Jeff20B

iTrader: (13)

If you read the other thread, you'll have an idea of what I'm talking about.

The final conclusion is:

MG:
Y plates ported to '74 spec
'74 rotor housings with cleaned up stock exhaust ports

REPU:
stock ported '3B '74 spec side plates
ported rotor housings to T2 (you'll see why below)

Baja:
unported Y plates
rotor housings from a delivery van in Japan (ask kenn chan for more info)

And now for the pictures.

The stupid upside down D port before correcting.


Comparing to a T2 port for rough cutting...


Getting there. I cleaned up the stock port too.


From left to right, T2, stock '74 x2, ported '74 x2


From the outside.


Now comparing delivery van/GSL-SE port timing with a stock '74 rotor housing.

Jeff20B

iTrader: (13)

Here's my current collection of short port intermediate plates.


These all have the same port timing and shape.


Upgrading from NO intermediate to 3B in my REPU engine. Some yayhoo rotary mechanic probably built it to play a joke on the previous owner. Then I got it and wondered why it was down on power. Looks like I'll have the last laugh.


The picture speaks for itself. Sorry about the difficult to read text. I probably should have used green.


Carl will like this. I bet the engine it came from always had one primary that outflowed the other. I picked it up for free so I can't complain. I may not use it though.

dj55b

iTrader: (2)

keep up the good work ... what the NO stand for? sorry if i skipped that info somewhere. Also about that one that has an offset casting... was it meant to be like that or was that a factory mess up?

Jeff20B

iTrader: (13)

I don't know what NO stands for. I see it as a warning. It's trying to tell you to not use it.

Starting in '74, all carbed engines had letters and sometimes numbers on the irons. I know of 3B, R5, NO, Y, and there is a rare H and T. I don't know what the 6 port 12A had, if anything.

The offset casting is a factory mess up.

Jeff20B

iTrader: (13)

Here's a side by side of the manifolds in case you were wondering what they looked like.

dj55b

iTrader: (2)

hmm i wounder if you can return that housing for a refund lol ... 30 years later. lol

Naegleria_Fowleri

Another great informative thread by Jeff20B.

In for the information!

I'd never have seen the porting on any of these had it not been for this post.

Jeff20B

iTrader: (13)

Thanks guys.

Would you like to see how the Cosmo manifold fits the MG? You'll see why I had to chop out the ACV section. None of the normal flow manifolds would fit the car without hitting the foot box. The Cosmo mani lets me install and remove it with the engine in there!

Naegleria_Fowleri

That is really close.

Jeff20B

iTrader: (13)

Yes. In the last pic you can kinda see where I hammered in the foot box to make the other manifold fit. I have about an inch of clearance with the Cosmo manifold which is just enough to get around the studs on the rotor housings.

Hyper4mance2k

iTrader: (40)

Just bite the bullet and bridge it. You do know that a bridge port makes more power across the entire rev range than any stock or street port right. It's just that it makes the best power up around 8k.

blwfly

iTrader: (4)

this combination would make your mg fly instead of making the exhaust porting change its degrees how bout widening the port like in the pic below

this porting below is judge ito's street port it looks to be on the center housing so thats pretty big primarys over stock y plate


cant rember your old thread but you were trying to figure what parts to use for a 13b 4 port? and were aiming for best flow efficentcy and torqueout put from diffrent types of porting?

trochoid

iTrader: (6)

Jeff, been reading your threads with great interest, can't think of anything to to add other than a couple of questions. Since you're limiting the baja to 4500 rpm, what configuration gives the best lowend torque/hp and why. I honestly don't know know myself. My only experience with that would be in my S4 6-port and it does have plenty of low end.

Other question is: Have you read the following thread?

http://www.nopistons.com/forums/inde...howtopic=67369

I found it quite interesting and was wondering what would the results be if one did maybe a 1/2 bp, yet left the stock ports untouched? Don't know it it would help your application or not.

flight_of_pain

imo if your limiting it to 4500 rpm why not go with a piston motor that will make decent torque that low. 4500 is crippling a rotary


isaac

Hyper4mance2k

iTrader: (40)

Bridge port!

Hyper4mance2k

iTrader: (40)

I'm a thief...
"Torque is force. Pounds of force per foot of leverage = lb-ft, for example.

