[hoffman7476]

I'm thinking about having my block zero-decked and running un-milled 6x-8 heads on my 455. I,ve read that this is the best way to increase compression ratio without running into detonation. Plans were for a RA IV type cam but I'm starting to calm down and I'm thinking about a 744 or 68 cam. Any thoughts? (You out there P-Dude )

[ August 20, 2002, 09:48 PM: Message edited by: hoffman7476 ]

[hoffman7476]

I'm thinking about having my block zero-decked and running un-milled 6x-8 heads on my 455. I,ve read that this is the best way to increase compression ratio without running into detonation. Plans were for a RA IV type cam but I'm starting to calm down and I'm thinking about a 744 or 68 cam. Any thoughts? (You out there P-Dude )

[ August 20, 2002, 09:48 PM: Message edited by: hoffman7476 ]

[Brian Baker]

Slap the 041 in there with Rhoades lifters and hang on!

[hoffman7476]

I like what P. Mcarthy said about the 041, "It will tear your head off."
What about zero decking though?

[73LeMans]

Hoff,

Any reason you are choosing to deck the block, rather than to mill the heads? Wouldn't it be easier to do the heads both from a cost point of view, and transportation of the units? I would think so...unless of course, the block needs to be decked i.e. warped? he way I look at it is this...the heads are interchangeable with any stock block. Once you start customizing the block, you’re stuck with it. You may not be making 1000 HP or anything, but wouldn’t it be nice to move your milled heads from stock block to stock block *all else being equal* and still get the same power out of it? Yes, its a good way to increase compression, but it seems like the harder way of the two. And regardless of what the deck is, the area for for the air and fuel is the same, so I don't see how this way is better in any way for detonation than the milling the heads. <<<<someone more knowledgeable than me might want to jump in here

I zero decked my block, but only because the heads were already cut .020 and I still needed more compression. **needed something in the 12:1 range** I'm not saying don't do it, but I just think for whatever gains in detonation saving this method MAY get you, if any, it hardly seems worth the extra work.

~Mark

[Skip Fix]

Zero deck wil help besides squaring the block by helping "quench". The close to ideal quench(space in the flat area of head) is about 0.040(head gasket thickness). This helps create more "mixture motion" and helps detonation from that aspect.Imagine blowing on a flat surface and the air goes out to the side that's what it does in teh chamber.

That's why zero deck and a dish are better than the piston "down the hole" to cut compression.

[hoffman7476]

The block is prepped and the mach. shop is turning my crank now. (Wait a minute, that didn't sound right.) The price for milling heads vs block isn't that much different. I'm sort of a fan of big cc heads cause the valves aren't as shrouded and it's gotta improve flow. I'm definetely no expert on this just kind of theorizing...I figure any hedge against detonation is pretty good and this is certainly the time to do it.

[PONTIAC DUDE]

I would just true deck the block. The quench thing is a Max performance racing thing and I feel over rated for basic Street/strip action.
The hp increase is not that noticable for most basic street engines. .010/.015 in the hole isn't going to be noticable. Plus most Pontiac blocks are alot closer then other manufactures as far as piston in the hole deal. (Sorry Skip, just my view point for the money and future combos or repairs)
Most Pontiac blocks are close (and closer then Chebies, LOL) and have found that usually one side to the other is off no more then .005
Mill the head to do what ya need for compression.
Shrouding is not an issue when milling for your street engine. The 14 degree valve angle of the Pontiac helps.

[Tomo]

Got a 40 over 455 in my 64 thats has been zero decked. It also has 6X-4 Spotts ported heads and a RA IV cam with Rhodes Lifters. Runs real well
tom

[hoffman7476]

Thanks guys. Tomo, Do you have any pinging with that combo and what kind of gas do you use? I'm scared of detonation and I think I'd rather sacrifice a little compression and not have the tuning issues.

[Tomo]

Running a msd 6al with hei.Timing is at 16 degrees
initial with a total of 34. I run 92-93. No ping.
tom

[Half-Inch Stud]

Have 48heads on a .030 455......no ping with 93 Octane.

BUT, I completely unshrouded the valves, and cut those 2 scallop areas out of each combustion chamber to unshroud the sparkplug. Hoping to up the cc's this way too.

Also, ground the piston eyebrows to be unsharp. My think was to avoid turbulent flow from sharp edges.

Also, cut back the sparkplug ground lugs and rebend for side-gap.

H.I. Stud

[Skip Fix]

Dude, Tried a 0.080 in the hole to reduce compression on a 455 with 72cc RAIVs and it was a detonating son of a gun! still made alot of HP on race gas though. Maybe the 0.012 typical down isn't a big deal but I'd rather use a dish, the right size chamber to begin with.

Milling heads, or decking blocks can sure throw off your intake bolts though. Need to be sure they line up.

[Robert Williams]

Pontiac Dude, thanks for that good info on the quench thing as i have been thinking the other way all these years. The late Smokey Yunick also said in his book how important quench is, but he was talking about racing engines, not street engines. Thanks again for clearing this up, for me anyway.

