Hardware
More Turbo
Joined: Nov 2015
Posts: 701
Likes: 109
A higher Static Compression Ratio (SCR) makes the engine more thermally efficient but it is the Dynamic Compression Ratio (DCR) that determines the minimum fuel octane requirement to prevent detonation.
The DCR is based on the SCR and the intake valve closing point ABDC. The DCR is also affected by elevation.
If you have a short duration cam that closes the intake valve very early then the SCR must be low enough for a DCR that will allow the use of the desired fuel octane.
The larger the camshaft with later intake valve closing point the higher the SCR can be.
The Ford 300 six works within a DCR range of 7.0 to 7.5 using 87 to 91 octane pump gas near sea level.
The DCR is based on the SCR and the intake valve closing point ABDC. The DCR is also affected by elevation.
If you have a short duration cam that closes the intake valve very early then the SCR must be low enough for a DCR that will allow the use of the desired fuel octane.
The larger the camshaft with later intake valve closing point the higher the SCR can be.
The Ford 300 six works within a DCR range of 7.0 to 7.5 using 87 to 91 octane pump gas near sea level.
Thread Starter
|
Cargo Master
Joined: Jan 2019
Posts: 3,369
Likes: 16
From: Caraway, AR
Fascinating stuff, would love to know more. Got any recommended reading on the topic? Whats the difference between static and dynamic and how do you calculate them? By thermally efficient do you mean it runs cooler or are we talking about combustion? Is a high as possible compression ratio best or is the ratio dialed in for whichever fuel is being burned for max efficiency? Also, does air-fuel affect compression and is there a relationship between total volume of air and fuel and combustion? I was thinking there about super chargers and adding more fuel plus compressed air.
More Turbo
Joined: Nov 2015
Posts: 701
Likes: 109
You can Google "dynamic compression ratio" to find more on subject.
Here is one of the better calculators. Use the actual intake valve closing point calculated using the .006" lobe lift advertised duration.
https://uempistons.com/p-27-compress...alculator.html
Thermal efficiency due to the static compression ratio is about how much work is being extracted from the combustion process in terms of the expansion rate.
Example: The combustion process does more work expanding 10:1 than it would expanding 9:1
In an effort to maximize engine power you look at the chosen camshaft specs and make the SCR as high as possible to get the maximum DCR for the fuel octane you want to use.
Another factor that will give you margin with the fuel octane is the amount of "Quench".
The closer the piston top is to the head surface at TDC the more "Quench" or cooling there is on the air/fuel mixture trapped between the head and piston surface.
As the fuel mixture is squeezed out from the quench area it causes turbulence which also reduces the chance for detonation.
We try to get the piston top even with top of the block deck (Zero deck clearance) so the quench distance is the thickness of the head gasket typically around .040"
The job is to have the piston at zero deck with the correct amount of piston dish volume and combustion chamber volume to get the SCR that you need.
This is all part of planning a well performing engine.
Turbocharging and supercharging is another large topic.
Here is one of the better calculators. Use the actual intake valve closing point calculated using the .006" lobe lift advertised duration.
https://uempistons.com/p-27-compress...alculator.html
Thermal efficiency due to the static compression ratio is about how much work is being extracted from the combustion process in terms of the expansion rate.
Example: The combustion process does more work expanding 10:1 than it would expanding 9:1
In an effort to maximize engine power you look at the chosen camshaft specs and make the SCR as high as possible to get the maximum DCR for the fuel octane you want to use.
Another factor that will give you margin with the fuel octane is the amount of "Quench".
The closer the piston top is to the head surface at TDC the more "Quench" or cooling there is on the air/fuel mixture trapped between the head and piston surface.
As the fuel mixture is squeezed out from the quench area it causes turbulence which also reduces the chance for detonation.
We try to get the piston top even with top of the block deck (Zero deck clearance) so the quench distance is the thickness of the head gasket typically around .040"
The job is to have the piston at zero deck with the correct amount of piston dish volume and combustion chamber volume to get the SCR that you need.