Power is using that force over time. James Watt (the steam engine guy) decided that a horse could lift 550 pounds one foot in one second. So, lifting 550lb per foot per second = one "horsepower". Convert linear motion to radial motion, divide by 550, carry the two, it equals that at one RPM, 5252lb-ft of torque is one horsepower. Or, at 5252rpm, 1lb-ft of torque is one horsepower.

The SI unit of power is the watt. Old James has a monopoly in the power buisness.

Notice, that the power is interdependent on torque and the speed at which it makes the torque. 5252lb-ft at 1rpm is the same power as 1lb-ft at 5252rpm. So, if we want more power, we can increase the torque or increase the RPM at which the torque happens

Torque is created by burning air and fuel. We get more torque by burning more air and fuel: larger engine, making it easier to get air and fuel into the same size engine (volumetric efficiency), forced induction, artificial air (nitrous oxide). More difficult, we make the existing air and fuel work harder for a bigger push: higher compression ratio, better thermal efficiency, optimal ignition timing.

Volumetric efficiency is the big one. An engine's V.E. curve is almost directly linked to its torque curve.

You're yawning, because this is all basic stuff that even magazines like Import Tuner and Sport Compact Car have covered in their tech articles. Don't worry, there's a point, and the point is:

A street port makes more power by taking the existing V.E. (torque) curve and while it does get a little larger, it gets mostly shifted to a higher RPM. The power increase is mainly due to the increase in RPM.

The bridge port, on the other hand, has a much higher V.E., almost double, and it does it everywhere. Down low. In the middle. Up top. They never stop. They make much more TORQUE than a street port does, so for a given level of power, they don't need as much RPM.

The V.E. comes from the port open time. The peakiness comes from the port closing time, which has a large effect on intake reversion at lower RPM, when the air's velocity (inertia) is relatively low. Street ports mostly make their power from extending the closing time later, which is where they get their low end power hurt. You could make a bridge port peaky like that, too, but it's not due to the overlap, it's due to the late closing.


The stomping was to kill the fallacy that low RPM engines make "torque" but high RPM engines make "power". The truth is, a lot of modifications that increase power also increase torque. The misconception stems from the fact that low RPM engines are necessarily low power engines for a given level of torque. Torque is what shoves you back in the seat, so a low RPM engine will feel a lot faster than it is, just like a high RPM engine will feel boring to drive because it never really seems to shove you back in the seat very hard. Cover ground quickly, though."

trochoid

iTrader: (6)

Yep, you're a thief.

That quote comes straight from the link I posted. I found it very interesting on the changes in VE between an SP and a BP, not at all what I expected or have been lead to believe. That's why I posted the question of adding a 1/2 BP, and not changing any of the other port timing with an SP.

Jeff20B

iTrader: (13)

The rotary's greatest strength is its easy portability. None of that complicated valve stuff to deal with is a plus. However porting can also be its greatest weakness for low end driveability. It moves the torque up out of the sweet spot for normal everyday driving. This is not so much a problem with a small light car like any 1st gen RX-7, but I want to be able to lauch the baja off of a whoopdeedo instead of backing up to get a run at it like the VW powered guys have to do. And that's what I currently have to do. I miss the instant throttle response that even my heavy, ported REPU has.

What's a typically good upgrade to your basic baja? A 1776 and a bigger carb? It already had that and it was a little better than it currently is with a 1600 and a stock carb. At least the stock carb has driveability.

The 1776 went to my friend's baja and I got his tired 1600 when I got the baja from him. I didn't mind because I was planning to do a rotary upgrade from the start. The 1776 still lacks power below 1500RPM where I feel more is needed (I was a little dissapointed the first time I rode in it after the swap). Neither of us will try an 1800 or larger because reliability flies out the window. Not to mention the added weight; especially with a heavier T4 based engine or the Subaru watercooled swap.

Man, for that kind of weight penalty, I'd just go with a totally stock 12A pulled out of a junkyard 7, like some VW rotary conversion guys have done. Of course my engine will be built specifically with the conversion in mind and it will get a lighter FC waterpump for some weight savings. The '74-'85 rotating assembly, while heavy, will be a benefit here, despite the couple extra pounds it adds to the total package. It's all for better low end, of course.

