march on firebird 400

hello im new to these forums and would like to thank you for any help you mit givem

now for the question im working on a 76 firebird with a 400. and we had to rebuil the motor. well when we did that we thought why not put some 455 head on there we had laying around(if you would like to know there sd 455 head) so we did and low and behold the old 400 bracket did not fit so we thought we put a set of march seprent conversion kit from march it very cool the underdrive pulleys and power coated clear. put we fell into a problem the p/s dosen't work it doesn't fit, at all so if any of yous guys have used the march on a 400 motor just wondering if you came into this problem any thing you did would help thanks

Welcome J rotten and I wish I could help but haven't used that set-up but hopefully one of our other member's will be able to help you out,
John

what kind of engine is it (make, year, miles on engine, etc..)

if you are using the block that origionally came with the car then ur going to run into trouble. are you sure its the 400 and not 403? the 76 had kind of a wierd set up as far as its block, it was said to be a bigblock but the block was proportionally smaller that the real 400 bigblocks. there was a reason they made it so bigger heads wouldnt fit right (they arent soposed to handle them period!) there isnt really anything u can do to get the p/s to fit with heads that big, unless you relocate the whole modual. and just to make sure, u do realize that you cant just slap bigger heads on the car and expect it to work. u need new pistons, new cam, good idea for a new intake, and you better be sure that your tranny can handle the extra power

Well all of you are confused a bit. The Pontiac is not called big or small since a 326,350,389,400,428 and 455 are all externally the same.The 1976 block is exactly the same as any other year!!! The difference in the blocks are in the main journal size. The 326-350-389-400 all have 3" journals and the 421-428-455 have 3.25" journals so you could call them big and small jounal engines. In compression you just killed any power that you would have had with the 400 heads. The heads in 1976 are 6X heads and have a chamber size of about 98 ccs and the 455 are 118 ccs. You will now be the proud owner of a car that has about 7-1 or less compression, that is way to low!!!!. The stock heads that were on the 400 are actually a good flowing head. You say the 455 heads are SD heads? I highly doubt that and if they are you will need different exhaust manifolds(Round Port). Look on the exhaust ports and there are some numbers on the center ones. They can be 2 or 3 numbers or letters. There is also some real small numbers that will be like L158 by where the valve cover mounts, its just under the lip. You can read this with the valve cover on and on the car. The letter is the month, the next two are the day and the last single digit is the year. So this would be December 15 1978 or 1968. This is also why I need the numbers on the exhaust port. The compression on Pontiacs are all based on heads and not from the piston dome like Chevys. All Pontiacs are a flat top piston and you change compression by just changing the heads. I run a 400 on pump gas that does 12 seconds in the quarter and 0-60 MPH in 3.7 seconds. The 455 heads are not good for any 400 since the chamber is huge!!!. You need to find a set off a 67-1970 400 for some good power. Also the 1976 400 0nly had 8-1 compression with is not very high. It was factory rated at 185 HP. If you can pick up #16s 62s 12s 13s 670s ,these will raise your compression to about 10-1. These are just a few of the performance D port heads.The CCs of the chamber are 72-76cc's. I am running a 400 that was built in 1991 for $999 in 1991 and am using non ported #16 heads and my times are mid 12s @ 106 with a 0-60 ft time of 1.67 and a 0-60MPH @ 3.7 seconds. This is on ARCO gas.

who told u that they r all "externally" the same, i had a 350 in mine before i droped the 455 in, and ur gonna tell me they r the same...u need too do some research

HELLO!!!! You are talking about a Chevy 350 and a Pontiac 350. I repeat " All Pontiac Blocks are the same externally. I have been into Pontiacs for longer than you have been alive and have had over 20 Pontiac Blocks and have done so many engine swaps for friends that I can do them almost blindfolded.. Heres one for you, All Pontiac connecting rods were all the same size since 1956-1979. Oh and by the way, the last Pontiac block was made in 1979. It was actually a 1978 but they ended up using the last of them in the 1979s. Then they came out with the dreaded 301 Pontiac which only lasted a couple years since they sucked. Then GM started using the 350 Chevy block. You need to learn a bit about Pontiacs before saying that I need to do research. Oh and by the way, I also have a 1989 GTA Convertible with a "Chevy 350" and a Full size Blazer with a Chevy 350. I also have a Big block Chevy in my Convertible Vette. This is a Chevy Big Block. There is no such thing as a Big or small block Pontiac! . I also was President of Western Washington Firebirds that have over 200 Members and I can assure you that all the Pontiac blocks are the same. They were painted 3 different colors through out the years. The newer Pontiacs have Chevys in them. There is also a difference in the transmissions. A Chevy transmission will not bolt to a Pontiac as a Pontiac transmission wont bolt to a Chevy. In the late 70s they did come out with a universal bolt pattern but most will not interchange. The Pontiac Transmissions are the same as the Oldsmobile and Buicks and Cadillacs up till 1979.

Here's a link to my site. You should also check out some other Pontiac sites to learn something about them or do you already know it all?

http://groups.msn.com/SixtyEightFirebird/shoebox.msnw?Page=1 I also highly recommend. www.performanceyears.com then check out their forum.

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who told u that they r all "externally" the same, i had a 350 in mine before i droped the 455 in, and ur gonna tell me they r the same...u need too do some research

Into which car are you talking about? The one in your picture?

326-455 used the same block with just a different crank diameter above 400 cubes. 326-400 it was 3.00", 421-455 it was 3.25".

265-301 used a different block.

