Mazderati

iTrader: (3)

I have recently purchased a 1985 Mazda RX-7 GSL with a dead front rotor. I am going to take on the project of rebuilding the motor myself and am wondering if there are any proven tricks of the trade when rebuilding the 12A. For example, the 13BREW is commonly upgraded with fuel jets in the eccentric shaft and smoothing of the air flow of the exhaust ports via moldable metal.

I am looking for reliability/longevity upgrades as well as any performance enhancing modifications. At this time I am probably going to perform a mild streetport using templates and advice from persons who have done this before.

On the outside I am considering a full exhaust system consisting of a RB header and straight pipe. With this said, what should I consider for fuel modifications? What will need to be done to accomodate the freer flowing exhaust?

I welcome any and all insight anyone can contribute.

Thanks.

Kyle

NanaimoRx-7

For example, the 13BREW is commonly upgraded with fuel jets in the eccentric shaft .

It must be late because this doesn't seem to make any sense, I don't see how it's possible, or the point. Maybe I'm missing something.

mperformance

for oil control...

metalliman

Yeah, you can replace the original nozzles with with Weber jets. Not necessary on a street driven car, though, more of a racing mod.

One thing you should consider is getting a hold of a oil pump from a 13B GSL-SE 84-85. It has larger rotors, and is capable of pumping more oil. If you plan on doing this, also get a rear oil pressure regulator rated for 85-90 psi, compared to the stock 70 psi, I believe. This may extend the life of your engine. One other thing you may want to consider an oil baffle plate that sits between the oil pan and engine. It helps take the foam out of the oil, so your oil pump is trying to pump air bubbles.

As for fuel mods, you should definitely look into an aftermarket carb. There seems to be a lotta guys in here partial towards side draft carbs, including myself.

rotarygod

iTrader: (1)

Moldable metal in the exhaust ports? I use machined sleeves or inserts but have never heard of that.

JEC-31

Me neither - please post a link to any pertinent info regarding such mods!

Mazderati

iTrader: (3)

The eccentric shaft in 13Bs is equipped with a ball and spring type of valve that inhibits oil flow until a given temperature is reached which is supposed to allow the motor to heat up faster. This, however, is not optimal as there is no oil flow until that given temperature is reached. It is a common for one to replace the ball and spring type of valve with a jet from a carburetor which allows constant flow of oil at all temperatures. I'm all for anything that has to do with reliablity.

Sounds like a plan. The more oil the better.

The sleeves you are talking about serve the same purpose; to smooth the airflow. With the "moldable meatal," a soft, moldable substance you can sculpt is placed in the port so the air is not ramming into a flat wall and then making a 90 degree turn. If you have had the chance to see Bruce Turrentine's video you will be familiar with what I am refering to.

Mazderati

iTrader: (3)

Just realized I said exhaust ports. Scratch that. I meant intake side. Thanks.

Kyle

rotarygod

iTrader: (1)

Ah now it all makes sense. You are referring to the plastic steel epoxy in the runners. I already use that stuff. Works great.

JEC-31

Regarding the "plastic steel stuff", or epoxy putty, don't use the Devcon brand. While it is an awesome compound, very strong and grippy, it is unfortunately soluable by gasoline. I was going to use it to patch a gastank once, but I did a test run: I set some up on a cleaned piece of steel, let it cure properly, and then dunked it in a can of gas. It came off after a few hours...

Wait a minute, you're saying, we're talking about the exhaust ports, not the intakes! Yeah, and what kind of little round motors are known to shoot flames out of the tailpipe upon throttle lift? Modified Wankel Rotaries, that's what kind. So hot unburned fuel will be slamming into the Devcon repeatedly, then after a while it won't because the Devcon will be gone and the port back to it's original shape.

If anybody's using Devcon and it's holding up, please post and correct me - perhaps they have a different formula now. The Devcon I used was labeled in Japanese, and this was 7 years ago.

diabolical1

iTrader: (3)

first, i'd like to commend you on your approach. i've never heard enough people taking the reliability-first approach - and it's a breath of fresh air to me. my first bit of advice is patience, patience and more patience ...

it sounds like you have a solid plan thus far. two of the oil mods (the rear pressure regulator and 13B oil pump) are things i would have suggested if the others didn't beat me to it. i would probably would not have recommended the Weber jets in the eccentric shaft and baffle plate , mainly because i would not deem them as "necessary" mods for the street, but they are definitely GREAT ideas -so go ahead and do them. if you really want to go all out ... then get a higher capacity oil pan as well. use this time switch to a radiator-type oil cooler if you have not already done so! be sure to have it cleaned before using it.
how complete of a rebuild are doing? i'm only asking because i wanted to know if you would want to get modified rotor bearings as well (to go with oil system upgrades) ... just a thought.


