78 Pontiac 400
 

ok, one thing Ive been trying to figure out is what are the differences between the Chevy SB 400 and the Pontiac SB 400. I know the pontiac has the B.O.P. bellhousing bolt pattern, and has a different intake bolt pattern, and I think I remember my brother saying the distributor turned the opposite direction. but what are any other differences? how do the head bolt patterns compare? Ive looked around quite a bit and there are not near as many parts for the pontiac as for the chevy, and most parts are more expensive. but Ive got the pontiac already, and I want more out of it that the stock 200 or whatever hp its got.

that 400 pontiac is a big block, it shares really nothing with the 400 chevy except they both have the same bore/stroke. the parts are nearly the same price, cams, intakes, etc,.......its really a wicked engine and sence its a 78' if its out of a t/a or formula will have the 6X heads, these flow fantastic and are still a "smogger" head, the joys of the pontiac is you can keep most all the stock stuff and still make lots of power. plus everything interchanges from all the 326-455 engines.

according to allmighty chilton big book, 78 poncho 400 4bb,
180 hp@ 3600 325 ft/lb @ 1600

76 ch*vy 400 175 hp @ 3600 305 ft/lb @2000

as far as not as many parts for poncho vs chevy, that was a GM bean counter descision to cut costs reduce the # of engines available. The chevy motor were just more plentiful, not neccessarily better.

Also parts availability depends on where you look. Jegs, Summit, P.A.W. have sheesh loads of parts, then there's Jim Butler, Kaufman racing, Bruce Fulper, and on & on........

Like said above, theres little to nothing in common between the Pontiac and the Chevy. And the Pontiac is not a big block engine, Pontiac doesnt have a big block or a small block, they just have a block.

As for parts, I dont know what planet you shop on, but parts for Chevy engines are dime a dozen and are always cheaper than anything else out there. Has something to do with the volume of parts sold.

yeah, the 400 is the small block, this I know. the 403 was the big block, and it was an oldsmobile. and Ive found that parts are much more expensive than chevy, and looking through jeg's Ive only seen 1 set of heads for the damn thing. I finally got the engine today and its missing a crank, but everything else is there. I just wonder if anyone makes headers that I could use in a 3rd gen. also, I havent had a chance to actaully look at everything yet, but will chevy heads bolt to it? I know it would make everything alot easier as far as aftermarket parts go, but if not, I guess I could always get a set of Ram Air IV heads and get head work on those. hey, as far as Im concerned, if I could spend even $500 on it and have a decent engine, Id be happy since I only paid $100 for it anyway. I would love to build it up into a nitrous monster or something, but right now Im putting money into the LT1. just curious as to what I can look forward to later on with the 400



well madmax, I went back and read your post a little closer, and I'm just guessing here, but I bet your comment about "little to nothing in common" would axe the chevy head idea :( oh well, I'll keep looking. any other ideas?

looking for RA IV heads, how much $$$$$$$ you got? Edelbrock head a sort of cheap. you most likely have the 6X-? heads kee these (smog friendley) get the usuall work done to them. After market or 75 & earlier intake. If no headers, don't worry, just run duall exhaust. There are plenty of setups you can do, inclunding converting the 400 to a 455. Not astroker, just a bigger engine on smaller mains. Pontiac Power is just one of many sites to go to.

headers
 

For headers for a 400 Poncho in a 3rd gen. Indian Adventures is making them, they are waiting for a donor car to test the fit.
Bob

headers
 

For headers for a 400 Poncho in a 3rd gen. Indian Adventures is making them, they are waiting for a donor car to test the fit.
Bob

thanks for the info guys, so $1600 a pair is cheap for Edelbrock heads? also, how can you tell which heads you've got? Ive seen the terms 4x and 6x but since Ive just got this thing I dont have any idea what that means. thanks for the link Pontiac, Im checking them out right now. Bob, any info on where to look for those headers? do they have a website? thanks

the olds 403 is not a big block. it is a small block still. Oldsmobile has/had three big blocks. a 400, a different 400 and a 455.

