[GoreMaker]

I'm planning to build up my 1977's W72 400 for some extra power, without going to any extremes. The 557 block used in that year has a lot of missing material from the casting, but this is an original matching numbers block and I really want to retain it. My power goals are around the 400hp mark without any stroking, which seems to be near the upper limit of what these blocks can handle reliably for years and years. So keeping this in mind, I was wondering if it's possible to stiffen up the webbing a bit to reduce the chances of cracking.

Would 4 bolt mains help to stiffen up that area? Are the bosses present in the casting to accommodate 4 bolt mains without removing too much material?

What about short-filling the block, is that something that might help?

Are there any main girdles available for this application? Would that help to stiffen up the bottom end?

[Gary H]

If you're going with the stock 3.750 stroke crank you won't have any issues at 400 hp. I've built several engines at that level with the 557 block and haven't had any issues at all. One, we actually used KRE D port heads on and a fairly healthy cam. No issues years later in the customers car. Nothing was done special in the main cap area. Stock bolts and caps. I would, however, be hesitant to use a stroker crank in one due to additional side loading of the block.

[TAKerry]

I am not a mechanic and all of the aforementioned lingo may as well be chinese. But I have a 557 block in my 77 T/A. The builder warmed it over slightly with a bit of a cam (whatever that means). He had no hesitation doing what he did. Car runs great! Never dyno'd but he estimated close to 400 hp with his knowledge of building motors and past experience. As far as I know he did nothing extra special as far as strengthening the block. I dont run it hard, never raced it and probably never will. Heck, I barely hit 60 going down the road. I do drive like an old man But the car will get out of its way when it wants to.

[ponyakr]

I'm on the opposite side of the fence.

Have pics of several 557 blocks with chunks missing out of main webs.

I'd do as many here have suggested in the past. Store your numbers matching engine, & save it for future sale with car.

Build what you want, using a stronger block. That way you want have to be worried whether it's gonna hold up or break.

Opinions differ.

I've read where some brag about how much power they made with a racing 557 block. That's fine IF you wanna take a chance. How lucky are you ?

[GoreMaker]

Originally Posted by ponyakr

I'm on the opposite side of the fence.

Have pics of several 557 blocks with chunks missing out of main webs.

That's really interesting and I very much appreciate the photos, I've been wanting more details about these failures for years now.

Looking at the photos, it seems all the failures you've come across were at the dowel pin. And in one of the photos, I see a solid dowel pin instead of a rolled one. My understanding is that Pontiac went with rolled pins on '77+ W72 engines specifically because there was a higher chance of cracking there when high-revving with solid pins. The rolled pin allows the cap to walk slightly rather than overstress the block.

Also, it seems to me like a splayed 4-bolt main cap would really help to secure that webbing and spread the stress into the area between the cylinders, perhaps as much as 50/50 between the two bolts. The splayed bolt ends up beyond the dowel pin, and wouldn't be drilled solely into the thin part of the webbing. Unless I'm seeing the photos wrong.

[tom s]

I built one not knowing anything about the bottom end of those blocks.The build was on this site.Got real lucky.4.21 stroke 3in main crank,everything inside was high quality and light weight.The engine made just under 600 HP,is in a 70 GTO running fine now for many years.Others have not been so lucky.Tom

[77 Canamman]

It's telling when Pontiac had to switch back to the XX481988 cast blocks in 1978 W72's due to warranty claims. Even the relatively stock sub 300 HP was too much for some of them. Another issue was quality control. The rod/piston assembly weights differed greatly in some of these. If the rotating assembly is quality and balanced, 400 HP would be my limit.

[Jay S]

Maybe I can help. I designed and built some girdles for Pontiacs for different levels of performance. I made 10 of this prototype, these fit in stock type oil pans with no modifications, I have plans for 3 of them. I will likely find homes for the other 7 at some point, and I can always make more. I have worked on this off and on, and haven’t pursued selling any, not sure what they would run for cost now with inflation. It was going to cost around $450 with all the fasteners before the feds decide to put us all into debt. Hoping to keep it all under $500.

Could possibly also just do the halos without the frame rail supports with studs for a little insurance, the one in the photos shims the oil pan down a .25”. It will fit any factory 3” block as long as it has stock factory 2 bolt or 4 bolt caps, may fit with some aftermarket caps too, it is designed for the milidon and canton pans. I am working on a second engine now that is more for testing.

Here is the photo of a 462 cid 500557 i did, which is the original engine in my 77 4 speed W72 trans am, likely 550 HP or so. It has the orginal 6X heads I ported and flow 292 cfm @28” intake and 224cfm on the exh. 2.125” intake valve, 1.77 exh, 192 intake port volume. Cam is a Bullet hybrid roller set up with .630” lift. It mostly a cruiser.

It has a Milidon 7 qt pan with the kick out. One picture is of it back when I installed it, it fit with no mods, the other with my enthusiastic assistant helping check the mains. Lol

I will put the stock intake back on eventually when I get a chance to port one and weld it so it seals up with the bigger RA4 size ports. Stock looking 550hp smog era engine.

