zero decking the block
 

In my quest to get my little naturally aspirated 302 in the 11's I am getting my block reringed and honed with new bearings and was wondering if zero decking the block to gain more compression was a good idea.

Re: zero decking the block
 

Depends on what your deck measurement is now. Also head configuration. Valve to piston clearance.

How about a thinner head gasket??

If it is the typical deck that is a couple of thousands down in the block, I don't think you'll gain a whole heck of a lot. I could be wrong.

Re: zero decking the block
 

Yeah, your probably right.

Re: zero decking the block
 

Zero-decking is an excellent way to increase the compression. You get the full effect for every 0.001" taken off the block compared to the head since a Windsor head is only a semi-open combustion chamber. I bring every block I've got to zero. Besides, it really evens out the cylinders. Its not uncommon to see 0.007-0.008" variation from corner to corner of a stock block.

Re: zero decking the block
 

Zero decking is a good idea for raising compression and cyclinder ballance, don't forget to test fit your heads and intake before final assemblly. I had a block that was .022 from front to back. It took .025 to clean it up. They had to shave a little off the pistons to get the zero. I have been running that same block for 8 years. It is in my car now as a .030 over 351 and makes 405 to the wheels on motor. Good luck with your build!!! :D :D

Re: zero decking the block
 

My factory deck ranged from zero to negative (piston out) .009". Don't forget that piston pin placement and rod centers affect the deck (even crank machining) - it's why racers select fit pistons and rods in the assembly stage

Re: zero decking the block
 

For maximum compression its better to run the pistons .005~.007 in the hole and select a small bore head gasket thats .030 thick. Or with an iron head you can have the pistons .020 in the hole and use a .015 steel shim gasket. Zero decking with a .037 gasket can give up a little because the bore size of the gasket is always bigger than the piston. But to do this accurately you need to have the block deck trued. This brings the deck perfectly parrallel with the mains, and makes sure both decks are set at 45 degrees. I have seen them be out as much as .020 from front to back and top to bottom.

Andy

Re: zero decking the block
 

This is really interesting, two of the guys opinions I respect the most on this board (Jeff & Andy) have different ideas on this.

I ALWAYS take the "twist" out of my blocks, and since it's at the machine shop on the right machine, I've always taken them to zero deck, talking hot rods here, not daily driver engines I've built.

Andy brings up a good point though, if you read that closely and invision what he's saying there, it makes sense. Funny what comes out of the woodwoork when you're talking to guys that are in a heads up class, have rules to follow, and are trying to squeeze every ounce of power out of an engine!

Great thread going on here!

Re: zero decking the block
 

Andy may correct me here, but some of his experience is based on the NMRA requirement that they maintain a minimum quench of 0.038". Over in FFW, we have no such requirement so we do everything we can to get the compression ratio as high as we can. My TW heads have been milled nearly .200" to 38cc chambers, with oversized valves to the point that the intake valve is actually proud (hangs below the head surface). I use a Yates-style gasket and relieve the block a little locally to clear the valve, a 0.035-0.040 head gasket and zero-deck the block. At 9000 rpm, the rod stretch is actually enough to bring the piston 0.003" or more out of the block for even greater dynamic compression.

Heads up racing baby! If you want the trick stuff, that's where you'll find it.

Re: zero decking the block
 

Nice post Jeff.

Your set-up is very hardcore.

"Heads up racing baby! If you want the trick stuff, that's where you'll find it."

I love this quote. :D

Ok with a zero decked block with .566 lift 224 duration Exhaust and .566 lift 218 duration Intake @.050 cam, Stock pistons and 2.02 1.60 valves on my Canfields.

The machine should be able to open up my valve reliefs enough for everything to work, right?

Re: zero decking the block
 

Kinda yeah, kinda no, Jeff. I never really understood why they put that rule in there. Btw, its gone from this years rules. Even at .035 quench everything I have built still has a combustion chamber mark on the piston. I dont feel comfortable running them any tighter.

All I was saying was, since you have to have a minimum quench distance, for max compression its better to have that distance be of as small a bore as possible.

Andy

Re: zero decking the block
 

I thought you both have been very clear about what you were saying..........

Re: zero decking the block
 

Me too!

Jeff's second post actually clarified a few things on how those Street Warrior's run like they do!

Then again, Andy has a valid point as well. Just for the record, and those of us that DON'T know, how does NMRA measure quench distance?


I DID NOT intended to put Jeff and Andy "against" each other, but I gahrun-dam-tee yah, I'm gonna sit back and learn what I can! Osmosis at it's best right here guys! Pay attention! ;)

Re: zero decking the block
 

When it was in the rulebook they measured it the same way you or I would: Mic the headgasket and use a bridge to find the relationship between the top of the piston and the deck surface.

