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Index > Engine/Drivetrain > Thread: Tell me about R5 plates
Thread: Tell me about R5 plates
Crit


Revvin Up
Finally REPUing
Posts: 90
posted May 21, 2005 06:47 PM

Tell me about R5 plates

I have an RX-2 with GSL-SE housings, R5 4-port plates, and an 80 RX-7 transmission. I'm missing the flywheel inspection cover and also want to know about R5 plates. Can someone tell me where they come from (so I know where to look for the cover) or how workable they are?
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77 REPU
84 GSL-SE

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klaus42


Rotorhead
Posts: 1877
posted May 23, 2005 04:17 PM

If I remember corrrectly...:

...they came from the Toyo Kogyo plant in Hiroshima, just like the rest! :b

But seriously-- Not 100% sure, but I think the 'R-5' ones were from '76-'78 Cosmo/rx-4/JDM engines. If they're a dull grey in color with no paint on 'em, they're the nitrided ones... far better durability on the harder surface; apparently even easier to port once the hardened surface is broken through...

That inspection cover shouldn't be all that different; you could always fab a functional plate to cover...

The real question is, what do you have for primaries in your center housing --tall or short ports-- and, does your center housing have the rectangular port that was designed to pre-heat the intake?

Also sounds like you'll be needing to strengthen the rest of your driveline, if you're headed where I think you're talking about with this...

       
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Crit


Revvin Up
Finally REPUing
Posts: 90
posted May 23, 2005 10:42 PM

Well, this drivetrain is in an RX-2, not a REPU. I have R5 irons and GSL-SE housings and looking to figure out what I've got. It's bolted to a 80 RX-7 tranny, but someone else put the powertrain together, so I'm just trying to research what I've got. I'm gonna need to get a 1-piece driveshaft, but I'm currently using an old steel waterpump, Weber 51 w/ extended fuel bowl, and a 83 GSL LSD pumpkin in the original RX-2 axle. I'm still trying to source rebuild parts for my brake booster and master cylinder as well as front suspension bushings, but everything else is on-hand. If y'all know of any nooks and crannies where RX-2 parts might be found, please let me know.

Thanks guys.
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77 REPU
84 GSL-SE

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Crit


Revvin Up
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Posts: 90
posted May 23, 2005 10:54 PM

Oh, and the intermediate plate is marked with "R5" on the backside of the oil filler. The irons, however, are really pretty rusted - more so than I'd expect, but I'll blast and paint everything, but without taking the engine apart (yet)

Pics are here:

http://www.rx7club.com/showthread.php?t=426815
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77 REPU
84 GSL-SE

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Jeff20B


Moderator
Posts: 661
posted May 26, 2005 01:43 PM

Nitrided R5 plates are interesting. They are nitrided which narrows it down to '79 or later. They have a high volume oil pump which we didn't get in an engine until the '83 or '84 12A and GSL-SE. The rear pressure regulator is the non adjustable type, which would mean '81 and later. They came with '80 1st gen RX-7 style electronic distributors (with the ignitor module box over on the inner fender well), but there is no way to know how long Mazda kept this type of dizzy around after 1980. All we know for dizzy history is when the 1st gen RX-7 switched from points to electronic ('80), and then to the next generation dizzy with the igntors on the housing ('81-'85). These engines had cast iron manifolds without an O2 sensor. As far as I know, these are the only 13Bs to ever have this combination because previous engines had a thermal ractor, and later engines such as the GSL-SE and 2nd gen engines had O2 sensors. The shape is also different and will fit fine in a '78 or older chassis, but good luck fitting it in a 1st gen RX-7. There was also no air tube fittings near the exhaust ports like '76-'78 rotor housings had for their thermal reactors, which allows you to use '74-'75 exhaust gaskets and won't leak, and it leads me to believe the nitrided R5 engines had catalytic convertors. 1st gen RX-7s didin't get catalytic convertors untill '81. The oil pans are very similar in shape to REPU pans except they are flat at the gasket surface and are painted inside and out. The bolts they had are the same as 1st gen RX-7 oil pan bolts. Water pumps look the same as any other '85 or older engines, being cast iron, but the pullies are painted sort of a beige tan color. The main drive pulley has an extra dual sheave pulley on it for AC and power steering, and I believe they're the same size as '76-'78 Cosmo pullies. 1st gen RX-7 secondary pullies are larger in diameter.

I've never seen an alternator or intake manifold or carb from a nitrided R5 engine, and have always used '74-'78 manifolds and carbs. As for dizzies and alternators, I tend to go with '81-'85 stuff because I'm into that sort of thing, and it bolts right in.

One way to tell if you've got R5 plates is to look at the rear plate near the oil filter. If it's got a curved rib leading down to the rear dowel pin, it's a nitrided R5. If the rib is missing, it's a R casting from a 1st gen RX-7. If the rib is thick abd the plate has paint on it, it's either a non-nitrided R5 from a '76-'78 Cosmo (RX-4?) or a 3B casting from an REPU. I think the REPU wa the only vehicle that kept the 3B stuff into '76 and '77 because it was a truck and could get away with the larger ported plates when the Cosmo and RX-4 had to switch to the smaller ported R5 plates. Nitrided R5 engines didn't have an oil pressure sender under the oil filter pedestal, or anywhere else as far as I know. It's just an unmachined casting there. The '80 RX-7 also didn't. In order to have oil pressure in my REPU, I drilled and tapped the plate.

