headers VS factory exhausht mainfolds . how much power is gained or lost ?

[rav440]

this may really be a dumba$$ question . but im asking anyways .  how much power is gained with headers , and how much does the factory maifolds restrict exhaust flow .

the reason im asking is while im going all SYBIL as on what to do with my 440 ,  i do want it to have some power 375-425 HP .
but i like the stock look of the factory mainfolds .
and can the manifolds be ported for better flow ?

thanks RANDY

[aifilaw]

the factory stock manifolds are inherently horrible as far as airflow. the HP manifolds were far superior, and even today a lot of people are using them instead of headers because of the nightmares with quite a few header manufacturers when it comes to conflicts with power steering, starters, or just plug and wire access unless you spend some money on a good set.

Regardless, with few exception on upgrading stock vehicles (and of course excluding nitrous) you cannot get a higher HP gain per $$$ than a header upgrade.

This has changed due to the exhaust deficiencies cleared up in the cylinder heads of a lot of the newer stuff int he mid 90's, but none of that applies to us.

[firefighter3931]

Randy, when building with HP manifolds in mind you need to be careful on the cam selection. The reduced scavenging of the manifolds can be compensated for by adjusting the valve timing. Reduced overlap and longer exhaust duration works effectively on restrictive exhaust systems. An x-pipe also helps a lot in this type of an application.

Those power levels are easily achievable with HP manifolds. 


Ron

[StockMan]

I read an article in mopar muscle where they built a 383 magnum to spec and ran it on a dyno and it produced 336 hp with the stock HP exhaust manifolds.  The next thing they did was install a set of headers, I can't recall the size??  But, an increase of 30 horsepower was achieved with this change.  This is what they posted, not sure I believe it.  I'm not a fan of headers.

[Musicman]

the factory stock manifolds are inherently horrible as far as airflow. the HP manifolds were far superior, and even today a lot of people are using them instead of headers because of the nightmares with quite a few header manufacturers when it comes to conflicts with power steering, starters, or just plug and wire access unless you spend some money on a good set.

Regardless, with few exception on upgrading stock vehicles (and of course excluding nitrous) you cannot get a higher HP gain per $$$ than a header upgrade.

This has changed due to the exhaust deficiencies cleared up in the cylinder heads of a lot of the newer stuff int he mid 90's, but none of that applies to us.

Randy, when building with HP manifolds in mind you need to be careful on the cam selection. The reduced scavenging of the manifolds can be compensated for by adjusting the valve timing. Reduced overlap and longer exhaust duration works effectively on restrictive exhaust systems. An x-pipe also helps a lot in this type of an application.

Those power levels are easily achievable with HP manifolds. 


Ron

DITTO 

[Mike DC]

I still think the best setup for these cars on the street doesn't exist yet.  Tri-Y setups are ideal for street motors but even the few sets that are made are still too small. 

I'd love to run a really big/long set of Tri-Ys.  Like something that doesn't even look any different from a typical 4-into-1 header until the first 4 pipes get all the way down to the oil pan area.  And then the two intermediate pipes would be LARGE diameter, and stretch all the way back to the tranny crossmember before the final collector merges them. 

And the ground clearance could actually be pretty darn good this way.  You'd only have the two intermediate pipes sticking down under the car in the tranny area instead of all four small pipes.  And you could arrange the two intermediate pipes to run side-by-side horizontally so it would only take up the height-space of a single pipe.  The whole thing probably could be made to clear the speed bumps better than a traditional 4-into-1 header collector.