I have a 1994 Honda Civic DX hatchback and I threw a 66mm throttle body and cold air intake on. Do you believe that it might be too much air or that I'm just tripping? Somebody recommended it to me but curious of what you might think. I haven't tampered with the fuel or would even know of how to properly go about it being new to the diy world.

 

The common misconception is that a larger throttle body provides more air flow than a smaller, factory sized throttle body and thus, increases performance or HP. In a naturally aspirated application, this is, in almost all cases, untrue. If, at higher engine RPM, your engine pulls greater vacuum than say about 2 or 2.5"... then a SLIGHTLY larger throttle body will produce more HP at peak engine speeds. The negative here is that the larger throttle body will reduce air speed at lower and mid range engine RPM, thus reducing efficiency and performance losses are encountered.
Now, because your engine cannot use the amount of air that is admitted into the intake manifold when the throttle body is simply cracked open, let alone opened all the way (full throttle), engine vacuum is lost and more fuel is introduced to the mixture than is needed, and thus, performance is reduced.

In short... remove the 66mm throttle body and re-install the OE one. The cold air intake probably isn't hurting performance unless it is a very large diameter pipe (greater than 3")... and it may pick up a pony or two at best... so you can use it.

Lastly, don't listen to the "somebody" that recommended the large throttle body anymore for future mods on your car... they don't know anything about engines.

 

The other thing that I think people miss is to figure their throttle body size increase in area rather than diameter... going from a 56mm to a 66mm is actually about a 40% increase in area, that's a HUGE change in air volume. Smaller throttle bodies are better for drivability too.

In general, every 10% more diameter gets you a little more than 20% more area.

Here's a good Webinar. If you go through the calculations they present on some familiar OEM engine combos compare a B18C1 to a B18C5, for example), you'll find that the OEM's typically do a pretty good job.

https://www.hpacademy.com/previous-w...throttle-body/

 

Does your car run worse (rough / less MPG / etc.) than before? If not, then enjoy your perceived 10 horsepower gain!