Hey everyone,
I have a 69 convertible. Over the last two years, I have had a 3.90 posi installed and a Tremec 5 speed overdrive manual transmission. I like the way it rides now, but I am not 100% happy with the engine. The engine is a 400 from an unknown 1972 Pontiac with unknown mileage. I always knew that one day I would want to have it rebuilt.......I am thinking about possibly having it done this winter. I have no idea what horsepower this engine is pushing and would like to know how to find this out so I can start thinking about how much additional horsepower I would be looking to gain with the rebuild. Thanks for any help.
John

The only way to know for sure is to run it on a dyno.
You can calculate using the known parts but that is just a guess as the "real" or measured HP is always different.

David

Which heads?

Typical 72 400 should be pushing 220-250 HP. Then deduct HP for worn cam, rings and valve seats.

When you are pushing a 3.90 rear with a sub par 200 HP motor, you will definately feel dissatisfied.

The motor will depend on current cam, carb and calibration, heads, exhaust and intake.

I am a firm believer in doing something right the first time, after many errors and plenty of trial. If you are going to rebuild a motor, find someone who has sucessfully built Pontiacs. They are different than Chevies, Fords and Mopars. I once seen a guy install domed pistons to increase the compression in a 400 at a cost of $850 when the builder should have done was to buy and rebuild a set of heads. Same result in the end, but Pontiac heads were designed for flat top for optimal performance.

I would earmark at least $3500 for a complete rebuild including torque plate bore/hone, align check on mains, new ARP bolts for rods, SERDI cut on valves and the best hard parts (Ferreas, cam, pushrods) that you can afford. Included is having the rotating assembly balanced. Within that $3500, distributor recurve retrofit, carb rebuild..new everything.

Dyno session is a great investment if you can afford it. About $400 for 1/2 day $600 for full. The dyno shop will tweak the jetting and timing for optimal performance.

I have learned that building it right initially saves money overall.

Power is in the heads and valve train.
68-70 head's with screw in rocker studs came with big valves and good compression.
Get a 68-70 intake manifold and Q-jet carb to match.
I like the 75-79 Q-jets best.
Most any cam in the 220*-230*/110-114 lobe separation range give you good all around power and still have good street manners.

When I bought mine it had a 72 400 in it....are the heads 7J2`s? if so it was a 200 hp engine...if 7K3s it was a 250 hp engine...

engine block : YX, YZ ZX were 200 hp engines, WK,YS,YT were 250 hp...IF the engine came out of a Firebird and not a 'big car'....

if engine is old and worn, listen to Banshee, rebuild it right...if its recently re built , you can get some better heads to pep it up...

mine had 9k on a rebuild,so I just got new heads for mine...

OK.....I just took a look under the hood again........I definitely have a YX engine block.........so apparently according to the info you guys are giving me, I've got about 200 hp if I'm lucky.

I'm sure I'll learn all about the different ways of rebuilding an engine for best performance over the next few months.

Let me ask this............and I'm sure it's all a matter of personal preference..........what amount of horsepower should I be shooting for and still have a nice ride around town (I don't go to the track)
thanks

You can stroke it to 461 cubes with a crank kit and have tons of torque.

We just rebuilt a '71 YX for my dad's car. Nothing in there that $3500+ won't make better.

We should get a relatively modest 350 hp pump gas friendly car out of it, with appearance 100% stock. Except for the very nice Hirsch blue paint and long branch manifolds, that is...

Vikki, Are you planning on a trip to the dyno when you're done? I'd be curious to know what you end up making.

Robert

If you want to do some reading on building Pontiac Engines:

http://www.amazon.com/How-Build-Performa...6765&sr=1-1

http://www.classicfirebird.com/hand/hand.html

http://www.petemccarthy.com/

After my disastorous rebuild attempts, yes multiple times. I have only one recommendation for anyone who is going to do a rebuild. That would be, roller cam & lifters. After wipping out 4 cams in a row (all with less than 500 miles on them), proper break ins etc. I will never rebuild another engine and not use a roller set up. More money yes, less potential issues yes!

Not too mention all the added benefits of roller, more hp, less heat are among the top. My engine now has almost 8k on it and all is well. Although it has not been properly dynoed, she did put out just over 400 rwhp several months back. We will dyno her again soon, maybe at the Turkey Run...

