(ENGINE) 12a Turbo Write-up
 

I am the type of person to always ask WHY!!

So you should ask your-self the same question before proceeding in this same direction if you are contemplating the act of turbo charging your first gen Rx-7.

I choose to turbo charge my 180,000+miles n/a 12a because I know that I could, but I needed to prove it to my-self. I also could not find any one that had done this, or aleast any one willing to talk about how they did it. There is also the plain and simple fact that I wanted my car faster than what it was.

So the above in combination with my, lets say stuborn to be understated, personality lead to me to begin my research on how in the world I was going to blow my 12a.

First thing you need to turbo an eninge is ,duh, the turbo:
This is easy; a second hand series 4 or 5 turbo can be hand for next to nothing. Usually they will be in usable condition. These turbos will provide plenty of air for 12a, the turbine is large for the 12a so turbo lag is more pronounced than if the turbo were on a 13b, but that is the nature of a turbo. The manifold can be hacked into place. What I did was cut of the mounting ears on a stock 13bt manifold. I then welded the "modified" manifold to a header flange I bought from Mazdatrix. Before I began modifing the 13bt manifold I lined up the manifold with the header flange to determine were the manifold needed to placed on the on the flange. All I did was line up the top and bottom of the mounting ears (before they were cut off) with the respective top and bottom of the header flange. I also made sure that the ports were eaqually centered on both sides. After marking the manifold with a Sharpie (you will need a lot of these) I removed the mounting ears from the manifold. IF YOU DO NOT KNOW HOW TO WELD, STOP. Go to a skilled metal fabricator and tell him what you need done, and show him your markings.

This is not the ideal setup, but a realiable alternative. This will also space the turbo far enough away from the motor to allow the use of a Weber rap around style intake manifold.

The turbo will also need an oil feed and an oil return. For the feed line I used -6an ss braided line with 1/4"npt fitting at the ends. For the return I used -10an with 1/2npt fittings. Instead of tapping the turbo for the pipe fittings I made flanges out of 1/4" aluminium and tapped those. I would recomend that you have the turbo rebuilt and have the turbo tapped for the pipe fittings at that time. I used a pressure/temperature adaptor block from Racing Beat for the oil supply. I drilled and tapped a new hole for the 1/4" feed line fitting because I am running both an oil temperature and oil pressure gauges. For the return I drilled and tapped into the front cover under neith the oil metering pump. THere are two locations you can drill and tap. One is directly under the OMP (very easy plumbing) I drilled and tapped the flt almost horzontal area under the OMP because I did all of this with engine assembeled in the car. If you choose my route (again not ideal) I flushed that oil pan with three gallons both through the oil fill and the new hole I made in the front crover to remove (fingers crossed) all of the metal shavings.

Turbo is done.

Exhaust; ALL CUSTOM. I used the 3" FC down pipe from Racing Beat. This down pipe is very close to the ground. If you can live with a 2.5" exhaust you should use the Bone'z down pipe.

Intercooler: Don't even try this stuff with out one!!! I used the 16 row NPR, and it works VERY well. The out let of the turbo is cool to the touch even after many hard runs. If you have a hard time fabricating the stuff for the turbo you should not attempt to mount the IC. This will take alot of inginuity. I mounted my intercooler to the tubular cross bar infront of the radiator and then to the header panel with a peice of 2" angeled aluminium. I fabricated radiator mounts with 4"x2" structural aluminium and oil cooler mounts with 2"x2" angled aluminium. Just a note, angled aluminium KICKS ASS!!!! You will need to relocate the battery to mount the intercooler.

Induction;
I would like to quote Peejay here "... besides 12a's and carbs are like pees and carrots...". So I choose to use a carburator. It is also cheaper than FI. I am using a Mikuni 44phh side draft. Mikuni because I picked it up for $350, side draft (most important asspect) there is no modifiactions needed. None. You do need to rejet for the new horse power level but I do not see this as a modification. If I had to do it again I would go with a Weber due the parts being much more availiable than the Mikuni. You will a need a fuel pump that can out flow you power needs, keep in mind that the pump needs to have the ability to provide base pressure PLUS boost pressure (ie 3.5psi base pressure plus 10psi boost = 13.5psi minimum!!) Plan on one gallon/hour for every two horse power desired. This is way over kill, but this is the area were you CAN NOT be buget minded. You will need a rising rate/boost referanced fuel pressure regulator getting it's boost signal from the carberator bonnet. I am using the Aermotive Street Rod fuel pump (way over kill) along with the matching Aermotive pressure regulator. I re-plumbed the fuel tank and the car with 1/2' O.D. tubing to accomadate the fuel pump and regulator (did I mention this fuel system is a bit over-kill!!!)

