🔧 BUILD Quest for improved 4th gen Fbody drivability

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I wanted to update this thread (June 2023) with a more detailed summary of the 14-year journey with my 1998 Trans Am. In my day job, I'm an automotive journalist, so I drive a lot of performance cars, and every winter when the TA is under the cover I’m tempted to buy something new after driving the latest and greatest all year, but then every spring I get back behind the wheel and regain enthusiasm to keep at it. My goal over the last couple of years was to give it as much updating as possible to build a well-rounded late-model muscle car that blurs the line between muscle car and sports car, just how the new Camaro and Mustang have evolved over the years. And to get there, I had to correct a lot of self-inflicted mistakes that ruined the car’s drivability without much gain. This is quite the write-up for an only mildly interesting car, but verboseness comes with the territory, so here we go:

I bought the car from my cousin’s husband in 2009 for $4,000 with 100,000 miles. Their priorities shifted and the car was in need a lot of maintenance; it ran poorly, had dry-rotted tires and was in barn storage so it came with a family of mice for no extra charge.

What I bought was a stock 98 Trans Am with 16-inch wheels, sleek beak hood and SLP loudmouth exhaust. I immediately added drag radials, addressed the maintenance items and went to the drag strip, hoping for high 12s, low 13s because that was my expectation after being on LS1Tech for 5 minutes. HA. Well, the fastest F-Bodies run those times in later build years with 3.23/3.42 gears, LS6 intakes and factory production tweaks to the cam/heads. In stock configuration with loudmouth exhaust, my 98 with 2.73 gears, LS1 intake and 853 heads ran anywhere between 13.6 and 14.0 seconds, which was slower than my (at-the-time) daily driver mildly modded Grand Prix GTP.

From there, I added a Yank SS3600 torque converter and rear tubular lower control arms, which knocked 8/10ths of a second off the quarter-mile time to run consistent 12.8s; sub-frame connectors also went on at this time and really helped clean up the rattles and looseness of how the car flexed over bumps.

And then I ruined the car for a few years with poor choices.

I put a lot of trust into a performance shop that picked an inappropriate cam and didn’t put the effort into tuning. The car wouldn’t start when hot, it inconsistently idled and the torque converter tuning would make the car lug and vibrate. It was really a couple of miserable years with a loud, annoying and slow car. The cam was 231/235 .617/.621 113+3 with stock heads and a really mismatched powerband for an auto car with 2.73 gears. The car also had an LS6 intake, 42-pound injectors, 1 3/4 headers, off-road Y-pipe and Magnaflow exhaust. From there, I found a new tuner who fixed all the drivability issues so it drove much nicer, and then added 3.73 gears.

I had it dyno’d a few times in this configuration. The initial shop’s dyno spit out 401 rwhp. On a Dynojet at Dean's Performance with the revised tune, numbers were 370/345 in third gear with the converter unlocked. And then I had it dyno tuned from Speed Inc where it made 380 rwhp and 355 rwtq on their Dynojet. But it I was still disappointed at the track, running a best 12.0 at 113 mph. Looking back, that initial shop’s first dyno was laughable considering the trap speed and how poorly the car drove.

During this time, I also played a lot with the exhaust, finally settling on a Kooks catted Y with true merge, versus the ugly T-merges from previous designs that created that awful hammering sound at part-throttle.

And then I decided to take a big swing at the car. Up to this point, I had been running QA1 shocks at the back with drag radials, while up front was stock shocks/springs and summer tires. I hated how the car drove with a clear imbalance between the front end’s tightness and rear end’s looseness. I also had a drag-oriented short torque arm. So off all that went and in come the final suspension setup: Koni shocks, Strano springs, Strano sway bars, UMI long torque arm, double-adjustable lower control arms, adjustable panhard bar and a few other things. Holy smokes. Besides the converter, it was probably one of the biggest changes to how the car drives. Tight, controlled, responsive. It was like driving a car 20 years newer, instead of a bucket of bolts like how it drove with the old suspension.

Under the hood, I had Pat G from LS1Tech spec out a combo that would give stock-like drivability but with 11-second potential. It consisted of a pair of 799 heads (Z06-equivalent) pulled from a junkyard, which I had cleaned up and checked out, and an EPS cam with the following specs: 222/226 .626”/.626” 115 LSA +3, as well as a refresh of the valve train with trunion upgrade on stock rockers instead of something fancy the other shop installed. With this milder cam and upgraded heads with more compression, the car saw a giant torque increase under the curve, and power was much more usable and better matched to the auto trans. Now, I was making 390/375 to the wheels on Speed Inc’s dyno, but with a lot more power and torque under the curve and stock-like drivability.

