[Formulajones]

Here's a better picture of it so you can see the L2257 part number.

[racerboy]

So just to stay with the connecting rod question. If I were going to replace these rods with new forged rods, which seems like a no-brained considering they are so cheap these days, I have a couple of options:

1. Buy new rods, and take crank, rods and existing pistons to machine shop to have entire assembly re-balanced. I’m assuming I should bring the block as well for a clean-up hone, and probably just do new cam bearings since it will be there.

2. Do the same thing, except maybe get new pistons as well?

3. If I was going to get both new rods/pistons, then would it make sense to just buy a balanced rotating assembly? I’m assuming if I did that, I’d have to have the block line bored because of the new crank? Is that true even if that was done when engine was rebuilt back in 2002?

If I were to go with a new rotating assembly, then I would definitely want to prep the block for something better than a set of 670 heads. Maybe even consider a set of aluminum heads?


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[racerboy]

Originally Posted by Formulajones

Here's a better picture of it so you can see the L2257 part number.

Thanks FJ
Would machining a dish be less expensive than buying new pistons?


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[steve25]

Those pistons themselves are fine as long as the ring to groove clearance checks good and you are not shooting for every last scrap of hp out of your build .

New pistons that use 1/16” in stead of 5/64” rings would free up some good power above 5000 rpm with that 4.00” stroke from less friction.

Yes, the crank will need to get rebalanced for whatever parts changes you choose to make.

If you go with better rods then the pistons would be removed and make it far easier for the shop to make the dish a bigger diameter.
This would also allow you to run 50 gram or more lighter new wrist pins and have the motor rev faster which can be very close to making for better performance as a higher level of power!

One thing that always pays dividends down the road is to put as much funds into the short block that you can even if it means running stock heads!

As long as you can get a livable compression you can always up grade the heads at a later point in time knowing that your short block is over built.

This I find is always a good calming feeling when my foot is bending the floor board under the gas pedal, lol!

[racerboy]

Hi Steve
I think you read my mind. I just got off the phone with my friend who owns a speed shop. I told him my story and he said the same thing about the short block. He actually said that if I had the funds, I should just buy one of the Butler rotating assemblies and then he’ll get the block tanked/honed by his machinist.

He put this engine together for me back in 2002. The shop that does all his machine work is LRB Performance. He thinks the block was likely already line honed back then since that is standard practice for that shop. He told me to look for a stamp on the frame rail or one of the main caps.

Lastly, is it foolish to invest in a stout bottom end of a 2-bolt 428 block?


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[steve25]

Nope!
I have run 2 bolt 455 stroke motors at the drag strip for many seasons in a row making 600 plus hp, so I would not question using it for your intended purposes!

The balance job at even at the 450 hp levels when running 2 bolt mains and a stroke longer then 3.750” is critical to low main web stress levels and in returning you long block life!

The shop ( a good high end race shop ) you have doing the balance work should be checked have to have the ability to provide a balance job of plus or minus 1/4 once at 1 inch , not the stock rebuild norm of plus or minus 1/4 once at 3 inches!

A crank balanced as such will have 3 times LESS imbalance left in it then a crank done at 3 inches, and that’s a lot, which makes for a lot less block stress and loads placed on the main Bearings!

[racerboy]

Thanks Steve. I only just learned that LRB sends out their balancing work to another shop so I will find out if they can balance to those specifications.

Of course I’d I buy a rotating assembly from Butler, then I don’t have to worry about that, right? Does anyone else sell rotating assemblies like Butler?


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[Formulajones]

Originally Posted by racerboy

Thanks FJ
Would machining a dish be less expensive than buying new pistons?


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Yes absolutely it would be cheaper to machine what you have further, if needed. As long as the pistons themselves are in usable shape.

Back when I did it, there wasn't an aftermarket forged dish piston available off the shelf for a 428 Pontiac. Just the 4 valve relief TRW flat top. They have plenty of meat, and are always accused of being heavy pistons anyway. So I just machined them to what I wanted, while removing some weight at the same time

[Will]

If I was in your shoes I wouldn't spend a dime on that 428 short block. It looks real clean and while the parts used aren't top notch by today's standards, there's nothing wrong with them, either. You aren't going to be revving to the moon, that Crower cam will be done making power by 5500 with stock heads, you should never need to rev over that and the rods and pistons that are in there are perfectly good for those RPMs.

CC a piston, CC a chamber, figure out your actual compression ratio and if it's under 10:1, run it.

[Formulajones]

I agree with Will

[racerboy]

Thanks guys. I have a feeling my wallet will agree with you. I definitely want to rebuild the original RA III 400 block to be as stout as possible, so I’d rather spend any ‘real’ money there. As Will suggested, I am going to cc the 428 pistons and the 670 heads and report back here. I just ordered a kit from Jegs to do this (this will be my first). I’m not opposed to swapping out cylinder heads if I need to pick up a set of 6X-4 (Jay’s suggestion), but if I spend $4000+ on upgrading the 428 short block, then I am going to have to delay the work on the 400 for a bit of time.


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[racerboy]

I’m still waiting for the head cc kit I ordered from Jegs to arrive but figured I’d ask some preliminary questions.

Will I be able to cc the piston while it is in the block? I’ve never done this process before (even with just a bare piston) but wasn’t sure if I had to remove one of the pistons to do this.

