350 SBC Nova Motor

You say the motor is built for high revs So,
Basically there are two things that could limit its speed, Timing and carb.
For your engine timing will need to be prety far advanced, something like 12 to 18 degrees before advance is added. (not sure how much myself)
If you have a timing problem, The motor will sound fine but simply not have the power it should.
If it's carb, you should be hearing some noise from the intake if it's lean, and from the exhaust if it's rich.
any crackling sound in the intake of a GOOD motor (no bend valves) will tell you that there is not enough gas for the air going into the motor.
a crackling or stettering sound in the exhaust should mean too much fuel.
anyone behind the car should see black smoke too.
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If this does not answer problem, add more details to question.
Good luck.

Good Valves, 185# Compression in all 8 Cly, i turned my NOS bottle off and Pushed the Button at WOT to put more Fuel in the Motor, No Change. I shut the Motor Down at WOT, pulled the Plugs, Nice Tan Color, not to Lean or Rich.

How about the timing?
Other than that I would not be able to help much, I am not real experienced with high output motors.
Sorry.
Good luck.

Set at 12-14 Degrees Base Timing. This Motor Ran Fine last time I took it out last Year

Roll the base timing back to about 6 or 8 degrees, and see what change you get.

Did you advance the cam during installation?

Cam is not Advanced, Installed Stright up. timing Set at 7-8 Degrees, no Change

350 runs faster than any other car in the world

Janiter,
WHAT?
You it's the fastest motor ever?, Not even close, or even in the same book.
You mean fastest per cubic inch? Not even close, or in the same book.
The SBC is a VERY good motor, It's a great platform. But, as for power because there is no such thing as a 'fast' motor.
There are plenty of motors that have more power per inch and there are plenty of motors that make WAY more power than you could ever hope to get from a 350.

You may have bad gas I would try a treatment . Then if that doesn't work try a diferent spark plug. I've had same problem mine ended up being spark plug I as useing a dual head plug we all know splitfire then found out they will fry a hole threw your piston head .

The first thig I check when any engine isn't reving like it should is to have someone push the throttle to wide open (with the engine off of course) while I look in the carb to be sure it is actually opening the butterflies all thye way. You may have been on the right track when you suspected the valve springs. I have seen a lot of good motors go weak due to the valve springs. A common practice in Hi-Po SB Chevys is to install oil restrictors to limit the oil delivered to the top of the heads. This is all right to keep the rest of the motor from starving for oil at high RPMs. BUT the only thing that cools the valve springs is that oil running over top of them and carrying the heat away. Besides the heat from the engine (heat rises and the springs are on the top) valve High Performance valve spring generate a lot of heat themselves. if they get to hot they won't last long. Short bursts down the drag strip are one thing but driving around town can ruin them fast. A wise investment is a valve spring tester that can be used without taking the motor apart. You just have to remove the rocker arm, make sure the piston is down in the cylinder so you dont bend a valve and use the tool as the instruction say.