engine upgrades
Seasoned Member
Joined: Apr 2012
Posts: 402
Likes: 2
From: East Texas
Year: 98
Model: Cherokee
Engine: 4.0
and port the head. Find a shop that knows what they're doing, particularly on that head and spend a little money getting it worked over. new valves seats and 3 piece springs if you're running an aggressive cam.
Last edited by denverd1; Oct 24, 2012 at 02:27 PM.
CF Veteran
Joined: Feb 2010
Posts: 1,152
Likes: 1
From: La Habra, CA
Year: 1988
Engine: 4.0 RENIX
if anything, add a cam, or do a stroker. roller rockers if you can swing it, but i dont think they're required for mild cams. dont waste you're time with a bored throttle body or throttle body spacers. the spacer wont do anything, and the bored TB only gives the illusion of more power, but really its just adding throttle response.
if you do a cold air intake, put it through the cowl, where there is actually cold air.
the injector upgrade should help a little bit
a less restrictive exhaust will help to a point. not enough restriction and you could loose low end torque. just dont straight pipe it lol.
if you do a cold air intake, put it through the cowl, where there is actually cold air.
the injector upgrade should help a little bit
a less restrictive exhaust will help to a point. not enough restriction and you could loose low end torque. just dont straight pipe it lol.
Seasoned Member
Joined: Feb 2011
Posts: 300
Likes: 0
From: east mesa, AZ
Year: 1993
Model: Cherokee
Engine: rebuilt 4.0
Correct.
Gasoline doesn't burn very well unless it's been vapourised (liquid gasoline doesn't burn, gasoline vapours are borderline explosive!) so you want the droplets to be as fine as possible.
Carburettors required some room to allow the relatively coarse droplets of fuel to finish evapourating before they were compressed. However, as fuel delivery happened closer to the cylinder, a finer division of the liquid fuel was necessary.
This was assisted greatly by the fact that most port fuel injection setups run a head pressure of 30-50psig - while a carburettor relied on differential pressure below atmospheric. A higher pressure forced through an orifice can result in finer division of the liquid - and being able to use a smaller orifice to get similar fuel delivery will also allow finer division of the liquic.
The "four-hole" injectors that Ford used were taking this a bit farther - instead of a single port to spray fuel, they used four ports that were roughly the same flow area (altogether) as a single port would have been. Smaller ports = smaller droplets = faster evapouration.
(I believe it is this property of gasoline that is proving a handicap in coming up with a working DFI setup. This would be far easier using propane or CNG - but either of those fuels has about half of the energy content per unit mass than gasoline, and the infrastructure for distribution isn't there yet.)
Gasoline doesn't burn very well unless it's been vapourised (liquid gasoline doesn't burn, gasoline vapours are borderline explosive!) so you want the droplets to be as fine as possible.
Carburettors required some room to allow the relatively coarse droplets of fuel to finish evapourating before they were compressed. However, as fuel delivery happened closer to the cylinder, a finer division of the liquid fuel was necessary.
This was assisted greatly by the fact that most port fuel injection setups run a head pressure of 30-50psig - while a carburettor relied on differential pressure below atmospheric. A higher pressure forced through an orifice can result in finer division of the liquid - and being able to use a smaller orifice to get similar fuel delivery will also allow finer division of the liquic.
The "four-hole" injectors that Ford used were taking this a bit farther - instead of a single port to spray fuel, they used four ports that were roughly the same flow area (altogether) as a single port would have been. Smaller ports = smaller droplets = faster evapouration.
(I believe it is this property of gasoline that is proving a handicap in coming up with a working DFI setup. This would be far easier using propane or CNG - but either of those fuels has about half of the energy content per unit mass than gasoline, and the infrastructure for distribution isn't there yet.)
