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-   -   FMIC and turbo question (https://www.rx7club.com/2nd-generation-specific-1986-1992-17/fmic-turbo-question-906859/)

markusparkus 06-02-10 11:23 PM

FMIC and turbo question
 
Admittedly, I don't know jack about the turbo system but I'm about to get one so I've got lots of noob questions. I'm hunting around for a FMIC and I see these really good deals on ebay and I don't know what I need to know.

I don't have plans on doing much over stock boost so what might be wrong about this IC: http://cgi.ebay.com/ebaymotors/CXRac...Q5fAccessories ?

I'm really curious about why you'd buy a $1000 intercooler?

On the stock turbo, if one wires/welds/removes the internal waste gate and installs an external boost controller, can the the stock turbo put out more than 8lbs?

How much boost before the stock ports begin to really hold you back?

hurleysurf24 06-02-10 11:48 PM

Also you get what you pay for. I have a rare greddy intercooler that originally cost 800 or so bucks, but people are more then glad to fork over 1500 for it now because of how well made it was back in the day.

RotaryEvolution 06-03-10 12:15 AM

there's nothing wrong with most of the cheaper ebay intercooler cores, so long as the welds are decent which usually they are just fine. the only issue you'll find with most of those kits is the cheap ass bubble gum "silicone" hose adapters they try to pass off on you, once they get hot they expand and burst even at stock pressure. be sure to replace any cheap ass couplers they pass off to you with some good quality threaded core multi-layer silicone couplers.

there is no reason to spend more than $500 on an intercooler core. the greddy cores aren't made any better, you are just paying for the name.

and no you can't weld up the stock wastegate and install a boost controller, you need to install an external wastegate if you try something along those lines and it is VERY difficult to weld anything onto cast iron and have it stay put for very long unless you pay for it to be professionally cleaned and tig welded. you can get higher than stock boost with the stock wastegate, it gets tricky trying to retain stock boost level once you start opening up the intake and exhaust however.

jon0886 06-03-10 12:49 AM

some of the terminology you're using is confusing, such as "external boost controller".

im going to guess you meant external wastegate.

yes it is possible to permanently shut the internal wastegate, weld on a flange to the exhaust manifold and fit an external wastegate. is it worth doing? probably not.

it is possible to increase boost levels past the stock 8psi using either a manual boost controller or electronic boost controller. however, the factory ecu will cut fuel when you exceed a certain level of boost (i forget the exact value at the moment, 11psi i believe). if you wish you increase boost beyond that, you have to get a "fuel cut defencer" which tricks your ecu into thinking that it is not exceeding the maximum boost limit. a downside to that system is that since your ecu does not know that there is an increase in boost, it does not add fuel or adjust timing to account for it.

how much boost you can run is more related to turbo compressor efficiency. this is where it gets complicated and more research should be done (search "compressor maps" and it should lead you in the right direction). basically, the turbo will get to a point where the heat it puts into the air negates the additional airflow, resulting in no power gain or loss of power. the stock turbos aren't efficient much past stock boost levels.

Aaron Cake 06-03-10 09:25 AM


Originally Posted by jon0886 (Post 10034988)
some of the terminology you're using is confusing, such as "external boost controller".

He never said "external boost controller".


it is possible to increase boost levels past the stock 8psi using either a manual boost controller or electronic boost controller. however, the factory ecu will cut fuel when you exceed a certain level of boost (i forget the exact value at the moment, 11psi i believe).
Actually it's something like 8.6 PSI.


how much boost you can run is more related to turbo compressor efficiency. this is where it gets complicated and more research should be done (search "compressor maps" and it should lead you in the right direction). basically, the turbo will get to a point where the heat it puts into the air negates the additional airflow, resulting in no power gain or loss of power. the stock turbos aren't efficient much past stock boost levels.
This is all known on the stock turbo. After about 12 PSI, you start over working the turbo. You can run higher boost but you need good intercooling and you will drastically shorten turbo life. After 14 PSI or so, the turbo will be exhausted.

markusparkus 06-03-10 11:30 AM

That helps. Thanks!

jon0886 06-03-10 12:28 PM


Originally Posted by markusparkus (Post 10034837)
on the stock turbo, if one wires/welds/removes the internal waste gate and installs an external boost controller, can the the stock turbo put out more than 8lbs?

:p

K-Tune 06-03-10 09:01 PM

use 2" or 2.5" piping for stock turbo, and you don't need a core that big. you will be losing response if your intercooler is bigger than it needs to be... as well as being forced to cut up the front of your car.

markusparkus 06-03-10 09:32 PM

too late! I already bought it. It was actually smaller than a lot of them I was considering and I did go smaller because of that reason. Oh well.


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