Don't stop now. I am trying to learn something here...
Don't stop now. I am trying to learn something here...
So I painted the water pump housing since the early RX7 housings are iron rather than aluminum. Bolted on the intake manifold and oil filter pedestal last night, noticed that the racing beat intake manifold center ports are much smaller in height than the ports on the center iron that Logan worked, so I wonder if I need to match those to really take advantage of Logan's work.
Then I thought I'd tear down the carb or change the choke size and size up the jets for the 13b, but I was greeted with some serious gunk. Don't soda blast your carb, even though I thought I had it taped off pretty well, I found buildup in the float bowl.
Worse yet, when I pulled the jets I found some strange oxidation/buildup, including this weird blue crystal substance:
I assume that this is what happens after 10-11 years of running pump gas with 10% ethanol? Either that or my carb has a crystal habit (how do we reach these kids?). I'm thinking the carb needs a full tear down and proper cleaning to be safe for the new motor. I'm reluctant to pull the float out in case it's adjusted wrong when I put it back in place, but if it doesn't come out I'm not gonna be comfortably certain that any and all gunk is removed. I don't want any hard chunks of media or fuel residue running through a fresh engine.
Do not port match. Power everywhere will suffer. The runners are short for a reason. Paul Yaw had a whole web page about the idiosyncrasies of the port geometry.
In reply to Pete. (l33t FS) :
I'd like to read that page if you can still find it. Also, do you have a preferred method for finding TDC and setting the distributor in place? I watched a video on marking the pulley in two places based on centering the rear rotor apex seal in the spark plug opening, then finding the middle point between those two marks, but I assume there are other ways as well..
You can't go off of the plug holes because the plug holes are not symmetric to the pinch. They also got moved around a lot, which is both why ignition timing depends in part on which rotor housings you have, and why FDs have cooling system issues - Mazda moved the (leading?) plugs so far up that one of the water passages is pretty compromised, and they didn't want to redo the tension bolt pattern for whatever manufacturing reason.
Whoever made that video is doing the rotary community a huge disservice, putting dangerous misinformation out there like that.
IMO the best way involves a rig with a dial indicator and a half assembled engine.
In reply to Pete. (l33t FS) :
Interesting, I believe my housings are from an RX-4. The engine is fully assembled though. I found the Paul Yaw page on port timing with early RX-7s, I'd like to read what he found out about the RX-8 just out of curiosity.
https://web.archive.org/web/20050207030202/http://www.yawpower.com/Flow%20Testing.html
He alludes to it here. I am getting a feeling that he wrote an article for the Mazspeed forum, which has been deceased for a long time now.
Essentially, the ports are tall, narrow, and curve along the worst axis. This makes for a high difference between the long and short walls of the runner. If you port match the intake runners, you not only increase the length difference between the long snd short sides of the runner, you make it diffuse while turning, which he said is a major, major no-no.
So what happens is, with the additional length difference, and the attempt to diffuse, you get big whirlpools of dead airflow in the bend, where the air is actually moving backwards in the port back up to where the diffusion starts. That is why flow suffers at low RPM and high RPM.
Remember that a difference in length from one end to the other is enough to hold an airplane up! Air really, really wants to keep its "shape" especially as it moves faster.
Anyway, this is why I managed to acquire not two but three different "flat" sidedraft manifolds. A Lake Cities for a 4 port 12A, an Atkins (LC clone) for a 6 port 13B, and a TWM dual carb manifold for a 4 port 13B.
Sadly the Atkins manifold is a touch too long to fit in an FB if you want an air cleaner. The 12A manifold is a little shorter, so there is just enough room. Both require a header with a Dell'Orto, the accelerator pump fouls on a box type exhaust manifold.
Supposedly the TWM with a pair of 40DCOEs with 32mm chokes flows more than a single 48 IDA but has Nikki-like drivability. Maybe I will put together a mild 4 port 13B some day and find out 
Ok, back to figuring out WTF is wrong with the welder
In reply to Pete. (l33t FS) :
I assume those side draft intake styles are ideal for high rpm power due to the super short runners? I did some more research on finding TDC and got a bit more done tonight. I sourced an FC eccentric shaft pulley some months ago because I was told it only bolts on clocked in the correct spot, whereas the 12a pulley will work 3 or 4 ways. Well, the FC pulley definitely only bolts on one way but I shouldn't have had it sandblasted, as the timing marks (I hope these are the marks) are so faint they don't look much different than pitted metal. I referenced my 12a pulley and it had really faint marks too, that appear to be done by hand with a punch. To verify that I was in the ballpark, I checked where the flywheel counterweight was in relation to the sight plate at the top of the motor, and I think I'm good to go, though I haven't set the distributor in place yet.
One other setback, when I bolted on the water pump one of the studs stripped the hole it screws into even though I felt like I barely snugged it up, hopefully I can run a tap through it and get good tension from it once it's cleaned up. Once I'm over that hurdle, the only other big question mark on this build is whether I have someone just modify the 12a racing beat header to fit, or have something custom built that fits under the car a bit nicer and makes more power. For some reason I didn't touch this project for weeks, but bringing home a broken Volvo to fix was enough variety for my brain to get excited about the 13b again..
