I am now leaning towards buying the correct part. These are for racing, like at the Bonneville flats. So will probably sell them. Looking for pistons to make 9:1 or so in .30 over & up
Nothing against Patrick's. But if I was buying pistons, and I have bought many, I would call Arias direct. 270 and early 302 engines have a .990 wrist pin. Later 302 engines have a larger pin. Do you know which your engine has? You need to have pistons that fit your rods.
Yep Thick gaskets are for decked blocks with standard Pistons. Short pin arebuilder Pistons are for decked blocks with standard gaskets. and really thick gaskets are for Pistons that come out of the hole. Mix it up wrong and big quench will detonate more than high compression.
Needing GMC 302 pistons that will help me get around 9:1 compression Can somebody give me some guidance here. Or would it be better if the machinist gets them?. Thanks 4 any advice
I'd start by contacting either Ross or Arias. It seems like most Jimmy guys use one or the other, so they must have specs if they've made them before? http://www.rosspistons.com/index.php https://ariaspistons.com/
I have bought pistons from both. Both made a good product. I contact the sales desk directly. Your machinist has machining to do. Arias has made plenty of GMC pistons for me in the 9 pr 9.5 to 1 ratio range for me. So I know they have the program. I am sure Ross does to.
And don't forget Big Nic Arias was racing GMC powered cars long before you were born. They know about these things.
You didn't respond to #18. But here's what I have somewhere in my garage and I'll look for the rest if your interested. 4-1/8" for a 990" pin, 1/16-1/16-3/16 ring lands, 1/8" pop up. For stock rod length. 99% sure they are Arias. I'm sure they are from what bought from Bruce Johnsons estate after his p***ing.
Damn. That looks like one of my old pistons. I sold all the turbo motor stuff to Bud Morrell and he sold some of it to Bruce. I ended up buying the 270 short block back from Bruce and ran it in Bob Dalton's car at WoS one year. Then sold it again to Bill Carlson.
Nick sr. still helps the young guys at Arias make the GMC slugs. Get a spec sheet (our parts gal downloaded it from computer), fill it out, tell them all the details & make a chamber cast. Send both to Arias "Att'n Nick Senior''.
Funny Rich, and their still brand new. Some day I'm going to catalog my garage. Geez I sometimes wish the piston boxes were all in the same place.
I don't remember how many spares I had. 6 seems like a lot. A Mike- and the Hourning head came from Don Kinkade's GMC Fever car. The injection was borrowed from Zeke. GMC guys stick together.
Ok I met with the machinist today. Head is at 113cc. Here is a list of parts that I need : 6 pistons +.30 or more, rings to fit 6 wrist pin bushings timing gears-crank& camshaft both Complete intake& exhaust valves and guides for both; 12 valve springs, 12 exhaust valve locks. Will any modern parts interchange? Other than "Patricks" for parts where else should I look? Appreciate any help
If you have the .990 pins, be sure to get 12 wrist pin bushings. They've been hard to get. I used 1.94 Chev intakes, Pontiac 1.60 exhaust valves work well if you still have the early keeper valve gear and want to replace with Chev stuff. Seats have to be cut to 45 degree. Springs have to be selected from a catalog. In about 5 minutes, my friend Matt at the shop found some which seated at 90 lbs., and 200 at .450 lift which is way more than it'll have. Guides are probably best re-lined nowdays, unless NORS US made are found. I've started giving guide to stem clearance an extra thou. since deathanol took over as fuel. I've had some engines seize valves if set by book info. If your rods are a factory set from one engine, weigh them. Seldom more than a couple grams difference, nice parts for a '50s truck motor. Jimmy, Rich, & old guys, fix what I've got wrong or whatever you can to add ... God, I love these engines ...
I used stainless valves 1.94 intake and 1.6 Exhaust. Off the shelf parts for a SBC with + .100 stem length.
