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Originally posted by masterjr33-2
guys.. you freaking weirdo turbo dodge guys are the only ones who i have ever heard about running a smaller motor..
well maybee cept for the guys i know that talk about 327's and spinning the piss out of them. but they normally are talking about 7-9KRPM...not six..
HMM a all out drag car? i will take cubic inches and quicker spool up along with the braoder power band..
guys there is NO reason other than whinning about traction that you would want a 2.2 over a 2.5 .... you can blame the RPM limit of the bottom end and breathing problems all you want..
the truth is i doubt there are 5 people on this board even getting near the "limit" of 2.5 bottom end strength.. and breathing problems are associated with using a head for a 135Ci motor on a 153Ci motor..
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Dude... you are totally missing the point. The 2.2 has a big stroke and poor rod ratio which makes it a torquer. The 2.5 is WAY worse.
The 2.2/2.5 common blocks have siamesed bores and the only way to increase displacement is to lengthen stroke...which is allready exaggerated.
HP potential of the 2.5 has alot more to do with stroke and rod combinations rather than the head being a poor flowing unit, and the limiting factor. I have witnessed *2* 2.5 motors with 16v heads and hybrid turbos doing pulls. One of these heads flows major CFM over a stock T-III 16v head and you know what? Peak hp is still under 6k rpms. Yes, there is an advantage of these 2 engines over the useage of a well ported SOHC head, but not as much as you'd think. Why? I will explain this as I have a few times in other posts.
5digits once told me RPMs = HP. It took me some time (ok... a couple years) before I realized exactly what he was talking about. I *had* thought this wasn't true as my VNT had seen 8k by mistake a couple times, and 95% of all turbo dodges making great power peak at just under 6,000 rpms. Then, I realized, "oh.. he must mean if the intake, exhaust, and head can support this." I visualized why, and found out that a head that has great flow usually has this at the expense of low lift and mid flow#s due to increased runner volume and lower velocity at these lower lifts due to those larger runners. RPMs increases piston speeds, which in turn also increases that needed velocity to flow air through the big runners. This is why you hear about having a head that has too much volume or one that isn't reccomended for the street. If your engine runs low rpms (6k and under) all the time, then piston velocities won't be high enough to make the head work, and low rpm drivabilty will really suffer.
Fast forward until this summer. I bought a Yamaha YZF400. I used to own 5 Honda XR 500's over a period of 10+ years. The XR500 had 4 valve technology, along with some other state of the art 4 stroke breakthroughs. This was a big thumper! I ride the YZF for the 1st time and was blown away. Ok, it does have a better head...5 valves, but HP feels almost twice as much, with a bit lesser torque. 11,000 rpm redline vs my old 7k which probably fell flat at 6k. What happened to me? I had a revelation on bore to stroke relationships and how important they are. My buddy has my old XR500 and it feels like a Harley vs CBR 929. The new YZF has a bore to stroke relationship of 95 x 63.4mm , revs past any 250 2 stroke and has a much wider powerband and 59hp. (I still like 2 strokes) The YZF250 revs to 13,500. That's a single cylinder, mind you.
I have figured that it's more than just a rod ratio and stroke theory. Piston acceleration is very important. Why? HP is torque accelerated via time and in my own wordings... HP is how fast you can accelerate torque, basically speaking. Remember RPMs= HP? Also remember piston acceleration for a second. This is my analogy(maybe someone has a better one though) Take a broom and hold the very end in your hands. Have someone time you to see how fast you can move the opposite end of the broom to go from left to right at a predetermined distance of let's say 3ft. Ok, you went left to right in like 1.8 seconds. Now... go left to right again, but in a distance of 6 feet. I think you'll see it's really hard to accelerate that motion faster to make it travel in 1.8 seconds. Longer stroke means the *piston* is traveling ALOT more distance from BDC to TDC at the same RPM, so the speeds are higher. Inertia and friction/heat is higher and when it gets to a certain point, makes it really hard to accelerate through the rpm range, thus making HP.
Again.... RPMs = HP.
TurboDodge.com 
Yep, some people just don't understand that there is a difference... A complete newbie can make a 500lb ft RWD car hook.
