351Mto400 Build Help
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Elder User
Joined: Feb 2000
Posts: 775
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From: Temperance,MI
351Mto400 Build Help
I pulled the old tired 351M out of the 77 tore it down now I have some questions on building it up,
The 400 crank is there a good place to find out for a decent price?
Pistons, Ohio or Badger witch ones will give more compression?
Oiling, before it was shut down for the last time it would build up to 50 cold drop to 15 at its most, will a high volume oil pump fix this? If not what about the moroso high pressure oil pump relief spring, it claims to bring oil pressure up to 100psi, isn't that too much?
Cams, roller how much does it cost to convert to one I know with my monte carlo having a older block roller cam swap is exspensive, im building this on a budget, I was looking at the 255DEH cam from comp cams, will I need to get the valve springs what do the stock springs flatten out at?
Water pumps how hot do these engines get? I know the 5.0s in trucks dont do well towing. would the high flow pump help out?
Is there anything else I should know about these engines and building it? This is my first engine build want it to last.
Thanks
Curtis
The 400 crank is there a good place to find out for a decent price?
Pistons, Ohio or Badger witch ones will give more compression?
Oiling, before it was shut down for the last time it would build up to 50 cold drop to 15 at its most, will a high volume oil pump fix this? If not what about the moroso high pressure oil pump relief spring, it claims to bring oil pressure up to 100psi, isn't that too much?
Cams, roller how much does it cost to convert to one I know with my monte carlo having a older block roller cam swap is exspensive, im building this on a budget, I was looking at the 255DEH cam from comp cams, will I need to get the valve springs what do the stock springs flatten out at?
Water pumps how hot do these engines get? I know the 5.0s in trucks dont do well towing. would the high flow pump help out?
Is there anything else I should know about these engines and building it? This is my first engine build want it to last.
Thanks
Curtis
New User
Joined: May 2003
Posts: 18
Likes: 0
351Mto400 Build Help
I am doing a similar rebuild and can tell you that it would be best to find a 400 core before you buy a crank kit. Mine was a $75 core charge.
You can look for Ohio, Dynagear or Badger pistons but they are not made in 9.5:1 anymore and are hard to find. Bushing the rods and using 351C pistons was the option I chose. With KB177 pistons and decking the block .040 my static compression should be around 10.5:1. This might be too much for a daily driver but there are many options available.
The cam I will be using is a Comp Cams 265DEH with all matching lifters, springs and retainers. This cam has a little more RPM range than a 255.
If you can add a performer intake, 4BBL and headers you should have added about 120-150 horsepower over a stock 351m.
Good luck!
You can look for Ohio, Dynagear or Badger pistons but they are not made in 9.5:1 anymore and are hard to find. Bushing the rods and using 351C pistons was the option I chose. With KB177 pistons and decking the block .040 my static compression should be around 10.5:1. This might be too much for a daily driver but there are many options available.
The cam I will be using is a Comp Cams 265DEH with all matching lifters, springs and retainers. This cam has a little more RPM range than a 255.
If you can add a performer intake, 4BBL and headers you should have added about 120-150 horsepower over a stock 351m.
Good luck!
Elder User
Joined: Jun 2003
Posts: 886
Likes: 1
From: Houston/Hope BC
351Mto400 Build Help
Check engine core supply shops. I paid $50.00 in Houston TX for a 10/10 grindable core.
I do not understand the infatuation with HV oil pumps. Build your engine to MFG specs and it is not required, IMHO. I get 25-30 PSI at idle on this fresh rebuild, at it is maxing out at 75 PSI (bypassing) by around 2500.
Go with a super-cooler radiator if you are doing any towing.
The stock springs bind at or about .500 lift. Throw them away.
I really really like the stainless valves, get hardened seats for the exaust side.
I am using stock cast pistons (around $8.00?), I have not problems running regular during daily driving, but have to switch to premium to tow.
What are you going to switch to?
If you want it to last, keep it simple.
Do a search here for Cams. I am running a 273 Cam Dynamics(?) RV cam, but I hear there are better choices. (Though I am not unhappy, by any means!).
Measure twice.... fit once!
I am assuming the rest is obvious, carb, headers, intake.
I do not understand the infatuation with HV oil pumps. Build your engine to MFG specs and it is not required, IMHO. I get 25-30 PSI at idle on this fresh rebuild, at it is maxing out at 75 PSI (bypassing) by around 2500.
Go with a super-cooler radiator if you are doing any towing.
The stock springs bind at or about .500 lift. Throw them away.
