This thread will be for informative purposes for machine shop services we offer in house at DCR.
Custom is our specialty.
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DCR Spherical Dish & Piston Correction Services. All shelf pistons are stepped dish or stock style. If you have shelf pistons beware and you need to know that we can correct them.
When we say we machine the pistons we do several things and not just correct the valve pockets lol. We machine in a
DCR Spherical Dish which removes the ineffective "stepped" out of the box dish. This new machined DCR Spherical Dish maximizes the effective push on the pistons yielding more horsepower with reduced knock retard and knock voltage and no additional knock retard and knock voltage. Our dish shape exceeds anything available and nets
15-25whp over anything out there for the SRT4! Ask Aaron at realtune! We add additional oil clearance on the wrist pin bores as the out of the box is .0002-.0006 to tight. We also correct the side portions of the piston above the top ring land and below by reducing the O.D. to a desired diameter to increase ring seal and clearance issues for 350whp and up applications. We add deeper accumulator grooves above the top ring land to keep the piston air suspended from the cylinder wall. We also reduce the skirts by request and balance the pistons to within .1 of a gram. No one else builds pistons correctly out of the box...sorry its sad but true. In order for you to know what changes that are to be made you have to run them and really run them for a loooong time and take them out and inspect. Thats real R&D and what lead us to doing pistons correctly. Also having Tony Ramos from JE Pistons on our Mopar Team for three years was a big help in doing pistons correctly. We are doing this to many V8 pistons now including high horsepower turbo V8s.
We add our DCR Spherical Dish, DCR Piston Clearances and DCR Valve Pockets to any piston except stock style ramp dome pistons. We correct Wisecos, CPs, Arias, Ross, and JEs as none of them meet our spec for performance and longevity. We have proven over and over on the dyno/street/track that the limits of any given octane (from pump to race) is reached way early when timing and fuel is correctly optimized.
The problem is partly due to the chamber design for this application and it being directly from a normally aspirated design. It made its way from the beginning of the 2.0 and 2.4 NA engines and stuck from there. The other problem is when Chrysler combined this NA chamber with the OE piston for the SRT4 which never brings the piston nowhere 0 deck causes other problems when trying to make dependable horsepower. The harder you push this design the worse it gets for tuning and the lower the limit is on any given octane from pump to race. This is why you have to remove timing and add fuel to control knock. Another problem is when you go to the shelf pistons (OE design JEs to all of the almost 0 deck Wisecos and others) is the problem remains and worsens when increasing from the increased compression and the "stepped dish". The compression increase from the almost 0 deck does not hurt this design and is not the probem alone. The problem is how they attain the compression increase with the stepped dish. With the piston near 0 deck they have a atepped dish with a squench and squish pad (.200thou-.400thou. wide) around the circumference of the pistons depending on brand. This stepped dish combined with the poor shaped OE NA combustion chamber is where the problems start to occur. High horsepower efficient dependable power begins with correcting the problems with the suench, squish and quench from the stepped dish. If you are going to run after market pistons out of the box in this engine changes have to be made to correct the problems to gain efficiency (same or more timing on ANY given octane), and to gain dependability and longevity. When we correct the pistons the power increases and parts will last much much longer due them complimenting the poor chambers. Simply smoothing out the chambers is not the right fix and is not enough alone to correct any problems. First the piston then the chamber if the budget allows. More on chambers a little later (another short story lol). The problem with compression on any engine is how you attain it and its effect on "swept volume" and swept volume efficiency. When you leave the piston well under the deck such as Chrysler did its good for filling the order of a 250-300whp application and thats it. It can make more power and as muck as you force it but the sacrifice is poor swept volume, dependability and tuning limits due to knock. When you grap a shelf piston with the stepped dish and bring it near 0 deck it even worsens the problem. The fix is designing a piston dish that reduces the knock limit, increases horsepower and increases longevity which is the DCR Sherical Dish. The shape of our piston is designed to increase swept volume and maximize the effective push on the piston on the combustion stroke. Because of the squench and squish pad is removed it allows for the best swept volume to occur. When we remove this area and shape it to our own spec two things occur.
Slight compression decrease and a large swept volume increase. Even though the "static" compression was slightly decreased the "runnng" compression is increased to or beyond the static compression. If the swept volume is increased the cylinder is being filled more efficiently on each intake stroke which when compressed on the compression stroke will = more running compression which will = more horsepower. The knock threshold is offset from our shape of the piston. This DCR shape allows for the combustion to spread the entire diameter of the piston while the piston leaves top dead center for an additional 20-40 degrees of crank rotation. Our stock bore pistons (stock, .020, .040) push as hard a 2.6 liter normal displaced piston due to the surface area shape increase of the dish and its shape in degrees. The degrees of the dish from lip to lip is in its sweet spot for maximized push. Our 2.6 liter pistons push as if a normal displaced 2.8 liter piston. When our shape is flatened out on CAD software its surface area proves this. This added shape retains optimal mixture motion, swirl and tumble. Compression is figured by many many factors other the just piston CR and dish volume. You have cam selection, turbo compressor size, chamber volume etc. I know, I know the long practiced normally aspirated mentality from years past just does not apply itself to super aspirated turbo and blown high horsepower per cubic inch four valves per cylinder engines. Sorry it just does not achieve the right goals. Other pistons work and work ok but not to our standard.
Stepped dish pistons out of the box are 20+whp lower than ours bottom line
. You can run them out of the box but do not expect the best on pump or race gas with any turbo set up at any boost level. Its worth a whole lot if your building it right and its cheap for the power gained as pistons out of the box will net no, none additional horsepower and will in most all cases consume a few hp from the stepped dish. The SRT4 combustion chamber hates these stepped dishes. Monitored knock with and without the right dish confirms this as the added whp also. We do not machine pistons for fun and our goals have been met by making the most reliable horsepower at any and every level.
380 would have been 400+.....500 would be 520+.....640 would be 660+
For consumers paying $500 for pistons for just strength with no additional hp, its nice to know you can add a little money to do it right to pick up 20+hp and have even more capability.
Turn around is one week. The advertised static compression drops .3 tenths from our machining and we can go lower if needed. Example is Wiseco 8.8 to 1 become 8.5 to 1. Combined with our DCR Sherical Combustion Chambers our 8.5 to 1 become 8.1 to1 when used with a DCR 5-Layer Head Gasket. DCR 8.1 to1 static compression
converts to a higher more efficient running compression in the end adding the additional horsepower.
Price is $60 each performed on your supplied pistons. Includes DCR Spherical Dish, DCR Piston Clearance Correction and Valve Pocket Correction. Total is $240 plus shipping.
We can set (file fit to our spec) the ring end gaps for additional $60 for a set of four. Ring end gaps must be file fitted with any aftermarket pistons. They all come oversized and have to have x amount of clearance per inch of bore to insure that gaps do not over expand and touch each other during operation. This will cause severe engine damage. The more the horsepower goal the more ring end gap needed. We have that spec. covered.
On the rods we correct the wrist pin bores to perfect round and add an additional .0002 to .0004 depending on brand. We also weigh them and correct weights as needed from big end to small end. The rod bearing bore is also checked and straightened as needed.
We do not just assemble engines...we redesign the engine and parts. We make the parts that deliver!
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