Topic: 2.5L stroker crankshaft

[sharpxmen]

I don't even own a 2.5 yet,

so you have a 4.0?

  Rods can be reused.  Custom pistons are preferable to many but not required. 

you need custom pistons or dished out pistons (which are still custom and not off the shelf).
I have no idea what you mean by reusing the rods, can you expand on that?

with a stock ECU / PCM you need a way to adjust the fuel in open loop regardless if it's OBDI or II, injectors are one way but you'll end up swapping a few to get it right, playing up and down a little with the fuel pressure would help.

Anyway, maybe I didn't phase it very well, but I'm sorry my expression of regret that you were correct and I'd have to continue dreaming is so annoying to you.

Rob

why do you think this is annoying to me, i'm rather enjoying it to be honest.

[Jeffy]

1. i don't think there are 150 active members with a 2.5 on this site (maybe over time yes but actual active members at 1 time i doubt it, Jeffy can provide more details)

15 Members for today and about 75 for one week period.

The majority of members on just about any forums haven't even torn into an engine.  Finding 150 people who are willing to tear into their engines will be low because of it.  If it was a kit, I think it would have had better luck as there is still a lot of leg work required to make it work and no clear path.

I've only heard of one person with a stroker 2.5L ever.  This was a JeepSpeed XJ.  I forget the car number and the guy's name unfortunately.

[xjcrazed]

so you have a 4.0?

Two actually, a '94 XJ and a '92 MJ.  But neither is a good choice for a commuter.  The way my XJ is built it gets worse gas mileage than my suburban.  I'd like to build something more efficient that I could use to commute in and utilizes a drivetrain that I am familiar with, as opposed to buying something which I know nothing about.

you need custom pistons or dished out pistons (which are still custom and not off the shelf).

If you follow the low buck stroker formula you would use stock 4.2 rods and off the shelf 2.5/4.0 pistons.  Dishing needs/capabilities vary by manufacturer and specifics of the build but are not necessarily required.  If you keep the stock 2.5/4.0 rod it does require a custom piston, but there are companies now that have standard products for this, and therefore are not as expensive or troublesome as a built to order custom piston.  Once again there is abundant information on all of this on the JeepStrokers forum.

with a stock ECU / PCM you need a way to adjust the fuel in open loop regardless if it's OBDI or II, injectors are one way but you'll end up swapping a few to get it right, playing up and down a little with the fuel pressure would help.

This is really close to what I said, however, on OBDII engines the pressure regulator is in the tank, part of the pump assembly, and there is no return line on which to install an adjustable FPR.  People still build OBDII strokers where an adjustible FPR isn't an option.

why do you think this is annoying to me, i'm rather enjoying it to be honest.

Maybe I read too much into that post, it just felt like I was being kicked while I was down after I had just agreed with you and conceded defeat.

Rob

[sharpxmen]

hmm, i wasn't enjoying your defeat or neither did i find your perseverence annoying, it's not a contest. Like i said, should a viable option as far as price goes appear i'd be one of the takers.

You can get an external fpr for the TJ, it's not that big of a deal but yeah you can get away with just the injectors however i still think it's not the proper way to do it unless you reprogram the PCM.

from my understanding the low buck stroker ends up being quite inefficient as the pistons don't reach the top of the cylinder, didn't research it or have first hand experience with it so i might be wrong, if i would do it i would get the correct height pistons and proper cc chamber (and like Jeffy said better to have a proven kit).

As far as mpg, i'm not sure if the 2.5 is that much better than a 4.0, a little but it won't be by much, could be that in stock form (stock tires, no lift) the 2.5 is more efficient but most of us already have them lifted and with 33'' tires so from personal experience it's really not a gas saver, i get 15 to 16 mpg and if i drive like a granny i might break the 17 mpg barrier

what mpg do you get on your I6?

[grumpygy]

sharpxmen  Just from memory the 4.0 vs the 2.5 MPG even stock the 4.0 gets better MPG.

I just had to look up 94 wrangler
2.5 15-17 MPG
4.0 14-17 MPG.

So its close.

[xjcrazed]

15 Members for today and about 75 for one week period.

The majority of members on just about any forums haven't even torn into an engine.  Finding 150 people who are willing to tear into their engines will be low because of it.  If it was a kit, I think it would have had better luck as there is still a lot of leg work required to make it work and no clear path.

I've only heard of one person with a stroker 2.5L ever.  This was a JeepSpeed XJ.  I forget the car number and the guy's name unfortunately.

