rustrocket Posted July 24, 2004 Share Posted July 24, 2004 I found these http://shop.store.yahoo.com/hm-performance/l2467f60.html , but the compression ratio they give is only for the 350 crank in a 400 block using 5.7 rods...so how is the compression affected with the 400 crank? Any other pistons suggestions for my 60 over 400 block would be great. Quote Link to comment Share on other sites More sharing options...
jap tin Posted July 24, 2004 Share Posted July 24, 2004 What crank and rod are you using with your 400 block? What cylinder head are you using and how much compression do you want? Quote Link to comment Share on other sites More sharing options...
rustrocket Posted July 24, 2004 Author Share Posted July 24, 2004 Just a regular ol' 3.75 stroke crank, i'd like between 10-11:1 compression, and heads are yet to be determined, they will come after the bottom end. Rods will come after pistons, so all of my options are open. The pistons seem to be the hardest thing for me to come by... Quote Link to comment Share on other sites More sharing options...
jap tin Posted July 25, 2004 Share Posted July 25, 2004 You need to know rod length to get the right c.h. on the pistons. The head cc also plays a role in the compression . Quote Link to comment Share on other sites More sharing options...
rustrocket Posted July 25, 2004 Author Share Posted July 25, 2004 Maybe this will help...This is what the piston description says: Compression Ratio: 10.33:1 w/350 crank, 5.7'' rods, 64cc head 9.15:1 w/350 crank, 5.7'' rods, 76cc head Flat top piston with 2 valve reliefs and pressed pin. Yields 378 c.i.d. Piston Size 0.060 How does the compression ratio for the given rod and head volume change when i use the standard 400 crank with a 3.75 stroke, in my 400 block. Quote Link to comment Share on other sites More sharing options...
jap tin Posted July 25, 2004 Share Posted July 25, 2004 Those pistons have a ch of 1.56. they will work in with a 3.75 stroke crank if you use the stock 5.57 length 400 rod. They will not work with a 5.7 350 rod. If you are building a 400 with stock rods and crank they will work. To figure compression with those pistons you would need to know how many cc's in the valve notches, how far down in the hole your pistons are , the thickness and bore of the head gasket , and how many cc's in the heads. Has the block been decked? do you know the deck height of your block? Taking a guess on the valve notches they are probably -4 cc's. Quote Link to comment Share on other sites More sharing options...
rustrocket Posted July 25, 2004 Author Share Posted July 25, 2004 The block has been decked to 0.010" clearance - so what does that make my deck height? I alo found these pistons 2 minutes ago, that seem to be better suited to my needs. What exactly is the crank-to-deck clearance? SPECIFICATIONS Bore: 4.125 Rod Length: 6 Pin Diameter: 0.9272 Stroke: 3.75 Comp. Ht: 1.133 Sizes: .030 .040 .060 Crank-to-Deck Clearance: 9.025 Weight: Piston / Pin: 448 / 132 Quote Link to comment Share on other sites More sharing options...
jap tin Posted July 25, 2004 Share Posted July 25, 2004 The pistons that you just listed are for a 6" rod. The 9.025 that they list would put the piston .025 in the hole. To get to zero deck you normally cut the block to a 9.00 deck heagth. I wouldnt know what your blocks deck is with out measuring it. Did they deck it .010 to a zero deck? That would make the deck heigh 9.010. Did they deck it .010 to clean up the surface? Most times the deck won't be even so decking each side an equal amount will result in one bank being lower than the other. You need a good machine shop that will cut to a specified heigth. On most street engines as long as you have a flat deck you will be OK. The first set of pistons you listed are for a 5.57 inch rod. The second set is for a 6 inch rod. What length of rod are you going to run in this engine? If you run the second set of pistons on a stock length 400 rod it is going to be in the hole so far it will look like the Grand Canyon. Quote Link to comment Share on other sites More sharing options...
rustrocket Posted July 25, 2004 Author Share Posted July 25, 2004 I'm aware of the differences in my piston choices. I found a set of 6" rods cheap, so i think i'll go ahead and buy those and use the 2nd set of pistons. I'm waiting for a e-mail back from the guy i bought it from, but in the meantime i'm pretty sure its 9.010. This means my compression will be a little bit higher, given the pistons have a crank to deck height of 9.025, right? By the way, i really appreciate your help. Where in CA are you? Quote Link to comment Share on other sites More sharing options...
jap tin Posted July 25, 2004 Share Posted July 25, 2004 Visalia Cailfornia. One thing to look out for when running a 6" rod and a 3.75 " stroke is rod to cam clearance. A rod cut for stroker clearance will help, another think to think about is a small base circle cam to clear the rod. On my sbc I have the stroker clearance option on the carrillo's and run a .900 small base circle cam to gain clearance. The way they listed the second set of pistons was .025 in the hole, if your block is 9.010 you will have more compression. ...Jon Quote Link to comment Share on other sites More sharing options...
rustrocket Posted July 25, 2004 Author Share Posted July 25, 2004 Did you build your engine yourself? Can i compensate for the lower deck by adding a thicker headgasket, or is this counterproductive / a step backwards? Please forgive me if i seem ignorant on the subject...this is my first engine build, so i need all the help i can get. I've done numerous engine swaps, but never done anything too mechanical beyond head swaps. I've considered the rod to cam clearance...What size cam are you running? Quote Link to comment Share on other sites More sharing options...
jap tin Posted July 26, 2004 Share Posted July 26, 2004 Yep, build my own engines. With the piston .010 in the hole you would want about a .025 head gasket. Shoot for about .035 fron the piston to the head. The cam is 282 290 @ .050 duration .736 .720 lift. on a 108 LSA, ground on a .900 base circle. Quote Link to comment Share on other sites More sharing options...
rustrocket Posted July 26, 2004 Author Share Posted July 26, 2004 That's a pretty wicked cam on there, almost as lumpy as my protein shake this morning...What does the rest of your engine/tranny buildup look like? Is that a street driven car? I'll keep the headgasket suggestion in mind. I'm assuming that i can have regular rods clearanced for the cam and that i dont have to have special made rods, right? Is this recommended? Quote Link to comment Share on other sites More sharing options...
jap tin Posted July 27, 2004 Share Posted July 27, 2004 If I ran it on the street I would need some one to make bail for me. I wouldn't get far as the fuel cell holds 3 gallons. Trans is a glide with a 9" ford rear. Quit racing on the street back in 1987, went to the track and never went on the street again. At the track you know exactly how quick and fast you went. You should be able to clearance your rods to clear the cam. I still have a street Z but hardly drive it any more as that $2.25 a gallon horse piss they call gas doesn't go to far. It is an old Scarab conversion with a 327 and 4 speed super t-10 3.36 r-200 in a 71 240Z. Quote Link to comment Share on other sites More sharing options...
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