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Pontiac 400.....tell me what you know about it

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Old 12-18-2008, 10:01 PM   #1
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Default Pontiac 400.....tell me what you know about it

I just posted this in another section on here but, I have found a 78 trans am with a pontiac 400 in it(not the olds 403).

I know absolutly nothing about these motors. Does anyone know anything about it...good or bad or whatever.
Do they take to mods well?
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Old 12-18-2008, 10:37 PM   #2
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i know it takes more to build them up then say a SBC.
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Old 12-18-2008, 11:13 PM   #3
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yeah i was figuring that....however, im not sure how many things dont cost more to build than an sbc
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Old 12-18-2008, 11:23 PM   #4
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yeah i was figuring that....however, im not sure how many things dont cost more to build than an sbc
What exactly do you want to know? $ for $ an LSx will make more power and be more efficient.
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Old 12-18-2008, 11:27 PM   #5
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What exactly do you want to know? $ for $ an LSx will make more power and be more efficient.

I know all about ls1's. Im looking at getting a 78 trans am that has the original pontiac 400 in it that has been "built". I dont know to what extent yet, but im going to check it out in a few days. I was basically curious about any high/low points about this motor.
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Old 12-19-2008, 06:48 AM   #6
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Take a look at butler performance. All they deal with is pontiac motors. The heads on them are very similar to an ls1 with symmetrical intake ports. The factory heads are crap. The cheapest head you can get for it would be the edelbrock heads. Butler Performance has some other heads but I cant remember what they are.
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Old 12-19-2008, 07:16 AM   #7
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Take a look at butler performance. All they deal with is pontiac motors. The heads on them are very similar to an ls1 with symmetrical intake ports. The factory heads are crap. The cheapest head you can get for it would be the edelbrock heads. Butler Performance has some other heads but I cant remember what they are.
thanks ill check that out.
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Old 12-19-2008, 06:47 PM   #8
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Yup stock heads suck. Very low compression.
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Old 12-19-2008, 06:50 PM   #9
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Originally Posted by BeefTip View Post
I know all about ls1's. Im looking at getting a 78 trans am that has the original pontiac 400 in it that has been "built". I dont know to what extent yet, but im going to check it out in a few days. I was basically curious about any high/low points about this motor.
They are great low speed tq. motors.
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Old 12-19-2008, 07:25 PM   #10
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If for some reason you loose interest in the T/A, let me know.
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Old 12-19-2008, 08:26 PM   #11
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Look at the casting numbers. On the heads, they're on top of the center exh ports. Then find the engine block code, facing the front of the engine, just above and to the left of the water pump, should be two letters (YJ etc). If you want to know if the engine is original to the car the vin is stamped on a pad on the lower left of engine beside the front cover just above the oil pan but is very hard to see in the car. With these numbers you can get an idea of what you're dealing with. Stock heads can be good or bad, you just want the right ones for the combo. Later smog heads had really large chambers for low compression. Generally, earlier 400 blocks were considered better because they are "beefier" and less likely to distort in high hp use. Stock intakes will work perfectly well on mild to mid hp combos, and can be made to out perform even aftermarket stuff with an afternoon worth of grinding. A Pontiac motor will cost more to build than a SBC, but how many do you see any more? Besides its what the car is supposed to have in it... Good luck !
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Old 12-19-2008, 11:06 PM   #12
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I had a black/gold 78. Blew the motor and found a SD 455 with a nice size cam. Sold it to a guy in Opelika in 82. This one wouldn't black/gold would it?
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Old 12-20-2008, 12:49 AM   #13
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They're interesting engines, to say the least. There were so many variables in head castings throughout the years, you just have to decode them to see what you've got. I used Google to find out everything I wanted to know about my old 400. The heads are lower compression #16's out of a '69 Grand Prix casted on October 9th of 1969. the short block is '73 vintage with flat-tops. It's torn apart at the moment, but will be up and running again soon. Being that it's a late '70s car, I'd bet it's got a set of 6X heads.

Seriously, Google "Pontiac Head Casting Numbers" and **** of that sort. There's a few good websites out there that tell you where to look and what it means. If you can find any of his publishings, Jim Hand is the business when it comes to Pontiacs.


They're physically large engines and weren't differentiated by big and small blocks. From 326 to 455 cubes, they all look the same externally. The displacement casting was on the front passenger side of my block. In my opinion, they're built more like a big block than anything. They make great torque, but don't rev too high. The rotating assembly is heavy, especially the crank.

