Building for reliability?

[Root Moose]

Maybe my search-fu is weak today... Is there a FAQ on building for reliability specifically?

I'm researching building a stroker that will run on 87 octane. Hoping for ~250+ hp / 300+ lb-ft but don't know how realistic that is using the crap gas that is available in the remote areas we travel. Even more horses and torks would be better of course!

I still need to dig into the math but was thinking DCR in the low 7s, SCR in the low 9s is the ball park? Quench around .045? I have no idea of the mechanical parts to get into that combination, just thinking hypothetical ideal for now and looking for input on what to be looking into.

Mechanically, long rods?

hyper pistons?

Roller valve train?

Re-use 4.0 rods or bother with stronger and/or different geometry aftermarket rods?

Source an NVH block or use a RENIX or HO block I have lying around? Vehicle currently is NVH but will be sourcing parts to bench build.

Other things to be looking into?

I'd like a cam that makes it's torque between ~1500 - 3500 RPM. Running out to ~5k is ok but it seems with my tire diameter and gearing (32s/4.56) this is the main RPM range I see when towing heavy.

Want to avoid any pinging when towing heavy (~9000 lb GCVW w/ trailer).

There is likely an AEM FIC in the future so building with the idea of adjustable maps depending on fuel availability is an option but I'm unclear if that really makes much difference to the mechanical configuration.

Target vehicle is my 2001 XJ that we use for long range trips. Getting broke down in remote areas sucks and I want to avoid it. Our last trip we got stuck for 5 days due to a fubar power steering pump of all things. Yeah, a spare of the accessory drive stuff is going into the spares box before our next trip.

TLDR; ?

Any input, pointers or links appreciated. Thanks!

[jbxx]

I have yet to run my stroker, but from lurking here for a few years most problems seem to be with the cam.
So if I were to build the most reliable stroker, I would be inclined to be very conservative on the cam specs., maybe even as far as to stay with a stock or RV style.
There are people here with much more expertise than I so hopefully they will chime in.
J.B.

[Root Moose]

Agree, not looking to build a race engine... just a torque monster.

Btw, wrt budget I figure somewhere around $3k is what I'm currently thinking. Depending on the spec I'll refine that further. I'm liking the idea of a new rotating parts with zero fatigue cycles.

[jbxx]

3K is what I was shooting for too. Probably past 6K at this point, I went over the edge!

[Cheromaniac]

Just build a modified poor man's stroker and reuse your stock '01 cam with new lifters.
A set of Accel 24lb injectors will be enough to provide the fueling, and FlyinRyan could help you with the ECU tune.
My recipe for reliability is to reuse as many stock parts as possible in the stroker build and minimize the use of aftermarket items.

[SilverXJ]

If you are shooting for a low CR to run 87 octane and want the 4.0L rods you will need a custom piston.

[Root Moose]

Yeah, I was thinking that I may do a Scat crank and a dished piston to get the numbers I want/settle on. I have 1980 something CJ7 carcass I can take a crank out of but for this Jeep I like the idea of new parts.

Looking at low quench numbers and thin head gaskets how much piston dish is too much if there is such a thing? Affects on reliability?

I've seen quench mentioned from 0 to ~.04x being ideal. I get that .04 is somewhat easy to get but... Over thinking?

[Cheromaniac]

Yeah, I was thinking that I may do a Scat crank and a dished piston to get the numbers I want/settle on. I have 1980 something CJ7 carcass I can take a crank out of but for this Jeep I like the idea of new parts.

Looking at low quench numbers and thin head gaskets how much piston dish is too much if there is such a thing? Affects on reliability?

I've seen quench mentioned from 0 to ~.04x being ideal. I get that .04 is somewhat easy to get but... Over thinking?

If you're going to shoot for zero deck clearance, a 0.043" quench, and run the engine on 87 octane, you'll need custom pistons to get the best result. A compression height of 1.380" would be ideal 'cause you could achieve zero deck without milling the block. A 30cc dish would get you a SCR of ~9.0:1 and the engine should run fine even with the crappiest gas.

[Jim K in PA]

If you're going to shoot for zero deck clearance, a 0.043" quench, and run the engine on 87 octane, you'll need custom pistons to get the best result. A compression height of 1.380" would be ideal 'cause you could achieve zero deck without milling the block. A 30cc dish would get you a SCR of ~9.0:1 and the engine should run fine even with the crappiest gas.

A nugget of gold there. Thanks Dino. I am just about to start a project thread. I have to find a machine shop first.

[Root Moose]

I must be missing a subtlety... What is the gain of getting custom pistons versus machining the block down? Is it just to save machine work?

[Jim K in PA]

I must be missing a subtlety... What is the gain of getting custom pistons versus machining the block down? Is it just to save machine work?

A custom piston will give you the pin height to eliminate decking the block, but also (and more importantly) the appropriate amount of dish in the piston top to give you the compression ratio you want.

Just my view.

[Root Moose]

So that is something worth pursuing IF you can't get a piston with the appropriate amount of dish...

Sort of related to dish sizes... when cleaning up the head what is the typical resultant combustion chamber size in cc's? Can't change much?

[Cheromaniac]

A custom piston will give you the pin height to eliminate decking the block, but also (and more importantly) the appropriate amount of dish in the piston top to give you the compression ratio you want.

Yes indeed.
Keith Black had designed the IC944 piston to have a 1.353" compression height and 21cc dish for a 4.0L block that was intended to have 0.020" milled from the deck to achieve a 0.050" quench and a 9.6:1 CR. With that CR the engine would probably need a diet of 91 octane brew.
If you want a lower CR AND a quench of 0.050" or less so you can run the engine on 87 octane, you're going to need custom pistons period. Therefore you might as well have the pistons designed for a 4.0L block that won't need to have the deck milled (saving you on that cost), and that'll require a piston compression height of ~1.380".

[Jim K in PA]

Yes indeed.
Keith Black had designed the IC944 piston to have a 1.353" compression height and 21cc dish for a 4.0L block that was intended to have 0.020" milled from the deck to achieve a 0.050" quench and a 9.6:1 CR. With that CR the engine would probably need a diet of 91 octane brew.
If you want a lower CR AND a quench of 0.050" or less so you can run the engine on 87 octane, you're going to need custom pistons period. Therefore you might as well have the pistons designed for a 4.0L block that won't need to have the deck milled (saving you on that cost), and that'll require a piston compression height of ~1.380".

Let's clarify a bit more. Are we really concerned about SCR? If all other variables remain the same between two engine configuration EXCEPT for DCR, isn't the STATIC CR irrelevant when determining detonation sensitivity? If two engine both have 9.7:1 SCR, but one has a DYNAMIC CR of 8.3, and the other has a DCR of 7.3, the engine with the lower DCR will not have the propensity to detonate on lower octane fuel, correct?

I did some simplified comparative analyses over in another thread relating to 87 octane in the basics forum. Please take a look and tell me where I missed the boat: http://www.jeepstrokers.com/forum/viewt ... =15#p40558

Thanks.

Jim