So there is the tuff stuff. I have much more info if you have questions, and I know you do, because I still have questions:D. So to any one contemplating this route DO YOUR HOME WORK!!!!!!!

Ryan:D

Good Job.

Mod's should archive this for the Newbies.

Multiple pics please :D

So, can you beat your brother's SE?

:p:

what about the carb bonnet?

Seems like a pretty simple and relatively cheap upgrade. Hope we start seeing some more attempts at this. Hell, I might try it next summer.

It'd be great to have a turbo without the full TII swap. BTW, what's the thought on HP after this, just out of curiousity? I like it because it'd be nice to just run a low amount of boost, which means better fuel economy, better longevity, easier on the old engines, and cheaper overall (stock tranny). I'm very much so looking forward to trying this.

Thanks for being the guinea pig Ryan!!

PS You should show me your system at the drift day this winter. :D

nice nice

a few questions:
what's your maximum boost level? Does it have a smooth acceleration, any hesitation while stepping on the gas?

got any pics?

P.S. Mods make his writeup sticky.

It better or this headache is going on e-bay!!!:cool:

I am using the Greddy profec B and governing it at 5psi right now. Anything over seven blows off the intercooler piping. I guess thats what I get for using smooth ABS.

No and yes. The compressor it self is producing a restriction in the intake track. Under high load and low turbine speed (in my case about 8" of vac and 2psi) the low pressure behind the buterflies "moves" out in front of the booster venturie. So what I get is REALLY bad fuel delivery, runs super lean. I do know that the turbo needs to be rebuilt, the turbine wheel does not spin very freely and I think that restriction is causing the condition. I can remove the piping from the turbo outlet to the intercooler and the problem goes away. I have not heard of anyone having driveability issues like I am having so I do believe this to be the cause.

I'm sure once I rebuild the turbo that issue will go away, I will be sure to update this thread when I do.

Yes!!!

2/3

3/3

damn dude your car looks good!! did you just get it bondo'd and repainted:D

https://www.rx7club.com/forum/attach...postid=1057334
https://www.rx7club.com/forum/attach...postid=1057338
https://www.rx7club.com/forum/attach...postid=1057339

Superb write-up not to mention a nice bit of work. :bowdown: That's really got me thinking about going along the same route.

yeap fix that turbo and enjoy your car ...

you got the hard stuff already installed and your job looks very nice.

congratulations! very well done!

Who makes that carb hat? I like it.

It is made by Claud's Buggies, I picked it up from an aircooled VW shop. www.chirco.com. They are in Tucson Az.

How about a close-up of the turbo itself? I'm just curious...and I like looking at turbos. :D

got ya covered

wonderful.....

I would love to see dyno numbers or quarter mile times.

now I want a turbo:D

How much for the rising rate regulator and I assume you went with a ~15psi @~100gph fuel pump about? So that gets regulated to 3.5psi when you have no boost with the regulator, correct? I'm sure that regulator doesn't buy itself though. :)

What is a safe boost level when you turbo a N/A motor? I know the true TII rotors have lower compression since they are running boost.

Excellent ! :D

That truly is a bad-ass setup. Congrats again.

Well written,and i agree,,well done man. besides the
plumbing issues what other problems have you ran into ? You use an MSD box ?? And you still use the stock
flywheel ??? how does the engine spin up ?? fast,,??
even ?? whats the high'iest RPM you've had the engine ?? and what is the temp like now under the hood ?? and how much $$$$$ have you invested in the conversion ??? I like the idea of longivity myself..be proud,,,and does it beat your bro's SE ??

Cool, thanks. I guess I should have dug out my old Hot VW magazines and looked myself.

What are you doing about timing? Locking out the distributor or what?

When ya gonna set up a kit, or at least a DIY page with nice pics? :D

Looks awesome, I'd love to do this for mine! Wait' I thik I will... :)

I think we're all gonna have turbed 12a's pretty sooN!