Can You Estimate My Compression Ratio?

[twenty mike mike]

I know it's a long shot, and I know an estimate won't be accurate...assuming the bore is standard, stock 516 heads, dished pistons (which I'm guessing are there because a PO stroked the engine), what's an estimate as to the compression ratio? I'm thinking about replacing the solid lifter cam with a hydraulic, and I'd like to be somewhere in the ballpark. I knew I should have done some measurements while I had the head off.     Maybe someone will recognize the piston style and know what connecting rods should be under them to figure out the stroke.

[cudaken]

Mike as you more than likely know there are a lot of factors that come in to play when figuring compression ratio. Has the heads been cut, new vale seat's, is the block at Zero deck height and what over bore has been done.

Do you know what stroker kit was installed?

One thing you could do is see if you can find the name and number of the cam you want to replaces.

By the way, why do you want to replaces the cam?

Cuda Ken

[twenty mike mike]

Yep, lots of variables, and I don't know the history of the engine. Everything was done by the owner prior to the guy I bought the car from, and there are no receipts for whatever work that was done, but most other receipts for the car are from the early 2000s, rather than the 1900s. However, the head I removed wasn't cut, according to the machine shop where I took it to check for cracks (a long story), so I presume the other wasn't either. So, assume unaltered 516 heads.

The cross hatching in the bores is worn enough that it doesn't look like they've been bored. So, assume stock bore size.

The big difference is the pistons...stock ones don't have valve reliefs, right? So I'm guessing the engine was stroked to some extent. How many stroke kit options can there be for 440s? Oh yeah, I left that little detail out. It's a 1968 coded 440, but not an HP. I was hoping someone could look at those pistons and tell.

I know it's a Purple Shaft solid lifter cam from seeing the stripe on it and seeing the lifters, but I couldn't see a number, and that brings us to the reason for changing. I don't want to bother having to adjust the valves, and hydraulic lifters are much quieter. I've looked at the specs for solid lifter Purple Shaft cams that are currently available, but the engine doesn't run like there is a lot of lift or overlap. Heck, it runs more smoothly than my 1969 340 did, and it had a factory high lift cam.

So am I looking at anywhere near 10:1?

[Cooter]

Unless you know the ACTUAL cc of those heads, head gasket thickness, camshaft duration @.050, how much was decked from block, how far in the hole those pistons are, etc.
This will be like trying to give you a haircut over the phone.

Btw stock style pistons commonly referred to as " SIX PACK" pistons have 4 eyebrows.
Those appear to be two. Eyebrows in pistons doesn't mean it was stroked, just means you can run s bigger cam with more lift.
Easy way to tell if its been stroked with the heads off is to rotate one cylinder down and measure from top of block to top of piston. If its anywhere under 4" then its stock 3.750 stroke 440 with aftermarket rebuilder pistons.

[cudaken]

Mike, you threw me off when you said they where dished pistons. I just played with the lighting of your picture and they just have eyebrows, no dish. They do look like 6 barrel piston's. But, there where other eyebrow pistons out there.

You should be around 10 to 1 but all we can do is guess at this point. Plus Maw Mopar was really slop in deck height! Most stock B and RB motors where as much as .30 (3 ten's ) taller than they should be. I had one 440 that was .30 over 0 deck height on one bank and .10 over on the other? 

Next step, is compression test.

Cuda Ken

[twenty mike mike]

Yeah, I thought this would be in the Too Hard category, but thanks for the replies. 

Guess the best thing to do is pull the current one and find a similar hydraulic lifter cam.

Or just find a Leaning Tower of Power and install that...that's how the car was born.

[Cooter]

Its not "too hard"....I don't see the problem imo...you know how many times I've had to set the valves in 17 years with solid cam???

Twice....contrary to popular belief, unless you have some abnormal wear going on, valves set and forget for about 40k miles.
I see solid lift imports all the time with no adjustment and well over 100k miles. Your making this fit into the too hard category.

[HPP]

The heads are off, measure the bore, measure the stroke, measure the heads. Bore and stroke can be measured with a tape, but be very defined on these little increments. You can see .030 over with your eye. Its the size of a spark plug gap. You can cc the heads with a measureing cup from the kitchen and convert ounces to cc. With those three things, you can be much closer to an accurate static measurement. Knowing cam specs will help you dal in dynamic ratio.

[twenty mike mike]

"Too Hard" refers to figuring out the compression ratio at this point, without having the measurements and with the head already back on. The picture is over a year old. Oh, well.

[firefighter3931]

Those pistons are aftermarket ; Ross/Wiesco etc... and will yield approx 10:1 with a closed chamber head and .039 compressed head gasket. As for the cam ; based on your description it's most likely the MP 528 solid which is a very smooth and street friendly grind. The 528 is ground on a wide 112* LSA which gives it the nice idle characteristics and linear power off idle. Easy to tune and makes lots of manifold vacuum for power brake assisted cars.



Ron

[twenty mike mike]

Thanks, Ron.