I bought a 91 TT with 79k miles that the previous owner had pulled the engine and had turbo's rebuilt along with changing out a number of other wear items including timing belt change, new injectors, new iridium plugs, one piece driveshaft, etc... He was a military guy that really took care of his stuff and it shows. Mods include cat and egr delete, bigger intercoolers, and single pop charger.

I bought a new Greddy Profec EBC, 740cc injectors with adapter kit, new gaskets and such (probably doesn't need yet), and a set PFR6B-11B plugs. Also pre-paid for a specialty Z ECU tune but I haven't sent my ECU in yet because I wanted to install the Greddy first to see where I was at.

I installed the Greddy and with mild tweaking I'm easily getting ~14 PSI (have it set to Alarm and drop at 14.5) using 93 octane. If I'm correct this is at the limit of my stock turbos, which I don't plan on upgrading anytime soon. I'm totally happy with 13-14 PSI and it really friggin' puts me back in my seat. Love the car.

Do I even need to put the injectors in and get the ECU mapped? Is it a problem running it the way I am with the EBC?

Thanks ahead of time.

First, welcome... and congrats on the purchase! I also just got a '91 TT a few months back.

With that, I'm still relatively new to learning about this car, but I've been digging pretty deep into guides, etc. even before I bought. As far as the injectors go, I don't believe you "need" to put them in (depending on the rating/condition of the currently installed ones). A general rule of thumb is that the delivery rating of the injector should be equal to or greater than horsepower you're getting. Now, since you're already bought them, I don't see why you wouldn't go head and install them.

Regarding the ECU, it's what pulls everything together to make sure the engine is running properly, based on your configuration of mods. As I understand it, SZ will need to know everything to tune accurately... especially if you're running at higher boost and with different injectors, as both of these have a significant impact on the fueling requirements of the engine. I suspect you run the risk of running too lean as you're at higher-than-stock boost and may exceed the adjustment capability of the stock tune, and since the ECU does control the injectors, I expect a new tune goes hand-in-hand with new injectors (well, different spec injectors, anyway).

Those are my thoughts - surely some of the guys who have more experience will be able to provide some insight or correction to my thoughts if needed. Honestly, if you've already spent the money, I'd go ahead and take care of everything to get the most out of your car... safely.

P.S. Did the seller provide documentation for the timing belt change? If not, it's better to be safe than to run the risk of a timing belt failure, which will essentially destroy the engine.

Yes and Yes, your stock injectors will be near the limit if not over with the kind of fueling you will need running 14psi on stock turbos. Since you are changing the injector size you have to get the ECU tuned to match, plus they should be making tweaks to the maps for the rest of the mods to maximize what you get out of them.

^This. You'll exceed the safety zone for the stock injectors. You don't wanna run the injectors at max duty cycle all the time. That'll create a dangerous situation in the event of even a slight misread of an O2 sensor or MAF reading, and possibly cause a detonation issue. 14psi is more than likely going to put you right at that max duty cycle, depending on what other breather mods have been done. You'll wanna swap to bigger, and with that, a tune is necessary. Gotta tell the ECU to step that duty cycle down due to the larger amount of fuel being metered.

Well... plenum is off and new injectors and plugs are in. Previous owner did an EGR delete and coolant bypass already so that helped A LOT. ECU is on it's way to Specialty Z. I should have a week or so to mangle this thing back together.

^ These guys -

Nice job getting into it! No doubt you'll be happy with the result. No coolant bypass for me - it was great that the car was about 98% stock when I got it, but damn, there's a lot I want to do. Although, there's no better way to learn about the car. Be sure to keep us posted. Once I get through the laundry list of stuff to get my car 100% and cleaned up via deletes, I'll be looking at stepping up the boost. Fortunately, it's it really good shape, just coming up on the 120k service and the clutch is starting to slip.

I'm about to do a plenum pull and i'm not sure if the coolant bypass has been done previously or not, does anyone know the potential drawbacks of doing this? Most sources I've seen say do it, but surely thrre must be some -possible- complications or drawbacks from doing it?

I've yet to do it, but it's on my list. As I understand it, the coolant routing to the throttle bodies is done to eliminate the potential for them to freeze-up in extreme cold. From all my research, I've yet to read anything about any negatives from doing the coolant bypass. Conversely, I believe just about anyone (I can't yet, technically) will testify that it greatly simplifies future plenum pulls. Plus, you eliminate a lot of potential coolant leak points.

I have to refer you to the plenum pull link in the "All you need to know..." sticky, if you haven't aready done so. I have it printed out and sitting on my workbench...along with the AIV and clutch bleeder delete.

Robo's site is excellent for plenum pull/coolant bypass as well... as well as TONs of other stuff, too:
http://www.twinturbo.info/63104/16304.html

Woodnutz78 wrote: ↑

Tue Oct 16, 2018 9:33 am

As I understand it, the coolant routing to the throttle bodies is done to eliminate the potential for them to freeze-up in extreme cold. From all my research, I've yet to read anything about any negatives from doing the coolant bypass. Conversely, I believe just about anyone (I can't yet, technically) will testify that it greatly simplifies future plenum pulls. Plus, you eliminate a lot of potential coolant leak points.

^^^^This.
A very common delete process, no real downside possible as the coolant lines were meant to avoid a situation that really never occurs and removal allows a far easier plenum removal and re-install, with the second-best benefit the lack of potential leak areas under your plenum where you can't fix them.