My baja feels stronger with the gutless 1600 than my friend's baja did because his has a full roll cage and is really built to take a beating. This obviously adds plenty of weight but feels a bit stronger with the 1776 than mine does with the 1600 (it's tired). I don't plan to take mine anywhere where a full roll cage is needed yet. This will help to keep the weight down until it's necessary.

Any person with a dremel tool and a steady hand can port a rotary and obtain good results, but without a basic knowledge of what works with what, ie larger intake and exhaust, you're better off leaving it stock. Lots of ported rotaries actually end up slower in stop and go driving. My REPU is a great example.

Back before the rebuild and a mild streetport job, the REPU was quick with a stock carb or a dellorto on '76-'78 sized ports (same size as 12A) in a nitrided R5 engine. After the port job, the dellorto only had power in a narrow range between 2000 and 4000. Anything above was a waste of time. Anything below was too slow for the big 48mm air slugs to make any power.

The dellorto had power up to 6000 on stock ports and that's what it was jetted for. RB never recommended the dell on a REPU or a streetport because it was too small for '74 spec or larger. Interesting, don't you think?

Jeff20B

iTrader: (13)

I'd say it's not so much about where it peaks but where it runs out of breath that I need to be concerned with. The old delivery van engine peaked somewhere between 2000 and 4500 like a GSL-SE with closed aux ports, but definitely ran out of breath where most other rotaries start to sing. The new engine for the baja will not suffer from this. I can almost guarantee it.

How do I know so much about the delivery van engine? I have several of the parts that came with it. The carb was jetted for ultra low RPM (which I tested on my Cosmo before rejetting it), the spark plugs were a very hot range, the thermostat was 190°, the spring loaded auxiliary bypass valve in the water pump lets heated water back into the engine under certain conditions, the tiny little NO sized primary ports run out of breath very early, the GSL-SE spec exhaust port timing delays port opening for more time to apply power to the shaft etc. It actually probably peaked closer to 3000 like the GSL-SE engine does, and ran out of breath by 4500-5000 around where the aux ports open on a GSL-SE. It has the same port timing as the four low RPM ports on a GSL-SE but lacks the aux ports and better overall power of EFI. Still, that sounds like a combination for good low end torque to me. Very simple too; less to go wrong. Plus I can add a few improvements that will make it sing with other rotaries without hurting the low end.

Mazda's other good low end torque engine from that era, the CD23C RX-5 Cosmo 13B, had '76-'85 sized intake ports and small (open early, close way early) exhaust ports for good all around power up to about 6000. The reversed runner manifold was the key ingredient to get that big boat up and moving on primaries. All four ports were the same size internally as a 12A and the outside intermediate ports were made tall to take advantage of the reversed runner manifold's secondaries which flowed through short runners directly into the intermediate plate. This intake scheme is great for primaries thanks to the long runners, but not as good for the secondaries. However since the Cosmo was a luxury car, most of the driving was done on primaries so it wasn't noticed.

I will take and combine the best parts engineered for low end torque from both engines to make a super torque monster that will fulfill every requirement/goal I set at the beginning of this project.

I don't have the list in front of me but from memory...

1. as much ultra low end torque as the stock delivery van engine
2. must keep going after the delivery van would run out of breath
3. must cost half of a typical $1500 1600/1776 short block or less
4. at least as much torque from idle to 1500 RPM where both our bajas are lacking
5. similar midrange and high end to atleast 4500 (that one should be easy)
6. only take a few months to complete (my friend's rotary baja took 8 years)

I can't think of any more at the moment.

I can list my chosen combination of parts with the reasons why and let you guys decide whether they will work together and yield the results I'm after.

I'm thinking goals 1 and 2 could be as simple as using the Cosmo's reversed runner manifold on some normal sized ports instead of the delivery van's tiny NO sized ports and manifold. I've experiemented a bit with the Cosmo manifold and believe its extra runner length flowing into normal ports should produce just as much ultra low end torque as the tiny ports, but not run out of breath as soon. I iknow how high stock ports can rev so I bet it will have power up to at least 6000 if not higher. Try that on a typical ACVW with stock internals lol

I will use the Cosmo's reverse runner manifold and normal sized ports. That means the intermediate plate must be changed to a tall port Y plate.

Therefore I will need to mimic the Cosmo carb as closely as possible (within reason).

