[mrsiding]

I have a 71 formula firebird, that I recently purchased for cheap. It is not original I know, but it has a YG coded 455 in it. The stamp on the head is #98. Anyone here know anything about this motor? What kind of car it was made for? It seems to run well. I was told it was a 280hp motor-isn't that low for a 455? Is it possible that this motor was confused in the factory for a YC code? I understand that a YC was a correct code for this year. Any help or info greatly appreciated.

[WDCreech]

1971 YG, 280hp 1-4bbl, 98 heads, 8.2 compression and an 066 cam from a B series (Catalinia, Bonneville, or Grandville).

[mrsiding]

Thanks, Bill.
So was this a common motor for big cars? Would I have problems finding parts for this motor or are 455's easily interchangable? Any thoughts about changing heads or cam? I really just plan to restore this car to drivable condition. It has a TH350 transmission--any problems with this and the lower hp 455? Transmission has been recently rebuilt and resealed. Motor seems strong, but runs a little rich and leaks a little oil, but I think it's from a valve cover.
It looks like your gto screams - what are you running in that?

[mrsiding]

1-4bbl? does this mean that it could be anywhere from 1,2,3,4 bolt main? Do you have to drop the pan or is there a code somewhere that will tell me? Any help?

[giles]

I think a '71 YG motor is actually a 455 2-bbl motor. It would have small valves and press-in rocker studs in the heads. You would not need to replace the heads for a street performance application, but should upgrade to big valves and screw-in studs.
The list of differences between a YG and a YC is not that long. The YC would have a quadrajet, 067 cam and large valves. Both engines have 2 bolt main bearings. Otherwise they are basically identical and there is lots of performance stuff available so hang on to your YG!
As far as the THM 350; it will die behind any 455 if it is stock and run hard. The torque level of the 455 is what will break a THM350, not the horsepower level. There are many capable trans rebuilders that can make a THM 350 perform well behind a 455 however.

[Formulabruce]

Its also very possible that 2bbl engine block is a 4 bolt block with 2 bolt caps. With a 4bbl properly tuned for it, it probably has 400 ft lbs of tourque RIGHT NOW!!, a 71 350 2bbl had 350 Tourque stock!

[mrsiding]

Thanks for all of the info guys. My THM350 is not stock. It has been rebuilt with a B&M shift kit and seems to work well. It looks like a previous owner tried to make this car have ram air as there are some of the heat shields still bolted on and the hood openings have been cut out. Unfortunately, no dual snorkel air cleaner. Don't you have to have the right heads for ram air to function properly? I am looking at going through the engine compartment soon and wondering what to do with a few things. This car has air conditioning- all the parts are there but the compressor needs to be rebuilt and i'm sure it will need all new hoses etc. Does running the air conditioner in the summer cause these hot running cars to overheat. Should I just get rid of the air? Do these old systems even work well enough to spend the money to fix the air? Again, thanks for your help and advice.

[giles]

mrsiding, If the trans builder knew what he was doing your THM350 may live! As far as "ram air" is concerned you don't need to change anything in particular other than the air cleaner to enjoy the minor benefits of ram air. Cool outside air is denser than underhood air. Whether the air retains that density by the time it is warmed by the intake manifold and inducted into the combustion chamber is a matter for debate (and maybe a few well-placed thermocouples). Most of the performance gains from Pontiac Ram air packages came through manifolds, valves and camshafts. The "ram air" part was as much marketing pitch as reality.
As to your question about A/C - the old Harrison 6 cylinder compressors were the gold-standard in their day. Ford bought them for Lincolns and several European makes installed them as well. Yes the A/C condensor will reject heat to the radiator and make your engine run hotter, but that is only when the A/C is actually turned on.

[mrsiding]

Thanks for all the good info. If the ram air is as useless as you are saying and considering that dual snorkel pans and boots and retainers will cost in the neighborhood of $500-$600, I think I can live with out it. Still debating on the air, I'll have to check what it would cost to restore the system.
Thanks again!