First post to the Diesel sections, but I do love my VW TDI!


A friend is willing to sell a non-running 1993 F250 with a 7.3 and ATS turbo kit for $500

In the next state over, someone is selling the rods, pistons, and block for a 6.9 for $300.
I could also buy a complete non running truck with a 6.9 for $500.

Is it possible (and worth it) to pull and recondition the heads (deck, valve grind, new seals) from the 7.3 and build up the 6.9 block? Or does the 7.3 head and gasket require a 4.111 bore?

If the heads and gasket will work, would it make sense to bore the 6.9 block for 1/2" 7.3 headbolts?

I'm assuming the 6.9 is a good block for a small overbore, or maybe I'll luck out and be able to hone and re-ring.

Will all the 7.3 accessories, brackets, and wiring correspond to a 6.9?

Are the 7.3 and 6.9 rods identical? I'm thinking that the turboed 7.3 rods are probably going to be beefier.

Any other tips or pointers would be really helpful.

In theory I think I could get a 6.9 block, with stronger rods and headbolts, "betterized" valvetrain, AND a factory turbo for less than $1000.

Pipedream? What am I missing?

 

7.3 heads are different and will not work on a 6.9 block... anything can be made possible but it is not that simple. As far as boring out the head bolt holes, RacinNdrmin just tried that and it did not work out. It would need precision machine shop equipment, not DIY tools. The depth of the holes is different, and would require custom studs of the correct length. You cannot drill a 6.9 block to the depth of a 7.3 fastener. Basically if you build a 6.9 block you need to use 6.9 heads and 7/16 fasteners. Again, anything is possible but not very cost effective. Might as well just sleeve all 8 cylinders on a 7.3 (around $1,250). I asked locally and was told I could sleeve a 7.3 to a 4.00" 6.9 bore size if I so desired.

Which brings up your next point. The crank and connecting rods are the same between 6.9 and 7.3 naturally aspirated engines. In 1993/94 the 7.3 was available NA or factory turbo (8th digit VIN=K). Factory turbo rods are bigger, and have bigger wrist pins so you can't put 6.9 pistons on them unless you bush the rods like RacinNdrummin did. The turbo rods use a different vibration damper and flywheel for correct engine balance.

You said the 1993 has an ATS turbo, and if it is not the Ford branded version of the ATS 093 turbo, the truck probably has the naturally aspirated 7.3 with an added ATS turbo. Check the VIN to know how much is compatible with the 6.9. The turbo kit itself is probably worth the $500, and the serpentine belt system is a nice upgrade.

I can't advise you concerning which non-running engine to buy and build. Any non-running engine can be a snake bag. But at least the block with parts option lets you visually inspect the internals before you buy. You could pick up a pair of heads for it and use the rest from the 7.3 in the 1993 truck.

Unless you plan to build for a lot more horsepower than a kit turbo and turned up stock pump, either engine will be adequate. If you want to run more fuel and higher boost on the 6.9, shave the pistons while they are out to lower the compression a little and use ARP head studs.

Hope this helps, btw I also love my TDI Jetta. It is a great car

Edit: all the pans, covers, accessories, brackets and miscellaneous peripherals will bolt right up to a 6.9 block. Externally they are the same. Keep the 7.3 rocker arms as well, they are stronger and work on 6.9 heads.

 

If the 1993 truck does happen to be a VIN code K factory turbo truck, here is a great PDF that discusses the differences from a naturally aspirated 7.3. In fact this is a generally informative manual for anyone with an IDI.

https://www.ford-trucks.com/ford-man...l%20Engine.pdf

If you are thinking of building up a 6.9, check the block serial number. I would avoid the early 1983 "a" block type if you can. The 1985 and later are the best.



To find the number you look next to the IP housing on the driver side:

 

Wow. That was incredibly helpful.

I think all the internet reports of weeping cavitated 7.3 cylinder walls turned me off to the idea of building a 7.3 block. Is it really that common for them to fail that way, or is it an absolute worst case scenario?

I believe the 7.3 ATS kit is factory, so it should have turbo rods. I'll have to check the VIN to confirm. Is there a go-to source for undersize pistons if I sleeve the block? I know machine shops can order them, I just like pricing things out completely beforehand.

