2.5L 4-cyl Engine/Chamber Dimensions
 

I've got a '98 Ranger with a 2.5L 4-cylinder engine that needs a bit more power. I'm trying to do it as inexpensively as possible, so I need to know a few specifics before I decide exactly what I'm going to do.

Is this an interference engine?
What is the piston-valve clearance?
What is the combustion chamber volume?
Are stock pistons dished, domed, or flat topped?

BTT

After running roughly a half-tank through my pickup, I'm getting ~30mpg in town. Not bad, I suppose, but I'd like to push that into the 40 range or so. Shouldn't be too tough...

Using various mods, such as PowreLynz, PowreRingz, Singh Grooves, Edging, high(er) compression, and ECU tuning, 40 mpg should be a daily figure.

www.fueleconomytips.com
www.mpgresearch.com

Well it is not an interference engine, and I think they all have flat top pistons.

check this one out as a 2.5 is a stroked 2.3:
https://www.ford-trucks.com/forums/s...6&goto=newpost
tom

That gives me a lot of information, but nothing specific.

Does anyone know how much can be shaved off a stock 2.3/2.5 cylinder head before hitting water? I want to get to ~10.5:1 compression...

10.5:1 is not problem. The 2.3 heads can be shaved as much as .200, maybe more. Racers cut them well into the manifold bolt holes. If you cut too much, it will throw the cam timing off, so you would have to use an adjustable timing gear. Pistons are flat on the 2.3, don't know about the 2.5 jd

Cool! Where would I go to get a low cost adjustable timing gear? The cam is belt driven so I'm guessing the timing "pulley" is what I'd be changing? I've worked on OHV engines but this is my first OHC...

Racer Walsh used to have adjustable cam gears.. I think
tom

The 2.3/2.5 liter lima engine IS an interference, not by much, however enough. The pistons are cast flat top for NA and forged dished for Turbo's. I've never seen a stock 2.5 turbo engine thou. To get to a specific CR you need to know exactly what you have. The factory number is bogus and if you measure it, you'll find it to be higher than produced. On the KB piston site there is a compression formula that you can use.

So to know what I have I would need to tear the engine down and make some measurements. If the engine is already slightly interference (without valve-piston contact) what would be needed to raise the compression? If I were to shave 0.18" off the head, would I also have to cut valve reliefs in the pistons?

At least check them and see what you've got to be safe. You'll want .090 on the exhaust and .060 on the intakes. If you're running an adjustable gear then check it retarded and advanced.

Well, someone should tell the rest of the world that the 2.3 is interference, as all I have read says not. I have not checked with a running engine. Heh. Nor have I checked with one taken apart, so I have no personal knowledge.
The Gates Rubber Co web site has a PDF file of engine timing belts with indication to their interference status, and that was one of my sources of 'knowledge', and the one I would go back to most.
tom

I have thru the years run into some (not many) that after throwing the belt, had to remove the head and change a slightly bent valve. I t has happened. In this thread discussion is to mill the head for more compression, which will bring things closer together. It's best to have an accurate measurement to be sure of possible problems.

I've heard of using modeling clay on the piston top and going thru a couple rotations to check for clearance. If you mill the head or the deck, for sure you should check clearance. I would do that on all the cylinders if I were putting some money into the engine, or changing the cam.
I would bet that some cam/rocker-follower/lifter/valve combos could lead to interference.
tom

Clay seems to be the best way after over 40 years, that I've been doing it. With zero or positve piston to deck placement and milled heads, you'll need eyebrows in the pistons of varying depth for any cam if the belt should take a holiday.

[QUOTE=Pinhead-227]That gives me a lot of information, but nothing specific.

Does anyone know how much can be shaved off a stock 2.3/2.5 cylinder head before hitting water? I want to get to ~10.5:1 compression...[/QUOTE

What have you found out yet? I am looking to shave the head on my 99 Ranger to raise the compression to 11:1. I am running E85 and want to make the engine more efficient on that fuel.

Dan