Another way to tell is the intermediate plate. If it says R5 or R near the oil filler tube, and has a machined surface with two threaded holes at the top center of the plate, it's from an R5 engine. R5 = rotor housings with three aluminum outcroppings around theh spark plug holes. R = semi-circle spark plug holes like 1st gen RX-7s. If there is a figure 8 pattern around the oil filler tube and the freeze plug, it's a Y casting from a 1st gen RX-7. This was part of Mazda's attempt to lighten the engine by reducing the amount of iron in the plates. I think each plate of a Y casting engine ways like one pound less than an earlier casting. For instance, the earlier castings were just straight up there. If it has NO near the oil filler tube and the top center of the plate has a hole for an EGR valve or port, it came from an EGR (possibly for California emissions) equipt '80 1st gen RX-7 (I'm not sure which other models had this EGR valve). Stay away from NO castings because their ports are pathetically tiny and can't be ported very far. If the plate is not nitrided and has just a blank casting up there, it's from a '76 Cosmo. Also, '76 Cosmo plates had tall intermediate ports, but no EGR port which means you can't install a Cosmo intake manifold on a nitrided R5 engine unless you figure out a way to block the EGR port, or seld some extra material tot he manifold. The REPU/3B plate has a bendable clip on the oil filler tube and a water temp sender in the top center of the plate. It also clearly says 3B near the oil filler tube in the usual spot.

As for the front plate, I'm not as familier with the differences and how to spot them. The water pump must be removed in order to see the letter/number raised letters in the casting. The rear is pretty easy if you remove the top inspection cover. The intermediate can give you the most clues, as discussed above.

Oh, before I forget, if you have access to the rear of an R5 engine and still can't figure out whether it's nitrided or not, simply count the freeze plugs and/or tension bolts. Nitrided engines had only four freeze plugs and 17 tension bolts with two blank castings. The intermediate had all 19 holes, which allows you to mix and match plates pretty easily (and it's great because R5 plates have tall intermediate ports like 1st gen RX-7s and help to reduce reversion for a better idle, and more flow at higher RPM). Non-nitrided R5 castings had five freeze plugs and 18 tension bolts with one blank casting, if I'm not mistaken. I'm not sure how many freeze plugs a 3B plate has, but they had the full 19 tension bolts. Y castings had four freeze plugs, 17 tension bolts and no blank castings. Again, a way to save weight since the casting is basically hollow on the inside without all the internal bracing in those areas since they were not designed for any more than 17 tension bolts.

I'm sure I left out a bunch of information. If you guys are interested in seeing pictures of an R5 engine, check this out. http://www.rx7club.com/forum/showthread.php?t=405995
____________
'74 REPU
'76 Cosmo
'77 MG Midget 13B
'81 RX-7

       
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klaus42


Rotorhead
Posts: 1877
posted May 26, 2005 03:21 PM

Dang, Jeff...

Can you put that all into a concise graph or something...?

Silly Mazda with their ongoing variations...

Crit, if your plates are rusty, odds are they're not nitrided.

       
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Crit


Revvin Up
Finally REPUing
Posts: 90
posted May 26, 2005 03:53 PM

Yeah, I figured that they're not nitrided because of the rust, but it's just a set of irons, as far as I can tell. I'm sure that my housings are from a GSL-SE with the oil injection but with no intake mani coolant passages. Basically, I know that the block isn't original to the car (duh) and has been bastardized as well. I just wanted to know where the irons came from. While I've got the engine out I'll modify a gasket and make sure to port the intake manifold to match the block, so it's not a big deal - I was just curious.
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77 REPU
84 GSL-SE

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klaus42


Rotorhead
Posts: 1877
posted May 26, 2005 04:39 PM

Bastardized vs. 'Fusion' motors:

...some combinations much better than others... GSL-SE housings are definitely the preferred ones; you might have a well-built combo there after all... who built it how long ago, and how well does she run?

       
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Crit


Revvin Up
Finally REPUing
Posts: 90
posted May 26, 2005 04:55 PM

Well, I've driven another 4-port 13B in my old 7 as well as the original 12A, but none of them pulled nearly as hard as this engine does. This one is breathing through a 51 IDA and pulls harder and harder as the revs climb - very unusual feeling. I guess I'm just used to tired motors. I have no idea who built it and I know it's not a bridge, from feeling down the passages, but it's definitely not rough-cast or anything. The front cover and water pump confuse me, as the water pump is steel and the cover is a 81-85 cover. If it didn't drive so well, I'd pull it apart, but I've got enough to do with the body of the car that I'm not anxious to invent problems for myself just yet.
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77 REPU
84 GSL-SE

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klaus42


Rotorhead
Posts: 1877
posted May 26, 2005 05:35 PM

Sounds excellent!

I take it it's equipped with a *proper* RB header, and no-BS exhaust setup... Sounds right-on! Definitely, why mess with success? Care for and enjoy what you've got, while it works well!!!

       
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Crit


Revvin Up
Finally REPUing
Posts: 90
posted May 26, 2005 05:40 PM

Yeah, the exhaust is the old RB Road/Race setup that's no longer made for the RX-2. I'm having the header ceramic coated and added O2 sensor bungs for A/F meter and later for EFI. The primaries have their own parallel silencers that only collect just before the axle. It's a bit loud, but it sure runs great. If one of you guys have painted an assembled block and have any pointers, I'll be jumping on that project here shortly, so any advice will be well-received.
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77 REPU
84 GSL-SE

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klaus42


Rotorhead
Posts: 1877
posted May 29, 2005 11:02 AM

Why EFI...

...an excellent-running 4-port motor that is loving breathing through a 51 IDA ? I wouldn't change that, except maybe tuning it...

       
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