2 Amigos

Hey guys, i need help calulating how much H.P I gained this week. I recently converted my stock 1971 Mustang with a 351-Clevelandexhaust system. It had stock cast manifolds, 2 collecters, Y-Pipe collecting the 2 pipes to a single 2 1/4 pipe to a singlestock muffler (thatblew up on me, which is why i got thenew exhaust system)for a single exhaust. I put in performance original Blackjack headers (original from the 1970's), 2.5' collector and ran dual 2.5' pipes to Flowmaster 40 series mufflers.No H-Pipe or X-pipe, just true dual exhaust. Anyone know how much H.P I gained approx.??Thanks

-Tony

BULLITT GT 390

I think it would be in the 30 to 40s hp that is!

BULLITT GT 390

headers can give you up to 20 to25 hp!!

SalikDDD

90000! jk i dunno, but i sure hope a lot more then the 9 horsepower i got out of my headers i just did on my Modular 4.6 this weekend :| 6 hours + 9 hp = waste

2 Amigos

30-40? NICE!! Bummer about your mild 9 H.P gain SalikDDD. I hear the H.P gain on headers depends on the size of the engine. Bigger engine, more HP. I figure my 5.8 would gain more than your 4.6. Also I changed from cast iron manifolds, single 2.25' exhaust and restrictive muffler to full length headers, 2.5' pipes and dual flowmaster 2-chamber mufflers. all 3 should transfer to more than 9 h.p

The stang II

You should REALLY get an h pipe of x pipe. Your car might make a popping sound when you let off even at low rpm's you need ah pipe to balance out the ehaust.

racin66coupe

get an x-pipe or h-pipe, itll increase your low end hp

musting

Headers are very much a benefactor in bolt on HP performance, but the real use of headers for race people are to loose as much weight from the car by removing cast iron manifolds 40-60 lbs,in their threory for every XX/00's lbs reduced from the car can give faster time on the clock..
I have a pair I had planed on useing on the '66 289cc but with all the lack of clearance I may just go back with a set of latter 302 manifolds and use an X-or H pipe as some have already mentioned.
thefaster U can flowthe exhaust scavaged from the engine the better the performance,

dr1965

30 to 40 hp???? I wish.

69thunder

No way 30-40 hp more on a stock motor from 1971. If it was that easy to get horsepower gains like thatno one would need to do anything else.