Parts are expensive, but that comes with the territory when messing with anything other than Chevy or Ford iron. Buicks, Ponchos, Oldmobiles, AMCs and Mopars always cost a pretty penny. They're interesting engines, but not common knowledge like three-fittys and five-ohs. It'll **** you off when you're looking at intakes or something and the Pontiac stuff costs twice as much.


The good thing is there are plenty production-based combinations that were strong runners back in the day and still make stout street cars.


http://www.pontiacpower.net/castnum01.html

http://www.yearone.org/updatedsingle...pontengid3.asp

http://www.angelfire.com/fl4/pontiacdude428/HeadID.html


There's shitloads of details that vary from one to the next. You just have to do your research.
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Old 12-20-2008, 01:26 PM   #14
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There is a guy locally around here that has a 489 pontiac motor that is 15:1 compression and has edelbrock heads and a solid roller setup that got butler performance to spec out for him. Its in a 67 firebird that has full interior and a cage. He was street racing with it and was beating everybody with it. Then one day me and my buddies saw him at the track and he had N/T on the windows and the track goofed and still showed his time it was 9.70 and that was on the motor.
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Old 12-20-2008, 10:54 PM   #15
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edlebrock aswell as kauffman make good heads for the pontiac motors. BTW, i believe all pontiac 350,400,455s have flat top pistons. the difference in compression is made in the heads. like said they have the engine size stamped on the drivers side of the block. checkout the new pop.hotrodding mag. one of the engine masters challenge guys built a pump gas (10.4 comp.) 400 (407ci) engine. with a flat tappet cam and kauffman heads, it made 628hp and 578 ft.lbs. trq. n/a.
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Old 12-21-2008, 08:06 AM   #16
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I think horsepower tv did a build awhile back on a 400 pontiac and they put in a mild cam edelbrock heads and intake and it dynoed somewhere north of 500 hp
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Old 12-21-2008, 04:15 PM   #17
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Some of the statements in this thread are way off.

1st, If you are looking at this car and it does have the original engine in it and the code is X7 it is 220 HP. The X7 is the best block for 1978. In building this engine you can get 400 HP pretty easy and the 6X heads can be milled down to get a pump gas compression of 10.5 to 1.

2nd, There are many good after market heads but you do not need them. Many of the factory heads are big valve and high compression. Some said the stock heads suck not true at all. You need only a set of 1971 #96 heads and a pre 1973 400 block and you are good to go!

3rd, Not all pontiacs engines had flat top pistons and compression was not based on head cc's alone. It had a lot to do with bore and stroke.

4th, You have 326, 350, 389, 400, 428 and 455 CI Pontiac engines.

5th, The vin number is not always stamped on the block.

I would say go for it and have some fun with an great American classic!

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Old 12-21-2008, 10:41 PM   #18
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Quote:
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Some of the statements in this thread are way off.

1st, If you are looking at this car and it does have the original engine in it and the code is X7 it is 220 HP. The X7 is the best block for 1978. In building this engine you can get 400 HP pretty easy and the 6X heads can be milled down to get a pump gas compression of 10.5 to 1.

2nd, There are many good after market heads but you do not need them. Many of the factory heads are big valve and high compression. Some said the stock heads suck not true at all. You need only a set of 1971 #96 heads and a pre 1973 400 block and you are good to go!

3rd, Not all pontiacs engines had flat top pistons and compression was not based on head cc's alone. It had a lot to do with bore and stroke.

4th, You have 326, 350, 389, 400, 428 and 455 CI Pontiac engines.

5th, The vin number is not always stamped on the block.

I would say go for it and have some fun with an great American classic!

N2
1. x7, why is it the best?

2. stock ports?

3. bore and stroke, how so?

4. what about 421?

5.It was after 1968.
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Old 12-22-2008, 09:28 AM   #19
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the infamous 301?
show some love for the crank breaker
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Old 12-22-2008, 04:42 PM   #20
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I read an article in Pontiac Enthusiast that got 100hp from heads alone!

They added 1.6 roller rockers and got another 20hp (crank hp on an engine dyno)

They tried two different types of headers (shorty and mid) and neigther made power on the stock motor...

The aftermarket intake only gained 4hp... so the stock intakes are fine (even the post '76 with the smaller barrels on the inlet are good without grinding, the test proved it)

So If I had that car/engine (I wish) I'd add some nice heads, a cam with stock 1.5 ratio -roller rockers, ignition upgrades, some headers and a full tune up...

Save up for a fresh paint job, and a 5/6 speed tranny swap...

Time to pimp.
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Old 12-22-2008, 04:42 PM
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