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Did some studying, read up a bunch on Holleys, and the book is chock full of general mileage / performance stuff!
The book: "Holley Carburetors and Manifolds", by Mike Urich and Bill fisher.
Where to start...
Well, the book highlights Holley carbs and Manifolds and then goes on to address the history of emission tuning (detuning) that the OEMs did in the 1970s and then the rise of engines that actually made power, mileage and emitted fewer pollutants. Generally:
Ignition timing...at the beginning of the "smog era" advance curves were tuned to make better efficiency and power...and were generally more advanced than they were a few years later when OEMs started retarding advance curves to reduce efficiency to reduce exhaust temps, which reduced HC and NOx.
Compression Ratio...Higher CR ensures better efficiency, and power, but also makes more pollutants and requires higher octane fuel. Higher compression ratio requires less ignition advance.
The OEMs dropped CR in the early 1970s to reduce pollutants.
Leaded Fuels...Leaded Fuel requires MORE advance to ignite.
The OEMs were required to build engines that would run on UNLEADED fuel in order to remove lead from the polutants and...to accomodate the new Catalytic Convertors to be fitted on all vehicles beginning in 1975. (Except for trucks...they all got Cats in 1979)
Catalytic convertors - introduced in '75...designed to convert CO into CO2, HC into H2O and CO2, and NOx into Nitrogen. Cats require high exhaust temps to light off the catylization. They do not work with leaded fuels.
EGR...EGR recirculates exhaust gas back into the intake manifold to dilute fresh air/fuel charge so to DE-EFFICIENTIZE the burning of the mixture in the chamber. This cools the combustion temp. Cooler combustion temp means cooler exhaust temp, which meant less NOx production.
CAMSHAFT EGR can also be implemented with large overlap cam shaft profile in a street driven car. It acts just like a lopey race cam -crappy idle, because exhaust gases are flowing back into the cylinder as it is filling with air/fuel charge. It runs like crap until the right RPM is reached and then it makes power...
THE ABOVE REASON is EXACTLY WHY 401s SUCKED! The camshaft profile in the 401s was WAY different than the 360 cam profile. Look it up in a 1975-1978 Jeep TSMs...they are a single pattern cam, but with 61* of overlap!!! Great for racing at high RPM...but the 401 in the trucks never revved high enough to reach that point. Maybe the Cam would work better in a built up race 401...but Desktop Dyno didn't really indicate this. I only tried it in a mildly built street 401...but it was only good for 370 hp and 370 torque. Edelbrock Performer cam in same motor was good for about 350 hp and 450 torque and had much better low - mid RPM drivability.
LOWER Gear Ratio...in the axles of course...this is obvious, the lower RPM the engine has to turn to make the vehicle attain the national 55mph speed limit in the 1970s and 1980s, the less total exhaust is emitted from the tail-pipe.
So what can we learn from all this?
Well, due to unleaded gasoline requirements for Catalytic convertors, the ignition in later engines can be decreased. But the larger chambers and lower CR means you need to increase the ignition advance. So you effectively cancel any change from normal.
Further...Due to Catalytic convertors the CR could be raised, and this would allow more efficiency and power. Unfortunately AMC never got in on this...8.3:1 ratio in 360 engines to the very end. So the 360 was rated at less power output than the 258 I-6 motor. The 258 went on to be the 4.0 liter which made more power and got better mileage...and I believe had a higher CR in later years.
Recommendations:
If legal...
EGR intake - the EGR is not any kind of performance equipment, it is simply there to dilute air/fuel charge. It will make the engine less efficient and produce less power. Edelbrock makes a good dual-plane...Holley makes the Holley 300-31Z, a single plane, low rise intake with balance tube. This is supposedly a really well engineered intake, increase low RPM drivability over a normal single plane, but increases power production in the high rpm range , where a normal dual-plane is weaker. it does have provision for EGR. block it off.
Exhaust- rip off the stupid air-injection crap and port the manifolds...I'm talking 1975-1979 manifolds because 1980 and newer exhaust manifolds are junk due to the driver-side log-style - just get long-tube headers for this.
The ported 1975-1979 Jeep mainfolds are good flowing, they outflow Shortie headers in many cases. But long tube headers are better. Run Dual pipes and free flowing mufflers.
Catalytic convertor...lose it. The stock cats were nothing good for performance very restrictive to flow. If you want to run an aftermarket Cat, I'd suggest a really free flowing set of smaller cats, mounted really close to the header collectors. The problem with this is you need to heat-shield the hell out of these to avoid grass-fires off-road, and the Cats require really finicky tuning...really hard to do with a carb and standard ignition.
