Rebuild the IDI, or swap in a Cummins

[MaxPF]

I agree if you can get an IDI down to 18:1 compression you can make it do some awesome things. Couple problems though. No one makes pistons with that low of a CR for us, which means you're into custom slugs already, probably cost around $1000-1500 for them, second problem is I hear that the GM 6.5 has something different about it to make starting at that CR not such an "adventure" By the time you deal with all that the IDI loses its "cheapness" factor and becomes nearly as expensive as a PSD with some mods or a Cummins conversion. All that said, if I ever get the cash I will build just such a 6.9 and see what it does. In Florida 18:1 I should be able to get away with it.

Pistons aren't the only way to drop the CR. On a 6.2/6.5, every .010" of deck clearance nets you about 1 point of CR reduction. The 6.9/7.3 should be similar. So, to go from 21.5:1 to 18:1, you need to either drop the piston crown .035", or raise the head by that amount. Obviously you could mill the pistons - .035" isn't that much off of a piston with .500"+ crown thickness. Unfortunately, the desirable pistons for a turbo motor have hard anodized crowns, so you would have to have them re-anodized. Another simple option is to have the effective connecting rod length shortened by .035". This is easy for a machinist to do by offsetting either the big or small end bore.

Probably the simplest way is to call up Cometic and order .035" thicker head gaskets. Total cost: $250ish. Cummins guys have been using them with fairly high boost and they seem to hold up until you get to stupid boost levels, where you are forced to o-ring the block. That is how I would do it.

The 18:1 6.5's usually use 60G glow plugs (12V self-limiting type) and simply glow them longer before starting. Some of the guys have also added a Cummins intake heater to warm up the intake air during startup. Obviously, the only real requirement for these start mods are 2 REALLY good batteries

The main cost as far as I can tell is the IP. DB2's are only good for around 250HP or so. If you want more than that you would have to use the mechanical Stanadyne DB4, which is good for about 350HP or so. So, a guy would need to get a DB4 pump that rotates in the opposite direction as the GM DB4 and have it's delivery rate adjusted for your app. DB4's are spendy compared to DB2's, so for the guy looking for big power it is going to cost you...

 

[david85]

For 300 Hp, here's what you do.


Pistons are available for the 6.9 that are shorter in the event of resurfaced heads or block. Get these ones or have stock pistons shaved down. I payed a machinist $75 cash to have my stock height pistons dropped by 20 thou, it really doesn't cost that much to put them in a lathe and turn them down. Going all the way down to 18:1 compression for only 300 Hp is not only unnecessary, but will also harm fuel economy and cold starting performance depending on the climate. You can have them anodized, but I don't think this is really needed unless you plan on racing it. I do know of one guy that is very happy with pistons shaved 40 thou in his turbo 6.9.

Install a set of ARP head studs and you can probably survive 20 PSI of boost or more depending on how much the compression was dropped. The studs deliver over twice the clamping force compared to the stock bolts when installed properly.

You will also need to install studs for the intake and exhaust manifolds if you go past 20 PSI.

Install a turbo, new or used if its in good shape and working properly, 15 PSI is EASY to get once you wind up to 3000 RPM with the fuel turned up.

Install a modified injector pump with matching injectors. Not needed unless you really want more than 250-260 Hp.

This will comfortably be able to reach 300 Hp without loosing reliability and fuel economy should still be quite good if you drop 20 thou or less of the pistons. For towing or other heavy loads, it may even be slightly better.

But if you can live with 250 Hp, than all you need is a turbocharger and if you really want, the ARP studs. If no studs, just keep the boost limited to 10 PSI. Maybe some one close by can offer him a spin in a turbo rig to see what its like? Anyone that has turbocharged their 6.9 can tell you its a night and day difference from n/a to turbo.

Oh, and swap the valves and rockers from the 7.3 over to the 6.9.

 

[RLDSL]

Probably the simplest way is to call up Cometic and order .035" thicker head gaskets. Total cost: $250ish. Cummins guys have been using them with fairly high boost and they seem to hold up until you get to stupid boost levels, where you are forced to o-ring the block. That is how I would do it.

That may work for a cummins, but easier said than done for an IDI. A couple of folks tried to talk Cometic out of some gaskets for these things a while back and sincethey hadn't done any, they had a minimum run requirement that was rediculous

 

[bull hauler30]

The turbocharger was not standard with 1993 and 1994 IDIs. Only some had them. 1994 was when ford briefly offered 3 different diesel options, the IDI n/a, IDI turbo (detuned), and the new powerstroke (most expensive). The boost is limited by the amount of fuel and air the engine can swallow. I have been to 15 PSI with mine before I rebuilt it. No point turning up the fuel up that high any more, because it burns nice and clean and has all the power I need as it is. MPGs were always my first priority even when diesel was at $0.87/liter (if only I knew what was coming!!!).


this is the option that my truck came with. it was one of maybe two or three that the dealership had when my truck was purchased new

 

[Papabear]

either way i would rebuild the IDI because even if you do the cummins conversion you will always find something to put the idi in

 

[MaxPF]

That may work for a cummins, but easier said than done for an IDI. A couple of folks tried to talk Cometic out of some gaskets for these things a while back and sincethey hadn't done any, they had a minimum run requirement that was rediculous

Ahh, you're right. They only have Powerstroke gaskets

Well, looks like the best option would be to have the rod offset technique. It's relatively easy to do and gets the job done.

 

[redneckaggie]

Not to hate on idis but a ford cummins rig is the BEASTIEST thing in this world. my bro owns 2 cummins a 91 gen 1 and 94 gen 2 both are monsters as far as power and get 20-25 mpg unloaded with his lead foot and pumps cranked to the max of what stock internals will hold. with my dad babying the 91 (bout 55 mph) and 8,000 lbs hooked behind it we got 20 mpg on a 270 mile long trip with half of that in texas hill country. I can smoke stock mustang gts with both trucks and i put chipped and programed strokers to shame when i line up with or without a load on. my bottom line is with fuel at 4.00 a gallon cummins are the most economical engines around they aren't espensive to fix and will pull a house down and get 20 mpg doing it

notice i said cummins engines are the best the trannys and front ends are $hit

 

[punkmechanic]

running WMO in my idi I get over 100 miles per gallon of diesel. I don't know how well a cummins likes WMO but that is just somthing to consider.

 

[MIDNIGHT RIDER]

running WMO in my idi I get over 100 miles per gallon of diesel. I don't know how well a cummins likes WMO but that is just somthing to consider.

A Cummins will eat anything dumped in the tank, SVO, WVO, MO, WMO, whatever.

 

[punkmechanic]

then Im gonna find a cummins. I have always thought the best truck would be a cummins with the right 5 speed in a ford frame and suspencion. un freakn stoppable, thats probably why they didnt do it, build the truck and wouldnt make a dime on repairs. lol.

 

[FordGuy100]

then Im gonna find a cummins. I have always thought the best truck would be a cummins with the right 5 speed in a ford frame and suspencion. un freakn stoppable, thats probably why they didnt do it, build the truck and wouldnt make a dime on repairs. lol.

Well here is an awesome cummins donor truck for you . Has the motor mounts all ready to go and everything

http://portland.craigslist.org/mlt/ctd/836593161.html

Or look at this, 2 cummins for $1300 a piece

http://portland.craigslist.org/mlt/pts/835096285.html

 

[Exekiel69]

If the hole truck is as good as it look then it is under priced by far.

 

[Cat_Rebel]

notice i said cummins engines are the best the trannys and front ends are $hit

Amen to that one brother!
That's a good part of why I ditched my 95 2500 before it sucked me into the bottomless money pit of tranny & front end repairs.

then Im gonna find a cummins. I have always thought the best truck would be a cummins with the right 5 speed in a ford frame and suspencion. un freakn stoppable, thats probably why they didnt do it, build the truck and wouldnt make a dime on repairs. lol.

Come on, without the Cummins the Derges would have much going for em. Infact don't know what all the dodge truck kids could brag about if it wasn't for that oil burning 6 banger.
I'll take my rusty Fords anyday thank you.

 

[punkmechanic]

I never said I was ditchn the idi. I will keep this old beast till it quits (most likly I will quit tickn for she does). I have always like the idea of a cummins in a ford but cost has been the big issue. I will start collecting parts here and there and will eventually wind up finding a reasonable cummins donor, then all I need is a 92-99 crew cab to shortn and stuff the cummins in. It will be a frankenstein, the idi will be there when the frankenstein doesnt feel like going anywhere. punkmechanic+parts= frankenstien/ mad scientist. its only crazy if your not in my head. lol

 

[Agnem]

I don't think that will be necessary, she obvously knows what she wants,..

Your lips move but I cant hear what youre sayin.