🔧 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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Bru

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I thought the car's performance at the track day was shit, so I was a bit sour on the thing, but I found some silver linings after comparing the track day's run with my previous best: a 12.1 versus PB 11.8.

60-foot: PB 1.61 to track day 1.66 -- Honestly, not too bad considering I changed the shocks from stock replacements to Koni Yellows, and didn't adjust the front shocks from street trim. Plus, I ditched the tunnel-mounted torque arm for a UMI long arm. Those Hoosiers at work! And maybe the lighter wheels. All I did was take the slack out of the converter and mash it.

Back-half MPH: The track day run gained 9/10 a mph in eighth-mile to quarter-mile mph versus my PB, and in 90-degree heat and 3,000-foot DA, versus the -700 DA and high 40s temps of my PB. My overall trap was down, though; perhaps this is just within variance, or it indicates the ram air is working considering it gained more MPH in the same distance.

Really stretching it: The drag times DA corrector spit out 11.6 @ 116 mph.

Anyway, that was a long way to say maybe something isn't wrong with the car like I initially thought. I still want to scan it, and like the last time at the track I'm not thrilled about it puffing black smoke at higher RPMs.

 

Bru

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Car looked good, I was watching you since I think we are pretty similar set up except I can't launch my car for shit and I'm worried about blowing up the stock 10 bolt, so my times suck. So I just compare to yours hoping I have that potential, LOL.

Ha! The stalled auto and 3.73 gear are great for getting out of the hole versus a manual car. That Vette caught me sleeping at the light but I still jumped out ahead until about the 1,000-foot mark where he came around (his 118 mph trap vs my 112 mph). It's the one thing I love about this current setup - that I can keep up with a lumpy cam wildly loud car with my stock-like idle and quiet exhaust.
 
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JFish75

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Ha! The stalled auto and 3.73 gear are great for getting out of the hole versus a manual car. That Vette caught me sleeping at the light but I still jumped out ahead until about the 1,000-foot mark where he came around (his 118 mph trap vs my 112 mph). It's the one thing I love about this current setup - that I can keep up with a lumpy cam wildly loud car with my stock-like idle and quiet exhaust.

Ok maybe not so similar then, :ROFLMAO:, I am manual with stock 3.42 gears. Last time I ran I kept bogging off the line, (clutch is like an on off switch with the Tick Master cylinder) I think my best was like a 2.0 60 ft or something, but MPH was about the same as you just over 112.
 

Gav'sPurpleZ

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Gav'sPurpleZ

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Looks like I didn't update this thread after track day, but later in the summer I found that the cruise control adjuster was out and the throttle had a ton of slack in it, preventing me from WOT. Definitely would have hit 9s without the slack. :mrss00ls:

Hilrod noticed this also on my car. Could be the reason for the lower or even dyno numbers.
whatever, my car is running great and some small items are on the schedule for 03/29/22
 
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Bru

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Installed a new stereo in the TA because new iPhones don’t work with the old ass receiver I had in there. Pioneer single din with a built-in phone holder instead of a CD player, and the mount rotates so I can use my phone in landscape or portrait for navigation. Genius, and works great.

PIONEER SPH10BT Single-DIN in-Dash Mechless Smart Sync Receiver with Bluetooth

Also installed a steering wheel control interface to make the steering wheel controls work, which haven’t for 10 years with that old stereo.

Also, I though I’d have to replace the fuel sending unit because the gauge dropped to zero, but would still do the full sweep at startup. Before that, I read a tip to fix a faulty fuel gauge by adding Seafoam to the tank that helps free gummed up contacts. And it worked. Fuel gauge functional.

On the downside, with the fuel tank full, I remembered that I have a problem where gas sloshes out of the filler in corners. Doh. Need to figure that one out. Thinking might be full charcoal canister or faulty cap. Appears like it’s coming from the vent holes in the filler neck.

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Turbocharged400sbc

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you have a buncha damage at the cap gasket, but the anti siphon float ball must be missing as its a primary anti reversion meassure like the metal flap is the secondary

with how cheap the vent solenoid is id suggest having one on hand to toss in....i constantly see em with leaks and every now and then plugged with dirt in its foam filter.

at least your filler neck hasent rotted a hole in it like my CrapG
 
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Bru

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you have a buncha damage at the cap gasket, but the anti siphon float ball must be missing as its a primary anti reversion meassure like the metal flap is the secondary

with how cheap the vent solenoid is id suggest having one on hand to toss in....i constantly see em with leaks and every now and then plugged with dirt in its foam filter.

at least your filler neck hasent rotted a hole in it like my CrapG

Interesting. I suppose I could stick a hose down there to verify.
 

Turbocharged400sbc

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did the tank come out recently?

this is a zr2 but yours will be similar, is your ball still there? it prevents a siphon tube from being inserted but since it floats it will seal against a ring inside the neck hose area to prevent liquid fuel from flowing into the fill neck durring a rollover accident.
pic is partway down a green plastic ball

but side from that the vent solenoid/hose cannister plugged is a possibility, keep in mind this is why they say not to "topoff" your tank during filling.
 

Bru

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A new gas cap fixed the problem with the fuel sloshing out of the filler neck while cornering. I believe two issues led to this: one, the o-ring on the existing cap appeared tattered and frayed, as well as slightly smaller diameter band. What’s interesting is that it was the exact same part number from AC Delco, GT299, which I ordered in 2016.

Secondly, the filler neck had some play and didn’t look seated in plastic shield that mounts with two screws, so I think the cap might have been bottoming out on the shield. The new cap tightens much stronger than the old one.

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