half bridge 12A, with a twist
Thread Starter
Joined: Aug 2001
Posts: 15,725
Likes: 91
From: Near Seattle
R5 is a set of raised characters on the front, intermediate and rear plates. The SA22C engines got R5 plates, but US-spec rotor housings (with thermal reactor ports) and 76-82 rotating assemblies with the half circle front counterweight and the small 12mm oil pump.
When I refer to modern R5 engines, they're the J-spec engines with a 17.5mm oil pump and oddball rotor housings set up for catalytic convertors. The rotating assemblies are probably the same as SA22C engines with the half circle front counterweight, but on this half BP R5, I swapped in an 81-82 front counterweight and will be swapping on an 81-82 flywheel today with a brand new clutch and pressure plate.
I'd been test running it with a 76-82 auto rear counterweight and my aluminum flywheel to put to rest all that talk about needing a stock flywheel with a half BP. Aluminum was just fine on this setup. But it does brap a little under light decel so a stock flywheel will make it that much more pleasant to drive. Every other driving condition was fine. Especially acceleration which the aluminum flywheel accels at. The nice part about going stock is the 81-82 stock flywheels are only 23 pounds, the lightest of all the 1st gens.
When I refer to modern R5 engines, they're the J-spec engines with a 17.5mm oil pump and oddball rotor housings set up for catalytic convertors. The rotating assemblies are probably the same as SA22C engines with the half circle front counterweight, but on this half BP R5, I swapped in an 81-82 front counterweight and will be swapping on an 81-82 flywheel today with a brand new clutch and pressure plate.
I'd been test running it with a 76-82 auto rear counterweight and my aluminum flywheel to put to rest all that talk about needing a stock flywheel with a half BP. Aluminum was just fine on this setup. But it does brap a little under light decel so a stock flywheel will make it that much more pleasant to drive. Every other driving condition was fine. Especially acceleration which the aluminum flywheel accels at. The nice part about going stock is the 81-82 stock flywheels are only 23 pounds, the lightest of all the 1st gens.
Thread Starter
Joined: Aug 2001
Posts: 15,725
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From: Near Seattle
with the P port the intake flange is like 1/8" away from the header flange, so intake temp changes a LOT, i did wrap the intake right at the motor and this helped, but it still kind of does it. after a little drive, the intake will be cold to the touch by the carb, but hot to the touch by the engine.
and the weber doesn't have an air temp compensation map.
so for me its a tuning thing, it feels like the idle is a little lean too
and the weber doesn't have an air temp compensation map.
so for me its a tuning thing, it feels like the idle is a little lean too
The idle does like to be rich, doesn't it.
Joined: Mar 2001
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From: https://www2.mazda.com/en/100th/
Thread Starter
Joined: Aug 2001
Posts: 15,725
Likes: 91
From: Near Seattle
I guess what I meant to say there was they like it when you give them fuel, at idle. The air screw is almost all the way in. It seems like it's too rich, and maybe it is, but it runs best.
Joined: Mar 2001
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From: https://www2.mazda.com/en/100th/
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From: vermont
I only let them sit so the sealant has time to set up before I let oil contact it, that's all.
My first engine (ten years ago last month) was with Hylomar and a Mazda engine gasket set, everything after that has been electric wire and Right Stuff. Although, I didn't do another engine until 2006 or so, whenever p-port phase 1 was completed.
After last year's plethora of engine rebuilds, I'm good and sick of trying to clean Right Stuff off of housings. Takes forever, requires lots of elbow grease and usually destroys a few wire brushes in the process. I'm going to try Hylomar and Viton cord now. Bought a bunch of it, made cutting guides out of 3/16" brake line just like we have at the machine shop for exact-fit cutting of stainless wire for block O-ringing.
My first engine (ten years ago last month) was with Hylomar and a Mazda engine gasket set, everything after that has been electric wire and Right Stuff. Although, I didn't do another engine until 2006 or so, whenever p-port phase 1 was completed.
After last year's plethora of engine rebuilds, I'm good and sick of trying to clean Right Stuff off of housings. Takes forever, requires lots of elbow grease and usually destroys a few wire brushes in the process. I'm going to try Hylomar and Viton cord now. Bought a bunch of it, made cutting guides out of 3/16" brake line just like we have at the machine shop for exact-fit cutting of stainless wire for block O-ringing.