If it turns out that with the 670 heads that the compression is too high to run pump gas safely (here in NJ i have easy access to 93 octane, but it also has 10% ethanol so I’m not sure what the ‘safe’ compression ratio), do I:
1. Install the Crower 60423 and run the 670 heads? My understanding is that the wiser LSA of the Crower over the XE274 will help bleed off some of this compression. I have seen others comment that this is only a ‘band-aid’ but this truly would only be used so I could drive the car while the RA III 400 was being built.

I’m assuming I have to get new lifters if I put the Crower in. Do I need Rhoads? I believe I have a new set of Johnson lifters on the shelf if I don’t need the Rhoads.

2. Get a set of 6X-4 heads to bring compression down. If I did this, wold it make more sense to reinstall the XE274? Again, my rudimentary understanding is that the Crower would work better with more compression and the XE274 works better at lower compression.

Thx


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[Formulajones]

CC'ing the piston in the block? Probably not, unless it sticks up out of the hole. See my pic above where I CC'd a piston and that'll make more sense.

I'd hold off on camshaft choice until you figure out exactly what the compression ratio is, and then choose a cam accordingly. You'll probably find with what you have, just a simple cam choice will allow the engine to live happily on pump gas without the need to spend a bunch of money elsewhere.

Like Will mentioned earlier, and I agreed with, if it ends up being 10:1 or less I'd leave it alone, stick a cam in it and run it. Save your coin for the RA III build.

[steve25]

if you know how much your piston is in the hole you can figure out the CC’s of that with a simple formula, and if you do not know the CCs of your valve notches or a dish then all you need to do is fill those up with clay and then remove them and drop them into your CC Buret to find out how many CC’s those are through displacement,

[Jay S]

Someone on this board might know what the volume is on the head of those 428 pistons is so you would not have to cc it. I don’t have them in any of my speedpro or TRW books. Speedpro may have changed them on the later years and made the dish a bigger diameter. Seems like the later production runs had a 8.5 cc dish and 5 cc VR’s and the older pistons like yours are a 5 cc dish with just under 6 cc VR’s. Measure the dish dimensions and see which pistons you have. Then check the deck clearance.

The 6x-4s on that 428 is more of an 87 octane combo with either cam. I am guessing there is just under 2 points difference in octane requirements between the Crower 60243 and the 274XE. I would not consider either cam big enough to be a “crutch”. I would not do Rhoads if you have the Johnsons already.

I agree with FJ, figure the compression and pick the
cam.

[racerboy]

FJ - thanks. In looking at your picture of the same 428 piston, you said you wound up with a 16cc dish after the machine work. I’m assuming that my cc amount of the smaller dish and 4-valve reliefs is going to be less than that. I’m a bit hesitant about pulling the piston out of the engine because I’ve never actually put one back in. I don’t have a ring compressor or anything like that. I could probably borrow one but would need baby steps on how to arrange the rings when I put it back in.

Steve - are you suggesting using clay to make an impression of the top of the piston? What kind of clay is used? Wouldn’t the dish be a dome in the clay? How do you cc that?

Also, how do you determine how far down in the cylinder the piston sits?

[Stan Weiss]

Yes, you can cc the piston in the block. Can you measure the cylinder bore and and depth of the piston to a thousandth of an inch?

As an example. Bore = 4.150" Piston Depth = 0.500" and your fill is 120.8 cc's You would have 10 cc's relief / dish.

Stan

[Formulajones]

Originally Posted by Jay S

Someone on this board might know what the volume is on the head of those 428 pistons is so you would not have to cc it. I don’t have them in any of my speedpro or TRW books. Speedpro may have changed them on the later years and made the dish a bigger diameter. Seems like the later production runs had a 8.5 cc dish and 5 cc VR’s and the older pistons like yours are a 5 cc dish with just under 6 cc VR’s. Measure the dish dimensions and see which pistons you have. Then check the deck clearance.


I agree with FJ, figure the compression and pick the
cam.

Yep, that L2257 number has long been superseded. Back about a year ago I posted that number and the pictures showing what I used in a 428 build (same thing here) and several members swore up and down those were 400 pistons. They are in fact 428 pistons and that was a good TRW part number at the time. I bought mine nearly 25 years ago.

They are flat top pistons originally, with 4 valve reliefs. I can't remember what the CC of the valve reliefs were anymore. The dish you are seeing in my previous picture, I machined in there. In the OP picture someone has done the same thing, although to a lesser degree. Way back when there weren't any off the shelf forged dish pistons for 428's, pickins were slim, so we had to make our own.

[John Milner]

L2257 and 2282P forged Speed Pro pistons have roughly a 13cc dish. I run several 428's with these pistons and 72cc heads on pump gas.

[Formulajones]

Originally Posted by John Milner

L2257 and 2282P forged Speed Pro pistons have roughly a 13cc dish. I run several 428's with these pistons and 72cc heads on pump gas.

Must be something new because 25 years ago the L2257 TRW 428 piston was a flat top.

I had to machine a dish in them, which ended up being 16cc. Then zero decked the block, or close to it (.004" in the hole) and with a .038 gasket and a 76cc head I had 9.7:1 compression.

Ran that engine for a couple decades on pump gas.