Benjin

This is a question that has been done over and over but i still cant make an educated decision. weel im pretty new to this site and i have been into rotarys for a while now and more specific gen 1 rx7's and my problem is i am looking to buy a rx7 i have the money side of things worked out. where i live i have access to plenty of 12a gen1's for sale but the i think the 13b would be a better starting point to build a high performence machine but they are terrably hard to find.i know a few differences between to two motors such as the 13b has more horsepower (30 or so) and its fuel injected where as the 12a is lighter so any help or advice would be muchly apreciated. also like to add that mechanically speaking a v8 would make a great starter motor for a rotary!!!

justint5387

iTrader: (1)

A v8 would not be a rotary

ZeikHunter

he means to use to start it

boohame

Go with a 12a if it's easier to find. You can still make the 12a extremely high-performance. Someone I'm sure will be along shortly to explain further...

My 4am input.

AcidAngel7477

iTrader: (16)

i personally love the 12a....only cause i like that old school sound..13b is cool but way too common in my opinion, i dont really know, what you would like but i guess if i had to chose it would be the 12a....cause, one they look hella good after you've done them up...easy as hell to rebuild, you get mad respect (at least i think..) although i have both a 12a and 13b (i own a first gen and second gen) the clutch on my first gen went out so i have to ride my second gen for awhile untill i get the clutch on....sucks but hey, gotta do what you gotta do....


:AA:

Benjin

hey thans 4 the replys i was affraid that i would be a loner. i really havent considerd the look or sound before i am seein ya point the look cool thanks again

shepski

12A, 3mm apex seals vs 2mm seals on the 13B, can make similar power in the long run, cope with the stress of performance mods better than a 13B. sound cooler i reckon.

Midwest 7's

iTrader: (4)

i like the old 4 port 13b's, they are like 12a's with more displacement.

JIMMY54

iTrader: (2)

if you asked me this question a few years back, I would have said 13b. But now I'd say 12A. Simply because 13b's have been done over and over, but a done up 12A car seems to grab my attention because even though High Hp 12A's exisist, they aren't as common.

Side by side at a show I think, I'd be checking out the 12A!

Also I'd keep the old school theme and go with some nice carb setup! Bridge Ported would be a dream!

my 2 cents!

PaulFitzwarryne

The main difference between the 12A and 13B is the differnce in capacity of about 0.1litre as the 13B rotor is marginally wider.

The basic difference in hp due to capacity is only 8%, the rest comes from other improvements. The 12A in the US model was detuned to 101 hp compared with 115hp in other markets. This can be improved to 150hp by bolt-ons such as better header and carb. Rebuilding with bigger ports can give you 180hp in a streetable car,while going bridgeport or PP can get you from 200hp up to 300hp in a full race version. Adding a turbo with different levels of modification can get you from 150 t0 350hp and still have a streetable car. You can also change from carb to efi. The decision on where between 100 and 350hp depends what you want to do with the car and how much money you have. Improvements cost from say $100 to $8,000! Remember the engine is only part of the improvements suspension, wheels,tires, drivetrain will need upgrading to suit the power.

The difference in weight between the 12A and 13B bare engines is under 50lb and has minimal impact on performance.

The first 13B engines came in 1972 and were also carbed. The 13B which went in some US RX-7s in 1984 were efi and produced 136hp. Latter versions of the RX-7 had engines which produced 145 and 160hp in carb form, and from 180 to 280hp in 13BT, 13BT RE and 13BT REW turbo versions. Dropping an engine from a later car in to a gen1 is common practice, as well shown in many threads on this forum; but it is not a simple bolt in procedure. The engines are relatively cheap being imported second hand from Japan, but the total cost of transplanting a 13GT would be $3000 up depending on how much work you do yourself and where parts are sourced. All the later 13B turbo engines can be improved to 450hp, and still be streetable and legal in most states.

12A or 13B? My advice is if the engine is in reasonable condition go with the 12A and have a long term plan of why, how, and cost of improvements. In reality a 12A will give you as much power you need for daily driving and the occasional track run. I have a Jspec 12AT and at 250hp it gives everything I need for fast daily use. However, if a good condition 84 GSL-SE with the13B comes up for sale at an affordable price, then look at it seriously. Its stock specifications are better. If you have more money to spend get a gen 1 with a 13BT already in it. The truth is you never get your money back on high performance modifications, so why not let someone else do the work and pay for the pleasure! Warning, get it well checked out before you buy in case it has been thrashed beyond redemption.

Finally, make a good friend of your local rotary enthusiast, they usually come more knowlegable and cheaper than the typical shop mechanic.

Asking this question is like asking how long is a piece of string. The answer is how much cash you have and I can make it any length you want. 12AT is my length.

EDIT. The above figures are best estimates, are at the flywheel with rwhp some 15-20% lower. Of course you can get 700+ rwhp from a 12A but only in 440 yard lengths.

j9fd3s

iTrader: (3)

we priced it out, building a 13b vs a 12a is something like a $50 difference in price (gap has widened since then), and its really easy to put a 13b into a 12a car. i'm talking non turbo mostly, adding the turbo adds its own issues

Radial GT

iTrader: (16)

Being a 13B only owner I have to side with the 13B. Easier to build, no they are the same engine, and still easy to build. If I were to build up a first gen, I'd be using 12A cast irons and 13B internals. You get the same saught after ports as the 12A and the greater power with the bigger displacement.

12A do sound great, on top of that they are butter smooth. I am yet to ride in a 2nd gen that has an engine or driveline that is anywhere near the smoothness of a 1st gen. Basically it is $, you have a 12A and eveything that a 12A needs to run. To change to 13B it will involve buying things.

Lee Lyons

I would obviously have to side with the 12a...I personally have a JDM-12a with a 40mm greddy turbo w/ wastegate...blah blah blah...and this little engine puts out tonnes of omph...more than fast enough to smoke anything in this area...I figure I'm pushing either close to 300hp or slightly over...the advantage with a 13b is that you can create more power with it put a huge twin turbo on there but then your into alot of money...I saw a fb with a 12at similar to mine but with about 20 or 30 hp more smoke a 700hp v8 on the track...if you build your motor well and are smart about it then you will be able to make one killer machine...its all preference...if you start off with a 13b you'll probably stay 13b...but if you have a 12a their alittle cheaper to build and mod but if you want a larger power ratio you will have to go to the 13b...

but going to something bigger means drivetrain changes...the stock rearend is rated for about 300hp so I'm pushing the limits...with a 13bt pushing more than 400 hp you'd probably want to get a 8'' or larger rearend...basically you have to change everything from the flywheel back on a 13bt to be able to handle the power its going to create...just pick one...you can always get another fb and put a 13bt in...lol...thats my plan anyway...

blwfly

iTrader: (4)

hmm interesting im also in the same boat tossing weather to start modifing my 12a n/a till i go turbo in future or just the 13bt swap im leaning towards the 12a as i probaly wouldnt need as mush power as 300hp an would do acasional drift or track day plus i all ready have a 12a and i can learn in it etc for a future 13bt im only young and have lots of time on hands

Naegleria_Fowleri

Since I have two 12a's I'm building one and its going to be turbo by the time it gets dropped back into my '84 rx7. I am going to do a 13bt in my '83. Why not have the best of both worlds? I have two 7's, may as well build them both with the two most common engines to see in them.