mobythevan Posted October 6, 2004 Share Posted October 6, 2004 I have done a fair amount of searching for dished pistons for my 350 and 21-22cc is the biggest dish available off the shelf. Has anyone seen pistons with 28-32cc dish for 350 with 5.7 rods? If not, I guess its time to go custom. I would like to stay with a d-cup type dish and not go down in the bore to lower compression. Quote Link to comment Share on other sites More sharing options...
Brad-ManQ45 Posted October 7, 2004 Share Posted October 7, 2004 What heads you gonna run Moby? Quote Link to comment Share on other sites More sharing options...
mobythevan Posted October 7, 2004 Author Share Posted October 7, 2004 Vortec L31 heads. I want 8:1 compression with quench distance of .040". I am already locked down to this head. One option would be to buy trw forged pistons with 21cc dish and make the dish bigger, but I don't know without talking to someone knowledgeable what that would cost and how much bigger the dish can be made without weakening the piston. Quote Link to comment Share on other sites More sharing options...
dladow Posted October 7, 2004 Share Posted October 7, 2004 Another way to handle compression is to change the dynamic compression ratio (which is really what the engine sees) with the cam. Since you are locked in with the heads, you might try different cam combinations to change when the intake valve closes. No compression occurs until the intake valve closes, and that is determined by the cam. There is a bunch of info on DCR and SCR (static compression ratio) in this forum. You might find that you can hit your compression target with the 21cc dish pistons and a cam with the proper timing of the intake valve closing, rather than changing the dish size. Dave Quote Link to comment Share on other sites More sharing options...
BillZ260 Posted October 7, 2004 Share Posted October 7, 2004 Why such low comp Moby? Your induction going to be pressurized??? Quote Link to comment Share on other sites More sharing options...
mobythevan Posted October 7, 2004 Author Share Posted October 7, 2004 No compression occurs until the intake valve closes, and that is determined by the cam. With all of my specs I get 8.78:1 SCR from the calculator. I get 6.5:1 DCR with the calculator. I have never seen any speculation on how much boost can be rum on pump gas versus DCR. What could 6.5:1 DCR support assuming an efficient intercooler and 91 octane? Just a guess would be interesting. Your induction going to be pressurized??? My pressure will be above atmoshperic Quote Link to comment Share on other sites More sharing options...
ZROSSA Posted October 7, 2004 Share Posted October 7, 2004 Moby, what about increasing the volume of the cylinder heads. Deshroud the valves a bit. You would still want the chamber to be biased towards the exhuast valve.....maybe costom pistoms would be the best. Douglas Quote Link to comment Share on other sites More sharing options...
dladow Posted October 7, 2004 Share Posted October 7, 2004 I just noticed that Kevin Shasteen's cd-rom book on engine building (see the forum's classified section to order) has a turbocharger calculator in it. You might pm him to see if he addresses your question in his book. Dave Quote Link to comment Share on other sites More sharing options...
A. G. Olphart Posted October 8, 2004 Share Posted October 8, 2004 I agree with both zrossa and dladlow... Clean up the combustion chambers per David Vizard's book (there is also a Car Craft article. I believe), measure the volume, and see if it is close enough to vary the DCR with a cam. If it still won't work, I'd consider some good aftermarket aluminum heads and garden variety pistons. True custom pistons get pretty pricey from what I've seen. This alternative makes even more sense if you have not yet had the Vortecs modified for lift... and even if you have, what would the price differential be if you sold the Vortecs? Quote Link to comment Share on other sites More sharing options...
mobythevan Posted October 8, 2004 Author Share Posted October 8, 2004 Well, I am just going to use the 21cc dish and run 8.78:1 compression and see how that limits my boost. The quench should be pretty good and I can clean up the chambers to prevent hot spots. I am also a little over 6000 feet altitude which gives me a little bit of an advantage. It will be interesting to see what happens and I can always order custom pistons later or change heads if this proves to be too high of compression for my boosting desires. Quote Link to comment Share on other sites More sharing options...
jap tin Posted October 9, 2004 Share Posted October 9, 2004 JE makes a extreme duty 23 degree inverted dome piston that are specially designed for forced induction and nitrous applications. They have a -22.0 cc dome volume, a 4.030 piston weighs 515 grams. They also have contact reduction groves and use spiro locks. Quote Link to comment Share on other sites More sharing options...
