what do you guys have to say about a comparison between the 6.9 and the 7.3?
what do you like better, why? power?
any kind of comparison is appreciated
chance to buy a 6.9 for $400 or a 7.3 for $500...
any imput?

thanks in advance

 

Some more HP in a 7.3, 6.9 is older but more cylinder wall thickness if you are looking for a rebuild. Are you looking at trucks or just a motor? What kind of milage is on each. I would look at condition and milage, which had regular oil changes and servicing etc, was one a dirt bogger vs, all highway miles?

 

Hmmm, My answer is 6.9L but then you have to make sure you have a certain vintage of those as well. 1985 to 1987 was and updated block for the 6.9L. The 7.3L has had the cavitation issue since it started in 1988 basically a bored out 6.9L to squeeze a whopping 10-15 horsepower out of it. The 6.9L has less issues than the 7.3L, in 1987 6.9L carried a lot of the 7.3L updates like glowplug and filter systems etc. I am running a 7.3L now have a 6.9L on an engine stand to rebuild plan on eventually switching to 6.9L as my other 7.3L wear out in my two trucks. I have had a 1996 F-350 7.3L Powerstroke a 2001 F-350 7.3L Powerstroke and a 2004 F-350 6.0L Powerstroke. Everyone one of those P'Strokes left me stranded somewhere computer issues, turbo issues etc. While I could go out to my old 1987 F-350 Plowtruck with a 6.9L and bang it would start everytime in the coldest winters. Each of my trucks gets faithful maintenance the best of everything for a piece of mind thing. So, I sold the newer trucks and opted for the old iron and refurbished my old Plowtruck with a southern body and bought another 93 F-250 7.3L IDI 2 wheel drive from a little old man who serviced his truck more than he drove it. Then truck runs great and I can work on it change pumps, injectors keep her ticking for a long time. The key to anything is how well were those engines maintained did they beat them or just use therm respectfully. Did the 7.3L gets it's 6 month boost of coolant additive to help prevent cavitation? I would opt for the 6.9L but that is just my opinion. There are many forums and many people who have experience with these old girls. Hope this helps and have a good day!

 

Winger235,
Welcome to FTE and the IDI diesel forum.

A 6.9 if it is between 1985 and 1987 for a production year.

Yes a 6.9 does have some issues, but they are far easier to overcome than the issues the 7.3 has.

 

Dave,

A question I have is from reading about your 6.9L rebuild the head bolt upgrades even though they are the 7/16-14 and not sure what stock tensil strength is. Just for ease of math for dummies like me, it would be like going from a grade 5 bolt to a grade 8? I have a 6.9L that could be rebuilt, but if needed sooner and swapping it for a long block was the game plan etc I would like to read the parts list and know the upgraded bolts were included. But if I rebuild it myself and go the route you did there will be a sweet engine and truck plus saving 40 grand at the same time.

 

What kind of issues?

Did I get screwed by buying a 7.3?

*panics*

10-15 HP and how much torque does the 7.3 have over the 6.9? Would I notice it if I went and swapped it out? Should I swap it out?

Is there a positive to having a 7.3?

*panics some more*

 

Depends on what you end intentions are, this is just my opinion.
We all know about opinions.

7.3 plus - 1/2" head bolts
6.9 minus - 7/16" head bolts
Cure for 6.9 - ARP head studs which are much stronger than the 1/2" head bolts on a 7.3 If you want to run a turbo and boost numbers above 12 or 14 pounds, you need head studs on both the 6.9 and 7.3 engines

7.3 plus - stronger lower block around the block heater
6.9 plus and minus - the early 83 thru the middle of 85 had some issues with using block heaters causing cracks, but the issue was resolved in 85 and later 6.9 engines.

Identification of the new 6.9 blocks:
6.9L New Style Block

Block Casting Number: 1807996C1 Note: Some new style blocks have casting
number 440. Above serial number 173828.
Visual Identification: *Has counterbored area for block heater
*Very defined relief area cast in side of block for dip stick tube.
*Thickness of cast iron around block heater 15/32" (.470")
*Latest style (not all new style 6.9) has ribs around head bolts, rear two on left side go from head gasket surface to pan rail - same as 7.3
Head Bolts: *Same as old style 6.9

6.9 plus - thicker cylinder walls - a 6.9 bored 110 thousandths makes a 7.3 - this means you can bore the block without using sleeves, with care and good cooling system maintence you could rebuild a 6.9 twice if you did a minimum bore just to have fresh cylinder surfaces (6.9 bore 4")
7.3 minus - the cylinder walls are already to thin, cavitation is a real concern - boring the block with out installing sleeves is asking for trouble - from my experience sleeves are more trouble - I blew three of them up in 28,000 miles with cracked blocks from the sleeves dropping (7.3 bore 4.11")

Both have a 4.18" stroke, same crankshaft

6.9 plus -Coolant passages
7.3 minus -Coolant passages
The lower corner coolant passages on the cylinder head on the 7.3 have been plugged. This change is introduced to eliminate lower corner gasket coolant seepage during cold start engine warm-up. Mating passages in the block are also plugged. (could be why we hear more 7.3 overheating issues).

