I was looking through my Paeco catalog (all the goodies in there keeps me motivated in my studies) and see that they can make stroker kits for any engine. This is done by lengthening the stroke of the crankshaft and enlarging the bore size of the pistons, and raising the compression ratio of the pistons. They claim that power boost of 30 to 40 % are achieved.

Well, I can understand the lengthening of the stroke of the crankshaft. But what does enlargin the bore size of the piston mean? What is bore size? How do they raise the compression ratio?

Also, they claim that these kits can be made with any size stroke increase and any size overbore and compression ratio pistons. Does this mean that one could potentially raise their 2.2 or 2.5 to a 3.0 or something? How do they determine what's best?

Sorry 'bout all these questions, but I just gotta know. Thanks all.

Well, every engine has a limitation to what it can be bored and stroked to. An example would be a B18C, you can stroke and bore it out to max of 2.0L from the 1.8L. The 2.8L VR6 from VW can be bored and stroked to 3.3L.

It's really dependant on how thick your cylinder walls are.

Stroke is how far up and down your cylinders move. The bore is the size of the diameter of the cylinder. The larger each are, equates to a larger engine size. Like, when you see 3.0 Liters or whatever, that's by figureing out bore X stroke. With a bigger size, obviously, more fuel to ignite, and more power

Well, then since the EJ25 is a bored out version of the EJ22, can the EJ25 be bored out even more? If not, what if you just increase the stroke? That would still increase the displacement and also the compression ratio right?

JUN successfully used a stroker kit on a EJ25 and got 2.6L out of it. A stroker kit is basically new crankshaft, rods and pistons that increse the stroke of the engine therefore increasing the displacement.

You have to remember anytime you bore a motor, you take away part of the cylinder walls, wich inturn, makes the block weaker.
Just something to remember if you plan on running a turbo or supercharger, I personally wouldnt take the chance, not on an daily driver, and only to get .1 liter. Money better spent on other car goodies.
Thats just an opinion.

Jay McDade
MY00 BRP RS coupe

I've had many discussions with JC Sports concerning this issue, and there are a few possibilities, but no real points to make. The three things you have to worry about with an engine's rotating mass geometry are the crank, rods and pistons. All work together to create a desired (or not) compression ratio. Changing any of these specs requires new parts or machine work at the very least. (Having come from the "Smokey Yunick" style of V8's, I'm somewhat knowledgable about engine geometry.)
Some of the specs I've dug up are very general. Overall, I can tell you that massive power gains can be found by playing with the geometry of the rotating mass and nothing else. (How do you really think they got 650 horsepower out of a 302 Chevy?) In short, the 1.8, 2.0 and 2.2 Subaru engines all have a similar stroke at 74mm(approx.)
while the 2.5 has a 79mm stroke. All have correspondingly bigger bores. Now, if you wished to change cranks between the 2.2 and the 2.5, things get real hairy, real quick. They all use the same height piston just in different bores, or diameter. The rods are the key. The smaller subaru engines have longer rods, while the EJ25 has shorter rods. If you tried to put the longer rods into the 2.5, you would need custom pistons, because the pistons would pop out of the top(or side??? http://www.i-club.com/ubb-files/biggrin.gif) of the block. That would be bad. Some interest has been generated in destroking a 2.5 using the 2.2 crank and rods, but I haven't heard of anyone who's tried it. (Speak up whoever you are!!!) That combo would give the largest bore, longest rod, and shortest stroke available for a subaru. I've had more interest than cash in this engine combination...I think I'd just be happier with a turbo http://www.i-club.com/ubb-files/biggrin.gif. Another combination would be the 2.5's crank and rods in a 1.8 block, giving the smallest bore, shortest rod, and longest stroke of a subaru. These are weird combinations of about 2300cc's for the destroker, and about 2100cc's for the stroked 1.8. If anyone else has tried this stuff, I'd love to hear about it. BR

what's the difference between having the biggest bore, shortest stroke, and smallest bore, longest stroke? They both will still suck in the same amount of gas/air. Is there an advantage of one over the other?

Bigger bore will give you more torque. Longer stroke will give you higher revving engine.

Really...

I thought that the shorter the stroke, the higher one could get an engine to rev.
I mean, logically (to me) this is correct, as an object that travels a shorter distance than another will require less energy to stop, and then set into an opposite direction...

