Towing with PMRs and RPMs

LakeBum · Sep 10, 2018

I've got a stock injector truck (SXE turbo) with 3.73s and 35s.

In third gear at 61 MPH Im turning 2200 RPMs. POWER and EGTS are GREAT.

If I shift to 4th, RPMs fall to 1750 and about 68 MPH. IMHO this is to fast of speed for what I feel comfortable towing at. But the truck will do it and pull to 75 MPH as RPMs rise. Again EGTs are not a problem.

I'd like to get a smaller tire to raise my 4th gear RPMs so I can use 4th for most things and then 3rd when I really need to pull a grade.

Question is what RPM is safe for towing with PMRs. Stock tires and gearing would be 1830 RPMs at 65 MPH. is 1800-1900 safe towing heavy with PMRs?

DieselDC · Sep 10, 2018

keep driving. Plenty of things to worry about. Pmr ain’t on the list.

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Petro · Sep 10, 2018

I'm trying to understand why you're worried about connecting rods at stockish power levels? If powdered metal rods were that weak, every 7.3 that used them would have blown up by now. If you get up closer to 500, then you can start to worry about low rpm torque/ cylinder pressure. Until then drive it like you stole it.

The Brad · Sep 10, 2018

There has been more than a handful of stock injectored 7.3s tossing rods back when tuning wasn’t as understood. Now that tuning is better, will it save the rods while running an SXE which can easily push over 20 psi at 1700 rpm sustained while towing? The S467 has been dubbed a forged rod killer, so can the SXE do the same to a PMR rod?

DieselDC · Sep 10, 2018

The Brad said:
There has been more than a handful of stock injectored 7.3s tossing rods back when tuning wasn’t as understood. Now that tuning is better, will it save the rods while running an SXE which can easily push over 20 psi at 1700 rpm sustained while towing? The S467 has been dubbed a forged rod killer, so can the SXE do the same to a PMR rod?

20psi huh.... keep DRIVING...

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...:uptight people suck:...

Calico5 · Sep 10, 2018

DieselDC said:
20psi huh.... keep DRIVING...

LOLLOL

Petro · Sep 10, 2018

The Brad said:
There has been more than a handful of stock injectored 7.3s tossing rods back when tuning wasn’t as understood. Now that tuning is better, will it save the rods while running an SXE which can easily push over 20 psi at 1700 rpm sustained while towing? The S467 has been dubbed a forged rod killer, so can the SXE do the same to a PMR rod?

Do you have any idea how f*cked up the tune would have to be to make that happen? I had several customers kick the ever living **** out of pmr motors for 2 or 3 years with 238's and a 38r, and only one had a rod issue when he hydrolocked his motor when a gasket failed. This isn't 2003, tuning has come a looooonnnnnnnggggg way. Start worrying when boost reaches 40 psi under 2k rpm, until then run the piss out of it, you won't hurt a rod on stock injectors with any sort of modern tune.

LakeBum · Sep 11, 2018

Petro said:
Do you have any idea how f*cked up the tune would have to be to make that happen? I had several customers kick the ever living **** out of pmr motors for 2 or 3 years with 238's and a 38r, and only one had a rod issue when he hydrolocked his motor when a gasket failed. This isn't 2003, tuning has come a looooonnnnnnnggggg way. Start worrying when boost reaches 40 psi under 2k rpm, until then run the piss out of it, you won't hurt a rod on stock injectors with any sort of modern tune.

Would be interesting to here from a Cody on the subject...

superpsd · Sep 11, 2018

Excessive cylinder pressure is what kills PMRs. Like running a tune with way too much timing advance. Jacked up SOI tables and multipliers were the cause of blowing out PMRs. On a stock injector truck you dont have much to worry about as long as the tuning is good. I think there has even been a few to run 300cc injectors in a PMR motor as long as the tune is good.