Any block work is going to be done by CNC at a reputable shop, so I was anticipating fairly precise machine work for any operation.If the shop can open up the 6.9 block for 7.3 headbolts precisely and reliably, is there any other reason not to use a 6.9 block?

I'm not trying to work around your advice, I swear! I just haven't priced out the machine work for either block locally so I'm just wondering if the 6.9 idea has any bigger issues if it turns out to be cheaper than sleeving.
I suppose new pistons or wristpin bushings for the turbo rods will probably eat those savings quickly.

I'm trying to research RacinNDrummin's 7.3 build, but the thread is 140 pages long (and very entertaining) so that's going to take a bit of leisure reading to see what he did.

Thanks !

 

I have only actually seen cavitation once. From what I've read from others if you buy a 7.3 with unknown SCA treatment, just treat it and run it. Most likely you will be fine but it still can be a problem. I think its an overstated problem, being as its not as common as some let it on to be. But thats just my opinion.

 

If the 7.3 block is not cavitated and you can get away with just honing it that is one thing, but boring the 7.3 oversize has mixed results. Some have gone .020" over, even .040" over and been fine, others bored 0.20" and could visibly see the pinholes. Since the damage occurs inside the water jackets the only way to really know its condition is to have it sonic tested. Even 6.9 can cavitate, with .110" more meat on the block... depending on the conditions. High cylinder pressures (running the hell out of it) and not enough pressure in the cooling system are contributing factors.

Putting 1/2 inch fasteners in the 6.9 block will probably be more expensive in the end than sleeves. The block bosses are smaller on the 6.9, the holes are not as deep, and the thread pitch is different. RacinNdrummin went all the way up to 9/16" but he tested 1/2" as well. There was some thread interference but it still worked. The problem he ran into is slight cross threading of the counter bore, and slightly off perpendicular holes. Perhaps your machinist can modify the block with better equipment, but Racin' is a machinist. He knows what he is doing. He just wanted to develop a DIY jig and stud kit for the rest of us. Keep in mind that the custom studs to make this work were over $500 his cost straight from ARP. Then there is the machine work to the heads and block to make the studs fit. Considering that the 6.9 block will also need normal rebuild work (hot tank, magnaflux, boring oversize, and possibly decking... say $250+) you very quickly approach the cost of a complete re-sleeve which includes all that, without any question of whether the fasteners will work.

Which brings up another point. The weak point in getting power out of these engines is the head fasteners stretching and causing head gasket failures. If you are concerned with fastener thickness you should already be planning on studs not head bolts. Racin' sells 7.3 studs for $390 I believe. The 6.9 studs can be had on eBay for $220-$240. A studded 6.9 will hold more than 7.3 headbolts. That said, a few folks have had HG issues with 90cc IP's and turbos prodicing mid 20's psi boost. It is just a fact that high compression ratio engines can't handle really high boost and exhaust drive pressure ratios. If you want to build this thing up a bit, I would say stud a 7.3 or stud a 6.9 and lower the compression ratio to ~18:1 by shaving .050" off the pistons. You will be plenty fine with that unless you go extreme with your fueling and turbo. If you are just running the factory turbo kit, you can stud a 6.9 and keep the wastegate adjusted for under 20 psi. That turbo is out of its efficiency range by that pressure anyway and producing heat pressure not oxygen density. It would really help to know what your power goals are, because a lot of this could end up being very expensive overkill if you are not dropping big $$ on a hight output IP and upgraded turbo system. Same goes for bushing out the turbo rods. They are beefier, but I don't think anyone has ever found the limits of an NA rod. They are plenty strong.

As far as undersized pistons, I don't think they exist. When prople sleeve a 7.3 it is usually for a standard 4.11" bore. You could, however sleeve to any 6.9 piston including overbore sized pistons. (Using NA rods for correct wrist pin size). In case you missed it, also be aware that 7.3 turbo pistons with the bigger wrist pins are very pricey. I seem to recall reading that they are no longer made, so NOS supplies fetch a premium. They also use keystone rings. These are generally still available on eBay. Just some cost factors to consider with the turbo stuff. While you have the engine apart, I would also recommend RacinNdrummin's custom cam grind for a turbo engine.

One last piece of advice, unless IDI stuff is really scarce in your area, hold off with buying a 6.9 until you open up the 7.3 and see what shape it's in... the $ you are thinking of dropping on a 6.9 could go towards repairing that engine. I would just see what you have first.