I dunno, but if you ask me, I think that an engine with a shorter stroke can rev higher than an engine with a longer stroke..

'eh?

Its more bore more revs, and more stroke for tq.

Yeah, a shorter stroke will give a higher rev. but as for a larger stroke and bore chyisan, when they are bigger, it WILL take in more fuel, and you'll have more power

Wow, thanks guys. I'm learning alot. So is 2.6 the biggest displacement that has been done to the EJ25? Is it possible to go all the way up to 3.0 whether through increased bore or stroke?

Hmmm, I guess I got it the other way around. Oopsy!

Screw it! Get the box 6 and a shoehorn! BR

I doubt that the new Boxer 6 will need a shoe horn considering it was rumored to be smaller and lighter than the current 2.5L.
I could live with that.
Rich

Of course the drawback to the new boxer 6 is the same as that of the old 3.3. It will only accept an auto tranny from what I understand. The 3.3 would accept the manual transmission from a skyline, if you can get one. I don't know if the the boxer six will or not.

The SVX had a box six, I think. What would work from that? Did it come with a manual tranny? BR

Owners in Japan are going to higher compression ratio's now as well as a couple owners who went with the 2.2L conversions. You need to have the engine machined so that it uses some custom liners but once done they are definately fast. Not sure of the costs involved but its a nice option. Especially when you talking about a engine designed to with the oil squirters and a few other features.

As a fellow Chevy enthusiast burninrubber, I want to respond to your questions / assertions about bore and stroke.

When you are talking VERY high rpm, piston speed will come into play and that would be the time to consider a shorter stroke. 7000 rpm doesn't sound bad at all on a 79mm stroke (3.11") but then again that's on a 90 degree v8. On a H4 that is probably a fairly long stroke.

Big bores and short strokes are great when displacement is restricted but it is foolish to give it away when you don't have to.

Besides, what good would destroking 5mm do?

compressions ratios


I was informed and under the impression that compression ratios is a very important issue when going turbo. The max ratio you want on a turbo car to run high boost is around 10.5 : 1, however if your staying N/A, then you can go higher. Infact the Langenfelter Vette's with twin turbo's were actually lowered the compression ration to a 8.5 : 1 in order to accomidate higher boost. I wouldn't do any boreing/stroking if your going turbo, you need the stronger block and no more than stock compression ratio, now if your going N/A then go for it, but I doubt it is cheap and worth the work. Take the $3,000 to bore and stroke, put it in a high intrest CD, save on the side and in a 5 months import a 2.0 turbo and ECU for $6,000 and you'll be much happier than a stroked 2.5. Don't get me wrong. I'm planning to stay N/A, but I'm not bore/stroking anything on my car.
sorry so long, and don't read into the stroking comments too much : )

Stroker kits are not the answer. They are a gimmick way to increase power to a motor that is lacking it in the first place. How often to you hear about stroker kits for Big Block motors? Not very often at all. Why? Because they usually don't lack power! Why? Because they have enough block space to put big pistons on top of a crank design that will give the RPM and Torque you want. Small block motors don't have the block size to play with piston sizes, that's why the crank is where people focus their attention on smaller motors.

Take the following example:
A stroker kitt for a Small Block Chevy 350 usually is a 400 crank. So if you think about it, you are really taking a small block 400 motor, and giving it smaller pistons. Why would you want to do that? You are basically making a lower powered SB-400. Now if you were to take a Chevy 400 block, and stuff a Chevy 327 crank into it, you'd basically be getting a 327 with huge pistons. The design of the Crank gives you the main characteristic of the motor. Short throw crank (327) higher revs and high horse power. Long throw crank (400) lower revs and high torque.

The moral of my story... Start with the Crank to get the RPM and Torque curve you want, then move to piston sizes. Or better yet, get a turbo. http://www.i-club.com/ubb-files/smile.gif

Thats my 2-bits worth.
--------------
00RS

Hello,

Skidd, I disagree. I think one of the most common mods for people who get into their big american engines is a stroker. Almost all the big power 5.0-based engines in existence have greater than 302 ci displacement. The "magic" number when it comes to pistons speeds (and no, I don't know how the number was created and yes, the number depends almost entirely on the material and construction of your rods/bolts/pins/pistons and is therefore useful only as a rule of thumb) is 20 meters per second. Do the math and you get a stroke of 75 mm at 8k rpms. Less rpms means more stroke. Anyway, at that piston speed, most decent parts are quite happy. Well, check out a 5.0. It's far from 20 m/s. So since old-tech pushrod engines take a lot of money to increase revs (ie, JE pistons and Crower rods still don't get you much above 6500 rpm, IF you have very good roller-rockers and great springs and lightweight valves) the other way to increase power is increase displacement. YOu can increase the displacement by boring and stroking. So long as you don't stroke too far, you'll keep piston speeds below 20 m/s, you can still bump RPMs to 6500 or so, and you get much more power.