Andy

Re: zero decking the block
 

On my engine with forged TRW flat top pistons, I think the pistons (cold engine) are in a slightly different position each time I check with the bridge and with the dial iondicator. I get a .000 to .005 " down in the hole after I crank it a few turns. That's for the same #1 piston at TDC on the balancer. Also get some slight variation depending on what part of the piston top I measure from. I don't think that variation actually makes any performance difference, but it it is difficult for me to say exactly what the deck height measurement (how far down in the hole) my pistons actually are at TDC.

Rev

Re: zero decking the block
 

This is because there is actually a dwell at TDC. You need to check for TDC at some distance before and after TDC....say .050 before and .050 after (coming back at it). Then split the difference and you'll really know where TDC is. Otherwise, you can any where from 3 to 8 degrees of dwell at TDC depending on tolerances, clearances, etc.

Re: zero decking the block
 

I check for TDC on the short block with a dial indicator right on the flat of the piston. Note when the dial stops rising and where it starts falling and TDC is center of those positions. I have a large degree wheel set up too. I also find TDC starting from both sides of the curve. When I have the dial on true TDC, I index the timing marker.

Re: zero decking the block
 

Have you pushed the connecting rod up to zero out the bearing oil clearance?

Re: zero decking the block
 

Since I'm back down to a bare block, I'm LOVIN this thread.

HARDCORE gear heads talking about things that I never would have even thought of 5 years ago!!!! Way kewl!

Since I'm already at "0.000" deck, I really have no choice on this motor, but the next one..... Hmmmmm!?!?!?!???

BOTH sides have made a substantial arguments in their favor, and I respect both sides of the equation here. This is literally a tough call.

Like I said before, pay attention guys, you're gonna learn yourself something on this thread!

Re: zero decking the block
 

No argument here. There's quite a few different theories on setting up a motor, but if you really want to see the tricks pay attention to heads up racing. Not intending to offend anyone, but bracket racers don't normally go to the extents that a heads up racer will.

Just dropped my pistons off at the engine shop today. Beautiful JE customs with all the tricks, titanium casidium coated wrist pins and Total Seal diamond finish ring set. Hell, the ring set alone cost more than most people spend on a full set of pistons. Just had the block punched for roller cam bearing.....sweeeeeeeeeet.

Re: zero decking the block
 

No need - you have that from micing the crank and rod bore or from plastiguage. Simple math - and the crank does not necessarily ride @ center at rpm anyway right? so, you know the tolerance "window" of measurements and affect on deck or other issues such as p-v @ rpm, which also needs to consider rod stretch, piston "growth" at temp, etc, etc. Details - the devil is in there.

Re: zero decking the block
 

Does this mean you're playing "Street Warrior" in '06? Thought you were wrenching for another team, how'd that work out? Or it this motor a "shop thing"? What's the skinny here bud?

I found a new machine shop, he does everything but leans WAY towards the blue oval. I like the way he thinks, and he's telling me we can get quite a bit more ponies out of the same motor with PROPER machine work. After reading this thread, I have to agree. But like I said before, this one is already at zero deck, so I have to stick with it. It is getting punched .040" over, so she's on her last leg, but what a ride it's gonna be! I can't wait!

Andy, I posted this "question" on my own forums, just to see. And MOST, I'm talkin 98% of the guys agree with you! All for different reasons, mainly reliability. I'm with Jeff at this point. I like my zero deck, but you make a darn good argument my friend!

Re: zero decking the block
 

Jester, glad I got you thinking..lol.. Actually I'm not arguing or debating anything. Theres nothing to debate. Its pretty clear. The reason people have a hard time accepting it is because they've never heard of it being done that way. Zero deck is all anybody has ever been taught. Well, that and .010 out of the hole is real popular with a bunch of douchebags around here.

So the people you are talking to say its better to have them in the hole for reliability reasons, and they cant comprehend that you gain compression by making up your quench distance with the bore instead of a headgasket that is bigger than the bore? Well, now I guess you know how I feel..lol..

Andy

Re: zero decking the block
 

Jester, I had a 351W that had a positive deck, pistons out of their holes, by .002-.003.

I sent the pistons out and had the piston crowns machined so I had .001, down in the bores, deck. Did it for reliability. Wasn't real hard to get done.

Re: zero decking the block
 

3 thou off the top of the piston is going to make the engine more reliable? :confused:

We have a fixture for our lathe that is specifically for this. It takes about 15-20 minutes per piston. I think the most i've ever taken off a set is .020.

Andy