Hi I had posted this letter a while ago, but have more questions. I ordered an engine kit from Flatlander Racing and they sent me Sealed Power H395P .040 hypertechnic pistons and we bored the 390 block to these pistons. Then we noticed that these were 360 pistons, so I called Flatlander and they sent me H304P .040 390 Hyp pistons.They both have 1.75 pin heights. The 360 is a flat top with 4-valve releifs the 390 is a 4- valve releif with a .080 x3.23 dish in it. I also have 2 used sets of pistons one set is the 1139 .040 silvolite's these were in a 410. I also have a used set of .030 pistons that have 381P stamped on them, these were in a 390. The 381P piston has a slightly shorter compression height maybe .005+ and a deeper dish about .030 and the valve releifs are .040 deeper as well so the 381p would be lower compression than the 1139. I am not sure who makes the 381P I asume Sealed Power (could anyone tell me). Back to the hypertectic pistons; now that I have a 410/428 crank I would like to build another 410 (the last one broke the piston(1139) and stretched the rod). would I have to turn one of the hypertectic pistons .100 down or do they make a lower compression piston for a 410 that is hypertectic. Also if I do turn the hypertectic piston down should it be turned just to the top of the cylinder bore or a little under I would like to run about 10-1 comp or less nothing higher. The valve releifs in both hypertectics is about .170 so I would still have some releif if I turned them down but not all will this matter thanks

 

The 381P is a cast piston for the 410 mercury, from sealedpower. The H304P is a hyper, for a 390, but the dish is too big- I wouldn't use them. The H395P is a 360 or a 390 piston, it is a hyper, and gives 8. something to 1 in a 360 and 10 to 1 in a 390. If you are building a 410 and have already broken a silvolite 1139, how about a fordged piston ? The TRW L2291F can be milled on top to get a zero deck, and would give something close to 10 to 1. I don't know if you can cut the top of the hypers or not, the ring groove is awfully close to the top.....DF

 

I'm not sure how true it is, but I've heard nothing but bad things about hypertectic pistons. Then again I haven't looked a lot of places.

DF is right on about the LF's. They're not cheap though, and milling them will cost more $$.

 

I have found that the 381p listed for the 390(68-76 ld,72-73mdtrk) as well as the 410(66-67 car). But I think that this is a truck piston that they are trying to use for the 410 merc because it states that the compression ratio for both 390 and 410 are both 8.2-1 wich is wrong the factory 410 is a 10.-1 and would be much higher in a 410 than a 390. The engine that I bought had a broken piston skirt because the connecting rod strethed out of round about a 1/2 inch and the skirt hit the crank and broke.
I measured the H395P and the H304P and they both have .290 above the top ring and I measured the 381P piston it has .220 and the 1139 piston has .255. How much do you have on the L2291F piston. The only reason that I wonder is because I have already bored it to the hypertectic and I have already paid for them, and if I can cut them down .100 or at least to top of deck I should have a good piston combo. Although this would take most of the valve releif away, is this a problem? I have a crank grinder friend that has a piston clamp and a milling machine and I can probably have the pistons done for about $80.-$100. and I only paid $325. for the complete engine kit, including the hypertectic pistons. So why buy another set of pistons that cost a whole bunch more if I can use these. These hypertectic pistons look awesome, and a good friend of mine uses them in his circle track car and loves them. thanks

 

It cerainly sounds as if the hypers have enough meat to cut the tops .100. You would also have to cut the valve notches deeper. You might want to contact sealed power and ask them their opinion about are they thick enough to cut. I knew my TRW L2291Fs had enough meat because I had seen it done several times before. I don't remember how much room there was to start with. Be sure NOT to ask Flatlanders anything....I think those guys have caused lots of problems for lots of people. What kind of fuel are you planing to run ? Your 410 clone would have close to 10 to 1, too much for he premium nolead available at most places. DF

 

I will probably be running 92 oct with an automatic and about 411 gears in a very light 67 fairlane ranchero. I know a few guys that run 10;1 compression around here with 92 octane and have no (they have solved) detenation problems. A machinest friend of mine told me that there are new camshafts that are ground specifically for high compression engines, and it takes a lot of tuning to the carb. he runs 10;1 in his 32 360 plymouth coupe, he had more problems when he changed from the stock chry electronic ignition to MSD because of the hotter and more complete burning of fuel. he detuned his carb and solved his detenation problem, I geuse with the MSD he was not needing as much fuel to perform the same. Another friend of mine is building a Dart (have you geused there are a lot of chry peopel around here) with a stroker 360 using edel alum heads a new EFI not edel, and running 11;1 we'll see how this runs on pump gas. This guy is a gear nut, he can come up with any gears, carriers, axles, rear disc brake setup,ect. He sets up N casses and send them all over the country, if anyone ever wants me to check on prices just email me.