high compression head= better gas mileage?
01-05-2008, 03:54 AM
#2
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Higher compression leads to higher engine efficiency. Higher efficiency = more bang for your buck. So yeah, most likely.
My highway mileage went up when I swapped heads. City got WAY worse lol.
My highway mileage went up when I swapped heads. City got WAY worse lol.
01-05-2008, 10:31 AM
#4
Compression is a double edged sword. At highway loads, you could get away with a lot more compression, and greater efficiency. The problem is your fuel octane is a constant, and the octane requirement gets to high at WOT when the Volumetric Efficiency goes up. Turbo cars have used water or metanol injection to allow for "variable octane" if you will, and nitrous guys have used a secondary fuel system supplying race fuel only under engagement.
In other words, when you are pumping more air, the octane needs to be there to control combustion. Add in all the different cam profiles available and there usage, and there is no one compression that works for everything.
Since these are performace cars, the best we can do is maximize the Static Compression as it relates to the cam profile (Dynamic Compression), and let the rest fall where it may.
For some real tech, here is a link to a David Vizard article in PHR with all the details, but these highlights:
Vizard is a Gen I small block chevy genius, but note that #4 applies directly alloy intakes, while #5 refers to the cylinder head architecture. Both items have changed for the better in Gen III engines, as have #11 and #13, and are partial contributors to the 10.1+ ratios used in stock LS engines.
In other words, when you are pumping more air, the octane needs to be there to control combustion. Add in all the different cam profiles available and there usage, and there is no one compression that works for everything.
Since these are performace cars, the best we can do is maximize the Static Compression as it relates to the cam profile (Dynamic Compression), and let the rest fall where it may.
For some real tech, here is a link to a David Vizard article in PHR with all the details, but these highlights:
15 COMPRESSION BOOSTING MOVES
1. Feed cold air to the induction
2. Keep water as cool as possible (170 F or less)
3. Keep the air cool in the intake ports
4. Put a heat-reflective shine on the outside of the intake manifold
5. Minimize heat transfer through the common exhaust/intake port wall
6. Keep fuel temperatures down (cool can)
7. Run with plugs a little colder than the minimum required
8. Use an ignition system that is gross overkill
9. Utilize as large a spark plug gap as possible
10. Use no more ignition advance than is necessary
11. Maximize quench action
12. Minimize head chamber volume
13. Use flat-top pistons if possible
14. Minimize under-hood exhaust heat--use coated headers
15. Do not ram in but vent out hot air through hood vents
1. Feed cold air to the induction
2. Keep water as cool as possible (170 F or less)
3. Keep the air cool in the intake ports
4. Put a heat-reflective shine on the outside of the intake manifold
5. Minimize heat transfer through the common exhaust/intake port wall
6. Keep fuel temperatures down (cool can)
7. Run with plugs a little colder than the minimum required
8. Use an ignition system that is gross overkill
9. Utilize as large a spark plug gap as possible
10. Use no more ignition advance than is necessary
11. Maximize quench action
12. Minimize head chamber volume
13. Use flat-top pistons if possible
14. Minimize under-hood exhaust heat--use coated headers
15. Do not ram in but vent out hot air through hood vents