Pontiac does not differentiate between small or big block. 301 or 455 they are just blocks.

the pontiac 400 has a bore of 4.121 and a stroke of 3.750

the chevy 400 has a bore of 4.125 and a stroke of 3.750

the short strokes of both motors make them essentially low rpm high torque motors. Besides bore and stroke being nearly identical thats where it ends. Distributor caps on hei interchange though...heh. And I don't know about that distributor turning opposite direction might have to pull the bs flag on that. :bs:

i could be wrong though. :confused:


"only dead men have seen the end to war" - plato

headers
 

For Indian Adventures go to ChiefManyHorses.com
To tell what heads you have (probably 6x) See if there is 6x on the middle exhaust ports. Then looking up from the first spark plug hole there will be a 4 or 8 stamped on it... wish I had pics, hard to explain ( plus I just woke up )
Bob

Forgot... distributer turns counterclockwise. When you get to IA... check out they're neoprene rear seal for 3" mains, get rid of that damn rope seal
Bob

well the 265 and 301 were a short deck pontiac block techinally you could call a small block and the 326-455 used the tall deck or could call big block. the 403 old is forsure a smallblock and the olds big blocks were the 400 425 and 455

I got a set of 6X-4 heads from my old 77 T/A engine. Will see about getting some pics.

Wait, I got pics of the heads in the V6 board, will see about putting up another pic w/ paint & have arrow where to look for the -4 or -8

lets see if the pic w/ the romper room graphics works.

Re: 78 Pontiac 400
 

:doh: I was going to reply to this one only because there is no such thing as a big block pontiac like you said pontiacs from326/455 are all interchangable which means right there it is not a big block you might think im nuts but i know alot of people who all race pontiac 455's and i asked them if there was a pontiac big block i got laughed at

85 Firebird 400 pontiac bored 30 over 100 shot nos lots of other peppy percs

fox, yeah I know how you feel, I found out through reading some of the other posts that there never was a big bloack, learn something every day


Project, thanks for trying to get the pics, but I looked yesterday and found the 6X on the side of the heads, so now I know what they are, but what does that mean? what is the difference between 4X and 6X heads?

also, in one of the other posts, someone said that if you got a 455 crank, reground for 3" mains, you could put it right in, still using the same rods. is that in fact true? that would be really sweet to put a 455 in but I'd like to get as much info as I can before I even consider it

Jim Butler is selling NEW 4.25" stroke 3" mains for the 400 blocks (326-389 might fit also) for $399 , but you must grind some clearence for the counter weights.
use stock rods & standard 455 pistons. bore 400 .030

difference between 4X & 6X? not much that I know of, need to look into some refrence material, but pretty sure they are interchangable.

The 6X-4 head will have a smaller combustion chamber than a -8 head.

The 2.8 head vs 6X-4 head this is the pass side head. The metal tab thing near the exhaust manifold, by the last set of rockers is where to look for the 4 or 8 stamping. you will probobly need to clean it up to see it.

thanks, I'll look as soon as I get home today and see if I can find the number. you wouldnt happen to know the two combustion chamber sizes would you? If I get some new pistons I would rather like to have about a 9.5:1 or maybe 10:1 CR, so that would obviously be helpful to know.

I believe the different comb sizes were 93 fro the -4 & 101 for the -8.

if your wanting 9.5-1 cr, I recomend different heads (edelbrocks should shave off a sheesh load of weight) or dome pistons. These heads are for lower comp (7.6-8.5), but put in forged pistons & you're ready for nitrous, turbo , or blower.

oh Id love to get a set of the Edelbrock heads, but $1600 is dreaming. Im definately going to get some forged pistons, Im not about to put the stock ones back in. Im cpnsidering getting one of the Jim Butler (I think was his name) cranks, good price I guess. but Im going to look around first and see if I can find any good used ones. I dont know though, Im definately going to be running nitrous, and Im not ruling out a poweradder later on down the road, so maybe a little lower compression would be better, maybe 8.5 or 9. I'll just have to see what I can get.

