To make a high compression N/A 20B, could I just use S5 rotors? How about the overall balance? Does anyone have figures on how much a 20B N/A with no acessories would weigh compared to a REW (RETed)? With mild porting, what HP could I expect with high compression?
Thanks,
Brad P.

 

Why? Well space is an issue, this is going into a 510. Not much room for the intercooler and piping. I will use this car for instructing, so engine response is fundamental. I have driven many turbo cars on the track, and I know it can be great fun, but I anticipate that the response of a N/A high compression 20B would be wonderful. I assume that the weight will be close. I have found a lot of info on this site since my last posting, but still have more to piece together. If I'm making custom intake and exhaust manifolds to suit N/A use, then is there any real need to buy a JDM cosmo motor. Couldn't I just buy a E-shaft from OZ or somewhere and build the motor up using 13B housings and rotors?
Maybe this is silly. Perhaps I should just stick with the REW idea, since it will bolt right into the FD subframe that is in the car right now, and make room for the intercooler that I already have. "Stop starting over" my wife says.

 

The stock twins are only good for about 5HP. You said you wanted a quick reving engine? Throw the twins as far from you as possible. Just the stock exhaust manifold, twins in their cast iron housing, and the downpipe together weigh 62LBS. This does not include any of the rest of the manifolding. A header I made for NA use weighs 21.5 but spreads its weight over a much larger area (most of it is behind the rear exhaust port).

Consider the weight of a stripped 20B. Take the weight of each S5 component and add 36LBS for the 80mm thick 20B-only intermediate (Without stationary gear) and everything else.

I actually spent some time weighing things to extrapolate a fairly accurate weight of a stripped NA 20B for my GLC compared to the REPU-ready 13B that's in it right now (getting pulled tomorrow). If I move the battery to the back and replace the heavy 13B with the light components of the 20B, the actual weight over the front tires will probably break even. Don't believe me? Check this out.

Let's see here. I'll list the weight followed by the name of the component to the nearest half pound.

13B
22 '74 13B carb and intake manifold
27.5 front plate Y
29 intermediate R5
34.5 rear plate Y
11.5 rotor
11.5 rotor
14 rotor housing
14 rotor housing
15.5 13B E shaft
33 flywheel (without P plate or clutch)
I'd estimate the tension bolts are about 5 or 6 LBS, but I could be wrong.

218.5 total without cast iron waterpump, alternator, pressure plate or clutch.

20B
9.5 UIM
10 LIM
27.5 front plate Y (I'm sure the 20B irons are lighter, but it's ok to...)
28 intermediate Y (use the Y casting weights for this comparison in...)
34.5 rear plate Y (order to over-rate the weight of the 20B a little)
36 special 80mm thick intermediate
9.5 rotor
9.5 rotor
9.5 rotor
13 rotor housing
13 rotor housing
13 rotor housing
15.5 13B E shaft
7.5 half of 12A E shaft
17 light steel flywheel with counterweight
I'd estimate the tension bolts are about 10 or 12 LBS, but I could be wrong.

264 total without S4 aluminum waterpump, alternator, pressure plate or clutch.

The difference is 46LBS. Right around the weight of a group size 24 battery, I think (I haven't weighed one yet). Either way, with no a battery up front, an S4 waterpump to take the place of a cast iron one (the S4 waterpump is a decent amount lighter than a cast iron one), and the front of the engine staying in the exact same location with the 20B's extra length going rearward, all this serves to come close if not break even over the front tires with the 13B that's currently in the car.

Hold on, I forgot to add in the weight of the cast iron exhaust manifold on the 13B. It's at least as heavy as the 20B header, but its weight is mostly concentrated right at the engine an only the downpipe goes rearward. Hmm, the front of the car may actually loose weight with a 20B in it. Now that's a scary thought!

Hey, I'm going to weigh the manifold tomorrow if I have some time. It'd be funny if it's heavier than the header.

 

Interesting, thanks for the weights. You mentioned mounting the motor such that the front rotor housing is in the same location as the 13B. In effect, the third rotor is being added behind the first two, like Mr. Farrells car for instance. How would this be done, what mounts would you use? I'm asuming that the 80mm intermediate plate is where the two e-shaft sections are joined?

 

'85 and older rotaries have a front cover mount. I swapped the stock 20B front cover for an '84 12A front cover. It probably won't handle 500HP, but it'll handle NA 200-250HP just fine. Infact, there are many 12As and 13Bs with front cover mounts pushing that much power that hold up fine.

Yes, having the extra length of the 20B go rearward is better than keeping the tranny in the stock location and having the front of the engine go forward, as is done in FC swaps because those cars were sort of designed with the 20B in mind. The extra length going forward doesn't really bother a heavy car like the FC too much.

