How Much HP Are Gils Costing Me
 

Plain and simple, how much HP are the factory high performance gils costing me? They are one of the only parts I re used from the 454 mags I pulled out at the urging of a few people saying not worth the upgrade to another manifold as they are a decent piece. Just built two fresh 540's, NA that are producing about 700hp per side on the engine dyno with their dyno headers. I just can't seem to get a solid answer. Engine builder thinks probably not much, maybe 20hp vs a higher performance header, but that was just a guess. If it's a big spread I think I'd like some EMI Thunders.

Thanks Guys!

The Gils are fine. Look at the Lighting header web site,they used to have some dyno comparisons

This graph was done by Fountain.

Exactly what I needed, thank you so much!

On an NA 540 700 hp engine I'd guess the Gils make 30-50hp less.