Mid range loss

Today, my wife and I were invited out to the Rednecks & Ridez Concert Benefit (what a name huh?) outside of Ellijay GA. The entire fire deparmtment got to enter a cruise in, and show (if they had a vehicle to enter) free of charge. While there, a salesman for DynoJet had a presentation set up of a new dynomometer. I had the opportunity to run my 98, I bargained for 200-210HP, seeing that Jeep quotes 190BHP, but with the slush box trans. I knew I had probably lost 10-20% in lag. With an intake, 3 inch exhaust, Xtreme Flow cat and Flowmasters, as well as the almost "famous" platinum 4 plugs (what a joke?), TB spacer, and some upgrades to the intake manifold, I thought this was pretty average number but to my surprise, the XJ popped off 221 horses, but at 29000 to 35000RPM? The rig then loss amazing amounts of power (down to 150-152 HP) between 3500-5000 RPM.... this was the story after 3 runs, the best averaging 223.6 Horses but still in the low range (which is understandable with the I6) but why such a loss at mid range. Gearing is 3.55, which shouldn't affect it that much with 31's. I have noticed (as you can tell from my many posts) that I get horrible mileage, and most of everyday driving is done at mid range..... Just doesn't make since to me, anyone have any ideas?

I thought maybe, O2's but I replaced them about 6K ago.

After talking to two of the other guys that was at the festival I have come to the conclusion that I am concerned over nothing at all. As a matter of fact, one drives a 99 Cherokee, and the other a 98 Grand Cherokee (both are 4liters) and they are bone stock, looking over their dyno printout....I have to say the upgrades I have done, have paid off. Both of their jeeps pulled an average of 140 horses. Jeep says that the 4 liter produces 190 and 225 lb ft, how in the world does the transmissions in BOTH of these jeeps lag off the engine that much. My 223 horses compared to theirs really takes the cake, I'm not as concerned now,................

Jeep numbers are at the fly wheel and do not take in all the loss through the drivetrain. The average loss is 22% to the rear wheels. Losing power at 3500-5000 is high range and not mid. How often do you sit up in those revs anyway? You want the power down low as you are driving a 4wd and that is what will get you up the mountains and towing with ease. You dont drive a 4 cylinder buzz box!

well I don't have a tach on mine I just thought, from my experience with other vehicles that Mid range was around 3500 rpm, seeing that, thats the number most vehicles run down the highway. (at 70 75 mph) but now that I think about it, I guess with the gearing in the AW4 2800 would probably be mid range,
I know where the power needs to be but, like I said at wide open throttle its there, and from the line its there, but I thought losing 70 horses from 2-4 was a substantial loss.

the technician thought I should invest in a power programmer or Jet Chip, stating that (and making alot of sense) my upgrades and performance bolt ons were doing the job as we could see, but the factory computer settings were trying to regulate the performance of the engine within factory guidelines. I have not even thought about the chip/computer upgrade, but it really does make sense.....probably save some gas too....

another thing I have noticed, after having nearly $450 worth of machining done to the intake manifold is that there is a constant whistling coming from the manifold, I have also developed a 4th!!!! exhaust leak after putting on a header, anyone else had a problem like this?

You've done all those performance mods including 450 dollars worth of machine work...............and don't have a tach??
Sorry, but that just struck me as odd.
Timbo

:laugh:

mgreen84 said:

another thing I have noticed, after having nearly $450 worth of machining done to the intake manifold is that there is a constant whistling coming from the manifold, I have also developed a 4th!!!! exhaust leak after putting on a header, anyone else had a problem like this?

Click to expand...

here is an $80 mod worth your time...
http://www.opiebennett.com/Gauge.htm