a streetport will REQUIRE an exhaust system, so there is no getting around that. my opinion would be to opt for RB SP-system over a straight pipe, but it's just my opinion.

get a lightweight flywheel and then have the whole rotating assembly balanced. also, use some silicone along the tension bolts when you re-assemble the engine.

have the radiator replaced, rebuilt.

for fuel ... get a pump/regulator combo that delivers good, steady volume as well as pressure. there have been some pretty good threads on intake systems here on the forum, so take a look to see what best suits you. you can mod the Nikki, but chances are with a streetport, you'll want to have something bigger.

i think that should cover my 2 cents worth ... good luck and keep us informed on your progress with time.

NanaimoRx-7

I get it now, I couldn't get beyond thinking about fuel...I knew it was late. No oil at all!!!! That's scary, that's a definate mod I'm doing to any 13B that I tear down, thanks.

Stripgear

iTrader: (2)

An alternate explanation of the check ball and spring:

At low RPM the oil volume and pressure is less than at higher RPM. A fixed jet would bleed off alot of oil that might be needed for the bearings. At higher RPM and higher pressure, the check ball is forced off of its seat, and that oil cools the rotors.

nimrodTT

That's correct, oil pressure will be substaintially lower before about 3k. Also, 12A's have it too, and Mazdaspeed (formerly Mazdacomp) sells a screw in replacement that's actually cheaper than a new weber jet.

Mazderati

iTrader: (3)

I don't mind going out of my way to make an engine, or anything else for that matter, reliable as possible. I would rather overkill on reliability now and not have to worry about things breaking later.

The 13B oil pump sounds good. The motor will be apart with the rebuild anyhow, so I will go ahead and do the eccentric shaft mod. The baffle doesn't sound like a bad idea either.

I am trying to keep things somewhat cost effective and have not really decided on a budget for this project. The motor, of course, will have to be rebuilt if I want to drive the car, but I would mind putting new gaskets in the transmission, maybe new U-joints in the drive shaft and checking on the rear end to see if it needs anything.
Oil cooler is also something I would like to add. If I decide to spend the money on the body, I will likely take everything off, prep the body myself and have my friend shoot if for me.

When you say modified rotor bearings are you refering to those already found in the 13BREW? I remember seeing something about how they were better in some way, shape or form.

Will a Holley, or other aftermarket carb., bolt up to the stock intake manifold?

Thanks for the responses guys.

Kyle

Mazderati

iTrader: (3)

Thought I might include a pic of the car in its present state.

Kyle

Mazderati

iTrader: (3)

Double post.

diabolical1

iTrader: (3)

I can't say that I'm very familiar with all the minor improvements of the REW, including the rotor bearings, but what I referring to, was getting the grooves deepened (or buying ones with that modification). they will cost some coin, but i figured it would be worth it.

nimrodTT correctly cited the fact that you oil pressure would decrease with the Weber jet mod, but I'm not sure if he saw that you would also be using the H/P regulator that would be giving you higher pressure anyway (so it may bring the pressure back to stock for your 3,000 RPM and under driving ... however, I honestly did not know that Mazdaspeed sold a replacement ... and it sounds like it may be a better idea ... so look it up and see.
I know that there was an adapter plate to fit a Holley to the stock manifold. I don't know if they are still available or not. I don't even know where to get them, but a friend of mine had one many years ago, so they do exist. However, my personal choice would be against using the stock manifold with the Holley ... I may be a bit slanted because I've felt the difference with using the RB/Holley manifold ... it's something else! I'm not saying not go with your plan, but for what it's worth, I just thought I'd add that.

BTW ... nice, clean car!

nimrodTT

Mazda part number: 8553-11-411
$2.45 each for the screw-in oil jet last time I ordered it. Weber jets are I think $4.50 from Pierce Manifolds

I've got the 17.5mm pump in my car and oil pressure at idle is about 10psi, about 25-30psi at 2800, then maxed out (regulated) above 3k.

Mazderati

iTrader: (3)

diabolical1,

I welcome any suggestions you, or anyone else, has to offer. I figured I might check on seeing if the Holley would bolt up to the stock manifold for savings cost, but who knows as of right now what will be the final result.

nimrodTT,

Wow. That oil pressure seems very low when compared to a piston engine or my other rotary car even. I believe my FD might idle at 30 psi when warm? The sending unit is, however, on the fritz which is all to common on the 3rd Gens.

Kyle