Hello, I'm new to the forum but been lurking for awhile. I'm working on 68 Firebird Convertible restoration. I'm considering swapping engines from the current 350 to a 400. I'm still trying to determine what engine I have (previous owner said 350). It appears the engine is not original as it appears to have some later emissions items that the 68's didn't have. Since it doesn't appear to be numbers matching I figured I'd swap for a 400. I've looked around on the site but can't find an article that discusses what Pontiac motors can be swapped into the 68's easily. For instance would a '67 Pontiac 400 Code XJ work? Or how about a '73 big block 400? Also, does it matter what car a motor comes from for instance would a 400HO from a '68 GTO work? I don't know much obviously about this engine swap, I'd just like to get some more HP and have the installation be something manageable. I've read some about LS swaps and I don't want to go that route as I'd like to keep the car period correct within reason. Any help directing me to threads already on the forum would be appreciated as I haven't had much luck finding any. Thanks ahead.
Any '67-'74 Pontiac V8 should be a direct bolt-in swap. This includes 350, 400, 428, & 455 engines.
BUT, the timing cover/water pump/pulleys changed after '68. Also, some of the later heads had more bolt holes on each end of the heads. So, if you use an engine from the mid '70's, you may have to round up all the accessory brackets & pulleys that will work on that engine. Of course, some make their own brackets.
Some of the '75-'79 engines didn't have the correct motor mount bolt holes, for the 2-bolt mounts you need. There are adapters. But some have had trouble with those.
Also, beginning sometime during the '75 model year, Pontiac began using a casting #500557 block, for the 400 engines.These blocks were significantly weakened, especially in the main web thickness. There have been many failures of these blocks. But, these are the easiest & cheapest Pontiac 400's to buy.
For the '78-'79 model W72 400's, Pontiac recast some of the stronger #481988 blocks, & added an XX before the casting number. So, they're known as the XX 481988 blocks. They have all 5 motor mount bolt bosses, but those I've seen, have only 3 of the holes drilled & tapped, on each side. If you use one of these blocks, you'll need either adapters, or to have the other 2 bolt bosses drilled & tapped for your 2-bolt motor mounts.
You can ID your engine & heads by casting number, date code, & block code. The block casting number is located just below the rear end of the passenger side head. It was cast into the block. The date code is a 4-digit number located back by the distributor hole. The 1st letter is for the month, 2nd 2 digits are numbers for the day of the month. Last digit is a number, which is the last number of the year cast. For example: A date code of A108, would mean that the block was cast Jan 10, 1968. The block code is located just below the front of the pass side head. It is usually a 2 digit code. It is usually 2 letters. But it sometimes has one letter & 1 number. There are some blocks with a 3-digit code. The block code is stamped on, not cast with the block.There is usually a string of numbers just above the block code. It's just a sequence number & is not important for making a positive ID of your engine.
Your heads will probably have a 2-digit number cast over the center exhaust ports. For example: A '68 2-barrel 350 would have come with #17 heads. A '69 2-barrel 350 would have #47 heads. Some heads had 3-digit numbers, such as 670, 7K3, and others.
Great answer. I am recommending this post for the Tech Hall of Fame.
1967 FB 400, original CA car (smog), now 455. After 22 years of work, it was trashed by the guy who was supposed to paint it. So I sold it. 2006 Mustang V6 Pony, factory ordered, retirement cruiser and future classic(?) 2019 BMW X3 (Titled to the wife, but I'm always driving it for her. So I'm claiming it) Old projects, gone but not forgotten: 1980 Turbo Trans Am 1970 Mustang fastback, 351C 4Bbl, auto 1988 Mustang GT, 5 speed 1983 F-150 4x4, built 302 1994 Chevy K2500 HD 4x4, 454 TBI
As a follow up to my original post what challenges will I face if I find a 400 that was originally mated to an automatic trans but I want to mate to my 4 speed Muncie trans? Are the splines the same size? What about the flywheel, can I use the flywheel from the 350 currently that is mated to the manual trans or do I need to find a flywheel specific for a manual trans for the 400? Any other parts I’ll need?
As a follow up to my original post what challenges will I face if I find a 400 that was originally mated to an automatic trans but I want to mate to my 4 speed Muncie trans? Are the splines the same size? Any other parts I’ll need?
