What determines engine redline?
Originally Posted by Gold Phoenix
What factors would considered for maximum engine RPM? Components quality, component weight, valvetrain components, power production? Will a billet crank & rod allow a 7000rpm redline? Will that depend on the the power around that RPM? I know if you make peak power at 5500rpm it is pointless to rev to 7000, but what about a 6200rpm peak? Maybe valve timing in risk to making contact with the pistons? Valve float of course? I really don't want to hear piston speed because I have seen mountain motors with really long strokes rev to 8000rpm. I am hope to hear from experienced engine builder here.
the answer is very simple.
Q. "What determines engine redline?"
A. whatever the weakest link is.
it will be different with every engine, and that's what the long argument above is.. so you'll have to narrow it down.
lets say for example, you're getting valve float at 6800... well, you put lighter valves in, stiffer springs, Ti retainers, and now the valves dont float. you spin the motor faster, and now find that the hyd lifters are the problem.. so you go solid lifter.. then you spin it faster and find the next weakest link... and so on, and so on..
really, you're asking a very open ended question...
TECH Enthusiast
Joined: Oct 2004
Posts: 607
Likes: 1
From: Anna, OH
Originally Posted by disco192
Well, the whole purpose of diffusers is to slow down the incomming air to appropriate mach numbers. Typical inlet mach numbers are typically in the ballpark of .4-.5 for either turbofan or turbojet engines. At mach 1.4+ you need to very carefully design the inlet to give you multiple oblique shocks instead of one large normal shock. I believe an F15 uses three oblique shocks. It is actually a cool variable design that curves the incomming air quite a bit at supersonic speeds.
On The Tree
Joined: Jan 2004
Posts: 188
Likes: 0
From: Houston/ Austin, TX
Originally Posted by LTSpeed
Yeah, aerospace is my first passion, cars second. But I try to use what I know from both whenever I can. Great discussion here!
TECH Resident
Joined: Dec 2004
Posts: 881
Likes: 1
You are looking at three basic things:
1. Is the valvetrain light enough, stiff enough, and the springs stiff enough to handle the engine speed?
2. Are the rotating assembly pieces light enough and strong enough to handle the peak forces?
3. Does the intake, heads, cam, and exhaust flow enough to run that speed?
If you wanted to, a 3.2" stroke 347 could probably spin over 10k with the right pieces.
Outside of LS1 land, there are engines with larger strokes running over 8k. That would be closer to 5k ft/min average in an LS1. However, you would have different pistons, pins, rods, and crank to do that. So why would you?
1. Is the valvetrain light enough, stiff enough, and the springs stiff enough to handle the engine speed?
2. Are the rotating assembly pieces light enough and strong enough to handle the peak forces?
3. Does the intake, heads, cam, and exhaust flow enough to run that speed?
If you wanted to, a 3.2" stroke 347 could probably spin over 10k with the right pieces.
Outside of LS1 land, there are engines with larger strokes running over 8k. That would be closer to 5k ft/min average in an LS1. However, you would have different pistons, pins, rods, and crank to do that. So why would you?
