Skyl3r

Hello All,

So, I guess I got lucky and stumbled across a guy in my area getting rid of his CarTech 12a intake manifolds. I bought them.
Before I begin asking, let me be upfront and say that while I've been doing research and trying to figure out how this works, I have never stripped down a 12a before, built a (or even driven) a boosted engine, or done much in the way of working on cars.

So first off, I saw in the original guide someone else posted for this kit that I should be using a 390cfm carb. The guy who sold me the intake told me it goes with a Holley 4150.
It shouldn't really matter what carb I use, right? Basically, any carb should bolt to the manifold? I can get a really good deal on a 500cfm Holley 4412, so I was considering jumping on that.

Now the question that's really been killing me... What size turbo is this for? I measured the inlet and outlet on the manifolds and was not able to find any information based on that.

Also, on a related note as far as Turbos go. I've been finding a load of "T3 carbon seal rebuild kits". Does any random T3 rebuild kit fit any random T3 turbo? Do I need a rebuild kit specifically for my turbo?


If I'm missing something obvious, please link me in the right direction or give me a proper term to search or something.

Qingdao

iTrader: (3)

Firstly cool find for sure.

Second you're gonna want to do lots of reading on boost. You're gonna need to muck with your ignition to keep it from pre-detonating under boost. As well as feed the turbo oil and subsequently return the oil to the case.

Almost any carb can be made to fit. but I imagine a Holley 500cfm carb will do fine. Obviously just about everyone on here will make mention the Nikki carb as a fine choice.

Size turbo.... dunno, what did you get? Picture? Turbo setups are all about piping. You can make a manifold for just about any turbo you want; its all up to your fabrication skill.

You're gonna want a rebuild kit made for your turbo. another words if you have a garret t25 you want a garret t25 turbo rebuild kit. Its like engine seals and bearings they are brand specific. there are Chinese nock offs (like Honda scooters and the wannabe Honda GY6) some parts for those turbos are transferable.

Skyl3r

First of all, thanks for the response. After a week of fruitless searching, I found out I was searching for all the wrong things.

I am quickly learning how much I don't know about boost haha
I was reading the CarTech guide on here (https://www.rx7club.com/1st-generati...ctions-780358/) and they made mention of retarding the ignition timing by 2 degrees. I assume this is what you mentioned? Is there anything besides that?

I was planning to go DLIDFIS, as I figured the better spark would be especially useful when running boost. Would that be correct?


I have two nikkis lying around now, but I've heard many people mention how much can be gained by going for a better carb. That was really my only reason. I'm not pro Holley or anti Nikki, I just want to get as much benefit as I can without spending a small fortune.

Haha... This one is hard to explain. First off, I don't have a turbo yet. I've been searching for one for the past couple weeks trying to find one that would fit my manifold. I didn't realize that I would run a hose on the compressor side of the turbo to connect to the manifolds. I thought the turbo would directly seat on the manifolds and I could not understand how to find what turbo would fit those manifolds.

On another note I was looking at the Turbo Exhaust Manifold here:
rotary-works.com: 78-85 1st Gen Mazda FA/FB RX-7 RX7 12A Turbo Exhaust Manifold

It looks decent and saves me from having to deal with too much welding, which I haven't done much (read as: "any") before. I do have a friend with a sizeable garage and welding equipment, which I figured I could use to weld on a wastegate.

Have you or anyone else heard of this manifold before? Any reason to avoid it? I read some good things about Rotary Works, so I plan to use this at the moment.


Okay, so my plan is to go with a Garrett T3 Turbo and then rebuild with carbon seals. My parts list is looking like:

• RotaryWorks Exhaust Manifold
• T4 to T3 adapter plate for exhaust manifold
• TiAL MV-R Wastegate
• IDK what turbo yet. Something between $700 and $1100 preferably though
• Oil Feed and Return lines
• Holley 500CFM 4412
• Hosing
• Carbon Rebuild Kit

That should hopefully put me right at or around $2000.
Am I doing anything stupid?

EDIT:
So we're on the same page, my plan is to go bridgeport + Turbo. I want to run around 10psi of boost, My HP goal is 300-350.

Qingdao

iTrader: (3)

Yes to a direct fire setup. That's a good plan. Depending on how much boost you run you might need to retard the timing more; or limit the amount the distributer can advance.



Nikkis are really good. Wankel=Awsome just got a similar turbo setup and mentioned the added benefit of a drawthrough boosting vacuum signal. In laymen's terms it makes a small carb bigger.