When I first bought my XJ I hadn't even changed a tire before.  Now there are few projects that I wouldn't tackle on it.  I'll admit the actual engine work is beyond my current skills, but so was my first lift when I installed it.  For those willing to learn there are a lot of resources available.  Worst case, I'd pick my parts and have a reputable shop assemble them.  It takes a good shop for the machine work required on an engine rebuild regardless.

I guess I'm just a visionary, because the stroker crank is the only piece missing from my perspective.  The one you heard of is Rex Lair's, JeepSpeed #1769 which I linked to and included all the email quotes from in my original post.  I would be very interested if Dave (dwtaylorpdx) could recall any more information about the 3.0 stroker that I also linked to.

Rob

[sharpxmen]

i'm pretty sure Dave was talking about drag engines meant to run 5 minutes (just historically his posts have a reference to drag racing and that's how i came to that conclusion)

usually on low rpm engine with the cam in block, flat lifter and rocker design and 2 valves per cylinder, build for street/DD, you'll see a limit to about 100HP for each 100 cubic inches, it can be pushed more but you're looking at increasing the rpm and have a good intake and porting job in the head to increase volummetric efficiency

for engines with overhead cam, 4 valves per cylinder and higher than usual top rpm (like 7000 and over) you'll find that they can make 100HP for every liter of displacement (1000cc) but we're talking about real performant engines running high CR and usually meant for high octane fuel (not the 91 you find at the pump in north america). downside is reliability, the more you push them they won't last as long.

forced induction will increase the resulting HP at the expense of mpg and time between rebuilds also but it is a replacement for displacement if you wish.

looking for more HP will also hurt your low end, variable valve timing is one way to get around that but again different design engine with independent exhaust and intake cams (so the overlap can be adjusted and controlled during runtime).

but all that being said the more displacement the more potential HP so a stroker is def going to be better than a cam and increase both low end torque and top end HP if done right.

[xjcrazed]

You can get an external fpr for the TJ, it's not that big of a deal but yeah you can get away with just the injectors however i still think it's not the proper way to do it unless you reprogram the PCM.

In that case I must once again defer to you.  I wonder if it's just not as common for people building OBDII stokers to do an external FPR, or if I just haven't paid as close attention because both my current engines are OBDI.  For what I'm currently considering though, I'd use AEM's F/IC and an adjustible FPR would likely just complicate things.

from my understanding the low buck stroker ends up being quite inefficient as the pistons don't reach the top of the cylinder, didn't research it or have first hand experience with it so i might be wrong, if i would do it i would get the correct height pistons and proper cc chamber (and like Jeffy said better to have a proven kit).

But it should still make more power than stock.  I'm not considering the low buck route, just mentioned it as a possibility.  Because of the differing design goals of each build a kit would be difficult.  Plus when you buy a kit you're letting someone else make the decisions about what is important to you.

As far as mpg, i'm not sure if the 2.5 is that much better than a 4.0, a little but it won't be by much, could be that in stock form (stock tires, no lift) the 2.5 is more efficient but most of us already have them lifted and with 33'' tires so from personal experience it's really not a gas saver, i get 15 to 16 mpg and if i drive like a granny i might break the 17 mpg barrier

That may be true for the Wrangler, but has more to do with aerodynamics than anything.  In 2002, the last year of the 2.5 the Wrangler was EPA rated 16 city/19 highway with the 5-speed and a 3110# curb weight.  The same engine in the same year but more aerodynamic Dodge Dakota was EPA rated 17 city/22 highway notwithstanding a heavier 3645# curb weight.  With a lighter and more aerodynamic body the differences would be even greater.

what mpg do you get on your I6?

When it was stock, and even after my first lift of about 3" and 31x10.5R15 tires I could get about 19 MPG in my XJ if I drove it carefully.  Now that I'm at about 8" of lift and 33x12.5R15 tires I'm lucky if I get 12 MPG.

Rob

[sharpxmen]

In that case I must once again defer to you.  I wonder if it's just not as common for people building OBDII stokers to do an external FPR, or if I just haven't paid as close attention because both my current engines are OBDI.  For what I'm currently considering though, I'd use AEM's F/IC and an adjustible FPR would likely just complicate things.

