[QUOTE=Roberto]They were talking about the reason they switched FROM the 2.3L to the 2.0L. The rod-ratio of a 2.3 stroker increases the piston speed ( I won't get inot the greater lateral forces here, but that is a factor as well) to a point that makes the bottom end ill-suited durability-wise for high-RPM applications. It's not the valve train they have to worry about on high-RPM use (providing its setup well), it's the rod bolts (or studs depending on the build) and rod bearings that take way too much of a beating with that kind of piston speed at high-RPMs (above 9K). Since they are using a massive GT42 turbo, the RPM operation range is shifted from 5-9k to 6.5-10.5k+ (approx.) to drive that large of a turbo. A measly increase of .3 liters is just not enough to keep the motor RPM operation range well matched to the turbo's needs. Sure, it would make it spool a bit sooner (maybe 300 RPM sooner on a GT42), but not enough to justify missing the 1.5K to 2K of RPM operation band up top where that massive turbo needs it to stay in its efficiency range for best quarter mile times and traps.


Think you mean stroke, not rod ratio. Stroke to rod ratio only effects tdc and bdc dwells. 11k is pretty out of hand though!

 

Increased stroke, increases piston speeds and forces IIRC. I think between Buschur, AMS, Shep, and maybe AL and Ttrix, there are a decent amount of people spinning the 4G at 10k+

Scorke

 

Damn thanks for clearing this up, this makes perfect sense! I guess with that large of a turbo your usable power is definitely shifted to the upper RPM range (even with the .3 liter displacement increase). Was it the stock valvetrain that did 11,000 rpm though? I couldn't imagine that the stock valve springs had enough tension to prevent valve float at those type of engine speeds. If these were stock springs than the EVO has a WAY better valve train than the DSMs, because a stock dsm head will not take this type of abuse. Interesting!

 

Ahh.. Stock 1G dsm heads are way burly... way back in the day when i was on a budget build up, i had HKS 272's in my car, but couldn't afford the rest of the valve train, so i threw some 3mm tall washers underneath the stock spings ( putting a little more preload on them,, essentially making a stiffer spring)
and and an ecu chip that bumped the rev limiter to 9700.
yep 9700 rpm,, stock valve springs... two years of use.. no problems

i think i put nearly 25,000 miles on my car with that set up.....

 

Yeah I've heard of people shimming the springs with spacers, this basically just increases the spring rate (just like running a stiffer spring). But thats cheating! =) I am very suprised that your engine could survive those types of engine speeds for so long. The 4G63 is amazing!

 

Dave would you mind posting up the whole slip of the run you did make without the launch control? That will be a hell of a monster next time out I am quite sure.

 

admittedly it was my daily driver, & i didn't let the motor bounce off the rev limiter every shift...
but the few times it did,, it held up fine.....

 

I do not have spacers (Not worth it... you need to do the same amount of labor to shim them as you would to put in new springs anyways).

I will rev my car under load (In gear) up to around 8,500 and during shifts it will bounce up to 8,800 or so. I have done this quite abit with no side effects yet. Our stock engine takes alot more abuse than I would have thought originally.