I really really like the stainless valves, get hardened seats for the exaust side.
I am using stock cast pistons (around $8.00?), I have not problems running regular during daily driving, but have to switch to premium to tow.
What are you going to switch to?
If you want it to last, keep it simple.
Do a search here for Cams. I am running a 273 Cam Dynamics(?) RV cam, but I hear there are better choices. (Though I am not unhappy, by any means!).
Measure twice.... fit once!
I am assuming the rest is obvious, carb, headers, intake.
Postmaster
Joined: Aug 2001
Posts: 4,270
Likes: 5
From: Delaware
351Mto400 Build Help
The high volume oil pump will do little for your oil pressure. It will help keep parts oiled when the pressure drops. Getting oil to all parts of the motor is what is important, not the oil pressure.
Elder User
Joined: Jun 2003
Posts: 886
Likes: 1
From: Houston/Hope BC
351Mto400 Build Help
Pumps make flow, restrictions make pressure. As your parts wear, restrictions diminish and pressure drops. Pressure is critical, without enough oil presssure metal to metal contact occurs. Theoretically, there is no journal to bearing contact. It is the oil pressure that prevents this.
IHMO, an HV pump is only useful in an engine whose tolerances have exceeded the ability of the stock pump to maintain adequate oil pressure.
Notice the name, it is called a High Volume pump, NOT a high-pressure pump.
IHMO, an HV pump is only useful in an engine whose tolerances have exceeded the ability of the stock pump to maintain adequate oil pressure.
Notice the name, it is called a High Volume pump, NOT a high-pressure pump.
Postmaster
Joined: Aug 2001
Posts: 4,270
Likes: 5
From: Delaware
351Mto400 Build Help
Tell me how much pressure does it take to prevent metal to metal contact?
Is it 100 lbs? Is it 80 lbs? Is it 60 lbs? Is it 40 lbs? is it 20 lbs? Is it 5 lbs? Is it 1 lb.
As long as there is enough volume the pressure will be enough.
True a new engine that is tight will require less volume to produce pressure, but in an engine that is known for oil problems at high RPMs a high volume oil pump is cheap insurance.
Is it 100 lbs? Is it 80 lbs? Is it 60 lbs? Is it 40 lbs? is it 20 lbs? Is it 5 lbs? Is it 1 lb.
As long as there is enough volume the pressure will be enough.
True a new engine that is tight will require less volume to produce pressure, but in an engine that is known for oil problems at high RPMs a high volume oil pump is cheap insurance.
Elder User
Joined: Jun 2003
Posts: 886
Likes: 1
From: Houston/Hope BC
351Mto400 Build Help
Ok this is rough, maybe out engineer moderator will clock in and check this math (PLEASE).
Say my engine makes 400 ft/lbs at the crank.
Work is spread over 8 cylinders. So that is 50 ft/lbs per cylinder. The crank length is 4" so it must be 3x or 150 lbs per cylinder.
The bearing diminsions are 2.3" by 1"? (diameter is in my book, not width) so we have 2.3 sq inches of load bearing area. (guesstimate)
So, 150 lbs acting over 2.3 sq in yields 65 PSI.
Say my engine makes 400 ft/lbs at the crank.
Work is spread over 8 cylinders. So that is 50 ft/lbs per cylinder. The crank length is 4" so it must be 3x or 150 lbs per cylinder.
The bearing diminsions are 2.3" by 1"? (diameter is in my book, not width) so we have 2.3 sq inches of load bearing area. (guesstimate)
So, 150 lbs acting over 2.3 sq in yields 65 PSI.
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Posting Guru
Joined: Aug 2000
Posts: 1,127
Likes: 3
From: (near) Denver USA
351Mto400 Build Help
Sorry, dude, but none of that math is even close. I'm not a moderator, but here's a few thoughts:
Calculating bearing pressure from net crankshaft torque would be an extremely complicated exercise. Torque is a measure of force (or energy) with angular momentum, and pressure is a measure of linear force divided by a fixed area. There's lots of calculus involved, if you want to get anywhere near a real answer.
In a 4-stroke engine, only half of the cylinders fire on each crankshaft revolution, so if each cylinder produced 50 ft lbs of net crankshaft torque, the total torque output would be only 200 ft lbs.
The force with which the piston pushes the crankshaft is borne by the crankshaft throw (where the conn rod bearing journal is located), and the throw length is 1/2 of the stroke. Maximum mechanical leverage occurs at 90 degrees ATDC on the power stroke, though the maximum force from combustion energy occurs much earlier (probably about 20-30 degrees ATDC).
