Jeep Strokers

Hi Gents,

The stroker has been running for near on three months now, and running quite well i might add. Power difference as far as I am concerned is far better over pre-stroker.

I've been patiently waiting for a unichip install for some time now (almost a 3 month wait here as there's only one shop here in Perth that can do them) and today I finally got it done. The results?... well... Before and after are to say the least, incredibly disappointing. When comparing it to the likes of fellow forum member Comanche91 (forgive me, i think his name is Don?) and his amazing results I can't help but feel i'm missing out. (Edit: I don't know his exact build but i'm sure it's much more than mine - I don't expect 260hp at the wheels with my configuration!).

I've attached the chart. The 4WD shop who installed, tuned and dynoed the chip could not provide me with torque figures or RPM range, (another point i'm not so happy about) so once i've sorted the ongoing cooling issues I will take it to a local performance workshop for another dyno run with more detailed information.

Anyway, 96kw (128hp) before, and 108kw (144hp) at the wheels after just doesn't cut it for me. My specs are good, the build was top notch and right now as a result i'm feeling largely defeated and more than a little disappointed.

Specifications are:

2001 TJ w/ OBDII (I used my original engine block)
4.2L 3.895" Stroke Crank 1981-1986 : 3235477 - 4 cwt, 46lb, 64mm, Ground 30 Thou
Keith-Black Silvolite UEM-IC944 +0.040" (3.915 in) bore pistons inc rings. Forged, 21cc dish, Moly Ring
Original 4.0L 6.123" rods
CompCams 68-231-4 Camshaft
CompCams 3219 Timing Set
CompCams 822-12 Hydraulic Lifters
Yella Terra YT6328 1.6 Adj Roller Rockers
Bosch III 27lb/hr Injectors - XF1E-A5B (Bosch Part Number 0280155849)
PERFECT Hi-Velocity 68mm Throttle Body by Painless
0630 Cylinder Head. 1.91"/1.50"
Mopar Performance Valve Springs : Valve Spring, Single, 1.418 in. Outside Diameter, 1.640 in. Installed Height, Each

I honestly believe I have the specs on paper and that i'm just not getting the results to match. The installer did mention that the transmission overheated at one point and spat transmission fluid all over the pipes resulting in a mini fire - i don't know if there's some serious power being robbed there. It is the 3 speed 32RH automatic. - i know it's a massive power hog.

I am also running standard ratios (they are 3.07 i think?) with 33" tyres - i have some 4.10's to go in within the next two weeks so i'm hoping they may make a significant difference. Given the above I doubt i'll see a hugely notable difference.

Your expertise and opinions/thoughts will be well appreciated.

Regards,

Anthony

I don't have my stroker finished yet, but I do have a TJ with 4.0 L and 32RH trans. When I first lifted it , I had stock 3.07 gears and 33" tires. I was unhappy, it was no fun to drive anymore. No power, the trans. shifted at weird times, it felt like I was pulling a 2 ton trailer all day. I went to 4.10 gears and life was good again. Power was good, it felt peppy again and the trans. shifted at normal points. I don't know about dyno numbers, but a gear change will your Jeep fun to drive again. I think due to the fact it was back in its power band at cruising speed, my fuel milage improved.

Assuming 33" diameter tires with a 1:1 3rd gear (converter locked) and a 3.07 final drive, we can then derive RPM.
with the RPM kw to HP to Lb/Ft is pretty easy.

+1 on the regearing. Your numbers are decent but I bet it's no fun to drive with the tall gears.
.

Mopud wrote:Anyway, 96kw (128hp) before, and 108kw (144hp) at the wheels after just doesn't cut it for me.

You should be very happy. That's a 12% HP increase just from the Unichip and you've gained torque right across the rpm range. The power-sucking 3-speed auto tranny isn't doing you any favours and neither are the stock axle gear ratios with 33" tyres. You definitely need at least 4.10's and they'll make a dramatic difference. You might also want to add an external tranny cooler 'cause with all that extra power, your torque converter's going to generate more heat.

Thank you everyone for the replies.