The only major thing you have to watch out for with different years is the number of mounting holes drilled and tapped into the block.

HELLO!!!! You are talking about a Chevy 350 and a Pontiac 350...

Zoiks!

Yep, that's one of the big reasons I love the Pontiac V8. Interchangeability of parts. I had a 350 with a 455 intake on it. Some people gave me puzzled looks, while others understood. I think the only division of GM that had an idea that I wish Pontiac would have used was Buick. Distributor in the front...

Hey Savagewolf, I noticed you are from Florida. Check out Pontiac Dude!!! he is one hell of a guy. He has an 8 second street car with stock suspension. This is 1/4 times. http://pontiacdude.cc/

Hey Savagewolf, I noticed you are from Florida. Check out Pontiac Dude!!! he is one hell of a guy. He has an 8 second street car with stock suspension. This is 1/4 times. http://pontiacdude.cc/

Darn you! Now I'm going to spend more money on my car.

Thanks for the link!

Darn you! Now I'm going to spend more money on my car.

Thanks for the link!
LOL! Don't you just love it when you find something new you just can't live without.

The Dude also posts alot on Performance years.
http://forums.performanceyears.com/6/ubb.x?a=cfrm&s=7286011111
Check out the street and race links. Lots of cool info. As far as a 455 is concerned for performance, they are only as good as their heads and cam, intake and exhaust. Their HP numbers were very low in the later years. 1976 was the last year. I have a 1970 4 bolt block that is just sitting there waiting for my H-beam rods and Edelbrock heads to be put on but my 400 is kicking butt and runs so damn good that the 455 is just going to wait. The 455s are bringing a premium dollar but now with the 400 stroker kits out there, they are proving that the 400 blocks with the small journal is stronger than the 455 since the mains are smaller and leaves more meat around the mains. As I said before the only difference in the Pontiac block are the crank size and bore size. 326-400s had 3" mains and the 421-428-455s had 3.25" journals. there are some suttle changes internally but they all can be built to around 650 HP before having extensive work done. The first thing to go on Pontiacs are their rods. The other problem is sucking oil to the top of the block and running the bearings dry.

Gunstar 1 is right about the journal size and the bolt holes for the engine mounts. They do sell kits to make any engine fit any year. The interchangability is great for Pontiacs but they did change some of the parts as in pully offsets, alternator bracketing, intakes went EGR in 1973. The 1968-1972 are the same on the 4 bbl cars weather it is a 350 or 455. They actually flowed really good. The heads on the 455 suck on anything other than 455s. But then the 350 400 4 bbl heads are sure to liven up any 455 as long as they are the 1971-1978s. The 67-70 would yield 12.5 -1 compression when most of the other heads will be 9-1 . Pontiacs are the first to use the Air Gap intake as they all run a separate valley pan with an air gap before the intake.

Well, actually, Pontiac was second to use the "air gap". Studebaker beat them by two years...
Guys like savagewolf are the reason so many people believe Pontiacs blow up and can't make power. None of the above... Myth and superstition abound, and Pontiac is no exception.
All of what sixtyeightbird and gunstar1 said are completely accurate.
There are many quirks to building any engine family. There's a new book (August, this year) out by SA Designs. Author Jim Hand is an old Pontiac racer from WAY back... He collected some of the better Pontiac "minds" and used their specialties to produce the most comprehensive study of the Injun Engine since the HO Racing book from 1976. it's called "How to Build Max-performance Pontiac V8s". It's available at BOP Enginieering, Performance Years, Ames Performance, Central Virginia Machine Service, Kaufmann Racing Engines, Jim Butler Performance, and probably a few other Pontiac outfits. Chevy guys won't like it. It spells out the history of Pontiac in racing, and the success they've enjoyed over the years. It also documents many of the engineering "firsts" from GM.
A couple other websites of interest:

boyleworks.com/musclecars
classicalpontiac.com

These sites have excellent Q/A sessions and vast data banks of ACCURATE Pontiac information.

As others have said, the compression ratio in that 400, with the SD heads, is woeful. 6.5:1 is probably more accurate. The SD heads, while the last real race head for a street car GM produced, was designed for 8:1 with 455 CID. You can raise the ratio by installing bump-top (domed) pistons. But Pontiacs have a unique combustion chamber design that does not respond well to domed pistons. It inhibits flame propegation badly. Speed Pro does still list the part number for the dome piston, designed specifically to increase the 8:1 to 10:1 in a 455.
Your best bet is to put those SD heads on E-bay or something, and take the proceeds and turn them into a pair of Edelbrock heads with the 72 CC chamber. That will REALLY wake up that 400! SD heads are desireable for high-end racing and restoration. Not much else.
FWIW

My limited understanding of the 455SD is such:

Redline was 6000 RPM (as opposed to 5200-5500 for other PMD V8's)

Compression in 73 and 74 was 8.4:1

The heads were basically modified RA IV.

Crank, rods, pistons were all forged.

4 bolt mains (only SD and HO PMD V8's had 4 bolt mains)

Bottom end of the engine could handle up to 600 HP without modification.

Exhaust manifolds were the PMD HO manifolds. They flow as good as headers, without rotting out.

Flow tests (as reported in an old edition of High Performance Pontiac) actually flowed better than Dodge's Hemi heads.

1973 was rated at 310 HP, and 74 was rated at 295 HP.

Fastest production car in the US in 73 and 74. Easily capable of 13's stock, stick or auto.
______________________

This is all from memory, so if I'm wrong, please let me know.