(ENGINE) How to build a high output 12a turbo without blowing up your motor
12-01-04, 01:36 AM
#1
Fabrineer
Thread Starter
(ENGINE) How to build a high output 12a turbo without blowing up your motor
Okay, this is the third time I have taken my engine out and torn it down, and it is starting to get old. Most recently, I was puting out 300+ horsepower at the engine and suffered from loss of compression. When I took the engine out of the car, and tore it down, I found the reason that my compression was low was the corner seal springs were FLAT. The corner seals were essentially not functioning. I wonder how the hell the engine even produced 55 psi of compression! So, I called Racing Beat, and found that they were flattened due to overheating of the rotor. So, now that I am rebuilding my engine for the third time, I have finally found all the things you need to build a 12a with more than 200 horsepower, using forced induction.
The most essential thing needed to keep your engine reliable under these high thermal loads is COOLING!!! I can not stress this enough! The reason my springs flattened was because of the high heat caused by compressing air in the engine, and further compressed by the rather high 9.4:1 rotors (not exactly thermally efficient for a forced induction engine). This causes the seals to anneal, softening them, and basically weakening them. To counteract this, you need to keep the inside of the engine cool.
Here is your "shopping list" for a successful, reliable, streetable, high output (above 200 hp) 12a:
1) Bigger oil pump. The GSL-SE oil pump bolts right up and is much larger. This is the most important thing you can do to keep your engine running strong
2) Higher oil pressure regulator from Racing Beat (85psi). This actually increases the volume of oil shot into the rotors. This, coupled with the oil pump, is enough to keep the rotors cool to about the 400 horsepower region.
3) Larger water pump from a S4 13b. There is going to be modification needed in order for this to fit. What you do is tap out the hole that is not used by the 12a with a 3/8 diameter tap (thread pitch doesnt matter). There is no need to drill out the hole. Then, buy a 3/8 diameter stud, thread it in, put a few washers on, then your alternator bracket, then your nut. Make sure it doesnt hit the alt belt!! If you fail to put this bolt in, it will leak, even with silicone sealant (it happened to me!).
4) Aluminum radiator from a s4/s5 car. This is essential to keeping the engine cool under its higher thermal loads. there is not enough room to describe all the mods needed to fit this, so if you have the know how, you can figure it out. If you have the money, you can buy a different radiator that drops right in.
5) 3rd gen corner seal springs. They are stronger and resist the higher heat from more horsepower better.
6) Lapped side housings. This helps the corner seals seal properly, which are extremely important in sart up and low speed operation.
7) Recommended/optional: Beefed up rear cast plate. The 12a's rear cast plate will break at approximately 350-400 hp and earlier if your engine is detonated (i broke mine at 250 hp under detonation). The 74 Us spec and 76 J-spec rear cast plate from a 13b has extra reinforcement around the dowel pin. With this mod, your engine should (debatable) be able to take in excess of 500 horsepower without breaking. This is an extremely cheap alternative to dowel pinning/tension rodding.
What is needed for high RPM (above 7500 RPM and below 8,500 RPM) operation:
Contrary to popular belief, our 12a's really wont servive for long if taken above 7500 RPM. This is due to their closer tolerances between the rotor face and the side housing, as well as the rotor "land" (the rotor gear on one side, the ring on the other side) and the side housing. The newer engines (86 and newer) have more clearence, so when the eccentric shaft begins to flex, the rotor does not make destructive contact or even get as close (which can possibly damage the corner seals or flatten the springs). Also, the oiling system can not support the higher RPM's.
For this high RPM operation, you need:
1) Hardened stationary gears. The rear stationary gear should have the 3 window race bearing installed. This prevents the rotors from "walking" as much.
2) GSL-SE oil pump. (you need that flow!!!)
3) High pressure oil regulator (good for keeping the rotors on the film of oil under the higher RPM stress)
4) Recommended: race clearence the rotors.
These mods will keep your 12a safe up to 8,500 RPMs, where your stock seals will no longer seal effectively and will create detrimental damage to the aluminum housings caused by chattering. I personally have taken my 12a to 11,000 RPM and kept it there (not on purpose) for around 15 seconds. After I tore it down a few thousand miles later (only because I cracked my rear cast plate from detonation), I found that the Eccentric shaft had actually touched the front and rear stationary gear bearings. It gouged them pretty badly. A few more thousand miles, and I would have had serious troubles!
The best thing to remember with the 12a's is that they are old technology, and they were not built with the intention of being boosted to 3 times their horsepower. If these steps are followed, then a powerful, reliable motor will be yours!