[GoreMaker]

I was planning on a replacement internally balanced rotating assembly with at least forged rods and pistons, and possibly a forged crank.

[Formulabruce]

Originally Posted by GoreMaker

I was planning on a replacement internally balanced rotating assembly with at least forged rods and pistons, and possibly a forged crank.

not boosted, I would recommend Hypereutectic pistons.
less wear and long life for your motor.
Other than that make 100% CERTAIN that you are balanced within 1/2 a gram and youll be good. Shoot for the torque you want at driving speeds. HP will almost always be way up past where youll use it or feel it.
Dyno's do NOT Measure HP...... only calculate it with a bunch of variables
that can be programed in to the machine.
The Torque is REAL, and you can feel it.

[tom s]

Just me,I would not want to put anymore holes in the web.Tom

[GoreMaker]

Originally Posted by tom s

Just me,I would not want to put anymore holes in the web.Tom

Yeah, I'm pretty hesitant about that too. The holes to accommodate bolts would be much larger than the dowel pin holes.

How come no main girdles exist for this? Seems like that would be a no-brainer solution, and there's stud girdles for every other engine block ever made...

[77 Canamman]

Originally Posted by GoreMaker

Y

How come no main girdles exist for this? Seems like that would be a no-brainer solution, and there's stud girdles for every other engine block ever made...

One main reason: There are TONS of great pre 1975 400's out there still. There are not too many 1975-78 Trans Am owners with the 557 blocks that want to push the limits of their design.

[Jay S]

I haven’t finished designing a windage tray to fit it., or tried modifying one to fit. One would work with it but would need to be modified and bolted to a couple of the bridge supports. The way it is now it should have some crank scraping action to it.

I am hoping to try some different stuff to see if windage is effected on this second engine I am working on. Some trials with and without it to see if there is any parasitic loss/gain from running variations of theses.

[Jay S]

Here are a couple others I modeled on solid works also to fit a stock oil pan. This one has billet aluminum bridges but cost was almost 3x more to make it. Looked like it offer better support on #1 main.

The other one that appears to have some type of windage tray on it is the expandable halo style with a tray designed to reinforce the 1 and 5 caps.

[Jay S]

The outside bolts (7/16” dia grade 8 gold bolts) your seeing go through the bridge support which tie the right and left halo’s together. Then goes through the pan rail support to tie the entire thing to the pan rails. The halo’s are sandwiched between the bridge support and pan rail support.

For a really high hp application the main caps can be machine flat and 1” thick strap on the bridge support. Those photos have stock caps and .25” bridge supports. No machine work other than a line hone on the mains for using main studs.

[Mike Davis]

A girdle won't help this. The webbing under the mains is very thin.
If you are investing in forged internals, I'd spring for an earlier block and save that one.

[JSuchma]

FWIW.....I purchased a Butler built 461 530 HP stroker off of facebook market place around 4 years ago. Had there E-heads with the street port job and port matched RPM intake. All parts had the job number stamped on them, including the 557 block. I just could not believe that Butler would have used that block! I even got a stack of paperwork with it to prove it was built by Butler. I have also seen another Butler built motor based on a 557 block as well.

[GoreMaker]

Originally Posted by JSuchma

FWIW.....I purchased a Butler built 461 530 HP stroker off of facebook market place around 4 years ago. Had there E-heads with the street port job and port matched RPM intake. All parts had the job number stamped on them, including the 557 block. I just could not believe that Butler would have used that block! I even got a stack of paperwork with it to prove it was built by Butler. I have also seen another Butler built motor based on a 557 block as well.

Ultimately, they'll build whatever the customer asks them to, even if it seems unreasonable. They'll just make sure you know what is and isn't covered if you choose to use a questionable component.

So far, I'm still leaning towards using my numbers matching 557 block for this build.

[ID67goat]

Originally Posted by GoreMaker

Ultimately, they'll build whatever the customer asks them to, even if it seems unreasonable. They'll just make sure you know what is and isn't covered if you choose to use a questionable component.

So far, I'm still leaning towards using my numbers matching 557 block for this build.

Actually, I don't think that they really care what the customer wants or what is best for the customer. I have one of these (4.25 stroke) short blocks from them....and when I was ordering the short block , I made it clear that it would be going in a 67 GTO, and that the heads/cam that I was using on my 428 (which would be put on this new engine) was making 420 rwhp.....but what I ended up with was a 557 based stroker, that was not balanced very well, with main journals out of round, and it required motor mount adapters for me to put it in my car. Last trip to the dyno was 460 rwhp......is it a ticking time bomb? Maybe?

Probably only reason I haven't had a problem is that the car is just a street car and only raced maybe once a year.

I think you will be fine building this up like you want for a street car, but there is no way I would trust a 557 block if you were going to the track every weekend.