13b 4 port (carb)
04-23-05, 01:24 AM
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13b 4 port (carb)
Hi i have a 13b 4 port carburated engine that I got from my friend.
Can someone give me some tips on finding the year of this engine or where it came from.
Thx
Can someone give me some tips on finding the year of this engine or where it came from.
Thx
04-23-05, 02:40 AM
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The 4 port 13B was manufactured between 1974 and 1978, and was used to power the RX-4, RX-5 and Rotary Pick-up. A few were subsequently manufactured as replacement engines with the vast majority being 'remanufactured' These were often made up of components from different batches as the parts were interchangable.
While the engines were numbered, unlike body numbers no definitive list was ever published. But you probably have a 1976 engine from a RX-4 as the most likely guess.
While the engines were numbered, unlike body numbers no definitive list was ever published. But you probably have a 1976 engine from a RX-4 as the most likely guess.
04-23-05, 03:23 AM
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Jeff20B- your write up on what you are doing to the 13B 4port was excellent. As you are the expert on the engine, I know very few 5s were imported as they were a marketing flop, but have many people imported the used engine? At one time it was suggested I import a half cut, port and refresh, then go IDA.
04-23-05, 10:30 AM
#5
I prefer the 79+ 12-A plates over R5 due to its small intake ports. when it comes to the old 13-B 4ports, I prefer the 76 blocks especially the Cosmo due to tall primary intake prots. Maybe if I find the time this weekend, I will take pics of the old R5 plates and the 12-A for comparison.
04-23-05, 05:08 PM
#6
wacky, I think it goes without saying that I prefer the nitrided R5 plates because they have tall intermediate ports and were nitrided. 
They also have a high volume (17.5mm) oil pump. The only things that need to be dealt with on those engines are the rear pressure reg because it has a non adjustable one, and there is no oil pressure guage sender threaded hole under the oil filter. Check out my write up, as Paul mentioned, for pictures and interesting info on these oddball engines.
Paul, I don't know if nitrided R5 13Bs were in '79+ Cosmos. I've got a '76 cosmo and it's got an unnitrided R5 13B with tall intermediate ports and no EGR port. All nitrided R5s had an EGR port, just like catalytic converter equipped 1st gens. Infact, mine has an REPU intake manifold complete with port mismatch in the correct FB style, an EGR blockoff plate, and the runners resemble other early manifolds so you know it outflows any 1st gen manifold (teehee). Also the stock exhaust manifold was meant for a catalytic convertor. I'm pretty sure it's more or less the same engine Mazda would have used in 1st gens if a carbed 13B was ever a choice in that chassis. Too bad it wasn't.
They also have a high volume (17.5mm) oil pump. The only things that need to be dealt with on those engines are the rear pressure reg because it has a non adjustable one, and there is no oil pressure guage sender threaded hole under the oil filter. Check out my write up, as Paul mentioned, for pictures and interesting info on these oddball engines.Paul, I don't know if nitrided R5 13Bs were in '79+ Cosmos. I've got a '76 cosmo and it's got an unnitrided R5 13B with tall intermediate ports and no EGR port. All nitrided R5s had an EGR port, just like catalytic converter equipped 1st gens. Infact, mine has an REPU intake manifold complete with port mismatch in the correct FB style, an EGR blockoff plate, and the runners resemble other early manifolds so you know it outflows any 1st gen manifold (teehee). Also the stock exhaust manifold was meant for a catalytic convertor. I'm pretty sure it's more or less the same engine Mazda would have used in 1st gens if a carbed 13B was ever a choice in that chassis. Too bad it wasn't.
04-23-05, 08:20 PM
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Jeff. It was really strange Mazda did not offer the 13B 4 port carby as an option right from the start. The press in 1977 were being advised the new car was to be powered by the 13B.
I have read everything around on the development of the RX-7. and the emphasis was on the body design[marketing] and keeping costs down[accounting].
Apart from brief mention of fuel consumption there is little public informationon why the 12A was selected.
Reading between the lines, I think the decision was really based on the little peak power difference between the two carby engines, 110 versus 100. In the case of the RX-5 which was heavier, the 13B 120lb-ft torque was significant. Certainly in 1977 Mazda were experimenting with an efi 13B using Bosch electronics and another with NipponDenso equipment. It was thought an efi would be ready for production in 1981. The marketing concept was to launch with the 12A, then after two years revitalize sales with a significantly more powerful 13B efi version. In the end the efi was 5 years later, with the 12A efi only coming out in the turbo version. It could also have been a bit of internal rivalry as they wanted to keep the Cosmo as the fastest Japanese production car.
Thus, the Mazda lost the chance to have a great 13B 4 port RX-7. Interestingly what you are now doing was being offered as early as 1982 by several tuners using twin Webber 45 DCOs, but without improved ignition.
