MLV hp calculator vs real hp
 

How accurate is it? I've not dynoed my car so I'm wondering how reasonable a figure it offers. I assume any figure would be off the crank and subject to a ~15% drive line loss?

This is all assuming correct info is given to MLV to start with I realize.

EG, today it told me my car made 340hp at ~6800rpm and 16psi.

2560 can't make 340hp, definitely not with a NA head and not at 16 psi... That said, you can use the number like you're supposed to use a dyno... relative numbers, i.e. if you play with timing and get the number higher, you're actually making more power.

edit: To be fair, a 2560 can probably make 340 at the crank, when perfectly tuned, but it'd probably be happening at a higher amount of boost. You probably have a gear ratio or tire size wrong, or you put the weight of the car as being higher than it actually is... there's a lot of room for error with these calcs.

I know power #'s are for comparison on the same measuring device but was wondering if there was a general consensus that it was say 10 or 20% high etc kind of like people have rough calculations to go between different brands of dynos.

Actually you were right on the slightly off #'s, I have the weight at 2350lb (car has all oem equipment including air, spare, me, jack + everything added etc) so too light and the tire size was undersized at 22" vs 23.1" actual. I did however have the gear ratio and rear (4.1) right as checked at using this FM page and used 2nd gear (6sp) to do the run from a roll.

Simply correcting the tire size raised the calculated hp to 359 hp, the weight with gas and me is probably closer to 2600lbs but I left it at 2350lbs. I know the hp # has to be higher than actual.

Ahh, cool. IIRC, one of the main things it doesn't account for is drag, which should make it read lower than actual. That's not a fixed percent thing though, When I played with it, I got numbers that were pretty inline with where I think they should be... But I put a bit of effort into making all the variables I put in realistic, and have only ever looked at it in 2nd.