The mythical stroked 2.5L V6

**JGTC MX6** · 4-18-07, 15:25

I can't tell where it started, there are only a handful of posts regarding stroking/destroking the 2.5L, the best of them goes on and on about what to call the damn thing. KL-DE/ZE based it's all the same, so who gives a damn, lets not bicker that point.

You need different rods, ones with a smaller big end bore. This is what lets you change the stroke. You would do best to find rods that are as close as possible to the stock rod width, without being narrower.
Aftermarket rods for the Integra GSR are a little wider than KL rods, the width needs to be cleaned up a tad on each side to center the rod in the bore. This is something that other posts seemed to miss, why I have no idea. You'll want to make sure this is done correctly.
The same rods are also a little longer, not a problem. They will work better to retain the relative high rod to stroke ratio of the KL if we stroke the engine, and they'll make it even better if we destroke it.

Offset grind the crank to any stroke that will fit a standard bearing designed for the GSR. Ok the forged crank will lose a little strength, the rod pin diameter will go down quite a bit. Yes you can even destroke the KL if you want, the key is the smaller rod pin diameter.

Now go back to the rod bearings for a moment, we forgot about the bearings, there going to be to wide. Well sure they will, You'll need that fixed as well. Stock bearings can be narrowed and camfered to match your freshly machined crank.

Pistons can be custom made, or you can look at other 4 valve per cylinderhead pistons. What you will be looking for is a compression height that keeps the face of the piston and the base of the cylinderhead from making contact. It just happens that there is an aftermarket piston that fits the GSR rod that is the same diameter as our stock piston. It also has a super short compression height.

All this is just an effort to bring this topic back to life, maybe gather some more information on the subject and nail down some numbers.

I think the most interesting thing might be that with a stroker engine of 2.7-2.8L the millenia S injectors and stock or KLZE computer might just run it. I don't know this, but the injector size would make me believe it is a possibility. If that were the case, this would become a cost effective upgrade in NA power.

I'd like to hear what you think. Good or bad, let it fly.

With this method there should not be any problem with rod clearance in the block. It's when you weld up a crank that you are messing with rod clearance issues.

**skiingman** · 4-22-07, 16:09

I don't quite understand what the point of building a stroked KL is. Its a lot machine shop money spent for something that is less reliable than stock with not so much added displacement.

I'm not sure I understand how this can be "cost effective" at all, unless you have much cheaper machine shops than I'm used to.

**pearsonmx6** · 4-22-07, 21:00

that is intristing

**JGTC MX6** · 4-22-07, 23:03

Skiingman;

1) Adding cubic inches is a big difference in every aspect of engine operation, and keeping the R/S ratio fairly high is not going to side load the piston or reduce the redline more than is acceptable.

2) Destroking the KL correctly will raise the redline, something some may want. The resulting loss in displacement will reduce some lowend torque, not a huge loss for road racers who keep the rpm's up.

3) What makes you think that a stroked KL is going to be any less reliable than what is out there today?

4) Cost effective NA power. It's a rebuild, performance rotating assembly parts, two extra machining operations, and a gain in displacement.

5) I could add solid cast iron sleeves raise the deck height (work over the stock I/M to fit) go way out on the bore, and go with fully custom pistons, that would add alot of displacement (3.0ish total). That is less cost effective when you look at the gain in displacement verses all that extra work on the block.

The value or worth of what we do to the car is equal only to our expectations, not the money we spend to get there.

**skiingman** · 4-22-07, 23:38

Quote:

Originally Posted by JGTC MX6

1) Adding cubic inches is a big difference in every aspect of engine operation, and keeping the R/S ratio fairly high is not going to side load the piston or reduce the redline more than is acceptable.

I haven't looked at the GSR rods. What is the displacement increase attainable with off the shelf parts? 200cc?

Quote:

2) Destroking the KL correctly will raise the redline, something some may want. The resulting loss in displacement will reduce some lowend torque, not a huge loss for road racers who keep the rpm's up.

Wouldn't it be a lot easier to find a KF crank that was built with the right journal size and throw to begin with?

Quote:

3) What makes you think that a stroked KL is going to be any less reliable than what is out there today?

Some aspects are quite straightforward. Machine shops have been offset grinding cranks for a century. Unless you go crazy you probably won't break a crankshaft. With the pistons and rods, you are playing parts bin engineer. Not that there is anything wrong with that, but it takes a lot of experience or hot air to claim your ground down whatever rods with your picked from a catalog pistons are going to be as reliable as the rods and pistons the motor came with.

I'm sure if you do it right it will last a good long time. Doing it right requires more expertise and more access to a good machine shop than most people have. Also, I can categorically state that reducing big end diameter and using undersized (and modified!) bearings will reduce durability. By just how much remains to be seen.