You're gonna have issues with this manifold. Its gotta be the right distance and location from the intake manifold. From the looks of it, it will space it out too far and improperly lined up.

Another thing to consider when using a newer turbo on a drawthrough setup is that newer turbos don't seal as well as older ones (like the original CarTech). Drawthrough is an older style of turbocharging. Most newer aplications use a blowthrough style and a good compressor seal isn't as important on such a setup.

What I'm saying is the easiest way for you to use this thing is to find the original CarTech turbo and exhaust manifold. That would require minimal welding and be the most effective.

You need an exhaust from the turbo back. So tack on another $500 or so depending on how much of the existing system you are gonna use and whether or not you are welding it up.

Also, you need to feed this thing more fuel. A better fuel pump is a MUST. Stronger return line is suggested, but since you are not blowing through it shouldn't be as big an issue. MSD 2225, or Mallory Comp 120. A real gauge type pressure regulator will help too.

Gauges are also a must. You need a wide band. I LOVE *** My Innovate LM-2. *** I cannot stress LOVE enough. It is absolutely amazing. In your case you could get the little throttle position sensor, the MAP sensor, and the O2 sensor and have information on all of those things. You'd be tuned in no time flat.






How many miles do you have on your engine?

Qingdao

iTrader: (3)

Honestly just do what I did....

hog out the nikki get your buddy to weld up a carb hat for your nikki.

Limit your timing.

Get a Mallory 4309 boost referenced FPR.

Bigger fuel return line.

Any turbo.

And go vroom vroom.

j9fd3s

iTrader: (3)

cartech actually made a few different kits, so pics might help. they even made one that was two weber 48ida's..

i'm not sure what turbo they used for a 12A, but for a 13B they used a T4, so you might have a T4 manifold.

i believe a T3 rebuild kit is a T3 rebuild kit, but don't hold me to that.

the rotary like a bigger hotside than a normal piston engine, they flow a lot of air.

Skyl3r

Yeah, good point. If I were to go bridgeport, would I want a bigger carb anyways? If the Nikki works, then I'll just use it. No point in paying a lot extra for no gain.

Ah... I was afraid of this. Well, I've been looking for the exhaust manifold portion of the kit and it seems it is nowhere to be found. I was hoping that with a good exhaust manifold and minimum fabrication, I could have a pretty good setup. If I know where the turbo is supposed to be, I don't think it'd be that big of a deal to extend the position of the flange.

Is the goal to have everything more or less angled towards the intake to promote flow?


I do already have a pretty high flow custom exhaust, so I was hoping to be able to reuse everything but the header.

I did forgot all about gauges... I've never done much tuning, so I'll need all the help I can get

My title says 70k, but I'm very suspicious about the odometer having rolled over once or twice. I just bought a new engine and transmission this past weekend since the one in my car now seized up. Engine and tranny have 60k. I am planning to rebuild with one of Atkins rebuild kits when I go to do the bridgeport.

Please correct me if I'm wrong, but wouldn't a carb hat be blowthrough? I thought the purpose was to equalize pressure so you don't have to do much or any modification to the carb. Or am I thinking of the wrong thing...
If so, I'm concerned that going this route would double the costs. When compared to drawthru. Especially considering I already have the intake manifolds.


Also, I was asked for photos of the CarTech manifold to help ID it. I'm on my phone and can't see who asked, but here's the pictures:

j9fd3s

iTrader: (3)

ah that one is draw through, they had a blow through one as well.

tuning should be pretty easy, you want to start so rich it barely runs, and then lean it out until it cleans up and then leave it there. if you have an AFR gauge, you should be around 11:1 AFR. timing should be around 10-12btdc Leading, and you want to keep boost pretty low to start with. maybe 5-6psi, and then once its dialed you should be around 8psi.

more boost than that, and you really should have an intercooler, these old school bits work best when you keep power to a medium

Qingdao

iTrader: (3)

No intercooler on a draw through.

fuel, atomized, pressurized, and in a canister hanging from the front bumper= bad news.

Yeah, I was suggesting blow through. Its cheaper, but you're already invested with the intakes you have.

You might have to get someone to weld up an exhaust manifold for that turbo. I don't think you're gonna find an off the shelf replacement. Save if you find a CarTech manifold someone is willing to part with.

You'll have to start with getting a turbo that fits the intake (or at least close enough). Then you can mock it up to the exhaust ports on the engine. Not too difficult, but not easy by any means.