CamShaft (401)...pull that stupid drag-race style bump-stick outta there and dump it in the recycler bin. Use a 360 camshaft or an aftermarket cam set up for good Truck performance. Don't go too big...the Jeep is not a race car weighing 2,000 pounds. FEW guys can and do run race motors in a 4600 pound Jeep. Install a good cam with very little overlap (if any) for good low RPM torque...the headers will raise this somewhat allowing good mid-range and high range power.
Compression Ratio...RAISE IT! you can mill your heads and deck the block to get pretty close to 9.5:1 and higher. Using most performance 360-401 pistons you can select less dish, but Domed pistons actually have a few problems, Domed pistons are not as good for side-thrust issues and a few other things I've forgotten. I've only dealt with this on a limited level. Also, aluminum heads can take about another point of CR than Iron heads using 91-92 octane.
Carb...lose the Motorcraft 4350. When you buy a manifold (do not use a 4-barrel carb on a 2-barrel intake...or a square-bore-to-spread-bore adapter, it screws your flow) get a decent emmission/street performance 4-barrel carb. Holley 4180s and some 4160/4150s in the 500-600 cfm range are a good choice. (If you like Holleys). I prefer Edelbrock/Carter carbs for obvious reasons, (Same cfm) though they tend to be slightly less tunable. You might think a 2-barrel carb is better for mileage. No, it simply limits power output in the higher RPM range. You can get a Holley 2300 500CFM 2-barrel, but its not gonna be set up for good lower rpm drivability. The cool part of a street 4-barrel - the primary side can have smaller primary venturis/bores to work well in low-mid RPM, then when you need to pass the dork in front of you doing 15 under the posted, you mash the loud pedal and you have a whole other 2-barrel carb to furnish you with more fuel/air volume at higher RPM! Best of both worlds.
Ignition Timing...depending on what you end up doing, you may need more or less ignition timing than the stock distributor came with. The cool thing is -they are somewhat interchangeable and tunable. You have alot of curves and distributors to choose from starting in 1970 with the 360 (or earlier if you count the 290,343,390) up to1991 with the last 360.
Any questions?
The book: "Holley Carburetors and Manifolds", by Mike Urich and Bill fisher.
Where to start...
Well, the book highlights Holley carbs and Manifolds and then goes on to address the history of emission tuning (detuning) that the OEMs did in the 1970s and then the rise of engines that actually made power, mileage and emitted fewer pollutants. Generally:
Ignition timing...at the beginning of the "smog era" advance curves were tuned to make better efficiency and power...and were generally more advanced than they were a few years later when OEMs started retarding advance curves to reduce efficiency to reduce exhaust temps, which reduced HC and NOx.
Compression Ratio...Higher CR ensures better efficiency, and power, but also makes more pollutants and requires higher octane fuel. Higher compression ratio requires less ignition advance.
The OEMs dropped CR in the early 1970s to reduce pollutants.
Leaded Fuels...Leaded Fuel requires MORE advance to ignite.
The OEMs were required to build engines that would run on UNLEADED fuel in order to remove lead from the polutants and...to accomodate the new Catalytic Convertors to be fitted on all vehicles beginning in 1975. (Except for trucks...they all got Cats in 1979)
Catalytic convertors - introduced in '75...designed to convert CO into CO2, HC into H2O and CO2, and NOx into Nitrogen. Cats require high exhaust temps to light off the catylization. They do not work with leaded fuels.
EGR...EGR recirculates exhaust gas back into the intake manifold to dilute fresh air/fuel charge so to DE-EFFICIENTIZE the burning of the mixture in the chamber. This cools the combustion temp. Cooler combustion temp means cooler exhaust temp, which meant less NOx production.
CAMSHAFT EGR can also be implemented with large overlap cam shaft profile in a street driven car. It acts just like a lopey race cam -crappy idle, because exhaust gases are flowing back into the cylinder as it is filling with air/fuel charge. It runs like crap until the right RPM is reached and then it makes power...
THE ABOVE REASON is EXACTLY WHY 401s SUCKED! The camshaft profile in the 401s was WAY different than the 360 cam profile. Look it up in a 1975-1978 Jeep TSMs...they are a single pattern cam, but with 61* of overlap!!! Great for racing at high RPM...but the 401 in the trucks never revved high enough to reach that point. Maybe the Cam would work better in a built up race 401...but Desktop Dyno didn't really indicate this. I only tried it in a mildly built street 401...but it was only good for 370 hp and 370 torque. Edelbrock Performer cam in same motor was good for about 350 hp and 450 torque and had much better low - mid RPM drivability.
