Limits of N/A connecting rods? Will turbo rods=rebalancing engine?

[DLSF350]

I am considering a major freshen up for my 93 NA 7.3. I would like to go the full route and add a 2nd hand used turbo on it (checking on fleabay). I know the compression is the same on factory motors (turbo and N/A), but wondered if the turbo rods were worth the upgrade (with pistons). I get the impression that since the flywheel and harmonic balancers are different on IDI turbos, that the rotating assemblies may be externally balanced and that adding heavier rods will mean rebalancing the crank/rods/pistons. What is the boost and HP/torque limit on a factory N/A rod with no external problems (keeping water and shrapnel out of the intake) and below 3200rpm? I saw some pics on the DPS site of stock N/A pistons that had been run with 18-19lbs of boost for 68k miles and they looked pretty good (except for the pockmarks from a GP tip in one of the chambers). Does anyone know if they make cometic head gaskets for 7.3 IDIs? if so, who sells them? thanks, Dan

 

[Diesel JD]

Well first of all I think the turbo rods and pistons give you slightly lower compression. I don't want to quote the number that pops into my head, cause I might be just pulling it out of my but. I think the main advantage to the turbo rods is the bigger piston pin boss and of course the lower compression. I don't know about the limit on stock rods. I doubt you will break them before you break something else unless you drop a glow plug tip or valve in there. I don't know what you mean by cometic head gaskets. I would just get studs and any good set of gaskets if I was building a high output IDI. The studs are a must if you're going to boost over 13-15 psi on a regular basis.

 

[Agnem]

I'd be interested to know if that lower compression comment is factual. To my knowledge, the only lower compression pistons are the ones for model A engines, which don't have the turbo wrist pins.

 

[icanfixall]

Mahle makes low compression pistons for both na and turbo motors. Diesel Dierct sells them along with the large pin turbo rods. The rods are $42.50 each without a core charge. Now thats just a really good price. I can't buy them for that anywhere. I have never heard any talk of the turbo rods being shorter for lower compression. As I remember the compression ratio is the same on turbo and non turbo motors. The non turbo rods will stand up to the higher horse power but they are taking a beating because they were not designed for the turbo. The Pistons from Mahle are part number 14418N STD for standard bore and cost $550.00 a set from Diesel Direct. The same set cost me $1100.00 here in Ca. I didn't know Diesel Direct could supply them.. My mistake. If you change out the pistons for turbo pistons and rods just balance it. Also sleeve the block. Then you will have a motor that will live on almost forever. Well, at least longer than me.....

 

[The Warden]

I'd be interested to know if that lower compression comment is factual. To my knowledge, the only lower compression pistons are the ones for model A engines, which don't have the turbo wrist pins.

I don't think the factory turbos have any lower compression than the N/A's, although as Gary pointed out, aftermarket lower-compression setups are available.

Also, FWIW, the lower compression pistons for the "A" 6.9l offers a very slight compression loss...I think it may be 20:1 instead of 21:1, but can't say for certain as my source for that info's on my other computer

Going back to the idea of lowering compression (sorry to go OT)...something I've been wondering. Does anyone have an opinion on the idea of making new precombustion chambers with a larger chamber, bringing the compression ratio down that way? If it could be done, it seems to me that that would be better from a starting/everyday driving perspective than custom pistons, since the extra air would be in the immediate vicinity of the glow plug (and would therefore heat up faster than the air in the "main" combustion chamber). Or am I just nuts?

 

[icanfixall]

Warden, I had a custom ball end mill made so I could "clean up" the precombustion area in my new heads. It had a small effect on lowering the compression ratio. What I did was mill out of the heads the 0.060 thousands that Ford had the injectors pulled up into the heads for the EPA. You know a cleaner running diesel....... Anyway the heads really looked great after this work but.... That motor overheated and I cracked both heads.... If you or anybody else wants to borrow my end mill just sent me an address. This is something that takes some thought so before anyone trys it the first thing you will need is a Bridgeport mill or similar machine and set up corectly it will come out just like mine did. I also opened up the precups to about 0.600 accross the width and about 0.400 on the height. They also have a small bump or trip inside near the throat that I "cleaned" out. It was probably for a cleaner running motor. Kinda like something that would create some turbulance at combustion.

 

[DLSF350]

Thanks for the replies - I think all 7.3 IDIs were 21.5:1 comp - Cometic gaskets

Thanks for the replies, It is my understanding that all 7.3 IDIs had the same compression (21.5:1) with the factory turbos getting a beefier (and heavier rotating mass) rod and 33mm wrist pin with a coated piston (and inconel ex valves). I was wondering if there were any members that were discussing twin turbo IDIs that got around to actually building them (hopefully with stock rods), or if someone had a pic or story about a stock rod that bent or broke due to too much boost rather than running it at 8,000+ rpm or sucking in a gallon of water. Do you remember what the rebalancing cost was with the new rods? Do you know the compression ratio with the aftermarket lower compression pistons?

----------- Cometic head gaskets are a MLS (multi layer steel) stacked gasket. They started being used in drag race applications about 5 years ago instead of copper HGs and have proven themselves up to about 1,800 hp. They are much easier to seal on aluminum block and head motors and are much less prone to water leaks than copper on motors that get heat cycled quickly and often. EGTs on a nitrous motor go from room temperature to 1600* and back in about 3-4 minutes so head gaskets take a beating. I have seen them for powerstrokes but not for IDIs. Dan

 

[icanfixall]

I think my balancing cost around $100.00. I balanced the crank, complete pisons with the rod bearing, the front vibration dampner and the complete 3 part flywheel flexplate with bolts. Really anything that is rotating needs to be inculded on the balance. Even the bolts. I used to balance large 60 to 120 ton steam turbine rotors and we balanced the studs and washers down to the 1 grams area. The rotors were balanced down to about 2 grams at 3600 rpm for a 60 ton rotor.

 

[The Warden]

With balancing tolerances that tight and happy engine mounts, I wonder how much vibration's cut down?

Gary, very cool on the ball end mill!! It would be a LONG time before I'd be at a point to experiment with this myself; I don't have any plans to pull the heads anytime soon, and I would need a wastegated turbo to take advantage of any compression loss in any event (and $$'s still nice and tight). Be interesting to see if someone else would be interested, though. Ken, maybe? (hint hint )

 

[icanfixall]

I have loaned out the ball end mill to a member in Oregon. The member has cut down a head so the webs inside and the relationship of things could be deminstrated better. Ever wonder how thick differant areas of the heads are? I sure have. But anyway some pictures are up and coming from Oregon and an update on how the truck runs now after the cleaning up of the heads.

 

[The Warden]

Can't wait to see those pics...very cool!!

 

[Diesel JD]

Hey, I guess maybe I was wrong about the factory turbo engines. I thought they were down into the 19.5:1 compression range. As far as the trubo rods/pistons, do you know if Diesel Direct has them for 6.9s or just the 7.3? Is this the company that is in Palatka FL? If so they are less than 1 hour from my house. Maybe I'll have to go see their setup and speak with those guys,
J.D.

 

[riphip]

JD, I think they are here in Memphis.

Gary, I may want to get with you later about that bit. I have a set of testing heads that came from Hypermax that I got off Ebay last year for $105 total. I'm looking to port and polish intake & heads (something else to do) When I do my rebuild. I'll balance everything also.
I'll be using turbo from '99 PS (I have 3. 1 is fresh in box IH reman)

Rick

 

[Agnem]

that bent or broke due to too much boost rather than running it at 8,000+ rpm or sucking in a gallon of water.

Baaaaaahaa..