i'm getting my block decked by a reputable shop ,and was wondering how to get it restamped for numbers matching. this is the original numbers matching block. it don't matter if it's done. but would like to keep it original as possible..

 

Try and catch them before they deck the block so they can stop just before the number pad so the numbers remain.

 

why deck it?

 

I'd like to get mine restamped too.

 

Even if you restamp the broach marks will be wrong. Try to keep the original numbers. If you can't make sure that it is well documented.

 

Typically you deck the block to get a uniform flat area for the heads to seal, and also to reduce quench area (aids in preventing detonation). The goal is to achieve nearly a "zero deck clearance" with your pistons. Idea is to have them come almost to the top of the bore. You choose gaskets of proper thickness to achieve your quench area target. Can a good machine shop stop the process just shy of hitting the number pad? Those machines are huge and it looks like they would want to make a complete pass over the block for uniformity in machining...

 

" Can a good machine shop stop the process just shy of hitting the number pad?"

Depends on which equipment they have.

 

unless it is blowing gaskets, don't deck it.
my quench is .040
.025 deck
.015 gasket

 

 

I would deck any performance motor I was building. It makes a difference. I deck the block, assemble the motor, measure how far down the pistons are in the bore then take that amount off again. It costs but to me it is worth it.
I also like a little thicker head gasket, to me .015 can't deform enough to take the irregularities out. I use a .040 and a zero deck.
Again stamp marks mean nothing to me.
I also agree that any one with a good decking equipment would NOT want to stop in the middle of a cut.

 

Flip side is I almost never deck a block. But the word "performance" does add a dimension to the discussion.

Never could draw a conclusive relationship between decking a non-leaking block and any type of performance figures. But I can't rule it out either. If there is some published testing that proves conclusively that decking is superior over other techniques for quench management... I would enjoy reading it (or some series of things you've done personally that are good reading). Not being confrontational here, just like to learn like everyone else. So if you have it, please post it.

"I also agree that any one with a good decking equipment would NOT want to stop in the middle of a cut. "

This is true... but that doesn't make it impossible. It can still be done if your milling machine allows it without affecting the consumables (i.e.- taking a chance on breaking a stone). A lot of NCRS guys do have it done this way when they find a willing & capable machine shop.

My relatively good machine allowed it... and I would do it on occasion when asked.

 

 

Here is some interesting reading... at least I thought it was...

Usher says engine builders who are not resurfacing blocks are missing a significant profit opportunity and exposing themselves to unnecessary risks of future head gasket failures. "You’re just turning away money if you’re not resurfacing blocks. If you’re boring and honing blocks, you should also be resurfacing them, too."

http://www.babcox.com/editorial/ar/eb30320.htm

 

Resurface yes, take a few thou off to make it flat by all means, but 0 deck on s street motor just might create more problems than it is worth.

I am not sold on this quench distance either I have never seen a dyno test on identical motors with the same compression ration and one motor has a 0.035-0.040" quench and the other 0.060" quench. How much HP can anyone say you get with smaller quench, without guessing.

I am not however doubting the detonation/pinging benefits of the closer quench but they would really only come into play at CR ratios not found on the street ( read race motor). I think if it was so important the major car manufacturers would have got the quench down under 0.060-0.080" and more like it has been since the Model T.

Again I am also not trying to be confrontational here either just food for thought

 

 

A tight quench makes the engine less octane sensitive. You can run cheaper gas without detonation. I am running pump gas with a stock 350/350 cam and 10.4 C/R using modern design heads and an 11:1 302 engine with the "30-30" cam and stock heads without any detonation because the quench is tight. Quench works for me.

Here is a quote from the Speed-O-Motive web site:

"If you are building an engine with steel rods, tight bearings, tight pistons, modest RPM and automatic transmission, a .035" quench is the minimum practical to run without engine damage. The closer the piston comes to the cylinder head at operating speed, the more turbulence is generated. Turbulence is the main means of reducing detonation. Unfortunately, the operating quench height varies in an engine as RPM and temperature change. If aluminum rods, loose pistons, (they rock and hit the head), and over 6000 RPM operation is anticipated, a static clearance of .055" could be required. A running quench height in excess of .060" will forfeit the benefits of the quench head design and can cause severe detonation. The suggested .035" static quench height is recommended as a good usable dimension for stock rod engines up to 6500 RPM. Above 6500 RPM rod selection becomes important. Since it is the close collision between the piston and the cylinder head that reduces the prospect of detonation, never add a shim or head gasket to lower compression on a quench head engine. If you have 10:1 with a proper quench and then add an extra .040" gasket to give 9.5:1 and .080" quench, you will create more ping at 9.5:1 than you had at 10:1. The suitable way to lower the compression is to use a dish piston. Dish (reverse combustion chamber), pistons are designed for maximum quench, (sometimes called squish), area. Having part of the combustion chamber in the piston improves the shape of the chamber and flame travel. High performance motors will see some detonation, which leads to preignition. Detonation occurs at five to ten degrees after top-dead-center. Preignition occurs before top-dead-center. Detonation damages your engine with impact loads and excessive heat. The excessive heat part of detonation is what causes preignition. Overheated combustion chamber parts start acting as glow plugs. Preignition induces extremely rapid combustion and welding temperatures melt down is only seconds away!"

Typical deck height for a factory deck is about .025" so if you add a .015" head gasket, you are right in the sweet spot without any machining and you get to keep the numbers. That is what those gaskets were made for. I might not want to run a blower with those gaskets but my 11:1 and 10.4 C/R normaly aspirated engines like them just fine.

-Mark.

 

Basically I am not doubting the pre-detonation/pinging benefits of a tight quench, my point is if you build a motor with aluminum heads and 11:1 CR that has a 55-60 thous. quench and runs fine at 35 degrees advance and you can go to 40 degrees if you wanted to, is there any benefit added benefit to decreasing the quench to 40 thous.?

The motor doesn't ping on pump gas, what am I going to gain by tightening up the quench ?

I'll need some documentation to back up any answers

 

I hang around a race shop. These are Nascar type cars specially built for a specific track. When talking to Roger, the own he swears that without Zero decking you are way down on horsepower. My block after surface cutting to true it up and then reasseble with new pistons was .032 down the hole. I had it decked this amount to bring the pistons flush with the block and then used O rings and a .040 gasket.
I am running up to 14.5 to 1 compression.

 

I beleive norvals right. WHy else do you think the General made the pistons on gen3 and gen4 engines sit out of the hole .010?
Here is an interesting article on quench
http://chevyhiperformance.com/techarticles/94138/

 

I couldn't agree more . (with Norval or anyone else who thinks quench is important) On my modified stuff I spent days fitting , cc'ing , and grinding to get the quench/surface area where I wanted it. I tried everthing from 16.7 comp. ratio on down . With everything right the best was 15.3-1. results: 741 hp. @9200 . Torque 472@7600. Oh by the way it's a 305. Another sign of a good chamber/piston configuration is it takes less timing.