ok i am lost Help on compression ratio goal PLEASE

[fe66comet]

Let me run over what I do know, I have a 445 stroker engine. The piston specs are 1.325 compression height, 4.080 bore, .25 top ring land and -26 dish. The rod is 6.7 my stoke is 4.25 and my deck is stock 390 deck height, whatever that is specified to be on a 1968 car engine? I can mill up to .060 off my head and go as small as .010 compressed height and I would suspect 4.100 bore on a copper gasket. So if we assume a 74 cc chamber as suggested, that would give me a minimum of 62cc chamber. Give or take a cc +or minus. So given the numbers that I have so far what are the possibilities? I hate to trash the rotating assembly from Barry and start over again that would be expensive to say the least being that the pistons have been fitted along with the rings and everything is balanced and assembled. I thought Barry stated it all worked out to 10:1 but I guess I was wrong.

[machoneman]

Devil's advocate here!

Go with what you have and don't be so concerned with hitting a target c/r for what essentially is a street motor. Agree that that a .040 quench is more important than hitting your alleged ideal c/r.  Jesh, if its a full race engine then you have WAY TOO LOW a c/r......so it's not.

Heck, have a lower than "idealized" c/r may pay more benefits than you'd suspect with a much greater tolerance to poor fuels......unless you believe that magically in the very near future much higher pump gas octane levels will be available....NOT!

JMO!   

[fe66comet]

No miracle fuels predicted here but I would like to get a little more than stock smog engine compression. At 9:1 to 9.5:1 everything I have done so far would be a waist and I may as well throw a two barrel on it and call it a day. I guess I will have to weigh the options. Maybe a piston change and rebalanced assembly? Hopefully it would not set me back too far to straiten out my dilemma? I had plans for further head work in the future but that would be pointless also.

[fe66comet]

I just looked on the Probe site rather than the SRP site and they gave a listing of compression per cylinder head cc. The ratio ranged from 9.73:1 for a 76cc head to 10.46:1 for 68cc, but no gasket specs. Stock gaskets spec out as .041 compressed and 4.440 Bore so if I plug in a copper.010 gaket with a 4.165 bore. What chamber size leaves me a 11:1 ratio? Sorry to be a pain in the but

[afret]

http://www.jepistons.com/Catalogs/SRP/Ford/390-428_invert.aspx

[ScotiaFE]

A .010" copper gasket will leak like a sieve.
I agree that you should run what you have.
Although I would use the FEL PRO 8554PT head gasket.
This is the gasket that comes in the full FEL PRO kit and has 4.232 bore and works great.

[fe66comet]

It is not a JE it is a probe piston, specs are different, if yo go to the probe site and punch in the part number 271155 it comes up. Specs are completely different for compression  ratio. If it were that low I would do a piston change for sure, my roller cam, valves, heads, intake and injection would never work. So the pistons would be at the sacrifice of every part i currently have.

[fe66comet]

I would guess at this point regardless I am asking the wrong question. The right one is what piston would best yield the correct ratio? I guess I will have to eat the rings, pistons and balance. Its only money right LOL another FE lesson learned the hard way.

[My427stang]

A question first, are you sure you have a 26cc dish?

My Probes are 17.5, Barry's website seems to hover around the 10:1 which would lead me to believe 17-ish for his custom Mahle, and Diamond makes a 6cc and a 17cc off the shelf for a 4.08 bore.  Were yours custom or are you remembering wrong?

That being said, the Diamond is a 6cc 1.33 CH for a 10.155 stack. 

Assuming a 4.08 bore, if you cut your heads to get a measured 72cc, run a Felpro1020 gasket, cut the block to 10.160 you'll be at 11.19 static, if you zero deck it, you'll be at 11.32, and if you go 10.165 (.010 below), you'll be at 11.07 static.  Although sometimes there isn't enough material to cut an old block square to 10.165, so I wouldn't bank on that.

