[DiamondJim]

Stewart, proper quench will help more with detonation than most realise. More compression and proper quench is more power. With my GTO's motor I was shooting for .038, ended up with .035. I am at 9.95 static and 8.3 dcr with absolutly no detonation and iron heads. Read this article, http://kb-silvolite.com/article.php?action=read&A_id=35 particularly the 4th paragraph down, pretty much says it all. Goodluck -Jim

[gtofreek]

Originally Posted by Cliff R

9.75 to 1? Paul, you know the "mechanical limit" for pump gas is 9.5 to 1, or so I keep hearing. I'm going to pull my 455 down tomorrow and install a head gasket thick enough to lower it from 11 to 1 down to 9.5 to 1, so I can effectively manage 92-93 octane fuel. Cripe, I'm already running it on 87-89 octane, maybe it's too late!.......Cliff

Naw, Cliff, it's probably too late now. You've obviously have pinged it to death already!

[Murf'sDad]

Originally Posted by DiamondJim

Stewart, proper quench will help more with detonation than most realise. More compression and proper quench is more power. With my GTO's motor I was shooting for .038, ended up with .035. I am at 9.95 static and 8.3 dcr with absolutly no detonation and iron heads. Read this article, http://kb-silvolite.com/article.php?action=read&A_id=35 particularly the 4th paragraph down, pretty much says it all. Goodluck -Jim

Morning Jim:

After all the discussions here I figure I will probably end up at about 10:1 if I zero deck the block. More good than bad with the better quench. It will be discussed with the machinist as well.

Stewart

[Cliff R]

Just a couple notes on zero deck clearance.

We have also noticed that the engines we build with the quench distance at or close to .035" run cooler. Not to mention they are able to manage pump fuel at relatively "high" SCR's.

The last two 455's that powered my Ventura actually run so cool/cold, that it is difficult to get them to heat up. Nothing used for cooling but a stock water pump with an iron impeller, stock clutch fan, and a 15 year old Modine 3 row replacment radiator.

The very first engine that powered the Ventura was a 400 with 6X-8 heads, and TRW forgings .028" down in the holes. It came with the car when I bought it. It ran HOT, and temps would creep up at idle speed past 210. No detonation since the CR was only about 7.7 to 1 at best. In any case, the first 428 I built to replace it, was around 8.8 to 1 SCR, pistons .018 down in the holes, and it ran hot, and temps would climb at cruising to 220-230 degrees.

That 428 died a quick and miserable death. I replaced it with another 428 and it ran for about 15 years, but it was not zero decked either, SCR still about 8.8 to 1. I used a different cam and heads, it ran a tad hotter than I would have liked, but not enough to damage the engine.

I started reading Jim Hand's articles, and built our first 455 at exactly zero deck height. It ran cooler at 10 to 1 with iron heads than any of the previous engines. Keep in mind that we used the same cooling system components with all of these engines.

The first 455 was also making a LOT more power than any of the previous engines, and at the same time effectively managing 89 octane fuel, where the last 428 required premium fuel with over a point LESS static compression ratio.

Now we have installed a 455 at 11 to 1 SCR, and run it on 89 octane (actually 87 octane on the street), and have yet to have the temp gauge climb past 180. It can sit for hours at idle when first started and never see 160 degrees. It is very difficult to get it to heat up in cool weather. I've even tied the clutch fan so it woln't spin, and it can run for 30 minutes in the shop and still hasn't reach full operation temperature now that it's cold/cool outside.

Part of our "recipe" during the build, in addition to establishing zero deck height, is to polish the piston tops to a near mirror finish. This is supposed to reflect some of the heat, instead of transfering it into the piston to be absorbed by the lubricating oil then transfered to the coolant.

In addition to establishing zero deck height at ideal quench distance, polishing piston tops, etc, we also have very close control of the timing and fuel curves. Our cooling system is not "state of the art", but in excellent condition and able to move enough water and extract enough heat from it.

I've been out in traffic on 100 degree days, and the highest I've ever seen the temp gauge go was 185. I usually sit there and remember back to the days when we had a 400 in place that would give me an uneasy feeling sitting at traffic lights as the temps would climb pretty quickly to over 210, and sometimes as high as 230, if you sat there long enough.

Anyhow, as mention previously, 100 percent of the troubled Pontiac engines we had brought to our shop had the pistons WAY below the deck at TDC. Another trend, was that many of them used "tight" LSA camshafts with advanced intake valve positions and closing points. Just a couple of things to ponder on?

