'68 400 H.O. compression and $ difference
 

Hey all!
I am corresponding about a 1968 Firebird 400 H.O.(I'm told). It is supposed to be correct and original.

I have 2 questions.
1) what is the compression ratio on this engine?
Just curious about buying fuel. I know someone who has a Firebird 400 that is 10.5:1 and that car doesn't run worth a darn on pump gas(pinging and vapor lock).

Also, what is the difference in value between a base 400 car and a 400 H.O.?

Justin,

All non-RA 400 4-bbl engines came with the #16 heads with 72-75 cc chambers and rated at an advertised 10.75 to 1 compression, which, if stock and original still, was closer to 10.0 to 10.25 actual compression, certainly enough to put you in detonation territory. If it has been rebuilt (most likely) to stock specs with clean-up cuts to the block deck and head surface, the compression could be in the low to mid 10's. The cam will have an effect on it's detonation tolerance with a larger intake duration able to bleed off cylinder pressure which will help some. A cam like the 068, or milder/smaller, will keep the cylinder pressure higher and more likely to cause detonation under less load.

The H.O. 400's came with the long branch D-port exhaust manifolds and 068 cam on 4-speeds, 067 with TH400 autos. H.O.'s do add value by at least 10% over non-H.O. 400 Firebirds if they are real documented cars IMHO.

Dennis

It is a 4 speed car. Supposed to be correct and untouched except for one repaint in the '80s. It has 69k that the seller says is actual.

Is there a "simple" way to get the compression down in the pump gas range? Like, for instance, swapping heads and just putting the originals on a shelf for safe keeping?

I have the 1970 version of the '68 400 H.O. Bird you're looking at, a Formula 400 with the RAIII 400 with #12 heads, but with the TH400. This engine has the 068 cam from the factory still (original and un-rebuilt) with 47,500 miles. I drove it to the TA Nationals last summer in the August heat (90+ degrees) over 600 miles round trip, and had no detonation driving normally on 93 octane unleaded. We checked the compression on a Whistler and it measured an actual 10.5 to 1 (1970 advertised is the same). We also checked the cylinder pressure and they measured in the 170 - 180 psi range. We kept the original jetting/metering in the Q-jet and kept the slow factory ignition timing with the heavy factory original springs and weights. The original radiator was replaced (since it was loaded with crud) with a new Cold Case aluminum unit and a 180 degree thermostat to make sure it ran reasonably cool (180 on the temp gauge and at the thermostat housing with an infrared temp gun). Keeping a eye on the tune (timing at 9 degrees BTDC and total at 34 degrees at 3500 rpm) it ran great with normal driving and short first gear bursts from time to time and had no detonation/spark knock. If I was going to race it, I would certainly add 5-6 gal. of 110 race fuel and recurve the distributor. The '68 400 H.O. is no different and should perform the same with these precautions.

Dennis

I wouldn’t let the fear of pinging stop me from buying the car that I want as there are some pretty simple things that you can do like retarding the ignition timing a bit and/or adding a can of octane booster to your gas. I do this with my ‘67 400 and have no problems.

I agree with the above. I have a 68 400 block out of a big car with #62 RA III heads that had a lot of work done to them in my 69 Firebird convertible. Someone dropped them off to a go-faster machine shop and then never picked them up. I bought them off eBay for about $1000 and bolted them on, probably 15 years ago. It also has an Offenhauser aluminium intake and I've never really looked into it much, mostly because I never drive the car. Anyway, the cam in it is meant to lower compression at the expense of horsepower. It really doesn't make sense to run the intake over a stock one and I will change it back eventually, but I don't drive it that hard. My experience with "hot cams" is that they run hot and while lopey is cool, to most it sounds like it isn't running right or has an exhaust leak. If you pulled up to a group of people in a car that sounds good that hints at what's in it, I like that better than the inverse where they hear you coming a mile away. I guess the point I'm making is build the car the way you want it. When it comes to the cam, no one but you will know what it is.

Regarding value, I would argue 10% is not enough to cover the difference between a 400 and a 400HO. Bigger is better and better is harder to find, especially with the original numbers drive train. I would guess it would be 30% more for an HO.

#62 heads is not and have never been RA III heads.

FWIW

My brother rebuilt the original '69 400 RAIII engine out of a '69 Trans Am with a TH400 and A/C. It was a loaded TA with the original 3.23 Safe-t-track rear end. It had 62 heads and it's my understanding that any 400 4-bbl with A/C got the 62 heads regardless of use TA, GP, GTO, etc. The 62's had larger combustion chambers to lower the compression a tad. This engine ended up with close to 11.0 compression, the 068 cam, new forged Eagle rods and Ross pistons and made 425 hp/475 lb-ft on the dyno and ran 13-teens at 106 mph weighing just over 3900 lbs with the 3.23 gears...very impressive.

I'm certainly open to corrections if I'm mistaken.

Dennis

Kenth is incorrect

#62 Heads are in fact 69 400HO and RAIII heads for cars with an automatic transmission.

About 25 years ago I was looking under the hood of a ‘69 T/A owned by Jim Wangers.

I can’t remember if it was a stick or an automatic car or whether or not it had A/C but I distinctly remember it had #62 heads.

I once owned a ‘69 400 4-speed Firebird with factory A/C, the standard 330 hp 400 had #62 heads as one would expect.

In '69 there weren't RAIII's, correct?, Weren't they 400 H.O.'s with the Ram Air package? The RAIII call out started in 1970?

Sorry about the thread hijack justincampbell!

Dennis

1969 Ram Air were the first that are known today to those of us in the hobby as RAIII.

All ‘69 T/As had Ram Air engines, standard RA D-port (RAIII) or of course the RAIV.

When I left CA in 1997 I left a 69 Firebird 4 speed car. Numbers drive train 400 4 speed posi and that was about it as far as options, but it still ran. It too had #62 heads, but according to Pete McCarthy's book it was supposed to have #48 heads. I wrote Pete a letter and he wrote me back stating he'd seen this before. While I wouldn't expect #62's on a 4 speed car rare, I would suspect the norm is the #48 heads.

FWIW I don't think there's any difference between the 1969 #48 and #62 and 1970 #12 and #13 72cc heads. If there is please enlighten me.

Other than a a few extra ccs in the combustion chamber on the #62 (75-77ccs) and the #13 heads (77-80ccs) they’re essentially the same as far as the ports are concerned.

The #62 and #13 were used on the more ‘bread and butter’ performance engines in most cases so the compression ended up a bit lower, although it wasn’t really reflected in the advertised numbers as such.

No worries. Never hurts to learn something new.

that is incorrect my friend. 69 firebird ra3 automatic cars got the 62 heads

I have seen 69 auto TAs with 62 heads.Tom

Bart,Jim’s TA was a auto.Tom

I stand corrected.
Seems like the 1969 Firebird 400 H.O. with code YW w/067 cam, and cold air induction, uses the same #62 heads as the 400 code YT, is named RamAir III.
My bad, never thought of the 067 cam being a RamAir item.

I own a 69 T/A auto and a 69 400 4spd firebird conv. Both cars came with 62 heads from the factory.