1st gen 12A vs. 1st gen 13B
 

i know this might be a stupid question but im going to ask anyways. which engine can you squeeze more power out of the 12A or 13B? now im not talkin about any kinda porting at all nor any kinda forced induction im talkin straight up HP. bolt ons like headers, exhust, after market carb sh*t like something that a normal joe can afford, and also about without going with an aftermarket ecu.i know that Hp is only dollar bills way in many cases many many dollar bills away. i did do a lil sheaching but i could have missed something or just not searched enough if this has been disscussed b4 can you pls point me in the right direction. thanks guys


charles

depending on which 13-B. 4-port or 6-port

it would the 6 port from the 84-85 GSL-SE

With no porting: 13b. With porting: 12 A or 13b 4 port (6 port is just crap for porting)

It doesn't depend on if it's a 6 or 4 port. The 13b is a larger engine, it moves more air, therefore it will make more power given equal modifications, compensating for the increased air and fuel needs of the larger engine, of course.

But you can't properly port the (is it exhaust or intake) ports on a 6 port.

not neccessarily true, the 12a is great as it, to an extent, needs less cfm to make equal power (under boost atleast). when you get in to porting it's even better. gotta remember the stock ports on a 12a are so pathetic. if you just opened them up to the equivalent of a TII block you would see very close numbers.

but yes, in stock form the 13b will make more power.

Also the 12a has left recipricating mass so can be made to rev to higher rpm with less stress.

There are a lot of factors that contribute to an engine's power level, of coarse, but the biggies are compression and breathing. 13bs can move more air through each revolution and have a higher compression ratio. Also, he asked about stock porting. I don't think there can be much debate about which engine will make more power with bolt-ons.

agreed, in stock port form the B motor will be stronger... but remember, the compression ratio is the same for the 12a and -se 13b.

I stand corrected.

and which one will rev safely without trying to make itself a claymore, this is the reason for my having a 12a, because i have killed too many 13b's.
power trophy goes to the 13b by default. the 12a will take more work($$$) than a 13b for the same power, but the 13b won't last as long and service will be more often
rambling a load of shit cos cant stop looking at the chick above- is that ur missus purple82?

Yup.

yes it does.

nope

Since when? The 6 port 13b is VERY open for porting. Check the dyno section in the 2nd gen tech, Kahren built a 6 port n/a motor that hit 195rwhp with a stage 1 street port and s5 n/a rotors. Header, test pipe, catback, TII manifolds, stock ecu, and tuned s-afc. He had to let off before redline because it was leaning out too much, otherwise it would've gone over 200rwhp.

With standalone, that port had 210rwhp potential with good tuning. His stage 2 streetport is also good for 220-230rwhp depending on tuning and exhaust. The guy that got 195rwhp before redline, with the stage 1 port, could have easily had more with a better exhaust setup and more fuel. Kahren himself got 185rwhp on a stock port 6 port.

The 6 port is very open for some good numbers.

This whole argument about 'less rotating mass', 'higher rev rpm', 'easier to port', is just crap.

Mazda chose to put the 13b in the SE's and EVERY RX7 THEREAFTER because it makes more power.

End of argument.

Trying to justify cost of modifications, porting, and all that is wasted time in the argument. The 12a was only implemented by Mazda in an attempt to get better fuel mileage in their fledgling sports car when they knew that would be a limitation for most new buyers in the market for a new car. With their efforts to make the 1981 and later motors with 'lean burn' carbs and cats to further help the emissions and fuel efficiency, this served to limit horsepower output considerably.

Base numbers for stock motors:

12a = 105 HP/100ft/lbs torque - it's entire life span in the 1st Gen RX7
13b = 135 HP/133ft/lbs torque - ending at 255 HP through development in the 3rd Gen RX7 - STOCK.

I guess the question that begs to be answered then, is why the 12at in j-spec form?

12at = 165 HP/166ft/lbs torque

Its just odd that if Mazda saw no future in the 12a that they would turbo it and add efi. Maybe a last horray or maybe they weren't so quick to kill it off in favor of the 13b.

The other odd thing being that it was launched in Sept. of 1983, making it a 84' MY. Why canabalize the 13b sales?

I thought the 12at was carb still, not EFI?

You can say the same thing about FC's, though. All jspec FC's were turbo, none were n/a. So why did Mazda have US spec ones as n/a and turbo? Because the US is a whole different market where emissions are stricter and fuel consumption are is more important to some people.

cehck the weight difference between carb and F/I.

From what I've read no. And from the 12at engine that I bought off a kid, it looks very set up for fuel injecting. Including the bosses for injectors in the irons, and the manifold that allows the turbo to nestle right against it, it looks pretty authentic.

And the point I was trying to make was, why would Mazda dump money into an engine they had plans to axe two years from then. Not about the differences in the Japanese market vs. American. To simple add a turbo is one thing, but to make it EFI is another. Maybe they realized it wasn't the way to go, interesting none the less.

Looks carb to me? But maybe I'm wrong.

the 12aT is NOT carb'd. it's a simple two injector tbi style injection.

longduck.. come on now, you can't keep comparing the later model B motors to the 12a because they added a TURBO. and they kept getting more RandD. the 12a WILL make the same power under even porting. as i said before, in stock form the damn ports are just straight up pathetic. tiny as all hell. if you bring them to the even size of the equivalent B motor and have the proper induction (carb/efi) you will be right there with it.

in stock form there is obviously no comparison, but when porting is involved then it's really a matter of preference as you can make your hp goals on the 12a, no doubt. i've seen plenty of 250- 300rwhp n/a ported 12a's... you barely ever see a 6port 13b break 200rwhp. ;)

the main reason i asked this question was i had a 84 GS about 5-6 yrs ago and it seemed like it had more power then my 84 SE and all i had done to it was remove the cat and straight pipe it. and on my SE i got it with headers, high flow cat , some kida muffler, light weight fly wheel, performance clutch, and an K&N airfilter. and i was thinking about go back to a 12A . but idont know if its the weight difference that makes it feel different or not!

The power difference you are experiencing could be from a multitude of things, such as blocked cat, bad plugs or wires, vacuum leaks, fuel filter, carbon build up, loss of compression and so on. In bone stock condition your Se should have 30 more HP, from there on its just a matter of modification....