jslabotsky

**EDIT - Title should say 425 not 455**

Okay, soliciting constructive feedback on whether this combination will work and will run OK on 91 octane pump gas. I will spare you the long story about how I ended up with this odd combination of parts. Just suffice it to say that I don't have much free time or disposabile income right now, so I'm making the most of what I have on hand.

1969 455 block
1965 425 crank and rods
TRW L2323F +.060" pistons milled for zero deck w/425 crank/rods (approx 2.5cc dish remaining)
Ported C heads, 84cc chambers (enlarged for previous owner's 403), valve springs setup for hyd roller good to .600" lift
Howard's roller lifters
Felpro .039" head gaskets
Harland Sharp 1.6 roller rockers
Torker intake manifold
Quadrajet carburetor
HEI distributor (also have an MSD 85296 ready-to-run dist available, but does not have provision for vacuum advance)
Flowtech 1.75" primary headers
2.5" mandrel bent exhaust
TH350 with stock converter
3.73:1 limited slip

Car is a 1976 442. Full street car with PB, PS and A/C. Has to be able to handle HOT Oklahoma summers.

Planning on using a hydraulic roller cam along the lines of a Doug Herbert COH5:
Dur Int-Exh: 280/285
Dur @ .050 Int-Exh: 230/235
Lift 1.6 -1.6 Int/Exh: 560/575
Lobe Center: 112

I want it to be fun at the strip, the primary mission is street driving so I'm tempted to go a little smaller on the cam. Was thinking the 112 LC would help avoid a smelly idle.

The highest octane readily available is 91. I'm concerned about detonation because I calculate static compression to be 10.3:1, with Dynamic compression around 8.1:1. Can I get away with running 91 without giving up too much timing advance?

joe_padavano

And now it does...

bigD

i'm a little curious about the pistons... are those 455 pistons that have been cut down on a lathe?

jslabotsky

Wow! Magic!

jslabotsky

I'm not sure how they were cut down, but yes the guy I bought them from had them cut down to the correct compression distance for a zero-deck 425. They took .1225" off, which leaves just a wee bit of the original dish. I estimate about 2 to 2.5 cc, but I haven't attempted to measure them yet. I suppose it would be relatively easy to turn them into flat tops, but it's already questionable whether it was a good idea to reduce the amount of piston wall above the top ring by .1225".

64Rocket

You need at the very least of .200 from the top of the piston to the first ring
I have been there and done that and the out come was NOT good.

Gene

cutlassefi

Yes, he'll need to check that and J you're at the limit with that cam regarding your stock converter. But if you go smaller on the cam you'll raise your static. 10.3:1 is marginal with iron heads and 91.

bigD

i'm going to put a 425 together for my cutlass and had heard of people trying the cut down 455 pistons without much luck so i thought i'd mention it and see if anybody chimed in.

i wonder, is the issue heat or structural support for the top ring? i wonder if a heat barrier coating would help? i suppose by the time a guy buys the 455 pistons, has them cut and then sends them to polydyne or jethot he'd be money ahead to just custom order some pistons from cp...

jslabotsky

Exactly. I picked these up cheap, which in hindsight may have been ill-advised. But I would not have gone out and bought them new. I would imagine the person who originally did this could do their own machine work, which makes the whole thing a lot more cost effective. For what it's worth, they were in a running car and are in very good condition, as are the rods. So it apparently does work, I'm just iffy on the compression ratio.

Do you mean it would raise the dynamic? What range should I be shooting for on 91? Looks like a cam along the lines of the Lunati 00083 I have lying around would actually work better. Advertised duration is 290/300, which gives a dynamic CR closer to 7.7. I was just hoping to capitalize on the roller lifters I already have on hand.

They finally started selling E85 around here, but only in the city, so that kind of rules out a road trip. (If I could afford EFI and switch fuel/timing maps as needed it would be a different story. Care to sponsor me? )

cutlassefi

Yes I meant raise your dynamic sorry.
I was going to mention you need to increase the off the seat time but you beat me to it.
I offer a roller that's 292/302, 228/236 @ .050 with .568/.544 lift.