This is all part of planning a well performing engine.
Turbocharging and supercharging is another large topic.
Thread Starter
|
Cargo Master
Joined: Jan 2019
Posts: 3,369
Likes: 16
From: Caraway, AR
Is there any way to identify my engines internals by looking from the bottom? Getting ready to put the pan back on, but before I do I was curious if I would be able to learn anymore about this engine while I have it open.
Thread Starter
|
Cargo Master
Joined: Jan 2019
Posts: 3,369
Likes: 16
From: Caraway, AR
Been referencing this quite a bit in the last week or so. Finally putting my truck back together. Really appreciate these torque specs. I can only find a handful in the shop manual. Quick question. What thermostat is recommended, 195*? I cleaned the tstat housing last night and had to pry the old one out. Not sure if it was fused to to the cast or if the gasket had everything stuck together. Got to looking at it when I got it out, it's 160*. I didn't even know they made them that cold. New to me anyhow.
Fleet Mechanic
Joined: Nov 2002
Posts: 1,643
Likes: 69
195 will give better efficiency and a cleaner burning engine. A colder one is sometimes used if somebody is trying to optimize volumetric efficiency, for performance, at the expense of efficiency. Sometimes somebody will install a colder stat to try and make up for some sort of cooling system inadequacy. I think some marine engines use a 160 stat
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
The way I understand it, 160° F. T-stat were standard before the widespread use of glycol based antifreeze coolant. Prior to that they used alcohol based antifreeze. A 160° didn't boil off the freeze protection. The shop manual should have the "opens at" and "fully open at" temperature. I wouldn't think there's any reason to use one today.
Thread Starter
|
Cargo Master
Joined: Jan 2019
Posts: 3,369
Likes: 16
From: Caraway, AR
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
10 Best Ford Truck Engines We Miss the Most!
Joe Kucinski
2026 Shelby F-150 Off-Road: Better Than a Raptor R?
Brett Foote
2027 Super Duty Carhartt Package First Look: 12 Things You NEED to Know!
Michael S. Palmer
10 Most Surprising 2026 Ford Truck Features!
Joe Kucinski
Top 10 Ford Trucks Coming to Mecum Indy 2026
Brett Foote
5 Best / 5 Worst Ford Truck Wheels of All Time
Joe Kucinski
Ford Super Duty: 5 Things Owners LOVE, 5 Things They LOATHE!
Joe Kucinski
Every 2026 Ford Truck Engine RANKED from WORST to FIRST!
Michael S. Palmer
The Best F-150 Deal of Every Trim Level (XL through Raptor)
Joe Kucinski
Thread Starter
|
Cargo Master
Joined: Jan 2019
Posts: 3,369
Likes: 16
From: Caraway, AR
Mine has that lol anything else? Seems like you'd want brass in every version. Or is there a reason they don't automatically put them in truck engines, other than maybe being cost prohibitive? Would the casting numbers reflect marine application or did they just use surplus blocks IN marine applications?
Thread Starter
|
Cargo Master
Joined: Jan 2019
Posts: 3,369
Likes: 16
From: Caraway, AR
And since my brain only operates in double posts... I was wondering, would there be any reason someone would add a colder thermostat to a sick engine to keep it going a bit longer?
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
It's often seen with engines that are overheating, possibly due to excessive rust scale and sediment in the block and radiator. The entire cooling system and radiator was sized by the engineers so that the engine runs in a certain range of temperatures when thermostat is fully open. Where people often make the mistake, is they don't fully understand what the engine thermostat does.
Thermostat temperature rating actually sets the minimum engine running temperature, not the maximum engine temperature.
So in reality there isn't much benefit to running a colder thermostat in the first place when the overheating issue is due to cooling system neglect. Engine will still overheat, just delayed by a few minutes at best. In southern states where freezing temperatures are rare, running straight water is the classic way to jam up cooling passages. Removing thermostat entirely is yet another solution in search of a problem, as it tends to increase condensation and sludge city. Most OHV engines were designed to run somewhere around 200° or 210°, what the gauge indicates versus actual temperature is something else, never mind the accuracy, and also where the sending unit is located also factors.
There is a trend over the years to remove actual gauges, whether oil pressure or temperature, in favor of idiot lights, or even dummy gauges. Too many variables and too many people axing questions of the dealer, apparently.
Modern gasoline is prone to vapor lock in older engines, so some experimenting might be necessary, but as a general rule any OHV engine a 180° F. should be fine for summer and a 190° for winter. I run a 195° F year round in my Y block. Where you want to be careful is pressure - the old cooling systems don't use 16 pound radiator caps! 4 or 7 pound caps are what the factory used way back when.
Thermostat temperature rating actually sets the minimum engine running temperature, not the maximum engine temperature.
So in reality there isn't much benefit to running a colder thermostat in the first place when the overheating issue is due to cooling system neglect. Engine will still overheat, just delayed by a few minutes at best. In southern states where freezing temperatures are rare, running straight water is the classic way to jam up cooling passages. Removing thermostat entirely is yet another solution in search of a problem, as it tends to increase condensation and sludge city. Most OHV engines were designed to run somewhere around 200° or 210°, what the gauge indicates versus actual temperature is something else, never mind the accuracy, and also where the sending unit is located also factors.
There is a trend over the years to remove actual gauges, whether oil pressure or temperature, in favor of idiot lights, or even dummy gauges. Too many variables and too many people axing questions of the dealer, apparently.
Modern gasoline is prone to vapor lock in older engines, so some experimenting might be necessary, but as a general rule any OHV engine a 180° F. should be fine for summer and a 190° for winter. I run a 195° F year round in my Y block. Where you want to be careful is pressure - the old cooling systems don't use 16 pound radiator caps! 4 or 7 pound caps are what the factory used way back when.
Fleet Mechanic
Joined: Nov 2002
Posts: 1,643
Likes: 69
True. Also, if you don't have a coolant recovery bottle on your rad it is a good idea to add one, and check it periodically to see if it is working properly and has the proper level of fill. Recovery bottles use a rad cap with two positive seals, unlike older caps with only one pressure seal and a brass diverter disc.
Coolant recovery system can add as much as 10% increase in cooling efficiency / capacity. You'll be pumping fluid, not suds.
Coolant recovery system can add as much as 10% increase in cooling efficiency / capacity. You'll be pumping fluid, not suds.
5th Wheeling
Joined: Aug 2021
Posts: 45
Likes: 14
49lexploded.jpg | Hits: 17819 | Posted on: 4/4/10 | View Low-Res
4.9L (300ci) I6 Exploded
IF THE IMAGE IS TOO SMALL, click it.
UPPER sizes:
8's bolts are 8mm (5/16")
9's nuts are 27mm
11's bolts are 9/16"
14 & 23 are 11mm (7/16")
24 & 25's nuts are 11mm (7/16")
46 & 49's bolts are 11mm (7/16")
50 & 52's bolts are 1/2"
74 is 1/2"
Smallblock distributors use Hold-Down Clamp Motorcraft DZ410
42 Oil Filter Motorcraft FL-1A
16 Oil Filler Cap Motorcraft EC743
17 PCV Breather Elbow Motorcraft FA1118
63 & 73 Standard AT155
LOWER sizes:
29 is 13mm after '87; 1/2" before
14 for auto trans stamped F4TE-6A372-AA
See also:
. 
Oil internal engine threads with engine oil, unless the threads require oil or water-resistant sealer.
Engine Block Casting Number Decoder
. . . . . . TORQUE SPECIFICATIONS
. . Item . . . . . . . . . . . . . . . . . . . . . . . . . . . N-m . . . . . . . . . . . . . Ft-Lbs
Connecting Rod Nut 55-61 40-45
Cylinder Front Cover 17-24 12-18
Cylinder Head Bolts (Follow bolt tightening sequence during each step) Progressively increase tightness using this sequence:
1st step: tighten all bolts to 67-75 N-m (50-55 ft-lb)
2nd step: tighten all bolts to 82-88 N-m (60-65 ft-lb)
3rd step: tighten all bolts to 94-115 N-m (70-85 ft-lb)
Damper to Crankshaft 177-203 130-150
EGR Valve to Intake Manifold 18-26 13-19
Flywheel to Crankshaft 102-115 75-85
Main Bearing Cap Bolts 82-94 60-70
Manifold to Cylinder Head Intake & Exhaust (Follow bolt tightening sequence) 30-43 22-32
Exhaust Manifold-to-Muffler Inlet Pipe 34-49 25-36
Oil Filter Insert to Cylinder Block 20-48 15-35
Oil Filter to Cylinder Block 1/2 turn after oiled gasket contacts sealing surface
Oil Inlet Tube to Pump 14-20 10-15
Oil Pan Drain Plug 21-33 15-25
Oil Pan to Cylinder Block (Follow bolt tightening sequence) 20-24 15-18
Oil Pump to Cylinder Block 14-20 10-15
Oil Inlet Tube to Main Bearing Cap 30-43 22-32
Pulley to Damper Bolt 48-67 35-50
Rocker Arm Bolt 24-31 17-23
Spark Plug to Cylinder Head 14-20 10-15
Valve Rocker Arm Cover (Follow bolt tightening sequence) 8-14 70-120 (In-Lbs)
Valve Push Rod Cover to Cylinder Block 2-3 18-27 (In-Lbs)
Water Outlet Housing 17-24 12-18
Water Pump to Block/Front Cover 17-24 12-18
Thermactor Pump Pulley to Pump Hub 12-15 110-130 (In-Lbs)
Throttle Body Attaching Nuts 19-27 14-20
Camshaft Thrust Plate to Cylinder Block 16-24 12-18
Distributor Clampdown 24-33 17-25
Intake Manifold Vacuum Fittings 8-13 6-10
Timing Pointer to Front Cover 17-24 12-18
Thermactor Air Manifold to Cylinder Head (Nut and Ferrule Assy.) 19-22 14-16
Thermactor Air Check Valve to Thermactor Air Manifold 22-26 16-19
Pressure Plate and Cover Assy. to Flywheel 27-39 20-29
Alternator/Thermactor Pump Bracket to Engine (all except bottom bolt) 40-55 30-40
Alternator/Thermactor Pump Bracket to Engine (bottom bolt) 53-71 39-53
Alternator Pivot Bolt 53-72 39-53
Thermactor Pump Pivot Bolt 40-55 30-41
Alternator Adjusting Bolt 40-55 30-41
Thermactor Pump Attaching Bolt 40-55 30-40
Air Conditioning Compressor to Mounting Bracket Bolts 24-31 18-23
Power Steering Pump to Mounting Bracket Bolts 40-55 30-40
Power Steering Pump/Air Conditioning Compressor Bracket to Cylinder Head Bolts 40-55 30-40
Power Steering Pump/Air Conditioning Compressor Bracket to Block Bolts and Nuts 55-70 40-50
Fan Blade to Fan Clutch Bolts 16-24 12-18
Fan Clutch to Water Pump 41-135 30-100
Oil Pressure Sender (Left Side Rear of Cylinder Block) 11-24 8-18
Engine Coolant Temperature Sender (Right Side Rear of Cylinder Block)
FTE Legend
Joined: Nov 2015
Posts: 30,828
Likes: 4,094
From: Angier, NC
. . Item . . . . . . . . . . . . . . . . . . . . . . . . . . . N-m . . . . . . . . . . . . . Ft-Lbs
IE: Connecting Rod Nut 55-61 (N-m) 40-45 (Ft-Lbs)
It is not the size of the bolt or nut but what they get tighten to.
Dave ----