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91 Firebird / LS9 Swap

4178 Views 35 Replies 8 Participants Last post by  Lonnies Performance
It's been a while since I started doing research on this project & I posted some questions concerning parts choices a while back.

Originally a 305/700-R4 with about 190 HP. I cruised it around in the summer months,
It handled great but was not as fast as the average minivan, although it cornered really well.

After driving it in relatively stock condition for over 5 years, I started a full rebuild of this car in 2011 & completed it in 2014.
The factory clear coat was starting to come off, so it was time to rebuild / start modifying.

To bring progress up to present day, I'll provide some history.
I tore it down to a bare shell with basically only the dash wiring remaining in the car.

The underside was really clean, so I repainted it along with some suspension upgrades.
A lot of lacquer thinner & rags took it to the original primer.
Hood Automotive lighting Motor vehicle Automotive design Car

Then for some fresh paint... no use painting the top only to leave the underside all ugly.
Tire Wheel Vehicle Automotive tire Hood

Tire Automotive lighting Hood Automotive tire Motor vehicle

The factory 10 bolt got upgraded to a 3.54 geared Strange 60 rear with 35 spline axles.
Automotive tire Motor vehicle Vehicle Road surface Automotive exterior

I also added a Watts link for better handling along with some Koni shocks, better springs & frame connectors.
Bicycle part Automotive exterior Auto part Bracket Metal

All this was underway, but still no engine....
I did not want to build another race car & insisted to make a very drivable vehicle.

I originally wanted a LS7, but there were none out there for a reasonable price... the LS9 was not in the plans as of yet.
A T-56 6 speed was acquired for a little driving fun over the factory auto.

I'll follow up with some more build pictures to get closer to present day.
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I ordered my Rossler Transmission's 4L80E with trans brake.
They are backed up about 2 months.

Still trying to pick the proper converter.
It will be a triple disc lockup for sure, but not sure what stall to go with.
It seems like i should not need with too high of a stall due to the available low-end torque.
I'm guessing in the 25-3000 RPM range.

Another issue was finding a 9-bolt flex plate, as all ZR1's were manuals.
JW Performance Transmissions makes a custom one... they built & shipped it within 3 days.

It sucks that I had to buy 2 packs of ARP bolts as they do not offer a 9-piece bolt kit for an automatic flex plate.
With a 2.48 first gear Id go 3200 or so.
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Thanks for the info.... i have 3.54 gears in the rear & the car weighed 3420 before the extra supercharger weight.
3200 should be abut perfect for that with a 4L80 and reasonable PD blower cam
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What is the max RPM you typically pulley the LS9 superchargers to?
I have a 9.55/2.65 on there now which will be overspinning it at high RPM.
I'm guessing it will make peak power at 66-6800 but will be able to rev much higher if necessary.

I'm planning E85 & a chiller to keep the air as dense as possible.
Cam is mid 230's/upper 240's on a 120 with .630/.600 lift.

Unfortunately, compression is only 9.25:1 as I did not want to excessively mill the heads or change pistons, which would have required a custom piston due to the odd length rods & pin size.
Once that process started, things would have escalated to a different rotating assembly, then different block, then a different charger, killing the budget part of this build.

I really only started this build due to the good deal I got on the engine & I must now resist the urge to get too out of control.
On most ZR1 I use a 2.35/14% which would be just over 24000 rpm at 6800

Your pulley combo would put you at 24500 at 6800 ish.

Cam sounds like a BTR 3 or very similar
You can always slow it down a little. DSX will make you custom size lowers to bolt onto either ATI or IW dampers. A race ported LS9 2300 spinning 24K rpm will make 20-21 psi on a decently cammed 376-377.
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