[RT]

I'm putting together a .030 over 454 with SpeedPro .95 domed pistons. The specs I've found online (not much noted on the box) say the dome is -13.80 cc. With the #1 piston installed, I'm getting a reading of about .012 below deck height on the piston.
My question is, for a street motor is it OK to leave the deck as is, or is it worth spending another $150.00 to have it decked to 0? I plan on using Edelbrock E street aluminum heads that are advertised at 110 cc rods and crank are stock.
Thanks,
Rich

 

[mfret1970]

What's your head gasket thickness? Add that number to your .012 in the hole number and that is your quench. .040-.050 is where you want to be.


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[RT]

The gaskets included with the kit I got from my machine shop (Kit#260-1009) has p/n 8180PT2 stamped into it. A quick search brought up .039 as the compressed thickness. I need to get a more exact reading on the piston/deck height, but staying with .012 for now, it seems that the total quench will be .012 + .039 or .051. According to your advice, mfret, it looks like I'd need to get a thinner gasket.
Rich

 

[bracketchev1221]

Make sure you rock the piston back and forth in the bore to see if you are high or low right now. I would not deck a block to zero, but if it has not been done, I would take a cleanup cut to the deck for better gasket sealing and to ensure the deck is square. That is usually about .003 cut. After that I would use what you have and put it together.

 

[Tom Mobley]

I get it about 9.7:1 as is, or close to 10:1 with 0.000 deck. What I'd do is check the deck on all 4 corners with the same rod and piston. if it's within a couple thou +/- I'd ask a shop to take 10 off the block. That'll get you a new gasket surface, tighten up the quench and get a little bump on the CR. Those Fel-Pro gaskets are good, run them.

 

[383ram]

I run those same Speed Pro pistons in my engine. Actually, I thought they were .110 domes. But anyhow, I basically zero decked my engine (I think it was only a thou or two in the hole when measured) and with a standared felpro gasket, which is what I think you have, I am at 8.9 to 1 on the calculated compression ratio with my measured 119 cc heads. If I remember right, Speed Pro specs those pistons at being .020 in the hole at the blueprint deck height.

Getting your quench total down is going to help with detonation, if your at .051 with deck height and gasket, i feel you have lost the quench. I cut mine down, putting the same piston and rod into each corner of the block and measuring. Then I took an average per side, thought about it long and hard and came up with what I truely wanted cut off--and I errored a little on the safe side having a thou or two clearance.

If it were me, I would cut it down or get a thin gasket--but the issue I have seen with thin metal gaskets is they really need two flat surfaces to seal right. Try and shoot for around .035-.040 total quench, that is good for a street engine, if you like being a little riskier you can go tighter, but I believe .030 is walking the line.

EDIT: Found my pics,

Here is the pic before I cut it--looks like I was at about .013" in the hole--and this was with a few though taken off so the honing plate would sit flat for machining---my original decks were out a bit, I think he took off about .003-.004 just to get a good surface:

And here it is after--I was at about .001 or less:

 

[RT]

Thanks for the replies, this is new ground for me.
383, did you make the fixture for holding the dial indicator? I need to have something like that to check mine b/c the magnetic base doesn't allow for bridging over the cylinder from both sides.
Rich

 

[Busted Knuckles]

Install pistons in the other 3 corners. If you're within a couple of thou's, pick a gasket that puts your quench where you want it.
If it's all over the place (like most are), you're better off having it decked to square everything up and even out your quench. I have my big blocks decked to 9.785, leaves piston .005 in the hole.

 

[66 chevelle 496BBC]

gm performance gaskets are .025. and good on alum. heads too.

jim

 

[MiketheSpike]

this is really good and informative . . . not to hi-jack the threat; but . . .
so, if I install a .020 metal gasket between my un-machined 400 sbc that has been used for drag racing by the previous owner and my un-machined vortec heads I'm due to have leakage problems?

 

[Tom Mobley]

not necessarily but it wouldn't be a surprise. surfaces need to be straight and clean.