[PONTIAC DUDE]

Skip, I agree with the race gas thing and .080 in the hole.
I have run .080 in the hole with the 455 TRW F.T. single trough pistons on a 428 crank and stock length rods with my ProCharger and ran fairly well into the low 10's with only 12lbs of boost and a P600B unit. But with race gas. Pistons looked great with No signs of detonation.

.015 or less won't hurt a thing for a street/strip combo. Lower Compression, unshrouding and cam design are more important.

[ August 23, 2002, 08:34 PM: Message edited by: PONTIAC DUDE ]

[Cliff R]

I would zero deck the block vs milling the heads. There are other side benefits from this procedure. Having the block decked/squared will insure that the distance from each head to crankshaft centerline is the same. Although Pontiac blocks are usually much closer in this regard than other brands, few are perfect. For medium compression engines built to use pump fuel it becomes much more important to maintain the quench distance of .035-.040". The engine will also run cooler zero decked. Without exception, every Pontiac engine I've had in here that had running hot/overheating problems had the pistons .020" to .030" in the holes.

The following is a recent example: We just finished a well prepared 400 engine for a 66 GTO. The owner is a very competant mechanic by trade, he owns several older high performance vehicles. Last year he completely rebuilt his 400 engine with catastrophic results. A set of #62 heads were used with stock replacement cast pistons, Summit 214/224 cam, Torquer I intake and Edelbrock 750 carb. The engine ran so hot he could not drive it. It also detonated under all circumstances, after an entire summer of tuning without improvement, he removed the engine and brought it here. We made a few minor changes.

The #62 heads were mildly ported, combustion chambers polished to a mirror finish and the exhaust crossover filled with aluminum. The cast pistons were the 8 valve relief replacements and were .030" in the holes, they were replaced with TRW forgings and the block was zero decked, a set of .039" head gaskets were used. A larger 221/229 cam was installed with HS high ratio rockers. The Torquer intake was replaced with an RPM. An 800cfm q-jet and HEI distributor were prepared for the new engine. The new engine manages pump fuel without problems despite being slightly over 10 to 1, compared to the previous configuration being closer to 9.5 to 1. It never gives the first indication of wanting to go past 190 degrees even on extended cruises at freeway speeds. The previous set-up would continue to heat up on extended cruises eventually reaching over 220 degrees where it had to be shut down to cool off.

I know that some of you suspect that it is the TOTAL package that changed the results. About 5 years ago I had a nearly identical 400 engine in here with the same history. I DID NOT rebuild the engine, but spent countless hours trying to tune it to get rid of the detonation/overheating. This included a new (expensive) radiator, waterpump/pulleys, several types of fans, etc. When I finally threw in the towel and pulled the engine, you guessed it, the TRW forgings were .032" in the holes. The engine was zero decked, slight cam change and no problems thereafter.......Cliff

[PONTIAC DUDE]

Cliff R.
Not to be a jerk, but an engine with 8 eyebrow pistons and .030+ in the hole running hot, then zero decking with Other changes (even uping compression?) won't prove that the piston in the hole caused his problems.
Been there, done that.
You changed the cam profile which has the biggest effect on engine heat and performance and...... did everything you needed to do to reduce detonation (by deburring and contouring the head)in the cylinder.
The opening and closing plus overlap.
Detonation causes overheating. And you changed the Cam again on your combo too!!!!!!!!

Years ago, John Ligenfelter did a Street Engine run with 14-1 compression and using pump gas. Cam/head combo....all in the combo.

Sorry.

Footnote.
Most overheating problems can be traced to;

Cam used, as in cam timing in relation to opening/closing/overlap and application.

Distributor timing curve.

Carb fuel curve. Lean somewhere in the rpm range or through out.

[ August 25, 2002, 12:31 PM: Message edited by: PONTIAC DUDE ]

[Cliff R]

Your comments are well taken. Never meant to indicate that having the pistons .020 to .030 in the holes was the ONLY factor in any of these engines running hot, just a common denominator. From the example above you can see how one quickly gets into trouble when selecting parts for his new engine. The 8 valve relief/chamfer all around replacement pistons .030" in the holes were a poor choice to start with. Combined with a piston to head distance of .080" (.052" gasket used) and a 214/224 cam, it was doomed from the start.

It would make little sense to simply deck the block for zero and put it back together just to find out that piston to deck distance alone was the main contributor. Of course we installed a camshaft more closely matched to the compression ratio and made other modifications to make more power and help manage currently available fuel.

Thru the years we've encountered some very successful Pontiac engines managing pump fuel. We've seen just as many if not more that went to an early grave or ran so poorly/hot/overheating that it makes you wonder why some are fine and others are not? As noted above, without exception all of the hot running/overheating/detonation prone Pontiac engines encountered have had the pistons well below the deck. For this reason we deck all Pontiac engines prepared here for zero, then select the best parts for the combination.

[hoffman7476]

Thanks for all the replies. I'm still waiting for rods and a balance job before I even find out what the deck height is on my block.