Congrats Jeff on getting this experiment together. It would be interesting if you had 2 intake manifolds, one with communication between the secondary ports only and one with out. I'm very curious how much difference there would be between the 2. how much affect would the dynamic effect have? I know you love your old school Nikkiis and Hitachis, (and manifolds, lol), but when you get around to building your personal 1/2 sp-1/2 bp, try to find a set of the RE DCD twin Webers. The venturi in those for the 13B are 28 primary, 36 secondary, 25/32 for the 12A. Going from the Mikuni 44 PHH to the DCDs on my 1/2sp-1/2bp saved the widebody. It was miserable to drive with the Mikuni. Seperating out the intake runners makes an unbelievable difference in driving manners and put the fun back into the 7.
With a steel flywheel and the short rear gears in the manual tranny REPU, it should have excellant manners along with towing ability with a divided runner mani and 1/2sp-1/2bp porting.
With a steel flywheel and the short rear gears in the manual tranny REPU, it should have excellant manners along with towing ability with a divided runner mani and 1/2sp-1/2bp porting.
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From: Yaizu, Japan
Thread Starter
Joined: Aug 2001
Posts: 15,725
Likes: 91
From: Near Seattle
You're welcome. I hope you're getting excited!
It likes to idle best around 1100 once warmed up. The part you saw in the video is with the choke still on (that's why it went to a lower RPM when I pushed the choke in and gave it a quick rev, because it wasn't fully warmed up yet).
It takes a little technique to get it started. Turn on key to ON position (fuel pump will run). Pull the choke, couple of pedal pumps to get some accel shot in there. Crank around 3 or 4 seconds and then it starts to want to fire (for me, in this car, with my exhaust system anyway, as yours will be different). Then it takes some feathering of the gas pedal while pulling the choke to a good position to allow it to run without stalling. I find that 3k RPM works for the first few seconds of run time, then try to lower it as soon as you can. Any lower RPM in these first few seconds and it'll tend to stall. This may be due to the half BPs or that it's a fresh rebuild and could improve over time as it breaks in. After that I like to let the choke in a little and keep attention on the gas pedal and tach to around 2k because I don't like high revs on a cold engine. After maybe a minute it can go down to 1500ish, depending on ambient temps. This technique worked for me in my car for the first four heat cycles. You may find a better technique as it breaks in more.
By the way I recommend 20w50 oil as it's got a lot of bearing clearance being an R5, which is great for high RPM (but please keep it at 8k and below as the apex seals are 3mm). I'm going to drain out the break in oil so it won't spill during transport. Please refill with 20w50 Castrol GTX or similar. Please do not use Fram oil filters. Get a Napa Gold 1347 (tall) or 1334 (medium). Don't bother with the small FD 3rd gen size filters.
It likes to idle best around 1100 once warmed up. The part you saw in the video is with the choke still on (that's why it went to a lower RPM when I pushed the choke in and gave it a quick rev, because it wasn't fully warmed up yet).
It takes a little technique to get it started. Turn on key to ON position (fuel pump will run). Pull the choke, couple of pedal pumps to get some accel shot in there. Crank around 3 or 4 seconds and then it starts to want to fire (for me, in this car, with my exhaust system anyway, as yours will be different). Then it takes some feathering of the gas pedal while pulling the choke to a good position to allow it to run without stalling. I find that 3k RPM works for the first few seconds of run time, then try to lower it as soon as you can. Any lower RPM in these first few seconds and it'll tend to stall. This may be due to the half BPs or that it's a fresh rebuild and could improve over time as it breaks in. After that I like to let the choke in a little and keep attention on the gas pedal and tach to around 2k because I don't like high revs on a cold engine. After maybe a minute it can go down to 1500ish, depending on ambient temps. This technique worked for me in my car for the first four heat cycles. You may find a better technique as it breaks in more.
By the way I recommend 20w50 oil as it's got a lot of bearing clearance being an R5, which is great for high RPM (but please keep it at 8k and below as the apex seals are 3mm). I'm going to drain out the break in oil so it won't spill during transport. Please refill with 20w50 Castrol GTX or similar. Please do not use Fram oil filters.
Get a Napa Gold 1347 (tall) or 1334 (medium). Don't bother with the small FD 3rd gen size filters.
I had a lot of catching up to do on this thread. It sounds good! Has a nice beat to it. Your cold start up procedure sounds eerily similar to mine, and my engine has stock ports.