It is much easier to tune a drawthrough. Cause you're not pressurizing the carb. its essentially just tuning a carb with a bigger engine under it.

Skyl3r

Alright, I'm feeling much more confident about tuning given what you and Qingdao have said. It doesn't sound that bad. We'll see when the time comes
I've read that 8-10psi is pretty standard for drawthru. It's not hard to find stories of people running 14+, but I have yet to see anyone recommend it haha

Yeah, I'm only a few hundred dollars deep, which given the scope of the project isn't really much. I think I'm actually more concerned with the learning curve. I'm not only financially invested in drawthru, but I've invested all of my time thus far researching it and finding parts and such.

I'm sort of confused by what you mean when you say "fits the intake"? What am I looking for with this?
You've inspired me to find some pictures of drawthru setups to see where the turbo sits relative to the intake. What I've seen is basically the turbo is just slapped up as close to the intake as humanly possible. The process you described here is probably what I'll end up doing (fitting the intake, then finding a way to get the exhaust to it). I have a friend who just finished building a custom exhaust for his mustang, so hopefully I can recruit him for helping with pipe bending.

Yesterday morning I was really just grasping at straws and now I feel like this is doable.

wankel=awesome

I am so pissed that I have had a want to buy thread fit that kit on this forum and many others for close to a year, and after I settle for a side draft draw through someone finally broke loose and sold one.

that kit had a very special turbo and exhaust manifold.

I have one of the turbos, and it's nearly identical to the Hitachi ht-18 (hint)

as for the manifold, good luck.


Start with a SMALL 4bbl. The 525cfm edelbrock AVS would be perfect for your needs.

that kit does orient the 4bbl correctly, but I would still avoid holley because of the design itself. They tend to not resist fuel boiling at all, and repeated warm up/cool down sessions causes them to leak from almost everywhere, and that's not a great advantage when it's perched atop a turbo.

I have the manual for that kit, and they suggest 2* retarded ignition PER PSI of boost. They also *highly* recommend the use of BR8ET spark plugs, and it literally says not to attempt the use of factory br8eq-14. I don't know the reasons behind this.

premium fuel required, and it specifically says to run the Holley at 4 PSI. They used a few different fuel pumps, but the most widely used were Facet and Carter. I recommend the Carter. It's the same one on j9fds's pport, part # escapes me atm.

Your idle speed also has to be a bit higher than normal, they recommend 900 RPM.

There's a drain at the bottom of the turbo compresser housing btw, and it leads to the intake manifold. You cannot omit this.



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Skyl3r

I bought it back in the summer. Are you in the Ohio Rotaries club on FB? I've seen a lot of rare items come up for sale for really good prices on there. You could try putting up a want to buy post, but most people seem to ignore those haha.

Do you happen to have a picture of the exhaust manifold? I haven't been able to find one and I'm really interested what they look like for design purposes.

Alright, hint taken. I'll do some research on the Hitachi ht-18. I assume something about the design makes it better suited to drawthru?

Okay, that's interesting. I've never heard that about Holley carbs. I'll check out the Edelbrock carb you recommended.

I was reading the manual here: https://www.rx7club.com/1st-generati...ctions-780358/
They recommend 2 deg retardation for 5-6 PSI. Is this not for my kit or something? I don't know much about timing, but I'd think there's a pretty big difference between 2deg and 10-12deg...



I was planning to get a better fuel pump for handling the increasing needs of a bridgeport and higher than 8psi of boost. I've seen someone on this forum say they were using the stock pump with a drawthru at 14psi. My understanding of this is, as Qingdao sort of mentioned before, the turbo creates more vacuum under the carb than the engine normally would. Even though the fuel pressure stays the same, because the carb pressure is lower, it should make the same pump more efficient, right?
To be clear, I'm not trying to be that guy that asks for help then argues with everyone. I want to learn and if I need a pump, I'll get a pump.

A drain at the bottom of the turbo compressor that goes to the intake? Do you have a picture of this or something? What does it do?

wankel=awesome

This fitting

it's job is to drain excess fuel from the compresser housing while cruising/low RPM. otherwise, fuel puddles and messes the AFR up completely.

Skyl3r

Okay, that makes sense. I haven't seen this on a turbo before. I'm assuming it's not a typical feature as most turbos aren't gonna have fuel running through them. Will I need to tap a hole for this myself?
I didn't see this on the Hitachi when I was looking at pictures, so I assume so...

