I have some 1968 #15 heads. These came off of a big car and are the smaller valves. (1.96/1.66). 92cc chambers. I'd like to have valves worked to be the 2.11/1.77. Will the 92cc chamber be a hinderence?

My #16 heads I am running now are 2.11/1.77 72cc chambers.

Could someone explain, I just ready Jim Hands book on pontiacs....he lost me in the cam area! Way over my head...

Lets say we have the exact same engine for comparison, what difference would you see if nothing else on the engine changed but the chamber size.

I think I am litterly going to copy one of the sample engines in the back for my build, but want to save money and use the #15 heads that came with the engine.

And on a side note, what is the difference between #16 HO, #31 Ram Air I, and R96A Ram Air II? The specs are the same except the RA heads are round port, and the others are D-port....is it other engine componants?

Here are the specs of them all

• 1968-69......16.......400/428 Ram Air & HO........D-PORT........2.11/1.77...72 CC
  
• 1968.........31........400/428 Ram Air...............D-PORT........2.11/1.77...72 CC
  
• 1968 1/2....R96A.....400 Ram Air II..............Round Port........2.11/1.77...72 CC

Somebody correct me if I'm wrong, but block cylinder size, head chamber size and camshaft are the 3 biggest items for planning an engine. Higher compression gives more horsepower. Lower chamber sized heads (like 72cc) give higher compression. Higher compression increases heat increasing the need for higher octane to prevent detonation. About a 10:1 compression ratio can be run on pump gas. 72cc on a 400 will give you about 10:1 compression. 92cc on a 400 will give you about 8:5-9:1 compression. Higher compression allows the use of more aggressive cams which can add more horsepower. Ideally the #16 heads will give you more horsepower. But if this is your first build, practicing on the #15 heads would be better IMO. Whatever mistakes you may make from the first engine build, you will make your second build better.

The camshaft can get pretty technical with the math. Read the posts in the Hall of Fame about compression ratio. I think it simplifies it more. You could also try a dyno program to see what works and ask others what cams they have used. Some camshafts are considered better quality than others.

If you are comparing engine building plans in the back of the book, use one that is comparable to your heads and block. I'm guessing you will probably make some changes along the way to make things work.

I really don't know much about the HO and Ram Air so I can't help you there. They are good heads but I'm sure they get a higher price and are harder to find too.

I guess a good title for this build is "Budget 400" Since the block I bought is a long block, (factory rated at 340 in its original set up). I want to use as many parts as possible, but reguardless of what I have, My goal of 400hp will ultimately determine what parts I have to re-buy.

Heads are just so darn expensive!

Ok, got the engine, and all the parts to go with it. Since I have filed my request forms for more of a budget, in triplicate of course, and not heard a responce. I am assuming the finance dept (i.e wife) is denying any further expenditures.

I am going to need to make one of the following sets of heads that I have work.

There are the #15's - from a 1968 pontiac 400 CI, D-PORT exhaust ports, 1.96 intake, 1.66 exhaust, 92 CC combustion chamber.

Or there are a set of #46's from a 1969 400/428 CI, D-PORT 1.96 intake, 1.66 exhaust, 72 CC chamber.

Almost identical except for the combustion chambers. I want higher compression for more HP, leaning the go-with needle towards the 46's and the smaller chambers. But I am going to take the bore .030 over, which means new pistons, which I can use to get higher compression also, which means I can use the 92cc chambers and still have higher compression, and is bigger better here, more chamber means more fuel/air, and more boom-boom power (for better sence of a word).

I am going to go over this with my engine guy who is going to machine it, but I want to know what I am talking about when I go in and start rattleing off my thoughts...

Do I need to go back to engines 101 and sit in the front of the class this time?

I just re-read the post in the hall of fame by 8point on CR...wow. Still over my head even at the front of the class. time to move to the back again and cheat...

LOL

Or you could simply ask the advice of the knowledgeable guys like Ponchoshop, Banshee, 428HO, etc., instead of trying to guess yourself into an expensive non-performing motor.

Factory HP ratings had everything to do with the way the engines were tested and the type & grade of fuel used. In the 60's, high octane (98 to 105) gas was common, and engines were tested at the flywheel with no accessories bolted on. You will not get similar numbers using today's pump gas.

If you want to get any level of performance, use heads that have large intake valves. Converting from small to large will cost you as much as buying large valve castings. There's few good reasons to do this, and 1968 #15's are not one of them.

Even though some heads have identical dimensional features, such as chamber size and valve size, there were significant differences in how those heads were set up by the factory. Single springs versus dual springs; heavy duty versus standard duty; different spring heights, etc. The casting designs, in terms of port volumes and runner lengths, were nearly identical for all of the large-valve D-port heads from 1968 through 1970 (#64 being an exception). The casting number was part of a bigger picture. It applied to the set-up of the head more so than just the casting itself. #62 and #48 heads (of which there are two variants) are nearly identical except that the factory used heavy duty dual springs on the #48 and standard duty dual springs on the #62. I have also found that #62 heads have 75 cc chambers, with some as high as 80cc, versus the almost-universally consistent 72cc for #48. 350 HO Heads (also #48) usually run at about 65cc. They are impossible to distinguish from the outside from 400 #48 heads, and must be measured. These heads are the 1969 version of the 1968 #18 heads.

