So right now I'm trying to figure out what the compression is going to be once I'm done rebuilding my 364. So I started to guestimate the compression I will have with the cast pistons I got from TA and started to freak out, but then decided to do some comparison and calculations on what the compression actually would have been around with the stock setup. So, let's get started with this. Stock bore = 4.125 Stroke = 3.400 Compressed head gasket = .015 (I think they were this tight stock) Deck height on the stock piston =.054 (I took the deck height of the replacements and subtracted the difference in compression height)(Also note I'm not taking into consideration that the block was decked a hair and thus would make that height more) Dome volume = 46cc (I'm sure it is really 45.something as I did not make a mold of one of my actual stock pistons yet. Combustion chamber = 126cc stock. Doing the online calculator thing I get 8.82:1. I could be a hair more or a hair less, but now I know that it was far less than the 10.25:1 listed in my Motor manual. Just so you all know, static compression changes with engine size. The same data on a 401 would get you 9.6:1. Alrighty, now that I know that my stock compression was most likely in the upper 8:1 range, I don't have to freak out with these replacement pistons. I will need to CC the pistons to get the actual number, but I played with some numbers and came up with 8.3:1 if I go with a .020 steel head gasket. That's 0.5:1 lower. Not the end of the world, but not fantastic. The replacement pistons (I'm sure they're EGGE) give me a deck height of .096, but here's the thing, if you measure from the wrist pin to the top of the dome on these, they are identical to the stockers. The difference is the .25" X .0445" deep groove machined into the outer surface of the top of the piston. So I tried assuming a low compression height with 46cc domes, and then used the compression height above the outer groove, but took away the 8.9cc's. One gives 8.31 and the other gives 8.25. I need to get a plexi plate and get to the bottom of this so I can get more accurate numbers. Hopefully the pistons have a little more meat on the dome and hopefully the combustion chambers are a little smaller than the 124cc that is written in my info from machining. Not sure if they wrote that in there as a guess or actually measured it. More to come!
Mike, You have to be EXTREMELY ACCURATE when doing any measurements with a buerete CC measuring devise. I'll just give an EXAMPLE. 401 bored .030". If you have the engine completely assembled & everything torqued down. Bring the piston to TDC & begin filling cylinder to the 1st. or last plug thread & it is 100CC's. Turn the engine over until the piston is at BDC & measure again & you have 1000CC's. Divide 100 into 1000 & you get 10.0-1 compression. NOW ADD JUST ONE CC, at 101 CC's & 1001CC's you NOW HAVE 9.91-1.
Very true Tom. That being said, I'm perfectly fine with "ballparking" it a little bit since in my case I'm working on building a close to stock, low HP motor with the intention of just getting my sled down the road. The point of this is that I've seen people having a hissy fit after calculating their compression with their new setup and assuming that the motors were 10.25:1 compression from the factory. From what I can tell, the 364's were in the 8.7:1 range, the 401's were in the 9.5:1 range, and the 425's were 9.9:1 or a little less. Knowing this is key to understanding the true hit you will be taking if the rebuilt setup yields lower compression. Just look at my case. I initially assumed my motor had 10.25:1 compression from the factory. When seeing that my new compression number was going to be in the mid 8 range, I had that sinking feeling that my new pistons were garbage. Once I put the stock specs into the same calculators I was checking against for the new specs, I realized that I am not really down much at all. Even a 1/2 point down on compression will only result in about 5hp or so loss in my case. I can live with that. The 4bbl, docs mod intake, dual exhaust, mild cam, electric fuel pump, and electric radiator fan are going to overcome that little loss by a long shot.
Last update for the night. I'm feeling much better now. I verified with TA that the combustion chambers are indeed 124 cc's now. I CC'd the new pistons and came up with 53cc domes. Some folks will raise the BS flag on this, but everything I measure on these supports this. These pistons come out identical to the originals when stacked up to each other except one thing. The Egge's have this machined outer ring on the outer edge of the top that measures .0445" deep and is .25" thick. I did the math and this alone accounts for about 8 cc's. You at that to a 45cc dome and voila. If I put one of these upside down next to the stock piston, the raised part of these before the dome lines up with the flat part of the stock one. The wrist pins also line up. The domes look exactly the same. Measuring the distance from the bottom of the pin to the top of the dome is damn near identical. It took me quite awhile of staring at both the new and old pistons to figure out what is going on here. So...with the correct numbers, my compression with .020 gaskets should be 8.77:1, which is right there with what the stock compression was. If I use the Best composites that I have, which are .040 compressed, my compression will be about 8.43:1. Even if I could get 300hp out of this motor with the higher compression, would it be worth the hassle to use steel shim gaskets in order to avoid losing 5hp? Are there other ill effects that I am missing out on here?
why not deck the block .021 thousands, you will have a nice flat surface to use the steel gaskets plus your compression will now be 9.17, pistons will now be .075 thousand in the hole.
It's best to cc domes by putting the piston down the cylinder 1" with a greased (old) top ring installed and pour the cylinder, subtracting the theoretical volume of the cyl. @ 1" length. I generally don't deck engines needlessly to arrive at a compression # unless the quench is being improved. (yes, I know there's not much quench on a Nail.) A tiny bit of compression is far outweighed by a minor increase in airflow. (agree to decking if the surface isn't parallel or great to begin with)
Too late for me to cc the old piston that way now that the block is bored. I wish I could find someone who has actually CC'd the stock 364 piston, but in the mean time I'll go get some modeling clay and do it that way.
