Most of the wear of these engine occurs during warmup. This is due to unburned fuel washing the oil away from the cylinders until the intake warms up allowing the air/fuel to stay in suspension. The flapper in the cold engine position puts lots of exhaust heat to the underside of the intake, warming it up in a very short time.
Without that feature, you will experience more cylinder wear than normal, and crankcase contamination which will cause undue wear to bearings.
If you don't have the original intake/exhaust setup with a functioning flapper valve, you would be well advised to check for gasoline smell on your dipstick frequently and change the oil more frequently that every 3,000 miles.
