351m redo
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Senior User
Joined: Mar 2001
Posts: 296
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From: Maryland
351m redo
Ok, I will take apart everything and check all clearance with Plastic guage.
I still don't understand why my combination will not work. I used the stock pistons. Printed on the box was:
Badger Pistons P745-30 (.30 over)
Cyl. Clearance .0015 At 0.93 up from the bottom. Cyl Bore 4.0
I used the 58.4cc Aussie heads. I searched through this forum and there are some related threads saying the aussie heads should bolt right on. I used the off the offshelf Felpro eng gasket set. The only thing I did to the heads was to rebuilt them and have them shaved just enough to make sure they were worped.
I did a compression check with and got 170lbs, is this too high? It looks to me that I should get a set of stock heads and forget about these Aussie heads.
Thanks Art
I still don't understand why my combination will not work. I used the stock pistons. Printed on the box was:
Badger Pistons P745-30 (.30 over)
Cyl. Clearance .0015 At 0.93 up from the bottom. Cyl Bore 4.0
I used the 58.4cc Aussie heads. I searched through this forum and there are some related threads saying the aussie heads should bolt right on. I used the off the offshelf Felpro eng gasket set. The only thing I did to the heads was to rebuilt them and have them shaved just enough to make sure they were worped.
I did a compression check with and got 170lbs, is this too high? It looks to me that I should get a set of stock heads and forget about these Aussie heads.
Thanks Art
Elder User
Joined: Feb 2001
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From: Porterfield
351m redo
You Need Zero to .010 Deck Clearance for the Aussie heads to work properly.. if it's more then that then you get turbulence in the Squish area and that heats up the long back side of the D shape combustion chamber and that causes your ping .....
But in making the deck clearance Zero to .010 with stock pistons your compression ratio will be 10.5 to 1 or better .... you need special order D dished pistons to help bring the compression down to 9.0 to 9.5 to 1 ......
But if you don't mind running the best premium gas you can find and add a little Octane booster to it then you could get away with the stock pistons and Aussie head combo you got there ....
But first thing you have to do is Check your bearings ........Worry about the rest later ....
But in making the deck clearance Zero to .010 with stock pistons your compression ratio will be 10.5 to 1 or better .... you need special order D dished pistons to help bring the compression down to 9.0 to 9.5 to 1 ......
But if you don't mind running the best premium gas you can find and add a little Octane booster to it then you could get away with the stock pistons and Aussie head combo you got there ....
But first thing you have to do is Check your bearings ........Worry about the rest later ....
Posting Guru
Joined: Jun 2002
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351m redo
Deck clearance on a 400 is .057" vs 351M at .017", with a .040" gasket the 351M has .057" piston to head clearance (not deck clearance).
.060" is the absolute maximum for any quench benefits.
See, http://www.speedomotive.com/Building%20Tips.htm
Because a 351 has a smaller displacement, compression is 9.75:1.
IF it were a 400, compression would be 10.1:1 with .057" deck clearance and a 58.4cc chamber. By the time the deck clearance was reduced enough for quench benefits like .017", compression would be 11:1 and too high for pump gas.
.060" is the absolute maximum for any quench benefits.
See, http://www.speedomotive.com/Building%20Tips.htm
Because a 351 has a smaller displacement, compression is 9.75:1.
IF it were a 400, compression would be 10.1:1 with .057" deck clearance and a 58.4cc chamber. By the time the deck clearance was reduced enough for quench benefits like .017", compression would be 11:1 and too high for pump gas.
Last edited by Brian S; Jul 7, 2003 at 07:10 PM.
Elder User
Joined: Jun 2003
Posts: 886
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From: Houston/Hope BC
351m redo
Art, No one here can answer that question for you because we do not have reliable numbers. I am coming up with 9.6 to 1. This, I believe is the LOWEST compression ratio you could have. Are the pistons dished? No? You just shot up to 11.2 to 1. This is a way out there, but did you have regular gas still in your tank from before the rebuild? Did you put in new fresh gas from a major after dumping the old crap into the family car? I am assuming that you checked the static timing to see that the damner was at least close. Point distributor at #1 plug wire and you should be damn close to 12 BTDC on the pointer.
There ain't a lot left after that. I don't know about all this quench area and hot spot stuff these other guys know, but I do know, if its that damn finicky, I do not need to be working on it. I do know that I am totally happy with my stock (but highly worked over) heads and cheap cast pistons and running good on regular gas at modest compression ratios. Best wishes you get this sorted out.
There ain't a lot left after that. I don't know about all this quench area and hot spot stuff these other guys know, but I do know, if its that damn finicky, I do not need to be working on it. I do know that I am totally happy with my stock (but highly worked over) heads and cheap cast pistons and running good on regular gas at modest compression ratios. Best wishes you get this sorted out.
