Hey Guys, I have a 68 400 (YT block) confirmed by PHS - but I am trying to determine what heads I have. I have identified two separate codes stamped on my heads;

1. EO 18 (stamped on driver side heads ) and
2. D2 68 (stamped on passenger side heads).

I assume that the EO 18 is the head casting ID but this indicates that I have 350 HO heads - which is not on my PHS could mean that someone swapped heads? Assume the D2 68 is a production date code of some sort. Any guidance on this?

Thanks in advance.

E018 is May 18th 68
D268 is April 26th 68

Head codes are on the center 2 exhaust ports.

Also...Check your cowl tag..

Cowl Tag ID

On the left side you will see something like 01D, 05E, 04C...Not particularly improtant, but that is your body broadcast date. Your heads for a late year 68 are 3 weeks apart. rare for a late year Firebird to have such a spread in date castings, but never say never. You typically find a wider range of date codes (2-10 weeks) for heads, block, rear, trans, water pump, regulator carb on early high production models. Somewhat narrower for 400 (2 to 6 weeks) and even narrower for HO and Ram Air (2-4 weeks) sans manifolds.

Also...

Did you check the EUN below the block code to the PHS?

Got it - exhaust port appears to be stamped with 16 (although somewhat difficult to be absolutely sure given rust) which confirms that I have stock heads. Thanks.

I am considering bolting on pair of 48 Ram Air heads. Have you or anyone you know tried to convert non ram air to ram air system?

The 16 heads are correct for a 1968 Firebird 400.

Coming from a guy who has machine shop background...

The #48 heads will NOT give you anything at all. I have flowed these heads in stock form. +/- a few percentages...the 16 and 48 heads flow the same. SAVE YOUR MONEY!

The difference is in the exhaust manifolds, cam, carb and to a lesser extent, the spring setup. You can replicate the same performance as a RAIII #48 motor simply with a cam swap, better ehaust and proper tuning.

Simply put...the RAIII motor ratings were due to cam, carb and exhaust differences over a typical 400. Yes, some RAIII had open ram Air scoops. That moniker was not really a huge difference over closed scoops. If you are going to replicate the RAIII, keep the heads and buy some aftermarket longbranch manifolds, RAIII regrind and tune.

However...you've opened up another can of worms...Need to know all of the engine, trans rear gearing particulars and budget.

Did you know....that on paper...the 400 WZ was 330 HP and the 1969 WQ RAIII was 335 HP?

The paper lied...

But the difference wasn't just 5 HP...more like 35-50. The difference was in the 068 cam (Firebird) or 744 grind (GTO) springs, carb jetting, long branch exhaust manifolds.

Doing one without the other is pointless. You can't just swap out the #16 heads for the 48's and expect results.

Swap the 16's for the 48's only? NADA.

Swap the cam and keep the 16's...20-30 HP.

Swap the cam and springs 30-35 HP

Swap the cam, springs, exhaust...40-50 HP

Refresh the existing heads with new valve job...and the above 50-60 HP.

A caveat...these are old world numbers with high octane fuel. Deduct 40% from the above numbers running 93 octane.

Thanks for words of wisdom. My 400 motor (YT Block, 300 HP, 10.75 C.R.), auto trans (PX code, turbo 400) and 3.08 axle ratio are stock - but previous owner installed an Edelbrock (Performer Pontiac) manifold and Holly 650 CFM 4 barrel carb.

Do you have suggestions on cam and exhaust performance upgrades that are bullet proof that you are willing to share? I'd consider changing the manifold and carb as well but not sure it is worth the extra money.

My 68 is my daily driver. I drive 15 miles roundtrip each day and want to keep the car a daily driver - but boost the performance a bit so I can show my wealthier friends in their new Teslas what a real car is!

There are limits on pump gas as far as compression and returns and iron heads. I would shoot for 9.0 to 1 but if you have tuning skills, can push 9.5 or 9.7 to 1 with dialed in timing and jetting. Over that, you need to blend fuel, not a good idea for a daily driver.

You will not get the 10.75 to 1 330 HP number published running lower compression with iron heads. I say with an old, tired motor at safe compression....you'd be 25-30% less.

I would start with checking the engine health before investing the time and money. Do a compression/leakdown test...Possibly find a local guy who only tunes older cars and has a dyno and can give you a real world idea where you are starting at. It is an additional expense, but knowing where you are at can be very advantageous. I have a local guy here who is so OCD and ADD he can blow my skillset out the door and dial in another 30 hp.

Just my opinion, I would have the heads rebuilt, have the heads ported and chambers polished (mild) have the chambers deburred, all sharp edges rolled back, go with an 068 regrind, change the intake back to stock and get a q jet. I love the intake (allbeit heavier) and loathe Holleys and tuning them. I prefer a Q Jet...but that's simply preference.

However..I am kinda weary going with a hotter grind in a daily driver. You'd want to confer with Scott Esterle at Summit Racing in Tallmadge OH for a cam selection for your trans, rear gearing...or scour the boards at Performance Years. There are way more test and tune guys over there. Also, pick up Jim Hands book How to Build Max Performance...as well as Pete McCarthys books. Any other Car Craft/Hot Rod reference material or advice is crap. Also check into the High Performance Pontiac website.

I would also switch over to HEI or Pertronix in the distributor and have the distributor rebuilt and dialed in. I would also invest in reading the above material.

In short, and I speak from experience and hearing stories and highly regard knowledge over trial and error if you work hard for your money. You can realistically spend 10k on an engine rebuild INCLUDING mistakes, redos (R&R of engine and trans) mistakes, goofs, what if's...Or you could realistically spend $6000 for the same engine including pre and post dyno time, post tuning time, head rebuild and porting, cam..all hard parts, carb and rebuild, long branch manifolds, oil filter adapter and angled housing.

Or if originality is a non issue..you could get the Edelbrock RPM 72 CC heads CNC ported for $2500, Edelbrock RPM cam/lifters, RPM intake, Q jet or Edelbrock carb, good set of 4 tube headers for roughly $4k. You'd be at 10 to 1 compression, lighten the front end 100# and probably be at 350-375 HP. Then, if the block needs a rebuild, you would be ahead of the game so to speak.

As well, Jim Butler and Jeff Kauffman have some awesome Aluminum heads and the supporting knowledge to choose the proper cam, lifters, rocker ratio...and all other requirements for your build. They also port stock heads. If I were you...I would go that route.

You could go with a roller cam and get even more out of a 400. But they are a PITA to keep adjusted. You could also go with a stroker kit and get even more but that requires a complete rebuild.

If you want a solid, stout, well performing engine, it's gonna cost money and time. I got the time...just not the money.

I agree with banshee regarding swaps. I have 68 HT original 4 spd car (Missing WZ block). Currently have a 400 in with the 16's believe they are original. i had a set of 48's which is didnt seem to think they ran any better than the 670 or 16's in my combo. I have a 67 ragtop YT block, PX trans, 3.08 gears, Q-Jet. Rebuilt it with the 670 head and got it to run really good. I run long branch with 2.5 exhaust. less hassle than headers if your going to drive it alot. have and good luck.

I will agree with most of what Banshee has stated. Where will I diverge? There are quite a few people running 10.0(closer to stock) compression ratios on today's pump gas. Now I'll concede that the people running these are skilled at tuning their vehicles to ensure they don't have detonation.

Other sources for info includes the tech articles at Pontiac Street Performance.com, among them a great article on compression by Jim Hand.

I agree with Banshee saying car craft and hot rod reference is crap. And the rest as well.