oh yeah, how much will milling the heads raise compression? depending on what that will do, I might have that done instead of getting new pistons. Im definately getting a 3-angle, will most like port and polish myself, so I think I might come out of this with a pretty good engine with not alot put into it.

i beleive the most "recomended" amount to mill the heads is .030". Get a pushrod length checker just to make sure everything works. & remember, the lower the comression, the lower octain fuel you need :)

yeah, lower octane would be good, but since Im already having to run 92 in the LT1, its not really a problem. any idea how much milling will raise the compression?

My dads got a stock 77 T/A with a pontiac 400/4speed
 

Yeah, my dad has a stock 77 t/a with t-tops and a pontiac 400 / stock 4speed......he wouldnt give me the f-ing car, so I am gonna buy my camaro instead. It desperately needs a carb, but thats only like 450 bucks.......i told him he should build it up, but he didnt listen.

So now it just sits, maybe when I am older I will take it off his hands and build a screamer.

77 T/A, 4-speed, posi rear, no T-Tops :mad: . My first V8 back in 92. Had the structural integrity of a peice of paper around corners. I still have the motor, taken apart, and have plans for it if/when the motor in the bonnie dies. The replacement motor in the T/A was built pretty good. Took it out of a 76 grand prix. thrashed that sucker, 40 in 1st, 80 in 2nd, 120 in 3rd, and ran out of road before we got into 4th. Speedo stops @ 120 so who knows how fast it would have gone? :burnout:

it was complete luck that I even got this engine. first, my brother found a white 78 t/a for sale in town, went and talked to the guy, bought it the same day for $250. supposedly was a "Smokey and the Bandit", didnt run, rear floor pans rusted out, perfect body, missing some trim, cracked windshield. this moron tried to tell us all of this stuff that "had" been on the car but had taken off and it was "at the house". well, turns out the guy was a lieing p.o.s. car was bone stock, normal t/a. didnt really matter though for $250. only reason it didnt run was a messed up distributor and needed new plugs and wires. also got a new carb, but probably wasnt needed. so now, for about $300 my brother has a running and almost driveable car. that was bout 2 months ago. ever since then he's been finding parts and stuff to besically quick-restore it for now until we can both put the money in to completely restore it. so last week, my dad is driving over to another town for some business, sees a black t/a for sale on the side of the road. for another $250, we get a second t/a. this one pretty bad, block was in the engine compartment, everything else except the crank was in the back seat. but it had an almost new set of Cragar SS's, tires with about 1000 miles, and every piece of trim my brother needed for his car. since he already had a running car, I bought all the engine parts for $100. its amazing really, for about $750, he's gone from having a car that was barely drivealbe, to one that still needs work, but is so much better than what we originally got. its kinda sad really, I hate seeing cars like this go to trash because people 10 years ago couldnt take care of them. they look pretty damn good in my opinion, some of the best looking cars from the 70's, and how many good looking ones are there still on the road? well, theres about to be one more :D ok sorry, had to have my daily rant and rave

its nice to see guys that know engines besides cheby. hehe. as it was said before, there are no big block pointiacs, except for maybe the 301(and most of ponitac would like to forget that engine was ever born, they are junk, i dont care how many people say they can build them)anyways. oldsmobile 260-403 is considered a small block, and the 400-425-455 are the "big blocks" the only difference is the deck height on the big block's is higher, hence the big block term. you can bolt any olds head on any engine, the main difference is the intake, the big block intakes are a little bit wider to compinsate for the wider deck height. my buddy and I built a 455 and put it in his 71 bird, the thing is insane. he picked up some "16" heads from a 400 which are some of the better heads and had 2.11/1.77 valves put in them. the bottom end is stock(crank/rod/cast pistons)with the smaller cc of the "16" head, his compression is around 10.5:1. he put the 274xtreme cam in it, 1 3/4 long tubes, performer intake and 650 holley DP with a TH350 and 2200 stall and 2.73 open rear end. the car runs 8.6's in the 1/8 as is. with a 2.1 or worse 60 ft, it is very traction limited(anything below a 40mph kickdown and it smokes tires and throws the car sideways)he just got a posi 3.23 rearend for it, that should make a huge huge differece, and with a better intake, bigger carb and tractions, 12's should be easy. i dont know how i got on this tangent, but long live the BOP's!!!!