The pictures show the additional ribbing on the rear dowel pin, all my engine goodies, as well as the brand new design for the 12a apex seals. Mazda seals rock!!! I don't recommend aftermarket stock replacements, these seals are a much higher technology than anything i've seen (other than the ceramic seals, of course).
Well, I can't think of anything else to write on, so if you guys have any questions or comments, please reply!
The most essential thing needed to keep your engine reliable under these high thermal loads is COOLING!!! I can not stress this enough! The reason my springs flattened was because of the high heat caused by compressing air in the engine, and further compressed by the rather high 9.4:1 rotors (not exactly thermally efficient for a forced induction engine). This causes the seals to anneal, softening them, and basically weakening them. To counteract this, you need to keep the inside of the engine cool.
Here is your "shopping list" for a successful, reliable, streetable, high output (above 200 hp) 12a:
1) Bigger oil pump. The GSL-SE oil pump bolts right up and is much larger. This is the most important thing you can do to keep your engine running strong
2) Higher oil pressure regulator from Racing Beat (85psi). This actually increases the volume of oil shot into the rotors. This, coupled with the oil pump, is enough to keep the rotors cool to about the 400 horsepower region.
3) Larger water pump from a S4 13b. There is going to be modification needed in order for this to fit. What you do is tap out the hole that is not used by the 12a with a 3/8 diameter tap (thread pitch doesnt matter). There is no need to drill out the hole. Then, buy a 3/8 diameter stud, thread it in, put a few washers on, then your alternator bracket, then your nut. Make sure it doesnt hit the alt belt!! If you fail to put this bolt in, it will leak, even with silicone sealant (it happened to me!).
4) Aluminum radiator from a s4/s5 car. This is essential to keeping the engine cool under its higher thermal loads. there is not enough room to describe all the mods needed to fit this, so if you have the know how, you can figure it out. If you have the money, you can buy a different radiator that drops right in.
5) 3rd gen corner seal springs. They are stronger and resist the higher heat from more horsepower better.
6) Lapped side housings. This helps the corner seals seal properly, which are extremely important in sart up and low speed operation.
7) Recommended/optional: Beefed up rear cast plate. The 12a's rear cast plate will break at approximately 350-400 hp and earlier if your engine is detonated (i broke mine at 250 hp under detonation). The 74 Us spec and 76 J-spec rear cast plate from a 13b has extra reinforcement around the dowel pin. With this mod, your engine should (debatable) be able to take in excess of 500 horsepower without breaking. This is an extremely cheap alternative to dowel pinning/tension rodding.
What is needed for high RPM (above 7500 RPM and below 8,500 RPM) operation:
Contrary to popular belief, our 12a's really wont servive for long if taken above 7500 RPM. This is due to their closer tolerances between the rotor face and the side housing, as well as the rotor "land" (the rotor gear on one side, the ring on the other side) and the side housing. The newer engines (86 and newer) have more clearence, so when the eccentric shaft begins to flex, the rotor does not make destructive contact or even get as close (which can possibly damage the corner seals or flatten the springs). Also, the oiling system can not support the higher RPM's.
For this high RPM operation, you need:
1) Hardened stationary gears. The rear stationary gear should have the 3 window race bearing installed. This prevents the rotors from "walking" as much.
2) GSL-SE oil pump. (you need that flow!!!)
3) High pressure oil regulator (good for keeping the rotors on the film of oil under the higher RPM stress)
4) Recommended: race clearence the rotors.
These mods will keep your 12a safe up to 8,500 RPMs, where your stock seals will no longer seal effectively and will create detrimental damage to the aluminum housings caused by chattering. I personally have taken my 12a to 11,000 RPM and kept it there (not on purpose) for around 15 seconds. After I tore it down a few thousand miles later (only because I cracked my rear cast plate from detonation), I found that the Eccentric shaft had actually touched the front and rear stationary gear bearings. It gouged them pretty badly. A few more thousand miles, and I would have had serious troubles!
The best thing to remember with the 12a's is that they are old technology, and they were not built with the intention of being boosted to 3 times their horsepower. If these steps are followed, then a powerful, reliable motor will be yours!
The pictures show the additional ribbing on the rear dowel pin, all my engine goodies, as well as the brand new design for the 12a apex seals. Mazda seals rock!!! I don't recommend aftermarket stock replacements, these seals are a much higher technology than anything i've seen (other than the ceramic seals, of course).