The area of the bearing would be the circumference (pi x r) times the length, which would be 3.613 square inches, assuming a 2.3" diameter and 1.0" width.
Calculating bearing pressure from net crankshaft torque would be an extremely complicated exercise. Torque is a measure of force (or energy) with angular momentum, and pressure is a measure of linear force divided by a fixed area. There's lots of calculus involved, if you want to get anywhere near a real answer.
In a 4-stroke engine, only half of the cylinders fire on each crankshaft revolution, so if each cylinder produced 50 ft lbs of net crankshaft torque, the total torque output would be only 200 ft lbs.
The force with which the piston pushes the crankshaft is borne by the crankshaft throw (where the conn rod bearing journal is located), and the throw length is 1/2 of the stroke. Maximum mechanical leverage occurs at 90 degrees ATDC on the power stroke, though the maximum force from combustion energy occurs much earlier (probably about 20-30 degrees ATDC).
The area of the bearing would be the circumference (pi x r) times the length, which would be 3.613 square inches, assuming a 2.3" diameter and 1.0" width.
Last edited by bubbaf250; Aug 25, 2003 at 06:03 PM.
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Elder User
Joined: Jun 2003
Posts: 886
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From: Houston/Hope BC
351Mto400 Build Help
I am certain that I took an overly simplistic view of the problem.
I was trying to solve the problem by looking at one "instant" in time. When the crank is at maximum offset (4").
The bearing area I am assuming is the planar projection, or the area covered by the arc.
And yes it is two revolutions for each cylinder to fire, but its hard to dispute the work is divided over all 8 cylinders.
This is going to be a lot of fun! Should we start a betting pool? (For bragging rights only, of course! lol) I really would like to know.
I was trying to solve the problem by looking at one "instant" in time. When the crank is at maximum offset (4").
The bearing area I am assuming is the planar projection, or the area covered by the arc.
And yes it is two revolutions for each cylinder to fire, but its hard to dispute the work is divided over all 8 cylinders.
This is going to be a lot of fun! Should we start a betting pool? (For bragging rights only, of course! lol) I really would like to know.
Posting Guru
Joined: Aug 2000
Posts: 1,127
Likes: 3
From: (near) Denver USA
351Mto400 Build Help
The work is not divided over all 8 cylinders, unless you're looking at more than one revolution of the crankshaft, and that would not be one "instant" in which to calculate the pressure on one conn rod bearing.
Also, at BDC and TDC, most of the force applied to the bearing surface is produced by the momentum of the reciprocating mass (conn rod, wrist pin, and piston). That force increases in proportion to engine speed, so that's another factor in the equation.
Near the bottom of the power stroke, there is very little force still being produced by combustion, and at BDC (the point at which the crank is at maximum offset), the combustion force contributing to engine output is zero. Indeed, any residual combustion force after BDC on the power stroke is reducing the engine's net power output.
Also, at BDC and TDC, most of the force applied to the bearing surface is produced by the momentum of the reciprocating mass (conn rod, wrist pin, and piston). That force increases in proportion to engine speed, so that's another factor in the equation.
Near the bottom of the power stroke, there is very little force still being produced by combustion, and at BDC (the point at which the crank is at maximum offset), the combustion force contributing to engine output is zero. Indeed, any residual combustion force after BDC on the power stroke is reducing the engine's net power output.
Posting Guru
Joined: Aug 2002
Posts: 1,214
Likes: 2
From: Minneapolis, MN
351Mto400 Build Help
If you are trying to calculate the amount of pressure to maintain an oil film between the rod bearing and the crank you'll also have to take into consideration the molecular film properties of the oil as well as the effect of the increase in pressure due to the oil being forced toward the rod journal by centripital force. And once you calculate the area of the bearing you must allow that the top of the circle will carry the most load which diminishes to zero at 90° to the applied force.
Also, a 4" stroke will only have a 2" throw.
I agree with bubbaf250.
Too much calculus for me.
Also, a 4" stroke will only have a 2" throw.
I agree with bubbaf250.
Too much calculus for me.
Posting Guru
Joined: Aug 2000
Posts: 2,416
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From: PacNW
351Mto400 Build Help
I'm certainly no engineer and the thought of trying to calculate the minimum pressure along with oil 'film strength' to prevent metal to metal contact gives me a headache. I've always used the simple formula of 10 psi per 1000 RPM to set the minimum pressure for oiling systems.
