Better build opinions 7.3 or 6.9

[OldIron82]

Hello all. Been busy operating my own business, but down time coming soon and now I have a good amount of cash to get things done properly. I was dead set on a 6.9 forever but after thinking about what I'm going to be doing I was wondering if the 7.3 would be better.

I want to...1: Have a 6.9 bored just enough to true up the cylinders. 2: Order pistons of that bore size shaved to about a 18:1 compression ratio. 3: Ceramic coat pistons and use the full seal 2nd ring.

After this is done and reassembled, Go with a Bull or Omega Moose with R&D's stage 3 intercooler turbo kit.

Now financially speaking, would it not be better to just use a 7.3, sleeve all 8 cylinders to a stock piston size and then do the ceramic coating and piston shaving? Reason being I'll be able to use 7.3 IDIT pistons, stronger Powerstroke connecting rods ( if I'm not mistaken ) and thicker 1/2" ARP studs. I guess what I'm asking is would sleeving a 7.3 cost around the same as boring a 6.9? You have to bore them both anyway. I already have all the gaskets, studs, and two rebuilt heads for a 6.9. It would be a shame to have done that for nothing but if the 7.3 is going to yield a night and day difference of a more bombproof product I must consider it. Seeing as how I want to be decompressed I see no reason why the smaller 6.9 studs should fail me. They're still studs after all. I would greatly appreciate any insight. Thank you all.

OI82

 

[83ford]

I was gonna build a 7.3 but I got to thinking and the 6.9 has a thicker block because of the smaller bore so I think it would hold up better. May not be true but also it needs to be a later 6.9 block of I'm not mistaken the early ones had cracking problems around the block heater I think but I'm not sure. Also 7.3's are prone to cavitation if you don't use sca's so I think the 6.9 block is better


Sent from my Iphone using Tapatalk

 

[crash-harris]

What is Mel using for his 7.1L blocks? I'd think the best of both worlds would be to sleeve a 7.3L a little narrower. That way you have slightly thicker cylinder walls and get the larger head bolt holes. Not to mention the rebuild-abilty of sleeves. Another reason why the Enterprise will get a DT360...one day...

 

[Hydro-idi]

Your choice really. I would go with the 6.9 build, mainly because you have lots of primo parts sitting in your garage. If you have good rebuilt cylinder heads, that's half the battle right there. I would also go with the updated rockers too.
Yes, the 7.3 Idi has larger rods & pistons with bigger wrist pins....just to name a few differences. But who has snapped a 6.9 rod due to excessive HP? They are stout enough to add the added HP no prob. The
7.3 displacement is also a tad bigger but not much to make a difference IMO. Cavitation is an issue on a 7.3 and very rarely does it happen with a 6.9.
7.3 Idi headbolts are also larger, but who cares IMO. Stick a set of arp studs in a 6.9 and your golden.
Having said that, they are both great engines. It will be costly to sleeve all 8 holes in a 7.3.....and you need to find a reputable shop to do it properly if you go that route.
Ceramic coating is a wise idea. But I have something to add to this. I got my reman engine up to 1400-1500 egts on a few occasions....don't ask why. When I tore her down a couple months ago, the Pistons were in great condition, & they were not ceramic coated. They showed no sign of piston tops starting to melt. However, all 8 precups were severely cracked & every intake and exhaust seat had a nice long crack traveling into chamber area on heads. Cylinder heads had 500 miles on them and they checked out "crack free" prior to me putting them on this engine. Sooo....when egts get above 1200, heads will start to crack waay before Pistons begin to melt.
I had to junk mine & find a set that were in better shape. Just my .02

 

[88 Ford]

^^^ What he said! The rods hold up pretty well to about 350hp. When you are getting over 400hp, that's when you are really pushing the stock rods. Also if you want PSD rods and a 6.9, you could always bush the PSD rods down to the 6.9 wrist pin. Additionally, if you only go with a Bull Moose, there really isn't even much reason to decompress the engine that much. An Omega Moose would be good to decompress with though. What cam would you go with and what would your turbo setup be?

 

[no mufflers]

if you decompress the motor I am curious to see how it starts and what kind of boost you can get. I would talk to Mel about a turbo setup to see what he has to say. I think heath has a moose boost on his truck, maybe he will chime in.

 

[IDIoit]

i started using the 7.3 right off the bat, because of the 1/2" head bolts.
there has been a few cases of cavitation but its not as bad of a problem as you may think.

if you plan on driving this truck on a daily, i would advise that you use nothing bigger than a bull moose.
my bull puts enough fuel out, that i can still cook the engine.

powerstroke rods will not work, unless you have them modified.
IDI rods are thinner. i dont like the idea of machining connecting rods, but if thats what you choose, ill pay attention.