Thanks for getting the 113cc. with a 4.030" bore and .020" in the hole you need a piston with close to 30cc to give 9.5 compression. Mine are 15cc which makes 8.5 to 1 which fits with Bruce's turbo engine. My best guess on your pistons are 12.4 to 1. As for valves 1.94's are great with 1.50's or you can go with 2.02 intakes and 1.60 exhaust all are SB Chevrolet. you will need to blend the ports and everything is 45*. My first GMC had Pontiac intakes because they were at 60* I quickly changed that.. All my head spring seats are for 1.550 diameter springs. Your mach shop should have the tool for that if you choose that diameter. Remember you can go .100" long on those valves too. I do with my 12 ports. Manley or Farea valves are both good I use stainless but for you ? . You may want to change the seats for the **** fuel we have. My machinist does it all the time but I run 116 octane leaded gas and don't care. I use Crane for the valve gear: 991 springs, 741 10* super lock retainers, 611 10* locks, and I use 621 lash caps to make the angle of the rocker better you will need to see that for your self. These springs are 122# at 1.990" but un-shimmed they are less where I run them. Your machine shop really needs to get the valves done and install a retainer and set of keepers on one intake and exhaust valve to see the length of spring you need. I go to the 1.550 diameter because you need a tall spring. My first set were Iskys for a 409 I think.. They were double and soon I was using just the outers @ 85#. 85 will turn all day at 5500 rpm. A Cloyes 2831S gear set will get you the ability to advance or retard the cam with different slots on the crank gear. Don't worry about what says it fits, it fits a GMC. One thing stock rockers are NOT 1.5 to 1 they are less but you need to set the rocker ***embly geometically correct to save the guide as much as you can. I have false bronze guides installed and machine the tops for PC type seals. A cast cam is fine with new lifters. Mys son and I run a 1/2 dirt Super Stock with a cast cam ( by the rules) at 6800 with 125# spring pressure and don't hurt the cam or lifters. Good luck..JD
I would like to locate everything if possible; and just pay for the machinist labor($100hr). So everything is "Chevy" parts that I am looking for. Should I be looking for the "performance" items? Guess JEGS or SUMMIT will have the items . Once I gather enough of the parts then I will go back to the machinist. I will print out everybody's notes to give to the machinist, for information. What do you advice about the pistons? Should I ask the machinist to make a casting?. THANKS for the guidance
You don't need to cast your chambers. Either Arias or Ross has made enough GMC pistons to know what they look like. Or you could buy the pistons that Jim wants to sell. Probably save several dollars over new. And mill your head to make up the compression.
I see stock chambers on that head at 120 CC. You get 113 so the head just had a cleanup cut. Arias made 12:1 for our race engine and they are jewlery. Ours had the dome relieved from the bottom for weight savings and they are about 1 pound lighter than the stock piston. Yours looks like non relieved. Ours went 133 in the standing mile in May. Patrick has not been good to us, he charged Marcia's credit card for Pistons and never ordered them. And refuses to refund the money, and the CC company says it's too old to go after. She got promises and excuses but no pistons or cash back.. We ordered direct from Arias and it took two months, but the results are worth it. They were very thorough. Frank
Thanks Rich but gas pumper shows 7cc are already off the head and he needs to get it to 95-98cc so mine might work if I can find them and they are 4-1/8" which is the last bore I'd use for the street when he is looking at 4.030". Sounds like he has stock block. For a street engine I would keep the head as thick as I can an call Ross, Arias, Venolia, CP, etc and them make you a GMC 302 piston set. Like said above on the order form, all you need is the cc's of the head and the compression you want, bore, pin, and keepers and they can do it. You don't build these engines in a day out of a catalog unless it is all stock and you are willing to leave it that way. Buying an empty 302 head for a racer is easy but not for the feint of heart. Same with a short block. I'm not going to spend hours here writing on low end ***embly when all you need is a1955 truck Motors Manual to know it will live. Racing is a whole can of worms you, I , and others have learned or self taught over years. Machine work for that takes $$$ if you are not doing yourself which you and I do because we can. Good luck too all
PM'd "Dry Lakes Racer"about pistons but haven't heard back. If those 1/8" popup pistons would work, depending on their bore size(+.30&up), then I AM interested; as long as the head can be milled the necessary amount. Am leaning on you veterans to guide me ......
I'm dry lakes racer too and have answered here. 2 different computers. I'll look for them but the pistons are WRONG for what you want to do after reading what you said here and nothing I sell is inexpensive. Just get the correct ones for the application you want and sell the set you have on EBay or if your calling Arias and since they have the work order # they may give you some credit and take them back if you order new from them, who knows. Don't bore the block any more than you need period. I race the **** out these and never, never had a 4.125 bore that's the last resort. You use a Langdon's avatar, have you talked to him? Tom has a wealth of knowledge on any inline probably more than any of us. Even tho I've been fast at Bonneville I'm a ham-n-egger working out my garage and using a couple of knowledgable guys for my machine work who understand what I want. You've gotten some good advice here already it's time to start looking stuff up online from the manufacturers getting the part #'s and searching Summit, Jegs, Speedway, and Amazon.
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