Rebuilding 4.2
#1
07-21-2010, 09:05 PM
Rebuilding 4.2
I am rebuilding a 4.2 to replace my current engine soon. For fun and a little extra kick I am having my machine shop do a "performance head job" and plan to port to gasket dimensions. The new engine is a 2004 and my current is 2001. How will this work with computer, EFI, etc. Will there be appreciable help by adding headers. Any other general guidance? Our company has run many of these trucks over the past 15 years and have yet to get less than 250k on any before sale. Some well over 300k.
#2
07-23-2010, 01:19 AM
Just port matching won't give you any real noticable power increase because the rest of the induction system has not been improved.
Also, this type of change is RPM dependent in that changes made that only improve air flow "where restriction" had become a significent factor in impedeing airflow. Usually at high rpm.
At normal driving speed, the airflow is not increased enough to make a difference because the throttle body at less tha wide open position is the limiting factor in allowing airflow.
What does make a difference at all speeds is compression ratio.
Problem with this is the fuel you have available everyday won't handle higher compression unless you run premium gas at all times.
Bottom line is you want to build the motor to some set of user specs such as racing, improved fuel mileage or a general increase in torque.
The best way to get an increase in power is a package of mods that compliment each other and that can be lived with on the street.
This is why a blower application is usually the bettter way for moden engines on the road.
Even then, the PCM programming usually always needs custom changes if for no other reason than ignition advance and fuel map changes to handle the mods becomes a must for best results.
So, you get into issues, due to the changes needed, and to pull togather all areas that are changed, requires an understanding of what is a compliment.
Exhaust is also dependent on the use you put the motor to.
For low to mid range pulling, a tuned header and system is in order if one can be found for truck use.
Bottom line is to build to improve the usage you intend.
Putting high RPM mods in place for average street use won't be very nice or usefull to live with on the street unless you are dragging from light to light.
On a V6, I would go for a bit more compression, use premium gas and have a tuner with custom program done to compliment the build, improve the transmission shifting and lower the rear gear ratio.
These changes should have a very nice feel for V6 without a super charger.
Good luck.
Also, this type of change is RPM dependent in that changes made that only improve air flow "where restriction" had become a significent factor in impedeing airflow. Usually at high rpm.
At normal driving speed, the airflow is not increased enough to make a difference because the throttle body at less tha wide open position is the limiting factor in allowing airflow.
What does make a difference at all speeds is compression ratio.
Problem with this is the fuel you have available everyday won't handle higher compression unless you run premium gas at all times.
Bottom line is you want to build the motor to some set of user specs such as racing, improved fuel mileage or a general increase in torque.
The best way to get an increase in power is a package of mods that compliment each other and that can be lived with on the street.
This is why a blower application is usually the bettter way for moden engines on the road.
Even then, the PCM programming usually always needs custom changes if for no other reason than ignition advance and fuel map changes to handle the mods becomes a must for best results.
So, you get into issues, due to the changes needed, and to pull togather all areas that are changed, requires an understanding of what is a compliment.
Exhaust is also dependent on the use you put the motor to.
For low to mid range pulling, a tuned header and system is in order if one can be found for truck use.
Bottom line is to build to improve the usage you intend.
Putting high RPM mods in place for average street use won't be very nice or usefull to live with on the street unless you are dragging from light to light.
On a V6, I would go for a bit more compression, use premium gas and have a tuner with custom program done to compliment the build, improve the transmission shifting and lower the rear gear ratio.
These changes should have a very nice feel for V6 without a super charger.
Good luck.
#3
07-23-2010, 08:34 AM
4.2 Options
I really appreciate your thorough reply and have a few follow on questions.
1. Are there any aftermarket package or complimentary options available for these engines. Right now lower end torque is more important, but as time goes on I may want to explore options of higher rpm responses.
2. You mention a "custom tuner" for the computer. How would I go about finding this service?
3. You mentioned the restriction of the throttle body on air flow which makes great sense. Are there aftermarket throttle bodies available or as a part of a package or should these be modified in the same manner as porting the heads.
4. Do you have any recomendations on tuned header brands or sources?
5. Are there any websites that specialize in modification of this engine. I am telling on my age, but the last time I did any extensive engine modifications were in the day of carbs. I now have time to explore this as a hobby again and am looking forward to the fun.
1. Are there any aftermarket package or complimentary options available for these engines. Right now lower end torque is more important, but as time goes on I may want to explore options of higher rpm responses.
2. You mention a "custom tuner" for the computer. How would I go about finding this service?
3. You mentioned the restriction of the throttle body on air flow which makes great sense. Are there aftermarket throttle bodies available or as a part of a package or should these be modified in the same manner as porting the heads.
4. Do you have any recomendations on tuned header brands or sources?
5. Are there any websites that specialize in modification of this engine. I am telling on my age, but the last time I did any extensive engine modifications were in the day of carbs. I now have time to explore this as a hobby again and am looking forward to the fun.
#4
07-23-2010, 02:28 PM
Welcome to the board.
Don't worry about your age. I am likely to be even older than you at this point.
The world of computer control makes things quite precise with all that is controlled and 'looked' at by the maintaince programs.
1/2/3/4. There are vendors that offer equipment and services for this engine.
I would reccomend you start by calling a company "Troyer Performance".
They can work with you for a full package, from programming, to hardware and tunning services.
Last time I saw these engines run on a race track, they were even nastier sounding than the V8s, in NASCAR.
Good luck.
Don't worry about your age. I am likely to be even older than you at this point.
The world of computer control makes things quite precise with all that is controlled and 'looked' at by the maintaince programs.
1/2/3/4. There are vendors that offer equipment and services for this engine.
I would reccomend you start by calling a company "Troyer Performance".
They can work with you for a full package, from programming, to hardware and tunning services.
Last time I saw these engines run on a race track, they were even nastier sounding than the V8s, in NASCAR.
Good luck.
