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  #31 (permalink)  
Old 06-04-2009, 06:21 AM
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A net measured piston/head quench clearance of .038" to .055" has been shown to be effective. If you rpm the motor very high, you want to be on the big end of that range so the piston does not smack the head at rpm.
I built a 350 with .033" quench that did not smack the head with 7000rpm but.....your mileage may vary.

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Old 06-04-2009, 02:30 PM
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Thank you all for the information! Now, the hard part I'm realizing (and probably shouldn't be) is finding a head gasket that has the 4.155" bore and compressed thickness of .020 - 0.030". I checked on Summit but only came up with copper gaskets. Do you guys have any other suggestions on where I can look?
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Old 06-04-2009, 05:27 PM
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You won't find a 4.155" bore or find one that thin for a 400 in a conventional composition gasket. Fel-Pro sells 4.166", 4.190 and 4.200" bore x .039-.041 thick, Detroit Gasket(now ROL IIRC) sold a 4.190" that was my favorite(.039" thick), but don't know if it still exists, got my last pair NOS off of Ebay. Mr Gasket has a 4.150 x ??? if you want to go really tight on the bore size, not something I would risk though and I don't know if it has steam holes. I have punched them in before, though. Fel-pro also has a 4.165" MLS gasket, and there are probably more if you search. Maybe GM still sells a .028" thick for the 400.
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Old 06-04-2009, 05:34 PM
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Quote:
Originally Posted by F-BIRD'88
A net measured piston/head quench clearance of .038" to .055" has been shown to be effective. If you rpm the motor very high, you want to be on the big end of that range so the piston does not smack the head at rpm.
I built a 350 with .033" quench that did not smack the head with 7000rpm but.....your mileage may vary.
Like you said, it may vary. We've got a 383, cast crank, forged pistons at .033-.034" and at last freshen showed the chamber shape in the carbon on the piston wiped almost see thru, running it to 7500 rpm drag. I think we found our limit!!

Last edited by ericnova72; 06-04-2009 at 05:38 PM. Reason: spelling
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Old 06-04-2009, 05:56 PM
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So if I can't get the gasket I'm looking for, what's the next best thing? Should I go with a standard bore (4.125") gasket? or should I go with the larger gasket (over 4.155")? I'm worried about hot spots...

Is my application that unique? I don't get it...
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Old 06-04-2009, 06:07 PM
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alright, so I called summit and they recommended this:

Brand: Mr. Gasket
Product Line: Mr. Gasket Ultra-Seal Head Gaskets
Part Type: Head Gaskets
Part Number: MRG-5801
Bore (in): 4.190 in.
Bore (mm): 106.426mm
Gasket Material: Steel core laminate
Compressed Thickness (in): 0.038 in.
Compressed Volume (cc): 8.586cc
Lock Wire: No
Quantity: Sold as a pair.
Notes: With steam holes.

They said that you should be atleast 0.030" over your bore size (still don't understand why) and that a single steel core laminate would be sufficient for a non-race application. What do you guys think? Compressed thickness OK with the piston to deck clearance being 0.025"? Also, not sure what this will do with my compression ratio...
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Old 06-04-2009, 07:17 PM
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At .038" thick, it doesn't give you very good quench (062" total), but it is the best you can do without decking the block or going to copper or a custom Cometic. Quench is important enough to me that I would go the Cometic route, but you should be fine with the Mr Gasket if you are not up over 9.5-1 or so compression.

Gasket bore has to be at least block bore size and not overhanging into the bore, it can't handle that much heat to say the least. About .010" bigger than the bore is about a minimum for composition, MLS can run right at bore size.

The thicker the gasket, the lower your compression ratio.

Unless you go custom, there are only so many available gaskets for any given engine, and gasket thickness/piston deck height/quench all need to be planned out at the beginning of the build process and the block decked to be sure that everything comes out where you want it in the end at assembly. I realize this doesn't help you now, with an already assembled short block, but you are not the first guy to find this out. This is why engine builders charge what they do.
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Old 06-05-2009, 05:50 AM
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Compression Ratio

So if I go through the calculation with everything I've learned / know about my set up, it appears like this:


Enter Cylinder Bore Size 4.155"
Enter Piston Stroke Length 3.75"
Enter Head Gasket Bore Diameter 4.190"
Enter Compressed Head Gasket Thickness 0.038"
Enter Combustion Chamber Volume In CCs 64cc
Enter Piston Dome Volume In CCs Negative For Dished Pistons -18cc
Enter Piston Deck Clearance Negative If ABOVE Deck (Use '-') : 0.025"

Compression Ratio: 9.67:1
Displacement Volume: 96.14


So with this all known, and understanding that I have a less than ideal quench of 0.062", am I going to have a reliable engine (on pump fuel)? I guess what I'm saying is that I have a bone stock 350 and a somewhat stock 327 sitting in my garage, am I better off freshening one of them up? It'd be awesome to think I could build my own engine to achieve 400hp... but I need to be realistic. Thanks again for any input.
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  #39 (permalink)  
Old 06-05-2009, 06:10 AM
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Quote:
Originally Posted by manchildau65
understanding that I have a less than ideal quench of 0.062", am I going to have a reliable engine (on pump fuel)?
Yes.

There are hundreds of thousands of SBC's buzzing around w/similar CR and FAR worse quench clearance than 0.062". This doesn't make yours "right", but goes to show you that the SBC will tolerate quite a bit of deviation from "perfect". No, it's not "ideal", but IMO it should run on premium just fine.

Obviously, take the time to tune the carb and curve the distributor correctly.
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Old 06-05-2009, 11:06 AM
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What's your thoughts on the 400hp level?
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  #41 (permalink)  
Old 06-05-2009, 11:13 AM
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Quote:
Originally Posted by manchildau65
What's your thoughts on the 400hp level?
Achievable, with a cam that is chosen to fit the combo. Actually, should be very streetable at that level, with good torque.
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Old 06-30-2009, 01:53 PM
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So I've learned that I need to get a high torque starter, however, I've also seen that the 400 had different mounting configurations. I may have just answered my own question but wan't to verify that I need to look for a special starter for 400's only, correct?
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  #43 (permalink)  
Old 06-30-2009, 02:24 PM
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Quote:
Originally Posted by manchildau65
So I've learned that I need to get a high torque starter, however, I've also seen that the 400 had different mounting configurations. I may have just answered my own question but wan't to verify that I need to look for a special starter for 400's only, correct?
Match the starter to the diameter of the flexplate/flywheel. Small diameter uses a starter w/the holes across from one another. Big wheels get the staggered holes.

Make sure the engine is also drilled and tapped for whichever you plan to use- the 400 I have has both patterns in the block, IIRC. As does most or all V8 blocks. Some V6 90 degree blocks don't.
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  #44 (permalink)  
Old 06-30-2009, 02:47 PM
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......"They said that you should be atleast 0.030" over your bore size (still don't understand why)"

When the machine shop bores and hones the block, they add a chamfer at the top of the bore to aid in getting the rings to start into the bore when you assemble the motor. The actual bore size at the very top of the bore therefore, is larger than the rest of the bore. So if you use a head gasket with a diameter the same as the main part of the bore or very close to it, the gasket will overhang the chamfered part of the bore at the very top of the cylinder.
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Old 12-28-2009, 06:05 PM
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Timing

Hi guys, sorry it's been so long since my last post, but I'm excited to say that the engine/truck are coming togethor quite well. One final question for you all, what timing do you think I should set it at? I'll be running 93 octane with the cam and specs described within the first post. Thanks again for all of the input!
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