Toyota MR2 Message Board - View Single Post - 4A-GE MK1 Engine new to mr N/A, i swear, this car is faster than it should be..

LokiRx7 · 05-01-2008, 02:52 PM

This debate is much like the intake porting depate, mostly because what is true with the intake is largely true with the exhaust.

Too small of a port, or exhaust port (same applies to exhaut pipe and intake pipe) Will cause excessive backpressure. No engine 'requires' backpressure. Anyone who tells you that you need backpressure knows nothing about what they are talking about.

What an engine needs is exhaust velocity, and with too large of an exhaust you will lose exhaust velocity. Some engines have very little exhaust velocity to help high rpm power at the expense of low end torque. We drive street cars and need to find a healthy medium.

The same rings true with porting, there is a such thing as too much porting or too big of an exhaust. I have read on some japanese 4A-GE specific tuning sites that the optimum exhaust diameter for this engine is between 2 inch and 2.5 inches. That was for an AE86/AE92. Depending on the length of your exhaust and the amount and severity of the bends is what should determine the diameter.

Alot of bends will make for a longer exhaust, it will probably be good to err on the larger side of 2.5 inches. Fewer bends will make for a shorter exhaust, I would shoot for around 2 inches. Also, I personally wouldnt use a glasspack on our cars. I would look for a nice chambered muffler, I have a Flowmaster, and I would have to reccomend it.

05-01-2008, 02:52 PM	#47 (permalink)
LokiRx7 MR2 + Flat Black = FAIL Join Date: Jan 2007 Location: N.C. Ohio Posts: 320 Thanks: 0 Thanked 15 Times in 14 Posts iTrader Rating: (1/100% )	This debate is much like the intake porting depate, mostly because what is true with the intake is largely true with the exhaust. Too small of a port, or exhaust port (same applies to exhaut pipe and intake pipe) Will cause excessive backpressure. No engine 'requires' backpressure. Anyone who tells you that you need backpressure knows nothing about what they are talking about. What an engine needs is exhaust velocity, and with too large of an exhaust you will lose exhaust velocity. Some engines have very little exhaust velocity to help high rpm power at the expense of low end torque. We drive street cars and need to find a healthy medium. The same rings true with porting, there is a such thing as too much porting or too big of an exhaust. I have read on some japanese 4A-GE specific tuning sites that the optimum exhaust diameter for this engine is between 2 inch and 2.5 inches. That was for an AE86/AE92. Depending on the length of your exhaust and the amount and severity of the bends is what should determine the diameter. Alot of bends will make for a longer exhaust, it will probably be good to err on the larger side of 2.5 inches. Fewer bends will make for a shorter exhaust, I would shoot for around 2 inches. Also, I personally wouldnt use a glasspack on our cars. I would look for a nice chambered muffler, I have a Flowmaster, and I would have to reccomend it.