dr_hunt Posted October 10, 2004 Share Posted October 10, 2004 basic questions: What gas are you running? What HP level are you trying to reach? What will the rest of the car handle? Seems that lowering compression is a crutch for low octane. Fuel management is the key to maximizing HP in shall we say overboosted applications. Ignition timing, Valve timing and exhaust port and manifold configuration is critical to extract all HP in +Pressure applications, the latter two probably being the most important. However, there is a limit to boost on any gas, especially pump gas, at some point you have to increase octane. Formula 1 racers run 60 to 70psi boost on alky with 10:1 static compression and turn 18K rpm. It doesn't matter what cam you have or boost you have if your exhaust port and manifold suck. Same goes for the intake. Got a lot of restriction on the intake port and all the boost in the world isn't going to help, actually it'll make it worse. Gotta get it in, burn it, and then get it out. We can bench race this all we want but actual running is the true answer, as all the variables are in the equation, are running under load, in real time, real life. If there were recipes, then there wouldn't be gearheads and everyone would be just as fast as the other. Quote Link to comment Share on other sites More sharing options...
mobythevan Posted October 11, 2004 Author Share Posted October 11, 2004 Dr_hunt Well, you certainly stated the obvious, but didn't answer my question. Is there a bigger dish piston than 21-22cc for 350? If not I will run 8.8:1 compression for now. I don't remember asking for a recipe, maybe for brownies? Quote Link to comment Share on other sites More sharing options...
dr_hunt Posted October 12, 2004 Share Posted October 12, 2004 Brownies on the way, hope the post office doesn't loose them, um oh, darned good too, smack, smack. Never heard of a dish volume larger than that, not even custom. Call JE, see if they ever made one, if they did, they'd have the cnc program for it and could whittle you a nice set. If not then nobody has ever needed any. BRC and Probe dabble in the monster forced induction arena, might check with them also. Quote Link to comment Share on other sites More sharing options...
mobythevan Posted October 12, 2004 Author Share Posted October 12, 2004 Thanks, I'll check on that, I did realize that I could run the 21cc trw piston in a 327 with 5.85" rods from eagle and get me down to a low compression, but the 327 crank is more expensive and the 5.85" rods are more expensive. More expensive than custom pistons, I am not sure yet. Another interesting option anyway if I decide I need that low of compression. Quote Link to comment Share on other sites More sharing options...
Guest Blazer406 Posted October 22, 2004 Share Posted October 22, 2004 JE has up to 31cc dish pistons for a 383 chevy. Just go ahead and build a stroker motor..... I'm sure you won't regret it. They also make a 36cc dish for a 406. Quote Link to comment Share on other sites More sharing options...
Pyro Posted October 22, 2004 Share Posted October 22, 2004 ------------------------------------------------------------------------ Vortec L31 heads. I want 8:1 compression with quench distance of .040". How do you get a quench distance of 0.040" with dished pistons? I think you need bigger combustion heads and/or less stroke to get what you what. Quote Link to comment Share on other sites More sharing options...
mobythevan Posted October 22, 2004 Author Share Posted October 22, 2004 The dish is shaped like the combustion chamber (d shape) so the part of the piston that goes up against the head for quench is still flat. Good question though. I could go 327 with 3.25 stroke, 5.85 rods and trw 21cc dish piston or srp 24cc dish piston, puts the piston .010 out of the hole at 9.025 deck height. I'll just stick with 8.7:1 350 and build it, either way it will make more power than I can handle for now. Quote Link to comment Share on other sites More sharing options...
Guest PROJECTRB240SX Posted October 22, 2004 Share Posted October 22, 2004 EVER THOUGHT OF THE HEADGASKET ROUTE? I MEAN ITS NOT THE IDEAL FIX BUT IT CAN BE USED PROPERLY TO LOWER IT THAT EXTRA FEW POINTS. Quote Link to comment Share on other sites More sharing options...
labrat Posted October 25, 2004 Share Posted October 25, 2004 IF I AM TYPING IN CAPS (LIKE NOW) I AM SORRY BECAUSE I AM AT WORK (DATA ENTRY) AND I HAVE NO CAPS LOCK BUTTON AND NO WAY TO CHANGE MY UPPER CASE LETTERING. SORRY! Thanks for the explanation on this, I thought you just liked screaming... Bill Quote Link to comment Share on other sites More sharing options...
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