[sea dog]

I would like to rebuild the pontiac 400 in my 76 trans am. So I need to know, are rebuild parts readily available for the engine?

However, in 76 the engine had a pathetic 180 hp. I would like to build it to around 300 flywheel hp. Are high performance parts available for the 400, and who sells them?

Thanks again, now that I have the 76, I'm sure I'll have many questions.

 

[Suron]

Are you wanting to do a complete rebuild? Or just upgrades for the motor?

 

[ponyakr]

Check the casting number of your block. If the last three numbers are 557, I would not do anything more than a completely stock rebuild. If you want to increase the power, I would start with any '70 up 400 block OTHER THAN the 557 blocks. One of the best and most common is the '71-'74 #481988 block.

http://www.pontiacpo.../engcast01.html

Yes, there are LOTS of HP parts for the 400 Pontiac engine. Your 300hp goal is easy to reach.

That's the good news. The bad news is that building a Pontiac motor ain't cheap, like a sbc is . You can buy a brand new 350 sbc crate motor for about $1600. But it will cost more than that to rebuild a Pontiac 400 correctly. Just to give you an idea, here is a 400 shortblock and a longblock from a well known Pontiac engine builder. These prices include everything except shipping charges.

http://lenwilliamsau...hort_Block.html

http://lenwilliamsau...Long_Block.html

If you supply the block and heads, you can save a few bucks. But you MUST use a machine shop / engine builder that is familiar with building Pontiac motors--NOT just Chevy motors. Chevy shops can really mess up a Pontiac build. I'm a witness.

 

[sea dog]

I plan on a full rebuild of engine.

Engine is still in car so I can't see the back to get casting number. But front is dismantled and engine code is XZ. According to the research I've done on the web, XZ would not be the original engine that came in car for 76, but an older 400 engine.

I'm not up on the pontiac engine family, so what'd wrong with a 577 engine for a higher performance rebuild.

Also thanks for the info so far.

 

[ponyakr]

I'm not up on the pontiac engine family, so what'd wrong with a 577 engine for a higher performance rebuild.

In order to save a few bucks per motor, Pontiac decided to put less iron in the motors back around 1975. One of the areas they removed metal from is the main webs. Because of this reduction, the main webs are not strong enuff to support a high performance build.

So, many of these motors have expired when one of the main webs broke, at the cap locating dowel pin. The 1st batch of these weak 400 blocks have a casting number of 500557. Then the last batch had a casting number of 568557. Some say these blocks are safe to 400hp. Some get by with it, but some don't.

https://sites.google.com/site/ksmsinc/technical-info/title-1/pontiac-engine-block-casting-numbers

Every time I mention this, some lucky guy will come on and say they have built 500hp motors with these blocks and some even used nitrous, and never had any problems. My neighbor built a mild street / strip motor, which barely lasted til the water got hot, so to speak. So, I reckin if you feel lucky, use it.

Here is a pic of one of the thin webs, and a pic of one of the blocks that broke a main web at the dowel pin.

 

[ponyakr]

... engine code is XZ. According to the research I've done on the web, XZ would not be the original engine that came in car for 76, but an older 400 engine.

If I'm reading this chart correctly, an XZ block is a '76 350 block, not a 400. But it does have the good 6x-4 heads.

But Pontiac used the same two letter codes on some motors in different years. A quick scan of the chart shows a '67 350hp 400 block that came with 670 heads, which has an XZ code. It will have only 2 motor mount bolt holes on each side. So, if you can't see the casting number, look at the side of the block. The cubic inch is cast into the sides in several locations. I'll show some pics. The casting # of the '76 350 block is 500810. I have been told, it also has the weak main webs. Can't confirm that.

http://www.classical...obal/engine.cgi

https://sites.google...casting-numbers

 

[ponyakr]

You can also ID the cubic inch of a block by the two numbers that are cast into the lifter valley.

