312 Exhaust Manifold Question


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By 312YBlock - 4 Years Ago
Hi all, I have a 1955 T-Bird with a 57 312. The exhaust manifolds however are set up as stock with the passenger side being from a Fairlane with a 6 3/4” outside diameter and the left side the typical 312 manifold with a 7 3/4” OD. The engine runs great but I’m wondering if It would be worth the effort to replace the right side passenger car manifold with a correct 57 312 manifold. The next time I take the car out I intend to take the temperature of both sides, I’m thinking the right side will be hotter but that’s yet to be determined. Any thoughts?
By Florida_Phil - 4 Years Ago
As I'm sure you know, the passenger side 55-56-57 Thunderbird exhaust manifold is the same as a passenger car.  The driver's side Thunderbird exhaust manifold is unique to the TBird.   It tuns down at a different angle.  My 55 Tbird is running 1957 TBird exhaust manifolds.  They are slightly bigger than the stock 55 manifolds.  I am sure there is a performance gain with the 57 manifolds, but I'm not sure if it would be noticeable.  The passenger side manifold is easy to find. I believe reproductions are available.
By miker - 4 Years Ago
Here's the link to Ted's exhaust test.

http://forums.y-blocksforever.com/Topic55379.aspx
By Florida_Phil - 4 Years Ago
Thanks for the link.  Ted's test shows a peak increase of 5 hp and 3 foot pounds of torque when switching from 55 to 57 manifolds.  That is an increase, but not as much as I would have thought. I have considered headers, but I'm trying to keep my car period for the sixties.  Headers were not something I could have afforded back then.  On the other hand, I couldn't have owned a TBird either.  Smile
By 312YBlock - 4 Years Ago
Miker / Phil thank you for your feedback and the great chart. It’s gratifying to know there are folks out there who share my passion for the YBlock V8. Back in the day the 312 was the engine my friends and I coveted and today it’s easy to understand why. I had an Isky 3/4 cam installed when the motor was rebuilt in 1985, I wish I knew the degrees of the grind. It comes alive in second at 11 to 1200 RPM, the low - mid range TQ puts a grin on my face every time. It’s crying for a 5 speed but I love my T86 OD too much. Do you know if the 55 left manifold was carried on from 55 to 57 in the 292/312 or if it was recast with different dimensions unique to 57.
By Joe-JDC - 4 Years Ago
If you have a few tools, you can improve your existing exhaust manifolds flow and save some money.  Here is what I did to two sets of manifolds for my '55 T-bird.  I use a die grinder and 6" diamond cut flame shaped carbide to open up the ports to match the Fel-Pro exhaust gasket, and then used 8" mandrel and cartridge rolls to polish the interior of the manifolds as much as possible.  I then used a large 1" ball stone rough grit to open up the flange to 2-1/4" or so on both manifolds.  A little elbow grease and time, but the results are worth it to me.  Just an idea if you have the resources.  Joe-JDChttp://forums.y-blocksforever.com/uploads/images/e3a43dd5-18cf-49be-b25e-ab77.jpghttp://forums.y-blocksforever.com/uploads/images/3408f4e8-1cba-4e0d-b2b3-ec5a.jpg
By 312YBlock - 4 Years Ago
Nice work Joe, thanks for the info.
By Florida_Phil - 4 Years Ago
312YBlock (8/17/2020)
Do you know if the 55 left manifold was carried on from 55 to 57 in the 292/312 or if it was recast with different dimensions unique to 57.
It sounds like your car is set up much like mine.  My first hot rod was a 57 Ford Custom.  Every time I drive my TBird it transports me back in time.  My wife likes it because it a convertible.  I like my Y-block engine and O/D transmission.  The '57 exhaust manifolds are unique with their own casting number.  The '57 driver's side TBird exhaust manifold is harder to find. 

By GREENBIRD56 - 4 Years Ago
The two best things I did to mine was - after getting a '57 sized flat top passenger manifold:
(1) Did away with the right side "warm-up" butterfly completely (had it wired open before). Now a free, open cylindrical spacer. 
(2)  Sent the two manifolds away to be "ceramic coated" at JetHot in Tempe, AZ. They will blast them inside and out to get a fresh surface - then coat them completely. The process lowered the observed external temperature of the manifolds by a couple of hundred degrees - and under the hood of a Thunderbird it is a very obvious difference. I got them finished in "aluminum" - but they offered to use a cast iron grey color that wouldn't be too noticeable if the car was a restoration queen.
By 312YBlock - 4 Years Ago
Hi Steve, anything to reduce the engine compartment temp has my interest: any chance you could upload a photo of the finish on the exterior of the manifold?