 

[riotwarrior]

Sleeve 8 in 7.3 if u can locate crank rods and balancer from factory 7.3 turbo engine u have the larger wrist pins.

PS rods need machine work to fit...factor that in...big end is too wide!

You can sell the 6.9 stuff or use the heads on 7.3 ream out the bolt holes to correct size...

So that leaves a set of studs...sell em a d get 7.3 studs.

Cam ip and injectors and IC you be golden

Ya zero gap second ring great idea as is ceramic and moly coating the pistons.

Sounds like a hellabuild either way.

JM7.3CW

 

[hesutton]

My question before starting anything with your build would be "what's your end game?" Meaning... what are you planning on doing with this engine and your truck? Very different build plans between a rig built to haul heavy/reliably vs. a toy to hot rod around in, a dyno queen, or smoke show/look at me truck.

If this rig is going to be just a toy for funzies, dyno numbers, and you don't care how it will actually work as a functional truck, dump all the fuel and air into it you can. If you want a truck that you can actually use as a truck and have it do that work reliably for hundreds of thousands of miles.... pick your parts, turbo, and fuel carefully... with that plan in mind.

Heath

 

[OldIron82]

@ Hydro-idi: That is insane! Wow! Good to know however. Just sucks you found out that way.

@hesutton: End game is a work/dump truck that doesn't get driven everyday but I enjoy driving it every time I do (which might be everyday) ; ) I'd like it to move like a stock 6oh no. That's plenty fast enough. I'm still torn heavily between dropping in my first gen Cummins and using the 7.3 in the truck now for a bottom up build specifically for a daily driver. Again, 300hp at the wheels would make me giggity happy. I keep hearing for a work truck use the Cummins but that's a lot of work. A idi will bolt right in, but I need to build it first. Trying to figure out how would the money be best spent, you know? Reliability is far more important than power/speed. To me anyway.

 

[hesutton]

If you are dead set on 300HP and want to haul with the truck, I'd be hard pressed to recommend building an IDI. The Bull Moose on my 6.9 crew cab truck with the GT3788R turbo is a happy medium between power and EGT's. EGT's are your enemy when hauling heavy with these IDI's. Immediate engine damage not withstanding, the heat stress on the whole system will make any excess fuel essentially useless.

EGT's drive oil temp. Oil temp drives coolant temp. Once the oil and coolant are saturated with heat, you're on a thin line between a running IDI and burning it down. Keeping your EGT's in check will keep you hauling with your rig for years, not months. Too much fuel, too small turbine A/R, inefficient turbo compressor, poor cooling system condition, and so on, all contribute to EGT and heat control.

Again, if 300HP is a must and you're seriously planning on working the truck, I'd personally start looking harder at that 6BT of yours.

Heath

 

[no mufflers]

heath, have you put your truck on a dyno since the upgrades, how does it tow?

 

[hesutton]

heath, have you put your truck on a dyno since the upgrades, how does it tow?

No I haven't. It tows well. Big hills are where the IDI struggles, but it struggle less than it used to. Relatively normal roads, I can run 70 in OD hauling the camper. Had to upgrade the wheels and tires on my camper to compensate for the increase in cruising speed. Lost way too many tires last summer on the fifthwheel running at that speed. My biggest gains from the turbo swap, less smoke (hate cleaning soot off the side of the camper), and much more controllable EGT's. With the Banks, I had to watch the pyro and therefore the coolant temps constantly especially in hilly terrain. Now, I will look at the gauges from time to time, but I'm not hauling with high blood pressure from high EGT's/water temps.

What gets my blood pressure up isn't the truck, but the tires (or the failure of) on the camper. Hope the up grade to 16 inch wheels with Michelin XPS RIBS will keep me rolling and not on the shoulder changing camper tires.

Heath

 

[OldIron82]

70 in OD hauling a camper would make me estatic. I still think I'll be okay with a IDI. If I have to haul really heavy I have my 4700 DT466E ( HATE the "E") International. The majority of the time the truck would be hauling, not towing. 13,500lb max. I don't need to light up tires or have the turbo glowing cherry red, acting like a clown. Just looking for the truck to be "peppy"

You have Mel's "Moose boost" turbo correct? Is that based on the Hypermax turbo, or is it the Hypermax plumbing with a custom build turbo?

 

[hesutton]

Yeah, I have the Moose turbo. Garrett GT3788R. It's on my Banks plumbing (modified of course). Once the intake manifold was modified, it wasn't too bad get installed.

13.5K total isn't crazy. Truck and camper on CAT scales was 16.7K total.

Heath