n/a 20b or single turbo 13b?
 

alright I know a 20b swap costs a whole shit load (still can't figure out where all the costs come from) but heres my cituation... I'm planning on buying a roller this summer and possibly sell my s4... I'm debating on either going with a pp 20b (rebuilt by me) or going with a single turbo 13b.. I'm only looking for around 350~400hp but I would rather do it without turbos... simplicity and torque is what I like.. don't get me wrong I love my turbo2 and I'd go with an ls1 but I could never be proud to open my hood... but I like the non laggy slightly torquey feel to my s4 non turbo. And I figure alot of the costs in a 20b cosmo swap is the turbo.. pipeing... intercooler... bov... wastegate.. custom maniflod etc. So I'll either get a higher compresion 20b built... or build one myself.. with porting of course.... and standalone.
So if it was your car what would be your reason for going one way or another? Through my searches it's all been about cost... but I havn't seen anything about a high hp n/a 20b... most people are shooting for the stars with their crazy turbo build ups.

I've seen powerbands on 13B-REW's or 20B's that started produced close to 300tq at like 3,000RPM....the car itself was like 500rwhp I believe. >___>

Recent thread too.

If you want torque, then rotary really isn't for you, IMO. :P

i would personally save up for a while and go NA 20B, but don't let my opinion swade you, take a coin make one side 20B NA and the other a 13B flip the coin and remember what side you wanted to land right side up for that split sec, that is what i think people really want to do on the outside but get confused. (most people get a "flash" of thought of which side they want to land up and that is a half ass lazy way of deciding.


if al else fails look at your check book and go from there. (I like the sounds of a 20B NA myself.)


Prôdigy

well.... I'm not a torque hog... and I've owned 5 rx7's so I do believe the 7 is for me... I sold my 00 2.5rs-t just cause I love rx7's better.... also money's not a huge deal for me... I can spend up to about 30k a year on my project... plus I plan on taking about 2 years to build this... but I'm hoping to keep the price as cheap as possible but still get quality parts (yes if you find deals you can have both), I don't feel like spending more than probably 25k on this project.... cause I have better things to spend my money on... ok thats a lie... nothings better than a nice rx7

N/A 20B gets my vote.. thats what I plan on doing when my REW goes out. 350rwhp is attainable, and the ability to literally beat the piss out of it, and not have to worry, is great. Although, it will get pricey. Figure at least 2.5k for a 20B core, then add rebuilding costs. Add the cost of either buying a new subframe, or fabbing up the stock one. Then engine mounts, then a standalone ( $1000+ for a Haltech or Microtech), then you are going to want another intake setup such as ITBs. Then tuning, etc.. I would easliy allot $15k to get it done and working properly.

Definitely 20B if you can. Heres what it might cost for the installation kit from GtoRx7: https://www.rx7club.com/20b-forum-95/20b-subframe-needed-493657/ Hes doing that set up right now.

You might want to ask this question on the 20B section.

GTORX7 did an awesome job on NA 20B. But if you want power, it will be cheaper to go with larger turbo on your FC.

Most running 20B engine will cost you 3+k. By the time you build it NA, 4.5+K. And this is if you do all the work yourself and just parts cost (not including PP and custom manifold).

Its almost better and cheaper to just use 20B UIM and LIM and go standard port.

For 4500, you could pick up a single turbo kit, ECU, used IC, and bigger injectors.

Good luck on your future project!

OH, I just read this..

Well, If you are going to spend 25K, you should go all out and add a turbo.

um, LS1 would get you what you want with only headers, intake and a cam..... and would be much less than the 20b. Go to torquecentral.com if interested.

NA/20B

http://www.rotary20b.com/

thanks for some of the info... by the way just to clairify... I'm getting a 3rd gen roller to put the 20b in... my fc will just be track/drift use with a stock port 13b to4e... and yes I will be doing all the work myself... I'm currently rebuilding my 88 n/a with a street port... just for practice. I'm gonna give it to my bro for his birthday. Also I may one day do a mild turbo setup on the 20b... but thats not the plan for now... I think my goals are achievable... and the only reason I don't wanna go with a ls1 is it kinda kills off part of the reason why I like rx7's... but I still support the swap as a good motor in a good chasis... whats wrong with that, I just don't wanna go that route.

