[superj]

in the past, on other vehicles, i have done larger throttle body swaps and sometimes it makes a noticeable difference that is positive, and sometimes its not positive.

since you guys don't have any complaints about a touchy gas pedal, you have not gone to large. i did it on a jeep 4.0 once and it made it a pain to drive so i swapped back to normal. that larger diameter helps at the upper end though, as you have both noticed.

throttle bodies are not like carburetors where the velocity of the air flow past the bowl ports and jets effect the amount of fuel you are getting and directly affect drivability. throttle bodies just let you control the air the engine is trying to pull into the cylinders so there is a lot less trouble when swapping to a slightly larger diameter tb.

back in carb days, venturis were used to maximize air flow around hte ports and jets to you could drive at a lower rpm and still have proper fueling. direct injection fueling doesn't require this anymore and you can get better throttle response and gas mileage.

its always good to see people trying stuff like this though. without people willing to test changes, we would all be driving the same vehicles and wishing we had something more.

 

[superj]

• MAF (lb/min): .01-15.00

.01 to 15 pounds of air flowing per minute, with .01 being when the tb is closed and 15 when fully open.

• Intake manifold absolute pressure (psi): 2.2-15.1

map is the pressure in the manifold compared to the pressure on the outside of the manifold, or atmospheric pressure.

• Actual air-to-fuel ratio: 0.727-1.992

this is the reading of fuel versus air in the exhaust and is used to adjust the fuel flow at the injectors. stoichiometric is perfect fuel mixture for burn and is adjusted for richer or cooler to keep power and temps within a specified range.

"The theoretical air–fuel ratio mixture for a gasoline fueled engine, for complete gasoline fuel combustion, the stoichiometric air–fuel ratio is about 14.7:1."


HomeEngine Maintenance and OperationAircraft Reciprocating Engine Basic Operating Principles

Combustion Process
Normal combustion occurs when the fuel/air mixture ignites in the cylinder and burns progressively at a fairly uniform rate across the combustion chamber. When ignition is properly timed, maximum pressure is built up just after the piston has passed top dead center at the end of the compression stroke.

The flame fronts start at each spark plug and burn in more or less wavelike forms. [Figure 1]

Figure 1. Normal combustion within a cylinder

The velocity of the flame travel is influenced by the type of fuel, the ratio of the fuel/air mixture, and the pressure and temperature of the fuel mixture. With normal combustion, the flame travel is about 100 feet/second. The temperature and pressure within the cylinder rises at a normal rate as the fuel/air mixture burns.

 

[superj]

yes sir. i cannot remember lots of stuff but some engine stuff i remember well enough from aviation maintenance school to know where to find it online to share with others.

i used to work on small private planes and helicopters, which run basically the same engines as in cars, just mounted differently.

 

[superj]

if you are ever bored, find a half price books and see if any aviation maintenance manuals are for sale. the engine theory book is very very good for any person who likes to do stuff on their car. a reciprocating engine is the same, air, water, or land based vehicle and the a&p books go into depth on stuff. you can also grab the others if you want to learn about metal working and carbon fiber/fiberglass works as its all done by a&p mechanics out in the field.