12a vs 13b power potential for csp auto-x car
 

i am planning on building a csp auto-x car out of my 1st gen, and am trying to decide which engine to go with. according to the rules, i could up to a 13b out of a gsl-se and be legal. either way, the engine would have a street port exhaust, highflow intake manifold, and upgraded performance carb, basically anything i could legally do to make power. roughly, what would the power output differences be between a 12a and 13b that were maxed out with stock ports/internals. i'm just trying to get a rough idea to make up my mind

Well, I'm sure somebody is going to contradict me on this, but the 13b;

1) with the same mods
2) with the same car
3) with the same driver
4) with the same durability
5) with the same weight
6) with the same porting (see also '6'-ports for the 13b)
7) with the same intake solution (EFI vs. carb/s)

...the 13b will always make more power than the 12a. It's because of those 1187cc's vs 1308cc's that make the difference. The housings are a bit wider, the rotors are a bit heavier (greater torque), and the fuel consumption will be a bit higher, but the 13b will put out more horsepower and torque, given the above constraints.

This is to say, that you can add a turbo to a 12a, and beat a stock N/A 13b. You can port a 12a and generate more power than an un-ported 13b, but all things being EQUAL, the 13b will put out more power. HTH,

yeah, i know it will be more power with the 13b, i'm just trying to get an idea of how much of a difference it would be so i can see if it justifies the added cost.

I dont think that there will be a great amount of difference in the hp/tq readings (30-40hp, 20-30tq?). I say that you go ahead a bridgeport a 12a engine. :D Just my .02

You can not port the motor or do anysort of forced induction and stay legal for CSP.
That being said the 13b will always make more power than the 12a.
Also, I will have to check my rule book, but I am pretty sure you can only run with the motor the car came stock with to stay legal in CSP.
Otherwise you will be bumped into a MOD class.... not fun unless you have $$$$$$$.
Stick with the 12a and do all the bolt on mods, that are legal.
As long as there arent alot of long straights the 12a should be very competiteve.

If you want a chance to WIN in a competetive CSP class, you will need the 13b, fuel injection, and Hoosier 235/50/13's.

If you just want to have fun and burn rubber, 12a is fine.

12a carb (stock) = 101 hp, ~100 lb/ft torque
13b EFI (stock) = 135 hp, ~133 lb/ft torque

Don't mean to steal the thread but, LongDuck is there a thread with specifics on your rex? I curious as to who did your bodywork & paint. Also things like pics of your interior and possibly cost. I'm planning on restoring my ride to a similar extent. Thanks.

Again, sorry for the off topic subject.

Not only higher peak, but the -SE makes more torque down low, too.

Halenstone - start a thread and I'll reply there.

As to the torque of a 13b, the SE EFI engine has a very flat torque curve from 2500-5500 and then starts to drop off. This is largely due to the 'breathing' of the '6'-ports when they open due to exhaust backpressure, in effect, providing a port location change that allows for higher rpm air intake velocity.

The added torque down low is a combination of heavier rotors, Dynamic Effect Intake (DEI), and better breathing. HTH,

This is why, if you have the choice, you want the 13b. Autocrossing, if you want to do well, is generally done without shifting out of 3rd gear. Because of this, you want an engine that's got a wide torque band for responsiveness in a wide range of engine speeds.

From everything i've heard, if you swap one aspect of an trim level (such as the 13b from an -se) you have to swap everything that came standard with that trim level, you cant mix and match.

I could be wrong, but thats the answer i always heard from the local scca guys when the question came up

The SE, although 300lb heavier than the base model, is still probably faster through the cones.

according to the csp rules, you can update a part, but it has to be done as a whole (complete engine, complete tranny, etc, not just one internal part like a lighter rotor form a 2g). since the 13b was an option in the same year, i can update to that spec 13b as long as i do not modify anything to make it fit (custom mounts or anything of the sort are illegal). looks like 13b for me. does anyone know if the 12a side housings bolt to a 13b (i am talking 85 or older while they still had the o ring in the rotor housings)?

I haven't tried it (next year, next year...) but my research tells me that they do bolt together. And this thread tells me that it would make for an illegal set up.

12a plates will bolt to pre-86 rotorhousings. very common. But not legal to 'make' a motor like that in csp or even ep classes.

a 12a will make about a max of 150hp on a stock port 12a.
1 advantage of the 12a is it will rev faster than a 13b.

I do agree with everyone though. a 13b SE motor is the way to go.
I personally would put it into an S model car though which has nothing power at all. It is perfectly legal.

You can remove quite a few things from the car in csp and be legal still.

most of the competive gen 1 cars ive seen run a 13b with some sort of stand alone ecu.

the car is a base model with all manual stuff, thats why its gonna get the race car treatment. i'm probably gonna go the carb route, although i have thought about running the holley fuel injection setup (think its 4 barrel throttle body injected). keeping it class legal is the big thing for me as i plan on trying to run some of the bigger events once i get the car sorted out.

From my reading of the rules, it was correctly said that you cannot mix and match parts on an engine, it has to be put in as a whole. In the 2005 rules, 15.1-C, "The updated/backdated part or the part to which it is being attached may not be altered, modified, machined, or otherwise changed to facilitate the updating/backdating allowance." Now, I am not 100% sure on exactly what needs to be done to drop a 13B into a 12A car, it's been a while since I have read up on it, but I don't recall it being an exact drop in. I thought it involved using a 12A endplate or custom mounts or something like that. Reading that rule though, only factory 13B mounts with a full factory 84-85 13B are allowed. If it doesn't specifically say you can do something in the rules, you cannot do it.

That being said though, my guess would be you would never have any problems unless you started winning at nationals and someone was just being a jerk. Depends how seriously you want to autocross.

Also, something you could possibly look into, an IT-7 prepped car very well may class as a CSP. It's something like that. I know spec miata runs in SP. But if you go that route, you have to fully prep it to IT-7. 3rd paragraph under section 15 (street prepared category) talks about this.

Good luck.

yeah, that was something i was gonna look into, the it setups. i know you can gut the interior along with some other stuff, just have to look into it more. i believe (this is info from other posts i have read, i could be wrong)with the gslse engine, you can put it in without any mods to the mounts (it has a different front cover)

If that is the case with the mounts, I'd definitely say go with the 13B. It makes a good bit more power over a wider range, which is nice in autocross.

Don't forget to add a limited slip when you do that though :). 15.10-P allows for those.

may REALLY GOOD competitive auto xers dont run an lsd in rx7's.
I forget their reason why.

cant mix rotars, housings and such.
has to be a completely unmodified original type se 13b.
you can put 2nd gen manifolds on it though and be legal if i remeber correctly.

i might add if you havent done this yet.

a set of adjustable tokico's and some Ground Control coil overs along with some slicks will make your car in its current condition much faster than adding a more powerfull motor.

the car is currently sitting under a tarp, and hasn't been touched in a few years. i got it from a fried who did not want it anymore. this summer i'm gonna start messing with it, and getting it ready to race. the suspension will be first, then the engine. i'm gonna get the 12a running (if i can), and use that till i can get a rebuilt se 13b put together to race on. thanks for all the advice

With my 81 w/ 12A street port w/ Holley I ran CSP. When I dropped in the 13B street port w/ Holley I ran SM. I also added a RB strut tower brace which may have also been a factor. Haven't looked at a rule book lately.