How does engine manufactures determine where the redline is and where fuel cutoff should be set to?

 

i have no clue, but i think it has something to do w/ how much your cams, pistons, internals, etc can take. i've also noticed that most cars that lack torque usually has higher redlimiters than cars that have alot of torque. i'm guessing it's to compesate(sp) for lack of torque.

 

I think this how gm determines theres
step one rev the hell out of it and listen to the engine
step two determine the rpm that engine starts to knock
step three subtract 100 rpm from the point where engine noises start and thats the redline

 

what does the tc redline at anyways? i test drove one before i got my car but i forgot.

 

around 6200-6300

 

omg....hope toyota comes out a reflash for the ecu's on the tc's to give them a lil more rpm's. tc's have more torque so it evens it out.

 

Engines are only efficient at a certain RPM range. Once it starts going too fast it can't breathe well enough and there is always a point where a very dramatic loss in power is noticed. Redline is set very close to this speed. Common sense would suggest that this is the most important factor in the way a manufacturer sets a rev limiter but I can't know for sure.

 

I guess I will revive this topic... Anyone else's tc cut off at 6500? Should I be careful or is it no biggie?

 

Its normal. Thats the fuel cut off for people who didnt pay attention to the red line. Ive hit it a few times but its probably not a good idea.

 

thats there to protect the engine from people(like you) reving beyond the engines limits...

 

deffinetly 6500

 

In a motor designed by engineers (B4, B6, I6, V12, B12), redline is usually determined by how strong/quick the valve springs are. When the valves start to float (i.e., they can smack the pistons), that's bad. Redline is below that. You can stick stronger/quicker springs in, but that wears the camshaft more.

Now in an engine designed by the marketing department (i.e., a 90 degree V6 or V8 or the rediculous V10), redline is set by how fast the engine can go before it shakes itself to pieces. If you don't know what I'm talking about, search on engine "primary vibration."

The I4 motor is a weird beast, used mostly because it has few parts and is cheap to make. It has quite a bit of primary vibration, but with 5 mains usually can go to 6000 before it twists the crankshaft enough to throw a con rod out the side. Balance shafts have pushed that up to about 6800 for a normal motor with a stroke long enough to have some torque. Old F1 4cyl motors pushed 14-18,000 rpm, but had something like 1200hp and 60lb/ft of torque and about as much stroke as a model airplane engine. Honda gets 8,000 out of their I4, but again, with such a short stroke they have the torque of a rubber band.

I'm actually surprised that the Camry motor has a redline as high as it does with such a long stroke.

 

Actually, thats completely backwards. Engines are most efficient the higher you rev them. The power produced at a given RPM range is determined by your cam grind. Hence things like variable valve timing to keep the vavletrain operating efficiently.

Redline on an engine is determined by 2 main factors. First off is crank balancing. The less rotating mass and better balanced crank will be able to rev higher more safely than others. Second is valve float. This is determined by the stiffness of valve springs used in the valve train.

Rotary engines since they have no conventional valve train technically don't have an engine redline, but instead are limited to how much centrifugal force the transmission the rotary is bolted to, can withstand.

 

Nice, then would the ZPI Stage 2 Head, which says that can make the tC to have an increase in Redline, would cause problems with the camshafts later on?

 

Actually, you're both sort of right. Engines are more efficient at higher rotational velocities, but only to a certain extent. Mike was correct about a dramatic loss of power & efficiency at high rpms, due to the lack of an engine's ability to breathe quickly enough and due to ever increasing frictional losses. From Engineering Fundamentals of the Internal Combustion Engine, by Willard W. Pulkrabek (pg. 52):

Both torque and power are functions of engine speed. At low speed, torque increases as engine speed increases. As engine speed increases further, torque reaches a maximum and then decreases. Torque decreases because the engine is unable to ingest a full charge of air at higher speeds. Indicated power increases with speed, while brake power increases to a maximum and then decreases at higher speeds. This is because friction losses increase with speed and become the dominant factor at very high speeds. For many automobile engines, maximum brake power occurs at about 6000 to 7000 RPM, about on and a half times the speed of maximum torque.

This is a good discussion you guys are having. Lots of good information being thrown out there.