A 5 / 0 is a 350, a 0 / 0 is a 400, and a 5 / 5 is a 455.

 

[sea dog]

Thanks for all the good info. Myself, I ask questions then follow good advice. If block turns out to be a 557 400ci engine, I will get rid of the block and buy an older 400ci.

Now on to the possibility of it being a 350 pontiac engine. I will look on the side of the engine in the next few days. Only part of the front end left on the car is the fenders. I'll pull them for a better view.

I take it that a 350 pontiac looks similar to the 400.

If engine turns out to be a 350, I will sell it also as car came from factory with the 400 engine.

 

[taman76]

I take it that a 350 pontiac looks similar to the 400.

They look exactly the same on the outside. Except for the numbers

 

[ponyakr]

If engine turns out to be a 350, I will sell it also as car came from factory with the 400 engine.

If it is a 350 and still has the original heads, they should be the 6x-4 heads. These are very desirable. They came on the higher horsepower 400's in '77-'79, which were called W72 engines. So, if It was mine, I'd keep the 6x-4's to use on a '71-'74 casting number #481988 400 block. They will also make good heads for a 455 or 400 block stroker motor.

http://www.wallaceracing.com/head1.htm

Also, I'd keep the other parts that are bolted to the 350. The timing cover, oil pump eccentric, HEI dist, oil pan, pulleys, brackets, and lots of other parts will work on a 400 or a 455. You may need all or some of these parts when you put your motor together.

What I'm trying to say is, DON'T sell the 350 !

These small parts are getting harder to find and more expensive.

 

[sea dog]

Thanks again, if I sell the 400 it would be just the bare block. If it's a 350 will keep it.

 

[sea dog]

Heads are 6X. Rest of engine is so heavily covered in sludge that I can't read anything. I will have to do some serious cleaning before any numbers show.

 

[sea dog]

Finally got around to cleaning the engine enough to read the numbers. The good news is, it's a number matching engine. The bad news is, it's a numbers matching engine. That is because it's a 400 with the 577 block. So I guess I'm stuck with 185 hp unless I get another engine.

 

[ponyakr]

Yeah, IF the motor is original to the car( matching serial number), then you definitely have a big decision to make. Many say the 557 block is good to about 400hp. But many others have lost 'em, with much less than that. I, personally would only do an almost stock rebuild, if it was going to be a show car only, or just for resale.

Otherwise, I'd just keep the short block, for future resale of the car, and use the 6x heads for a 400 block stroker build, or just a good 400 build. Hey, you could even use the original intake and carb, if they are usable, and have a numbers matching motor, except for the block. Most guys are not gonna look at an engine close enuff to read the numbers on the block. And, unless they are a collector, most would rather have a motor with the stronger block, anyhow.

So, if you decide to find another block to build, the 481988 blocks are probably the most common. Hey, if you can find a W72 motor with the XX bolck, for a decent price, you'd have a good block, plus a set of 6x-4 heads. But I'm guessing that you can probably buy an older block, then a set of 6x heads separately, much cheaper than a complete W72.

If you decide to build a stroker, you don't even need a crank. All you need is a bare, rebuildable block. Sometimes you can buy a block for a reasonable price from the shop who will do your machine work. Most shops that build lots of Pontiac motors, keep some usable blocks on hand. Hey, you can even build a 350 stroker that will make 350-400hp. And there are guys that will give you the block, cause very few are using them.

Inquiring minds wanna know. So let us know what you decide.

 

[sea dog]

Unlike the past, machine shops around my area have gone the way of the dinosaur.. There is one about 20 miles away who does questionable work. Then we have a guy with a home machine shop in his garage. My racing friends say to stay away from that guy. Back in the day, every auto parts store in town had a quality machine shop running.

So I'm taking my engines to a guy in Homasassa Springs, about 60 miles from me, to do my engine work. He does good work on sbc and olds engines, but I don't know how good he is on pontiac engines.