I am contemplating making some modifications to my stock 12a engine. I have read a lot of posts about people putting on turbos and swapping to the 13B. I eventually would like to put in a 13BT engine...but my current engine is in great shape so i would like to keep it around awhile.

I am thinking about having the engine ported and also changing the carb to either a Weber or a Holley. This should up the horsepower considerably without a huge amount of modification.

What do y'all think? Any ideas?

Thanks in advance

 

Welcome to the forum. There are alot of info on this in the Archives.

You do realize to port the motor you are doing a complete teardown of the motor? If it is running fine and you plan on putting in a 13b i would not go this route. Most people that decide they want to put in a 13b or turbo never really finish or even start the project. It is alot of work and alot of $.



As far as the best Hp gainer you can do to your motor without porting is the exhaust system. Recommend the complete Racing Beat system, if you decide to get the motor ported anyways then get the street port system. If not stay with the regular system.
As far as Carb/Manifolds, if you want the most Hp then Weber is your choice. If you want to settle for alittle less Hp and want better Gas milegae then find either a used Mikuni 44phh or get a 45OER from Robert at Rotaryshack.
Another member that i have worked on his car has Roberts Oer 45 carb, Racing beat streetport exhaust system and a mild streetport 12a and gets around 22mpg combined and even with full out bonzai runs for long distances the least he has gotten is 17.5mpg.

As far as freeing up Hp the lightened steel flywheel is the ticket. Electric fan is another one to free up HP.
Se diff is a good upgrade for power transmitting along with the Se trans.
Good ignition wires are a must.
that's all you get, now do your research and see what people are doing. The search button and Archives are your FRIEND.

 

In my opinion it seems like you want streetabilaty and performance, than the best carb for this would be a rb holly 465 double pump. Easy to tune . the weber on the other hand in the rain is for crap. dont just buy take your time and come up with a budget and what you want your car to do. and execute. also read, read, and when your done read again. research man thats the key. good luck with your 12a love it, i love mine. and welcome.

 

IMHO the Holley carb does not put out Hp for the money that you spend. He wants HP and the only way he wil get it is with either the Webers or Oer45 or OER47 for the street port or a modded mikuni 44phh.

 

To add to Doc's usual good and thorough posts, you might look into a Sterling carb. It is one of the least expensive options for a carb upgrade and one of the few that comes with technical support.

 

^go on Racing Beat's site and look @ the chart comparing Holley's + Webbers, you'll see which one gets the most HP gains (at least from RB experience).

http://racingbeat.com/FRmazda1.htm

Ryan

 

easy to tune? a holly... if im not mistaken you cant change venturis, emultion tubes or air jets in them.... making them NOT easy to tune... im no professional but im more than happy with my Mikuni 44. Havent really been able to use it much yet because im having some issues but from what little i have driven it its ben a joy, and easy to strip down and rebuild, with plenty of tunability

 

I for one don't believe the hp numbers that RB put on that chart. Especially, the number for the Holley 465, 155 seems about 20ish hp optimistic for a non ported engine. However, the design of that carb seems to be a better match for the motor with the way the mains and the secondaries are mapped into the exhaust ports. I would bet that Webers have more peak hp but the Holley spreads the power more evenly across the rev range. The latter, for me, is a better match to the street. Webers were made for short intake path Italian 4 cylinders motors. A 2 liter Alfa twin cam with dual webers makes a righteous noise with right now throttle response.

 

wow...you guys are great. It is so nice to be on such an active board. I was surprised to find so many posts in the first few hours. Thanks for taking the time to educate your fellow enthusiasts.

Thanks for all the info Rx Doc. To be honest...what I am looking for is a little bit more power but yet retaining all that street driveability. I am not looking to race anyone I am probably leaning more toward the Weber carb...I have been a fan of them for a long time. The exhaust changes make a lot of sense as well.

I am wondering if there are any shops here in Minneapolis that will do the street porting...

Feel free to contribute more ideas since I will be reading this thread.

Thanks guys and gals!

 

Stock, the 12A puts out 101 hp. With a full header and exhaust upgrade, along with an after market carb, you are looking at 140-150 hp. Try to find gains like that with simple bolts ons with a piston engine.

As far as street porting goes, it will require a complete engine teardown and rebuild, for a 20-30, possibly 40, hp gain. If you don't have the skills or tools to do this, shop rates will run you anywhere from 1800-2500. I would think long and hard about that before investing that kind of money. The exhaust will need to be upgraded for the streetport from the standard RB stock port system.

Many members favor the RB exhaust system, but there is better header out there, more expensive of course, but for the same price, a full system can be built that will yield about 10 hp more than the RB.

 

what might that be?

 

What, haven't you been paying attention, done your searches? lol, just being a smarts ***.

The SDJ header produces the best performance of any header on the market. Add to that a Borla XS/XR1 as a pre-silencer , 2-1/2" piping and a high flow muffler of your choice, it will give a better hp gain than the full RB system. The SDJ header has been dyno proven to yield about 10 more hp, but it is, iirc, 450 for the header only. Check Rotary Innovation for pricing.

 

Engine porting is the way to go! Weather its a SP, BP, or PP and all the in between type of porting I think that should be your 1st step. After that you can get all the bolts on performance parts you need according to the port job!

 

That much huh.

I just finished, well a buddy mine did the actual work, a mini-resto on an 84 GS I had layin' round (bought it to race ITA but got a two stroke racing kart instead so it sat for 2 years). RB Holley, NAPA electric fuel pump (real quiet, btw), edelbrock regulator,full RB exhaust, tokico blues, RB springs, new pads/rotors/shoes/bearings front and rear, RB sway bars front and rear, Mazdatrix short shifter and Compomotive ML wheels with Hankook Rs2 Z212's (195/50's in front and 205/50's in the back). I must say the car is pretty responsive. About the only thing I have left to do is MAYBE replace the steering box (I'm real partial to good steering) and get the A/C fixed.

 

The 1st aftermarket header system and carb i ran was from Rotary Reliability when most of you guys were in diapers,lol. The header system with the Mikuni 44phh dyno'd at 146hp.
It was extremley throttle responsive and got 22-26 Mpg on the Highway on my non-ported 12a.
Trochoid, thanks for the tip on the header.

 

SDJ header for the win. But I thought that BanziToyota was selling them now under a different site.