RPM limit

[Shamoke]

've looked around and haven't seen any posts about the rpm limits of the 7.3 IDI. The tach caution line is set at 3400 but that seems extremely high to me. I had my 88 F-350 5 speed on the highway yesterday and got up to 65 mph with the tach reading 2400 ish but that engine sounded like it was wound up pretty tight and I started to get concerned about it flying apart. At 60mph it was reading 2200 ish as still sounded a bit high but more tolerable than the 2400.
I grew up around over the road trucks and drove then for 13 years, the Cat's and Cummings engine I am used to top out at 2200 to 2300 and are governed for that rpm. Anything higher sounds wrong to my ear so I am wondering about what speed I should limit my IDI too.

 

[Thewespaul]

I daily drive a bone stock engine other than head studs that sees 4500 rpms, these engines have pumps calibrated to run as high as 3800 rpms by purposeful design from the manufacturers, and in a lot of medium duty, and f-superduty applications that have low gearing for heavy loads they will run up against the governor for hours on end without problems. Calvin (rip) ran a fleet of tow trucks with these engines for many years and ran them all day against the governors to maintain highway speed without a turbo, these engines are designed for the high rpm use that most in-line big displace 6 cylinder engines are not.

 

[mexicanjoe]

Wes, I would guess that with stock tires my '89 with 4.10 gears and 5 speed will top out at 95 mph. Am i correct? I have never got LuluBelle past 3 grand.....dont want to take a chance picking up pieces of engine( ).

 

[FordGuy100]

Stock valve springs float around 4500 RPM's iirc, or probably depending on their condition.

4500 RPM gives a mean piston speed of 3135 FPM.

 

[hesutton]

I know hauling with the 6.9 crew cab, RPM's are your friend. If I let the RPM fall below 2100-2200 on hills, the EGT's start climbing quickly. So I just downshift and let her sing between 2500-3000 and the EGT's come down and the girl keeps on rolling. I don't often need to take it past 3000, but I do when a climb is steep and/or long.

Heath.

 

[Jimbanjer]

I know I’ve gone 95 with my E40D at 3,800 rpm for several hours without any issues on one of my trips through Texas. Just don’t tell Johnny law! although I normally go the speed limit, I have a hard time sitting for hours on long road trips lol!

 

[Shamoke]

Thank you for the replies, coming from the big displacement engines I guess I'm just use to never revving them too high. I can't imagine letting her go to 3500, let alone 3800, It may only have 140k on the odometer but I have no clue if that's accurate and it's still a 31 year old engine and all original as far as I know.

 

[nelstomlinson]

I like to keep my RPMs low, but Ford and International probably put the redline that high for a reason.

 

[saburai]

I know hauling with the 6.9 crew cab, RPM's are your friend. If I let the RPM fall below 2100-2200 on hills, the EGT's start climbing quickly. So I just downshift and let her sing between 2500-3000 and the EGT's come down and the girl keeps on rolling. I don't often need to take it past 3000, but I do when a climb is steep and/or long.

Heath.

Yep, exactly the same here. 2500 is a happy spot, decent fuel economy and power on tap. Tow 10k- ish, if I hit a big hill much below 2500, I've really got to watch the egt's. If it's steep enough, I've got to slow down enough to make a down shift so that I can keep the revs up and the egt's down.

 

[Shamoke]

Yep, exactly the same here. 2500 is a happy spot, decent fuel economy and power on tap. Tow 10k- ish, if I hit a big hill much below 2500, I've really got to watch the egt's. If it's steep enough, I've got to slow down enough to make a down shift so that I can keep the revs up and the egt's down.

My truck doesn't even have a temp gauge for exhaust temps but I do appreciate the info.

 

[saburai]

My truck doesn't even have a temp gauge for exhaust temps but I do appreciate the info.

It'd be a good idea to run one. However, at stock boost levels and the factory exhaust, Ford didn't think that you needed to monitor the egt's. Most idit guys here have the boost and fuel cranked up at least to 10 ish psi. If you're stock, your probably going to be fine.

 

[Shamoke]

It'd be a good idea to run one. However, at stock boost levels and the factory exhaust, Ford didn't think that you needed to monitor the egt's. Most idit guys here have the boost and fuel cranked up at least to 10 ish psi. If you're stock, your probably going to be fine.

Ahh that's the difference I think, mine is non turbo so EGT's probably wont be an issue I'd imagine.

 

[ttman4]

I grew up around over the road trucks and drove then for 13 years, the Cat's and Cummings engine I am used to top out at 2200 to 2300 and are governed for that rpm. Anything higher sounds wrong to my ear so I am wondering about what speed I should limit my IDI too.

I bought my '90 CCDually 5 speed new & turbo'ed it quick. But that was exactly my prob too! Been used to 18-22 or 2300 RPM working range & had a hard time getting used to fact these IDI's wound/pulled higher. But even now it's still hard for me to wind mine up to 3K or above!

In '72 company I was driving for leased new '72 Pete with a 903 V8 NA Cummings. I was told to pull it at least up to 28-2900 & shift. I had hell, but did up to 28. (it would hi idle 3500) Few mo. later engine spun an insert, put it in shop. While there they sent pump off for rebuild. Went to pick up truck. Shop foreman started grilling me about way I'd been driving, ask how hi I been pulling up to and shift. I thought I was in trouble so very quietly I said "2800 & not a penny more."

He got to hollering at me, told me to drive Hell'out'a that thing! Pull up to at least 3400 then shift. down shift at 2900 or more!
My point, that's when I found out those/these V8's work better Hi/higher RPM's. V8 Detroits, Cummings, Cat, etc, etc.
Inline's work better lower RPM's generally.

And as FordGuy100 said the stock valves will float at way up there!

Once me & couple other drivers cranked pump up to 2900 on an inline 335 Cummings. I made a trip & suddenly beat up couple of pushrods slowing down for an intersection. Found out they kind'a did ok under a steady pull, but coasting at hi RPM they tended to float valves & beat up pushrods.

But working my IDI I still work it mid to hi 2000's, & 3000rpm.

 

[IDIBRONCO]

mine is non turbo so EGT's probably wont be an issue I'd imagine.

Actually, EGT's are a bigger issue on a N/A engine. A turbo will give the engine more air to burn more fuel. An engine that's N/A can only draw in so much air. That's why, generally, a N/A engine will blow more black smoke out the exhaust. The black smoke is unburned fuel, which raises EGT's. I have a pyro on mine and I haven't gotten around to installing a turbo yet. Even running empty at highway speeds, it will raise the EGT's by 300 or so degrees while maintaining speed on longer, steeper hills.