LilJay, man that sounds like a sweet car, I love the 71's, we are trying to find the front end of one of the 70-73 to put on my brothers since his is pretty messed up. but you say any oldsmobile head will bolt to the 400? thatd be great, just that many more possiblities. and is the "16" head the olds equivilant of like the 4X and 6X designations?

no, i guess you misunderstood me. you can bolt any oldsmobile head on any oldsmobile, not pontiac. if i am wrong about the olds thing, please someone correct me. cylinder heads are not compatible between manufacter's. "16" heads for pontiac are real good heads, the better heads are the Ram Air heads, but good look finding them. also, "61" heads are really good heads too. they are found on mid 70's smog engines. the port velocity on the heads are good. you can put big valves in these heads. the only draw back are they have extremely large combustion chambers, like 96cc or something. you can either have them shaved way down, or use different pistons. the only problem with shaving the head is sealing the intake, when you shave the heads, in result you change the angle at the heads and intake. hope this helps.

shave the intake as much as the head to keep the sealing angles the same.

Nice cars, interesting wheel choice ;)

if you shave the heads AND the intake, wouldnt that increase the distance between the two surfaces? if so, wouldnt you have to use a much thicker gasket or do they normally compress enough so that its not a problem?

LilJay, yeah guess I just misread it. but how do you know if you have 16 heads? I looked on mine earlier, they are 6X, and then on the last exhaust port, there is something like GM with a 12 below it. its kinda hard to read between the gunk and rust. where else should I look for numbers, theres a lot of buildup on them right now so if I know where to look I'll know where to clean.

you know how the 6X is on the middle two exhaust ports? "16" heads are the same way, except the the 1 is where the 6 is, and the 6 is where the X is. hope this helps.

shaving both surfaces will not increase the distance betweenthe two, it will help keep proper alignment. Technically, shaved heads will move "closer" to each other because of the angle they're mounted on. shave enough, & the intakewill sit on top of the ppports, & not line u. Shave the intake& it will line up. I remember hearing/reading somewhere that this is only neccessary when milling more than .030" off the heads.

Also, if you stick woth the larger cc smog heads, if you convert the 400 block to a 455 , by way of crank swap, you will raise your CR.

i dont think you can just put a 455 crank in a 400 and viola' a 455, i think the main's are different, and the pistons are different to, i think. i will ask my buddy today and get back with you. the reason i am saying this is because he was gonna do the same thing, but looked into it and found out some problems with it. later lil jay

you must grind the block to clear the couter weights in one area of the block, bore the block to get the same bore as the 455 ,030", & get standard 455 piston size. connecting rods are the same. not sure if the new Jim Butler cranks will fit the 400 block without any clearance issues.

if you use an origonal 455 crank, it will need to be machined to fit the 3" mains & have thrust surface corrected, checked for fatigue, polished, balanced,

This website is slated to be renovated soon Jim Butler Performance

yeah, I checked out the Jim Butler cranks and you can get them with the 3" main for the 400 block or the main for a 455 block. and yeah you do have to clearance the block for that crank, but it sure as hell seems worth it to me. thanks for the info Project about milling the heads, that seems the best way to go, get higher compression and get a straight head in one process. any ideas how much the 455 crank would raise compression? Im still looking but so far I havent had much luck finding a crank except for the Jim Butler one.