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Old 03-11-2008, 09:45 PM   #1
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Default Cartech IHI RHB5 Downpipe

I have picked up a Cartech setup for my 90 NA, looks very complete and in great condition, over the last few weeks I have also sourced an Innovate WB, Bipes, O2 clamp and tan top injectors. So it's installation time. The setup is designed to mate with the stock down pipe. Looks like it will fit well, but the stock DP looks rather small , quite a bit smaller then you flange from the turbo. I will put it together like this if I have to, but this would be a good time to replace it with something better. The turbo is a 4 bolt flange. Can anyone suggest a better alternative?

Thanks
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Old 03-11-2008, 10:01 PM   #2
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use it...just build a larger exhaust from that spot on....
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Old 03-11-2008, 10:14 PM   #3
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"use it", I do not have the skill to make a new pipe. How can I get a section made? It should not be tough as I could give someone the stock piece and ask them to "make one like that but larger".
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Old 03-11-2008, 11:45 PM   #4
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Neat! I'd forgotten just how cute my old BEGI System III+ looked ...

Seriously, its optimum range is in the 8 psi area on a 1.6 liter Miata. Two options:
1) use it as is
2) unbolt the portion of your exhaust between the catalytic converter to the exhaust manifold joint, bolt it to the IHI downpipe you have on the turbo, and have a good shop weld you up a new one-piece downpipe in the size you want.

Personally, I wouldn't waste the time on it; just bolt it up with a cat-back exhaust and drive. The RH5B turbos would max out around 190 rwhp with the rising rate fuel pressure regulator with J&S timing unit and 215 rwhp with the Link computer. This tended to be right on the ragged edge. 160 to 170 rwhp would be found with a system tuned for a large margin of safety with much more peace of mind. Going for more power with higher boost would result in a peaky torque curve as the mass flow fell off at higher rpms.

It's a fast spooling turbo at low rpms and pretty good for autocrossing. It is not a drag racing turbo.

It's your time and your money. For the time and money you put into a custom downpipe you will never get the performance increase you can get by going with a larger turbo. 3" downpipes are sexy and give great bragging rights but an important engineering maxim is..."Better is the enemy of good enough".

I'm not talking down your purchase; it sounds like you got a great deal. I'm on my fourth forced induction system (three from Corky Bell and one (an expensive mistake!) from a competitor) and I'm ready for my fifth (Corky, natch) . I would just hate to see you spend extra time and money for very marginal gains. Every bit of money you saved on the used system will go into "improvements" that don't really obtain you "bang for the buck". Enjoy what you have; Corky did a great job designing that system and you have a classic.

Like I said, it's a great turbo well-mated to the Miata's 1.6 liter engine. I think you'll enjoy it quite a bit no matter what decision you make on the downpipe.

Best of luck to you.
Barry
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Old 03-12-2008, 01:20 PM   #5
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Barry, thanks for your insight, 170 was my expectation. So I will put it together as it is and look for a cat-back system as my next upgrade. I have the matching intercooler to go on as well.

Thanks Again

Graham
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Old 03-13-2008, 03:34 PM   #6
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Suggestion ref the intercooler...if it's the original one in the kit it installs with the top bracket under the hood latch. Difficult to bolt in and I twice had the bracket break off of the intercooler.

Corky can, for a relatively low cost, weld the new-style brackets onto your old intercooler. The setup he developed on my car requires removal of the tie-down hooks and the intercooler mounts bolt in at those locations.

Contact Stephanie and see how much they would charge to install the new brackets.

Also, be sure the intercooler clears the AC hard lines in the nose; rubbing will destroy the AC lines (as I discovered....).

Regards,
Barry
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Old 03-13-2008, 04:51 PM   #7
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Default Intercooler

Barry, here are a couple of pictures of the intercooler. The mounts look sturdy with no signs of cracking or damage, are these the before or after setup? And how about the cool heat shield.

Graham
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Old 03-14-2008, 09:03 AM   #8
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Your intercooler already has modified brackets. They're not the same as what Corky uses now but they're stronger than the early "single bracket on top under the hood latch". You should be good to go with your setup.

Enjoy!
Barry
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Old 04-12-2009, 01:55 PM   #9
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I know this is an older thread but instead of creating a whole new thread, i thought it would be better to resurrect an older thread to ask a few questions.

I recently picked up an older na miata myself, it is also equipped with the same cartech turbo kit. My intercooler and heatshield look similar as well. The problem im having is figuring out what are all the components of this kit. Don't get me wrong, the kit is a complete kit, it came installed on the car with only 73k miles on it, however i just want to know what exactly I have. My car currently is set to 5-6lbs of boost, it has an externally mounted fuel pump, fpr, bluetop injectors and a stock exhaust with the catalytic converter. What im not sure about is, whether there is any type of fuel/timing control device used in conjunction with this kit..IIRC stock 1.6 injectors are tan, correct...its not my first turbo car, ive had lots of DSM's and love em however this is my first turbo miata. Thanks.

Nomie
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Old 04-12-2009, 05:55 PM   #10
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I have switched to a Megasquirt and a 3" full exhaust. I am still tuning on the MS, but so far I am very happy with the results. It does into boost much harder and sooner.
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Old 04-14-2009, 03:51 AM   #11
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^ as i read this thread i thought to myself, he should get a megasquirt and a 3" dp.
good call on the mods, looks like you got a pretty decent setup.
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Old 04-14-2009, 05:50 PM   #12
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Quote:
Originally Posted by NoMiEzMX-5 View Post
The problem im having is figuring out what are all the components of this kit. Don't get me wrong, the kit is a complete kit, it came installed on the car with only 73k miles on it, however i just want to know what exactly I have.
Shoot me an e-mail. I have copies of older parts lists and instructions. It may take me a few days to get everything scanned in, but I can send them.
Stephanie
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