[macx]

Such as any of the Vortec's?

Planning some mild upgrades to my 81 Vette but I know they're fully dished pistons and I need something with quench style pistons (i.e. flat tops or D shaped dish) that will work with Vortec style heads to allow a higher compr ratio (i.e. 9-1) that will avoid detonation and still run decently on 87 octane.

Trying to determine if any good used shortblocks are available (of course also a roller capable block) that might be less costly than re-building my L81 motor with upgraded pistons.

I'm on a budget so a crate engine or shortblock is out.

[cool rockin daddy]

Buy any roller block engine that came with vortec heads on them. That will give you everything you need.

[Chevrolet4x4s]

Keith Black makes some d dish pistons that can be purchased from summit,they work great with vortecs.
Shane

[macx]

I did some lengthy research and found that all 5.7 Vortec engines (only came in trucks) had fully dished pistons - nothing with flat tops or D shaped dish, and even the GM crate Vortec engine with 9.1 cr requires 91 octane which bears that out. SBC engines have been built that ran fine on 87 octane and 9-1+ comp ratio with good quench from Vortec heads and quench type pistons.

So the only way to get a decent quench in any 350 SBC is to change pistons, and even with the inexpensive Sealed Power / Speed Pro type hypereutectics that would run well over $300 by the time I pay machine costs, not to mention R&R & the work on the engine which I wouldn't do if I don't change pistons. And available D shaped dish pistons are significantly more expensive.

And calculting comp ratios with available inexpensive pistons and the largest (67cc) comb chambers available on low cost aftermarket Vortec heads, I'd still likely have to run at least 89 octane, so wouldn't be gaining much in the way of reduced gas costs, if anything.

Figuring a max miles on that car during my retirement at 50k miles, if I leave the stock shortblock alone, except for a cam change, it will cost less to use the small chamber 64cc heads and run 91 octane than changing pistons. Not to mention all the work. And I'd probly gain a few lbs of low and mid range torque from increased timing advance and slightly higher compr ratio, and maybe even a mpg or 2.

With 64cc heads, .02 x 4.1 coated gasket which should seal a non-machined deck, stock 9.9cc no-quench dished pistons, .05 actual deck height (.045 at blueprint block height value) = 9.09-1 compr ratio. With .055 deck height about 9.07.

So as "nice" as it would be to have the more modern quench setup, it's just not cost effective for my situation. Going with the above setup saves me
at least $300 up front plus a whole bunch of work, and ends up saving probly $100 or more cost over time.

[oldbogie]

Originally Posted by macx

I did some lengthy research and found that all 5.7 Vortec engines (only came in trucks) had fully dished pistons - nothing with flat tops or D shaped dish, and even the GM crate Vortec engine with 9.1 cr requires 91 octane which bears that out. SBC engines have been built that ran fine on 87 octane and 9-1+ comp ratio with good quench from Vortec heads and quench type pistons.

So the only way to get a decent quench in any 350 SBC is to change pistons, and even with the inexpensive Sealed Power / Speed Pro type hypereutectics that would run well over $300 by the time I pay machine costs, not to mention R&R & the work on the engine which I wouldn't do if I don't change pistons. And available D shaped dish pistons are significantly more expensive.

And calculting comp ratios with available inexpensive pistons and the largest (67cc) comb chambers available on low cost aftermarket Vortec heads, I'd still likely have to run at least 89 octane, so wouldn't be gaining much in the way of reduced gas costs, if anything.

Figuring a max miles on that car during my retirement at 50k miles, if I leave the stock shortblock alone, except for a cam change, it will cost less to use the small chamber 64cc heads and run 91 octane than changing pistons. Not to mention all the work. And I'd probly gain a few lbs of low and mid range torque from increased timing advance and slightly higher compr ratio, and maybe even a mpg or 2.

With 64cc heads, .02 x 4.1 coated gasket which should seal a non-machined deck, stock 9.9cc no-quench dished pistons, .05 actual deck height (.045 at blueprint block height value) = 9.09-1 compr ratio. With .055 deck height about 9.07.

So as "nice" as it would be to have the more modern quench setup, it's just not cost effective for my situation. Going with the above setup saves me
at least $300 up front plus a whole bunch of work, and ends up saving probly $100 or more cost over time.

Yep the only time this wraps up into the words cost effective is if the engine has to be rebuilt anyway. Then you do it right the first time.

This is like my wife setting in line at Costco to save a dime a gallon when filling up her Prius.

Bogie

[Chevrolet4x4s]

9.7 with Vortecs (singh groved,polished and deburred chambers) on 87 on a 406.
Shane

[Jim Rockford]

Just to update this, Any 87-93 Police caprice with the LO5 tbi 350 will have factory flat tops and be a roller engine.

This was the engine in my 90 Caprice 9C1 ...

[cobalt327]

LT-type engines came w/FT's, used metric rings.

[ap72]

In most cases those people who go chasing down the last mpg on anything with an sbc spend dollars to save cents. The 350 is not an ecotec 2.2L or even an LS3- accept it for what it is and go from there.

As already said the only time it makes sense to change something for mpg's is when you need to change (rebuild) it anyway.

[CJ_1080]

The L31 vortec out of my 1996 k2500 was a roller block and had flattops like the above pictures. Obviously had vortec heads as well as 4 bolt mains!! Win win. With some block decking or thiner head gaskets you could come up with real good quench numbers! Factory vortec engines are about 9.1 compression stock so plan on a bit more if decking or thinner headgaskets.

[techinspector1]

Here's a 1.560" hyper flat-top 350 piston for under a hundred bucks for a set of 8....
http://www.summitracing.com/parts/SUM-17350-30/

[cobalt327]

Originally Posted by CJ_1080

The L31 vortec out of my 1996 k2500 was a roller block and had flattops like the above pictures. Obviously had vortec heads as well as 4 bolt mains!! Win win. With some block decking or thiner head gaskets you could come up with real good quench numbers! Factory vortec engines are about 9.1 compression stock so plan on a bit more if decking or thinner headgaskets.

My L31 has those cheesy round dished pistons, PM rods. Oh well.

I think you'll find the stock CR higher than 9:1- my engine measured to be ~9.5:1 w/the dished pistons and a thin-ish (0.028") head gasket.

[Jim Rockford]

Originally Posted by ap72

In most cases those people who go chasing down the last mpg on anything with an sbc spend dollars to save cents. The 350 is not an ecotec 2.2L or even an LS3- accept it for what it is and go from there.

As already said the only time it makes sense to change something for mpg's is when you need to change (rebuild) it anyway.

But their is a difference between a smog motor running inefficiently and getting 10MPG and a nice well matched small block running efficient and getting almost 19mpg.