Something else to think about, if your heads come in at 75ccs, zero deck gets you to 11:1 without having to touch the heads, just cut the block to 10.155

All those combos have a nice quench distance too

As far as balancing, that's a 510 gram piston, if you are close, you may not even have to rebalance.

As far as reusing the rings, depends on dimensions, but if they are the same size and you can take them off gently, you can reuse them.  I sure wouldn't throw them away unless someone wanted to buy the pistons and rings from me as a package. 

[My427stang]

It is not a JE it is a probe piston, specs are different, if yo go to the probe site and punch in the part number 271155 it comes up. Specs are completely different for compression  ratio. If it were that low I would do a piston change for sure, my roller cam, valves, heads, intake and injection would never work. So the pistons would be at the sacrifice of every part i currently have.

OK, here is something odd.  271155 is a SRP number and in Google it showed me a 26 cc dish, but I typed it into the Probe site search bar and brought me directly to the normal 17.5 cc piston everyone is using.

http://www.probeindustries.com/Ford_445FE_17_5cc_Reverse_Dome_SRS_Pistons_p/14785.htm

We need to figure out what you have.  17.5 wont get you to 11:1 either, but it's better than 8.8:1     

[fe66comet]

Unfortunately the engine is nearly completely assembled except the intake. I guess I will have to remove the heads, pan, a rod and piston to tell for sure? I doubt Barry would have sold me a set up for 8:1 though? It is a SRP box but I do not actually know what was in there or if they were custom cut due to a shortage at the time. It took quite a while to get the pistons as I recall. If they are 9:1 even those will have to go bye bye as it would turn my engine into a gas guzzling smog hog. I guess I will have to knock it down and give it a look see, at least pull the heads and see if there is a job number on them.

[afret]

It is not a JE it is a probe piston, specs are different, if yo go to the probe site and punch in the part number 271155 it comes up. Specs are completely different for compression  ratio. If it were that low I would do a piston change for sure, my roller cam, valves, heads, intake and injection would never work. So the pistons would be at the sacrifice of every part i currently have.

Really?   Then why did you say it was a SRP?  This is the quote from your first post on this thread:

At one point I had all this figured out and lost my notes, I decided to go with a higher compression ratio but the numbers do not add up? So here it goes I have a basic 390 block with a 10.17 deck height. Stroke is 4.25,rod 6.7. Piston is a SRP 271155 compression height 1.325 inverted dome -26 dish. I thought originally with a Fel Pro 4.060/ .040 gasket I would be at 10:1 with the Edelbrock head, it looks more like 9.5 which is dismally low? I would like to be at about 11:1,  the hard has a max mill of .060 and I could get a copper gasket I suppose. What do I need to do to acomplish my goal?

[fe66comet]

At the time Barry had to put a piston set together for me, none were available and the label on the box is marketed over with a black permanent marker. Also being four years ago my memory is not exactly sharp on the brand. It. Could have been a used box with new pistons?


Well I pulled the head on one side and apparently it is a custom piston, started off as a flat top and went from there, no markings, job # or anything else. It is equal to or slightly above the deck, as a strait edge catches it at TDC. I guess I will have to CC the dish and see what I got?

[TimeWarpF100]

If its sticking up slightly @ TDC do you have a dial indicator to measure that? Do you have a way to measure CC's?

If sticking above deck the best way is to pick a number for piston below deck, I like to use .100 in the hole then measure the cc's
Easy to figure out from there.

Only way to get the proper numbers is to physically measure everything.

I did not catch it but where do you live?

[fe66comet]

I used a feeler gauge and a stainless strait edge, it has a .005 pop up on one side, the other is slightly lower on the smaller area by the reliefs total volume when I filled the entire piston was 28 cc with a 17 cc dish. I measured the piston with a syringe, slow but extremely accurate. So I am guessing it is made up like a Probe as I thought. So where does that put me now?