I bought a 450 biondo box and will be buying a throttle stop and they told me the electric one that goes under the carb is the best one to use. But I was also told that it steals hp? Is this true? IF so what throttle do you recomend that does not take away hp and works best all around?
If you use the one underneath the carb and not put any time in it will it affect or not?
I appreciate your input thanks!

Yes most will rob some HP...The best ones as far as keeping as much HP as possible would be the disc type dedenbear's or one of the inline linkage types. Otherwise you have a restriction under the carb at all times. Why worry about it personally, if you are throttle stopping the car ultimate ET is not a huge concern anyway.

something to consider, if you use a 1250 dominator the bore size is 2.100. The under carb throttle stops and most 4 hole spacers are only 2.00. That will rob some hp. I have inline c02 linkage style. IMO, K&R Prostage is the best of both worlds as it will work as sle and downtrack stop on the same run with different rpm.

about how much hp will it rob? Anyone else with exprience in this?

Its going to depend on the combo as to how much your going to lose.

As Al said, if your running a 'stop you've got more than enough power to run the number, whatever it may be. 1 mph at the finish line isn't going to make that big of a difference.

A throttle stop is no different that you letting up on the throttle going down the track and then putting it back on the floor. How much HP do you loose doing that?

A plate under the carb resticts the amount of air going thru the air pump also know as the motor. Ask the NASCAR boys how much HP it takes away.

There are different arguments as to which system is best.

Different strokes for different folks.

MegaDart, is that a chevy big block I see there?

Who knows how much HP it will drop. Not sure if anyone has ever done dyno testing but I am sure someone has. I know mine was not dynoed with a T stop on it. If the stop is like mine a dual T Stop with butterflies well there is certainly something in the way to impede flow which would cost some HP, just common sense I guess.

I guess a better question is why are you so concerned with the amount of power it will rob? I am sure it wont be a very large amount of power and some may loose less than others but why all the concern? One sure fire way to not cost any power is an in line linkage stop. It simply goes inline with the throttle linkage and is external to the engine, thus costing no horsepower. But the added weight of the equipment will cost you a couple of ten thousandths maybe