Help me stroke my 4.0!

[Reelm n Rubi]

Well the engine is together. .060 over KB944 pistons, balanced, Hesco aluminum head, Avenger Supercharger, 4.0 rods, ARP rod bolts, Comp cams custom cam, Comp cams valve springs, HV oil pump, 4cw crank, .061 quench total, RR stainless header, bored throttle body, and a lot of patience and help from this forum went into it. Thanks, hopefully it'll be running by Sunday.

stroker.jpg

kb slugs.jpg

[Reelm n Rubi]

Well It's a driver now.I got the fuel map and timing dialed in pretty close. I want to take it to the dyno after I get it broke in and have a chance to moniter and play with the open loop AFR. Here's a pic of the Fuel map program and the OBD-II programs I use.

Fuel cells.jpg

both programs.jpg

fuel trims.jpg

[SilverXJ]

What OBD software are you running.. also, the one thing I never understood about some of the piggy back computers is why do you need to get the fuel trims to 0? Maybe I am misinterpreting it, but if you get the fuel trim to 0 with larger injectors, unless they are perfectly sized to your engine, wouldn't it run rich? I.e. the engine is reading fro the O2 sensor and adjusting the trim accordingly.

[Reelm n Rubi]

I run a BR-3 program. I can't give you a real good explanation as to the advantages of having your trims avg near zero. I will read up on why. I run 36 lb injecters FYI.

[gradon]

When you use larger injectors, the engine runs rich @ certain rpms, the o2 sensor tells the computer this and then the computer pulls fuel out once it detects it, thus producing a negative trim(vice versa for running lean). The closer you get the trims(short and long term) to zero, the less the computer has to work to keep the afrs @ the 14.7 stoich mark. Basically you flatten out the trim "waves" and keep the afrs tight, waste less fuel, and make transitions throughout the rpm range smooth. I'll be tuning my psc1 w/in the next month. Before the lt1s, my lt trim was +25%, so the ecu had to dump 25% extra fuel to keep the 14.7 mark and it wasn't smooth throughout the rpm range. After the lt1s my trims stay w/in +10 and -10% and the acceleration throughout the rpms is smooth. I do know that I'm running rich at idle now, so I will be pulling fuel out, but maybe at WOT, I need to add fuel--you can do this with a piggy-back, but not with an adjustable map. When I bought the 96, I wasn't sure if I was gonna like the obd-2 setup, but the information it gives you(fuel trims for example) is very helpful in monitoring and trouble-shooting. Before this stroker, I had the 96 modded out with the same mods from my 94. I feel that my 94 was a touch quicker--it could be due to the different stock cams, or the diffs b/t the 94 and 96 jet2 chip(the 94 chip made more of a difference than the 96 IMO), or maybe the 94 was "hotter" from the factory, but I have had suspicions of OBD-2 interfering too much.

[yuppiexj]

Having driven both a 94 and 96 XJ,
I will concur that the 94 is hotter from the factory.

[SilverXJ]

My 19 XJ also felt hotter than my 2000 XJ in stock form.

On the fuel trims, if it is at 0, isn't it putting more fuel into the engine with larger injectors? I.e. it is telling it to put the same amount of fuel through the larger injectors as it would with stock injectors.

[Reelm n Rubi]

My 19 XJ also felt hotter than my 2000 XJ in stock form.

On the fuel trims, if it is at 0, isn't it putting more fuel into the engine with larger injectors? I.e. it is telling it to put the same amount of fuel through the larger injectors as it would with stock injectors.

Exactly, but remember we're also stuffing more air through the engine to match the injectors.

[SilverXJ]

Exactly, but remember we're also stuffing more air through the engine to match the injectors.

Yes, but the computer is looking for a certain AFR (14.7 iirc) and it will try to maintain that in closed loop. If the fuel trim is pulling fuel out, I don't see what getting it to 0 is actually doing.

[Reelm n Rubi]

Sorry I haven't been on in a while but here's a quick Youtube of the Jeep. I am taking it to the dyno in a week or two. http://www.youtube.com/watch?v=eKDXQh677ig

[SilverXJ]

Nice... I'm sure having that much lift helped to make the wheelie more significant. But.. where is the sound.. NEED SOUND!!!

Any how, how long is the warm up on those pistons before the slapping sound goes away?

[Reelm n Rubi]

There's no slapping sound If I can find my video camera charger I'll post up a new video with sound. I've almost got my Innovate MS aux box wired in so I can get my fine tuning done and then it's off to the Dyno.

[SilverXJ]

What clearance were they installed at?

[Reelm n Rubi]

I can't remember exactly, but forged pistons require slightly more clearance due to expansion. I've never once heard a rattle come from this engine.

[SilverXJ]

I can't remember exactly, but forged pistons require slightly more clearance due to expansion. I've never once heard a rattle come from this engine.

IIRC, its .00035 to .0005. KB recommended .0004" to me.

-Chris