Then with fully warmed up oil (190F-200F) at below 1k we have 10psi. That's a little lower than I would have liked to see, but on the upside, I've had two other R5 engines that read the same ie 10psi at a really low idle, or 15psi above 1k. This half BP tends to idle best with a little brap at 1100, oil pressure is around 15psi. Then you rev it and the oil needle jumps up quick, basically matching RPM almost to a T. 
The L.Hanover trick of removing the oil pickup tube screen, brazing a washer on and putting some nice curves on it helps too. It was a fun project. Some fine detail grinding in the oil filter adapter area helps too....
Nice job either way Jeff, bridgeports add to the fun factor.
Old [Sch|F]ool
Joined: May 2001
Posts: 12,865
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From: Cleveland, Ohio, USA
You don't need to do all that work to the pickup, it flares very easily.
I prefer to leave the screen on, though, ever since the time I was adding oil and the little cardboard disk from the oil bottle fell straight down the funnel and into the engine, necessitating an emergency oilpanotomy.
I prefer to leave the screen on, though, ever since the time I was adding oil and the little cardboard disk from the oil bottle fell straight down the funnel and into the engine, necessitating an emergency oilpanotomy.
Joined: Mar 2001
Posts: 31,835
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From: https://www2.mazda.com/en/100th/
You're welcome. I hope you're getting excited!
It likes to idle best around 1100 once warmed up. The part you saw in the video is with the choke still on (that's why it went to a lower RPM when I pushed the choke in and gave it a quick rev, because it wasn't fully warmed up yet).
It takes a little technique to get it started. Turn on key to ON position (fuel pump will run). Pull the choke, couple of pedal pumps to get some accel shot in there. Crank around 3 or 4 seconds and then it starts to want to fire (for me, in this car, with my exhaust system anyway, as yours will be different). Then it takes some feathering of the gas pedal while pulling the choke to a good position to allow it to run without stalling. I find that 3k RPM works for the first few seconds of run time, then try to lower it as soon as you can. Any lower RPM in these first few seconds and it'll tend to stall. This may be due to the half BPs or that it's a fresh rebuild and could improve over time as it breaks in. After that I like to let the choke in a little and keep attention on the gas pedal and tach to around 2k because I don't like high revs on a cold engine. After maybe a minute it can go down to 1500ish, depending on ambient temps. This technique worked for me in my car for the first four heat cycles. You may find a better technique as it breaks in more.
By the way I recommend 20w50 oil as it's got a lot of bearing clearance being an R5, which is great for high RPM (but please keep it at 8k and below as the apex seals are 3mm). I'm going to drain out the break in oil so it won't spill during transport. Please refill with 20w50 Castrol GTX or similar. Please do not use Fram oil filters. Get a Napa Gold 1347 (tall) or 1334 (medium). Don't bother with the small FD 3rd gen size filters.
It likes to idle best around 1100 once warmed up. The part you saw in the video is with the choke still on (that's why it went to a lower RPM when I pushed the choke in and gave it a quick rev, because it wasn't fully warmed up yet).
It takes a little technique to get it started. Turn on key to ON position (fuel pump will run). Pull the choke, couple of pedal pumps to get some accel shot in there. Crank around 3 or 4 seconds and then it starts to want to fire (for me, in this car, with my exhaust system anyway, as yours will be different). Then it takes some feathering of the gas pedal while pulling the choke to a good position to allow it to run without stalling. I find that 3k RPM works for the first few seconds of run time, then try to lower it as soon as you can. Any lower RPM in these first few seconds and it'll tend to stall. This may be due to the half BPs or that it's a fresh rebuild and could improve over time as it breaks in. After that I like to let the choke in a little and keep attention on the gas pedal and tach to around 2k because I don't like high revs on a cold engine. After maybe a minute it can go down to 1500ish, depending on ambient temps. This technique worked for me in my car for the first four heat cycles. You may find a better technique as it breaks in more.
By the way I recommend 20w50 oil as it's got a lot of bearing clearance being an R5, which is great for high RPM (but please keep it at 8k and below as the apex seals are 3mm). I'm going to drain out the break in oil so it won't spill during transport. Please refill with 20w50 Castrol GTX or similar. Please do not use Fram oil filters.
Get a Napa Gold 1347 (tall) or 1334 (medium). Don't bother with the small FD 3rd gen size filters.i bet once it breaks in, it'll improve