Compression heighth and dome volume?

[Tom Kochtanek]

I need some sage advise regarding piston choices. The local machine shop has my 409 block "cleaned up" at around .075" (4.3895 inches). We are looking for options on ring sets and pistons (must be forged). My machine shop guy tells me I need to be prepared to know "compression heighth" and "dome volume". I am not that smart when it comes to these things, so I'll ask the group what the heck I need to know :).

Here's the stuff I do know:

E 24 61 409 block (068 casting) bored initially to 4.3895, probably will take it to 4.40 since Chrysler has some ring packages at that size.

Stock 409 crank and connecting rods.

"Hi perf" 348 heads (1147s) with stainless steel valves

Cam will be solid lifter type, specs TBD

I'm looking for a set of new forged pistons that will fit my "to be bored" final sizing.

What do I need to tell the piston manufacturers about compression heighth and dome volume?

Thanks in advance!

TomK

[CDNpontiac409guy]

Tom, the most critical concern is the block's deck.
Has it been decked before ? If so, how much ?
If not, does it need to be ? If not, can you STOP your machinist from doing it ?

First thing...
need to know where your deck is.

I'd shoot for 10.5:1.... .004" - .006" above deck, using FelPro composition gasket.

I don't see any problem with your selected bore size.

[fatride]

Tom, the most critical concern is the block's deck.
Has it been decked before ? If so, how much ?
If not, does it need to be ? If not, can you STOP your machinist from doing it ?

First thing...
need to know where your deck is.

I'd shoot for 10.5:1.... .004" - .006" above deck, using FelPro composition gasket.

I don't see any problem with your selected bore size.

Remember, if you zero deck the block you are all done, you can not deck again. I would use the steel shim gasket and shoot for .015 below deck, this will give you a .035" quench height.

[models916]

You don't need to deck the block if you are buying pistons and you can still be out of the hole. A call to Childs & Albert for pistons is easy and they have all the numbers you need except the distance from main to deck, get that from the machine shop. They will build the piston and pin height from there. C&A uses Ross forged blanks. Ross direct seems too busy to help with the numbers, C&A will go over it with you. My Quench is 28 with the felpro gasket. Too hard to get Steel head gaskets anymore.

[Skip FIx]

If you need to deck again options are shave the pistons accordingly or get new ones with a different pin height, or use a thicker head gasket. I'm not sure if Cometics makes a W motor head gasket but theirs can be had in a variety of thickness so you make that up there. They are the premium head gasket of most engine builders now.

[Ronnie Russell]

An interesting subject. An observation from an innocent (:rofl ) bystander.. Several different , correct suggestions from guys who know what they are talking about. :clap :clap

[fatride]

You don't need to deck the block if you are buying pistons and you can still be out of the hole. A call to Childs & Albert for pistons is easy and they have all the numbers you need except the distance from main to deck, get that from the machine shop. They will build the piston and pin height from there. C&A uses Ross forged blanks. Ross direct seems too busy to help with the numbers, C&A will go over it with you. My Quench is 28 with the felpro gasket. Too hard to get Steel head gaskets anymore.

Good tip on the custom pistons, I don't know how many blocks are still out there that don't need at least a clean up on the deck. But still you can get your quench distance correct by using a custom piston. Decking the block for quench and using a stock pin height piston opens up the problem of the intake manifold fit. My Ross pistons have a stock pin height and are .015 in the hole. I can't remember offhand how much was removed from the deck but the intake almost was to the point that it would require mill job to get a seal! I managed to hog out the intake bolt holes a few thousands and just made it. Yes the steel shim gaskets require some searching but are still out there. That is a tight quench Models. :eek:

[CDNpontiac409guy]

You don't need to deck the block if you are buying pistons and you can still be out of the hole. Ross direct seems too busy to help with the numbers.

It's the only way I supply my pistons, Models:deal ... and my guy at Ross is NEVER too busy to spec them EXACTLY as I request:bow , while providing me with unparalleled race piston recommendations.
I know I'll never go anywhere else.

Decking ?
MAKE IT STOP.... oh God.... MAKE IT STOP:bang :bang :doh :dunno
45 year old non-replaceable engines... unecessarilly milling them away.
A cylinder can be sleaved.
A deck cannot be rebuilt.