The Cosmo carb had:
100 primary jets
60 primary air bleeds
130 secondary jets
90 air bleeds

The delivery van carb had:
90 primary jets
90 primary air bleeds
140 secondary jets
160 air bleeds

I've since moved the primay 90 air bleeds to the secondaries (you can do that on Hitachis) and used some 60s from a water damaged Nikki. The fuel jets were upgraded to 100 pri and I think 145 sec. With the smaller air bleeds, this carb will flow great up high now.

I may need to fatten up the secondaries a little more but when I test ran this carb on my bro's RX-4 to break it in before the SC install, the 100 primaries ran extremely well even with mild streetports. I bet they'll be just fine with the stock ports and long runners I'm planning for the baja engine.

I'll be using a set of three Y plates because they're light, nitrided and available.

The rotor housings have very nice chrome; at least as good as the ones we used in the RX-4. If the torque it produced with streetports and a normal flow manifold was any indication of things to come, the baja engine will produce even more with smaller ports and later opening exhaust ports (we copied T2 ports onto some GSL-SE rotor housings for the RX-4). Oh man I can't wait!

Another thing we did on the RX-4 was to use all new seals. I have mainly new and some used but in excellent condition seals waiting to be installed. You can't have good low end and driveability with leaky seals. Rest assured the used seals are well within spec or I wouldn't even consider them. Hey, I'm trying to bring it in under $750.

For cooling I have an S4 T2 waterpump already modified to fit an NA or earlier front cover. A few minutes grinding aluminum from the back is all it took. I'll install an electric temp sender and a new impeller because the old one had a dripping weep hole.

I'll use a dreaded beehive because it;s more practical than trying to rig up some small fans to blow through an air oil cooler. I've seen others' attempts and it just looks shoddy I'm sorry to say. There's nothing wrong if it cools and all that, but I don't want to rip off an oil cooler line out in the woods. The hard steel line of the beehive is right up next to the engine and fairly ridgid. The spark plug wires would get ripped off by sticks before the beehive's tube even comes close to moving.

I have a good tall '83-'85 radiator to either mount in the back above the engine like my friend's aftermarket aluminum radiator, or I'll try it up front like everybody else does. His engine doesn't overheat. It runs really cool and the oil stays at a healthy 180° all the time (with a beehive). He drilled a 1/4" hole in the thermostat on my advice (which I got from zenjoe). I'll probably do that too.

So that describes the ports, carb, jetting, manifold, side plates, rotor housings, seals, cooling... Anything else?

Oh yeah, I'll use an old style high volume oil pan like those found on old school 13Bs, with load spreaders between the bolts and the pan, so hopefully hte pan won't leak the first time it encounters a rock.

I'll throw in a high volume 17.5mm oil pump and shim or crush the ROPR for high pressure. Even though it won't be reving to the moon, I want the higher oil pressure for a safety cushion.

The clutch will be a KEP 1700 stage one because that's what's on the 1600 and it's new. If it needs anything stronger I'll swap in a stage 2 and superdisc.

The current tranny is from a bug. I'll look for a 3 rib when the bug tranny breaks. I'd prefer a 3 rib over a 5 rib because the 3 rib is geared shorter.

The exhaust will be 2" OD 1/8" wall U-bends and straight pipe cut to fit from Racing Beat. No wimpy thinwall muffler shop junk. The mufflers will be two medium length rotary engineering glasspacks. I already installed my two short glasspacks on the GLC with huge exhaust ports and it's not too loud. Still debating whether to get a megaphone to act as a stinger.

trochoid

iTrader: (6)

Sounds like a very well thought out plan. I do enjoy reading your train of thought as you talk this build out to yourself on the forum. I learn more every time you do.

I'm curious about this delivery van. Until you posted about it, I was unaware that there was one. Do you have any pics/info on it? Building one of those might be a fun project simply for it's uniqueness. Seeing some of the Japanese and European minivans produced over the years, a rotary one might rate high on the 'cute' scale.

Jeff20B

iTrader: (13)

Thanks. I try.

