Casey_L Posted March 13, 2009 Report Share Posted March 13, 2009 I am looking for some lower than stock compression pistons. Don't ask why, I know what I am doing... hopefully. Is there a way to get one without getting custom forged pistons? Link to comment Share on other sites More sharing options...
JustPaus_88TSi Posted March 13, 2009 Report Share Posted March 13, 2009 Thicker head gasket? Link to comment Share on other sites More sharing options...
Zack_Morris Posted March 13, 2009 Report Share Posted March 13, 2009 lower than 7.0:1? what do plan on pushing? 60psi?? Link to comment Share on other sites More sharing options...
BlowinUp54B's Posted March 13, 2009 Report Share Posted March 13, 2009 lower than 7.0:1? what do plan on pushing? 60psi?? no about 85psi on a 133 trim. Link to comment Share on other sites More sharing options...
Komeuppance Posted March 13, 2009 Report Share Posted March 13, 2009 Felpro makes a head gasket spacer "8770SP" Buuuut... I've never heard anyone use it before, it's made for cylinder heads that have been machined too much. -Robert Link to comment Share on other sites More sharing options...
Casey_L Posted March 13, 2009 Author Report Share Posted March 13, 2009 I have looked into head spacers, but other then success in VR6 motors, they seem to be nothing more then a band aid, and do not hold up well in boosted applications. Hopefully someone will prove me wrong because it seems like the easiest and cheapest option. I will look into that felpro head spacer, thanks. Link to comment Share on other sites More sharing options...
Casey_L Posted March 13, 2009 Author Report Share Posted March 13, 2009 I looked it up and well, it is cheap enough to buy and investigate. http://info.rockauto.com/Fel-Pro/8770SP_TOP.jpg Lists for $15.76 at rockauto. I wonder what kind of material it is made from and whether or not I can stack them. How do you use one? Do you use two head gaskets in a felpro sandwich? Link to comment Share on other sites More sharing options...
jahjah Posted March 13, 2009 Report Share Posted March 13, 2009 you could always buy a piston and get a huge(ER) dish cut into it.... Link to comment Share on other sites More sharing options...
Casey_L Posted March 13, 2009 Author Report Share Posted March 13, 2009 I was thinking about that, I have a lathe, but I wouldn't want to take off too much material, I would have to do some calc's to see how much I could safely take off. Link to comment Share on other sites More sharing options...
Casey_L Posted March 13, 2009 Author Report Share Posted March 13, 2009 Did some more research, looks like it is made from stainless steel and goes between the bock and the head gasket. The HeadSaver is an innovative technical solution from Payen that does the job of compensating for materials removed after re-machining cylinder heads. It is a stainless steel shim that normally sits between the engine block and the head gasket. The HeadSaver enables a cylinder head to be reused and ensures the integrity of the new gasket, which in turn prolongs engine life. The HeadSaver restores the original compression ratio, provides a durable sealing surface and helps to reduce further distortion or indentation. Link to comment Share on other sites More sharing options...
PDX87Starion Posted March 13, 2009 Report Share Posted March 13, 2009 Did some more research, looks like it is made from stainless steel and goes between the bock and the head gasket. You could probably take stock style dished pistons (forged or OEM) and machine down the outer edge (top) so that they are below the deck height. You probably wouldn't need to take that much material off...maybe the same thickness of the shim.... but I'm not 100% sure. If thats do-able, it would "safer" than trying a shim that might or might not hold. Link to comment Share on other sites More sharing options...
TopDawg_43 Posted March 13, 2009 Report Share Posted March 13, 2009 (edited) Don't ask why, I know what I am doing... hopefully. I'm interested in knowing what you plan on doing. The only vialbe reason there is to run low compression pistons is to run boost. Or in this case, more boost in a race car. And I assume that you are trying to build power. The straight forward way to get low compression piston is to special a set of forged pistons. But for some reason you don't want to go that route. Milling stock pistons is a shoot into a dark house, there's a good chance you are going to mess something up, just not sure what. The "hopefully part is where all the questions start with me. If you'd tell us what your plans are, we'd be more able to better advise you in a economaical way to make them happen. But I'll be the first to tell you, building power is not cheap. And there are really no shortcuts. Note: I really big turbo coupled with low-compression pistons and stock injections will run like a dog down low and if you ever get it to spool, you are still going to blow the engine up. And with NOS, you'll blow the engine up faster. Edited March 13, 2009 by TopDawg_43 Link to comment Share on other sites More sharing options...
TurboRaider Posted March 14, 2009 Report Share Posted March 14, 2009 (edited) You could probably take stock style dished pistons (forged or OEM) and machine down the outer edge (top) so that they are below the deck height. You probably wouldn't need to take that much material off...maybe the same thickness of the shim.... but I'm not 100% sure. If thats do-able, it would "safer" than trying a shim that might or might not hold. Over the years I have modified the piston tops on a lot of motors to fine tune CR and combustion chamber fit. In general I would leave the outer edge alone if you have the same deck height. There is not a lot of squish... But that tiny bit does help. Not a deal breaker... Most pistons have enough deck to take a small cut. Measure a few and you will find that some brands leave you more to work with. I did this on a small block Dodge to allow me to run a stroker crank with off the shelf pistons and convert the motor to a closed chamber design. Starting out with low CR parts I ended up with a positive deck height and machined the cyl head chambers to match, converting the motor from an open chamber to a closed chamber. I put a .025 dish in the pistons to fine tune the CR. 10.5 to 1 without breaking the bank, one of the better motors I have built. On my current ACL's in my 2.6 Turbo I cut a .020" dish to get a 7.7 to 1 CR. I started out with the 8 to 1 pistons. A lot of the times the piston manf does this to offer a lower CR version of the same part. Most machine shops are set up do do this and its pretty simple to do on a 4 cyl. Also a number of the after market replacment pistons are "decked". If you measure the real deck heigh ( or look it up) you will find that they drop the CR by 1/4 to 1/2 point assuming that a rebuilt motor will have the block or the head milled. Its safer to have to low a CR and not detonate. BTW one theory on spoolup is a lower CR puts more energy into the exhaust with higher EGT's.... The idea is the motor spools up faster since there is more energy in the exhaust to spin the turbo. Depending on the piston manf if you build a motor using certain replacment pistons and a new head you probably ended up with a 6.8 tp 6.5 to CR and never knew it. There are a number of sub 7 CR Starion motors out there already! Kevin C Edited March 14, 2009 by TurboRaider Link to comment Share on other sites More sharing options...
Dad Posted March 15, 2009 Report Share Posted March 15, 2009 You can bush the rods and shorten the center distance. all depends on how much you want to shorten them Dad Link to comment Share on other sites More sharing options...
chiplee Posted March 15, 2009 Report Share Posted March 15, 2009 no about 85psi on a 133 trim. it'll spool at 5500 RPM but it'll make 1200hp. Good luck. Link to comment Share on other sites More sharing options...
TurboRaider Posted March 15, 2009 Report Share Posted March 15, 2009 You can bush the rods and shorten the center distance. all depends on how much you want to shorten them Dad Good point.... also you can go the other way. On my Wiesco pistons when I had the rods bushed I had them offset slightly to move the piston up in the bore. Since I needed the rods bushed it did not add any exta cost. I got a bit better squish and the bushing were a bit better centered in the rod. Kevin Link to comment Share on other sites More sharing options...
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