I actually cured a 400 one time that ran hot/overheated/detonated by retarding the camshaft 4 degrees. We tried in vane prior to that move, even installing an aluminum radiator to get the engine to quit overheating. This was quite a few years ago, and it just so happened that particular engine used TRW forgings, which typically end up about .028-.032" down in the holes at TDC on the 400's.

For the reasons above, we continue to recomend decking/squaring of the blocks, and establishing a more ideal quench distance by zero decking them. Even if you end up with a tad bit higher SCR, the engine will still be less octane sensitive, than if you were to leave the pistons down in the holes at a lower SCR.......Cliff

[Murf'sDad]

Good info Cliff, thanx. I guess I'll be zero decking the block.

Stewart

[Cliff R]

Stewart, good choice. It completes the engine "blueprinting" process anyhow. Besides all the benefits already mentioned, it eliminates deviations in the factory deck height from the crankshaft centerline, brings the compression for each cylinder closer, and provides a "fresh" surface to seal up the head gaskets......Cliff

[Murf'sDad]

Originally Posted by Cliff R

Stewart, good choice. It completes the engine "blueprinting" process anyhow. Besides all the benefits already mentioned, it eliminates deviations in the factory deck height from the crankshaft centerline, brings the compression for each cylinder closer, and provides a "fresh" surface to seal up the head gaskets......Cliff

Thanx Cliff. When I dropped off the engine yesterday, zero decking was one of the topics of discussion. I can't wait to get this thing up and running.

Stewart

[grivera]

Originally Posted by Cliff R

Part of our "recipe" during the build, in addition to establishing zero deck height, is to polish the piston tops to a near mirror finish. This is supposed to reflect some of the heat, instead of transfering it into the piston to be absorbed by the lubricating oil then transfered to the coolant.

I realize this is an old thread, but can you describe how you polish the piston tops?

[rohrt]

Originally Posted by Cliff R

Just a couple notes on zero deck clearance.

Part of our "recipe" during the build, in addition to establishing zero deck height, is to polish the piston tops to a near mirror finish. This is supposed to reflect some of the heat, instead of transfering it into the piston to be absorbed by the lubricating oil then transfered to the coolant.

In addition to establishing zero deck height at ideal quench distance, polishing piston tops, etc, we also have very close control of the timing and fuel curves. Our cooling system is not "state of the art", but in excellent condition and able to move enough water and extract enough heat from it.

I've been out in traffic on 100 degree days, and the highest I've ever seen the temp gauge go was 185. I usually sit there and remember back to the days when we had a 400 in place that would give me an uneasy feeling sitting at traffic lights as the temps would climb pretty quickly to over 210, and sometimes as high as 230, if you sat there long enough.

Anyhow, as mention previously, 100 percent of the troubled Pontiac engines we had brought to our shop had the pistons WAY below the deck at TDC. Another trend, was that many of them used "tight" LSA camshafts with advanced intake valve positions and closing points. Just a couple of things to ponder on?

I actually cured a 400 one time that ran hot/overheated/detonated by retarding the camshaft 4 degrees. We tried in vane prior to that move, even installing an aluminum radiator to get the engine to quit overheating. This was quite a few years ago, and it just so happened that particular engine used TRW forgings, which typically end up about .028-.032" down in the holes at TDC on the 400's.

For the reasons above, we continue to recomend decking/squaring of the blocks, and establishing a more ideal quench distance by zero decking them. Even if you end up with a tad bit higher SCR, the engine will still be less octane sensitive, than if you were to leave the pistons down in the holes at a lower SCR.......Cliff

What happen when a rod bearing starts to give up and having a zero deck? Do you risk destroying your heads? Can an aluminum piston ruin an iron head? I assume it can ruin an aluminum head. I understand the benifits of the zero deck but what about the consequences?

[77 TRASHCAN]

Originally Posted by rohrt

What happen when a rod bearing starts to give up and having a zero deck? Do you risk destroying your heads? Can an aluminum piston ruin an iron head? I assume it can ruin an aluminum head. I understand the benifits of the zero deck but what about the consequences?

Zero decking a block is usually taking off around .020 inch...leaving the .035-.040 piston/head clearance (cold). If a rod bearing is bad enough to get the piston into the head on a zero deck engine, it would be a problem even if it wasn't zero decked....

