why does my 5th generation require premium fuel?

 

10:1 compression ratio.

if you need further explanation, check out www.howstuffworks.com and find out how engine static compression ratios, ignition timing, internal combustion, and fuel octane ratings affect you, your motor, and your car's performance.

 

taht is a low compressino ratio

 

you must be shittin me on that rite? 10:1 is low?

 

for an import sports car 10:1 isn't very high

 

um, ok. the highest stock compression GAS driven street cars are 11:1.

 

It's not all about compression. The 86 Integra and old SR20s had 9.5 compression and ran on regular. Probably had more to do with output per liter.

Wait, scratch that, the 91 GTI 16V had a 10.8 compression with only 134 hp.

isn't the SVT Focus also high?

 

the F22/F23 motors were also 9.5 and required only regular.

it's due to dynamic compression. actual ignition timing plays an important role on the dynamic compression. the static compression is the compression with the piston at TDC. combustion happens after the piston begins to move away from TDC, not right at that moment... so if the piston is beyond TDC, actual compression is lower than the static rating. the further you retard timing, the lower the compression.

the H22 on the other hand has it's timing advanced more than the other motors mentioned.


so in all truthfulness, it IS all about compression... just not static compression.

 

Is this why Hondas ( or is it just the VTECs) retard the ignition timing in hot weather thus losing power? It seems worse in my Prelude that any previous car I've had. Any way around this?

 

all high compression cars, especially OBDII vehicles do this to prevent detonation during high temperature environments.

this is performed by the Intake Air Temperature (IAT) sensor. when the air intake temps are higher, the air is less dense and therefore more prone to detonating the fuel charge. the IAT allows the ECM to properly redistribute fuel and/or alter the timing maps to prevent detonation/knocking and also in conjunction with the O2 sensor and coolant temp sensors, keep the motor operating cleanly, even at a loss of output.


technically speaking, you can cut the IAT sensor lead and install a resistor of the right resistance so the ECM receives a signal simulating a 70 degree intake air temperature, thus preventing the ECM from retarding the timing on a hot day.... but it may result in knocking/pinging/detonation on a hot day. you can measure the range of the sensor with a backprobing ohm meter to help you find the resistor to meet your demands.

also, 96-97 Preludes have known knock sensor and other emissions control issues and had their warranties extended to 14 years/150,000 miles. you may want to have the dealer check it out if you run into problems accomplishing an emissions inspection.