There are 2 problems that you could encounter.
(1) SOME cranks, in auto trans engines, were not machined to accept a pilot bearing or bushing. Some were. Obviously, you need a bearing or bushing for the snout of your manual trans front shaft.
(2) Some of the late '70's engines had cranks with a smaller centering ring on the crank. I think the early cranks were 2 3/4", & the later cranks were 2 1/2". PRW sells flywheels that come with an adapter ring, so that you can use their flywheel on either crank.
But, if you find an engine with a 2 3/4" centering ring, your flywheel will work. I assume you could use it with the 2 1/2" ring, if you could buy an adapter ring. A good machine shop could probably make one. Don't know if anybody sells one or not. Guessing that PRW does not sell their adapter rings separately.
Checked online. You can buy an adapter ring from a Pontiac guy on Ebay.
Well now I’ve got a quandary. With oldskool’s great guidance I went searching for engine #’s. My assumption was that the engine was a later model as there were some misc vacuum hoses that appeared to be later emissions type stuff. Well the engine decoding proved otherwise. With a wire brush, the numbers cast into the block cleaned right up. The #’s that were stamped took a bit of degreaser and a tooth brush and they cleaned up well enough. After I verified the Date and Block codes I looked this up on the Wallace cross reference tool. Everything indicated it was a 68 engine not a later engine (see attached screenshot of the results). Well, armed with info, I now had to hunt for the engine Vin # to see if it matched the Car’s Vin#. Surprise, surprise they did match. I had a hunch they might match as I purchased the car from a lady that had it for (38) years. She indicated no major engine work was performed in the time she owned it. I just wasn’t sure what had happened in the previous (12) years of the cars existence. What had thrown me originally was the thermostatic vacuum switch which was not connected and the presence of loose vacuum lines. After finding the engine was a 68 I checked my repair manuals and sure enough these were installed in 68 and later to help with engine cooling over 230F.
So now to the quandary part. I was thinking the motor wasn’t #’s matching to the car and since it needs a refresh I figured I’d try and find a 400 and refresh it and end up with added horsepower. Know with the numbers matching discovery I’m not sure that is the right path forward. Maybe I should spend the money refreshing this motor. Quite a difference between 265 hp 2BBL and a 4BBL 290 or higher hp motor. I’d appreciate any thoughts about which way to head. Given it’s a convertible I’m really after a dependable Sunday driver not looking for race car.
Block Casting #9790079 Date code. E148 which translates to May 14, 1968 Center Exhaust #’s. 17 which indicates 17 heads Block code. WC
I'd keep the original engine in it ONLY if I wanted to keep it looking absolutely original, for shows perhaps.
Otherwise, most would probably recommend bagging the original 350 & going with a 400 or larger engine. Would keep all the original parts, for possible future sale, with the car. Some will pay more for original numbers matching stuff.
Since you don't seem to want a lot of power, a decent mild pump gas 400 would probably work well for you. and I'd go with a good rebuilt Q-jet carb. You can either use a factory iron intake or an Edelbrock Performer intake. Obviously, the iron intake will look more factory correct, for your Bird.
You can go with a front timing cover, pulleys, and all the bolt-on items that came on your car. Or, if you buy a '70-up engine, you can switch over to the bolt-on stuff that matches those engines. It's always a great idea to get an engine that comes with as many original bolt-on items as possible. They're getting harder to find & more expensive. Some guys are selling small items for ridiculous prices nowadays, or at least trying to. I consider some of it price gouging. But, that's where we are today.
If you decide to rebuild the 350, you could easily up the performance, with a 4-barrel and bigger cam. Easy to make 300 or more HP, with a mild 350. But, it'll cost just as much, if not a bit more, to rebuild a 350 as building a 400. Pretty easy to make around 350 hp with a mild pump gas 400.
Your #17 heads are good heads to use as cores to make a set of high performance heads. But, having it done right, with good parts will cost probably $800-$1000. Or you can just have a simple valve job done & get by pretty cheap, if you just wanna build it for low rpm cruising.
As the power increases, so does the cost. So, it might be a good idea to decide just how much you are willing to spend on an engine. That might make some of your decisions for you.