6.9 or 7.3?

[SuperDave]

The current 6.9 in my 86 f350 has become a little lackluster in the performance department and is pretty hard to start in the colder months so I am planning to build another engine for it but I cant decide whether to stick with a 6.9 or go with a 7.3. I am kinda leaning towards the 6.9 because I have had so little trouble out of them and I have a better chance of getting a good core with a 6.9 whereas the 7.3 has a chance that cavitation could be an issue. On the other side of that I had a 94 f350 with the factory turbo idi and I liked that turbo setup much better than my current first generation banks sidewinder so finding one of those id take the gamble that it could have the cavitation problem.

My ideal setup would be an 87 6.9 because of the updated rocker arms/ glow plugs and then use the factory turbo setup from a 94 idit. If anyone knows of a rebuildable core for sale in reasonable driving distance of Atlanta Ga I would like to hear about it.

Before anyone has to ask I'm looking for another engine because the one in the truck is currently running and driving and I want to keep the truck on the road. At this point I'm thinking there is something internally wrong with the engine because it has no grunt whatsoever, my n/a 6.9 in my f250 will leave this truck in the dust with no problem especially with a loaded trailer. I have replaced my injectors with new stanadyne units and my pump has been rebuilt by a local and very reputable shop and is a turbo 7.3 pump turned up just slightly. Boost builds quickly enough and max is about 11psi and holds 6-8psi under normal driving conditions. I have also done a compression check and its right around 400psi in every cylinder. I have tried tweaking the pump and all that gets me is black smoke and high egt's and I have tried playing with the timing and its gotten a little better but not much. Its also very hard to start in winter I have new motorcraft glow plugs and controller and they do work correctly and it don't get the white smoke normally associated with glow plug problems. It's a cheap reman engine with who knows how many miles on it or what was done to it during the reman process but I'm going to run it till I get another one or it won't run any longer.

Readers digest version: my current 6.9 has one foot in the grave and the other on a banana peel and I can't decide between a 6.9 or a 7.3 . and if anyone knows of a good core near Atlanta let me know. Thanks a bunch!

 

[The_Josh_Bear]

To answer your question 6.9 vs 7.3... how much boost do you want to run and will you stud the engine? If you're keeping boost in the low teens go with the 6.9. Stud it if you can, then boost up to the high teens. Otherwise do the 7.3, but do the coolant mod during the rebuild.

Your N/A 6.9 will dust your other 6.9 that has good compression and pushes 11psi of boost?!?!? Especially when towing?!?

The only scenario I see that even maybe being possible is if your turbo rig has very retarded timing. This would build boost but be low on power, and cause black smoke.
For reference my 7.3 pushes about 13psi with a maxed out stock IP. Has a big air filter and charge air cooling. It's not a hot rod but has probably double the power it ever put out as N/A.

Point being your engine sounds *healthy*, not dying! Obviously that's not the whole story but a compression test is a great indicator of health.
Trouble starting: does the starter turn over faster than you can count? If not, that's the first route I'd take.

 

[SuperDave]

As far as the starting system it turns over very fast, it has the pmgr starter, 4/0 positive cables and 3/0 negative, 2 new group 27 batteries at 850cca each maintained by a 3g alternator that does way better than my old 1g alternator. As far as boost goes I dont plan to make any more than a stock turbo is capable of however, what ever engine I go with will get head studded in case I get a wild hair to do something more. And yes my n/a 6.9 has more giddy up than my turbo one, granted some of that is the n/a truck has a 4:10 axle vs the 3.55 in the turbo truck but that turbo engine should have way more power than it does. That turbo engine has just never been right, its always been down on power and hard to start during cold weather (less than 40 degrees) but it has good compression and does not smoke. Really you are probably right, the timing probably just needs to be correctly set and I have messed with it but not a lot right now it's set slightly toward the passengers side (maybe 1/8 inch)of the static timing mark on the gear housing.

