350 vs 400 rebuild
 

I found a good video on YouTube of a Pontiac 350 rebuild.

https://youtu.be/TnyrvGtMIfA

The link is actually putting it back together. There is another one showing tear down.

Anyway question is: Is rebuilding a 400 pretty much the same deal as the Pontiac 350? I've got a couple 400's pre 75 and I might try building one just for cruising and to check it off my bucket list. Thanks

Other than bore size (3.875” vs 4.120”) they’re essentially the same engine.

Build it.

With the way competent auto machine shops are falling into the Abis these days, no less shops in general then, go forth and build the 400.


Both motors basically weigh the same and It’s a lot easier to find good pistons for the 400 and unless about 12% higher fuel cost matter to you, once again do the 400.

What year heads do you have to with these motors?

Steve, I've got a 69 XH w/ 62 heads complete. And a 73 Y4 block with mains and a pair of 7k3 heads. Thanks

A 400 will get the same gas mileage as a 350 +- 1 MPG. The extra bore size and 50 cubic inches make more "smiles per gallon".

Thanks, yeah I definitely want to build a 400.

Nothing wrong with a well built 350P. DSS is now producing quality forged pistons for the 350P, along with the 326 and 389.

Agreed, I kept my original 350 in case someone ever wants the car back as it left the factory. I currently want to rebuild a 400 to swap out a YS block 400 that's in my car now.

I’d consider building a 350 for 2 reasons.

The first one being if I owned a 350 HO car.

The second would be when all the big-bore blocks have disappeared, and they haven’t yet.

Come to think of it I’d build a 350 instead of a 400 if all I could find was a 557 casting 400 block.

The beauty of owning a Pontiac is all the engines are physically the same size and weigh within pounds of each other no matter the displacement. The 455 is the best bang for the buck hands down, the 400 is an awesome performance engine as well with an edge on fuel economy.

To me it makes little sense not to maximize your cubic inches, within reason. Sometimes the 455 is a little too thirsty and the massive torque is hard to harness so the 421/428 or 400 makes sense depending on how you set up your car.

A 350 or 326 just isn’t in the cards for the majority of us, unless we’re restoring a 326 or 350 numbers matching car.

Bart, serviceable 428 and 455 blocks are increasingly rare here in the Ohio Valley. 400 blocks are still available but the prices have gotten totally stupid. There was a guy on Marketplace asking $1,500 for a 557 block.

They run great with 4" cranks in them. Does anyone even sell the cheap cast 4" crank with 3" mains anymore.

Butler Performance 557 Casting Budget Short Block Kit, 400 Block, 433-440 ci, 4.000" Str. These are rated by Butlers' for up to 500hp only. There was a thread not long ago that properly inspected & prepared 557's were good for 500hp.

A 326-350 can be built to make very reliable power and last a very long time. I equate these engines to a SBC 305-307. They too can be built to make reliable power and last a long time. But why do that when 350 Chebby's are still around and a dime a dozen. Unless a factory HO engine, hard to make a case to build one. Bill Rink was a long time friend of mine, (RIP), he and a few others proved the 350 Pontiac was no slouch if you were willing to invest allot of time, energy and $$$$ into making it the little engine that could. IMO the saying "No replacement for displacement" really applies to an engine family designed to make low RPM torque.

Trying to recall what the usual items to consider when using a 350 block, will take a shot at it strictly from memory for amusement:

* Large valve heads may have issues with the smaller bore, chamfer needs to be scrutinized

* Piston selection may be minimal

* 350P blocks have thick bore walls (can't recall specifics)

* Care needs to be taken on block inspection/prep, cap fitment, line bores, deck, etc (core shift)

My first engine build was a 350P, and went big on the bore because of piston availability. I think it was like +80 or maybe even +100, would have to dig thru notes. I abused that engine, RPM-wise especially, rod let go fairly early on in it's life. OE prepped rods with good bolts. My intro into Pontiac engines!


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Pistons for the 350P aren’t an issue anymore now that DSS is producing forged pistons for this engine. Tom S and I had a conversation about building a 350P a while back. We both agreed that using an LS blank made tremendous sense. Paul Carter tried to get people interested in a limited run LS based 350P piston from CP/Carrillo but no one was interested at that time.

I know of one 557 based 400 that made 500+hp, but you’ll have to contact Tom S to find out exactly he had done to the block so it would survive at this power level. Replacing the main cap roll pins with solid dowel pin would be the first thing I would do along with a thorough NDT examination. A very light reciprocal mass would lower the stress on the bulkheads. Pontiac went to the 481988XX blocks in the later W72 400s for a reason.

Well, my friend ran a 557 for 3 seasons of bracket racing. RAIV cam, home ported 62s with a Warrior and 750 DP on top.
It ran really well, beating my 455 for a bit and he let me know about it.
Then it broke every main bulkhead in the block.
Stock-ish only blocks as far as I am concerned.
He has moved up to a good 400 block with Butler Scat 4" crank and rods with the same heads. Car runs 10.50s now.

Butler is doing what any smart business would do now that the good 400 blocks are becoming scarce.

Using up that pile of 557 blocks that otherwise would be getting scrapped and capitalizing on them.

Personally there’s absolutely zero chance I’d invest 8 to 12k or whatever to build an engine off of a questionable foundation.

For those of you who are willing to roll the dice on a 400 - 500 hp 557 block build be my guest.

I agree, Bart. Considering the money spent on the 557 block to make it live, I would add a few more dollars and get a reliable block. Used 455 blocks are still around and a good source. A forum member is on his second 455 block and even that one has needed some work done to make it live. This one would last ages and and be rebuildable and easily sold:

http://www.krepower.com/Pontiac%20MR-1%20Blocks.htm

Considering the $$$$ spent, the MR-1 iron block starts to look good. FWIW