Well, I can't think of anything else to write on, so if you guys have any questions or comments, please reply!
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RX7BRUG (11-30-22)
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12-01-04, 02:00 AM
#3
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NOOB QUESTION!!
How do you do FI on a 12A without the middle iron having injector bungs? Do you usse an SE iron, or just big injectors in the manifold, or what?
How do you do FI on a 12A without the middle iron having injector bungs? Do you usse an SE iron, or just big injectors in the manifold, or what?
12-01-04, 06:12 AM
#6
My wife bought me 2 RX-7s
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I agree with the sentiment about the Mazda seals. If I'm not mistaken, all Mazda seals now use the RX-8 design, wich is supposed to be much better in terms of sealing and longevity.
12-01-04, 07:20 AM
#7
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That's are all good ideas but I don't quite get something. You stated that the reason for the corner seal springs flattening was high thermal stress within the engine. The problem is none of these fixes seem to address that! You can do all the cooling and oil mods you want but that won't significantly change the heat caused during combustion. For that you need to concentrate on intercooling, correct turbo sizing for your intended hp level, correct a/f ratio and ignition timing, sufficient oil injection etc. Also, water injection is a great way of reducing thermal/mechanical stress in the engine.
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12-01-04, 07:25 AM
#8
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Originally Posted by shm21284
1) Hardened stationary gears. The rear stationary gear should have the 3 window race bearing installed. This prevents the rotors from "walking" as much.
12-01-04, 08:24 AM
#9
Fabrineer
Thread Starter
Originally Posted by REVHED
That's are all good ideas but I don't quite get something. You stated that the reason for the corner seal springs flattening was high thermal stress within the engine. The problem is none of these fixes seem to address that! You can do all the cooling and oil mods you want but that won't significantly change the heat caused during combustion. For that you need to concentrate on intercooling, correct turbo sizing for your intended hp level, correct a/f ratio and ignition timing, sufficient oil injection etc. Also, water injection is a great way of reducing thermal/mechanical stress in the engine.
12-01-04, 08:26 AM
#10
Fabrineer
Thread Starter
Originally Posted by REVHED
What do you mean exactly? I know of rotor gears "walking" which is solved by machining the rotor to accept a circlip which retains the gear in the rotor. I'm not sure what 3 window bearings have to do with this as they simply provide better lubrication.
12-01-04, 08:27 AM
#11
Fabrineer
Thread Starter
Originally Posted by Tanjo
NOOB QUESTION!!
How do you do FI on a 12A without the middle iron having injector bungs? Do you usse an SE iron, or just big injectors in the manifold, or what?
How do you do FI on a 12A without the middle iron having injector bungs? Do you usse an SE iron, or just big injectors in the manifold, or what?
I used throttle body injection. You can see the throttle body with injector bungs in the lower left corner of the picture of all my engine stuff. go to www.tweakit.net/shop for throttle body kits. It is under the intake category.
12-01-04, 09:24 AM
#12
Did anybody else notice that there are *four* rotors in that first picture 
Building a monster behind our backs eh shm?
Good writeup. I didn't know the GSL-SE oil pump bolted right up. I'd say that and the pressure reg are good upgrades for any 12a engine builder, because oil does it's share of cooling as well as lubricating when it comes to the shaft IIRC.
Jon
Building a monster behind our backs eh shm?
Good writeup. I didn't know the GSL-SE oil pump bolted right up. I'd say that and the pressure reg are good upgrades for any 12a engine builder, because oil does it's share of cooling as well as lubricating when it comes to the shaft IIRC.
Jon
12-01-04, 09:56 AM
#14
Tennis, anyone
over-boosting the 12a will always result in rebuilds often. the 12a is not designed
for that kind of internal stress, and live. i'll hand it to 'ya for the R&D and where one area is beefed up the next in line will fail. it's a step by step re-design as area's fail.
there is nothing wrong with trying to make the little 12a a fire breathing monster but the key for the engine to live under those conditions, well it's still aways to go.
you might try(if you can afford it) is a dry sump oiling system. it seems anything internal doesn't quit cut-it. a large amount of oil, and a remote tank, a large air-to-air oil cooler(s) a hi-volume pump vs a hi-presure pump and mod. the oil passages of the entire engine not just the housings but the moving parts. isn't that how the real race 12a's of there hey-day were designed untill switching to the 13b for strenght. i've got an old rx7 performance book and in it mariah talks about the 12a's and dry sumps. something to consider.