I don't have any picks of the delivery van or any info. Until this thread, I didn't even know what these engines came out of, though I suspected some low reving thing from Japan like a Luce or something. https://www.rx7club.com/forum/showth...t=delivery+van

It was RX3SP who said it came out of a delivery van. He even posted pics of the crazy oil (not ATF) filled torque convertor. No wonder so many import 13Bs have that little drain sleeve fitting at the lower corner of the rear plate. I've blocked off two so far. I also had to install a blind plug in the shaft of the engine pictured in that thread (the painted one, not the old rusty one lol). It was a bonafide delivery van engine that I brought up to tallport R5 standards by swapping in a Y intermediate plate and RX-4 rotor housings with US-spec port timing. I then ported the intakes out to '74 spec and enlarged the exhaust ports 2mm up and 2mm wide so the owner could use it in his REPU as a backup engine. He mentioned possibly installing it in a 1st gen instead so I threw on a GSL-SE oil pan, which happens to be compatible with the REPU as well so he's set regardless of what he does with it. He just needs to come get it out of my garage lol.

trochoid, after reading that thread, I kinda doubt you'll want to actually build a delivery van engine. Of course it is something that could be accomplished. Use the end plates from a 1st gen because I doubt you'd find any non-nitrided R5 plates. Get a set of US-spec GSL-SE rotor housings. Don't use the earlier opening, earlier closing RG-EGI housings from a Luce. They look exactly the same on the outside with the only difference being port size and position. The short ported intermediate plate will be a problem unless you get one from me or possibly Atkins. The last time I was there I noticed an NO plate sitting in their back room. I wouldn't recommend NO plates because they have an EGR port at the top and two of the water jackets are physically blocked. There is a way around this by cutting little communication channels around the edge of two tension bolt holes in the rotor housings like the '74-'75 rotor housings had. Did you see the pic I posted? Anyway if given a choice, I'd choose the actual R5 short port plate from an actual delivery van over an NO plate. Don't forget the rotating assembly. I think any 1757 rotating assembly from '74 to '83 would work. You could also use GSL-SE stuff since it's the same weight. A real Hitachi carb would be nice but they're so rare a Nikki on an REPU manifold would suffice; it would need to cover the ACV port because GSL-SE housings flowed like that. Drill and tap four new holes in the12A pattern and cut channels connecting primary to secondary. The carb spacer is already sort of connecting both primaries together, which is what the delivery van had. Use 91 primary jets because they came stock in some carbs and they're close to the stock 90. I doubt you'd find 90s. Change the secondaries from 160 down to 140. Drill the primary air bleeds from 70 to 90 and the secondary bleeds to 160. The stock pump shot will be adequate. The vacuum secondaries will be fine.

Well there you have it. How to build a delivery van engine with more available parts. But would you really want to?

trochoid

iTrader: (6)

Jeff, I wasn't thinking about building the delivery van engine but the van itself. Foreign vans of that era were were short, in both height and length, and narrow. Building something like that with a 250 hp 13B NA would be a hoot. Now if if the rearend was tubbed, it had the brakeing equivilent of a TII, the handling of a well setup 1st gen and weighed in around 1500-1800 lbs, it would be the schnizit..


Just picture the look on the faces of the F&F wannabe ricers getting smoked by some odd looking tiny delivery van that that's not much bigger than an old VW bug. It would even have some practical useage for hauling parts and camping gear/tools for the occasional 2-3 day rotary meet. Slapping the old Toyota motorhome dually rearend under it, with the appropriate fender flares would set it off even more.

Jeff20B

iTrader: (13)

Ah lol, I gotcha. That would be totally cool. I gotta finish my current run of projects before I can begin to think about other possibilities like that.

I still want to do a single rotor 13B with GSL-SE end plates and flow a Nikki into the four ports it would have. No need to rotate the aux port sleeves because the secondaries wouldn't let them flow until they open at higher RPM. With a custom manifold there would be no need for channels because you could make the runners whatever diameter and length you want (that's the reason for channels according to peejay - because the FB manifold primaries flow like crap, so giving him the benefit of the doubt here). Also I'd get some pineapple inserts and do a late leading and direct fire trailing ignition system. The dizzy would need two reluctors (one stock and one with only two teeth) but that would be fine since the cap would be of no use whatsover, other than to keep out fingers and prying eyes.

I wonder what I could install it in... A Subaru 360? Those are kinda rare these days. Hmm...

dj55b

iTrader: (2)

Out of curiosity, do you have any pictures of all your projects somewhere. Really interested. Thanks

trochoid

iTrader: (6)

Not familiar with the 360's but an old Honda 600 might work if you could adapt the fwd.