Delmont 88 PA

I am building a 455 for medium street performance. So far it looks like Sealed Power L2323F pistons is the best reasonably-priced alternative. The have a 18 cc dish. With the 80cc C heads that I will be using and a thin head gasket it looks like the compression will be 9.5:1 or so. I was hoping to make 10:1 but 9.5:1 will have to do... I think.

Now, a really dumb question. Is there any setup that would allow the use of 425 pistons--which I have? The 7" rod and 1.595" wrist pin center to top of piston on the 425 would be about 0.140" longer than the 455 set up. Is there enough "meat" on the 425 pistons to machine around 0.140" off of them. The only thing is that the dish in the 425 piston, even if there is enough "meat" would become very small--raising the compression even more.

Any advice or shared past experiences would be greatly appreciated.

Thanks,
Chris

ah64pilot

Have you looked at KB IC886's? They have a 14cc valve relief and are not much more than the 2323F's...

Delmont 88 PA

Thanks and I will look at those pistons.

Chris

Rickman48

Milling the 425 piston was a trick the 'new' Mondello's used to pull - last 'til the first time over 2000 RPM and break into the upper ring!
Don't do it!!

64Rocket

You need to measure how deep the pistons set in the block. Also CC the heads to know what you have for sure. All the cast heads I have ever done have been 80cc's or more, pretty much all have been 84 CC's. You can mill the heads to bring down the chamber CC's.
For what you are doing, I would mill .020 off the heads and .020 off the block, that should get you where you want to be. But you need to measure for sure and CC the heads to get an exact figure.
Also if you use those pistons, make sure you have the machine shop give you .005 between the piston and the cyl wall. If you use the info on the instructions, you will gall the pistons and trouble later on.

Rickman is correct. That was a trick they use to do. But NOT a great idea. You have to have at the very least is .200 from the top of the piston to the first ring. Major trouble after the first hard run. To much heat on the ring and the tops get all warp out of shape. Ben there, done that.

Gene

Delmont 88 PA

Thanks for all the advice.

The more that I think about it, 9.5:1 with a cam at around .500 lift and a 750 cfm I'll probably be able to pull some decent hole shots! I'm a simple man....

Seriously, I'm sending the bumpers and a few other items for rechrome and have to totally redo the interior, which will probably eat up my Olds allowance. Another option is to use the 425 crank, pistons and rods and have 10:25 to 1 compression; however, the additional cubic inches of the 455 would allow for a little more power at a lower rpm.

Thanks again!

Chris

VinMichael

For my 455, after much thought, decided on the KB IC887. They have a -25cc dome, valve reliefs, and are lighter than the 2323's. They do have thinner than average ring landings; but, I chose them anyway for a street/strip application. You should be able to get 9.5 with these, although I am shooting for 9.1.

cutlassefi

It'll be harder to get 9.5:1 with those unless his heads are less than 80cc and 0 deck.

hotrodpc

I was also thinking of running those 18cc dish Forged pistons with E heads. Anyone know if it's true if the E head really has smaller combustion chambers than the rest of the heads? I have a set of E heads and a set of G heads. Both are small valve I assume. I was hoping to get into the high 9's to 1 with the E heads and 18cc, and thin gasket without milling. Just a resurface to clean up on the head is all. Maybe I should also look into that 14cc piston.

cutlassefi

The 455 I just did had the IC886's .008 in the hole with 80cc heads. Came in right at 10.0:1.

hotrodpc

And with a 77cc head it would be even be higher. I want to run pump gas, 91 octane at best so I should run the 18cc then.
I'd just CC the heads, but they are bolted onto a motor. So my real question is, does anyone know if the E heads are in the 77ish area instead of the 80ish are like most BBO heads.

64Rocket

'E' heads are 80cc's or more. Pretty much all the BB heads are 80cc's or more.

"D's" and "F's" are the exception .

Gene

hotrodpc

Great, that's the info I needed. Can you tell I been lurking at 442.com. It claims E are 77cc and/or 80. So then maybe I should go with the KB 14cc pistons instead. I don't worry as much about having to much compression as I do to little compression. To little compression I can't fix, to high of compression, just means I get a bigger cam and that normally won't hurt my feelings. Thanks for the info.

hotrodpc

I know it's a piston thread, turned into head conversation due to compression ratio so forgive me another second here. I think I've figured out I'll go with the KB 14cc pistons. But as far as head choice. I can either use those E's I just asked about, or I can use a set of G's I also have. I'll just assume the E's would be the better choice, but for confirmation, anyone have an opinion on which would be best to use given the choice? Both sets are small valve and the budget doesn't allow for going with larger valves, but if one cast is better than the other I'd want to use the better one of course.

Delmont 88 PA

I believe that E heads are the best stock Olds heads with C being next.

64Rocket

I would use the "G's". They have the factory induction harden valve seats. with the unleaded gas, they will last longer.
With the small valve head on a semi-hot street engine, going to the big valves on the street you would not see the difference between the two .
You would see a bigger improvement if you do some pocket work and some clean up in the runners. You also need to test the valve springs for the correct seat pressure. Or do you have the springs recommended for the cam. Too weak of a spring will cause problems also.
Again you need to measure the piston depth in the hole, and measure the heads for sure. You don't know if the block or heads have been milled before you.
Use one of the calculators online with all the measurements, and that way you will know what you have.
Do all the right stuff now, that way you won't have problems latter.