for that kind of internal stress, and live. i'll hand it to 'ya for the R&D and where one area is beefed up the next in line will fail. it's a step by step re-design as area's fail.
there is nothing wrong with trying to make the little 12a a fire breathing monster but the key for the engine to live under those conditions, well it's still aways to go.
you might try(if you can afford it) is a dry sump oiling system. it seems anything internal doesn't quit cut-it. a large amount of oil, and a remote tank, a large air-to-air oil cooler(s) a hi-volume pump vs a hi-presure pump and mod. the oil passages of the entire engine not just the housings but the moving parts. isn't that how the real race 12a's of there hey-day were designed untill switching to the 13b for strenght. i've got an old rx7 performance book and in it mariah talks about the 12a's and dry sumps. something to consider.
12-01-04, 10:54 AM
#18
Originally Posted by shm21284
2) Higher oil pressure regulator from Racing Beat (85psi). This actually increases the volume of oil shot into the rotors. This, coupled with the oil pump, is enough to keep the rotors cool to about the 400 horsepower region.
3) Larger water pump from a S4 13b. There is going to be modification needed in order for this to fit. What you do is tap out the hole that is not used by the 12a with a 3/8 diameter tap (thread pitch doesnt matter). There is no need to drill out the hole. Then, buy a 3/8 diameter stud, thread it in, put a few washers on, then your alternator bracket, then your nut. Make sure it doesnt hit the alt belt!! If you fail to put this bolt in, it will leak, even with silicone sealant (it happened to me!).
(5) 3rd gen corner seal springs. They are stronger and resist the higher heat from more horsepower better.
6) Lapped side housings. This helps the corner seals seal properly, which are extremely important in sart up and low speed operation.
3) Larger water pump from a S4 13b. There is going to be modification needed in order for this to fit. What you do is tap out the hole that is not used by the 12a with a 3/8 diameter tap (thread pitch doesnt matter). There is no need to drill out the hole. Then, buy a 3/8 diameter stud, thread it in, put a few washers on, then your alternator bracket, then your nut. Make sure it doesnt hit the alt belt!! If you fail to put this bolt in, it will leak, even with silicone sealant (it happened to me!).
(5) 3rd gen corner seal springs. They are stronger and resist the higher heat from more horsepower better.
6) Lapped side housings. This helps the corner seals seal properly, which are extremely important in sart up and low speed operation.
3) used to keep the "cast, aluminum, cast" theme going.
5) i put these in my rebuild just cause they're stronger than the stock "wire" style corner springs of the early engines.
6) should be done with any rebuild.
12-01-04, 11:23 AM
#19
Fabrineer
Thread Starter
Finished product wont be done for another month, when I get my aluminum housings returned from being ceramic coated.
The GSL-SE oil pump is just a higher volume pump. It's 17.5 mm instead of the standard 12 mm or so for the 12a. It does bolt right up. The 86 and newer oil pumps are monsters in comparison, and do not bolt right up.
Also, when I spoke to Racing Beat, they said that the GSL-SE pump with higher pressure will suffice for the 3-400 hp range. Mazdatrix recommended that I port out the intake and pickup in the front cast plate for the oil system. I also am going to remove the plug in the pressurized side of the oil system just after the pump, and clean out and port out that passage.
The GSL-SE oil pump is just a higher volume pump. It's 17.5 mm instead of the standard 12 mm or so for the 12a. It does bolt right up. The 86 and newer oil pumps are monsters in comparison, and do not bolt right up.
Also, when I spoke to Racing Beat, they said that the GSL-SE pump with higher pressure will suffice for the 3-400 hp range. Mazdatrix recommended that I port out the intake and pickup in the front cast plate for the oil system. I also am going to remove the plug in the pressurized side of the oil system just after the pump, and clean out and port out that passage.
12-01-04, 12:17 PM
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Do I need to seriously consider never turboing my 12A if I don't plan to rebuild first? I was thinking there are guys here who have done exactly that with no problems so far. Maybe they are only pushing at best 200hp. If 200hp (S4 turbo with like 8-10psi max) is the most I push through it, would my engine still be at risk of detenation?
I thought the 12A's only had like 8.5:1 rotors (er, somewhere around that #)
I thought the 12A's only had like 8.5:1 rotors (er, somewhere around that #)
12-01-04, 12:37 PM
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Originally Posted by shm21284
1) Bigger oil pump. The GSL-SE oil pump bolts right up and is much larger. This is the most important thing you can do to keep your engine running strong
Thanks,
Mark