 

[The_Josh_Bear]

Nice work on the starting/charging system! I love my 3g/poweraster setup, spins so fast and is always charged up. Plus the 3g is so cheap and easy to rebuild it's nuts.

"This engine has never been right" makes me wonder if something with the timing gears is off...but that's not my department. I've never even had the timing cover off of mine.

The part with good compression and good boost makes me think it might be something simple and you have a perfectly good runner, she's just hiding her true self.
The static mark means about nothing, the one on the pump can be way off or sorts close, the static mark just gets it close enough to start.

If you want to get closer on timing I would:
Listen on a cold start for the "powerstroke rattle". It should hurt your ears if you're at the front of the vehicle and you have good hearing. Then, when the cold idle drops down that rattle should go away by quite a bit.
If you're not there yet, advance the pump towards the passenger side another 1/8" or even a 1/4" if you want. Too advanced won't hurt it in the yard. I've had mine from +2° ATDC to 17° BTDC for example. Driving way advanced isn't advised but you have to be quite advanced for glow plugs to get consumed.
Bear in mind that tuning by ear will only get you close, but close can be great. Experienced IDI'ers can only get within 3° by ear.

The reason I mentioned going 6.9 unless you want to do a lot of boost is that studs are only good for the high teens in a 6.9 even with studs. While the 7.3 will bend rods before blowing the HG with studs. Plus the 6.9 already has the cooling mod from the factory and will get better MPGs, all things being equal.

 

[u2slow]

Fummins. (12-valve)
Life's too short to mess with V8 diesels.

 

[SuperDave]

Fummins. (12-valve)
Life's too short to mess with V8 diesels.

I guess if I wanted to be like everyone else I could do that, I just don't believe the antiquated technology of a 12 valve is any better than that of the idi when taking into account the time and costs required to make it all work correctly. Maybe a 6.7 or an 8.3 would be worth the effort but I have never seen anyone do that before. Not knocking it but it ain't this fellas cup of tea.

*edit* I lied, it evidently is my cup of tea... I forgot about the f800 with the 24v Cummins its a torquey little s.o.b

 

[SuperDave]

Nice work on the starting/charging system! I love my 3g/poweraster setup, spins so fast and is always charged up. Plus the 3g is so cheap and easy to rebuild it's nuts.

"This engine has never been right" makes me wonder if something with the timing gears is off...but that's not my department. I've never even had the timing cover off of mine.

The part with good compression and good boost makes me think it might be something simple and you have a perfectly good runner, she's just hiding her true self.
The static mark means about nothing, the one on the pump can be way off or sorts close, the static mark just gets it close enough to start.

If you want to get closer on timing I would:
Listen on a cold start for the "powerstroke rattle". It should hurt your ears if you're at the front of the vehicle and you have good hearing. Then, when the cold idle drops down that rattle should go away by quite a bit.
If you're not there yet, advance the pump towards the passenger side another 1/8" or even a 1/4" if you want. Too advanced won't hurt it in the yard. I've had mine from +2° ATDC to 17° BTDC for example. Driving way advanced isn't advised but you have to be quite advanced for glow plugs to get consumed.
Bear in mind that tuning by ear will only get you close, but close can be great. Experienced IDI'ers can only get within 3° by ear.

The reason I mentioned going 6.9 unless you want to do a lot of boost is that studs are only good for the high teens in a 6.9 even with studs. While the 7.3 will bend rods before blowing the HG with studs. Plus the 6.9 already has the cooling mod from the factory and will get better MPGs, all things being equal.

I guess it's entirely possible that its a tooth or so off on the timing gear as it would probably still run ok just one tooth off... Hell my brother in laws gm 6.2 ran and drove down the friggin road with the pump timing 180 degrees out granted it wouldn't do more than 35 and smoked black like a coal train it did in fact still run. I wish I could afford some sort of timing tool to use on it, I bid on one off eBay but got in a bidding war and said f@$! It at $250 that's happened twice now

 

[IDIBRONCO]

You're getting 11PSI out of a first gen Banks? I'm impressed if it hasn't been modified.