Quote:

4) Cost effective NA power. It's a rebuild, performance rotating assembly parts, two extra machining operations, and a gain in displacement.

Several hundred bucks in extra work any way you look at it. Plus the large (1K plus) cost in the performance rotating parts if you aren't going with OE style replacements. I've never asked a machine shop to machine something like a plain bearing. I'm not sure I can envision how to cheaply do that without messing it up.

Quote:

The value or worth of what we do to the car is equal only to our expectations, not the money we spend to get there.

True. I don't doubt that as far as NA modifications go, it could be pretty good. But that is in light of the reality that through history NA mods for the KL have been utterly disappointing.

**skiingman** · 4-23-07, 0:12

I just want to clarify: I think this is an awesome idea. I disagree a little bit with the value proposition but I'd love to see someone actually do this.

**JGTC MX6** · 4-23-07, 0:57

I'd say that the KF or K8 crank for that matter would work out fine if you had them. There is the added cost of the crank now if you were to go that route in the kl block. I do like that option for doing a very high reving engine. The problem would be finding longer rods to make up for the reduced srtoke.

As far as stroke: you can go from 74.2 to 82.19
So the stroker comes out to be:
84.5/2=42.25*42.25=1785.0625*pi=5607.939236*82.19=460916.5258*6=2765499.155
thats 2.76L

And the stock KL comes out like this:
84.5/2=42.25*42.25=1785.0625*pi=5607.939236*74.20=416109.0913*6=2496654.548
thats 2.49L

We gain .27L or 16.47ci. or 10.84%, not bad in my book, not bad at all.

**jarnold** · 4-23-07, 9:29

Why not just swap in the new 3.0 and trans out of the New "6"? 220hp stock. There's your stroker for about the same money. You would have to do some fab work but it may work? I know it is a Ford Bottom end with Mazda heads but I think that would be an interesting "Monster Garage" thing.

Kinda funny how Mazda can build heads for the same motor and get 20 more hp than Ford?

**JGTC MX6** · 4-23-07, 12:26

I've got no idea if that would work? Maybe it could, I just do not know about size and fitment. I'll look into it.

**Nealio** · 4-23-07, 15:09

Well if anyone can get a hold of a Cougar's, or any duratech 2.5L, the 3.0L is basically a bored and stroked version of the same engine.

**jarnold** · 4-23-07, 16:28

The heads are different though on the 6. They are Mazda Designed and flow better. Someone needs to find out . Come'on there are some MOnster Garage crazy's here I am sure. I mean if they have a kit to put a 5.0 Mustang in a Miata then why couldn't this be done? www.Monstermiata.com

**skiingman** · 4-23-07, 17:14

Quote:

Originally Posted by jarnold

Kinda funny how Mazda can build heads for the same motor and get 20 more hp than Ford?

Variable valve timing.

There are duratec applications using direct acting mechanical buckets...I'd pick one of those.

I don't doubt that someone with enough motivation could shove one under the hood.

**Mike 94PGT** · 4-23-07, 20:00

If you want to puff up the KL it would seem that the easier route would be that old standby for increasing effective displacement: the turbocharger.

**easyBob** · 4-24-07, 5:25

Quote:

Originally Posted by Mike 94PGT

If you want to puff up the KL it would seem that the easier route would be that old standby for increasing effective displacement: the turbocharger.

QFT.

-Chris

**JGTC MX6** · 4-24-07, 8:13

Quote:

Originally Posted by Mike 94PGT

If you want to puff up the KL it would seem that the easier route would be that old standby for increasing effective displacement: the turbocharger.

I in no way disagree with you on this one, turbocharge anything and you have a winner.

I myself like the small displacement high revving power, and most of all the sound that comes with it.

I'll have a spare crank to play with hopefully by the end of this week. I just need to find a trusted machine shop to do the work on it.

I'm going to go with the long stroke first. It seems to me that this is what most people are interested in anyway. If it all works out I'll edit the dimentions if need be but I do not expect much of a change.

I think the base power levels are well known for your standard I/H/E which is my current KLZE setup, so I'll dyno the stroker when it's done. Mind you this is planned to be a zero bore 2.7L.

kind of off topic;
I do not have any leads on solid sleeves as of right now. I did make some calls and sent a few emails to interprep or whatever a while ago, all about an extreem overbore sleeve system for the KL, it seems they had little interest in the project. Any one with ideas please chime in.

For me, a solid sleeved block extreemly overbored, a very short stroke, and some super long rods is the route I want to take. I'll turbo that and have all the power I need for quite some time.