Rotorque

I have a 86 rx7 with auto tranny which has been turbo converted by a previous owner. This means I have very little knowledge about how thorough the job was done. How many ways are there to do this conversion?
Judging by the occasional rumours I hear from people who knew the car before I had it, my guess is that it may have suffered the old pulsation damper leak and fried the original engine leading to someone popping in a turbo engine. What makes me think this is the fact that at some stage the headlight washer switch was converted to be used as a fuel cut switch. I have to turn off the car by flicking the switch, waiting for the engine to die, then turning the key off.
Anyway, now that I have bored you with that, my real reason for this post is to get your opinions on a few mods I am considering. I have found out from searching this site that a stock TurboII runs about 5.5psi boost and that seems about right on my turbo conversion too. My mechanic mate has offered to make 3" exhaust from the turbo back (I don't know the proper terms) to replace the dodgy 'hotdogs' that are on now. My understanding is that 'hotdogs' means that I already have no cat or muffler as such. Anyway, what effect will the new exhaust have on my car? Will boost go up with better flow? Or do I really need to do something to the pre-turbo part of the exhaust too? I think fuel cut occurs around 12psi boost (?) but I would be in no danger of having to worry about that would I? Please give me your invaluable opinions on this matter. I will be forever in your debt!

Felix Wankel

The fuel cut comes in at about 8.6 psi. If you run a full 3'', you'll most likelybe hitting fuel cut for sure. Some people swear against them, bu I'd get an FCD, and either a bigger fuel pump or rewire the one you have (provided it is a TII pump and not an NA one).

Also the NA auto trannies are weak. I don't know if you got the turbo ones on Australia.

RETed

You're running a J-spec car, so things are a bit different.&nbsp I know the overboost fuel-cut is at LEAST around 8.6psi, so if you're already running a non-cat FC turbo, it should've hit the stock overboost fuel-cut by now - check to see if you already have an FCD installed or a reprogrammed ECU.

With the 3" full exhaust, you're going to easily see 12psi of boost.



-Ted

Rotorque

First of all thanks Felix and RETed.
So, does a 3" exhaust from the turbo back constitute a 'FULL 3" exhaust'?
Also, I am actually not sure if I still have a cat or not. If I still have a cat (I'd check, but I won't know what I'm looking for - I have sod all practical knowledge about engines and the like, I leave that to my mechanic mates) would a 3" exhaust still reach such high levels of boost?
Other questions: Will an FCD be the only thing I need to run higher boost or will the computer need reprogramming too? How can I check whether the computer is already reprogrammed? How much boost do you think my gearbox will handle assuming it is a N/A auto? (I wouldn't know how to tell if it is N/A or otherwise, and the same goes for whether the fuel pump is Turbo or N/A).
Thanks for humouring a newbie-know-nothing. I do use the search link but these are things I have not found answers for.

RETed

Yes, there are many names it goes by, but "full exhaust" is something I use most of the time. It has also been called "turbo back exhaust" or "full turbo exhaust".

If you can get under the car, you'll see this largish metal canister in the middle of the car.&nbsp If it looks like it's made of heavy cast metal, it's probably a cat...&nbsp If it looks like a muffler (you know what a muffler looks like?) than it's a pre-silencer that replaced the original cat.&nbsp If you have the original cat still there, your boost would be held in check.

The FCD is purely to keep the stock ECU from triggering overboost fuel-cut.&nbsp Now, if you're going to push higher boost, it's recommended to add more fuel - the easiest way to do this is to install an upgrade fuel pump.

The J-spec auto's on the turbos should be able to handle 300hp easily.


-Ted

Rotorque

Ted, you rock! Thanks for all that.
I was a bit worried that a full 3" exhaust would create more boost than I want (as in, I don't have enough money to start getting stronger parts here, there and everywhere) but I just had an idea that a 'boost controller' may be a good way of keeping this in check if it does. Hope thats what it does anyway. Thanks again mate.

Felix Wankel

A boost controller can't lower boost. A ported wastegate will help a lot though.

Rotorque

Ted, even if I get a bigger fuel pump, how does the ECU know to actually send more fuel to cope with the higher boost, considering that the FCD would be telling the ECU that there is only 8psi or so? Does the bigger pump send more fuel by itself? If so, how do I stop it from doing that at lower engine/turbo speeds?

RETed

There's a big debate on what the boost sensor does on here...
So far, the jury is out on if the boost sensor actually tells the ECU to add more fuel.

My experiments have proven that the boost sensor doesn't tell the ECU to add more fuel.&nbsp It probably just retards the timing a bit.

Add to my boost sensor experiment, it has also shown that the primary sensor for fuel delivery is the airflow meter.&nbsp More boost, more air inhaled.&nbsp The ECU will keep adding fuel due to increased airflow up until the AFM slamming wide open...

To control rich "spots", I recommend an A'PEXi S-AFC, Field SFC-HyperR, or HKS Super AFR (happy jerk_racer???).


-Ted