What would be the max RPM limit of our 400 engines? Do you go by the RPM range of the cam or is the limit where the max HP drops off? I know the red line begins at 5200-5400 and the tachometer relines to 8000. What do I not want to go above?
For example, When I had the engine dyno'ed the max HP was 365.2 @ 5400. My RPM range under my cam specifications is 1300 to 5500. Is 5500 my max rpm or is something higher? Is 5500 my beginning of my redline?
I'm sure this applies to racing and not on the street...:)
I have read that a "rule of thumb" is your shift point is 500 RPM above your Max HP. That being said, my shift point would be 5900 RPM. Does that seem excessive?
I'm sure this applies to racing and not on the street...:)
I have read that a "rule of thumb" is your shift point is 500 RPM above your Max HP. That being said, my shift point would be 5900 RPM. Does that seem excessive?
Yes, on a stock build, 5900 is excessive. Max RPM can be dictated by valve train capacity and bottom end build durability.
A stock valve train will start to float valves around 5500-5600 RPMs.
I just watched a great video on how you get the max redline. It seems the most important factor is piston speed. You want to keep the piston speed down under 4000 Feet per Minute for a stock engine.
To determine piston speed the Calculation is: RPM x stoke / 6
6000 RPM x 3.75 Stroke / 6 = 3750 FPM. So right at 6000 RPM is about max. so the 5700 RPM is a safe bet which makes our Piston speed 3562 FPM.
FYI from Jim Hand's engine book - 1) peak HP in stock motors is about 5200 rpm. You are just flailing the engine after that. 2) The rough limit for the stock rods is about 5600 rpm or so.
2012 Mustang Boss 302 #1918, Competition Orange. FGF replacement 2006 Mustang V6 Pony, Vista Blue. Factory ordered. 2019 BMW X3 (Titled to the wife, but I'm always driving it for her. So I'm claiming it) Old projects, gone but not forgotten: 1967 FB 400, original CA car. After 22 years of work, trashed by the guy who was supposed to paint it. I had to sell it. 1980 Turbo Trans Am 1970 Mustang fastback, 351C 4Bbl, auto 1988 Mustang GT, 5 speed 1983 F-150 4x4, built 302 1994 Chevy K2500 HD 4x4, 454 TBI
Depends whether you are talking about max rpm before your engine blows up or max rpm your engine will produce power at. Theoreticaly the 400 will survive a higher rpm than the large journal 428 and 455s. The larger the journal the higher the bearing speed. And the longer the stroke the faster the piston speed. The piston, rods and journals just have further to travel in the same amount of time as a short stroke with the same rpm. Some build over bore engines with shorter strokes and buzz them to very high rpm.
I wouldn't spend much time above 5000 rpm with a stock parts built engine and not expect a rod through the block. The 8000 rpm on your tach is what the $100,000 nascar engines are running at WOT and look at how many of them blow up.
I built my 428 with steel crank, steel rods, custom forged pistons, roller everything, the best valvetrain I could afford and still put a camshaft in mild enough to reach max power output below 6000 rpm. It straight-lined the horse power output from 5400 rpm to 6000 rpm. Scared the hell out of me with the 4.21" crank roaring at 6000 rpm. But if I ever want to do the dragrace circuit I can put in a big camshaft and make power to 7000 rpm and feel confident the thing won't fly apart. I sure as heck wouldn't do that with stock 46 year old parts. You can see on the sheet I'll post the max power is in at 5500 rpm and drops from there. The camshaft is a rather mild, for this buid, 230/236. A 238/246 will have an increase in total HP but a drop in torque and the horse power will be at a higher rpm. But the redline for the engine would be the same with both cams, that being the rpm that the engine will run without damaging itself.
Unless you're racing our Pontiac engines have enough torque at lower rpm do do most anything you want while driving.
5400 is the rpm your engine quit increasing power at, same as mine. Your redine is whatever rpm is the max you can run your engine at without damaging it. I'd set the redline pointer on your tach to 5000 rpm and put in a rev limiter set to 5500 RPM, just in case you miss a shift.
I've had mine on a dyno a couple of times and he operator always asks how far you want to rev it. I have a 5800 chip in the box so I tell them not to sweat it. It's always stopped making more power before it got that far. The first time it draped after 4800( stock valve springs). Pontiac used weak springs from the factory as rev limiters( for warrantee purposes most likely). The second trip it stopped making power at about 5200. No real need to go more until you spend a lot of dough on the motor. But I have hit the limiter on the track so I was glad it was there.
Harold, I don't know if we answered your question or just muddled it up. The redline is the max RPM you can safely rev your engine without fear of damaging it. Whether or not your power band is below or above this line isn't relevant to the redline. The redline depends on the internal components, what material and alloy they are made from, the manufacturing process, design operational range and limits, structural integrity and the skill of the builder. I don't know what the factory redline is but I would think a factory stock 400 would be shifted below 5500 RPM. 46 years later the fatigued stock rods may not survive 5500.
When we rebuild we must choose a camshaft that will deliver the power within the components RPM limits. A big cam that's said to make 600HP at 7000 RPM wont do much good for an engine that has a reline of 5500 RPM