Check out how many 5.0 or 5.7 engines (if you're a chevy fan, which I guess we all should be since GM owns us now http://www.i-club.com/ubb-files/tongue.gif), that are not competing in specific classes that require them to maintain stock displacement, have greater displacements. Almost all of them do. Mustangs commonly go to 327, 34x, 35x and some brave souls go to 38x before stepping up to a 351 block.

"There is no replacement for displacement" if all you want is broad, raw power. A built 5.0 (stroked and bored to 355ish) designed to run on 91 octane gas can put 400 ft-lbs to the rear wheels from about 2k rpms to about 5k rpms and peter off to still over 300 ft-lbs by the rev-limit at 6200 rpms. And I have the dyno chart to prove it. Sure, a turbo smaller displacement 4-banger can get higher peaks, but it won't be broad like that.

BTW, that's why the 2.5 is better than a 2.0. With the 2.0, sure, more turbo means just as high or a higher peak power (though I'm starting to doubt the 2.0 can even reach the peak 2.5 powers we'll be seeing in the next few months), but the power will be concentrated over a very narrow power band. The 2.5 has a much more useful, broad powerband.

Anyway, the point was that a stroker kit, assuming you don't want to increase the rev-limit by much, can be a perfect way to increase power. And while you're at it, you'll be replaceing the pistons (don't stroke without boring http://www.i-club.com/ubb-files/smile.gif) with stronger units, the rods with lighter and stronger units, and you'll be balancing and stress releiving your crank after it gets worked over. Your entire bottom end will be more solid.


Now, what Alex said might be a limiting factor. It might be pointless if all you can get is 0.1 liters. But if you plan on building the engine with new rods and pistons anyway, then you might as well get that 0.1 for near free anyway. I wonder if the 0.1 is from stroke only. You could get a little more with bore, too. Then you might get a noticeable increase in displacement...

BTW, Cobb tuning should soon have built bottom ends online for your purchasing pleasure. He's making available full-bore racing engines with closed decks (he and I disagree on the utility of that mod, but it does allow higher boost since it does provide a better gasket mating surface) AND those little piston oil squirter things that so many of you think makes the 2.0 a better engine http://www.i-club.com/ubb-files/tongue.gif. Those two features plus built cranks, rods, and pistons and you've got a nuke-proof bottom end. Slap on your Cobb turbo heads and cams and you'll have the fastest impreza in the US until the next guy buys the same http://www.i-club.com/ubb-files/smile.gif

Joel (probably "the next guy")

Hello,

Oh damn, I did it again. Damn that was a long post http://www.i-club.com/ubb-files/smile.gif

Edit: Added "Hello" to the top just to make Sev happy http://www.i-club.com/ubb-files/smile.gif

[This message has been edited by Joel Gat, 1.8L (edited September 05, 2000).]

Then after you do all that and increase the output you can start finding a replacement tranny, diffs, and axles.

Hi Joe.
Well, I don't disagree with you. But I fear that my point wasn't really all that clear in my message. What I was trying to point out was an extreme case where a large number of combinations in bore and stroke are available. Like my e.g. with the 327 and 400. Someone mentioned the Chevy 302z motor. One of the toughest small blocks ever build. It has a 327 block with a 283 crank. A well setup 302z can rev in excess of 9000rpm and produce a wicked number of ponies. I used to race on a small dirt oval track in a class dominated by the SB Chev 400. But one guy had a 302z and he had no problems keeping up with the rest of us. In the case of this motor, stroking would take away what makes it so powerful, RPMs. Then one of the guys decided to build a SB 400 block with a 327 crank. Well this thing was an animal, unfortunately it was also a grenade and blew during it's second outing. This is where the size of the block became an issue. Thin cylinder walls and poor cooling ports were the cause.

oops. I've digressed. Sorry.

If the last thing available to you is a longer throw crank, and it still produces the rpm curve you want, then by all means go for it. But don't stroke your motor just because it increases the displacement. You might not get from it what you are looking for.

I guess what I'm trying to mumble out of my gobb is that the EJ25 might already be at the max stroke that will produce a nice result. And unless the stroke mod is an extreme case, I can't see the point.

Cheers.
------
00RS

Stroker kits are not gimmicks. My friend's 347 Ford was pumping out as much horsepower and torque N/A, as mine was supercharged. He then turboed his engine. Thanks to the stroker kit, when he's off boost, he still gets great power and zero turbo lag, but when he gets on the gas, he doesn't have to run much psi to make huge amounts of hp. A lot of people go with stroked small blocks because the big blocks are too damn heavy. The small block Ford weighs 460 lbs. The big block Fords weigh 730 lbs. Do you have any idea what adding 300 lbs. to the front of your car does to your handling? That's the equivalent of moving a small block a foot and a half forward in the chassis! Big blocks may not lack the power, but they are too damn big for small block equipped Fords, unless drag racing is all that you want to do. Small blocks do not lack power either. Engines that lack power don't push their cars to low 14 second quarter miles stock.


BTW, the bore done to my friend's engine in the conversion was so minimal that it will never affect the amount of hp the block can take. It only increased displacement by 5 cid. The stroker kit is what did the displacement increase.

[This message has been edited by EscaFlowne (edited September 06, 2000).]

Regarding the JUN 2.6L engine, I'm looking for more information regarding this setup. The information I have, from the Japanese "IMPREZA MAGAZINE vol 5" states that they use the 79mm stroke crank from their 2.2L stroker kit, and 100mm pistons. So, stock stroke, with +0.50mm oversized pistons. How do they get 2.6L from this?

If anyone has more information about it, I'd definitely be interested.

As for stroker kits in general, I think they do create benefits. They typically don't give you as much performance enhancements as a good set of heads and cams will, but if you have already done that, and are looking for the next upgrade to the internals, then increasing displacement through stroke isn't necessarily bad. I just wouldn't bother boring and stroking a stock head, stock cam motor.

Cheers,
Trey
CobbTuning.com

Hello,

Trey, I agree with completely. Of course there's no need for a rock solid bottom end stuck under a stock top end...

I think I see where I went a different direction from Skidd. You're talking about mixing and matching parts that are already available. Since everything for the Subaru has to be custom made, we're in a different boat. We can't take 283 rods and stick them into our 327 since we basically have 2.5 rods and that's it. If you want new forged rods or anything like that, someone has to make them for you. Given that, there's not much point to sticking to stock dimensions IF other dimensions are equally priced and will give you a benefit.

So if you're getting a bottom end built and for the exact same price (or slightly higher since you need your crank built up instead of just balanced, etc), you can get a 10% increase in displacement, then go for it. If the engine can't take more than a fraction of a mm of stroke increase, well, then maybe forget about it http://www.i-club.com/ubb-files/smile.gif

So, Trey, when do we hear about bottom ends http://www.i-club.com/ubb-files/smile.gif Hurry up and finish the turbo heads and cams and all that stuff http://www.i-club.com/ubb-files/smile.gif and get going on replacement cranks, rods, piston, etc.!

Heh.
Joel

To clear up a couple of misconceptions: First, the 2.5 rods are LONGER than the 2.2 rods (131.7mm vs 130.5mm). The pin is raised in the piston 3mm to make up the difference. Just shortening the rods does not mean you can get a longer stroke in the 2.5. The problem is the clearance in the case and piston to counterweight. There just isn't much room in the case to get more stroke. You'd have to offset grind the crankpin to something smaller, then get some pancakes to server as pistons to clear the counterweights. Point being- stroking the 2.5 isn't easy. However, if you have a 2.2 you can easily swap in the 2.5 crank and rods, BUT you have to have custom pistons made since the pin has to be raised.

Ah, now there is something I can totally agree with. If your getting a totally custom high strength forged crank, rods and pistons, then why not go for a bit of a stroke. A couple of mm are not likely going to affect the RPM curve in a bad way.

But if your just getting a replacement crank for your stock one, then I'd say spend your money elsewhere, Cobb heads and cam. Get that "air pump" working better.

---------
00RS