quote:

ORIGINAL: SAVAGEJIM

At first glance of those numbers you are shooting for, I'd say, by first intuition, that those timing profiles would make any engine perform much better that stock. By my own initial guess, that is a timing profile that most modders would shoot for in a "stage1" or maybe even a higher higher mod level to get the engine to perform more in the mid to upper RPM bandwidths.

Aside from impoving volumetric effeiciency at higher PM bandwidths (which is what increasing timing profiles generally do), another consideration to bear in mind is deciding how fast is too fast. For long stroke engines, getting the engine to turn too fast can be a bad thing since the linear piston speed in the sleeve can cause several problems (primarily friction). Lets say a big block has a particularly long stroke and it is modded with a timing profile that can get it to 40000RPM: the linear speed of the piston will be much greater at 40000RPM than a short stroke engine also turning at 40000RPM. The friction could in this case be great enough to cause the teminal max RPM of the engine to only reach about 37000 and no amount of futher duration increases can get it to ever turn faster. (Of course, affecting the engine's terminal max RPM in only one major problem. Other problems include the lubricant breaking down due to tremendous heat from the friction, the inertia of the innards of a long stroke engine can be high enough to hamper acceleration, etc.)

Though considering linear piston speed was never discussed in detail before as a concern for shooting for a desired timing profile, it is definitely one of the factors modders do take into serious consideration. That (among other reasons as well) is why they say "Depending on the engine, I will only increase the duration so much." No, I do not know what the bore and stroke of the TRX2.5 is, but given the stroke of the 2.5 is known, I can calculate what the linear piston speed will be for any RPM.

And of course, there also is the consideration of materials science and the points of failures of differnt metals. Some engines might be able to actually rev to 45000RPM with no ill effects on the parts because of their geomtry of the inner parts. Other engines will result in the conrod journals "ovalling" out and finally snapping due to the massive foces of otating so fast.

quote:

ORIGINAL: Grits
All of this information is older than jbcomp so it may not stand today but mechanical advantages and "guidelines" don't change much, metal and lube quality can but math formulas seldom do. This is not meant to flame anyone or disagree, just food for thought.

quote:

ORIGINAL: Colt4g63

You can EASILY over time and engine and lose power AND most importantly power band. The combustion chamber has alot to do with this as well. I have seen too much timing KILL and engines power and power band 1st hand here on my dyno. SO I suggest more mild timing alterations and ease your way into it.

quote:

ORIGINAL: ugly duck

You're down to 45* of crankcase compression timing on your modded motor, down from 65* - I don't know how that relates to the really wicked engines, but I know that too little crankcase compression time means bad things.

You've also increased the exhaust-transfer port offset to 20* from 16*. Adam, would I be right in thinking that for a higher performance motor you'd want to decrease this offset by opening the transfer/boost ports by a greater amount than you open the exhaust port? Or is the exhaust port more important for the high speed motor?

JB, this is an awesome idea. I tried to get this kind of thing going in another thread, but maybe because I'm a newbie on here I'm not going to get alot of response. The only one that got added to my thread was for the Dynamite Mach 28, with 120* boost port, 124* transfer port, 166* exhaust port, and intake port duration of 48ABDC to 50ATDC for 182* total.

quote:

ORIGINAL: JB COMP
Oh man, I forgot to time the SPI, well I'll have to do that tomorrow. I think the SPI is suppose to be around 70-80 degrees of duration.