Personally I don't care what the numbers are as long as the seat and pedal response are highly satisfying, but I think my dad is interested. So we'll be hunting down a local dyno facility once we have a few miles on it and the bugs worked out. There is literally not one single bolt or panel on this car that is not being removed, so the debug stage may take a while.

Actually, the code 'YX' on the block tells us very little about what you have. For example; In 71 the code YX is for a 400 block. In 74 YX was a 455 block. And last and least, in 1977 it was a 301. Since engines are often swapped over the years, saying the engine came out of a unknown 72 Pontiac doesn't mean very much.
So you will need to read the date code near the distributor hole or the casting number to narrow down what you have and if you can even use the block for what you want as a finished product. And as I asked in my earlier post, which heads do you have? The heads will be a major factor in the end product. I'm sure you are interested in whether you can even use the heads you have.
If you need any help with finding the locations of the 'more important codes' we can help with pictures of example codes on blocks and heads....

If it is a 72-400, its a good block(thicker mains then later years).
Not sure about the 455.
When did Pontiac blocks go thin(74-75-76)?

Wasn't necessarily "thin"..

Was more of a nickle content and hardness issue.

why play with these 400,455 engines?you really need to go with a jet engine

I would not recommend porting the heads on a motor unless you plan on running "hot". Makes no sense spending $6-1000 on port work when the optimal region where porting kicks in is in the upper realm of street crusing RPM band. Likewise, porting IMO, is best served in typical street motors running a compression ratio of 10 or above or forced induction with decent boost.

I would consider though milling the spring pads down for a stouter valvetrain similar to the RA of 67. You do not necessarily need the 1.71 installed valve height for a low compression rebuild, but can be nice if you are at or above 10.

I would base my decision on compression on a few things. Miles per year, street or highway, rear and trans.

Since we know you have a Tremec with a possible overdrive final ratio of .6 to .7 and a 3.90 gear, I (personally) would build it to 10.5 and take the sharp edges out of the chambers with a polish to reduce hot spots, recurve distributor and calibrate the carb well to further the detonation issue. I ran a 428 with polished chambered and ported 48's at a 10.9 ratio on a blend of Sunoco 94 and 10% 110. Toulene can replace 110 octane rather inexpensively.

I will be rebuilding my 400 HO soon. I decided to go with a final CR of 10.5 with a 3.55 and M-20. I'll drive it to work and around town. I do not plan on shows, or more than 3000 miles a year. I calculated that my milage will be roughly 20% less than the T/A which will result in 20% more fuel, but with additives or a blend, what is $50 a tank? Would rather have the "fun factor" myself.

Just an opinion, but these cars do sound better...different and smell better with period correct compression, cam and fuel.

I definitely enjoy the smell of real leaded gas exhaust coming out of the tailpipes. I just don't inhale.

Pontiac went to a thicker main web block around 70(?) when they stopped using hard steel(Nickle).
Then around 74-5(?) they used even less steel.
East to check.
If the engine # ends in 557, its a thin block.
Another way to tell is if the main cap bolt holes go all the way thru.
I would'nt use one over 350 HP without a good prep. Over 400 is a gamble.
Pontiac went back the 488 casting in 78 due wipe'n out rod-n-main brgs in FB/TA's under warrenty.
What were those...180-220 net HP?

Also agree with Banshee.
Unless you know what your doing, or know someone who does, dont go grinding on the heads.
Just clean the imperfections and casting flash.
Seen many sets of clean valuable heads ruined.

I use longer valves-n-springs instead of machining the pads since the old vlvs usually need replacing.
Springs are a "throw away" item.
Thier junk compared to whats availible now.

Compression ratio vs tadays gas...thats a topic for anther day.
My cars run on regular unleaded.
But if had Banshee's $$$$$$ salery...

Hey, they did experiment with a turbine engine back in the day. I think it was canceled due to the heat that was generated.

Jay Leno has a motorcycle driven by a Bell turbine. A Y2K I believe.

I love the smell of hydrocarbons in the morning, it's the smell of Horsepower!

Yea, you don't want to get your leg burned from the exhaust on that bike.

From the kneeslider.com

"I remember reading that Jay Leno was at a light with his and the guy behind him pulled up too close (to get a look at the bike?) and the front of his car began to melt from the exhaust".