Best pistons for vortec heads

[jkade]

I know flat tops will have around 10:1 and I wanna stay around 9:1 so what do I need?
Thanks

[PhilaTruck]

Here, this may help.

Comp ratio calculator

[tll74]

Many factors involved when picking out pistons.
1. cubic inches of engine, the bigger the engine the more compression with the same combustion chamber.
2. combustion chamber size.
3. deck height of block compared to piston height.
4. head gasket thickness.
5. cast, hyperutics, or forged.
6. iron or aluminum heads
7. how money you can spend without your wife or girl freind knowing about!!

Your Vortec head has 64cc chambers.
The most over looked thing in common everyday engine building is not checking the deck height of the piston. Nearly all pistons are destoked. Ive seen pistons on sbc's be as low as .060 down in the hole. This is a compression killer. I believe most, if not all, compression advertized spec's are based on zero deck height and a .038 head gasket. I find that 9.2:1 to 9.3:1 with a carb is max and that is with a very finely tuned engine. A heavy truck doing lots of hauling or towing will like a lower compression than a lighter truck running empty. Gear ratio can also can be a factor. I would deck the block to near zero to obtain .040-.045 "qench". Cast and hyperutic pistons work fine for stock to mild street engines.

These factors should help you figure out the best piston for your application.

[Myself]

Speed pro flat-tops, and vortec heads will put you at exactly 9.5:1. Which is exactly where you want to be for street performance. And, with a fast burn head, you won't have to run premium gas!

[jkade]

Well the motor is in my 86 k10 which will be sporting 1 1/4 ton drivetrain with 4:56 gears and 37x12.50's so I am going to need something to get this thing motovated Already have a 262H cam, vortec's, elcheapo ebay cyclone intake but the motor needs to be bored before it goes back together. Any input is appreciated.

[Billla]

The Vortecs are 64cc chambers, and you need the deck height (do you plan to zero-deck?) and the head gasket compressed thickness. Have you made the decision for hypereutectic or forged pistons? Forged is required if you're going to use any power adders (NOS, blower, etc.) Finally, I'm assuming this is a 5.7" rod 355 (.030 overbore)

Typically, a flat-top with two sets of valve reliefs (for installation on either bank) will have about a -5cc volume, which provides around 9.8 CR with a 1.560 compression height and an .025 deck. You need something with around a -11 dish - a Speed Pro H670CP30 or something comperable.

Best bet is to talk to your machine shop - chances are they have preferences for the pistons they work with and can get 'em at about the same price you'd pay somewhere else.

NOTE that this is not a recommendation - as you didn't provide all the information needed Translation: if you buy these and they don't work it's your fault and not mine

[tll74]

Have you thought about increasing the cubic inch? Your 37's, 4.56 gears, and heavy axles are going to need some torgue to get the ball rolling. Not trying to confuse ya just hate to see a engine get built and then not be happy with the performance. A 383 would only require a new crank, balancer, flexplate and balancing. The rest of the parts needed are required for the 350 rebuild. It's only money but worth it!

[Billla]

Originally Posted by tll74

Nearly all pistons are destoked. Ive seen pistons on sbc's be as low as .060 down in the hole. This is a compression killer. I believe most, if not all, compression advertized spec's are based on zero deck height and a .038 head gasket. I would deck the block to near zero to obtain .040-.045 "qench".

I'll respectfully disagree with a few of these comments. Compression height is 1.560; the only reason for a "shorter" piston is to compensate for a significant cut to the block deck. If the piston is at anything other than .025 standard deck height (block deck of 9.025) then someone ordered the wrong piston.

Compression is usually expressed at standard deck (.025) for hypereutectic pistons, and at zero deck for forged - but you MUST check the specs and not assume. The standard compressed gasket thickness is typically .039.

While I agree that an .040 quench is ideal, it's not quite as simple as just zero-decking the block - this is a decision that's made as part of the overall build. Note that you can achieve the same quench by using a thin steel "shim" gasket at .015 compressed thickness...combined with an .025 deck, there's your .040 quench. All that's required is a very smooth deck and head surface; you just need to let the shop know that you'll be using these types of gaskets.

Lots of ways to skin a cat, but the important thing is to PLAN the build and build to the plan.

[Billla]

Originally Posted by tll74

A 383 would only require a new crank, balancer, flexplate and balancing. The rest of the parts needed are required for the 350 rebuild. It's only money but worth it!

Agreed that some of the parts are a wash - specifically the crank - but by the time you pay for block clearancing, stroker-clearanced rods and the other stuff (including better heads for the extra 33 CID) it's real dollars.

No pushback that if you have the cash the 383 is the best way to go.

[tll74]

[QUOTE=Billla;2610386]I'll respectfully disagree with a few of these comments. Compression height is 1.560; the only reason for a "shorter" piston is to compensate for a significant cut to the block deck. If the piston is at anything other than .025 standard deck height (block deck of 9.025) then someone ordered the wrong piston.

