LS376/480 - Major power loss.

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Well-Known Member
Jul 28, 2014
Rochester, NY, USA
Pictsidhe has it right.

The fish tail exhaust on the Merlins were to increase exhaust gas speed for jet thrust & some flame dampening.
The power loss in back pressure was far less than the approx. 200 hp equivalent in thrust at full throttle at high altitude.

Keep in mind this is on a 1650 cubic inch engine with lots of exhaust gas. A IO-360 isn't in the same league. But typical installation can benefit a lot from exhaust boosted cooling air flow. ( also a big deal on FW-190 design ) There was a lot of "stealing" & customer spec stuff between Allison and RR, exhaust systems were airframe maker's responsibility. The B rits bought a lot of P-40s and may have spec'd the fish tail. Then everyone wanted them. ;)

A V-8 in a Titan 'stang just doesn't have room for a proper header. But your loss is at a higher rpm than you lose, so win.

Instead of sleeves, how about crushing the tubes into a fish tail & test? Pure speculation. Don't blame me.... ;)


Super Moderator
Staff member
Log Member
Oct 18, 2003
Saline Michigan
Bill's useless information (worked in both guns and powertrains...)

The visibility of the exhaust plume is largely a function of how small the time is over when the visible light comes off the gases. With short pipes, it is very much like gun gas coming off the muzzle of a firearm. Much of the light coming off both short pipes and gun muzzles happens as the gas expands and cools through various electron jumps, emitting specific wavelengths with each one. If the whole charge coming out goes through the same jumps at nearly the same time, we can see it well. Spread them out and it becomes much lower intensity at any moment. We figured out a long time ago that you can hide the flash by breaking up the "bottle" of gas coming off muzzles so that the light emission is spread more in both time and in position. The fishtail nozzle will do this nicely, on top of accelerating the flow aft for a bit of thrust and perhaps making the exhaust pipe feel like it is longer to the combustion chamber during the exhaust stroke.

Personally, I would make the pipes LOOK as original as possible. If the glare and or noise from the exhaust is too much, I would look into messing with the nozzles to control light and sound.



Well-Known Member
Apr 25, 2012
markham, ontario, canada
Hmmmm ...
Well, keep in mind that you're going to lose a significant amount of power with altitude.
table 1 Effect of Altitude sm.jpg

Roughly a 25% power loss at 8,000'. So at you cruise power of 300 hp you'd be looking more at 225 hp. On the side, the lower density is going to lower pumping losses so there will be a gain there.
Supercharging or turbo charging will more than reverse this.

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It looks like the area of the outlet is about 40% of the area of the exhaust port.

My favourite start up pics: