What's everyone think as far as setting up an idi engine for maximum economy?
I see a lot of comments such as "these injectors I got run great" or "it likes more timing" but little actual concern about economy.

I read that the timing should be closer to 9.5btdc to account for ulsd?

what about injectors? If they are set to pop higher will it burn cleaner?

would a person be better off using injectors from a 6.9? Do they have a tighter nozzle?

I've been averaging just under 20mpg us, and I think that's exceptional for winter. I think my pump and sticks are factory with 200,000miles on them but with mileage like I'm getting I'm feeling reluctant to mess with stuff and replace.
but if I DID order new parts, what you guys think would be the way to go for clean burning economical running?
it's a 94 idi factory turbo

 

I think the transmission and gearing will have more of an effect on your fuel mileage than the injectors and injection pump. Does your truck have a ZF5? Does it have 4.10 or 3.55 gears?

 

if you have 200,000 miles on the engine, i really doubt it has original injectors and pump in it. service life is only around 150,000 miles.
the best i ever got was 175 on a pump and injectors, and by then it was running like crap.

 

e40d, and I thought 3.73 as it runs 1700 rpm at 100km/h

 

I've heart of them lasting a very long time, but I'm thinking mine are original since there wasnt a single paint chip of the injector line bolts

 

I don't think there's much you can do with these engines to increase economy. It seems like fuel is directly proportional to RPM with much less regard for load than a gas engine (i.e. crack the throttle at light load on a 460 and it'll turn 2000 RPM just off idle while an IDI will turn maybe 900 RPM). Exhaust system and head porting gains are mostly minimized by a turbo, so very little gains to be had there. Indirect injection doesn't care nearly as much about injector spray pattern or atomization as direct injection, the precombustion chamber does most of the work.

That being said timing does make a difference. When I got my truck it was at 6.5* at 2000 RPM and getting a gray hazy 8.25 MPG. Adjusted to 9.5* at 2000 RPM and MPG went to 10.56 on the rest of that tank, averaged 11-13 MPG thereafter. That was with a very worn out pump and injectors. I put a new 100cc pump and 2200 psi injectors (from Conestoga) when it got bad enough that it wouldn't start when hot. Power was significantly increased, MPG might have dropped slightly (likely a heavier foot off idle since it could almost keep up with traffic at that point). This was all with a Banks non wastegated turbo.

I swapped a ZF5 into it and gained about 3 MPG from that, regardless of stop and go or highway. I changed to a wastegated Banks at the same time, as the non wastegated would not fit with the ZF5. It does best on two lane blacktop (lower RPM). It'll do 15 MPG highway, that's at about 2000 RPM at 70 MPH with 3.55:1 gears. RPM kills it. I later swapped that 6.9 to a 7.3 when it blew a head gasket. The 7.3 has a R&D cam, studs, and total seal rings. Finally I think it can keep up with my 460 truck so long as it's not pulling a load up a long hill (EGT), MPG seems to have slightly improved over the 6.9. All time best MPG was with the fresh 7.3, 18.56 MPG. I think with this engine it could pull a double overdrive (~1600 RPM) unloaded on level ground. EGT would probably be an issue at times though an intercooler should fix that. Realistically it'll need a larger turbo at minimum and probably more fuel to be able to comfortably pull a double overdrive. I suspect that would result in a higher average MPG on the highway, but no change around town. I suspect high teens is about as good as it gets, maybe a tick over 20 in a regular cab 2wd (mine is a crew cab 4x4).

 

I've definitely noticed how linear the rpm is to throttle position. I was very surprised to learn that the pedal is simply controlling the rack. It feels like an rpm governor.

more overdrive seems like it would really help, but that option would cost as much as the truck lol.

has anyone ever removed the pre cups and removed some material from the outside so they have less contact with the head and can get hotter?

 

You need to determine what your goals are. Maximizing MPG and the lowest possible TCO are different goals. Make a spreadsheet that accounts for the cost of whatever change or upgrade and calculates ROI in both time and miles. It will help when determining if a particular upgrade is worthwhile for your use.Keep in mind they're all $10k trucks, and it's typically cheaper so far as any vehicle goes to just get whatever vehicle you want and keep it for the rest of your life or until some very distant date when your needs change.

This sounds like a bad idea to me. I don't know that there's any measurable efficiency improvements to be had here, and every IDI head I've ever had apart has had cracks in the precups. More heat will accelerate failure (when cracks reach past the fire ring). For seeking MPG in the heads I would be porting them. Just clean up any flash on the intake, but go with the usual strategy on the exhaust side. There are appreciable gains to be had. https://www.ford-trucks.com/forums/1...vs-ported.html

Since we know timing has an appreciable affect on MPG and power, you could try running more timing. Much over 10* and you'll be damaging glow plugs. Engines that do not use glow plugs typically run significantly more timing than these IDIs do. There is also the consideration of the relatively high compression of these engines and the additional load on rods and bearings with more advanced timing. If you are seeking lower TCO or lower cost per mile rather than higher MPG, this could be an expensive experiment.

 

Got to agree with this guy's post on the referred to thread:
Porting and headers on a relatively slow turning 3400 RPM engine? Years ago a guy bought a non-turboed IDI with headers, in time he pulled them off and said he saw no power decrease whatsoever.

 

I will jump in here for my .02. Timing definitely can and does affect economy, to a large degree. That said, there isnt a [this number is best]. I went from 8* to 5.5* and 13-14mpg to 15-16mpg respectively. I do however have a 110 pump, "stage 1" injectors, as well as justins cam, pushing a 64mm turbo. When i retarded my timing, my egts dropped 50* across the board, idle, part throttle, cruise, load, etc. I feel i did a pretty good job duplicating the before and after tests too. Best advice i can give is to tune by the pyro, the lower the better because youre either A: Burning less fuel, B: Burning i the same fuel more eficiently, or C: Both.

On my old engine, i went as high as 12* from 7* in 3 adjustments, each time yielded higher EGTS, lower mileage (14.5 to 12), and harder starting. However, it did seem like it made more power, by a very small margin, at 12* you could start to hear a bottom end knock if you really got after the throttle under 12-1300 rpms. This was a pump and injectors that had ~270k on them, and i strongly suspect that the internal timing bits of the pump were not working correctly.

 

I've also read that the IDI headers don't do much for performance and fit poorly. I imagine it would be easier to find a used turbo setup than used headers. There's only one source I know of for IDI headers (other than custom).

Headers for Ford, Mustang, Pinto, Bronco, Cougar, Ranger, exhaust parts for home built do it yourself automotive headers.

 

Ok some excellent points here everyone.

I hate to be a stickler on the precup temperature thing, but since the precups have a large part to do with combustion, wouldn't their temperature have a large influence on timing as they essentially control how fast fuel ignites and burns?
seeing as how they're made from inconel and already can crack, maybe the design is already at its limits, so I guess theres no point in theorizing. I would be interested to see precups made from an even higher heat stable metal, with little wall contact running at far higher temperatures.
In my head it stands to reason that less heat going into the heads is more efficient and higher precup temperature would give cleaner faster combustion. All I need is to win the lottery and have custom precups made from tungsten lol. Or maybe ceramic coated 🤔

I'm also wondering after reading a bunch of threads regarding 2 stroke oil in fuel, and it's been stated many times how the engine runs quieter with 2 stroke oil..... well if it runs quieter that's a pretty good sign that the fuel is burning slower. So I guess fuel quality and additives are also something to consider when setting up timing.
after reading some threads about timing the pump and watching videos, everyone seems to want a timing system instead of going off ear and sound, but what I'd really like is a transducer to see what cylinder pressures are. I think timing by ear but with a transducer would help set the timing up way better than going by degrees. Now I'm thinking too much.

 

Yep, poor fit and leaks is what the guy said so he finally removed them. I was trying to think of the name and you're right, Stan's Headers. Back then they didn't appear to be a huge seller, at least not for IDI diesels.

 

I just replaced my muffler with a pipe and it's clear by looking inside that this truck wasn't designed for much exhaust flow.
I'm thinking even if you did everything you could for more intake and exhaust flow you'd gain some power on the top end but not much if any mileage.

 

The theory from the big boys (factory engine reps) has always been that a turboed engine consumes 1/3 more air than non turboed. ATS with their turbo kits included a complete 3" exhaust versus 2 1/2". They stated in their info with all their R&D that an exhaust bigger than 3" showed no power gain at all.