How much RPMs is comfortably for engine ?

[Nacho-RT74]

Being that I'm trying to get a HP camshaft ( mild )... how much RPMs do you consider a 400 engine is comfortable on 60-100 MPH speed rate. Highway

[aifilaw]

what RPM the engine at is really a factor of the drivetrain, not the powertrain.

Therefore, example 3000 RPM with a 727 and 3.55's in the back + 28in tires = 65mph

I'm not sure what the question here is...but I'd say that anything over 4000 for extremely long durations is a bad idea (aka highway speeds, not the occasional bug you get to run it into triple digits for a few seconds).

The 400 and 383 have a distinct advantage in that they are relatively low stroke to high bore ratio, the engine will spin more freely and easily and make power up top readily. Therefore the maximum RPM you can run is a factor of that, your valvetrain, your balance, fuel requirements, and ignition abilities.

A soundly build and balanced 400 engine with a solid roller-rocker valvetrain, a cam capable of making power up top, and a carberator capable of feeding it, along with an ignition system capable enough can hit 8-9000 RPM without damage, valve float, or otherwise. But I wouldn't do it for extended periods of time.

[Nacho-RT74]

Sorry, didn't know how exactly to made the question, but I think you got it... tires are 255/60-15, so 27".

I'm also trying to decide between 3:55 and 3:23. Have both pinions and rings in hands to choose and didn't remember but I have a great excel porgram what gives me all numbers, speedo gear included ( 34.41 for 3:55, so I think must choose 34, if I go with )

A soundly build and balanced 400 engine with a solid roller-rocker valvetrain, a cam capable of making power up top, and a carberator capable of feeding it, along with an ignition system capable enough can hit 8-9000 RPM without damage, valve float, or otherwise. But I wouldn't do it for extended periods of time.

WOW... NEVER THOUGHT WAS THAT MUCH... of course very different from my project build.

[firefighter3931]

Personally, i wouldn't run anything less than a 3.55 with ah heavy car and a 400ci engine. As long as the engine is balanced it will run effortlessly at anything less than 6500 rpm. With a hydrailic cam you're into valve float at 6k so that's a reasonable redline. Of course the cam profile will dictate where the power starts and stops.


Ron