Regarding TDC, I've always found the best way is to reference the keyway on the eccentric shaft. I don't think Mazda ever changed the relationship between the lobes on the eccentric shaft and the key way so it's a good approximation. Sure there's always manufacturing tolerances at play but if you're good it shouldn't be off by more than a couple degrees. The keyway should be at the 9 o'clock position when viewing the front of the engine. Also, remember the FC had different timing marks than the 12A FBs. FCs are 5 deg ATDC leading and 20 deg ATDC trailing. IIRC all 12A FBs are 0 deg ATDC and 15 deg ATDC.
In reply to infernosg :
All RX7 12As, SA and FB, are at zero and 20ATDC. GSL-SE are, IIRC, -5 and -20.
I'm going to have to play with timing to find a sweet spot for the half-bridge, I'm thinking it's going to land somewhere around 22 BTDC leading and 12 BTDC trailing, but I don't really know. Logan at Defined modified my distributor so that it doesn't use vacuum advance, and is only adjustable via turning it and then re-tightening the set bolt. I'd like to get the engine running and broken in before I bother with any ignition upgrades or changes like an MSD box or direct fire stuff..
22 leading and trailing seemed to be the sweet spot for me. (No split possible with my ignition system) It didn't make any more power with more timing but drivability suffered. I mean, it is never awesome, but you need to grab what you can, you know?
I am curious why he locks out the vacuum advance, even with a bridgey it is beneficial for fuel economy reasons. You can run it leaner under cruise without the vacuum advance but it is a net loss because you still are moving more fuel through the engine. I spent a lot of time figuring out what got best economy
I'm almost ready to set the engine into the car, but I almost forgot about the coolant feed for the heater core:
whenever Logan cleaned up these housings he must have removed the pipe that's press fit into this hole, and it's a weird size so I might have to get someone with a lathe to work something up.. I'd prefer not to drill and tap it to 3/4," I think that would make the boss too thin. I tried extracting the pipe from my old 12a with a propane torch and channel locks to no avail, plus it would be nice to keep it on that motor for use later on. Minor setback, but once that's sorted and the engine is in place, I'll load the car up to have the header and collector built.
That is the only sketch part of my full bridge. When Chips redid the housings he pulled that out. I scavenged one but it was not the best press fit, so I did what I could and also used Right Stuff as sealant.
My '81 is early enough that the hose fitting was thread in, not press in...
I ended up drilling and tapping for a 1/2" NPT elbow fitting with a hose barb fitting on the other end, so that's out of the way. I got this far today before the heat and humidity got to me:
i wasn't able to get the splines to line up and "thunk" into place yet, I don't know if I'm on a bad angle or if the engine just needs a better shove from the front than what I'm capable of without any leverage. Hopefully I can trade beer for an extra set of hands tonight or tomorrow night, I'd like to get this ready for exhaust work. While that's happening I can get the Volvo back together.. I always tell my friends not to do 2 projects at once but I never take me own advice:/
The engine is now bolted up to the bellhousing and mounted up front on the engine mounts. Over the weekend I flushed the oil cooler and got it all hooked up, ran the wiring harness that I've previously simplified, and got all the ignition stuff connected. I also got an FC starter from rock auto the other day because I like the sound better, and I found shorter bolts for the water pump pulley so that I don't have to run the clutch fan snout, which will free up some room in front of the motor and look a little cleaner. Next up is to refit the radiator and hook up the cooling system, then add fluids, and wait for my friend to become available to do the exhaust. Fingers crossed that I get to drive this thing through September and October.
Pulley without the fan snout:
Said snout:
The little 13b in its new home:
Current residents of the garage:
That is a great fleet. I love me some S1 Scirocco.
In reply to 10001110101 :
I store that car for a friend. It's an 8v 1.7 which doesn't look like much on paper but I think it's a riot to drive. Once we come up with a better damper/coilover solution, it will be a great car for the two lane roads around here. It has a little Weber 32/36 carb that makes a nice intake growl and it still seems to be pretty frugal with fuel consumption. I know later VW engine swaps have been done in these cars, but I can't imagine the chassis would handle a big increase in power very well, and it's an awful lot of fun as is..
In reply to dannyp84 :
I have 7:1 pistons for it when you want to get more boosty
At least I think they are 7:1. They are from an old non intercooled 2.1 Audi, I would like to say WK engine code.
So basically everything on the car is buttoned up except that the exhaust has not been built yet. BUT, I recently picked up an SCCA ITS FC RX-7, and amongst the load of spare parts that came with it is a 13b header that looks like it'll work on the FB, so I'm waiting on some remflex gasket material to arrive so I can try and put it together. That will be a temporary solution, as I want to redo the entire system to optimize for the 13b rather than the 12a. I'm hoping the first attempt to start the car will be next week, and then I'll find out if I got the starter wiring right, and whether the timing is close enough to run decently. I do also want to come up with at least a temporary functional airbox till I can get something nice made, I ran the 12a with open velocity stacks for a decade without issue, but due to the investment in this motor I'd rather be a bit more careful.
Aside from potential fitment issues, headers made for FCs usually have larger primaries because FC 13B exhaust ports have larger outlets than FB and earlier.
So the car is now up and running, I had to swap to my old 12a oil pressure sender as the new one was faulty, and I wanted to run an FC starter but the one I got from rock auto has been unreliable, both not engaging and then staying engaged once the engine was running, so I've gone back to my original starter and will return the new one. The car fired right up, so my timing settings must be in the realm of correct. I still have some little things to do before driving it, I'm not going to drive the car without a good air box and filtration system for instance, but it's exciting to hear it run after all this time! Video linked below:
https://www.instagram.com/p/CyZJ2LVPSJM/?igshid=MzRlODBiNWFlZA==
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