Joe67

or is that a flaw in desktop dyno
with my almost bone stock 289 with factory exhaust it shows 225 hp @ 5300
but when i click shorty headers with mufflers it goes to 280 @ 5700

is there that much to gain with headers?

1sweet65stang

i dont know but if so looks like im buying some headers

Gun Jam

No...no way
maybe +- 10 hp 15 ftlbs torque

Starfury

Agreed. They do really hurt performance, but not 55hp. Even shorty headers will provide an improvement over stock, but a set of tri-y's work pretty well on stock or mild motors.

Joe67

That's ok, it my first car, im not racing, and i def. dont want it around a pole =/

plus i favor the look of shorties or stock over tri y's

67BullittCoupe

i have long tubes and a full 2.5 mandrel bent exhaust with an x pipe, so i probably lost power due to back pressure. but even so i doubt you'll gain 60 with just headers, but as you increase your engine capacity exhaust is a corner stone to performance.

67mustang302

Maybe if you have an engine already making 600hp you might find 60 by going to headers from a stock manifold.

Realistically you're stock 289 is like 185hp and with headers would be like....188? Maybe 190 on a really good day.

2+2GT

The stock manifolds are pretty pitiful. However, they are a good match to the horribly small exhaust ports in the stock iron heads, even the 289HP heads. The 289HP manifolds are much better, and if you port-matched your heads to 289HP manifolds, you'd see significant gains. If you have an upgrade cam, it would be even better, because the potential gains from your cam are being strangled by the ports. No matter what headers or exhaust you use, these ports are killing your performance.

jwog666

desktop dyno is just an estimate. it can be off by alot, especially if you dont have flow files for the heads and intake you are going to run

Starfury

Very good point. The stock exhaust port castings are absolutely horrible. I port-matched my exhaust ports and was stunned with the amount of material I removed. Comparing side by side with my original heads, it's amazing that the motor can breathe at all through those tiny ports. I'd guess at a 35% increase in port area, with a significant improvement in flow due to the removal of the smog hump and excess material just inside the port.