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help picking out pistons
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bigtizzles
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PostPosted: Sun Apr 01, 2012 7:13 pm    Post subject: help picking out pistons Reply with quote

I'm ready to assemble my 68 327 with vortec 907 heads. I'm gonna use the factory forged crank, and standard rods. I need to pick out some pistons. I want to run on pump gas, nothing crazy. Maybe spray it a little in the future Very Happy I figure I'll go with flat tops. I want it to be a dependable motor, but make as much power as possible. I don't want the compression to be too high. How do I know which pistons to go with? I hope I don't sound like a retard, this is my first v8 build and there is not alot of support where i live. I'm gonna run the Lunati Voodoo 268 cam, and the heads were decked to smooth out the surface. Oh, and the motor is .060 over now.
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af2
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1933 Willys Coupe

PostPosted: Sun Apr 01, 2012 11:07 pm    Post subject: Reply with quote

If you could go with a longer rod the choices are much greater.
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clay
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PostPosted: Sun Apr 01, 2012 11:09 pm    Post subject: Reply with quote

There are a few ways for you to figure out what you need. The easiest is to subscribe to the automath on here. Then you can play with various pistons and see what you need. I'm betting a flat top will be a really safe setup. Now here is where some assuming comes in. Vortec heads are advertised as 64cc chambers. They were probably more than that from the factory. You did mill them but it doesn't sound like much. Normally you will have around 0.020" - 0.025" from the piston to the deck at tdc. Without mocking something up, no way to know for sure. Next is how much do you have to spend. There are some really good somewhat budget forged pistons. Speed Pro makes some really nice looking pistons. I have a set for a 302 but haven't used them. I have used SRP pistons and they are really nice pieces. You will probably find a somewhat limited selection as the 327 just isn't a popular as it once was. I don't really think I answered your quesiton but this is an oportunity for you to learn. Do some reading, play with some numbers, look around, see what's available and see what you can come up with first. We'll be happy to help but there is satisfaction in figuring it out yourself. Clay
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af2
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1933 Willys Coupe

PostPosted: Mon Apr 02, 2012 1:41 am    Post subject: Reply with quote

Like I said, If you can get the compression height lower you have a lot of options.
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bigtizzles
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PostPosted: Mon Apr 02, 2012 3:11 am    Post subject: Reply with quote

ok, thanks. How big of a factor are valve reliefs? 2 or 4 or true flat top?
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Big Dave
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PostPosted: Mon Apr 02, 2012 6:41 pm    Post subject: Reply with quote

Minor change in compression (figure maybe 2cc difference in volume). Most off the shelf pistons have eyebrows that allow up to a 0.500 inch of lift without having to cut anything. So 90% of the cams you will find are around that number or under it.

An old block is probably no longer square so you most likely will not be using stamped steel head gaskets. If you have the block machined it will be square and you will have a beter idea as to your piston depth in the bore.

Big Dave
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af2
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1933 Willys Coupe

PostPosted: Mon Apr 02, 2012 9:34 pm    Post subject: Reply with quote

You better have at least 2 valve reliefs. You need a forged piston if you are going to spray. 4032 or 2018 if going big. 4 valve relief pistons are going to be cast or Hyper at best.
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squeeezer
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PostPosted: Tue Apr 03, 2012 11:16 pm    Post subject: Reply with quote

If you go 4 eye remember if you change heads or cam you will run into problems with bigger valves ie 2.02 or bigger
Radiuses suck on 4 eyes
Id recomend 2 vr forged but hypers will work
vms75 high silicone content is the a affordable forging
For a performance build for the street get 4032 alloy
Strip oriented is a 2618 alloys
Icon makes all 3 these days and have become a premium piston and gr8 for the $$$$$$$$$$

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squeeezer
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PostPosted: Tue Apr 03, 2012 11:22 pm    Post subject: Reply with quote

Whenever i had iron vortecs(062) they cc'd @65ccbest w/ stock valves
I usethem. 016 steel shims for the head gaskets u can put in a bigger cam to bleed presure
what is the comp ratio on that...would it be a a 337? Almost 10to 1?

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af2
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PostPosted: Wed Apr 04, 2012 2:24 pm    Post subject: Reply with quote

Here is some info you need to look at from Summit.

5.7" rod/ 1.675" CH you have 2 piston options.

6.125" rod/ 1.250" CH you have around 20 options.

6.250" rod/ 1.125" CH you have around 10 options.

If you are going to spray run a VMS 75 alloy or 4032 piston at the least.
2618 would be the best.
Stay away from Hyper.

Hope it helps.


Last edited by af2 on Wed Apr 04, 2012 11:40 pm; edited 2 times in total
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squeeezer
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PostPosted: Wed Apr 04, 2012 9:44 pm    Post subject: Reply with quote

IN ADDITION TO Adam vms75 alloy at least
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af2
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1933 Willys Coupe

PostPosted: Wed Apr 04, 2012 11:30 pm    Post subject: Reply with quote

squeeezer wrote:
IN ADDITION TO Adam vms75 alloy at least


I'll change that up. Squisher

Just kidding Jon. Laughing
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jeep_406
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PostPosted: Fri Apr 06, 2012 10:52 am    Post subject: Reply with quote

One thing I'd really look into is updating the rods. As Adam mentioned there are a lot more options in pistons with the longer rod. A set of Scat or Eagle rods wouldn't cost that much more than rebuilding your stock rods and you'd have a much stronger rod with better fasteners. You're going to have to balance the rotating stuff anyway. That's how I'd go especially if you're going to use nitrous.
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jeep_406
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PostPosted: Fri Apr 06, 2012 10:55 am    Post subject: Reply with quote

Another thought. . . . Depending on how much spray you're going to use, make sure the ring end gap is wide enough for the added heat.
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squeeezer
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PostPosted: Fri Apr 06, 2012 11:09 am    Post subject: Reply with quote

yes follow ring manufacturers directions
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