Okay, I thought of another question...
If I had a hole with a little line run to the intake manifold from the compressor of the turbo, wouldn't this be a problem? I mean fuel and air would be constantly pressed through the hole at a lower pressure than the air that goes all the way through the compressor, right? Am I missing something?
Is this a common practice? I was trying to find images on google to see how the complete setup looks and couldn't find any.

jim_chung

iTrader: (2)

OP those are my Cartech Installation notes that you linked to. I have the full 12a Cartech Drawthrough system. PM for questions you might have. I don't want to publicly refute a whole lot of conjecture that really isn't true and embarrass other members.


regards,


Jim

Skyl3r

I appreciate it. I sent a PM

wankel=awesome

Or you could post it here, where it does some good. I only just acquired a system such as this myself, and everything I have been telling him is a direct result of my own research on the subject, or what I have in writing from barely legible manuals.

If you have other knowledge on these setups, or real experience with a running one, you'd be doing everyone a favor by posting it here. If I'm wrong about something, I'd love to know before following the bread crumbs of almost totally diminished data. Most of it being hearsay, or even rumor, and damaging the system or my own engine before installing it.

​​​​I do have parts from that particular system, and the exhaust manifold most certainly is unique, and the turbocharger is special as well, being a carbon seal.

Qingdao

iTrader: (3)

Refute away. I want to know more. I honestly don't know much about drawthroughs as I have never done one.


I was thinking about the after turbo cooler though. I was told "don't put an intercooler on a drawthough" a couple of years ago and I just took it at face value. I assumed it was because of the pressurized fuel being dangerous. BUT today I was pondering on it and I think that its more because of the nature of suspending a liquid in a gas then cooling it. The fuel in the intercooler would have the tendency to fall out of suspension.... am I right?

wankel=awesome

The common belief is that it puddles, and creates an explosive hazard in the event of a backfire.

Qingdao

iTrader: (3)

^^^ a reputable source advised me against it years ago when I was doing a Honda CMX250 turbo project.... I listened to him and never questioned it.

I figured it was something to that effect; just didn't know for sure.

Skyl3r

This is what I've been told. You have compressed air and fuel in a metal pipe. I've never seen nor heard of it happening but I can imagine that if it were to be lit, it could be catastrophic.

Something I've heard that seems to be overlooked is that the fuel from a drawthru is actually chilled when it reaches the engine. That's supposed to be one of the perks of drawthru. When you compress gas it creates heat, then when it's rapidly expanded it can actually reach subambient temperatures. I haven't seen it, but I've seen several people say that after a few pulls in their drawthru setup, they'd actually get frost building up on the intake.

This is hear se but I imagine if the turbo can absorb the heat from compression, this could be the result. You can't deny that it'd be cool to see frost building up on your engine BECAUSE you're driving it haha.

jim_chung

iTrader: (2)

Ok, so I'm going to answer Skyl3R's questions that he emailed me here in his thread for all to see. I'm no expert but I have lived with this setup for more than a decade and I like it because it is so period correct and it drives as smoothly as stock, starting the car is no more difficult than usual and I see no fuel starvation issues when driving fast around sharp corners that many attribute to the Holley carb float design.

I bought the unit used, but essentially new since the original owner crashed his car shortly after it was installed. He removed it and it sat on a shelf for many years.

The original Cartech used an IHI RHB6(?) turbo from a diesel application but the heat and lack of turbo timer means life is short for the turbo. Still it pulls very nicely and I was running 7 psi boost. I think I drive the car maybe 500 miles a year. After putting maybe 3000 miles on the turbo, the car started spewing smoke on idle at the stoplights. I spied a crack in the exhaust/turbo manifold. Removed the unit hoping to have it weld repaired .... but the cheap alloy casting cannot be welded. I had the turbo looked at by a specialist and it was on its last legs as well. He put together a T3 unit for me that would occupy the same footprint and I had to have a custom manifold fabricated using the RB exhaust flange.. Car still smoked. We pulled the engine, cracked it open and with less than 70,000 miles on it the housings showed massive chrome flaking. I don't know if the damage was due to boosting, poor lubrication etc. So I now run premix just in case in addition to running to OMP.

So onto Sky's questions.

1. Retard ignition 2 degrees per PSI?

I don't recall having to change the timing at all. People also talk about locking the distributor's auto advance mechanism. Just run conservative boost and use high octane gas.

2. Drill a hole in the turbo compressor (I guess?) and run a line from the turbo compressor to the intake manifold to drain fuel.