Thanks for the correction. Although I don't fully agree. It's the "stock production" cheap replacement cast pistons that production shops use and push that all seam to be destroked. This is to compensate for deck surfacing to maintain close to the standard .025 deck height. Again I'm talking about "production shops". I find that not all shops surface decks and if so only a clean up pass. This is what I was referencing to. So many people go in to a shop and have a engine built and come out with less compresion than they went in with.

[Billla]

Originally Posted by Billla

I'll respectfully disagree with a few of these comments. Compression height is 1.560; the only reason for a "shorter" piston is to compensate for a significant cut to the block deck.

Originally Posted by tll74

Thanks for the correction. Although I don't fully agree. It's the "stock production" cheap replacement cast pistons that production shops use and push that all seam to be destroked. This is to compensate for deck surfacing to maintain close to the standard .025 deck height. Again I'm talking about "production shops". I find that not all shops surface decks and if so only a clean up pass. This is what I was referencing to. So many people go in to a shop and have a engine built and come out with less compresion than they went in with.

What don't you fully agree with - isn't what you're saying in bold EXACTLY what I said (also in bold)? If the shop is only taking a clean up pass (.003 or so) and they install a piston with .020-.025 less deck height...then they're installing the wrong piston. Certainly if as you note the piston ends up .060+ deck height someone's made bad choices! As a home rebuilder, it's your job to talk with the machine shop - BEFORE any machine work is done - and determine what the final deck height will be and ensure you know the piston specs. If you don't ask and keep an eye on the specs - and do the math - then it's not the shop's fault...which was also my point.

[68c10owner]

alot of "builder" pistons do come up short in the deck height dept. Not sure why exactly, probably as mentioned about having the blocked decked and keeping a "standard" deck.

To my knowlenge all performance pistons hyper or forged are speced at .025" unless specified different by the manufacturer.


Now, depending on deck height and gasket thickness flat tops will get you closer to 10:1. If you want to keep it under that you`ll need a small dish piston. Look at the Gm 350HO vortec motor. They run dished pistons and are listed as 9:1. I don`t know off hand what head gasket they use but if it`d not the steel shim .015-.018" gasket then using this gasket will get you about 9.5-9.7 but again it depends on gasket thickness and deck height. also, alot of vortecs cc out at 66cc`s, not the 64cc`s they are listed as.

[tll74]

Billa, sorry for confusing ya. You are completly correct. I wasn't fully reading what you were saying. [Not enough sleep and way to much work] As you mentioned and my point was that the "home builder" must ask the right questions to get the right parts & build. I might be a little vocal about the "builder" piston due to learning the hard way, years ago.

[tll74]

Billa, sorry for confusing ya. You are completly correct. I wasn't fully reading what you were saying. [Not enough sleep and way to much work] As you mentioned and my point was that the "home builder" must ask the right questions to get the right parts & build. I might be a little vocal about the "builder" piston due to learning the hard way, years ago.

[70rs/ss]

I think a flat top and Vortecs are OK as they are not a knock prone as the old school iron heads are. If you are going to rebuild the 350 (new rod bolts, resize the robs, recondition the crank, bore the block, deck it etc, etc) the cost of a cast 383 stroker kit really isn't that much more. They come with pistons, ring, gaskets, rods, crank, for like $900. Then all you need is your block prepped, a cam and a set of heads. I'd figure a good 350 build would only save $3-400 over a 383 build. By the time you condition a set of rods and a crank you are near $400, then you need to buy pistons as well, so you really only spend a few hundred more and get a lot more by way of torqu and you'll need it with big axles and tires. Just a thought.

[Billla]

Originally Posted by tll74

the "home builder" must ask the right questions to get the right parts & build.

I might be a little vocal about the "builder" piston due to learning the hard way, years ago.

With you on both points, my friend. Measure twice, cut once

[tll74]

Originally Posted by 68c10owner

alot of vortecs cc out at 66cc`s, not the 64cc`s they are listed as.

Good point. I cc'd several heads such as the 487, 993, 882, and others and found them to be closer to 78 cc compared to the listed 76 cc. These were virgin heads that have never been surfaced. Two cc's will make a .2 difference on a 355.
http://www.rbracing-rsr.com/compstaticcalc.html

[jkade]

Dang guys there is some good info here, I haven't been around in a week or so and had forgot about this. I have been trying to find a gm short block but they don't seem to make a short block anymore that is the less than $1000 price range.

[70rs/ss]

I just dropped my Vortec roller cammed 350 off at the machine shop and when I pick it up it'll be a 383. I don't believe I'll have more than $2k in it. Using the Vortec heads 062's. I may use a bit of a dished piston, Summit sells a balanced ready to use kit with a dished piston for $7-800, get a cam and you're ready to go.

[jimfulco]

http://webpages.charter.net/beckracing//page25.htm shows some D-dished 350 pistons from KB, with info on dimensions and compression ratios. CR's are calculated using .030" overbore and .040" piston-to-head clearance.