 

By the time you fool with all/any of that, you could almost buy a 4bt mated to a T19 and with minor fueling mods (starwheel/afc/gsk) and a junkyard intercooler, make more power and *way* better fuel efficiency.

 

There is nothing wrong with a Cummins swap... really a nice option especially if you are starting from zero as far as an engine is concerned. However I would caution that the mechanical Cummins 4BT and 6BT are getting older and mostly needing rebuilds by now also. Then there is the cost of adapting it to the Ford truck. As far as way more power and using way less fuel doing it... the Cummins is going to need some upgrades to beat a turbo'd IDI. Driving empty the smaller displacement has the upper hand with mpg, but when working I think you will see less difference. The V8 design has a really nice power band and lower rpm pull, it all depends on what you want. Like I said, I am not anti-Cummins, but I don't buy the statement that they are superior in every way to the IDI... some of us just like the V8 diesel clatter and these things offer outstanding performance potential for the money... more than most people give them credit for.

 

Hey Odie. Don't let that Turbo Truck go to the scrap yard... share the info if you don't buy it... Many people have been trying to find one for parts or to rebuild the truck if it has a good frame and title. Its always a good Idea to pass on the info if you find a good deal on some IDI parts. I'm looking for one myself..But I wont be able to swing it till spring...

 

Thanks again to everyone for the info.

Short reply:
I have a lot of engines to choose from, and a lot to think about.

Long reply
The reason I'm considering doing so much mixin' and matching is that I currently have a 84 F250 with the 351W. I figured that buying the (non-running) 6.9 truck and building it up could leave me with a second truck in which to put the orphan 351 to write off or give away to a local family in need (though the terrible mpg makes it a mixed blessing).

The truck with the 7.3 is pretty much good for just the engine (rear ended), and compared to the cost of a Banks or a Hypermax system, I feel it's a solid buy just for all the bits and pulleys hanging off the long block.

As for power, I'm totally happy with stock boost numbers or maybe just slightly pushing the listed numbers Ford's engineers designed. I've always had a "gears over gas" mentality- I'd have way more fun with a Honda engine mated to Rockwells than a BB 460 that's undergeared at the axles.
I'm not trying to win a tractor pull or drag race...in fact, the truck in it's current form gets at most 500 miles a year hauling horses or hay or exploring mountains at 11,000 feet of elevation. As it's been rehabbed over the past few months it will be getting more use next year, but ultimately the 6.9 build and drivetrain is intended to outlive the truck.

After joining the TDI cult, it's hard for me to look at any vehicle that doesn't get 50+ MPG as anything but a toy or tool. If I can rebuild a "toy" engine that will be solid for another 250K miles after it's current practical use, then the initial cost of that toy is amortized, for me, over several decades, regardless if it winds up in a tube buggy, hunting truck, or my jetta.

No offense totalloser, but I almost literally facepalm every time I hear that suggestion because I get it a lot.
Old Fords are just weirdly plentiful in desert states. Despite what I read online, the 4BT is the Diamond-poopingSpaceUnicorn of powerplants around these parts. Maybe it's because it's become increasingly popular as a swap, but I can't find a complete one locally at any price. Maybe it's me; I can't identify what skid steer/snowblower/Bread Truck/asphalt paver the 4BT was installed in without an internet connection, but I can spot a Ford truck in a junkyard from the highway with 95% certainty.

 

So are you proposing to put your project engine into the 351W truck? The Diesel engine swap is a bit of a project and you might want to consider the non-running 6.9 truck for the 80-86 model diesel specific parts that will make your conversion considerably easier. Where are you located? Is the gasser vs diesel VIN any issue for registration and/or emissions where you live? Many of us can't do that. Also what transmission are you planning to use? Since you are staying with stock-ish power and boost levels, the most engine for the money will be a quality rebuild of a 6.9 fitted with the factory turbo. Use head studs for an extra bit of insurance if you can afford them. Diamond-poopingSpaceUnicorn huh? I love it. I have never seen a 4bt on CL or in local yards either..., 6bt sometimes come up, but I think they price them by the ounce.

 

Ummm, if it's a 351 trans, that is THE trans patter than a cummins bolts right up to using the common small block ford engine adapter that comes on many 4bt's. It's limited to a smaller flywheel and a somewhat oddball starter, but just something to know.