The 80mm plate has a stationary gear and is basically where the two pieces fit together. The front piece slides onto the main shaft and I think it joins together right there at the 80mm plate.

The 13B cast iron exhaust manifold weighs 21.5 which is the same as the 20B header I made! Again, the 20B header is better because most of its weight is behind the engine rather than concentrated right off to the side.

 

every now and then a i hear something about that but know im actualy looking for info and cant find anything, ive searched alot and havnt found anything? does anybody have any info on this or what words to use to search?

 

Jeff, I thought about the high Comp idea myself, and you should be pushing right around 330 or so with a street port, I know that the stock front mounts hold up to around 400 before they start to crack the aluminum cover, (friends 13b Turbo monted in a SA body). The biggest problem I think is not the HP but the frigging torque of the monster! All the guys over hear convinced me to single turbo mine, but I still dream of a 1st gen with a non turbo 20b!

 

but couldnt you use the e-shaft and the intermediate housing and use 13b parts for the rest? but if you did it this would you be able to use the 20b oilpan?

ps is are the motor mounts of a 20b on the intermediate housing?

 

you can buy a 3 rotor e-shaft from a place called precision engineering based in auckland new zealand and the guy to talk to is jeff

he makes them and sends them to australia and usa

ph 0064 09 4153264

just say brendan from no camz motorsport passed you on to him

he also makes a 4 rotor e-shaft as well, along with a stat gear modification and through bolts to use standard centre plates

hope this is of some help

 

So what counter weight would be needed when going with the higher compression rotors?

 

so you would need a custom 20b e-shaft to do what i said above?

 

A lot of questions. The guy's name is Jeff Bruce. I think his 4 rotor E shafts are phased 90º which will give the awesome 26B engine sound. His three rotor shafts are phased 120º which will give the awesome 20B sound.

13B parts can be used in a three rotor engine, but it's best to use S5 rotors because the 20B counterweights have the correct offset angle and should work fine in a three rotor 13B. As for the four rotor engines, the rotors themselves should offset each other. I'm not sure of the two counterweights on the ends thought. Contact Jeff Bruce for that kind of info.

S5 rotors have 9.0 (low) and 9.7 (high) compression ratios. That should give you enough range for NA or forced induction use.

 

thanks jeff20b, but what ive been trying to ask is can i take a factory 20b e-shaft and intermediate housing and use 13b housings and end plates for the rest of the motor? or would have to get a custom e-shaft?

 

Good luck making 368hp on the dyno with an NA stock-port 20B with 9:0:1 rotors and pump gas.

I'm not sure about the 13B end plates, but the 13B rotor housings will work just fine. If your goal is to save money and/or use 13B rotor housings, you would probably be better off just buying a used 20B-REW and replacing the rotor housings with 13B rotor housings. The 20B will also have more standard goodies, such as hardened stationary gears, a useable intake manifold, an oil pan, useable fuel rails, a nice big alternator, etc. A new 20B eccentric shaft costs over $1,000, and the two 20B intermediate housings are more expensive than 13B intermediate housings.

The 20B-REW rotors are the same weight as S5 13B rotors, so the stock counterweight would work just fine with the S5 9.7:1 rotors. However, if you convert to a MT flywheel, you may need a different or modified counterweight. For example, I am using a very light Mazda Comp flywheel on mine, and the counterweight needed some milling. Mazda Comp was nice enough to supply a milling diagram for my set-up.

 

im just researching diffenrt options, im looking to put a n/a 20b into a fc and use a carbed set up and ive read that racing beat makes a distributer for 20b's and later on upgrade to F/I and a better ignition setup i know its not the smartest way to do things but thats what im thinking.
im just doing some basic research. im not saying im doing this its just something going thru my head right know

but i was trying to find other ways with the motor then buy a full 20b and what not there's not to many 20b short blocks that come around

 

I'm currently trying to figure out ways to do ignition with a MegaSquirt which was originally a fuel-only ECU.

 

I'm a little confused. I thought any FD aftermarket flywheel would fit the 20b counter weight? So basically what your saying is that not all MT flywheels will fit the 20b counterweight the same?

 

I was referencing the rear counterweight. You will notice that aftermarket lightweight flywheels usually come with a corresponding counterweight. I'm not sure how well an FD kit would work with the rest of the 20B internals because I do not know much about FD's. I think it's best to ask somebody with experience in this area (Mazda Comp, etc.), and/or have your rotating assembly balanced by a rotary shop. Another option is to use the stock 20B flex plate for your project.

 

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should bolt up no problem
matt

 

this thread really interested me when i saw it. i just have a few questions:

- what would you use for an intake manifold when you are going NA on a 20b? is the stock manifold fine or does it have to be modified in some way (other than the obvious removal of turbo related items)

- what are ECU considerations? do the same rules for a turbo setup apply? all those options in a Wolf3d and Haltech seem like a waste without a turbo...