64Rocket

What is the measurement of the top of piston to the first ring?
Can you post a pic?
If it was a running engine, why did they take it apart?
What brand of piston is it?

Gene

jslabotsky

Here's a pic. This one has the most wear. Several have almost no visible wear. I mentioned up top that it's a TRW L2323F.

I don't have the world's most accurate tools, but I get about .160" above the top ring. .170" between the top and second ring. The ring grooves are consistent all the way around (i.e. no distortion).

It was taken apart because the previous owner upgraded. These pistons were actually installed by the guy before him. He built a pretty serious motor: Nitrided 425 crank offset ground to 4.25" stroke, H-heam rods, JE custom pistons, 11.5:1 compression, etc. The bearings were worn when he tore it down, but none were spun and it ran normally. My guess is the clearances were too tight.

bigD

doesn't look bad at all. i wonder if he opened up the top ring gap? the kb hyperutectics have a higher top ring position and they call for a larger ring gap to accomodate the high ring temperature... interesting!

64Rocket

That piston looks great. When I did the job with "Mondello" converted pistons about 10 years ago. I never thought about the ring gap. That could have been the problem. Every piston had warp the tops. It ran great for about 10 runs, then went down hill.
Just make sure you have good ring gap.

Gene

jslabotsky

Thanks. I'll measure the gap on the old rings that came with the pistons. How much piston to bore clearance do I need to run with TRW's? I seem to remember reading a post where someone said the recommended clearance wasn't enough for even mild performance use.

bigD

as for the rings, i'd check on the KB website but i think they call for about .0065" gap per inch of piston diameter. in this case that would be a .027" gap. i don't know that measuring the old rings at this point in time will tell ya anything or not as they have taken a "set" and aren't gonna measure the same as a new set of rings... the thing to do when you get your new rings is to check them in the bore and figure on filing them.
i suppose that i'd run .003" to .004" piston clearance, i certainly wouldn't run any tighter than that and i'd be happier at .004" but i'd ask around, talk to your machinist.

jslabotsky

The bummer in all this is I thought I had scored a cheap, usable mild 455. However, I bought it cheap enough that if all I ended up with was a core, then fine. But I am REALLY itching to get my car on the road. After the initial inspection I was hopeful I could drop this thing in as-is and play for the summer, then tear it down and redo it this winter. But as I take a closer look, that's looking like less of a possibility.

At first glance, it looks like someone did a basic re-ring/overhaul - new bearings, double roller timing set, crosshatch in the cylinders, fresh valve job - and it had never been run since being assembled. Apparently they reused existing cast, +.030" shallow dish pistons, which isn't great, but would have been adequate for cruising.

But upon closer inspection I noticed very light pitting in a couple of cylinder bores. It's mostly discoloration, but you can just barely feel that the surface is not smooth, and can just barely catch a fingernail in a few places. Seems like more than you want to try and take out with a drill mounted hone. And as much work as it is to swap an engine, I don't feel like taking the risk of running it as-is.

And that's when I did something dangerous and started thinking. If the block is already +.030", and I happen to have a set of +.060" pistons, why not bore it over and use the 425 parts I had prior to buying the 455? And that's what brought us here. But honestly, my enthusiasm for this idea is starting to wane.

I think I have enough parts to repair the 350 that's already in the car and make it drivable. It'll be a bit of a dog with what I've got, but a dog still beats standing still.

Ugh.. just when I think I know what direction I'm going, something derails my plans.

64Rocket

If your just going to run on the street, then .004 will be good, but if you plan to abuse the engine, .005 would be better.
With out really knowing what all you have and the condition, it is up to you to take inventory and weigh the cost and what your plans are, to get to your goal.
Seams like you have a good base to work with. You'll need to watch your gap on the rings. If the block is set up for those pistons, go with it, I would run .005 wall clearance. Pick up a little better converter. get it together and run it.

