I have a 91 Firebird for a project car and it has the V6. I was wondering if I have to switch to a V8 crossmember when I put a new engine in. If not, can I do it anyway, or is that out of the question?

 

No need to change it in a '91. '82-'83 w/TH200 had shorter length requiring a different crossmember.

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82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R4. 2.93 limited slip. Cat-back from '91 GTA, ZZ3 intake, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LG4 w/'87 LB9 block, ZZ3 cam, ported World 305 heads, Hooker headers & y-pipe, 3" Catco cat & 3" cat-back).
57 Bel Air, my 1st car. '66 396, 9.7 CR forged TRWs, Weiand Action+, Edelbrock 1901 Q-Jet, GK 270 cam, Magnum rockers, Jacobs Omnipack, 1-3/4" Hedders & 3" Warlocks, TH400 w/TCI Sat Night Special conv & Trans-Scat shift kit, MegaShifter, 3.08 8.2" 10-bolt w/Powertrax, AMSOIL syn lubes bumper-to-bumper. Idles smooth @ 600 RPM in D. Best 15.02/95.06 @ 5800' Bandimere (corrected 13.93/102.4 @ sea level).

 

the only thing, you will need to change the motor mounts, witch will sit higher but the holes are already drilled.

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LT1 POWERED
HEADMANS HEADERS
NEARLY 300 HP.

next mods:
crane roller rockers 1.6
lt4 hotcam kit
airfoil
58MM edelbrock trottle body
new paint (wet look blue)
17' rims with 275 zr 40 and 245 zr40

 

You can use the V6 setup simply by changing to V8 motor frame mounts. You will also have to use a V8 passenger side front brake line or bend up the one you've got.

As far as changing crossmembers there is no point in it unless you go with a lightweight tubular setup such as that sold through www.paracing.net .