Have you ever ridden in a modded twin-turbo FD still running sequential? You get good torque from 2500 rpm up and can still make 350rwhp+. It will also be a hell of a lot easier/cheaper than going 20B and you will maintain better weight distribution.

If money isn't a option 20b deffinately but it's not like a 13b single turbo would b bad lol got boost?

I would go N/A 20B just because its so rare.

9,000 rpm is gonna tear up a motor faster than 15psi will.

On a piston engine sure, a rotary, not so much, there's no reciprocating motion and 9000 RPM isn't really that much of a strain of the motor that is built properly. For the goal of the original poster, its pretty much flip a coin though, both a turbo 13b and a n/a 20b will do the numbers wanted pretty easily. Personally I'd go 13b turbo since parts are more plentiful and its a much more well documented path.

Not on a rotary it won't.

bmike has a very good point with my thinking... since it's still basicly a flip of the coin and will be up till the point that I purchase one or the other.... the fact that the turbo 13b route is obviously more comon and hence documented more is also a big factor in the route I go.... remember 9k rpms in a rotory isn't a far stretch and 15 psi isn't either... I would assume that 15psi is less forgiving (thinking lean condition) than a n/a with same hp... and with my s4 experiances... an n/a motor usually gets rebuilt after 200k miles.... and a turbo'd motor gets rebuilt less than 150k miles

There are guys on this forum that have spent far less than that on their turbo charged 20b conversions. If you want low end, stay with the stock twins as they are free and usually come with any 20b long block(less stuff to fab). Also get a cheap ebay front mount. Thrust me there are ways to do the conversion without spending an arm and a leg.

To add AtillatheFun has a 20b with stock twins and has well over 50k miles on his stock rebuilt engine and makes the hp you are looking reliably and shit loads of torque. His set-up makes more torque than hp and has low end V8 like performance but revs higher. :eek:

Rotary or not you need to take into account that 20b's handle high rpms differently than 13bs. Both engines will need similar mods to handle that rpm for sustained periods of time, however a stock 20b e-shaft (especially the 1st batch) isn't the best choice for those levels due to it's tendency to flex. You would most certainly will have to buy an expensive 2 piece e-shaft with center bearing to be on the safe side at that rpm. Below is my quote from another thread explaining why this is so


It would have been nice if Mazda built rotary's with more bearings on the e-shafts. But they didn't because it wasn't necessary for a production vehicle.

if the rotating assembly is lightened and balanced and the motor is pinned, it'll handle it just fine. but it'd be cheaper to do a 2 rotor turbo.

has anybody on here used 9.7 s5na rotors in a streetported 20b? how much power could you make with that type of setup?

Your right, but everybody has a single turbo 2 rotor. Be nice with something different.

I'd turbo the 3 rotor. But that's just me.

i agree. but the way i see it, it's just not cost effective to do a high revving n/a 3 rotor assuming it has the same power as a turbo'd 2 rotor. of course that's just my opinion...to each his own.

all the same, if he does do a pp 3-rotor i wanna see the pics :)

GtoRx7's NA 20b is built with S5 nA rotors. Search that link above. My 20b will also be built with those rotors and turbo charged.

Ever since i saw the hot version Battle at 10,000 rpm NA 20B has been i my mind if i end up keeping my car that long. Sounds really nice and the power delivery is smooth and at close to 400whp for a street. what more could you ask for?

Hmmm I didn't even think of useing some s5 na rotors in there.... I think I'll be budgeting them in also.. along with some custom beveling of the rotors... on a side note... I put one of my na s4 motors in my other fc and damn I love the feel of an n/a granted my t2 would blow it out the water... the n/a just felt better... more responsive I guess.. then again it's street ported with a rb header and track pipe to a single can. I'll update this later once I've figured out what I'm going to do, then I'll drop a price list and I'd apretiate it if some of you can critique it so I can see if this is gonna be what I really want to do... oh yea and thanks for all the responses.. they've been helpful!

i'm not bashing on the streetability...especially when i used a turbo bridgeport as a daily driver.

but do you know what it costs to make a 3 rotor capable of 10k rpm?