CF Veteran
Joined: Jul 2012
Posts: 3,132
Likes: 356
From: Andover, VT
Year: 1999
Model: Cherokee (XJ)
Engine: 4.0 L
To reiterate what has already been said, the 4.0 motor is too old school to slap all these bolt on mods to and expect crazy gains. All you can do is open up the flow. You got the right idea with the cowl CIA and injectors, with that the next best thing would be headers, high flow cat, and muffler. If you can afford it the bored tb will add some snappiness to it. For ignition/electrical there isn't much you can do. Some chips/tuners claim to get +100hp and 100mpg but its mostly just for marketing. Unless you really want to dig ***** deep into the motor and do a 4.6 stroker with all the goodies then there really isn't much room left to build on with the stock setup.
CF ADMIN
Joined: Sep 2010
Posts: 34,088
Likes: 257
From: Lantana, Fl
Year: 1996
Model: Cherokee (XJ)
Engine: 4.Slow
Got a 4.9L in mine. As for ignition, the stock Renix ignition is a Chevrolet design. Im working on a swap so i can use the Chevy 4.3 HEI distributer just like they do with 4.2/258s. The 4.0 Renix is just a destroked 4.2L w/fuel injection and higher flowing head.
But your right on not expecting crazy HP. These motors (232/242/258) were designed for TQ and reliability.
But your right on not expecting crazy HP. These motors (232/242/258) were designed for TQ and reliability.
Last edited by Outlaw Star; Oct 25, 2012 at 09:18 AM.
CF Veteran
Joined: May 2008
Posts: 3,018
Likes: 23
Year: 1988
Model: Cherokee
Engine: AMC242
Got a 4.9L in mine. As for ignition, the stock Renix ignition is a Chevrolet design. If you swap the distributer drive gear over and wire a little, you can use the Chevy 4.3 HEI distributer just like they do with 4.2/258s. The 4.0 Renix is just a destroked 4.2L w/fuel injection and higher flowing head.
But your right on not expecting crazy HP. These motors (232/242/258) were designed for TQ and reliability.
But your right on not expecting crazy HP. These motors (232/242/258) were designed for TQ and reliability.
Besides, torque should be considered more important in a working vehicle than horsepower - because torque lives at low RPM, while horsepower peaks high.
(I blame marketing - they market truck engines by horsepower, and how often do you push the crankshaft speed of a working truck engine up past 5252rpm? I bump the redline on my 88 twice a year, just to make sure nothing's wrong. Normally, it lives at 3500rpm or less (cruise rpm 2600-2800rpm. Don't listen to the "Shift" lamp, it's not helpful in gaining fuel economy...)
Oh -and how much work do you have to do to fit the V6-262 dizzy? I've seen that mod mentioned before, but I haven't gotten any details yet. If it's mechanically doable for RENIX, I may want to play with it later...
CF Veteran
Joined: May 2008
Posts: 3,018
Likes: 23
Year: 1988
Model: Cherokee
Engine: AMC242
CF ADMIN
Joined: Sep 2010
Posts: 34,088
Likes: 257
From: Lantana, Fl
Year: 1996
Model: Cherokee (XJ)
Engine: 4.Slow
Originally Posted by 5-90
Destroked and overbored, but with a great deal of parts commonality.
Besides, torque should be considered more important in a working vehicle than horsepower - because torque lives at low RPM, while horsepower peaks high.
(I blame marketing - they market truck engines by horsepower, and how often do you push the crankshaft speed of a working truck engine up past 5252rpm? I bump the redline on my 88 twice a year, just to make sure nothing's wrong. Normally, it lives at 3500rpm or less (cruise rpm 2600-2800rpm. Don't listen to the "Shift" lamp, it's not helpful in gaining fuel economy...)
Oh -and how much work do you have to do to fit the V6-262 dizzy? I've seen that mod mentioned before, but I haven't gotten any details yet. If it's mechanically doable for RENIX, I may want to play with it later...
Seasoned Member
Joined: Feb 2011
Posts: 300
Likes: 0
From: east mesa, AZ
Year: 1993
Model: Cherokee
Engine: rebuilt 4.0
CF Veteran
Joined: May 2008
Posts: 3,018
Likes: 23
Year: 1988
Model: Cherokee
Engine: AMC242
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