The cummins is tuned extra dumm from the factory, but this is easily remedied (and cheaply) to vastly outperform the IDI engines even with a turbo. A 4bt will be close to it's unmodified longblock limit to compete with a turbo IDI, but will far outperform it otherwise (durability, efficiency). Mods to get there are very cheap and easy- I listed them, but I'll spell it out for clarification.

4000 rpm governor spring kit to prevent the progressive defuel as rpm increases
turn starwheel to increase max fueling
remove fuel plate (or buy more aggressive one)
Modified AFC makes the boost/fuel ratio more responsive
And probably turn up boost- about 30psi on the stock turbo

These mods are way cheap and will take a 4bt with an intercooler past the HP of a basic turbo idi. This is assuming a p series IP, but a VE pump actually has more potential for efficiency since it has variable timing. The VE has fueling limitations, but until you are doing studs, this is irrelevant IMO. And with a 351 housing, the clutch will limit power anyway.

There is no way to make an IDI compete in fuel efficiency. You lose about 20-25% off the top for combustion chamber efficiency. This is why I am looking into the zf swap so I can drive the Ford with similar fuel efficiency to my Dodge. Even with OD and 3.55's in a standard cab I will never be able to attain the same efficiency I get out of a extended cab cummins 4x4 duallie on big rig rubber (23+ in combined driving- hand calculated). I hope to break in to the low 20's from about 17 in my Ford.

I do like my 6.9 and have no intention of swapping. But there are limitations that are a reality. I prefer reliability over power, and an IDI is much less forgiving of mods. Older cummins are roughly as simple as an IDI. Maybe even more simple depending on how you look at it. The P series pump doesn't do timing, and the cummins doesn't use hydraulic lifters or a roller cam. But they are HEAVY. Even with half as many cylinders the 4bt still weighs about the same as a 6.9.

Basically the issue with serious mods on an IDI is that it hit's it's limits quickly, and will always be less efficient. So serious IDI mods merit serious swap considerations as I see it.

Cummins problems: 53 block, KDP (killer dowel pin), vp44 actuator housing/diaphragm failures. Weight and initial cost. Adapters that accommodate a big clutch are EX$PEN$IVE.

As a final note: Odie- some folks giving advice are unimpressed by offensive comments. I don't think you have the experience or knowledge to merit a face palm in response to information I have presented, though I am all ears if there is something factually incorrect I have stated.

 

I was pretty explicit in where my frustration lay with repeated 4BT suggestions. It's like throwing a birthday party for your mom, then having that drunk guy in the corner keep yelling, "You know what this party needs? This party needs some goddamn SUPERMODELS! "

Of course there are "better" engines. I could pull the 6.6 Duramax and Allison from my Denali. Maybe I could pull one of the two LS1 crate engines from the tube buggies we have in the shop. When, in my limited knowledge and experience, I get in over my head, I guess I'll have to break down and call the guys at Novak. Maybe they'll bail me out since we've been on a first name basis for the past decade.
I get where you're coming from, I really do, but the scope of the project is limited purposefully. Horsepower in a $500 Turboed IDI is plenty enough for me with proper gearing, and mileage is more or less irrelevant for a truck that was pulled from the weeds in the back acre to make a hauler for the days when we don't want to wash the good trucks. Though I've yet to go elbows deep into one, the 6.9 appeared to be a good replacement for when the 351 tires, and given that I can find IDI trucks literally by the dozen out here, it seems like a natural choice for a small side project.

Again, my (facepalm inducing) problem with a 4BT is that I can't find one locally. It wasn't a dig on the size of your Cummins knowledge stick.
I do appreciate the advice though.

 

Ah, maybe your obnoxious "drunk guy in the corner" comments confused me.

The reason I made the suggestion was because of how costly and involved the hybrid 6.9/7.3/turbo combo would get. By the time you are done, much more expensive options are available in the same price range.

Were it me, I'd simply find a cheap runner IDI or a rebuildable engine.

Availability for 4bt is quite easy. They are all over Ebay for about $3k with free shipping.

Hey do what makes you smile. Diesel efficiency, with old skool v8 sound makes me smile.

But don't flatter yourself, I am answering this thread not for the offensive and insulting banter, but for the several hundred other folks interested enough to read the thread. You can put a 1.6 in your TDI if it makes you happy too.