LOWER Gear Ratio...in the axles of course...this is obvious, the lower RPM the engine has to turn to make the vehicle attain the national 55mph speed limit in the 1970s and 1980s, the less total exhaust is emitted from the tail-pipe.
So what can we learn from all this?
Well, due to unleaded gasoline requirements for Catalytic convertors, the ignition in later engines can be decreased. But the larger chambers and lower CR means you need to increase the ignition advance. So you effectively cancel any change from normal.
Further...Due to Catalytic convertors the CR could be raised, and this would allow more efficiency and power. Unfortunately AMC never got in on this...8.3:1 ratio in 360 engines to the very end. So the 360 was rated at less power output than the 258 I-6 motor. The 258 went on to be the 4.0 liter which made more power and got better mileage...and I believe had a higher CR in later years.
Recommendations:
If legal...
EGR intake - the EGR is not any kind of performance equipment, it is simply there to dilute air/fuel charge. It will make the engine less efficient and produce less power. Edelbrock makes a good dual-plane...Holley makes the Holley 300-31Z, a single plane, low rise intake with balance tube. This is supposedly a really well engineered intake, increase low RPM drivability over a normal single plane, but increases power production in the high rpm range , where a normal dual-plane is weaker. it does have provision for EGR. block it off.
Exhaust- rip off the stupid air-injection crap and port the manifolds...I'm talking 1975-1979 manifolds because 1980 and newer exhaust manifolds are junk due to the driver-side log-style - just get long-tube headers for this.
The ported 1975-1979 Jeep mainfolds are good flowing, they outflow Shortie headers in many cases. But long tube headers are better. Run Dual pipes and free flowing mufflers.
Catalytic convertor...lose it. The stock cats were nothing good for performance very restrictive to flow. If you want to run an aftermarket Cat, I'd suggest a really free flowing set of smaller cats, mounted really close to the header collectors. The problem with this is you need to heat-shield the hell out of these to avoid grass-fires off-road, and the Cats require really finicky tuning...really hard to do with a carb and standard ignition.
CamShaft (401)...pull that stupid drag-race style bump-stick outta there and dump it in the recycler bin. Use a 360 camshaft or an aftermarket cam set up for good Truck performance. Don't go too big...the Jeep is not a race car weighing 2,000 pounds. FEW guys can and do run race motors in a 4600 pound Jeep. Install a good cam with very little overlap (if any) for good low RPM torque...the headers will raise this somewhat allowing good mid-range and high range power.
Compression Ratio...RAISE IT! you can mill your heads and deck the block to get pretty close to 9.5:1 and higher. Using most performance 360-401 pistons you can select less dish, but Domed pistons actually have a few problems, Domed pistons are not as good for side-thrust issues and a few other things I've forgotten. I've only dealt with this on a limited level. Also, aluminum heads can take about another point of CR than Iron heads using 91-92 octane.
Carb...lose the Motorcraft 4350. When you buy a manifold (do not use a 4-barrel carb on a 2-barrel intake...or a square-bore-to-spread-bore adapter, it screws your flow) get a decent emmission/street performance 4-barrel carb. Holley 4180s and some 4160/4150s in the 500-600 cfm range are a good choice. (If you like Holleys). I prefer Edelbrock/Carter carbs for obvious reasons, (Same cfm) though they tend to be slightly less tunable. You might think a 2-barrel carb is better for mileage. No, it simply limits power output in the higher RPM range. You can get a Holley 2300 500CFM 2-barrel, but its not gonna be set up for good lower rpm drivability. The cool part of a street 4-barrel - the primary side can have smaller primary venturis/bores to work well in low-mid RPM, then when you need to pass the dork in front of you doing 15 under the posted, you mash the loud pedal and you have a whole other 2-barrel carb to furnish you with more fuel/air volume at higher RPM! Best of both worlds.
Ignition Timing...depending on what you end up doing, you may need more or less ignition timing than the stock distributor came with. The cool thing is -they are somewhat interchangeable and tunable. You have alot of curves and distributors to choose from starting in 1970 with the 360 (or earlier if you count the 290,343,390) up to1991 with the last 360.
Any questions?
)
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