[Ronnie Russell]

Aubrey, Take a sip of milk and calm down...... It is most important to have true decks. If it takes a little shave to true it up, I dont see a problem. Afterall, head gaskets are available up to .080. I don't think people whack off a big chunk just for fun. Life will go on. :) :) :)

[CDNpontiac409guy]

:coffee:
Need a good deck ?
Of course.
Pursuing the optimum piston height, by milling the deck away ?
I keep hearing about these super thick gaskets. The thicker the gasket, the greater the chance of blowing them out. As Fat said, if possible, use steel shim ( they ARE superior ).... trouble is, nobody's re-making them.

"Don't think people whack off a big chunk just for fun" ?
I firmly BELIEVE that some machine shops do JUST that:mad:

[gearhead409]

piston compression height on a stock 409 piston is 2.425". dome volume would be figured using this pin height. zero deck and the 16 degree deck.

[Tom Kochtanek]

Wow, great responses and information. Here's what I know.

Not sure if she's been decked, the numbers are still on the pad. AllI asked was for the block to be cleaned and the bore checked. It was at .060" with some taper when I handed it over to the shop. Told him to clean the two holes to see where they would be, then match the rest of the holes to those sizes. Final bores can be about .078 or slightly larger. We did sonic check the block before. This block has no "X" on it, if that even matters :).

I have some sets of steel shim gaskets, think they are correct, laying around. Will see if that works for this build. I am willing to mill the tops of the pistons as needed, did this on my stroker build :). I was thinking I'd just order them to be made to whatever specs I finally determine. Hopefully this won't break the budget... :).

Thanks to all who have contributed to this conversation. Lots of experience out there. Will have to get out the old math book to calculate the values from GearHead's data :). I like doing that sort of stuff :).

Any more suggestions?

Thanks!

TomK

[CDNpontiac409guy]

HEEE HEEE !!
Tom, thanks to gearhead, at least your original question finally got answered:p

[Skip FIx]

Somebody needs to get Cometics to spring for a 409 template. They are by far the best out there now for any motor. Some guys even reuse them, even the N2O boys! They are a tri layer and that is how they change thicknesses.

[Tom Kochtanek]

Aubrey mentions Ross' technical support as being superlative, and I agree! I have called them several times and each time they directed me towards an individual (I forget his name right now, it's been 2 years) who knew the 409 well, and responded very professionally to my questions. We were dealing with optimal quench values, as I recall.

I did contact my local machine shop and asked if the block was previously decked, and he was unsure just how to measure to detect that. Just by observation (presence of machined marks) he was pretty certain it hadn't been decked as yet. This block had obviously been bored at least once (it was .060" when I got it). How can one tell for sure? BTW, I asked him to check for squareness but not to deck until we figured out exactly how we were going to handle the piston choice, etc.

Best,
TomK

[fatride]

You could place the stock crank, rod and stock piston in a few holes and measure to deck. That would give you an idea if you would be able to order pistons with a stock pin position. Whatever the outcome you need to shoot for a quench of .035" to .045". Less may be ok but I would not settle for more. Any more than .045" could result in a detonation condition that will not go away with timing or fuel octane rating. In any case forged pistons would be the prudent choice. You could just tell your machine shop to place the stock pin height pistons in the hole where you want and use either a composite gasket or a steel shim. Keep in mind if you choose to use the composite gasket, .040" compressed to get the desired quench you would still have to zero deck with the stock pin height piston!

[jim_ss409]

I noticed that Showcars has head gaskets in there catalog at .022, .045, and .060
http://www.dr409.com/

[Tom Kochtanek]

Fatride, that's a great suggestion! I like the pragmatic or empirical approach to problem solving, why didn't I think of that? I'll drop off a crank, fresh bearings and a few pistons (maybe all 8?) and ask them to mock them up and take measurements ith respect to the existing deck. That''ll tell us where we stand. Great suggestion!

Cheers,
TomK

[1958 delivery]

You should use 1 rod and piston (the same one) at all 4 corners to square up your block.

