How much more horsepower does the 13b make over the 12a
 

This may have been covered before, but all things the same how much more power would the 13b make? From the factory the 13b makes quite a bit more, but that could be due to the fuel injection. The 13b is about 10% bigger, so it should be compareable to the difference between a 350 and a 383 SBC, correct? So for instance, if you had a stockport 12a and a stockport 13b, both with weber carbs to keep thingsg the same, would the 13b noticeably faster?

Yes.... Your question is kind of self explanatory, lol. Kind of like buying a short candle and a tall candle and wondering which one will burn longer.

12a stock: 100 (101)hp
13b stock: 130hp

Trust me, you can really feel the difference.

Here is a guide Racing Beat uses to compare carbs....when you get into bridgeport engines, not so much of a difference...

hmm 180 hp from a nonported 6port... that's pretty good!


there might be more torque from a 13b bridgie than a 12a bridgie

roughly all things considered equal (porting, exhaust, carb, etc) the 13b will give 10-15% more power however the midrange torque is where you really "feel" a difference.

I would highly recommend you try to find someone with the 13B. I had a second gen that was really nice (but the car felt heavier and way too stable for me).

I also drove a 13B SE (84 or 85) and that was a completely different feeling - it ran like a raped ape compared to my 82 12a (and this current 12a has more power than my 82 with 20K miles that I had in 1983 so it is no slouch).

Scott

i put a 88 13B in my 84 SE and it was faster than most S5's and it was pretty quick it ran low to mid 15's and i had no experince what so ever that was also b4 i put the S5 intake (VDI) on

as far as a HP number no clue but most likely more than 140

The 13b does have more power and torque but it's also a lot heavier. I prefer a racing carb, straightpipe exhaust, and peripherally ported 12a. Then that motor will scream and the difference between the 2 with those mods is pretty minimal.

A 13b is 'a lot' heavier?

All of that extra weight is in what exactly? Wider rotor housings for greater displacement, that's what. That greater displacement creates more power because you have more fuel/air mixture being burned.

So, the excess weight you're referring to must be,... the larger oil pump? Oh, the longer oilpan? Maybe the longer eccentric shaft? Or you must be referring to the 1mm wider apex seals...

The reason why ALL new production rotary engine RX8's these days have a 13b in them is precisely because they can develop more power than a 12a, and is also the reason why nobody still makes a 10a from the original Mazda design.

It's pretty simple, really.

more weight, lol......

Weight difference is minimal. Unless you are talking a full blown stock EFI setup on the 13B vs. perhaps a naked 12A running a carb.

The late 13Bs actually have rotors that weigh less than the 12A ones. The RX-8 e-shaft (can be used in any 13B..about $160 new) is 0.6 lbs lighter than a typical 13B e-shaft. Not sure how it compares to the 12A, but I imagine they are about equal. 10mm wider rotor housings (aluminum), 20mm longer oil pan about round out the differences. All in all, you are looking at maybe a few pounds more for the 13B block vs. the 12A one.

If you compare apples to apples, the 13b will win the power to weight ratio.

I can make a 13B weigh less than a stock 12A. Aluminum flywheel, FC waterpump, aftermarket carb (they usually weigh less than a Nikki/Hitaci with their cast iron throttle body).

I once added an aluminum GMB aftermarket waterpump impeller for an FB to an aluminum FC waterpump housing. Even greater weight savings over a stock FC waterpump.

this is true ... but
... this is false (comparing one shortblock to another).
this has nothing to do with anything because you're either comparing a PP 12A to a stock ported 13B, which is pointless; or you're comparing a PP 12A to a PP 13B, which would make this false.

side irons went on a diet too, i bet the REW core is within 10lbs of a later 12a. the early (68-73) 12a's are probably 50lbs MORE than the 13B, THOSE are heavy

This is also an extremely streetable setup, good for daily driving, practical powerband, and a civil exhaust note to avoid unwanted attention.

generally 13b>12a...with a few exceptions

MeCalledEvan:

You need to hold back on presenting opinions as fact. Glad to see you on the board, but try not to steer anyone in the wrong direction with incorrect information. You recently told one poster that a 2,000 rpm idle is "not that bad", and that you like yours to idle at around 1,600 rpms. That is just a little bit ridiculous...

I was surprised to see that RB rates a 12a bridgeport at 250 hp. I guess I thought it would be a bit less than that, unless they are talking about a "total" build (all the little mods you need to run at 10k+ rpms)...

Huh???

I don't believe that I've ever heard a peripheral port described as "extremely streetable" before. "Civil exhaust note"? "Practical power band"?

This goes against everything I've read and understood about P ports. What is your information based on? Very curious :scratch:

Ummm... I think he was being facetious (sarcastic, polemic, take your pick).

'teal' is the Lounge color to mean sarcastic. :)

this is it. 7 cookies for you (3 for this, 4 for helping me with my car!)

I'm semi colorblind. actual teal looks like regular text to me. :) you are correct though!

lets just call it what it is... sarcastic asshole. :icon_tup:

+1

The midrange torque is where it's at.

i was gonna say, i own one, that's sarcasm!

although it will happily idle @850 rpms...