Again I don't recall that being a part of the original Cartech setup. I suspect any condensing fuel will quickly reevaporate with all that air rushing into the system from induction.

3. Holley carb is a poor choice because it can't handle boiling fuel?

I'm not familiar with this phenomenon. All I can say is I used the 4160 Holley that rated at 390 cfm flow. It works. The big no no is using a monster carb since the tiny 12A can't theoretically flow even that much air and monster carbs just produce very poor throttle response and no mileage economy that a small four barrel with secondaries can.

4. Do I actually need a new fuel pump for 8-10psi when running drawthru? The guide says for 8psi most stock mazda pumps are fine. Is this tried and true?

Yeah, you do. Stock pump might be good for normal city driving but if you're boosting you want to run slightly rich to avoid preignition which will quickly kill a rotary. So why take a chance, get a stronger pump. I used the red Holley which is not the best, too damn noisy.

5. Is the Nikki a good choice compared to a 500CFM Holley? I've seen other places that upgrading the carbs would lead to sizeable gains.

A modified Nikki would be a very good carb, but you have to take a grinder to it to improve its flow. Sterling and others on the forum used to sell modified Nikkis and they can sometimes found for sale second hand. Again 500 cfm carb would not give you any HP gains and only reduce driveability.

6 I mentioned using the Rotary Works 12a Exhaust Manifold previously. That seemed to get shot down, but I'm not sure if it's actually a bad idea or not. Do you have an opinion on this?

I dunno, looks like its only the exhaust flange which you definitely need as a foundation to have a custom manifold fabricated. Or go Racing Beat.



regards,

Jim

t_g_farrell

iTrader: (1)

I think a hogged out nikki modified for boost would be a lot cheaper for you than getting another
4bbl carb like a holley. Check out Jeff20B thread on boost prepping a nikki. Hogging it out is not
that hard given all the other stuff you need to do for this. Plus using the original nikki carb with
the classic CarTech turbo, priceless!

Jeff20B

iTrader: (13)

Yeah, I'd have to agree. The methodology I use to modify Nikkis is many times better than what Sterling ever did. He never really embraced the air bleeds for some reason, which I've found to be the key to better running. But it's all the little things too (I mean big things, like my hogged out venturis) and avoiding his errors in judgment.

But I will say this about a draw-through. Because you can't take advantage of pressurizing the float bowls, nor increasing the incoming fuel pressure above the 2.5psi base, it keeps the Nikki as the smallish carb it actually is. Only by using a Nikki is a blow-through configuration, can you experience the whole enchilada.

With that said, I am planning several NA projects with hogged out Nikkis of various venturi sizes (some that would make your heart skip a beat) due to the disadvantage of having atmospheric pressure only to play with. You have to go big or go home when NA, but you can't go too big because then you'll get a flat spot between 1700 and 2100 as the stock transition circuit was never designed for venturis sizes of this magnitude, and this circuit can not be modified as far as I know (and believe me I've tried). Anyone smarter than me want to try? All I can do for now is get rid of the pr-reversion lip in the baseplate by gently hogging it out and making sure there are no other lips the might encourage reversion along the way into the ports. This is why it's a stupid idea to hog out an intake manifold most of the time, but lots of people do it anyway.

Skyl3r

Thanks for the response!

1. Okay. I assume it should be easy to tell if I'm getting detonation, at which point I'll want to adjust the timing.

2. I'm not gonna drill a hole unless it's really necessary. I still feel like that's gonna act as a leak.

3/5. I'm still confused. Lots of conflicting information

4. Alright, I'd probably have had to upgrade sooner or later anyways.

6. Yeah my intention was to use it for the exhaust flange and it'll have the basic pipes I need already. So... should be as simple (at least in theory) as welding on a wastegate and running a pipe to the turbo and back to the exhaust.

I'm a little confused at this point. If the Nikki will work fine, I'll use it. Otherwise, I'll plan on upgrading to a 390CFM Holley.


I thought I'd also ask about this. I was researching turbochargers again and I was seeing if there's any out there that come with carbon seals. I saw people saying that Dodge/Mopar and Ford turbos had carbon seals for a long time even when they weren't drawthru. I'm deeply considering dropping by a junkyard and pulling a T3 turbo out of an old Dodge or Ford. That'll basically cut my costs in half. Save me having to rebuild/balance a turbo with carbon seals and not really lose anything while I'm at it.

Is there any reason I should avoid getting a Turbo out of an old Dodge or Ford?