AEM F/IC def a better option

[xjcrazed]

My primary goals are efficiency and longevity, but there's no reason that better performance can't play a part along the way.  With my personal goals an offset grind is out.  The custom billet stroker crank would fit my goals very well, but I don't know if I can handle the cost.  A new nitrided cast stroker crank would be ideal and not break the bank.  But it would appear that is a dream that isn't going to come true.  And with just the custom crank costing about as much as an entire 4.0 build, I will probably end up going with a 4.0 instead.  But, the 2.5 fits my goals better, and I really wish you were wrong about the level of interest.

[dwtaylorpdx]

The engine I mentioned a while back was in Rod Halls desert racers. I cant find the magazine right now but it was back when he was running the Cherokees.

As I recall he was pulling some pretty extreme horsepower but when I called SCAT and talked to them they said it was before the crank manufacturing was CNC, and they did not have the data on the exact measurements any more... I asked what the cost would be to grind a billet crank, he thought north of 5000 would be the starting number... 

After spending the time and money on my 2.5 if I had it to do over I'd just do a engine swap.

Mine runs good with all the machine work and build but I am still fighting the mileage issues. (12MPG at times.) it HATES the alcohol fuel. When I can find farm gas I get close to 20...

Dave

[xjcrazed]

Thanks for the comments, Dave.  Using them I found this Petersen's 4 Wheel and Off-Road article that mentions Mike Lesle's 3.0L MJ.  I was then able to find information in two books about his 3.0L build:

Tom Morr's "The Joy of Jeep":

[Mike Lesle's] 3,900-pound MJ was powered by a 2.5L four-banger, which was punched out to 3.0 liters.  It produced about 230 horsepower thanks to a Holley four-barrel, custom intake and exhaust manifolds, a billet crank, and a solid cam.

Mopar's "JEEP ENGINES - Speed Secrets and Racing Modifications for Jeep-Built 4, 6, and V8 Engines" P/N P4529529 also mentions a 3.0L build that matches Lesle's, but may not cite him by name.  I didn't see the book itself, just what was mentioned here, but all the specs detailed are identical.

All three sources state an output of 230HP, without forced induction, albeit with a huge amount of modifications (and $!!!).  However, it does seem to validate jpfrk2001's estimated 220HP, and the Mopar book was discussed in YJ_and_Corey's build thread on Pirate4x4.  It wouldn't fit well with my efficiency goals, but it shows what has been done before with the 2.5.  It also has me wondering what kind of performance could be had with a 3.0L build and forced induction.  Unfortunately, as previously covered, the current premium to get there makes it cost ineffective unless 150 interested individuals can be found...

Rob

[sharpxmen]

It also has me wondering what kind of performance could be had with a 3.0L build and forced induction.

imo a realistic estimation for a street drivable and lasting stroked 2.5L with forced induction is as follows (just straight up calculations based on displacement increase and equivalent displacement when using boost, not based on dyno results or anything like that)

2.5L stock / cam and other mods = 120 / 160HP
3.0L stroker = 144 / 192 HP
forced induction 8psi = 200 / 265HP (unless you go with forged pistons and cooling nozzles i would think this is probably as high as you'd want to push the boost to make it last, i would still lower the CR unless you retard the ignition a lot and use high octane with some added octane booster, the calculation is using an optimistic 10% loss).

[Bikerjr1]

XJCrazed,
A few years ago I was wanting to try and do the striker 2.5 and one option for a crank that I've yet to get solid info on comes from a Chrysler tech of about 20 years.  According to him there is a drop in crank and rods, pistons he wasn't sure of.  The crank is from a Chrysler 3.0L in-board marine engine.  I have three people at boat places trying to get me a blown or other-wise dead engine cheap (ie free).  I tried to get the spec manual but it is dealer only download and about 300.00.  Chrysler did make a couple of other similar in-board engines that are NOT the right ones.  I don't know the years but I think that they would be in the 80-90's.  Maybe you can find out more I just haven't had the time or luck to come up with the engine.  The crank, rods, and pistons are the only parts out of the marine engine you need trash the rest it is a true boat anchor in the marine world.
I've just about given up on it and will just re-build my 2.5 back to mostly stock.
If you come up with anything solid post it, it would be fun to build on a second engine for the YJ.
luck,
JR

[sharpxmen]

i've hear the exact same thing a long time ago but after countless hours of searching i came up empty. Don't quote me on this but i somehow remember that was an option for the pontiac 2.5 that was in the Jeeps initially (iron duke or whatever its called) and that had a marine 3.0 equivalent that you could use the crank and rods from, again it's been a long time since i looked into this so i could be wrong.