Best Regards
By GREENBIRD56 - 4 Years Ago
Will try to find my old file photo - taken when they came back from JetHot. They are not the only vendor of this high temp ceramic coating - just happened to be near me.
http://forums.y-blocksforever.com/uploads/images/1942255d-79af-4977-b9b9-efd1.jpg

http://forums.y-blocksforever.com/uploads/images/8fd0b6d3-c6af-4bc4-a6c0-29ca.jpg
They are coated inside and out as standard practice at this vendor. Guys have told me that the coating lasts virtually forever......
By 312YBlock - 4 Years Ago
Nice, it would be interesting to benchmark the temperature of the stock manifolds vs your ceramic coated manifolds. Hopefully later this week I’ll have time.
By Florida_Phil - 4 Years Ago
Some time ago I installed a dual master cylinder in my TBird.  When I did, I left out the stock battery heat shield.  Within 6 months, the heat from the engine cooked the battery to the point of cracking the case.  After cleaning up that mess, I reinstalled the heat shield with no further issues.  It gets hot under there. 
By GREENBIRD56 - 4 Years Ago
The standard iron exhaust manifolds - parked at hot idle in my driveway with the hood up - 525º F.
After the coating process, same exact conditions - 325º F

The fellow I talked to at the vendor - this is many years ago now - told me to expect about a 200º drop and he was nuts on. My buddy just called them the other day to get a Jeep manifold coated and he told me that they quoted $115 for the single, 4 cyl casting. I think the bird set cost me $225 plus shipping - best money I've spent!

Yes, I put a heat shield on the battery and it works - but looks - not so great. May end up at right rear in the trunk someday. My bird is a HOT ROD - not a show car.  
The air pan for the carb really drops the intake air temp a huge amount - old info from the Holley manuals says you get about 1 HP per 10º F drop. The radiator on a T-bird ducts its air right into the carb and except in the winter in Michigan, or Wyoming - can't be good. When the pan is in place ( I designed it for easy removal ) you can feel the torque difference on a hot day. 107º here yesterday. Seals to the hood with MOROSO fire resistant foam.




By 312YBlock - 4 Years Ago
I took the temperature of my stock cast iron manifolds yesterday Left 538, Right 496. I would have thought the right smaller diameter passenger car manifold would have read the higher of the two 🤔. I’m going to order 2 replacement manifolds from CASCO and have them ceramic coated. I’ll post results. Be well!
By 55blacktie - 4 Years Ago
Do you have hood clearance issues with the oval air cleaner? Using a carb spacer?

I have a Billet Specialties oval air cleaner, 15 x 8 1/2 x 2, on top of a Holley 4150 Street Avenger 570. There is no room for a carb spacer, but hood will close if just using a paper gasket between B manifold and carburetor. The oval air cleaner has a flat base. It looks great, but I would like to use a phenolic spacer. I might get a cheap drop-base round air cleaner and use 1/2-1-inch spacer. If I want to show my car, I can swap air cleaners. I just have to remember to not close the hood.
By GREENBIRD56 - 4 Years Ago
Mine has a Moroso 1/2 inch spacer on a "B" four barrel manifold with a "Demon" Holley 4160 style carb. Thermal break works just fine at 1/2 inch. After many trials - I found that it would fit the oval air cleaner up under the hood scoop. The air pan (hot air deflector) is mounted on nylon standoffs attached to the bottom of the air cleaner. It all just pops right off.

There is a fellow here in Tucson with a '56 truck that he shows - used to be seen here a lot. Every time I saw it with the hood open, he had the engine dressed differently! After talking to him about the changes, I adopted a similar approach just for the fun of it.  Takes a pair of valve covers, three wing nuts and an air cleaner that clears the hood. I know he has at least four different set-ups and I have the street driving air pan as well as three or four others I have gathered after I knew the drill! I have a set of chromed "Mercury" script covers in honor of my dad (he was the family Merc man), several tins with various Y-block decals and script - and a set of the Aluminum t-bird dress-up covers. 55 and 57 stock air cleaners and several other aluminum versions. Let your pocketbook be your guide! (My mrs hates this attitude).  
By 55blacktie - 4 Years Ago
Sounds like you're having fun.

I prefer function over form, but occasionally we can have both. If a car is trailered, or sits in a museum, function is not important. Personally, I can't see owning a car that can't/won't be driven. 

My original, oil-bath air cleaner for the Tea Pot was modified for a pcv valve. the steel mesh was compromised, and I feared it could be sucked into the carburetor. I sold it for $25. I should have kept the base, but it would not fit a 57-up carburetor. A 57 repop air cleaner is $450. 

I have nothing against originality, but I don't get seeing a dozen identical cars, parked side-by-side. You've seen one, you've seen them all, so to speak. However, I have retained all original take-off parts, other than the air cleaner and leaf springs. There are no mods that can't be undone. 
By DryLakesRacer - 4 Years Ago
From what all you are saying I’m guessing the right side of an early or late, Thunderbird or passenger car will exchange and the exhaust pipe will fit. My 56 car has a flat top on the left and a 55-6 round on the right. I bought a right side flat top but have not put it on because not knowing if the exhaust pipe would fit as is. I also see there is a butterfly eliminator available and mine is wired open. Now I think I’ll purchase one and put it on thanks to this discussion.