Originally Posted by
Spec R
It seems that I've offended you somehow. I wont even bother my explanation, in an effort to keep you from getting upset. I dont have a doubt in my mind that you know more about your J30A1 than I do, so please enlighten me, and anyone else reading this thread.
thanks
Right.
It's due to three main factors: conservative VTEC system, conservative ignition timing, and conservative air/fuel management. The J30A1 uses an economy VTEC mode below 3500RPM which is designed to save fuel. It opens only one intake valve on the low cam. Also, the ignition timing is extremely conservative for this type of engine. Because the J30A1 has no MAF sensor (unlike the J30A4, which fixes all of the J30A1's downsides), it's unable to properly adjust the air/fuel ratio to provide for optimal power. Finally, the J30A1 has a pretty low compression ratio and runs pig rich most of the time. I don't feel like explaining any further
But it has very little to do with it just being a Honda engine. Had they gone more agressive on the low cam, advanced ignition timing or raised the CR, the engine would have much better low end torque output but would likely use more fuel at highway cruising speeds. I routinely get low 30's highway. Yes, the GM 3800 also sees those numbers, but it also has much higher gears. The J30A1 used a stupidly high 4.2 final drive ratio and a 0.61 4th gear. The 3800 uses a 3.05 final drive anda a 0.70 4th gear.