 

[383ram]

Thanks for the replies, this is new ground for me.
383, did you make the fixture for holding the dial indicator? I need to have something like that to check mine b/c the magnetic base doesn't allow for bridging over the cylinder from both sides.
Rich

Rich, yes, I made that fixture. You can buy them too. I think its 3/4" square stock if I remember right. It was easy to make, and I just belt sanded the bottom to get it flat (you could use sand paper on a flat surface or a long file--but the belt sander is best). Just cut everything as square as you can before you weld it up. The set screw you see is just snug--it just needs to hold the indicator snuggly so it doesn't move. If you can find a thumb screw, it probably would work better.

Not as accurate, but if your magnetic stand and arms can be set firmly so they do not move, you can set your indicator to zero on the deck and turn the mag base so it swings ithe indiator over to the piston to see the difference. Don't pic up the base and put it back down, just turn it on the deck. The problem I have found with that is some cheaper stands don't lock the arms down enough and you can get some movement. It can be done, but you may have to check it several times. That become's a pain when checking all four corners.

And to me, I would rather cut the deck down to zero deck hight, but getting a gasket that is say around .020-.025" would work fine for your application if you didn't want to tear back apart or spend the extra cash--as long as its truely .012" in the hole.

 

[MiketheSpike]

Here's another noob question . . . Can deck height be measured with a straight edge and feeler gauges?

 

[Busted Knuckles]

Mike, you might be able to use a straightedge and feeler gauges to determine how far in the hole your pistons are, but deck height is calculated from crank centerline and will have to be measured as such to get a true reading.

 

[bracketchev1221]

Here's another noob question . . . Can deck height be measured with a straight edge and feeler gauges?

That can be used to see if the deck is square across the surface.

 

[ChevelleFan70]

this is really good and informative . . . not to hi-jack the threat; but . . .
so, if I install a .020 metal gasket between my un-machined 400 sbc that has been used for drag racing by the previous owner and my un-machined vortec heads I'm due to have leakage problems?

Mike, yes -- I had that very thing happen when I put my first aluminum heads on my 400. Heads were brand-new, block was stock (un-machined) and I used Cometic MLS head gaskets. I got a slow drip of water between the head and the block by #1. Composite head gaskets are more forgiving.


383ram -- I thought when measuring how far down the pistons are in the hole, aren't you supposed to try to measure more in the middle area of the piston (over the wrist pin) to eliminate piston rock from skewing the reading?

-Dave

 

[383ram]

383ram -- I thought when measuring how far down the pistons are in the hole, aren't you supposed to try to measure more in the middle area of the piston (over the wrist pin) to eliminate piston rock from skewing the reading?

-Dave

Sometimes with domed pistons, you have to just do what you can. As you can see in my pics, the dome and valve reliefs take up the middle area of the piston. I actually take multiple readings--everywhere from middle-ish area, to the edges and I also rock the piston. This way I can see what is there and going on and take a good average reading. But yes, closer to the middle the better for a straight up answer.

 

[ChevelleFan70]

Ahh, ok.. good point, I didn't notice those were domes when I first commented.

-Dave

 

[Philip]

this is really good and informative . . . not to hi-jack the threat; but . . .
so, if I install a .020 metal gasket between my un-machined 400 sbc that has been used for drag racing by the previous owner and my un-machined vortec heads I'm due to have leakage problems?

Thinnest gasket I was able to find for my 400sb was .039". My pistons are .010" in the hole after the deck was cut to use that gasket.

 

[RT]

Today, I checked all four corners using a fixture I made after the idea 383 had in his photos.
Here's what I did; I Set #1 piston at TDC and zeroed the dial indicator at the center of the .095 dome. Then I kept that setting and moved the indicator to the deck surface and found the result to be that the deck is .023 above the piston top (not the dome) on that #1 piston (Indicator reading of minus .072 minus the .095 dome height=.023). Then I checked the dome height at cylinders #7,8 and 2 using the same piston/rod assy. Here's what I got:

#7- .002 more than #1 (which places the deck .002 lower than #1, or .021 in the hole)

#8- .000 (same as #1, .023 in the hole)

#2- .004 more than #1 (.019 in the hole)

So, it looks like from today's more careful checks, my pistons are from .023 to .019 below deck height.

I hope I explained this clearly, but the main points are that the pistons are further down than I thought and the deck surface varies by .004 relative to the crank.
Should I have the deck cut?
Thanks,
Rich