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Old 05-27-2010, 12:10 PM
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Best Combustion Chamber for 406 SBC

Iím building a long rod (5.7Ē) 406 SBC with the rods clearanced to allow the use of a flat-tappet cam. Iím using Comp Camís XE262H with .462/.469 lift and 218/224 degrees duration at 0.050Ē lift, along with 1.5 ratio roller rockers. The flat-top, four relief cut pistons are 0.025Ē down in the cylinders at TDC. Iím guessing the compression is somewhere between 9.5 and 9.8. Using a 0.41Ē thick head gasket, the quench area is 0.066Ē. After reading several articles about the effect of a zero deck clearance on quench, I donít know if what I have is good or bad. I want to use cast iron heads and be able to drive on the streets and cruise the highways using pump gas without octane boosters. Given this goal, is it better to us heads with combustion chamber of 64cc, 72cc, or 76cc? Or, do I start over and cut 0.025 off the block deck to achieve zero deck clearance? Are there piston to valve clearance issues with zero deck?
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Old 05-27-2010, 01:10 PM
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Last edited by cobalt327; 05-27-2010 at 04:15 PM. Reason: I had used the specs of a 350, not a 400 (gaskets, CR calculations, etc.).
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Old 05-27-2010, 01:25 PM
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While there are those on this forum who feel that a very tight squish is unnecessary, I am in the opposite camp. Engine builders such as David Vizard and John Lingenfelter have spoken of the advantages of a very tight squish (0.035" to 0.045" on a SBC) and Vizard has said that he picked up more power the tighter he went on the squish.

Thing is, you need a piston to mate up with the underside of the head to form a squish (sort of like dropping a book on a desk for those of you who are new to squish. Just as air is forced out from between the book and the desk, fuel/air mixture is forced out from between the underside of the cylinder head and the crown of the piston as it ascends on the compression stroke. This jetting of the mixture across the chamber homogenizes the mixture and creates turbulence in the mixture for a more complete burn while dampening the tendency of the mixture to detonate).

Thing is, you need a large flat area on the piston crown to accomplish this. Pistons with a crater on the crown will not work, as there is insufficient material around the perimeter of the piston to produce a squish against the cylinder head. Shown are two examples of crowns that would not produce much squish.

Here is a link to an 18cc dish piston from Keith Black that has an excellent large squish pad. See the right side of the photo.
http://www.kb-silvolite.com/test/kb_...tails&P_id=234
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Old 05-27-2010, 01:41 PM
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You will have to pay attention to gasket bore size when looking for head gaskets as many are too small for the 400's 4.125+" bore. The first two that come to mind is mentioned in Cobalt's post, the Fel-Pro 1094 is only 4.100" and won't work, as is the Mr Gasket 1130. I'm not sure about the GM #10105117 but don't recall it being on my list, and 400's are my favorite engine to build.

I don't think there is a thin 400 gasket unless you go to Flat-Out or Cometic($$$ race stuff).

I end up just zero decking all 400's and using a commonly available head gasket. It kills three birds with one stone - you get good quench with a more inexpensive common gasket, the block deck is now perfectly flat for good sealing, and every manufacturer carrys a gasket that will fit the bill without going to custom or copper.
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Old 05-27-2010, 04:03 PM
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Zero deck the block and use KB168 pistons and 64cc vortec heads or 64cc Brodix IK-180 heads on your 400 with the xe262cam. The KB pistons have a -22cc D cup dish.

If you want to use a 70-72cc head use a KB147 -18cc cup piston and zero deck

if you want to use a flat top piston, have the block decked for a .016" piston deck clearance, use a 75cc AFR 195 eliminator head #1036 and felpro .039" 400 gasket.

The cr will be 9.8:1 in all examples.
It will "cruise" just like you want. Ya the details matter.

