CRG Discussion Forum
Camaro Research Group Discussion => General Discussion => Topic started by: Z28Project on July 25, 2016, 01:16:26 PM
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I'm looking at doing a 302 +.030 rebuild and going to buy a set of pistons. There was a good thread on this a few years ago discussing the various pistons available, but it looks like piston choices have really narrowed in the last few years. It looks like you can change rod lengths and use 350 pistons, which have more choices, but if I stay with a 5.7" rod, the choices I'm seeing are hypereutectic or the JE/SRP forged.
I don't really want to go hypereutectic, and I have no problem with the JE/SRP piston, I'm just wondering what others have done (if anybody has done any recent rebuilds), or if I'm missing something in my searches.
JE offers the pistons and rings along with some nice looking MLS head gaskets in various thicknesses (.027, .030, .039, .051").
One goal I have is to keep the compression UP! 11.0:1 at least. :)
I plan to run the stock 30-30 cam.
Thanks for any info/opinions.
John
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I thought to go to a 350, you have to change the crank, and the rods stay the same.
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That would give you a 350 CI engine. In some of the posts I was reading they indicated you could change the rod length to compensate for the different wrist pin location of the 350 piston, use 350 pistons (more choices), and still end up at 302 CI.
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New one on me! ;D
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If you are looking for an exact replacement piston, the JE #123567 is the exact 302 factory replacement. It is not a SRP piston but is the NHRA approved replacement piston for the 302ci engine. It will give you the stock compression ratio of 11.1 and it has the original size ring grooves.
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Thanks! Let me see what I can find out about those.
John
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Here is a link to the JE web site......http://www.jepistons.com/Catalogs/Automotive/NHRA.aspx (http://www.jepistons.com/Catalogs/Automotive/NHRA.aspx)
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JE are good pistons. Maybe lighter then stock, a plus with theses engines. Stock are heavy. Rod failure secondary to " yanking" them back down during high revs. All in all stout rods, after stress relief, good forged cranks.
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Thanks for the link Jerry. I was having trouble finding them on their site. From your link I see I needed to click on NHRA.
Yes, everything I've read sounds like JE makes good stuff. I think it will come down to either the 123567 or the JE/SRD 202890.
Thanks, John
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I just finished my 302 build and used the JE pistons. Excellent pistons. I noticed the dome configuration slightly different as well as the quench area when compared to my NOS DZ pistons but nothing that affects much of anything.
My compression with the pistons .005 in the hole, .039 gasket and 62cc heads came in exactly 11:1 They are slightly lighter than the stock piston.
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Thanks for the info X33RS, especially the numbers!
Did you use the SRP series?
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Yup, SRP series 202890 part number full floating with a 1/16 ring package and went with total seal rings.
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Great. Exactly what I was looking at!
Thanks, John
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X33RS, why didn't you use pressed pins instead of full floating pins? I believe Jerry McNeish uses pressed pins for the safety issue.
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There were a few reasons, one of which was to stay true to form. I've used floating pistons in several builds without issues over the years so no real concern for me.
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Here ya go, a pic of my NOS piston and the new piston side by side.
You can see the dome configuration is slightly different but it was the quench area that caught my eye. The new piston is designed for the more modern heart shaped combustion chambers. Not of any real consequence for the build but interesting.
(http://i755.photobucket.com/albums/xx200/Firebirdjones1/P5250009_zps4wvryqq1.jpg) (http://s755.photobucket.com/user/Firebirdjones1/media/P5250009_zps4wvryqq1.jpg.html)
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Thanks, that was a nice comparison picture (for a little while anyway). :)
I ordered those same pistons.
John
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asm69, IMHO, the floating rods and the piston ARE one of the distinct sounds of the 302. The solid lifter is the other half of the distinct 302 sound. Changing parts could result in the loss of this legendary sound. The 302 and other engines like the 435 h.p Corvette, you don't even have to see them at a show to know what it is, then when it come in sight, yup, I thought so. The pressed pin Would make a lot of difference.