I completely agree with the suggestion to regear the diffs, it's only a matter of time before that happens - all the gear is ready to go I just can't afford for it to be off the road at the moment.

From my understanding a standard Jeep wrangler w/ 4.0L puts out 135-140hp at the wheels so i was feeling well and truly robbed given that's about the mark i made. I guess because my initial horsepower estimates were 250hp+ (at the crank) I was quite defeated when i saw it only managed 144 hp. I will go for a dyno rerun after the diffs are done, hopefully i see a higher mark come through.

Dino, believe it or not I already run an external cooler - a B&M 70264 Automatic Transmission SuperCooler rated at 14,400 BTU (11"x6"x1-1/2"). I question if i have the pipes plumbed correctly now (i didn't think it really mattered to be honest, but i will double check). It is a passive cooler but apparently it still blew oil out the dipstick even with the thermo running and an external workshop cooler blowing air into it also. I have a temp gauge kit to go on too, it's essential now i believe.

Anthony

Please repost when you do the second dyno run. It would be interesting to see how much gears and tires change things on the dyno. My 2000 XJ with header and intake did 149 hp on the dyno with 3.55 gears and 31" tires.

Mopud wrote:From my understanding a standard Jeep wrangler w/ 4.0L puts out 135-140hp at the wheels so i was feeling well and truly robbed given that's about the mark i made.

Yeah, a stock 4.0 Wrangler typically puts down about 145rwhp and 190rwtq but that's with a manual tranny and stock tyres. Having an automatic and big tyres will give the rwhp number a big hit. I'd be interested to see the rwtq numbers.

Cheromaniac wrote:Yeah, a stock 4.0 Wrangler typically puts down about 145rwhp and 190rwtq but that's with a manual tranny and stock tyres. Having an automatic and big tyres will give the rwhp number a big hit. I'd be interested to see the rwtq numbers.

That makes 2 of us. I found it strange when the installer told me (after the job was done mind you) that they 'can't provide torque readings for automatic transmission vehicles'. Prior to the first dyno run he informed also that he disliked working on them because of the way they operate on his machine. I can't wait for a real dyno!

See if you can find a Dynojet. The Dyno Dynamics is a load type dyno and automatics invariably put down lower numbers than expected due to torque converter slippage so your dyno operator is right.

Thanks Dino.

I've just done the ratios (4.11) and had the diffs completely serviced at the same time - turns out the clutch plates had disintegrated and i had stray metal chunks and filings (and silver coloured oil) all over the place.

Just trying to track down the dynojet for another run sometime this week.

Anthony

I had another dyno run at another workshop and also got the guy there to re-tune it for me as I didn't have a lot of confidence in the mechanic who installed it initially.

This time running I had the 4.11s in place but unfortunately there was no difference to total power output. This power run came in at 142rwhp and again I was not able to provide a torque reading - something he said dynos can't do. He mentioned that the chip was tuned just fine - except that it was running a bit rich at the top end (the installer told me it was too) so he dialled that down.

Other than that, nothing more to report. All I can assume is that I've created a torque monster because it drives like its life depends on it but I have no way of really measuring it other than how it performs. I'm going to look into the cam dynamics (Crane 68-231-4) and the overall engine build to see if I can piece together more of a technical understanding of the engine characteristics. I might even look at a 1/4 mile run at the local drag strip too.

Mopud

Post the results.

Torque is not RPM dependent, HP is.

With RPM (or even wheel speed) you can derive HP numbers from torque and vice versa.

Mopud wrote:All I can assume is that I've created a torque monster because it drives like its life depends on it but I have no way of really measuring it other than how it performs.

At the end of the day, it's the seat of the pants dyno that counts and if that's measuring a significant improvement in performance, why care about how many rwhp the Jeep puts down? Just count how many more smiles per mile you're getting.

Right you are Dino. I'm well aware of that and certainly don't feel like it's a failed build, i know how it drives and that is more than enough for me. I was simply confused that the output reads the same as a standard wrangler and feel that it won't be received too well in the third part magazine article i've written.

I enjoy every part of it, i'm sure even more so once i take it on its maiden trail run. Especially now with the new front diff locker and ratios