Twin Turbo 89 IROC-Z

This page is currently under construction

Intro

This page covers the build-up my favorite project, my '89 Twin Turbo, Twin Intercooled L98 IROC-Z. I have owned this car since I was in high school, and it became the basis for my first turbo project. Before the turbo project was even in the works, I swapped out the 700R4 auto for a Tremec TKO 5 speed, and installed 3.70 gears in the Borg-Warner Austrailian 9-Bolt rear axle. With no other mods, it was running 14.0s at around 97.0 mph at my local track. Around this time, I got interested in turbochargers, and began researching the possibility of a turbo system for the 5.7L L98. The more info I read, and the feel of turbocharged cars I drove, got me set on turbocharging. Turbos are a somewhat unique power adder on V8 powered American cars, and I absolutely love the feel and sound of turbocharged American Muscle!

When starting this project, I set several goals:

It had to be turbocharged- anyone could buy a supercharger kit and bolt it up- I wanted something unique
I wanted to spend about the same or less money as compared to a similar belt driven supercharger (Vortech, etc)
Out-perform a typical belt driven supercharger system installed on the 5.7L L98, while running the same boost pressure (shooting for 12 second, 110+ mph 1/4 mile passes)
It had to be reliable enough for daily commutes, as well as long trips to cars shows (like the Wildwood NJ Cruise)
I wanted to maintain a stock appearance with no exterior clues that this is not a run of the mill '89 IROC (of course the surprise would be over once the hood was opened!)

Below I will cover the build-up in two main sections. Phase I is the intial build using two small junkyard Volvo TB03 turbos. For Phase II, I upgraded the turbos to Garrett T3/T4 Hybrids while the rest of the car was apart for a complete restification (this is why the Phase II pics show and orange body instead of black).

Jump To:
Phase I:
System Design
Clearing the Way
Exhaust Manifold Construction
Phase I (J/Y Volvo turbochargers)
Intake and Exhaust Plumbing
Fuel and Ignition
Turbocharger Oiling
Performance Results for Phase I
Phase II:
Intro to Phase II
Phase II Turbo System (T3/T4 Hybrids)
Performance Results for Phase II
Misc Pictures

Phase I

System Design

The first step in building a turbo system is the designing and planning. Since I had never built a turbo system before beginning this project, I purchased every turbo book I could find. Unfortunately, I did not have internet access at the time, so that was not a viable info source for me (there is a a lot of poor info on the net anyway). The two books that helped me the most for my first turbo project were Turbochargers by Hugh McInnes and Maximum Boost by Corky Bell. You can read more info about these books in the 'Turbocharging 101' article on my FAQ page, but I must say that these info sources were one of my best investments in the beginning stages of this project. I spent nearly a year planning this system before actually turning any wrenches. I actually started the build in the fall of 2003.

By this time I had finallized the following design aspects:

Cost dictated a JY (junkyard) type system- turbos and certain other parts, wherever reasonable, would be obtained either from local salvage yards or eBay
Twin turbo- the system was going to utilize two small turbos instead of one larger unit. This decision was made because I felt that two smaller turbos would possibly cost less, were going to make packaging easier, and because 'Twin Turbo' just has a nice ring to it! Packaging theoretically would be easier because all the plumbing could be sized smaller for a given HP goal (for instance, two 2.25" downpipes instead of one large 3.25"-3.5"downpipe). Also, on paper, cost seemed to be a benefit because it would be cheaper to obtain a decent pair of small turbos than trying to find a properly matched large turbo. I also love the look of of the twin turbos and it's associated plumbing snaking through the engine bay.
Two small intercoolers from '89 Ford Probe GTs would be used in front of each front wheel, mounted on a forward facing angle. After air would pass through the IC core, it would be released into the front wheel well area.
I wanted to utilize the stock TPI fuel injection system and ECM. Extra fuel would be added with a RRFPR, larger injectors, and an inline booster pump. Timing would be pulled down under boost with an MSD BTM (boost timing master). I chose this route to maintain stock-like driveablity and reliablity and of course to keep prices in check. Aftermarket EFI and custom computer tuning could easily be added at a later date as performance needs and budget dictate.

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Clearing the Way

The first step I took was to make room in the engine bay for the turbo system. Reluctantly, I decided to delete the A/C to aid in fitting the turbo system. The additional space obtained by removing the A/C would not only make things easier, but would also allow for a 'cleaner' (nicer looking) install, which I felt was important. In order to make the A/C delete look correct, I seriously modified the stock A/C evaporator/heater case, reforming it with custom layed fiberglass. This made the case much smaller, and got rid of that big ugly evaporator case protrusion. I would have just installed the factory non-A/C heater box, but you would be amazed at how hard it is to find one! If I had it to do over again, I may have made more of an effort retain the A/C, however I am happy with the clean look afforded by the delete.

In addition to removing the complete A/C system, I removed the AIR and EVAP emissioin system and related plumbing. This is not exactly legal, so make sure you know the rules =).

The accessory belt drive system also needed modification. My '89 came factory with a serpentine belt system, but I opted to swap in a modified accessory drive system from an '87 Camaro. The '87 uses a ribbed V-groove alternator belt and a standard V-Belt to drive the power steering. I modified the alternator mounting brackets to position the alternator very low on the front of the RH cylinder head. The power steering remained in the stock location, low on the LH side of the cylinder block. This was a pretty straight-forward swap, and looked very much like a factory install. However, if I had it to do over agian, I would have tried to retain the serpentine belt system. The serpentine belt drive would have required some reworking, but I feel it is more relible and provides a cleaner, more modern appearing system (I'm not too fond of the way multiple V-belt arrangements look).

The next items to hit the can were the window washer reservoir and coolant overflow. The coolant overflow would be replaced with a very small (2 Qt capacity) racing type coolant overflow tank. Window washers were not really needed, as the car is not driven in foul weather.

Probably the hardest part to relocate was the battery. I moved the battery to the spare tire area in the RR corner of the car. This gave me more room in the engine compartment for the turbo system, as well as helped give better weight distributuion (a battery is very heavy- its better to that weight hanging over the rear wheels!). I shouldn't say it was hard to relocate the battery, but it was more in-depth than I though it would be. I built a battery box frame in the spare tire well, then installed an Optima battery into a sealed battery box. I made sure the battery was securely fastened so that drag race tech inspectios would not be an issue. I also wired the positive battery cable through Flaming River master switch to keep it NHRA legal. From the master switch, I ran a 1ga cable front to the starter. From the starter, I ran a smaller cable up to a battery junction block on the RF fender (I used the junction block from a 4th Gen F-Body). I attached all the fusible links and the alternator charge lead to this junction block. I was very happy with the final appearance of the battery and junction block (it looks factory). The battery grounds to the rear sub-frame, and I had to build a heavy ground cable to ground the engine to the frame.

The following pictures are the best I have of the rear mounted battery system. The first one has a good view of the positive cable junction on the RH inner fender. The second picture is of the battery itself mounted in the area that the spare tire once occupied. Notice that both these pics weres taken during the repaint process, please ignore the sanding dust!