Round port heads were VERY different, and were designed to flow a lot more air than the d-port heads, even though they have comparable chamber and valve sizes to D-Ports. They have larger intake ports and very different exhaust ports than D-Port heads. (Though early RA II heads I believe had similar intake ports to the D-Port heads.)

The three primary drivers for detonation are the chamber volume vs. displacement (Static CR), the intake closing event (Dynamic CR) and the quench volume (which is dependent on the bore and the deck height). The article referenced in the hall of fame section boils down to running the dynamic compression at 160 or so PSI. The dynamic compression ratio is influenced by the static ratio, but is more dependent on the ICE. You can run Iron heads at 10:1 on pump gas with the right combination of Dynamic CR and minimum quench volume. TOHCan is the most knowledgeable source I've met for squeezing high compression out of pump gas with tremendous detonation tolerance. It takes a proper set-up on your distributor and carb as well.

If you attempt to run 93 octane pump gas with a basically stock set-up, you should probably limit yourself to about 9.5:1 static compression ratio. Of course, adding the camshaft choices and possibilities to this discussion could change that, but most factory cams have a rather early ICE which tends to raise the dynamic CR. Longer duration cams will drop the Dynamic CR, but could affect the vacuum level. If you are running power brakes, this can lead to some challenges. One solution for that is Rhoads lifters, which shorten the duration of the camshaft at low RPM, boosting idle vacuum.

Was that the explanation you were hoping for?

Please dont confuse my attempt at humor as a lack of willingness to learn...I am a young guy, with 4 kids ranging from 10 to 15 y/o running around here somewhere, time and money are very important commodities, but rather than standing around at a car show, hitchin up my britches, sayin "Yeeeep, built it muah self" I'd like to get a feel for the what, why, and how of it all. Ultimately the machine shop will tell me if I am crazy or not.



That helps tremendously. When I got the engine the guy passed on three sets of heads. #15's, #46's, and #50's. From my reasearch all were "junk" for what I wanted, but I definately wanted to compare the option of reworking them vs. scraping them.



manual disk brakes, with no intention of going with power.



Yes, it helped alot. I have #16's on my car right now, I didnt want to swap them, but if the best option is big valves, then I will probably go that way unless I come across another set. I mainly wasnt sure if you could overcome the shortfall of smaller valves with different pistons, cam, combustion chambers, ect.

Don't bet on your machine shop helping you out unless they are a Pontiac shop, and even then I'd be concerned. People here, such as those mentioned, will be a far greater value to you since they have nothing invested in the process.

There are way too many opinions and possible combinations to give you a "recipe" for a good engine, but starting with the heads is pretty safe. Cam choices are a whole different ball of whacks! (Yes, I know.)

BZ..keep on asking the questions. Between your questions and mine, Im learning a ton. As you and I have already discussed, we're in the exact same situation. Ive got my heads discussion going on as well, and thankfully people here are kind enough to give advice without insulting.

Just like you, I could simply clean, put in new bearings, rings, paint, etc, use the same heads, and it would probably run fine for my usage, but I wanted to be more educated about engine rebuilding while trying to recreate that Firebird 400 4v setup the 68-69 buyer would have received from the dealership.

I dont have 4 kids running around the house (mine are all in their 20s now...Thank God!), but I can relate to the cost-time situation..

I love em, but cant wait until I just visit them!

I know everyone has personal experiences and opinions, I guess I am trying to establish my own. Trying to decifer it all is the fun part. Its not rocket science, but it is a science. One persons idea of a piece of sh*t, is anothers dream engine.

Way off subject but my last sentence reminded me of a joke that was passed around my unit when I was in the Marines.

It went like this:

THE PLAN

In the begininning was the plan

And then came the assumptions

And the assumptions were without form

And the plan was without form

and darkness was upon the faces of the Marines at MCAF

they spoke among themselves, saying
It is a crock of sh*t, and it stinketh

And the enlisted men when to their NCO's , saying
It is a pail of dung, and none may abide by the odor thereof

And the NCO's went unto their SNCO's saying,
It is a container of excrement, and it is very strong, such that none may abide by it

And the SNCO's went unto their officers saying,
It is a vessel of fertilizer, and none may abide its strength

And the Officers spoke amongst themselves, saying to one another
It contains that which aids plant growth, and it is very strong

And the Officers then went unto the XO, saying unto him,
It promotes growth, and is very powerful

And the XO went to the CO, saying unto him,
This new plan will acctively promote the growth and vigor of this unit, with powerful effects

And the CO looked upon the the PLAN, and saw it was good

And the plan became policy

This is how sh*t happens


All depends on who you hear it from I guess....

#16s are big valve. Just freshen up what you have.

Was there 2 different year 16"s?
One big vlv, and one small vlv?
Think i've heard or read that, but never seen small 16's.
Not familiar with small vlv hds cause i've never ketp any.

Yes. Actually, 4 years: 1968, 1970, 1973 and 1974.

1968 are big valve; 1970 are small valve.

Not to ever be confused with 1973 and 1974 #16 heads.