Is decking worth the money

[Alan Roehrich]

I guess I'll play the devil's advocate here. There is NO way you will be able to tell the difference by decking .010" off of a low HP engine. As long as the deck is in decent condition sealing wise.

And I disagree. Taking the time to do blueprint level work is what makes engines run well and last longer. All those "little details" that supposedly "don't make a difference" tend to add up.

[MadBill]

Anyone have experience on deck accuracy/height of Dart SHP blocks? (specifically SBF, but I expect they apply the same tolerances to all)

My machine shopped checked out my SBC SHP block it was pretty good. Maybe .001"-.002" going by memory so we went with it. My piston were .002" above the deck so I did not want to take anything off we did not have to. Serial number is around 400 so a first year block if that means anything.

Thanks TA.
Don't have all the parts on hand yet to verify numbers, but depending on which rods we go with a nominal 8.206" deck will leave the pistons either 0.029" out of the holes or 0.021" down . Appears either thick or really thin gaskets will be needed to avoid the need for decking...

[robert1]

I guess I'll play the devil's advocate here. There is NO way you will be able to tell the difference by decking .010" off of a low HP engine. As long as the deck is in decent condition sealing wise.

And I disagree. Taking the time to do blueprint level work is what makes engines run well and last longer. All those "little details" that supposedly "don't make a difference" tend to add up.

He's adjusting the deck with gasket thickness. He's not blue printing the block. There's no way it could make 10 HP more from this. Is decking a good idea, yes, will he see a performance benefit at this level I still say no. I'm redoing an LS1 for myself right now and I'm not going to deck it. How in the hell do all of these motors even run from the factory with the blocks machined so poorly.

[roadrunner]

I haven't read the whole 3 pages but was thinking that if the block was bored/honed with a torque plate in place then whatever type of headgasket the borer used will give a cylinder shape that is closer to round, going to a shim gasket might pull the cylinders out of shape if a felpro type of gasket was used during machining (and vice-versa).

[340king]

One final thought on this discussion of decking and that is the chamfer at the bolt holes. It is probably not quite as important on a SBC, but on SB Mopar it is very important to redo the chamfer at the bolt holes to ensure proper head gasket torque is achieved. Otherwise the deck pulls up with the threads and causes a slight high spot that allows the head to bridge from hole to hole. This reduces the gasket clamping force and hence reduces the sealing. It is just one more thing to check when you get the block back. Good luck!

[Alan Roehrich]

I guess I'll play the devil's advocate here. There is NO way you will be able to tell the difference by decking .010" off of a low HP engine. As long as the deck is in decent condition sealing wise.

And I disagree. Taking the time to do blueprint level work is what makes engines run well and last longer. All those "little details" that supposedly "don't make a difference" tend to add up.

He's adjusting the deck with gasket thickness. He's not blue printing the block. There's no way it could make 10 HP more from this. Is decking a good idea, yes, will he see a performance benefit at this level I still say no. I'm redoing an LS1 for myself right now and I'm not going to deck it. How in the hell do all of these motors even run from the factory with the blocks machined so poorly.

Were he not looking for performance, he probably wouldn't have started another thread looking for better heads and opinions on a camshaft. He was, and may still be, considering using a stroker kit to build a 383 instead of a 355. If he sets the deck clearance correctly, as suggested by several, odds are he will see a real increase in performance, and he'll probably be able to run more timing despite having more compression, as the correct quench distance will help deal with poor quality lake gas in a heavy boat.

[wyrmrider]

use the gasket style you are going to run when you use the torqueplate
especially felpro o ring style
and studs if you are going to run studs, the correct length studs that you are going to run
good point on the mopars 340king, check em all

[MT Jeff]

Thanks for all the responses. I went to the machine shop and told them to deck the block. On a side note i'm changing the heads out for some Dart iron eagle s/s 10024360 heads. It's only money Now it has me rethinking the camshaft selection.

[wyrmrider]

post up darts head flows

[rally]

I had my 69 396 block decked a few years ago. I had them clean it up enough to square the block on both top banks.