Gene

hotrodpc

Thanks for the response 64R and D88, yes I do intend to do all that, clean out the AIR bumps in the roof etc, and yes, I"ll likley just go ahead and get matching springs in a kit with my cam. To much money to spend and not go that far too. For all I know, these springs are 32 years old no matter the mileage on them. And yes, I was uncertain if the E's had the hardened seats or not, and I know that's another added not so cheap expense. I've heard the C's flow best, but it seems to me any of the common OEM Olds heads can be cleaned up as you mention and perform very similar, so staying away from the J as in Junk and any of the rest should be workable. I just wasn't sure of the differences. I've seen claims that E's are 77 CC, I've seen, these use big rotators avoid them, these don't so this and that, and wasn't sure which is best and thought there was something magical other than the "C's flow best".

64Rocket

As far as flow goes, maybe "C's" do flow more, compared stock head to stock head, but once you put a die grinder to them, it is a whole new ball game.
Like I said "G's" have the harden seats. When you order the springs and retainers for the cam, be sure to tell them you have sallow or deep pockets. Be sure to measure the installed height so you can get the correct springs. Once you do a valve job, it changes some.

"J'" heads make a great street head. Granted you have to do some work on them. Mainly on the exhaust side. But if you have better heads available go for it. But "J's" is all you have, all is not lost. They can be made to work.
Trust me all the BB heads are 80cc or more. There are exceptions, but for the most part they are 80 or more. Again you need to "CC" them for somebody before you may have done some work.
And measure the deck height of the pistons. The closer to the deck the better off you will be. If you get the pistons within .010, you an adjust the amount you need to mill off the heads to get the compression you want.
It is all about the squish in the combustion chamber.

Gene

hotrodpc

Well, it's a toss up anyway, the G's or the E's. BUT, the G's are loose and not on a running motor, so they can worked while the other motor runs until it's tore down, so with that advantage, and the hardened seats is another adder, I'll likely go with the G's then. Being off the motor I can also CC them and decide if I'll go with the 18cc dish forged Speed Pro/TRW or the KB 14cc dish. As said, I'm leaning toward the 14cc KB anyway since I'd rather have to much compression than to low compression. Can't fix low compression, but if it's to high, that's just a great excuse to go bigger cam with a bit more overlap and drop the Dynamic CR and be able to run pump gas.

Warhead

Smokey Yunick engine building book recommended no less than .150 deck to top ring. We ran a 455 piston cut down to that number in a 425 and had no issues. We did not run nitrous oxide. Car ran 11.80's.
Jim

hotrodpc

Better safe than sorry if you have the compression to give up in a little more cc. Just curious though, and not being a smart ***, but I'm not understanding, so maybe I'm about to learn something. When you say .150 to the top ring from the deck, what do you mean you had pistons cut down to that number? My thinking is, if the compresion height of the pin in the piston is what it is, cutting the top of the piston off isn't going to chance the distance of the top ring groove is it? Seems to me you'd have to mill the deck to get to that # is your were over .150. ?????

64Rocket

You measure from the top of the piston to the center of the pin.
So if you take some off the top of the piston, you change the distance of the the pin.
So if you take some off the top you shorten the distance.
But if you remove a lot from the top, you make the top ring closer to the top, of which if the ring is to close to the top,
will cause problems.


Gene

hotrodpc

I guess I've got to give this some deep thought. It would seem to me, no matter what you take off the top, it's not going to change the distance of the ring to the deck. The piston being connected to the con rod at the wrist pin, the ring distance is always going to be same no matter what you take off the top of piston. Taking off the top, just gives more valve clearance which normally isn't going to happen anyway on a dished piston, or lowers compression. In theory, milling the deck will make the ring closer to the deck. Shortening the rod will make the top ring lower in the hole, lengthening the rod will make the top ring closer to the top of the deck. Sorry, I'm just not getting it. Sure wish I did because this seems to be a very important measurement.

Delmont 88 PA

My KB's have around 5/32" (0.156") or so to the top ring. The top of the piston to deck is around 0.010".

Octania

wait, what?

You have 425 pistons on hand, but are bent on building a 455?

Get the 425 crank and rods and make a 425

You will be quite pleased with the results.

hotrodpc

Sounds like you're well in safe range with those. Do I understand right, you want at least .008 top of the piston, and .150 from the top ring? So you're safe by .002 and .006. Did you have to do any mods to the pistons or is that out of the box? Any block decking or milling?

hotrodpc

Man, don't even start that. I've been on the fence about that myself. I have a 425 crank that is OEM but will need a turn since I gouged a journal during tear down of a seized motor. The block is long sold for good profit, but I sure thought of running the 425 crank in my 455 block since I'll buy pistons anyway. I passed up a set of 425 rods not long ago for $71 + shipping. I used the, "I don't have an early bolt pattern flexplate" to throw me over the edge of going with 455, and the 455 being more common and likely easier to find a deal on the parts.