- what about Renesis rotors? are we looking at the same issues that there are with putting these rotors in a 13b (i.e. seals and different counterweights)? if so, i think it may be feasable and actually a really good idea, considering they are both lighter and cheaper than the S5 NA rotors...oh, plus not to mention 10:1 comp


if i could get some responses to the above, that would be great. it looks like this may not actually cost that much more than converting to a big turbo setup on the NA FC...THAT'S why i'm interested

 

The stock intake manifold and throttle body would work just fine, but some people may want to use a custom manifold for higher-hp applications.

Over the years, I have found that most of those on the internet who think that an EMS is a waste of money on an NA have never actually tried it, or simply recommend against it for people who are broke. The boost control and anti-lag functions are the only EMS functions that I can think of being a waste on an NA engine, and some EMS products don't even have these functions to start with. Everything else still applies. You could even use the "turbo timer" function on an NA if you like.

Some EMS products, such as those from Microtech, do not allow the user to redefine the load bands for an NA. I guess that could be called a waste, but the EMS could still run the engine on its remaining non-boost load bands.

Professional racers mostly use a top of the line Motec EMS on an NA 20B - enough said.

The process of using Renesis rotors in a non-Renesis engine is still under development, but this would be an advantage in theory. NA 20B's are capable of over 475hp without the Renesis rotors, so I'm not sure if it is worth bothering with experimental Renesis rotors at this time.

The cheapest way to run a 20B-REW in an RX-7 is to keep it stock with the turbos. Anything other than that will require extra parts.

Also, you should not bother installing a 20B engine into an NA RX-7. I did this, and I can assure you that starting with a TII is much easier and less expensive in the long run.

 

thanks for the responses evil. yeah, i figured that most of the standalones would still work great on an NA setup (as they do on 13b NAs that i have seen).
i guess any good EMS would be a good choice? other than the mentioned Microtech and other systems that dis allow certain functions of course...

in terms of the Renesis rotors, i was more asking about the issues installing them in a 20b. are they the same as in a 13b, or are there extra things to consider? one thing i am really wondering about is where to use the front and rear Renesis rotor in the config...like would it be all rear or front rotors, or would there actually be the need for using both...

and why do you say that the cheapest way with the least amount of parts would be with the stock turbos? if you think about it, you wouldn't have to buy and install a front mounted intercooler (easily $1000 there), there are less oil lines to fabricate, and i'm sure you can get rid of a lot of the turbo related items (oil lines, vacuum lines, etc.). not to mention you could also sell all these parts to recover some cost, so i don't see how going NA would cost MORE...
plus, i would expect it is a lot easier to work with things and fabricate parts to fit because of the extra space.
i would also be looking for a used 20b that i would rebuild, so that i wouldn't just be ripping apart a working engine to put high compression rotors in...plus the fact that a prepped engine from a shop can cost quite a bit...

and i agree with you on starting with a TII instead of an NA, that is definetly what i would do. i was just saying that if you compare a 20b swap into an NA vs. a 13bt swap w/ a large turbo upgrade into an NA, i don't think the costs are going to be that much more. in both cases you still have to get a stronger transmission and clutch, and the larger turbo on the 13bt to get the same power levels as the 20b would obviously require money to be spent...
but yeah, definetly starting with a TII that has a dead engine seems like a good way to go

 

The Renesis rotors are differant. If you want to run them in any peripheral exhaust ported rotary angine, you will need to mill the apex seals grooves to exept regular 2mm or 3mm apex seals. The Renesis apex seals are thinner and are not designed to travel over the exhaust port (they will warp from the extra heat).

Next thing to tackle is the side seal issue. The stock Renesis side seals are factory pre-cut and have alot more clearence between them and the corner seal. In the Renesis this extra clearence is needed because the heat from the side exhaust will cause the side seals to expand more than in the other rotarys. If these side seals are used in a perifpheral exaust rotary, you will have sealing problems and lower compression because the seals wont expand as much. A quick fix here is to use regular side seals that you can buy for other rotarys. These will have to be ground down to the correct clearence.

Do not use the oil scraper ring. (not needed)

Lastly since the Renesis rotors are lighter than the 20b rotors, you will have to have the rotating assembly balanced(rotors,e-shaft, and both counter weights). With everything properly balanced there shouldn't be any issues with putting which rotor front, center, or back.

 

you will also find that the pitch of the gear on the rotor and stationary gears on rx8 rotors are different to early 13bt and 20b engines

which will mean to run rx8 rotors in a na 20b you will need to have a custom centre stationary gear made..