Differences between the 6.9 and the 7.3.

CrippledEagle

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I have an opportunity to buy a couple of 7.3 IDI engines. In a previous post I asked about pulling the heads off of my 6.9 in the truck. I bought an ARP headstud kit, a head gasket kit and an intake manifold gasket.
I know that the head studs won’t interchange because of thread size. Might the intake gasket and head gasket set interchange?
Is there a plus for upgrading to a 7.3? Better torque? More power?
My old oil distributor had the International 7.3/444(?) in it and it lost the high pressure oil pump once on the way to the job site and quit running. Does the 89 7.3 have these high pressure pumps? Not sure if I want to upgrade to the 7.3 if they do.
The 7.3s that are available were both in the same truck. The person whose truck they came out of decided he wanted a lower mileage engine and had the lower mileage engine put in his truck. The very next day that truck got t-boned and totaled. The shop owner fell in love with my 57 Ranchero and is trying to talk me out of it. I could have bought a rebuilt engine for what I paid for the Ranchero and had it installed but I bought it quite awhile before my 6.9 dumped. I really don’t want to get rid of the Ranchero, but having the pickup is certainly more practical.
What ever I do, I will have the 6.9 from my 83 to play with and learn.
Thanks in advance!
 

Philip1

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Most bolt on parts for the 6.9 and 7.3 are the same except for the long block. The 7.3 has the benefit of 1/2" head bolts instead of 7/16 on the 6.9. This allows the heads to resist lifting better allowing better boost thus more power. The injection systems between the two are almost identical except for the 7.3 being larger internally (you can interchange them if you wanted) the high pressure oil pump is a 7.3 powerstroke thing. Other differences are the 7.3 cylinder walls are thinner which leads to it having issues with cavitation. Early 6.9 blocks had issues with cracking around the block heater. The 7.3 has an upgraded glowplug system. The 7.3 has a few coolant passages in the heads blocked off which makes the head gaskets different. Intake gaskets should be the same also. You can knock the plugs out of the head and block then use the 6.9 head gaskets to allow better cooling.
 

Selahdoor

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Could the 6.9 head bolt holes be tapped out to 1/2"?
 

chillman88

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Could the 6.9 head bolt holes be tapped out to 1/2"?

Yes but not safely. There's not enough difference between the two thread sizes to leave good threads and if you were to do that the end result would actually be weaker than the 7/16 bolts were.

The 6.9 heads can be drilled out to be used on the 7.3 though.
 

IDIBRONCO

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The 7.3 (IDI) was rated at a little bit more horsepower, but you may not be able to feel the difference between the two. Yes the intake and head gaskets will interchange between the two.
 

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