[steve25]

The standard performer can make well over 400 hp with superior drivability up to 5500.

Here are Edekbrocks own recommendations for there intakes and as you can see the performer rpm has a power band of 4500 to 6000 rpm.

If your motor is not Camed and you do not have a converter to flash up to 4000 rpm then you have simply put yourself behind the 8 ball.

Don’t advance the cam until you have done an across the board compression test so you have a base line to refer to .

To save yourself a mess jack up the ass end of the car after you have drained the rad and before you pull off the lower hose.
This will get the water level in the block below the water pump holes and keep coolant out of the nose of the pan.

This is easier then removing the 1/8” pipe plugs each lower side of the block when you have headers.

The motor has the same stroke as a 400 and is only a mire 13% less in total CID.
I had a 350 in a 4 door Tempest with a 2 speed trans.and 2.93 gears.

Once I put on a stock 70 intake and carb , stuffed in a used 067 Cam and swapped out the Super Turbin 300 for a TB 350 I was very pleased with what it had for low speed power and mid range power up to 4000 rpm.

Basically your motor is suffering from too little power in too narrow of a rpm band.