Gene

jslabotsky

Still doing some math and thinking things over. Does anybody know the original dimension from the top of the piston to the first ring groove on the L2323? I'd like to verify how much was milled off the ones I have.

cutlassefi

I don't know that that matters. There are performance pistons out there that have about the same distance from the top ring as you have. If you're worried about potential ring problems buy a set of Ductile iron moly top rings/set. That'll handle anything you're going to throw at it.

jslabotsky

Actually, I'm trying to figure out if they were set up to be zero deck or .020" in the hole. Assuming the L2323 is normally .020" down in the hole, I wanted to see how much was taken off these and see what it all adds up to using 425 components. I can't drop them into the block to check since the block hasn't been bored yet. And I don't trust my accuracy measuring the compression height.

If they are .020" in the hole, that would put it right at 10:1.

bigD

if you have a caliper you should be able to measure from the top of the piston to the top of the pin bore fairly easy, then add half of the pin diameter. figure .490 for half the pin dia. (980")...

jslabotsky

Oh yeah.. duh! I'm making things overly complicated again. If all you knew about me were the things I post here, you'd never believe I'm actually competent at a very technical job.

jslabotsky

Thank you guys for the constructive input. I did some more measuring and I think this might just work out.

Keep in mind, I'm measuring with a $30 vernier caliper, so I'm going to have everything double checked by a machinist next week. I found one who seems to understand what I'm trying to do, and is willing to talk through it and educate me along the way.

If I'm right, they actually took .100" off the pistons, resulting in:
Comp height: 1.635
Piston dish volume: 4.6 cc

That *should* leave the pistons .010" in the hole. With a .039" gasket it should be around 9.85:1 or so. If I end up with zero deck after cleaning up the block, it should be right at 10.0:1 with good quench.

That CR should be OK with 91 octane, right?

64Rocket

With steel heads, 10 to 1 is pushing the limit. If you went with aluminium heads, would be better plus weight saving.
Take just a clean up cut on the block and should leave you about .005 to .008 deck. Should be in the ball park for you.

Gene

SBORule

Ever thought about a Water/Alcohol injection system for your engine ?

jslabotsky

Well, with the parts I have lying around, there are lots of ways to skin the cat. I'm trying to decide on an inexpensive compromise for the short term so I can have some fun with the car this summer. Then I'll start working on my "real" engine. But the other consideration is the effort involved.

I could bump the compression of the 350 that's in the car up to 9.5:1 and change the cam. That would be the least out of pocket because I already have most of the parts. Plus I could continue to work on doing the 455 the way I really want it. But that's just as much work - if not more, really - as swapping engines. So I'm having trouble getting excited about the idea. I would just drive it with the stock 350, but it's got a loud tick that I've yet to diagnose. If I'm going to have to tear into it do find the problem, might as well go ahead and do something about the gutless performance.

I could sell my ported C heads to fund a rebuild of the 455 short block with new pistons. The 455 top end is in good shape, it's just nothing special. Stock CA heads with a fresh valve job, stock rockers, new Lunati 00083 cam and lifters. It wouldn't impress anybody with fancy parts but it would run well enough to make me happy, for a while at least. (Enough is never enough, right?) The drawback to this being it's a PITA to upgrade the engine after it's already in the car.

J-(Chicago)

What I'd do, is locate the 350 tick. Most likely a lifter or push rod, or maybe even as simple as a broken rocker strap.

If it has good oil pressure, run it.
You'll be back on the road for 100 bucks.
Do your 455 right.

and if the 350 eventually blows itself in half, so be it. You have a better one coming up anyway.
No need to overthink this, you will drive yourself batty, and not drive your car.

johnny5

I didn't see any mention of checking the piston-valve clearance. You might want to do this since the original dish negated the need for that.

cutlassefi

His engine specs do not warrant any concern there. he'll have plenty of room.

johnny5

Even with a .560+ lift cam and flattops?

jslabotsky

I have basically decided to take J's advice. I plugged all my parts into a spreadsheet and figured out the net cost of all my options after I sell the left over parts. If I sell the ported heads and other stuff I don't need, I can build a 455 with a full roller valve train for no cash out of pocket. Or I can do one with a flat tappet and stock rockers and have enough money left over to buy a set of tires.

Meanwhile, tonight I'm going to bite the bullet and dig into the 350 to see what is causing the noise. It's a dog, but maybe having a properly running car will get me motivated.