Bryan
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Byron302, I didn't realize that the full floating pins would make a difference in the sound. I do realize that solid lifters do make a cool sound.
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I went with pressed pins myself on my current 302. Many years ago, mid 70's, I did a 12 to 1 piston 302 with the 2nd design road race cam with my first 69 Z. When that engine started up it was the noisiest I've ever heard. Turns out I had 3 pistons slapping the heads. Didn't even have a clue what it was until the engine shop that did the machine work checked it out. Not even sure what they even did to fix it now that I think about it. I was young dumb and full of you know what then, and was just learning about engines at the point of my life. But boy did that engine scream.
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Put headers and Flowmasters on it and you will know the difference.
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The floating pins are there for ease of assembly and disassembly only. No need for a fixture or a torch with floating pins and it saves the rod from being stressed repeatedly. The pins do not sound different or change the performance in any measurable way. If you plan on tearing down your engine regularly to replace pistons after every race event, or you just want to do the assembly yourself in a hobby garage then floating pins make sense. Otherwise pressed pins are fine.
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I'd be curious to know what Chevrolet's reasons for full floating pins really were. There must be some justification other than ease of disassembly/assembly. They obviously are more expensive to manufacture since there are extra parts (the retainers) and extra machine work required for the grooves to hold the retainers. And I would think they would be more labor intensive to assemble than pressed pins on as assembly line. I've been led to believe it had something to do with the high performance engines they were used in, but I don't know reasoning other than it possibly had to do with the pin being able to rotate in the rod.
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It's a debate that goes on. Failures many years ago scare people, but I tend to believe assembly methods or subpar parts could be some of that blame. Nowadays not much worry, and the big 3 are still using floating pistons in some engines today.
There is balance weight to consider, and the fact that the pin isn't stuck in one position while the engine runs. Some arguments made that floating pins are beneficial for short stroke engines, some say frictional gains, and many more reasons. Pros and Cons with both. The machine shop I used does dozens of high end racing engines every year that make well over 1,000 hp, and he makes your head spin with knowledge. When we discussed the issue, by the time we were done I was comfortable with the choice. Plus, that's the way 69's were and I liked the idea of keeping it that way.
Excellent machine work goes a long way here too. I bought new Eagle rods and he made sure he checked and "tweaked" each rod and piston pin to make sure clearance was spot on. Even the big ends of the rods were also "tweaked" for proper bearing crush. Pistons call for .002" to .0025 side wall clearance so they run very tight in the bore as well. That's snug for a forged piston. Not only does that make them very quiet, but you also gain better ring control which means better compression and oil control. Sloppy pistons cause all kinds of oil consumption and ring flutter issues.
Lots and lots of details went into this build looking for HP as well as longevity while keeping things stock, or stock appearing, including coatings where applicable and other tricks that are trade secrets with these engine builders I'm not even aware of.
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I am confused. I called JE and was sent to tech where I inquired about piston part #123567. Specifically ring width, the gentleman I spoke with claimed the top rings were 1/16", weren't the original pistons 5/64"? Is he misinformed? Or am I mistaken on original width?
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I think the tech guy messed up. JE literature says the 123567 piston uses the original ring sizes as mandated by NHRA, which would be 5/64.
The newer style JE/SRP pistons use the 1/16 rings.
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That's what I thought I'll call back
Thanks
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So, is it agreed that full floating piston pins do not generate a sound that makes the 302 sound different than a 302 with pressed piston pins.
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If a floating pin setup makes noise, something is very wrong with the machine work.
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Full floating is to minimize the chance of destroying the engine if one or the other were to freeze up... either the pin in the piston or the pin in the rod.
Pin Freezing with push in pins will rip the bottom of the piston apart then the rod causes all kinds of block damage. Even if the locks screw up with full floating typically you get scoring in the cylinder, or if one or the other freezes there is no damage at all to the block - only whatever issue is within the rod piston assembly.