6.9 minus - the rockers are on the weak side
7.3 plus - stronger rockers
6.9 rocker problem fix is use 7.3 rockers when you rebuild the engine, they just bolt right in

6.9 minus - the exhaust valves are not as good as the 7.3 exhaust valves
7.3 plus - better exhaust valves due to alloy change
6.9 fix is to install 7.3 exhaust valves (6.9 valves can not go in a 7.3 though)

6.9 plus - smaller precombustion chamber gives a compression ratio of 22.5 to 1 (18.34 cubic centimeters)
7.3 minus - bigger precombustion chamber gives a compression ratio of 21.5 to 1 (20.42 cubic centimeters)

This can be a minus to both engines if you want to run big turbo boost, the Power Stroke engines have a base compression ratio of 18 to 1 and can run around 30 PSI boost in stock form. Both IDI engines can run boost in the mid 20's if you mill the pistons down before you install them and use head studs.

6.9 minus - 175 HP & 318 ft.lbs. @1800 RPM in stock form
7.3 plus - 185 HP & 338 ft.lbs. @ 1600 RPM in stock form

I am sure I forgot a few things when I was typing this, but that is my take on the 6.9 versus 7.3.
After 3 different 7.3 remans took a crap on me I went back to the 6.9 and have been smiling ever since.
I spent the same money for the 6.9 rebuild that I did for the drop in 7.3 turbo reman.
Since I did all the labor myself you could say it was more expensive to rebuild the 6.9. But it is not a normal rebuilt 6.9 either.
Those 7.3 turbo engines don't hold a candle to the power I have now, and I have already outlasted the first two remans I installed mileage wise.

Save your dollars, do an engine rebuild on a 6.9 with the changes listed above, add a turbo running boost in the mid 20's, big exhaust, max out the fuel delivery on a 7.3 turbo IP, run some 7.3 turbo injectors, set the timing at about 9 BTDC, raise the RPM limit a bit.
Then go load it up and go find a Cummins or a Stroker, you might be surprised how well the 20+ year old motor can do against that pricey new truck.
But another thing to consider, you will pay for all that fun when you fill the tanks.

 

Do the later 7.3's or Stock turbo 7.3's address the cooling or cylinder wall issues?

 

Any fuel mileage/power difference setting the timing 9 BTDC? I personally do not want to mess with the timing but if it gives that much of an increase it might just be worth it...

 

The extra timing is a very small part of the power.

Fuel mileage ....about 10 to 11 MPG.

Also remember my truck weight is about 8,060 pounds with nothing in the tool boxes and the bed empty but the fuel tanks full. Add two guys, 100 gallons of off road fuel plus the tank and pump and fill two under bed tool boxes and then throw a jumping jack that weighs 150 pounds and a bunch of hand digging tools in the bed. Now you are looking at a little over 10,000 pounds on a normal day.

When I am hauling as a dump truck, I am usually 16 or 17 thousand gross weight.

When I am towing, then it is usually in the 23,000 range.

Considering what I do, I am very pleased with the fuel mileage.

As I said, it is a lot of fun to drive, but you pay every time you fill it up.

Pele, all the 7.3 IDI motors have the same issues. Other than minor almost "cosmetic" changes they are all the same block.
There are also very few parts that are not interchangeable between a 6.9 and 7.3 engine.

 

Well Dave, I can honestly say that I probably wont be messing with the timing until I can afford the extra fuel! For now I will just turn up the fuel for a bit more power. I'd like to shoot for 20's for mpg and right now I'm sitting at around 17

 

When you dump 9700 pounds of stone in the bed, fuel mileage isn't really a concern.

Remember, you are typing at the owner of the most abused Ford truck on the planet according to several members of this forum a year or so ago.

It is a badge I wear with honor, because I will be firing it up at 5:30 AM tomorrow just like I have for 21 years to go do it all again.

 

6.9, my 2 cents.

 

You could not give me an 88-92 7.3L. I worked for a farmer that had an 84 & 86 f-250 6.9L, 4x4, 4spd, 4.10 gears, reg. cab, he also had an 89 & 91 with the 7.3L. All of these trucks were used to pull a 24ft. gooseneck stock trailer along with other trailers. The 86 ran 350k and never touched the engine, and it was turned up as far as the pump would go. The 84 ran 250k before the cab and box gave up, never touched that one either. The 89 & 91 gave up at 100k. All these trucks had regular services. IMO, the 6.9 was the best ever built, but a close second would be the 7.3L from 99-03. To bad you couldn't take todays tech and put it on that engine.

 

Right, but to solve the thin cylinder walls and coolant passage problems, I need to change three major parts... The block and both heads.

Looks like it's time to scout the scrap yard...