me agene! (Question regarding Pantera headers)

You get my vote...cut them back to at least 2.5 inches...3 would be even better...Old school says " If you can make it breathe,, you can make it run"

lbb,thanks,my toughts exactly,i don't know if i'll be able to push it too 3"have to have my brother look at them first,anyone else with some thoughts?les

Just remember that an engine is baically a pump and all pumps need a little back pressure. I have a friend who had a good running Pantera with a 351c, cam, etc..He put the 180's from Precision ProFormance on the car (this was the only change at first and then re-jetting the carb and adjusting timing. The car ran worse than ever, and he had to put some restrictor cones in the exhaust(6 of them and some steel wool) to get the back pressure back, so he could get performance back to normal. Bigger is not always better. I think the 2 1/2" would be the correct choice.

Les,

The correct answer of course is that the correct "size" of your exhaust system will be dependent upon the power output of the motor.

I don't have the experience I would like to have with the Pantera exhaust system to be able to advise you properly, but I think it is safe to write that for most owners a 2 1/2" system will be adequate. It will obviously be a far cry better than the oem system. Increasing the size of the tubing alone is not enough however, the oem mufflers are themselves a significant restriction.

The mufflers sold by PI Motorsports have no baffles inside at all, they are simply lined with sound deadening material. I have had the opportunity to hear them on Brad Grooms' Pantera, equipped with a 427 Windsor. The sound level is very docile compared to some Pantera systems. The construction quality is very high.

Les, the oem exhaust was undersized for two reasons, (1) to meet federal sound level standards, and (2) to maintain the same back pressure as the exhausts in Mustangs and Torinos, otherwise deTomaso or Ford would have had to re-jet the 351C motor for use in the Pantera. This in turn would have required all new emissions testing & approvals just for the motors installed in Panteras. So when you read that the oem exhaust system in a Pantera was good for 30 additional bhp compared to Mustangs & Torinos, you just have to roll your eyes a bit.

Many of the aftermarket Pantera headers are designed to bolt up to the oem tail pipes, so you'll find they have dramatically undersized collectors. Most aftermarket Pantera headers also have collectors that are too short as well. Those design compromises will limit the effectiveness of those systems.

The headers sold by Pat Mical at Future Auto have recieved repeated praise here on the DTBB.

your friend on the DTBB

I say 2 1/8 primaries and 3 1/2 collector, that makes "SWEEET" sounds.
hehe

> Just remember that an engine is baically a pump and all pumps need a little
> back pressure.

That myth dies hard. First of all, the atmosphere provides back pressure all
by itself. Second, back pressure is not beneficial to exhaust flow. What may
appear as a static back pressure increase may in fact actually decrease dynamic
back pressure. This results in higher flow not due to an increase in back
pressure but due to better scavenging via pressure and sonic wave reflections.
Vizard does a good analysis of how various muffler types appear to the
collector in the May 2005 issue of Popular Hot Rodding. "Exhaust Science
Demystified".

Some engine combinations are more sensitive to exhaust systems than others.
In particular, cams with narrow lobe centers need a very good exhaust system
to work properly. Big port heads like 4V Clevelands tend to work best with
narrow lobe centers. The typical 10.5:1 compression ratio 351C-4V works
best with a lobe center of around 107 degrees. That requires a good exhaust
system.

> The correct answer of course is that the correct "size" of your exhaust system
> will be dependent upon the power output of the motor.

The article I referenced above gives the best design equations for exhaust
system sizing I've seen. They are based upon what your exhaust port flows
at peak cam lift at 28" H20. I use those equations as a starting point for
Dynomation simulations and it's usually pretty close. FWIW, some of the
other published equations aren't even close.

> Increasing the size of the tubing alone is not enough however, the oem
> mufflers are themselves a significant restriction.

Restricitive mufflers can kill most of the gain from good headers.

> The headers sold by Pat Mical at Future Auto have recieved repeated praise
> here on the DTBB.

Pat's headers sacrifice primary length for collector length. Given the
space limitations in a Pantera that's probabaly a pretty decent trade-off.
He also uses the 3" collector diameter so he can run 3" intermediate pipe
and large bore mufflers. May not make much difference on a mild engine
but on a big inch stroker, should be worth a fair bit.

Dan Jones