Author Topic: Suggestions to add a 400bigblock to my T/A (Read 3666 times)

deerjerky · « **on:** November 01, 2006, 10:12:33 PM »

First of all, let me say VERY NICE FORUM
Ok, now, I have a 1980 T/A bought straight from the Corn Field, yes, it needs alot, but is very daily drivable. has a Stock 301, and I bought / traded for more like it, a 68 GTO 400 i would like to replace the powerless 301 with. I am being told that there will be alot of Modification to get the engine to mount up correctly, maybe Universal Motor mounts and such. Came here looking for advice before i bite off more than i wanna chew.. Any help would be greatly appreciated. Thanks

Ron 1973 · « **Reply #1 on:** November 01, 2006, 11:02:05 PM »

Who told you a lot of mods would be necessary? Putting a 400 in place of a 301 should require no mods at all. The tranny will bolt right to the 400 and the mounts should be no different at all. Might not hurt to have a set of mounts from a 400 equipped bird on standby. The block outer dimensions on the 67-79 Pontiac block are essentially the same, I beleive the earlier 389's and 421 blocks were also the same, they just changed a few internal things around in '67. The Pontiac 301 was sort of a derelict engine, but you should have no trouble at all doing a swap. Pontiac has no big block or small block designation, there's just 1 block, a Pontiac block. I think the actual mass of the Pontiac block is probably about the same as a chevy or ford big block.

Ron

Tin Indians Rule · « **Reply #2 on:** November 02, 2006, 01:24:29 AM »

This is probably the wrong place for this question but I'm gonna through the turd out on the table anyway for everyone to see.

Where did the term "Big Block" Pontiac come from? I guess there is really not a small block Pontiac and the so called "big block" Pontiac is tiny (externaly) in size compared to Olds, Buick and Chevy. :shock: If a Brand only makes one size how does it get labeled???

Aren't the Pontiac blocks all roughly about the same size externally and don't most all brackets and bolt-ons interchange with the exception of the 301? :shock: When one refers to a 400 big block Pontiac engine aren't they really saying there is also a small block Pontiac 400??? :roll:

deerjerky · « **Reply #3 on:** November 02, 2006, 04:40:28 AM »

I have had 2 garages tell me the major issue would be the motor Mounts. Something to do with a difference of the 68 Engine. Honestly, I dont know. just want to get her done. thats why i came here --- for advice from from individuals who know the car,not some back street mechanic.
As far as Big Block, well that is what I was told by others. And let me tell you, it is big. Completely rebuilt, 0 Miles and I am just Eager to het it in. Also have a th-350 to replace the stock tranny with. Is there a torque converter anyone would reccommend? I want a hard driving, Tire burning, Ear Busting machine, but also would like to be able to drive on the interstate.

Ron 1973 · « **Reply #4 on:** November 02, 2006, 05:01:11 AM »

Not sure where it came from Tin. I usually never assume, but, I would assume because most people are familiar with the billions of chevy and ford engines having the big and small block designations and because of the large displacements of some of the Pontiac engines, that they assume they are big blocks. I've heard many times when someone asks me "what engine you got in that thing?" about my 73 and I tell em its a 350. "Oh you got a chevy small block in it eh?" No, it's a Pontiac 350 not a chevy.....lol Then they look at me with the blank look like they have never heard of this.
The 326-455 are pretty much identical outside dimensions and most internal parts will interchange. The 301 was the oddball. I think you can still use the timing cover/water pump from a 301 on the bigger engines though......

Ron

Ron 1973 · « **Reply #5 on:** November 02, 2006, 05:11:54 AM »

The garage may possibly be right about that. I seem to remember something about the early mounts...not sure though. The difference shouldn't be much at all if any. Is the 301 out of the car? You could compare them side by side and do some measuring. I'll do a little asking around and get back to you on it.
Your torque converter kinda has a bit to do with your cam....Do you have te specs on it?

Ron

Ron 1973 · « **Reply #6 on:** November 02, 2006, 05:28:05 AM »

Deerjerky,
You sure its a 68 400? Back by the distributor hole there will be a large 2 digit number there. If it's a 68, it will say 68 plain as day. Also look on the side of the block by the dipstick tube, there it will say the displacement. Yours should say 400....cant miss it. It'll be on both sides of the block.
Once you get it all put together, be careful with that tranny. If it's not already, get it beefed up. A 68 GTO 400 will eat up a stock th350 with a quickness. That engine is putting out well over 300hp and a whole lot of torque if its stock. A TH400 is a much stronger tranny and can take a lot of abuse.

Ron

deerjerky · « **Reply #7 on:** November 02, 2006, 03:53:42 PM »

It is not stock, and i am not sure of the specs, but it has a .30 over bore, High performance cam, 800 cfm rodchester carb, 6X heads, and i found the date code, F258 and the Number by the Dipstick is GM12.Also, ther eis a Serial number stamped next to the water pump and YC is also stamped next to the water pump. The tranny is Plane Jane stock as I was told by the guy i got it from. He stated that he had it Dyno tested at 375 hp with the 800 on it, but no documentation to prove it. Other than the Dyno test, He stated that it has no Miles on it since the complete rebuild. traded a 2000 Wolverine with a blown Motor ( Thanks to my 16 yo in the coal pits ) for it, a Th350, and the 87 Firebird that I listed for sale in the classified parts area.

deerjerky · « **Reply #8 on:** November 02, 2006, 05:06:25 PM »

there is no Displacement on it at all. Have spent 20 minutes looking it over. Can not find it.. What is GM12

deerjerky · « **Reply #9 on:** November 02, 2006, 05:16:24 PM »

Also, will a T-5 5speed work with this ?

Ron 1973 · « **Reply #10 on:** November 02, 2006, 09:13:08 PM »

OK Deerjerky,
the motor mounts are similar but the early 400's used a slightly differnt mount. If it were a 70 or later block, it would go right in place of that 301. Performance Years and Ames Performance Engineering sell the motor mounts that you need to put the early block in the later model car. All you gotta do is change them and your set.
The F258 is a date code and it means that block was made on June 25, 1968(or78??) but if it were a 78 it;d have the displacement cast on both sides. The displacement will not be cast on the side of a 1968 400. They started doing that to the 428's in 68, but the 400's didnt get the displacement cast into the side of the block until 1971. The GM12 I think is something to do with a foundry line....Look on the passenger's side back of the block. There should be a casting number there somewhere. That will identify the engine. Are you absolutely sure that is a YC ? I was trying to find it but the lists I've seen do not show YC as a block ID code for 68. They may just be incomplete lists though. I have a 73 455 and it is a YC code block, but that is a 73 not a 68. That letter code will ID the displacement and horsepower. According to "my sources" the casting numbers for that engine should be located at the back of the passenger side of the block. Lemme know what they are. Also, what are the numbers on the 2 center exhaust ports of the heads? That can be an indicator also of the engine if the heads are the originals. Be sure to clean off around the water pump really good, if you hadn't already, to make sure that letter code was YC.

Ron

deerjerky · « **Reply #11 on:** November 03, 2006, 04:26:43 AM »

The casting numbe ron the backis 9790071 and then there is a number stamped on the front next to the waterpump 807332 YC

jclockga · « **Reply #12 on:** November 14, 2006, 07:01:15 PM »

you can find the casting nuber here
www.gtoalley.com/engcodens.html
It list as a gto engine.