[Dan Timberlake]

I'm building a new engine for my boat, it is .030 over 350 sbc with 76cc heads. It is at machine shop now. I'm using a 1.56 comp height speed pro flat top piston in an uncut block which should put it at .025 below deck. If i used a .028 GM gasket it should put the quench (squish) clearence at .053. The machine shop gets $150 to deck the block. Would this be worth it on a 9:1 or less engine? I could get is closer with a shim gasket but I really don't want to retorque it in the boat. BTW it is a closed cooling sytem not raw water cooled. I guess what i'm asking is it worth it for .010"

Are those quench/squish dimensions based on 100% parts measurements? i think there must have been SOME variation in the deck at the block corners.
Stock rods? Depending on the rebuild history of the con rods you may find their lengths vary nearly 0.010".
Can't speak for the crank stroke variation potential.
I'd >>expect<< the piston heights to be within a thou or 2, but would reserve comment (or making chips) until all 8 were measured.
If by chance machine work is done based on the short combo installed on the short stroke journal then there will be some tallmen in the crowd elsewhere.

I would make some effort to keep actual squish < 0.045" for the detonation resistance

[cpmotors]

Please consider using Fel-pro's #1094 shims at .015" thickness. I've used Indianhead, Krylon aluminum spray paint and also dauber brush and spray-on Copper-Cote to seal them fine through the years.

And I strongly recommend using a fine-cut triangle file to smooth both the heads and the decks of the block.

Just work slowly/easy going from bolt-hole to bolt-hole while watching the file clean/cut the surfaces smooth.

NOW, this is a feelie/touchy deal so go easy. Use WD-40 as a cleaning solvent while doing this.

I've done this for years everytime that I rebuilt a hopped up stock engine.

Now if you have the $Bucks to resurface the heads and decks, then by all means do it, but I never seemed to have the extra cash.

pdq67

Fel Pro 1094 is a rubber coated steel shim gasket now, no need to spray with anything.

[PackardV8]

I'm redoing an LS1 for myself right now and I'm not going to deck it. How in the hell do all of these motors even run from the factory with the blocks machined so poorly.

FWIW, twenty-first-century factory builds are better than what we used to call "blueprinted." The further back you go in time, the worse the Ford/Chevy V8s were as far as material quality, factory balance and dimensional controls. Surprisingly the smaller guys, Mopar, Studebaker, Packard, had better dimensional controls, as they didn't have to move the line so fast and/or crank out so many units.

I remember an apocryphal story about Chevrolet engineers having to tighten the tolerances on the SBC deck height. They gave the production line an allowable deck height range. To move the line as fast as possible, the guys there set to the max height, so as to have to remove as little iron as possible. This meant that most engines were coming through at the lower end of the allowable compression ratio range and thus making less than advertised horsepower.

Back in the day, making more horsepower, making it smoother, more fuel efficient by optimizing tolerances and materials was not difficult, because the OEM build was so crude. The 1970s-early 80s were some of the worst. Today's engineering and builds have gotten all the easy out of it; they don't leave much room for improvement if it still has to pass emissions and maintain the warranty.

[MadBill]

That story's not apocryphal Jack. When I worked on emissions calibrations in the early eighties, I heard it from a senior GM engineer and later had it confirmed by the Flint Engine Plant Manager. Test engines would always be built to the high tolerance limit compression ratio for knock testing, etc., but somewhere along the line it was noticed that production numbers never came close. Studying the plant data, they realized the line was maintaining way tighter tolerances then what they were given and so naturally enough they had focused on the deliverable goal of putting out the most in-spec engines per shift. (At its peak, the plant churned out 5,000 SBCs per day.) After that, the specs were narrowed considerably.

As far as improving tolerances, during the 7 years I managed the Players/GM Motorsports Series for GM of Canada (showroom stock Camaros and Firebirds) from the mid-eighties on, we went from building and dynoing over 200 units in order to select ~ 75 as close as possible to equal (+/- 3 HP) for the sealed engine program to building a dozen or so spares and discarding the few that were not +/- 1 HP.

[robert1]

My point is if the deck is good enough to seal and the builder sets the height via gaskets there will not be a measureable performance gain from decking. He is having this one decked so it's a moot point now. The .040 minimum quench is constantly quoted here. I just redid a 2006 5.4 Ford engine with .120 quench.