Safe but effective quench clearance is .038" to .055" net with the gasket.
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Old 05-28-2010, 08:21 PM
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Decking Block to Improve Quench

Thanks all for responding and giving me an education on the importance of having the right quench area. I like F-Bird'88 recommendation to cut the deck to 0.016" using the flat-top pistons, and use heads with a 72cc combustion chamber. Especially since I might have an opportunity to get a pair of Iron Eagle Platinum heads at a reasonable price. These heads have 200cc intake runners, 72cc combustion chambers and 2.20/1.60 intake/exhaust valves. I'm thinking they will work well on my highway cruising 406 powered Impala.
I do have another question about taking the deck down to 0.016" Why not cut the deck to 0.002" and use the 0.038" Mr. Gasket Ultra Seal gasket? This would put the quench at the target 0.040", wouldn't it?
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Old 05-29-2010, 01:35 PM
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Quote:
Originally Posted by SeniorRodder
I do have another question about taking the deck down to 0.016" Why not cut the deck to 0.002" and use the 0.038" Mr. Gasket Ultra Seal gasket? This would put the quench at the target 0.040", wouldn't it?
Yes it would. You can do it any of several ways, as long as you measure from the flat crown of the piston to the flat underside of the head with the head gasket thickness included.
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Old 05-30-2010, 09:44 PM
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Wait a minute. I thought I understood, but after re-reading the posts (including my reply), there are still some voids in my understanding that I hope you can fill. I feel confident that I now understand the importance of getting the quench area right so my motor is less octane sensitive. I have flat-top pistons with 4 eyebrow relief cuts. I'm not sure of the manufacturer. They were part of a 406 kit I purchased from Speed-O-Motive about seven years ago and am just now using. These pistons are 0.025" down the cylinder at TDC. I now know that I need to have the block decked so that with the gasket installed (0.038" Mr. Gasket Ultra Seal) the quench is between 0.035"-0.055".

Also, in an earlier reply, F-Bird'88 recommended decking the block 0.016", then using a 0.039" gasket, and AFR 1036 heads if using flat-top pistons. These AFR heads are aluminum and I want to use cast iron heads. I'm hoping RHS or Dart heads with 190cc-200cc intake runners and 72cc or 76cc combustion chambers will work. I've been reading several other posts about 406 builds and the prevailing wisdom appears to be zero deck and KB147 pistons. I'm sure these must be great pistons since that come so highly recommended, but can't my "no-name" flat-tops work? Is the recommendation to deck the block to 0.016" with using flat-tops to keep the compression ratio in a reasonable range, or are there piston to valve clearance issues? I don't mean to belabor the issue and I really appreciate you sharing your time and knowledge. I'm just trying to understand.
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Old 05-30-2010, 09:56 PM
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I think the 0.016" deck was just so the CR would be 9.8:1 like the other examples he used- not that there was any special need for there to be that deck measurement.

I see no good reason your "no-name" pistons wouldn't work for your application, as long as you're not running a blower or a big nitrous hit or something stressful to the pistons like that. In a NA street performance engine build, they'll be fine, IMHO.

Just keep the quench as close to =/> 0.040" as is practical and it doesn't especially matter if that is w/the piston some amount down the hole w/a thinner head gasket or a zero deck w/a thicker gasket.

The valve to piston clearance should be verified when the engine is mocked up, it's not a good idea to figure this "on paper", there are manufacturing tolerance variations that can stack up against you if you trust them w/o actually measuring.
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Old 05-30-2010, 09:59 PM
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you can enter the numbers in this online cr calc. and juggle it for yourself.
You do not want excessive compression ratio for trouble free cruising on pump gas.. Ya it matters.

http://www.wheelspin.net/calc/calc2.html

the typical head gasket for a 400sbc is typically 4.20" by .039 or .041
flat top pistons typically have a valve relief volume of -5 to -7cc

keep the cr under 10:1 for goof proof cruisng .

Under 10"1 will run on any bodys preminum pump gas.

Pushing the envelope with over 10:1 requires high quality decent unleaded preminum 92 minimum. 93 or 94 best.

The afr heads are bolt on goof proof and make big power.

ya they cost a bit more.

Last edited by F-BIRD'88; 05-30-2010 at 10:07 PM.
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