Brilliant flash of the Obvious.

I was chatting with a fellow HIIC'er (Funkdrmr) and he taught me about something very basic that I was just never aware of.

I know quite a bit, but nowhere as much as I'd like to, about increasing displacement by adding some form of air compressor along the intake tract. I also know about having the cylinder walls bored out to a larger diameter along with larger diameter pistons. I never put 2 and 2 together wrt to stroking, though. I even knew about how installing a different sized headgasket would not only change your compression, but also your displacement (I don't know if that's true, but it makes sense to me.)

While I do feel pretty dumb (which I soon intend to remedy with the help of the internet and some of my tuning books), I didn't realize that you could increase or decrease the travel of the stroke effecting a larger combustion chamber. I guess I've always assumed when I saw cranks for sale, or when I heard about a stroker kit, that it was simply a strength upgrade. Like some folks were having problems with their crankshaft breaking after they were seeing xxx amount of horsepower.

What are some of the implicit benefits and/or possible dangers of going this route as opposed to increasing the bore?

I know no one's probably paid much attention, but the last few questions I've been asking here in the tech forums are embarrassingly n00bish. Reason is, I'm starting to realize (and eagerly wanting to correct) the fact that as a n00b who has fixated on EM for essentially the length of time I've had my WRX (which is coincidentally about the same amount of time that I could call myself a car enthusiast.), there are so many other critical but basic things that I need to learn to be able to fully tune my car to it's potential.

I apologize for the clutter, but I know Alex would love to see more traffic in these tech forums, so the asinine questions will continue to come. I'm earnestly wanting to learn and not trying to be a smartass (read: I really am this dumb) so flame away, ignore, tell me to search, whatever. I know others would like to see a discussion on some of these more basic principles.

 

Upside to stroker kit: More displacement, higher compression, more power.

Downside: Piston speeds. As you increase the distance that the piston moves with each crank rotation, it has to move faster. The problem this causes is that the speed at which your bearings or rods will fail now occurs at a lower RPM. With a stock EJ257 block, it's probably somewhere between 8500-10000 RPM. Adding piston speed lowers that number to below the intended 7000 RPM redline. So, basically, stroking lets you make more torque at teh expense of top end power. The best place to really discuss the ins and outs of this effect is actually with the V8 tech crowd. When they build stroker motors, they lower their redline to below 5000 RPM sometimes.

 

Thanks for reading, Ban.

I had no idea how ignorant I am on the subject. I get off work in a few hours and will do a little more research.

 

I can see the great information coming on this already!

I have a question for you BAN. I, too, am a n00b to all this stuff. My initial exposure with stroking came from looking into the AXIS and Crawford Performance blocks. Quirt informed me that he had the pistons, rods, and crank to stroke my EJ22T to 2.4 liters and maintain compression around 8:1. My next question to him was what my redline would be with that setup. His answer was that the redline on this setup wouldn't be dictated by the shortblock, but more limited by the heads. I completely understood this theory, but your post above has me wondering.....

Has CP built their parts with the thoughts of stroking the motor and maintaining the high (or higher) RPMs? I'm hoping the answer here would be yes, as I don't think they would design a shortblock that would kill itself after a couple of trips up to 7000 rpm or higher.

Please let me know if I'm wrong!

 

The Crawford motor uses very strong components, better then the already good stock rods and bearings. If Quirt says his engine is good to 7-8k, I'd believe it.

 

Couple of questions while ban is at it.

I was under the impression that the bearings where not the main load point in a stroker motor but the rods and connectors became the fail point. Is that true?

Secondly, isn't a 2.2l already a stroked 2.0l block? How much stroking can the ej20t block take before boring out the motor is the only option.

 

I can answer this one for you....

The EJ22T is an entirely different block. It was stock in the 1991 through 1994 Turbo Legacy's. It is considered by a lot of people to be the strongest block Subaru ever made due to the closed deck design. It comes with oil squirters, which the 2.0 and 2.5 do not come with.

 

This article which syncopation recently posted to help me learn, addresses stroking pretty darn good.

...and according to it, I believe you're correct.

 

Catastrophic failures happen to the rods. Fatigue failures hapen to the bearings. Can be either/or.

 

Aye thanks captin

One thing sorta baffles me on the ej20 block motor. For its displacement the stroke is pretty minimal compared to the bore of the motor compared to a mitsubishi motor which has slightly more stroke than bore.

I have to wonder why the redline could not be easily brought beyond the 7k limit without machanical failure for a given period. Whats becoming the limiting factor, rods, bearings, lubrication pressures, valve springs?

I would like to see over 8k on a motor if possible.

 

So whats the main concern once your get the crank, pistons, and rods in order?

Number of bolts on the heads? springs valve coating?

I just want some solid info so i can play with other motors too

 

Weight and stiffness of valve springs and retainers.

 

Sweet thanks ban