When its time (or when I have time) to swap in the 455 in place of a 425
I am wondering whats the gain vs. headache ? I am wondering is 25-50 hp
needed or worth it ?
Anyone race in stock classes with manifolds ?

Kinda thinking I'll have more torque than traction anyway . Am I just getting old ? (no need to answer that one)

What do you think ?

 

I raced both my Alero and Delta with stock exhaust manis, but only the Alero has expericened both.

The Alero ran about a 15.3 with stock manis and with headers it ran 15.002. I was pissed though. I wanted 14's so bad Of course that a long time ago.

On a stock 3400 Alero, the HP increase boasted 20 HP at the wheels, and considering the .3 drop I'm willing to believe it. The Alero was rated at 170 HP but probably around 146 at the wheels.

Basicly said, it was a 13.6% increase in HP in my case. Typically you are looking at anywhere from a 10 to 15% increase in HP with a full exhaust, but I think that the more power a car has, those % drop. I just have my doubts that a 400 HP car would gain 60 HP (15%) from an exhasut upgrade

 

I have installed headers on most of my cars over the years. I always thought it was worth it.

 

I agree. Also, in my opinion, don't waste your money on shorty headers. If you don't want to put up with the hassle of installing full length headers, just keep your stock manifolds.

 

Whats up with shorty headers Joe ??
mike

 

Equal length tuned headers have the primary tube diameter and length sized to match the exhaust pulses at a certain RPM band. The scavanging action of the pulses actually improves flow in the headers. Shorty headers don't have this design and in my opinion don't provide enough of a flow improvement to warrant the cost. I'm certainly willing to listen to anyone who has real back-to-back dyno or quarter mile test data, however.

 

Couple things about me and headers.

There seems to be more to the installation than first thought.

I always thermo coat them after test fitting.

 

I had a 68 W30 years ago that ran it's best time after re-installing the stock manifolds to run a pure stock class back in the late 80's. It ran a 13.93 bone stock. The 400 long stroker was a great engine. IMHO good mufflers are a better bang for your buck with lower hp engines. On a 454 Biscayne we ran it was an honest .02 improvement with headers.