Renix 4.0 questions

I just read in my Chilton's manual that my 87 4.0 only makes 150 hp, I read in another book that it makes 173, what is the true output of my engine, and if I only make 150, how did the newer renix engines (from 88 to whenever they stopped making them) which still used most of the same parts (ECU, head, ect.), make 37 more HP (to give it a total of 177)? I can understand a small 4hp boost (from 173hp to 177hp) from changing somthing small, but a 37 hp gain is a little hard to belive. So does any one know how much HP and torque a 1987 4.0 makes, and at what RPM. Also, Chilton's has the 87 4.0 listed as 210 while other sources have it at 220.

Well the Chilton Book is a "general" source of information. I have always thought it was in the 177 range for the Renix 4.0 and 13 more HP for the HO 4.0 engine.

I also have a 88 XJ. I recommend you get the manuals from Chrysler if you plan on looking up tech specs on your XJ. At least they are published by the people who made the vehicle and covers only 1 year.

A 1987 Comanche sales brochure lists the 4.0L engine as producing 173 horsepower and 220 foot-pounds of torque. The specs don't quote the RPMs for those ratings, but there is a small graph. Looks like the HP peak is around 4,800 RPM and the torque peak is at around 2,500 RPM.

All 87-90's are 177hp. There are no differences in the engines between '87 and '90.

Not that it matters so much, but 177-150=27 not 37.

The XJ 4.0's have the following factory rated outputs:

'87-'90 Renix 4.0: 177hp @ 4500rpm, 224lbft @ 2400rpm, redline 5000rpm
'91-'95 HO 4.0: 190hp @ 4750rpm, 225lbft @ 3950rpm, redline 5250rpm
'96-'99 HO 4.0: 190hp @ 4600rpm, 225lbft @ 3000rpm, redline 5300rpm
'00-'01 HO 4.0: 193hp @ 4600rpm, 231lbft @ 3000rpm, redline 5300rpm