That resulted in 11.82 @ 115 mph, and it has trapped as high as 117 mph. I consider this very impressive because it drives like it did when stock and power is accessible all over the place. Since then, I’ve installed a chrs1313 A/C ram air and have a dedicated set of C5 17-inch wheels with Hoosier drag radials to try and hit 11.50s, but my last time to the track with the setup was a bust because (as I discovered afterward) the throttle blade wasn’t going WOT thanks to the throttle cable adjustment being unclipped.

I still enjoy driving the car. I debate what to do with it (sell or keep) because I also feel a sense of stewardship to keep this car on the road looking and driving as good as I can make it. All the kids in the neighborhood turn around and give it a thumbs up when I drive past, and my kids (2 and 5 years old) call it “Dad’s Trans Am.” They pretend work on their cozy coupe (like dad’s car). I know it’s superficial, but I don’t think I’d get that kind of engagement in a CTS-V or newer car. Or maybe I would, because they could actually ride in a car that properly fit child safety seats … the debate continues.

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Gav'sPurpleZ

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Exhaust work is done. The Kooks Y hugs the floorboard better now and doesn't hit, and I can clear my garage entrance. The tips and fixing the Kooks to Magnaflow leak has cleaned up the sound. Those Magnaflow cannons projected the sound like, well, a damn cannon. The quad tip corsa clones have a punchier sound with less blasting and have completely changed the tone of the exhaust. They need to be raised a little. It's also nice they make the rear look wider.

3649c0ef985812c2197c0fa5623acc98.jpg


Also, I wanted some new floormats so ordered these, which seem decent enough and were more affordable than the others but feel of high quality.

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Any sound clips after the exhaust update ?
 

Gav'sPurpleZ

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thanks for the clips. I've been looking up exhaust stuff.
I know the clamp for the Y to I pipe needs to be replaced and I think the thunder racing bushing for the Y pipe needs to be adjusted because the exhaust hits the floor board here and there.
thanks to the first shop, WTF

I'm going to talk to HILROD HILROD to see what can be done. I've seen some true dual setups but I do not want to sacrifice ground clearance. I also do not want to spend money and be unhappy with the sound or exhaust note.
I spent too much time yesterday @ work looking through LS1tech threads.......
 
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Bru

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thanks for the clips. I've been looking up exhaust stuff.
I know the clamp for the Y to I pipe needs to be replaced and I think the thunder racing bushing for the Y pipe needs to be adjusted because the exhaust hits the floor board here and there.
thanks to the first shop, WTF

I'm going to talk to HILROD HILROD to see what can be done. I've seen some true dual setups but I do not want to sacrifice ground clearance. I also do not want to spend money and be unhappy with the sound or exhaust note.
I spent too much time yesterday @ work looking through LS1tech threads.......

Once the car is out, let’s meet up and go for a ride. Hear it in person.
 
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Bru

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I dropped by my brother’s place yesterday to do a birthday burnout in front of his house and only one wheel spun. I think the auburn diff in this 98 is on its way out. I believe it’s a clutch pack style versus the later year Torsen. Add it to the list :rofl: Still drives fine otherwise so might not worry about it until it breaks or if a deal pops up on a replacement.
 

greasy

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I dropped by my brother’s place yesterday to do a birthday burnout in front of his house and only one wheel spun. I think the auburn diff in this 98 is on its way out. I believe it’s a clutch pack style versus the later year Torsen. Add it to the list :rofl: Still drives fine otherwise so might not worry about it until it breaks or if a deal pops up on a replacement.

Sounds like it is time to go with a crazy custom 9" ;)

That stinks though!
 

Bru

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That would be sweet. This one’s got fresh fluid and friction modifier (all GM stuff) but it isnt the first time it’s given me a peg-leg burnout. When I was last at the track it was also hit or miss, which prompted the fluid change in the first place. This was just the first time I’ve given her a good ole brake torque (or rather an attempt at one :rofl:) burnout since then.
 
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Gone_2022

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I dropped by my brother’s place yesterday to do a birthday burnout in front of his house and only one wheel spun. I think the auburn diff in this 98 is on its way out. I believe it’s a clutch pack style versus the later year Torsen. Add it to the list :rofl: Still drives fine otherwise so might not worry about it until it breaks or if a deal pops up on a replacement.

Have a 10 bolt sitting in my garage on 2 stands. Nothing wrong with it, took it out to go 12 bolt for racing.

3.42 gear with girdle.

Located in Plainfield. Come get it for $100 bucks or some handles of good vodka.

95d6fec47bad55f7beaa00eec4d378b3.jpg



f1186f5c6778979470dd8f1cf60f3eed.jpg
 

Gone_2022

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3.42 should have come out of an M6 car, so its probably Auburn.

SLP was changing them from auburns to Torsen's for some of the 4th gen models, but I can't remember which.

Mine in the GTA is a Torsen unit out of a 4th gen.

02 trans Am. It’s not original. It was totally changed by GM at 40k miles. This unit probably has 32k miles on it

Then I had the gear changed when I got the car. Before the 12 bolt
 

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