What kind of engine would have came in a 91 formula firebird?

 

https://www.thirdgen.org/newdesign/tech/techdb.shtml

Scroll down to the year 91.

 

Looks like you could get it in a LB9 V8 (305) or a L98 V8 (350). My question is... would these two motors have the same exhaust manifolds on them?

 

Yes.

 

Is that necessarily true? The L98 would have the dual cats and larger exhaust, whereas the LB9 could come with the single cat/small exhaust, or the dual cat/larger exhaust.

 

But does that really effect the manifolds? I thought all that effected was the Y-pipe part(s).

 

I believe the manifolds on the '91-'92 single cat TPI cars were the same as TBI cars, which are smaller than the '86-'90 TPI and '91-'92 dual-cat TPI cars.

I think...

 

Comon guys, I need to know.. Put those thinking caps on!

Any way to tell them apart? Casting Numbers, Exhaust port sizes, etc?

 

8th character of the VIN. "8" = L98 350, "F" = LB9 305.

Casting numbers on the block and heads. The block casting # is behind the driver's side head above the bell housing casting - a # ending with 638 would be a 350, there may be others. The head cast #'s are under the valve covers - a # ending with 081 is 305, 083 is 350.

Look under the car on the passenger side. Report the number of catalytic converters and the size of the pipe(s) going into the cat(s).

Measure the outside diameter of the exhaust pipe below the exhaust manifold. A 350 would have about 2.25" pipes, while a 305 may have 2.25" or 2.0". I think...

 

Also, search on "RPO codes". I'm not very well versed on them, as my car's data sheet was missing, and I just haven't studied up on the details. I believe it is normally under the center console arm rest. Your search will tell the truth.

 

Thanks for all that information, but I should have been more specific. I need the numbers on the manifolds themselves, they aren't on the car anymore. Let me explain the entire situation. One of my racing buddies (dirt track racing) found a set of exhaust manifolds off a 91 formula with a 350. He put them on a motor on a dyno and they flowed great, produced good horsepower. So I'm looking for a set like them. I've found a set that came off an 85 Z28 with a TPI 305, which appears to be the same 305 that came in the 91 formula. So now I'm trying to figure out if these are the same manifolds that my buddy got off the 91 formula with the TPI 350.

Make sense?

 

IIRC, "N90" was the dual cat RPO code.

 

this is the most complete compilation I've come up with: RPO Codes

 

Anyone else have any idea on these manifolds?

 

Are headers an option?

 

I've heard that diving into a set of cast iron maifolds with a die grinder and a lot of patience will yeild some decent flow rates. I'm sure that the overall design unltimately limits flow, but i'd bet there's at least some potential to be realized. of course, it would be way less work with probably better results if you were to just bite the bullet on a set of decent headers.

 

Rules say you can't run headers or center dump type manifolds.

 

I found the casting numbers for the exhaust manifolds I'm looking for.

RH 10223614
LH 10168544

Anyone know what all years of car this came on? The guy who gave me the numbers said he got them off a 91 formula firebird.

 

You should read this post.

https://www.thirdgen.org/techbb2/sho...threadid=14501