[CDNpontiac409guy]

Absolutely, Tom:deal ... I just checked my Stocker engine ( DAMN it's loose )... I had approx .003" taken off the deck... can still read all the numbers on the pad. Block is within .0005".
Bear in mind though... crankshaft throws can and will vary. My crank has been blueprinted / indexed... set to NHRA rule limit of 3.515" stroke. It's VERY accurate, which makes for an ideal way to confirm block deck height.

Also, if you find one end low/high for no apparent reason... you might want to swap that rod/piston assembly with another, just to verify. Rod lengths can be inconsistent too.

[Ronnie Russell]

All good information. Aubreys point about the rods is especially good. 409 rods, resized, could and probably will have some differances. Another factor to consider would be if you find it neccessary to align hone the block. Will probably move the crank assembly up .002 or .003. I like to do full mock up , measure deck height. decide how much each deck needs to be shaved to put shortest piston (per side)height at zero , then measure the rest and shave the others to gain zero height. Pretty much what Ray said. Takes a lot of time, so this may n0t be a good option for the machine shop due to costs. Another thing to consider is what is the engine used for? Pure street use? Pistons with stock compression height will probably measure .008 to .010 in the hole with unshaved decks. It is my opinion you could put it together as a rebuild and go with it. .005 off of each deck and with or without align hone, you would be in a good ballpark for a good street motor. Okay TomK, you have plenty to think about and plenty of decisions to make. Good luck,,,,,,,,,:)

[fatride]

I had the factory figures on the piston to deck height at one time; you had to read between the lines of the shop manual to come up with a measurement as I remember. Seems to me it was in the .026” to .030” range. If I have time to sit and look for it I’ll post. As Ronnie says, it would be a good idea to mix and match the rods and pistons to square the engine up. My machine shop had my pistons placed in the Ross box in the order that I was to install them. They did the measuring for me. I’ll tell you I have never had as much fun putting an engine together as when I was putting this last 409 together. Damn thing runs way better than I could have imagined. When I put the car away last fall the best time was 12.6. Didn’t get a chance to run it again but on that day every time I took it on the track it would turn a little better time. I can’t wait to see what the engine will top out at this year.

[Tom Kochtanek]

Ronnie asks what sort of build I am heading towards. Initial plans were to use parts I had laying around the basement, a sort of "budget build". Had a that weird "068" block at .060" with some taper, had a set of used Mickey Thompson 6 60 over forged pistons in good shape, had a good crank, had those 1147 heads (bare at the time), had a nice rebuilt tripower setup, had some 348 hiperf exhaust manifolds, that sort of stuff. Another "Frankenstein" build.

Last time out I did a stroker and it took me forever and a dollar to get it together. This time I was going to be budget conscious and not spend $10K. It's destined for my 1961 Belair Sport Coupe, a pretty solid but rough car in its own right. Plans were to slap it (the engine) together, finish the sheet metal work on the bubbletop, cover the car with primer, and make a driver out of it. A 1961 BA (originally a 348 three speed car) now equipped with a 409 bottom end, 348 top end. Sounded kinda nice. Sort of a backyard "rat rod" build. Should look great :).

Now that I got into it, I realize that to do it correctly, I need to start pouring $$$ into it, and I don't have all that much to spare. I'm not like that guy who buys NOS 3x2 setups for $2800. I'd pay maybe $280 for a rough setup, then take it apart and make it right. So I'll probably try to do the engine correctly, spend the dough for new pistons (ouch!), then stick it in a bare frame and break in the cam. Hope to accomplish that in the coming months. After that I practice my welding skills and replace the pans on the '61. Then reassemble the body onto the frame, and hang the sheet metal (doghouse, doors, trunk lid). Then do the body work, and replace the interior. By the time I'm done, which will be years from now, I'll have another piece of nostalgia to drive and enjoy.

It's surprising how much time and money one can commit to these sorts of projects, and how long the process can drag out. Last one took me two and a half years, 1200 hours of my time, and I don't want to say how much cash in case you ever meet my wife :). She thinks I spend a couple hundred here and there... It's the time that bothers her. If she only knew....

So it looks like I'm moving from making a bare bones driver to a "shiny car", as my friends call them. Not quite like a show car, or like Tommy's beautiful restorations, but nice enough to drive around and be proud of. I hope you guys get to see her someday. As soon as I finish I will start on the next one....

Cheers!
TomK