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Joined: Jun 2002
Posts: 1,099
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351m redo
Use the on line KB compression calculater, http://www.kb-silvolite.com/calc.phtml
and enter these estimated numbers for a stock 351M. Recalculate with your figures to estimate new compression rates.
Cylinder Head Volume (cc) - 78cc stock
Piston Head Volume (cc) - 13cc stock
Gasket Thickness (in.) - .040" stock
Gasket Bore (in.) - 4.100" stock
Cylinder Bore Diameter (in.) - 4.0 stock
Deck Clearance (in.) - .017" stock
Stroke (in.) - 3.50" stock
As previously mentioned, figure out your own compression ratio the long way to double check the online calculators.
https://www.ford-trucks.com/articles...ompression.php
and enter these estimated numbers for a stock 351M. Recalculate with your figures to estimate new compression rates.
Cylinder Head Volume (cc) - 78cc stock
Piston Head Volume (cc) - 13cc stock
Gasket Thickness (in.) - .040" stock
Gasket Bore (in.) - 4.100" stock
Cylinder Bore Diameter (in.) - 4.0 stock
Deck Clearance (in.) - .017" stock
Stroke (in.) - 3.50" stock
As previously mentioned, figure out your own compression ratio the long way to double check the online calculators.
https://www.ford-trucks.com/articles...ompression.php
Last edited by Brian S; Jul 8, 2003 at 12:28 AM.
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Thread Starter
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Senior User
Joined: Mar 2001
Posts: 296
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From: Maryland
351m redo
I used the KB Calulator and came up with a CR of 9.7, looks like hightest for me.
I used the following info:
Cylinder Head Volume (cc) - 58.4cc Aussie Heads
Piston Head Volume (cc) - 13cc stock
Gasket Thickness (in.) - .040" stock
Gasket Bore (in.) - 4.100" stock
Cylinder Bore Diameter (in.) - 4.0 stock
Deck Clearance (in.) - .017" stock
Stroke (in.) - 3.50" stock
The Pistons were listed and they are Silverlite Part # 1167,
OE assy # D5AZ6108A
At this point I am going to leave it alone. As shazam said I need to fix my oil problem first. But I will be considering removing the heads and looking for stock one's. Thanks for all the help. Time to get dirty. I will keep you guys up dated.
I used the following info:
Cylinder Head Volume (cc) - 58.4cc Aussie Heads
Piston Head Volume (cc) - 13cc stock
Gasket Thickness (in.) - .040" stock
Gasket Bore (in.) - 4.100" stock
Cylinder Bore Diameter (in.) - 4.0 stock
Deck Clearance (in.) - .017" stock
Stroke (in.) - 3.50" stock
The Pistons were listed and they are Silverlite Part # 1167,
OE assy # D5AZ6108A
At this point I am going to leave it alone. As shazam said I need to fix my oil problem first. But I will be considering removing the heads and looking for stock one's. Thanks for all the help. Time to get dirty. I will keep you guys up dated.
Elder User
Joined: Jun 2003
Posts: 886
Likes: 1
From: Houston/Hope BC
351m redo
you are over 9.7 if you used those numbers, you forgot you .030 overbore, you did mill the heads, so you are somewhere under the 58.4 cc. Is that gasket thickness compressed or out of the box? GL again.
New User
Joined: Jul 2003
Posts: 13
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351m redo
Originally posted by shazam
I once had a bad set of Lifter in one of my motors , they where for a Windsor and it would let oil be pumped to the top of the motor all the time . The little oil hole never came out of the oil groove.. It would pump the valve covers full in minutes of just idling and never had really good oil pressure from the get go..
Installed a different set of lifter that would shut the oil off when the valves where in the closed position and I gained 40 Psi in oil pressure..
Rule of thumb... 10 Psi for every 1000 Rpm's your motor is turning.
sitting at idle only need 7 Psi.. turning 3500 Rpm's need 35 psi to keep things well lubed ...
I once had a bad set of Lifter in one of my motors , they where for a Windsor and it would let oil be pumped to the top of the motor all the time . The little oil hole never came out of the oil groove.. It would pump the valve covers full in minutes of just idling and never had really good oil pressure from the get go..
Installed a different set of lifter that would shut the oil off when the valves where in the closed position and I gained 40 Psi in oil pressure..
Rule of thumb... 10 Psi for every 1000 Rpm's your motor is turning.
sitting at idle only need 7 Psi.. turning 3500 Rpm's need 35 psi to keep things well lubed ...
Sorry to hyjack the post.
Elder User
Joined: Feb 2001
Posts: 829
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From: Porterfield
351m redo
NO Blow by is usally caused by bad rings seal.... More then likely you'll have to have it honed and install a new set of rings at the very least ....... And at the worst case have it bored .010 and get new pistons and rings ...
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