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.