 

[u2slow]

I guess if I wanted to be like everyone else I could do that, ... Not knocking it but it ain't this fellas cup of tea.

I respect the dedication!

Inline turbodiesels are what I've gotten hooked on - not specifically cummins (although that's the easiest route)

 

[stealth13777]

I don’t know how current some of these are. But might help:

https://www.oilburners.net/threads/timing-service-registry.70126/

 

[SuperDave]

I respect the dedication!

Inline turbodiesels are what I've gotten hooked on - not specifically cummins (although that's the easiest route)

I generally prefer inline 6 diesels as well but what I'm familiar with is way too large for our trucks i.e. cat 3406 and c15, Detroit series 60 and Cummins isx. I would like to one day attempt to put a ford/new Holland 6.6 diesel in a pickup truck if I could find one.

I certainly appreciate the guidance from every one, I am going to need to do a water pump on that engine soon enough so that will be a convenient time to check the gear alignment and maybe solve the problem.

 

[SuperDave]

View media item 835View media item 834

Nice work on the starting/charging system! I love my 3g/poweraster setup, spins so fast and is always charged up. Plus the 3g is so cheap and easy to rebuild it's nuts.

"This engine has never been right" makes me wonder if something with the timing gears is off...but that's not my department. I've never even had the timing cover off of mine.

The part with good compression and good boost makes me think it might be something simple and you have a perfectly good runner, she's just hiding her true self.
The static mark means about nothing, the one on the pump can be way off or sorts close, the static mark just gets it close enough to start.

If you want to get closer on timing I would:
Listen on a cold start for the "powerstroke rattle". It should hurt your ears if you're at the front of the vehicle and you have good hearing. Then, when the cold idle drops down that rattle should go away by quite a bit.
If you're not there yet, advance the pump towards the passenger side another 1/8" or even a 1/4" if you want. Too advanced won't hurt it in the yard. I've had mine from +2° ATDC to 17° BTDC for example. Driving way advanced isn't advised but you have to be quite advanced for glow plugs to get consumed.
Bear in mind that tuning by ear will only get you close, but close can be great. Experienced IDI'ers can only get within 3° by ear.

The reason I mentioned going 6.9 unless you want to do a lot of boost is that studs are only good for the high teens in a 6.9 even with studs. While the 7.3 will bend rods before blowing the HG with studs. Plus the 6.9 already has the cooling mod from the factory and will get better MPGs, all things being equal.

You sir were correct, the injection pump drive gear was 2 teeth off! I took a picture with my phone but can't figure out how to attach it without a lot of extra steps. But yeah totally different truck now, starts right up and has a ton of power also sounds completely different from before. It actually sounds like an idi and even has a slight turbo whistle that it's never had before. Just wanted to give an update even though it's been a while.

 

[IDIBRONCO]

You sir were correct, the injection pump drive gear was 2 teeth off! I took a picture with my phone but can't figure out how to attach it without a lot of extra steps. But yeah totally different truck now, starts right up and has a ton of power also sounds completely different from before. It actually sounds like an idi and even has a slight turbo whistle that it's never had before. Just wanted to give an update even though it's been a while.

Great to hear this. I'll bet that you're happy with the results of all your work too. It sounds like it's a good running truck now.

 

[SuperDave]

View media item 833
I think my pyrometer done had died it's stuck where it is now and won't move. It's got power and a good ground and is connected to the probe still it's just not working. Anybody got any idea how to diagnose these to tell whether the gauge or the probe is bad or where I can get one that looks the same so it will match my boost gauge. Truck is running great but I'd like to get that pyrometer back working. Thanks.

 

[u2slow]

A pyro probe is a thermocouple... will produce a millivolt response when heated.

Not sure if the Banks gauge direct-reads the millivolt signal, or uses a module to step it up to a 0-5V signal (for example). In the case of the latter, the gauge is 'dumber' and you could feed it an appropriate voltage directly as a test. Beware, you can easily cook you gauge applying the wrong voltage to things.