely, but I cannot for the life of me find any for the 12A that are produced any more. For the PP, I'd have the rotating assembly balanced and side clearanced so it could withstand up to 10,000 RPM, and carbon seals would still be preferable, but not as necessary thanks to the 13B's 2mm seals being able to take higher RPMs than the 12A's 3mm.
This is just going to be a fun weekend car with the odd track day, so noise and drivability isn't a massive issue. I'm looking to stick to a Weber carb, 48 or 51 IDA depending on the application. I know both will be loud, however, I understand a PP is slightly less tolerant of exhaust backpressure than a BP, so how much louder would it have to be to get some nice power out of it as opposed to the BP? You guys are more experienced than me, so I'd love to hear your opinions on what you'd choose for my situation.
As a sidenote, so far the car has a completely stock drivetrain with a GSL-SE rear end. I know the rear end can take about 300hp max, but this is going to be on street tyres, not launching on sticky drag tyres, so would it hold up alright?
Many thanks
Last edited by Nailhead; 09-19-23 at 04:57 PM.
09-20-23, 07:40 AM
#4
In my opinion, and as I get older, I've realized I'm more than willing to leave some horsepower on the table if it means the car has better manners and is tolerable to drive. I've built cars chasing every last ounce of performance, and in the end, I hated the car. It was too loud, too hot, too painful and I regretted making it more racecar than streetcar. Keep this in mind while trying to wring out as much performance as you can from such a small engine. The compromises might leave you never driving it.
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Richard Miller (09-22-23)
09-20-23, 07:48 AM
#5
Rad Potential's video on street driving a bridgeport shows what you have to put up with.
Realistically think about how often you're going to the track. Quite often people ruin their cars by making them too loud, hard riding, bare interior, etc. but the car ends up being great at the track and nowhere else.
Realistically think about how often you're going to the track. Quite often people ruin their cars by making them too loud, hard riding, bare interior, etc. but the car ends up being great at the track and nowhere else.
09-20-23, 08:52 AM
#6
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if your 12A comes apart, and is in good shape, i think a BP would be easier, you don't need to buy housings, etc.
Carbon seals are NLA from Mazda, not sure what people are using instead
idle for a bridge might need to be a little higher than a PP, but its not hard to get a 900rpm idle in the PP, everyone seems to have this thing about making it idle high, and its not really for a reason
the 48 IDA has a hard time lower than that, it won't transition right.
the noise is a thing, the funny bit is that the exhaust note won't change much, most of the new noise is from the intake. a filter box helps, a lot. if i run mine with an airbox its ok, if i take it off the neighbor comes out holding his head
it will want an exhaust that is sized to make ~250hp with a rotary though, so 70 or 80mm pipe. its also going to be more picky about all the tuning stuff, where you put the collector, mixture, etc. the PP was actually kind of nice to tune, because it only runs in a narrow AFR window, if you're wrong it gets mad at you.
so street BP or PP can, and have been done. it does end up being a hardcore setup, and that is after you've spent a lot of time tuning it, and making it not loud.
but its also really fun.
Carbon seals are NLA from Mazda, not sure what people are using instead
idle for a bridge might need to be a little higher than a PP, but its not hard to get a 900rpm idle in the PP, everyone seems to have this thing about making it idle high, and its not really for a reason
the 48 IDA has a hard time lower than that, it won't transition right.
the noise is a thing, the funny bit is that the exhaust note won't change much, most of the new noise is from the intake. a filter box helps, a lot. if i run mine with an airbox its ok, if i take it off the neighbor comes out holding his head
it will want an exhaust that is sized to make ~250hp with a rotary though, so 70 or 80mm pipe. its also going to be more picky about all the tuning stuff, where you put the collector, mixture, etc. the PP was actually kind of nice to tune, because it only runs in a narrow AFR window, if you're wrong it gets mad at you.
so street BP or PP can, and have been done. it does end up being a hardcore setup, and that is after you've spent a lot of time tuning it, and making it not loud.
but its also really fun.
09-20-23, 02:25 PM
#7
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Thread Starter
That's partially why I'm leaning towards the 13B PP idea. I can buy all the parts beforehand, get the rotating assembly balanced and make sure all my parts are in top shape before I even take the engine out. This takes away a lot of hassle.
Also, you mentioned exhaust sizing. Have you had any experience running a Racing Beat Streetport exhaust with a PP, or would it be preferable to fab up something myself out of 3" tubing?
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09-21-23, 08:48 AM
#8
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FM has one of the older Italian made systems, so not sure what the current one would do.
09-21-23, 09:24 AM
#9
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Thread Starter
09-21-23, 11:25 AM
#10
Rad Potential's video on street driving a bridgeport shows what you have to put up with.
Realistically think about how often you're going to the track. Quite often people ruin their cars by making them too loud, hard riding, bare interior, etc. but the car ends up being great at the track and nowhere else.
https://www.youtube.com/watch?v=61q8tgFsPEI
Realistically think about how often you're going to the track. Quite often people ruin their cars by making them too loud, hard riding, bare interior, etc. but the car ends up being great at the track and nowhere else.
https://www.youtube.com/watch?v=61q8tgFsPEI
This is as much a function of carb and dizzy as it is being fully bridged. So long as you're not running bonkers light rotational assemblies - the real race flywheels with 5.5" multi disk clutches, not the RB/Mazdatrix 9lb hefty stock diameter discs - one can make a very drivable car.
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j9fd3s (09-21-23)
09-21-23, 02:25 PM
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I’m happy to leave some hp on the table for a bit of streetability. I assume, even with the loss, the PP would still make a bit more power than a BP with the same exhaust? For context, I’m working off of Racing Beats HP vs Intake guide for power numbers. They state 300 FWHP for a good PP with open header exhaust, so with the added exhaust restriction, do you have any idea what it would drop the power to?
my idea for the exhaust is to buy some clamps and some tubing, RB sells 4 foot lengths, and some clamps, and then that gives you like 3 different lengths to try on the dyno and just see what it likes.
the competition manuals are here: https://foxed.ca/index.php?page=rx7manual
there are two for the Rx3, and then the Rx7
09-21-23, 02:26 PM
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This is as much a function of carb and dizzy as it is being fully bridged. So long as you're not running bonkers light rotational assemblies - the real race flywheels with 5.5" multi disk clutches, not the RB/Mazdatrix 9lb hefty stock diameter discs - one can make a very drivable car.
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