There's too much performance gain, and other factors, as Cliff, states, to not zero deck an engine...
Your question is good, but you've probably got a MAJOR blowed up engine, regardless...

An engine malfunction could ruin aluminum or iron heads...proven...

Polishing piston tops is cheap insurance to avoid hot spots. 220 grit wet dry sand paper on the sharp edges, and scotchbrite on everything else is what I use. You only need to knock down the sharp edges, nothing major. I'ts best to polish them, before everything gets balanced, and after any machine work is done to the pistons. (if needed).

[grivera]

How does one get the tops to a "near mirror finish," like mentioned by Cliff? Is there a point where one may do damage to a protective barrier?

[amcmike]

Even with timing and a/f dead on, isn't there going to be a film of carbon buildup on the piston top, thus making it ineffective after some run time?

[rohrt]

Originally Posted by 77 TRASHCAN

Zero decking a block is usually taking off around .020 inch...leaving the .035-.040 piston/head clearance (cold). If a rod bearing is bad enough to get the piston into the head on a zero deck engine, it would be a problem even if it wasn't zero decked....

There's too much performance gain, and other factors, as Cliff, states, to not zero deck an engine...
Your question is good, but you've probably got a MAJOR blowed up engine, regardless...

An engine malfunction could ruin aluminum or iron heads...proven...

Your saying the benifits out weigh the costs? It just seams a little scary to maybe have $3k sunk into head and only having the thickness of a head gasket protecting them. On the other hand I can't say that I have heard of to many stories of this happening either.

Originally Posted by amcmike

Even with timing and a/f dead on, isn't there going to be a film of carbon buildup on the piston top, thus making it ineffective after some run time?

I was thinking the same thing.

[77 TRASHCAN]

Originally Posted by grivera

How does one get the tops to a "near mirror finish," like mentioned by Cliff? Is there a point where one may do damage to a protective barrier?

If the piston top is coated, you leave it alone, only polish uncoated pistons. A coating has some of the benefits of polishing.

[grivera]

I was under the impression all pistons had a type of barrier.

[chiphead]

Nope, most are bare aluminum.

Zero decking and quench distance are two different things. You zero deck the block to the pistons. The head gasket thickness and head chamber design affect quench distance, which is optimally .035-.040" with steel rods and typical skirt clearance. Piston rock and not bearing clearance or rod streach affects safe quench distance with steel rods. The tighter the skirt, the tighter the quench can be within reason. Just don't run it so tight that the pistons scuff in the bores.

It's a good rule of life: Don't skuff da skirts!

[grivera]

THX

[Mr. P-Body]

The "reflective" qualities of the piston "head" aren't compromised when carbon "builds up". We used to polish the heads in olden times, when modern machining techniques had not yet been applied to piston making. With "diamond turned" surfaces, there's much less distortion in the surface. "Coating" with a thermal barrier is commonly done today, too.

When we (CVMS) "zero-deck", we leave the pistons .005" "in the hole" to prevent the piston from "kissing" the head at higher revs. Yes, a rod bearing "going bad" can beat the SNOT out of the piston AND head...

FWIW

Jim

[grivera]

Originally Posted by Mr. P-Body

The "reflective" qualities of the piston "head" aren't compromised when carbon "builds up". We used to polish the heads in olden times, when modern machining techniques had not yet been applied to piston making. With "diamond turned" surfaces, there's much less distortion in the surface. "Coating" with a thermal barrier is commonly done today, too.

When we (CVMS) "zero-deck", we leave the pistons .005" "in the hole" to prevent the piston from "kissing" the head at higher revs. Yes, a rod bearing "going bad" can beat the SNOT out of the piston AND head...

FWIW

Jim

When I assembled my engine, I attempted smooth the tops of the Speed Pro Forged with a scotch-brite pad. The pistons have engraving on the top so I only accomplished so much. I didn't realize I could have wet-sanded for better results.

Have you seen the same distance in the hole for Speed Pro's in stock deck height 400's as others here- as much as to .039?

[Mr. P-Body]

Will,

Speed Pro "lists" deck clearance at .020". That may be a bit optimistic. But more than .025" would indicate a "short" connecting rod or "short" stroke. That is, when the rods were resized, they were massively "cut" or... The crank's stroke wasn't indexed exactly "right" when it was ground, OR... A combination of those things.

We installed a set of Speed Pros in a 400 block last month, that uses an RPM 4.21" stroke and standard-length rods. All new. Deck was .015".

Jim