I made one oversight on cars getting the 13B, the Roadpacer was sold in Australia as a GM/Mazda project in competition with the non-rotary 929.
Now, if Mazda had gone ahead in 1977 with producing the 15A that would have been a real RX-7!
I have read everything around on the development of the RX-7. and the emphasis was on the body design[marketing] and keeping costs down[accounting].
Apart from brief mention of fuel consumption there is little public informationon why the 12A was selected.
Reading between the lines, I think the decision was really based on the little peak power difference between the two carby engines, 110 versus 100. In the case of the RX-5 which was heavier, the 13B 120lb-ft torque was significant. Certainly in 1977 Mazda were experimenting with an efi 13B using Bosch electronics and another with NipponDenso equipment. It was thought an efi would be ready for production in 1981. The marketing concept was to launch with the 12A, then after two years revitalize sales with a significantly more powerful 13B efi version. In the end the efi was 5 years later, with the 12A efi only coming out in the turbo version. It could also have been a bit of internal rivalry as they wanted to keep the Cosmo as the fastest Japanese production car.
Thus, the Mazda lost the chance to have a great 13B 4 port RX-7. Interestingly what you are now doing was being offered as early as 1982 by several tuners using twin Webber 45 DCOs, but without improved ignition.
I made one oversight on cars getting the 13B, the Roadpacer was sold in Australia as a GM/Mazda project in competition with the non-rotary 929.
Now, if Mazda had gone ahead in 1977 with producing the 15A that would have been a real RX-7!
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04-24-05, 03:20 AM
#8
Oh man, the 15A is the stuff dreams are made of! The only way any of us can experience more displacement than a 13B has to offer is with a 20B or 26B. Of course the added weight and length can get in a way. A 15a is only 20mm longer than a 13B and would be a peice of cake to fit into an REPU, Cosmo, RX-4 etc similar to going from a 12A to 13B in a 12A chassis like the 1st gen. Of course the torque won't be nearly as high as a 20B, but that's what forced induction is for.
As for the nitrided R5 engines, probably the best way to determine aproximately when they were produced is to find out when Mazda went to a 17.5mm oil pump and a non-adjustable rear pressure reg. The three oil pump sizes that are interchangeable on all '85 and older front plates are 12mm, 15mm and 17.5mm. Accurately determining the years each large size increase was introduced would be helpful.
Having an exhaust manifold with no O2 sensor tells me that R5 13Bs were carbed with a catalytic convertor. My question for some of you more knowledgeable types with '76-'80 engines is about the EGR ports, or lack thereof under the intermediate plates. Those engines had a thermal reactor and air holes under the exhaust ports. The nitrided R5 rotor housings were a similar casting and had this air hole, but it was blocked by an aluminum plug. This allows the use of '74-'75 exhaust gaskets which lack any kind of support for an air hole (I'd be affraid to use one of these gaskets on '76 style rotor housings for fear of leaks). There is a tube that sticks up in the exhaust port and it communicates with the EGR cavity in the intermediate plate. I simply grind the tube down flush instead of welding it closed because I have a crummy flux core welder and my '74-'75 intake manifolds cover the EGR port. An ACV block off plate seals the deal. I'm sure the manifold would be cooler if I did weld the tubes closed after grinding them down, but if I was worried about manifold heating, I'd add a couple 20mm freeze plugs to the rotor housings. The very earliest '74-'75 REPU and RX-4 13B gasket set from Mazdatrix is perfect for these engines.
As for the nitrided R5 engines, probably the best way to determine aproximately when they were produced is to find out when Mazda went to a 17.5mm oil pump and a non-adjustable rear pressure reg. The three oil pump sizes that are interchangeable on all '85 and older front plates are 12mm, 15mm and 17.5mm. Accurately determining the years each large size increase was introduced would be helpful.
Having an exhaust manifold with no O2 sensor tells me that R5 13Bs were carbed with a catalytic convertor. My question for some of you more knowledgeable types with '76-'80 engines is about the EGR ports, or lack thereof under the intermediate plates. Those engines had a thermal reactor and air holes under the exhaust ports. The nitrided R5 rotor housings were a similar casting and had this air hole, but it was blocked by an aluminum plug. This allows the use of '74-'75 exhaust gaskets which lack any kind of support for an air hole (I'd be affraid to use one of these gaskets on '76 style rotor housings for fear of leaks). There is a tube that sticks up in the exhaust port and it communicates with the EGR cavity in the intermediate plate. I simply grind the tube down flush instead of welding it closed because I have a crummy flux core welder and my '74-'75 intake manifolds cover the EGR port. An ACV block off plate seals the deal. I'm sure the manifold would be cooler if I did weld the tubes closed after grinding them down, but if I was worried about manifold heating, I'd add a couple 20mm freeze plugs to the rotor housings. The very earliest '74-'75 REPU and RX-4 13B gasket set from Mazdatrix is perfect for these engines.
