Another day another question for experienced big block guys

[Centerline]

Working on collecting parts for my Max Wedge recreation and I have a question on valve clearance. Picked up a new set of Speed Pro pistons for a 70 high performance 440 (engine vin code "U"). These are .040 over and are flat tops. My question is this.... with no valve reliefs what is the highest lift cam I can run without valve to piston interference? I'm using stock 452/906 heads.

 

[Cranky]

Need to know exactly what pistons you have. What's the part number? If there's no visible part #, you will have to take a measurement from the pin center line to the top of the slug to get the compression height. I usually measure from the top of the piston to the top of the pin bore then add half of the pin diameter for that. Also need to know if the block has ever been decked. If you don't know, then you will have to take a measurement from the crank center line to the top of the block and then add in head gasket thickness. Also, not all blocks are created equal. There are always machining tolerances. You can get a rough estimate without doing all of that but then that's like using the dot method when setting a cam. Without a degree wheel, you really don't know exactly where it's at......

 

[Centerline]

Need to know exactly what pistons you have. What's the part number? If there's no visible part #, you will have to take a measurement from the pin center line to the top of the slug to get the compression height. I usually measure from the top of the piston to the top of the pin bore then add half of the pin diameter for that. Also need to know if the block has ever been decked. If you don't know, then you will have to take a measurement from the crank center line to the top of the block and then add in head gasket thickness. Also, not all blocks are created equal. There are always machining tolerances. You can get a rough estimate without doing all of that but then that's like using the dot method when setting a cam. Without a degree wheel, you really don't know exactly where it's at......

Virgin block which hasn't been decked. The piston CD is 1.990 Planning on .020 head gasket. CR somewhere around 9:1 with 88 cc chambers.

 

[miller]

Might plan on doing a rod/piston mock-up, to check how far in the hole the piston is at TDC. While your at it, you can check for clearances at BDC, to the crank.

Another option would be, after deciding how much, have reliefs cut into the pistons...as long as there's enough meat.

 

[Cranky]

Virgin block which hasn't been decked. The piston CD is 1.990 Planning on .020 head gasket. CR somewhere around 9:1 with 88 cc chambers.

2266 pistons? The blue print dimension for an RB block is 10.725 (but that can vary depending on machining tolerance from the factory) so a 1.990 piston should come in at .092" down in the hole. Should be plenty for a big cam but a piston that is that deep is not going to give you any quench benefit. You can still make it run good but you need to 'pick' your cam wisely but that should always be done anyways.

Might plan on doing a rod/piston mock-up, to check how far in the hole the piston is at TDC. While your at it, you can check for clearances at BDC, to the crank.

Another option would be, after deciding how much, have reliefs cut into the pistons...as long as there's enough meat.

Doing a mock up is always a good idea.

 

[mentor70]

i ran those pistons on my first 440 build many years ago, the biggest cam i installed in that engine was the MP .484 cam, but im sure i could have stuck a .510 lift cam in it.

it was a very mild engine. not very impressive as far as 440s go.

if you have not purchased pistons yet, id recomend getting some SRP forged 10.1s.

the Speed pro pistons sat like 1/8th of and inch down in the bore. way low compression

the best that engine ran is when i cut .030 thou off some 452 heads, and installed a Comp Cams XE268 with a six pack.

that was a tire shredder.

 

[Centerline]

2266 pistons? The blue print dimension for an RB block is 10.725 (but that can vary depending on machining tolerance from the factory) so a 1.990 piston should come in at .092" down in the hole. Should be plenty for a big cam but a piston that is that deep is not going to give you any quench benefit. You can still make it run good but you need to 'pick' your cam wisely but that should always be done anyways.

Doing a mock up is always a good idea.

.092 is what I had figured as well. I know I'll have the block decked just to clean it up and I might also have the heads shaved a tad to bump up compression a little. Not trying to build a monster, just a reliable cruiser with some grunt. I'm old enough that I no longer need to impress people with tire shredding burnouts. I'm more concerned about being able to drive 300-400 miles to a show and back without worrying about a temperamental HP monster under the hood.

I am looking at camshafts under .500 lift and it sounds like I should have plenty of room. However, I do intend to do a mock up and check valve to piston travel at TDC before buying a cam. Does anyone know if there is a recommended minimum valve to piston clearance for these engines?

Thanks for the input guys.

 

[lewtot184]

i'd be looking very carefully at retainer to guide/seal clearance with a set of stock iron heads and .500" lift. LSA, duration, installed centerline and closing ramp speed have a noticeable effect on piston to valve clearance, not just valve lift.

 

[383man]

Your going to be limited and have to be sure and check all your clearances like piston to valve and guide to retainer. When I ran the .484 cam in a 383 with stock flattops on a 104 centerline I had just about .110 clearance and I cut the guides down some as it was close. Ron

 

[miller]

Also going to depend on how the heads are built, the parts being used, and machine work done. You need to be sure there is the minimum clearances for all valve related parts. From the guide seal you use, to valve spring bind, since valve to piston clearance is only one part of the picture. Cam profile will also be a huge factor, as already said. If I recall right, valve to piston minimum clearance is .050-.055, depending on who you ask.

 

[Centerline]

Thanks guys. I'll be finishing the disassembly in a few days and then its off to the machine shop. At the moment the cam I'm considering has an intake/exhaust lift of .486/.473, just a few thousands difference than the P4120235AE MP Purple camshaft which has an intake/exhaust of .484/.484.