You can also seal the piston in a ring compressor with the top lined up to the top edge and the Plexiglas for CCing the head chamber on top when filling. It needs to be the old style ring compressor the one that uses an allen wrench to tighten it. You can use masking tape and grease to seal the piston in the compressor, tape the ring grooves and smear some grease on the tape before you install, easy peasy. Derek
So that is how I got my original number on my new piston, but I was concerned with the ring compressor being oblong and skewing my numbers, so I put one in the bore and did it that way. This time I came up with 57cc's! I went and got modeling clay, found the perfect size small tupperware container to fill with clay, made an impression of the dome on the stock piston, and came up with 46cc's for it. I was actually surprised because I started to think that the 364 pistons HAD to have bigger domes than the 401-425 pistons, otherwise the compression will be real low. Guess I was wrong. I did the clay impression on the new piston and came up with 58cc's. So even though it sits a little lower in the bore due to the outer machined edge, it is a wash in the compression calculator if I use .020 thick head gaskets. I'm fine with that.
I made a simple fixture to measure piston cc..... 1" thick plexiglass, used a router to make a cavity, 1/2" deep. The round opening fits around the dome and seals on that machined outside edge. Used a flat plate on it to measure volume of cavity (100cc). Then replace flat plate with piston and refill. Both my stock 401 and replacement Zollner pistons were a bit over 46 cc. A TRW was 45.3 and a Ross was 44.4 cc.
I am hoping to get an answer to my question here I have stripped a 364 out of a 58 special and I am a little confused about the engine kit to use There appears to be 2, one for the 40 series and one for the rest From what I have been told by "Old Parts" (seller) there is a difference just in the pistons From them " The compression height of the pistons is different as well. The 40 series pistons have a compression height of 2 11/32 while the 50, 60, 70 series pistons have a compression height of 2 13/32" What I am trying to find out is why I cant use the higher comp pistons? Am I asking for trouble by using this kit Valve clearance ect I hope you guys can help here, as your playing pistons as well Cheers Mick
Unfortunately nobody has any answers for the 364. Let me know the casting numbers on your heads. Maybe I can help and see if there is any difference between yours and the later ones. If not, the taller pistons should not be an issue since the deck height, crank, and rods are all the same.
something does not add up. stock height is 1.925. they are saying 2.344 and 2.406, does not make sense, unless there are measuring to the top of the dome and not the real pin height. as stated in early post stock pistons were about .054 in the bore. with these pistons they will be sticking out of the bore about 3/8 of a inch. if they are adding the dome in you need the height of the dome then minus it from 2.344 or 2.406 that will give you the real pin height, also the cc of the new piston domes.
Egge measures compression height to the top of the dome because they machine a groove into the outer ring of the top of the piston and that throws everyone off. If you measure compression height from that groove, it worries you because you assume the compression is going to be super low if you don't realize the dome CC's bigger. Anyway, I measured my '59 pistons to the top if the dome and got 2 and 13/32. What you need to do now is get the casting number off your heads and do some research to see if someone has combustion chamber data off it. If not, CC them for find someone to CC them and measure the valves as well. If they need rebuilding, then just see if you can find some later style heads and newer rockers. Then you can definitely use the taller pistons.
The casting numbers of my heads are 1172889 and I am going to have to go through them I might just have to go with the 40 series ones because I dont have the pistons here to measure and I really do not want to get a set over and find that they are going to hit the heads Dont think I said it before (?), but I am in Western Australia Cheers Mick
It looks like '57-'61 364 heads. Before you shoot yourself in the foot with low compression pistons, notice that the compression was lower than stated as I am pointing out here. If I were you, I'd investigate the heads a bit more before getting pistons that you will regret because your compression will be too low. Now that being said, by head casting #'s are 1185485, which are for a '61-'66 40-425. The heads I have were rebuilt at some point and it seems like the originals were exchanged for these. I was told everything '59 and up is the same (I have the newer style rockers), but I wonder now. Can you measure your valves for me? I'd like to compare. Also, is there any way you can get your heads CC'd?
Between the casting number info chart on teamBuick: http://www.teambuick.com/reference/casting_numbers_nailhead.php and the NHRA engine blueprint specs for 1960 Buick: ('58 specs not available) http://www.nhra.com/competition/blueprints.aspx?AspxAutoDetectCookieSupport=1 the chamber volume and valve size looks to be the same as the later 401-425 heads. Note the NHRA spec is for minimum allowable cc's. stock heads will be higher. My 401's are between 125-127 cc's. Here's the info from ther NHRA site: >>>>>> Issued: 27 May 1966 Revised: H.P. Disp. C.R. Ind. Make Model/Transmission Manifold R.R. Lifter Head cc Notes 210 364 8.50 1-2 Cart WGD-2979S,SA/ALL 1.6 H 123.72 235 364 9.00*1-2 Cart*WGD-2980S,SA/ALL 1.6 H 123.72 1 250 364 10.25*1-2 Cart WGD-2980S,SA/ALL 1.6 H 123.72 1 300 364 10.25*1-4 Cart*AFB-2981S/ALL 1.6 H 123.72 3 325 401 10.25*1-4 Cart*AFB-2982S/ALL 1.6 H 123.72 2,3 Notes 1 Alt carb - Stromberg WW-713A/ALL 2 Alt carb - Roch 4GC-7015040/ALL 3 Carb sizes - 1562x1686/1186x1562 Deck Piston Type H.P. Disp. Cl Dish/Dome Ht/Vol Valves Cam Lift Springs 210 364 .028 1875/1500 403/403 Outer & Inner 235 364 .028 1875/1500 439/439 Outer & Inner 250 364 .028 1875/1500 439/439 Outer & Inner 300 364 .028 1875/1500 439/439 Outer & Inner 325 401 .028 1875/1500 439/441 Outer & Inner Head H.P. Disp. Gasket Cast 210 364 235 364 250 364 300 364 325 401 <<<<<<<<