Posting Guru
Joined: Aug 2000
Posts: 1,127
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From: (near) Denver USA
351Mto400 Build Help
Oh yeah, I was wrong about this:
Actually, if each cylinder produced only 50 ft lbs of crank torque, then the total output would only be 50 ft lbs of torque, unless all four of the cylinders fired at the same time. In that event, the torque produced would be cumulative (i.e., 50 x 4).
In reality, each cylinder that fires on a single crankshaft revolution provides all of the torque for its part of the revolution.
In a 4-stroke V8 engine, that happens four times per revolution, or every 90 degrees of crank rotation. In a 4-stroke 6-cylinder engine, it happens three times per revolution, or once every 120 degrees of crank rotation.
In a 4-stroke engine, only half of the cylinders fire on each crankshaft revolution, so if each cylinder produced 50 ft lbs of net crankshaft torque, the total torque output would be only 200 ft lbs.
In reality, each cylinder that fires on a single crankshaft revolution provides all of the torque for its part of the revolution.
In a 4-stroke V8 engine, that happens four times per revolution, or every 90 degrees of crank rotation. In a 4-stroke 6-cylinder engine, it happens three times per revolution, or once every 120 degrees of crank rotation.
Elder User
Joined: Jun 2003
Posts: 886
Likes: 1
From: Houston/Hope BC
351Mto400 Build Help
Curtis, sorry I/We got so off your original topic.
The 400 seems to be pretty much bullet-proof, provided that one is careful in the assembly/machine work. I have not had any heat issues with mine using all stock cooling, an HD clutch, and a super-cooler radiator. (This is with A/C in TX) A transmission cooler add-on is a great idea if you are towing anything. My headers make a lot of underhood heat and on a really hot day standing still it will try to vapor lock. A return line to the gas tank and an insulating spacer would take care of this, but I just try not to stop for now... lol. A fresh air box would be a nice addition also. Best of luck to you.
The 400 seems to be pretty much bullet-proof, provided that one is careful in the assembly/machine work. I have not had any heat issues with mine using all stock cooling, an HD clutch, and a super-cooler radiator. (This is with A/C in TX) A transmission cooler add-on is a great idea if you are towing anything. My headers make a lot of underhood heat and on a really hot day standing still it will try to vapor lock. A return line to the gas tank and an insulating spacer would take care of this, but I just try not to stop for now... lol. A fresh air box would be a nice addition also. Best of luck to you.
Posting Guru
Joined: Mar 2002
Posts: 2,070
Likes: 2
From: Boise, Idaho
351Mto400 Build Help
The clearances around the rod bearing has an effect on oil pressure. The spinning of the crank causes the oil to want to drain off; centrifugal force.
As I understand it, you want to keep the clearances in the rod bearings on the low side to slow down the tendency of the oil wanting to flow out of the space between the bearing and the journal. Good rod bolts, properly torqued, is a big help. They'll keep the big end of the rod from deforming.
Oil requires a very specific amount of room to work in. Too much clearance and it loses its ability to maintain its film strength. Not enough clearance and you'll get metal-to-metal contact and heat.
Tell your machinist that you'll use synthetic oil or semi-synthetic oil and ask him to machine the crank for tight clearances. Use regular 10w-30 synthetic Mobil1 motor oil (WalMart 5qt jugs are about $15). The synthetic oil can flow into the smaller clearances well and has superior film strength.
Check out Melling's web site for discussions about high volume oil pumps. They recommend them. They say there's no down-side.
Oh, and use a good oil filter, not a Fram. Use Motorcraft or Purolator PurOne or NAPA/Wix or Bosch or Mobil1.
As I understand it, you want to keep the clearances in the rod bearings on the low side to slow down the tendency of the oil wanting to flow out of the space between the bearing and the journal. Good rod bolts, properly torqued, is a big help. They'll keep the big end of the rod from deforming.
Oil requires a very specific amount of room to work in. Too much clearance and it loses its ability to maintain its film strength. Not enough clearance and you'll get metal-to-metal contact and heat.
Tell your machinist that you'll use synthetic oil or semi-synthetic oil and ask him to machine the crank for tight clearances. Use regular 10w-30 synthetic Mobil1 motor oil (WalMart 5qt jugs are about $15). The synthetic oil can flow into the smaller clearances well and has superior film strength.
Check out Melling's web site for discussions about high volume oil pumps. They recommend them. They say there's no down-side.
Oh, and use a good oil filter, not a Fram. Use Motorcraft or Purolator PurOne or NAPA/Wix or Bosch or Mobil1.
Last edited by pcmenten; Aug 28, 2003 at 11:59 PM.