Which engine do I have? 91 Firebird Formula. VIN indicates 350. Catalyst sticker on underneath side of hood indicates 350. Hood scoop badge says 5.0 L fuel injection. Seller says it has 305. It still has exhaust manifolds so I suspect the engine has not been removed.looking for casting number but can't get it


Asked by Aug 16, 2015 at 05:13 PM about the 1991 Pontiac Firebird Formula

Question type: Maintenance & Repair

9 Answers


The eighth character of the vehicle identification number will tell you what engine was originally in there. Sounds like the hood or the hood scoops have been replaced. Run a vehicle history report and see if it's ever been hit. HTH. -Jim


The hood has 2 stickers that contradict each other. Decal says 5.0, catalyst sticker says 5.7

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I'd believe the emissions decal (catalyst sticker) over the hood scoop decal. Especially if the 8th character of the VIN agrees. There's less likelihood of the emissions decal being replaced. HTH -Jim


8th VIN character would be an 8 for the 350, E for a TB 305, and F for a TPI 305. While you are checking, the 5th digit should be a W for either a Formula or Trans Am. If it is an S, it started life as a base Firebird and someone has done some parts swapping. I agree with Jim, it is unlikely that someone would bother to swap the catalyst decal and a base Firebird could only be bought with a 305 TB V8 or a V6.

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Agreed. VIN states 5.7 as does catalyst sticker. It still has exhaust manifolds which leads me to think that the engine has never been pulled. I'm assuming that the previous owner stating that it is a 305 came from his use of the hood badge's 5.0L FI, as it has two other sources stating it is the 5.7 (L98 ?) (unfortunately, the console options stickers are missing). I guess this weekend I will have to get to the casting stamp on the block to truly know, but I'm anticipating finding that it is a 5.7. Otherwise, 2 factory size indicators that an owner can't alter are incorrect and a decorative sticker that could have been added by an owner is correct. Thanks guys

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You're welcome. Glad to help. Thank you for letting us know what you found. -Jim


Once I get the casting numbers, I'll post which engine I'm dealing with.

1 of 1 people found this helpful.

Ok, sounds good. Thanks for keeping us posted. -Jim

I have Pontiac firebird formula I can't get ran it do have fire will not ran can any one known

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