How accurate are these calculators?
For example I ran a 13.5 sec 1/4(PPE 320 tune) and they all caculate to roughly 640hp can this be right?

Launched in 4x4 at 1850 rpm with 33x13.5 R 18 mtz

No that doesn't sound right to me. 650rwhp and you should be well into the 12's

That would be 640 crank hp, would it not?
With me in it truck wieghts roughly 8000lbs

imo, but considering all the variables that go into drag racing ET's I would say they are have a lot of room for error. IE if you have a crappy 60' from those 33's it'll affect your ET greatly.

someone shoot holes in my theory here, but I don't like hp calculators, but maybe someone that has ran their truck on the track and rollers could chime in here and see how close they are.

Pretty sure thats flywheel hp. Assuming (yeah, I know) 15-20% loss thru drivetrain and your truck weight is accurate, then your ET numbers look close. (using DD's calculator)

I figuered it to be pretty close. Now this brings up another ? How can one use a % to calculate the drive train loss. What I mean is if a 300 hp engine has 10 % = 30hp drivetrain loss wouldn't a 600 hp engine have 5% =30 hp loss as the drive train loss should take equal amount of hp not % of engine hp.

Figuring by MPH is more accurate than E.T. Going by MPH mine is within 10hp of repeatable dyno #'s . Figuring by E.T. it's off by 20 hp or more.

I figuered it to be pretty close. Now this brings up another ? How can one use a % to calculate the drive train loss. What I mean is if a 300 hp engine has 10 % = 30hp drivetrain loss wouldn't a 600 hp engine have 5% =30 hp loss as the drive train loss should take equal amount of hp not % of engine hp.

I wouldnt even begin to know that. Like I said, it was an assumption on my part. Ive used that figure in the past to est my truck, and its usually close.
Chris is right, though....mph is a better gauge, although you do not mention that in your post.
First thing you may want to do is lose some of the excess weight from your truck when you're at the strip. 8000lbs is a lot of mass to get moving.

I figuered it to be pretty close. Now this brings up another ? How can one use a % to calculate the drive train loss. What I mean is if a 300 hp engine has 10 % = 30hp drivetrain loss wouldn't a 600 hp engine have 5% =30 hp loss as the drive train loss should take equal amount of hp not % of engine hp.

Not how it works. The more power you make the more loss you have. A percent is the most accurate way to do it. The harder your motor pushes on the trans and moving parts the harder they push back. Kind of hard to explain.

Well mine dynoed on level 6 of the PPE hot+2 and put out 506hp at the tires. That was with a 35" tire, 4:10 gear and all the other mods you see.

I dont like HP calculator.... the do not calculate torque into the factor.

MPH will get you in the neighborhood on power, most dyno's differ with setup and operator. Load, rate of accel, air density calculations all affect dyno numbers. Peak horspower numbers don't win races, average power numbers can. We don't race dyno's last time I checked either. Dyno's are just a tool to help get you in the neighborhood with your tune the track will tell the tale with MPH, now lets discuss chassis set up.........that is where the ET is found.