TJ: Mopud's Stroker Buildup

[Dom]

Nice looking Val Mopud!

I have to add my two cents on the above comments on over fueling.

I did a very similar build (see "Stroker CJ" thread in this section). Same cam, same RR's, similar block profile etc. Main difference is that you're going 0.060" where I left it at 0.030". So I think you'll end up with a 4.7L while mine is 4.6L.

I too followed the formulas exactly and ended up at Bosch 27lb injectors - this is what I started with.

The stroker runs superbly in open-loop. That's when cold, when accelerating and at WOT. Never missed a beat.

In closed-loop it had - and still has - problems getting the adaptive fuel trims (both short and long term, correct. This is because the system tries to nail the 14.7:1 stoichiometric point by "hunting" around the oxygen sensor's lambda value of 0.65V.

The system alternately adds and subtracts a default time interval from the pre-calculated injector pulse width, creating a continuous sequence of long-short-long-short-long-short...etc injector pulse widths. In return, the computer expects to see a string of O2 sensor voltage readings showing hi-lo-hi-lo-hi-lo volts. If it gets a sequence of hi-hi-hi-hi-hi etc O2 sensor readings it determines that the mix is too rich, adjusts the short term adaptive fuel trim and recalculates overall pulse width until it gets it right.

Initially, with my 27lb injectors (and even with a replacement set of 25lb injectors) that "default interval" I described above is too big and results in the delivery of too much fuel. In other words, with bigger injectors and more fuel pressure at the rail, it continually over-controls and the computer can't establish the correct trim settings.

A dealer near where I work put it on an genuine Jeep scanner and the consistent reading was LOW OXYGEN. The effect when driving it in closed loop is that it tends to stumble until you either back off, or nail it to get it accelerating in open loop mode again.

I'm going back to stock injectors, with a slightly elevated fuel pressure setting, in the hope that it is the right compromise.

To make sure I don't lean-out in open loop (cold/accel/WOT) I have build a MAP adjuster so that the PCM believes the incoming air charge is denser.

My setup is OBD1, so I have vacuum-modulated fuel pressure ranging from 34 to 44 psi at the rail, depending on manifold pressure. As you are using OBD2, you will have a constant 49 psi at the rail. The 27lb injectors are going to deliver a metric a*seload of fuel!

Not saying it won't work, but this is where you might end up and I hope my experiences help.

Best of luck!

[Mopud]

Thanks for the compliments on the val guys. FYI it was originally a 69 VF but the front end was changed some time ago and it is now a '70 VG'. I call it a 69 1/2 VFG

Comprehensive post there Dom! Many thanks for the info. Admittedly, my knowledge of fuel injection systems is limited so it was a great read. Honestly i'll just have to see how it runs when it fires up and operates - some people seem to get away with these mods rather fortunately, others have told of some real horror stories.

If fueling is an issue i'm just as likely to get a unichip installation, tweak and dyno ($1500), one of these jaycar units http://www.jaycar.com.au/productView.asp?ID=KC5385 or perhaps even knock up one of these http://www.angelfire.com/my/fan/MAP_adjuster.html if it applies to obd2 and is easy enough.

We'll see in a few months!

Regards,

Mopud

[Mopud]

After a shitty couple of weeks the bane of my existence has finally arrived - the lucrative keith black pistons.

A word of caution to anyone else ordering through Summit, their advertised ETA for parts not in stock mean nothing. I had to call summit and see what the hold up was after waiting 2 months for pistons that were only a 2 week ETA when I ordered them. Their advertised ETA is computer generated and not indicative of real world in anyway! I didn't get anywhere with their rep so I rang Keith Black Pistons myself and found a guy who was VERY helpful and he noted that no order had been placed for my 60thou pistons and that they weren't going to start production on those for at least another 6 weeks.

He had a set of 40 thou over in stock so i went with those. I then rang back summit and got them to call keith black to work out the details and change my order. Following that I cancelled my order of pushrods with them (ETA rubbish with the pushrods as well) and used the money already paid for those to go towards the shipping of the pistons.

Two weeks later and they're in my hands - They're now at the machine shop with everything else.

I'm also getting them to port match the intake manifold and exhaust headers to cylinder head and bore out the intake manifold inlet to match 68mm throttle body.

I'm just waiting for them now to complete their work. Funny you know now that i've supplied all the parts ready for work they're full on busy and understaffed!

**To anyone else out there considering this, don't waste your money with the Mopar 'Complete' Engine Teardown kit, it's rubbish . Comes with cork gaskets (stock units much better) and is also an incomplete set! Very disappointed with the money wasted there.**

[Mopud]

I got the block and bottom end back from the machine shop and set about checking all of the ring gaps and crush on the mains' bearings. It's thou inch perfect, they did a great job.

I picked up some brass freeze/core plugs from Coventry's (as directed by the Jeep dealership). I thought i'd just need a set of 7 but it looks like the cam one is slightly bigger. They were about $3.80 each on trade and product code is RBC20 if ever you need some.

I'll be bolting down the crank and mains tomorrow as well as rods and pistons.

I also received my new brown dog offroad engine mounts today - http://www.ausjeepoffroad.com/forum/...ad.php?t=99713 and really like the look of them so I can't wait to mount them up.

I also paid an arm, a leg and a testicle for some replacement gaskets from the dealership. The machine shop needed the intake/exhaust gasket to keep working and the one i received from the mopar 'complete' teardown gasket set wasn't the right fit. So off I went and got served like a skinny white kid in an american gaol because i didn't want to wait another day for delivery to save a few $ and cause more delays.

Thankfully I get trade price there, but still at the end of the day the prices are extreme. (Try $90 EACH trade price for the plastic little clips that hold the sunvisors in place on my parents' 1996 ZJ...).

Forwards, not backwards, not to the side but forever twirling, twirling towards completion. Pics to come as I go along.

Mopud

[stroked]

sounds good pud, keep it coming along hey!

[grit]

then all of a sudden "nothing". leaves you wondering if it is ever worth it....

[anthonygubbin]

Worth it? Well that depends on what you place value on. I am in the process of collecting stroker bits and hope to one day actually complete the build. Unless your loaded then a stroker takes a long time to build.. Mine is a five year project. ATM I am about 9-10 months in and only have a manifold, crank and pistons. Mind you I am yet to have some of my parts sent from interstate mainly due to the cost of freight.

Regards A