^ agreed. This is my vote even though I love the 20B

-josh :)

I know this an old thread but we are now in 2019. Does anyone think anything has changed? We now have faster boosting turbos but we also have some guys making good power with 20b na motors

I am somewhat reluctant to chime in here, but will anyway. I love the NA 20b and have spent a lot of time working on different things with them. I would say that, if you would be happy with about 350 whp, the 20b is a great alternative. Its a great motor. Pulls great and is extremely reliable. Plus it weighs less as installed than the usual single turbo 13b setup. I made 397 whp with mine but heard a little pinging and backed off the power to about 375-380. But 350 is a good number that is attainable without spending a fortune. Defined Auto made 425 with an extreme 20b before going to 4 rotors.

RIP guitarjunkie28 :(

Hey G!

Are you going to sevenstock this year? I'd love to see that beautiful car of yours again.

I know that the 3 rotor na rx8 in Imsa made over 400. I wonder if it could be reliable at that hp. I would love to have a 3 rotor na making 430wrhp but I dont think it would be reliable or to steerable with a peripheral port. I imagine it would require that type of port to make that type of power.

There are simply too many factors that go in to this decision. Doing a big single 13B or building an NA 20B will most likely cost around the same by the time you turn the key. Now, you can definitely get a better street driving experience with a big single 13b as you don't need the porting a 20B will need to make equivalent power. One thing you should absolutely consider is parts availability with the 20B. I've heard a lot of issues with people finding that rare center iron for the 20b as it's a very special item and comes at a premium cost when needed. I know you said you didn't care too much about cost, but it's still a consideration. The only problem with the turbo 13b I could see is if you cheap out with your cooling and system design i.e. buying a front mount intercooler from ebay. Cheaping out does no good as does a lack of education in the matter. Howard Coleman has a website that you can get lost in that teaches such about the importance of system design. Whatever you do, just be sure about it and don't look back. The biggest importance is research and to do it right and do it once. Don't forget that the 20b does have better power potential if you ever decide to throw a big single at it. Don't forget about that future planning step either!

PPorts in race cars (no compromises) make about 150hp per rotor at a min. That Grand Am Rx8 3 rotor made "450ish with Grand Am restrictions on RPM."

Based on your experience how much do you think it would cost to build a similar setup to what you have today?

And what engine mount would you use?

Hi, Johnny. I'm not really sure about the cost today. A lot depends on what you start with. It's hard to get a nice 20b short block. They are pretty expensive these days, I think. The short block, ITB's, headers, exhaust, and EMS are the big costs. I would think you build a solid 350 whp motor for maybe $25-30,000. Going from there to close to 400 whp will add at least $10,000 for the "little things". For instance, to get a motor that revs to over 9,000 rpm you need to dry sump the engine. That adds maybe $3-4,000 right there. I'll tell you that an NA 20b is a connoisseur's motor. There is no way its cost-effective for the power it can make. It is simply a much different kind of power, as I have gone on and on about. Far better for twisty roads and tracks.

Hi, Johnny. 20b shortblocks have become very expensive. Not sure what that cost is, but it could be $7500+++. Then, you need ITB's and they are maybe $3500. You need a good EMS system. I am using Motec and that's at the high end of cost, but there are others that would work, although MicroTech won't work well. Maybe a better Haltech. Figure maybe $3000 for the EMS. Then, you need good headers and exhaust fo0r a few grand. Plus, porting and assembly, including improved oiling. I would think you could get to 325-350 whp for maybe $25-30,000 on the low end. Getting over that means you have to push everything. In particular, you need to dry sump the motor to run over 9,000 rpm and that will pick up a lot of power. Dry sump costs about $3500 or so. Hope that helps a bit.

Yes. Very helpful thanks for all the info Gordon.

holy threadsurrection! I started reading from the top without looking at the dates then suddenly "$2.5k for 20B core" and I was like wut? where? when? It's like $7.5k last i checked! And then i looked at the dates! :) :lol: