6.9l vs 7.3l
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Postmaster
Joined: Nov 2008
Posts: 2,851
Likes: 3
From: Buckley, WA
6.9l vs 7.3l
im just looking for advantages of each motor. my buddy and i are going to do a full build on a idi. just deciding on which one. He claims the 7.3 is far superior to the 6.9, but from what ive read on here the 6.9 seems like the best bet for mods.
now i know it has all been talked about before, i did the whole search thing and found good info in multiple threads. im just trying to condense it all in to one so that i can print it out and give it to him.
so please help me out here with the pros and cons for each motor.
ive already read the "optimum idi build" thread so im assuming the 6.9 will be what we go for.
now i know it has all been talked about before, i did the whole search thing and found good info in multiple threads. im just trying to condense it all in to one so that i can print it out and give it to him.
so please help me out here with the pros and cons for each motor.
ive already read the "optimum idi build" thread so im assuming the 6.9 will be what we go for.
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Postmaster
Joined: Nov 2008
Posts: 2,851
Likes: 3
From: Buckley, WA
optimum idi build
I haven't built my next engine yet, but when I get around to it this is what I'll be doing.
-6.9 block and heads: hot-tanked for cleaning, and magna-fluxed for crack detection
-Hone the cylinders or give a minimum overbore for clean cylinder walls
-Considering a Typefour camshaft, it has a special grind that lowers max torque by 200 RPM's
-Fresh bearings
-New pistons, milled down to lower compression to run more boost
-Fresh piston rings
-ARP head studs
-Victor Reinz head gaskets
-Been reading about porting and polishing the heads for better flow, sounds like a good idea
-Fresh valve springs
-7.3 IDI Turbo valves (I think they were better...could be wrong though!)
-7.3 IDI rockers
-Victor Reinz valley pan gasket.
-Home-brew Grade 8 intake manifold studs to keep the coolant out of the oil at 22 psi of boost.
-Home-brew exhaust manifolds for a better angle for better up-pipes, routed like a Powerstroke. Under/behind the head and above the bellhousing. (Note: truck probably needs a 2" body lift for clearance)
That's a 7.3 powerstroke engine
-Home-brew Grade 8 exhaust manifold studs
-ATS 093 Turbo with 3" downpipe and 4" exhaust
-Ram air, open up the grille for more air
-Rebuilt oil cooler with fresh O-rings and gaskets
-All new gauge sending units and switches
-Motorcraft/Beru glow plugs on manual control
-'93 7.3 IDI Turbo Injection pump with some tweaks from the fuel shop
-'93 7.3 IDI Turbo Injectors, I believe they are BB code.
(Make good friends with the local fuel injection shop, they'll take care of you
. My local shop told me they can tweak a pump for me when I'm ready.)
-6.9 Fuel filter header with aftermarket fuel/water seperator
-If you feel the need for a block heater, a tank-type coolant heater would be good. ZeroStart Tank-type Engine Heaters - JCWhitney Though a good set of glow plugs doesn't require the truck to be plugged in...
As a sidenote, there has been some talk about a Moose pump and injectors which are apparently built by a member over on OilBurners. I don't go over there, so I don't know about that stuff. But F250HDXLT has talked about it before and has posted dyno results from using that fuel system. Expensive and out of my price range, but apparently great results.
The basic rule is more fuel and air in and more exhaust out. Find a way to get more fuel in, and get your air in faster with a custom intake.
The '85.5 and later 6.9 blocks have a thicker casting around the block heater. The 85.5 and earlier blocks could have a crack from the concentrated heat from the block heater. I wouldn't be afraid to use an 83-85 block as long as it wasn't cracked...because I wouldn't use the stock block heater, use a tank-type heater.
If you begin with the 87 6.9, you'll be ahead from the start. The 87 6.9 is the best because it already had the upgrade 7.3 style rockers and the later glow plug system, which is apparently superior to the 83-86 system.
The 7.3 block can also be built up. DPS sells a 7.3 head stud kit. If you find a 7.3 that only needs a honing and isn't a victom of cavitation, then you might use a 7.3 instead. I wouldn't bore a 7.3 though, the cylinder walls are too thin in stock form, nevermind shaving more off. If I went with a 7.3 it would have to be in great shape and only need a honing.
-6.9 block and heads: hot-tanked for cleaning, and magna-fluxed for crack detection
-Hone the cylinders or give a minimum overbore for clean cylinder walls
-Considering a Typefour camshaft, it has a special grind that lowers max torque by 200 RPM's
-Fresh bearings
-New pistons, milled down to lower compression to run more boost
-Fresh piston rings
-ARP head studs
-Victor Reinz head gaskets
-Been reading about porting and polishing the heads for better flow, sounds like a good idea
-Fresh valve springs
-7.3 IDI Turbo valves (I think they were better...could be wrong though!)
-7.3 IDI rockers
-Victor Reinz valley pan gasket.
-Home-brew Grade 8 intake manifold studs to keep the coolant out of the oil at 22 psi of boost.
-Home-brew exhaust manifolds for a better angle for better up-pipes, routed like a Powerstroke. Under/behind the head and above the bellhousing. (Note: truck probably needs a 2" body lift for clearance)
That's a 7.3 powerstroke engine
-Home-brew Grade 8 exhaust manifold studs
-ATS 093 Turbo with 3" downpipe and 4" exhaust
-Ram air, open up the grille for more air
-Rebuilt oil cooler with fresh O-rings and gaskets
-All new gauge sending units and switches
-Motorcraft/Beru glow plugs on manual control
-'93 7.3 IDI Turbo Injection pump with some tweaks from the fuel shop
-'93 7.3 IDI Turbo Injectors, I believe they are BB code.
(Make good friends with the local fuel injection shop, they'll take care of you
. My local shop told me they can tweak a pump for me when I'm ready.)-6.9 Fuel filter header with aftermarket fuel/water seperator
-If you feel the need for a block heater, a tank-type coolant heater would be good. ZeroStart Tank-type Engine Heaters - JCWhitney Though a good set of glow plugs doesn't require the truck to be plugged in...
As a sidenote, there has been some talk about a Moose pump and injectors which are apparently built by a member over on OilBurners. I don't go over there, so I don't know about that stuff. But F250HDXLT has talked about it before and has posted dyno results from using that fuel system. Expensive and out of my price range, but apparently great results.
The basic rule is more fuel and air in and more exhaust out. Find a way to get more fuel in, and get your air in faster with a custom intake.
The '85.5 and later 6.9 blocks have a thicker casting around the block heater. The 85.5 and earlier blocks could have a crack from the concentrated heat from the block heater. I wouldn't be afraid to use an 83-85 block as long as it wasn't cracked...because I wouldn't use the stock block heater, use a tank-type heater.
If you begin with the 87 6.9, you'll be ahead from the start. The 87 6.9 is the best because it already had the upgrade 7.3 style rockers and the later glow plug system, which is apparently superior to the 83-86 system.
The 7.3 block can also be built up. DPS sells a 7.3 head stud kit. If you find a 7.3 that only needs a honing and isn't a victom of cavitation, then you might use a 7.3 instead. I wouldn't bore a 7.3 though, the cylinder walls are too thin in stock form, nevermind shaving more off. If I went with a 7.3 it would have to be in great shape and only need a honing.
Post Fiend
Joined: Feb 2009
Posts: 8,005
Likes: 7
From: Ottawa, Ontario
The one and big problem about 7.3's is you can't really safely overbore them. The cylinder walls are already to thin from the factory. Boring them out even more is just asking for trouble.
Both are the, a 7.3 is a 6.9 block bored over 0.110 over.
So you want want maximum displacement for maximum HP etc. get a 6.9 and over bore it .110 and you'll have a factory 7.3
Or.... be smart, get a 6.9, give it minimum bore just to clean out the cylinders, don't worry about Cavitation and you'll still have room for future over bores for another rebuilt later on, if needed!
Just be sure you get a 85+ year engine so you can safely use the block heater without worrying about cracking. It will also need 87 6.9 or any year 7.3 rocker arms as those are updated beefier design.
Your buddy, like alot of people preffer the 7.3 over the 6.9 simply because "it's bigger"
Like alot say, no replacement for displacement
Both are the, a 7.3 is a 6.9 block bored over 0.110 over.
So you want want maximum displacement for maximum HP etc. get a 6.9 and over bore it .110 and you'll have a factory 7.3
Or.... be smart, get a 6.9, give it minimum bore just to clean out the cylinders, don't worry about Cavitation and you'll still have room for future over bores for another rebuilt later on, if needed!
Just be sure you get a 85+ year engine so you can safely use the block heater without worrying about cracking. It will also need 87 6.9 or any year 7.3 rocker arms as those are updated beefier design.
Your buddy, like alot of people preffer the 7.3 over the 6.9 simply because "it's bigger"
Like alot say, no replacement for displacement
Freshman User
Joined: Feb 2011
Posts: 33
Likes: 0
For maximum power, I'd go with a good low mileage 7.3 with no cavitation and do all you've said. For slightly less power with the same mods but probably slightly better overall life, I'd do the late build 6.9. Seriously though, the Powerstrokes can go well over 250000 and handle 25-35lbs of boost without blowing up and they're essentially the same 7.3 block, so I wouldn't hesitate to use a good 7.3 as a starter.
Fleet Mechanic
Joined: Jan 2011
Posts: 1,709
Likes: 4
From: 8600 ft in Colo
The only problem with the 7.3 is the cavitation issue, but it's a big one...
The cyl walls are borderline too thin when new. Overboring is just asking for trouble. If I could find a new 7.3 block, I'd build it up in a heartbeat, and just be very diligent about coolant additives.
Short of that, I'd rather find a late 6.9...
The cyl walls are borderline too thin when new. Overboring is just asking for trouble. If I could find a new 7.3 block, I'd build it up in a heartbeat, and just be very diligent about coolant additives.
Short of that, I'd rather find a late 6.9...
Thread Starter
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Postmaster
Joined: Nov 2008
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From: Buckley, WA
does anyone know how many miles is actually needed to get the cavitation with out the additives? If you were looking for a used 7.3l with low miles, how low (or high) would be safe to assume no problems with the cyl walls?
Freshman User
Joined: Feb 2011
Posts: 33
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Here's what I'd do. Talk to the guy selling the motor. If he gives you a blank stare when you ask him about SCA, don't buy it. If he says, Oh yeah, it's always run SCA, tell him, OK I'll buy it as long as we write a receipt saying I can bring it back if I tear into this thing and find cavitated cylinders. If he says no, don't buy it. Probably make it really hard to find one, but the right person will have the knowledge required and will stand by the motor he sells. Still kinda a crap shoot though. I bought mine from a diesel mechanic who told me before I asked him that it's run the SCA additive, so that put me a lot more at ease, even though the truck has over 200K on it. Besides that, he put in a PSD E4OD, a new banks sidewinder kit, had the front end completely rebuilt and a bunch of other stuff. That stuff right there was worth the price of the truck and then some.
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Post Fiend
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