Borla Long Tube Headers

[STORMCAT]

The Borla add in this weeks Auto Week shows: Borla XR -1 Long tube headers " Now available for 05 -07 Mustangs, Shelby Gt 500 and Ford GT " Anyone looking at these? Are they the same as the Ford Long tube headers? Not street legal...

 

[lthlvpr]

In the end, it will be interesting to see if headers really add much, if any power. So far, the results I have seen say little to no power. For the cost of the headers and the install time, unless the power was significant, I would pass.

However, if you want to be heard, then this is your dream come true. The cars I have heard with full headers are seriously LOUD. I mean rattle your fillings loud. Sounded like a full race car with all the popping on decel and everything. Too much for me as I like to have conversations with the passenger during drives....

 

[Gulf GT]

My wife and I talk normally the entire time I am driving with no problem, we don't even have to raise our voices. As far as the the people behind me, that is a completely different matter.

 

[Black2003Cobra]

In the end, it will be interesting to see if headers really add much, if any power. So far, the results I have seen say little to no power. For the cost of the headers and the install time, unless the power was significant, I would pass.

Yes, and there is a good reason for that. The main control of airflow into the engine at WOT is the supercharger. Since a P-D supercharger is more or less a constant-volume machine, as you improve the efficiency of the engine, the mass-air flow rate remains more or less fixed (at any given rpm). Since to first order, air + fuel = power, power (and torque) won’t change “much”. Yes…there are second-order effects, which are discussed in more detail here:
http://www.modularfords.com/forums/...positive-displacement-supercharger-41735.html

To some it is worth it, and to others it is not. And some like LTs for other reasons.

 

[jj1987]

Don't headers do more for throttle response and even the power band more than increase the peak hp?

 

[californiacuda]

If I may, regardless if the supercharger controls the airflow into the engine, I think the questions really is, does the existing exhaust system restrict the exhaust flow out of the engine? If it does, then changing to a system that reduces the restriction will show improvement.

If the existing system does not restrict exhaust airflow than a change to a larger, or more free flowing system will have no effect.

I know that there are more complex issues such as scavenging, and turbo charging, but I was try to keep the discussion and example simple.

 

[Fast Freddy]

if you do a whipple then i would do headers. :thumbsup

 

[californiacuda]

I would have to believe that the cats are reducing exhaust flow. So, a change to eliminate the cats would cause an improvement in power. I also wonder, with the full length headers, if there would be a weight reduction?

The existing exhaust manifolds are cast iron and the cats have to weigh more than the header material alone.

 

[californiacuda]

I went to a previous thread and Nota4re saw a 70 lb weight savings going from stock exhaust to Ford racing headers and muffler.

 

[lthlvpr]

If there was a 70lb weight reduction, it may have been in spite of the headers...

Replacing the stock muffler with straight pipes drops around 60lbs. The cats will drop another 15-20+. Then the all the material in the long tube headers may actually add some weight back unless I am missing something here...

 

[Black2003Cobra]

If I may, regardless if the supercharger controls the airflow into the engine, I think the questions really is, does the existing exhaust system restrict the exhaust flow out of the engine? If it does, then changing to a system that reduces the restriction will show improvement.

If the existing system does not restrict exhaust airflow than a change to a larger, or more free flowing system will have no effect.

I know that there are more complex issues such as scavenging, and turbo charging, but I was try to keep the discussion and example simple.

Hey cali – See if this briefer explanation helps. First off, what goes in must go out (except for blow by). If it didn’t, manifold pressure would continue to build ad infinitum. But as you suggest, the idea behind LTs is to improve exhaust scavenging, (i.e., to pull the residual gasses out of the cylinder), which results in an increase in the engine’s volumetric efficiency VE, (which is rpm dependent). For a normally aspirated engine, if VE increases X%, the amount of air-flow would increase X%. But for an engine w/ a positive-displacement SC on it, if you increase the “internal” VEe of the engine (from the intake ports and out), all that happens is that the boost pressure will drop, while the airflow remains virtually unchanged, (if there are no other changes). So to first order, there would be no increase in power or torque. There is some gain however because the pumping loss of the supercharger is reduced at the lower boost pressure, (i.e., it is easier for the supercharger to pump in the air at a lower boost pressure.) It is also true that the VEsc of the blower will go up a tad with a lower pressure ratio, (outlet pressure over inlet pressure), but this is typically a fairly weak function of manifold pressure. And the more (volumetrically) efficient the blower, the lower this effect. (In either case, there won’t be a commensurate gain in power of X% for an X% increase in VEe. It would be considerably less. There are some examples given in the thread I provided the link to, albeit not for exhaust changes. But they should give one an idea.) Hopefully this is a little clearer.

 

[californiacuda]

So, in a positive displacement supercharger system, where the airflow is controlled by the tight seal in the supercharger mechanism, a flow improvement down stream would not improve performance, but only improve VE and maybe lower boost pressure. Very interesting.

So, I guess a way to get improvement out of reducing flow in the exhaust track would be to put a smaller pulley on the sc to create more airflow, and performance while maintaining a lower boost level than if the exhaust restriction had not been removed.

 

[Black2003Cobra]

So, in a positive displacement supercharger system, where the airflow is controlled by the tight seal in the supercharger mechanism, a flow improvement down stream would not improve performance, but only improve VE and maybe lower boost pressure. Very interesting.

To first order, yes! (However, if boost pressure drops some, the parasitic drive power of the SC goes down, yielding a little more “net” power as meas’d at the crankshaft or wheels. Again, it’s just not as much as one might otherwise expect).

So, I guess a way to get improvement out of reducing flow in the exhaust track would be to put a smaller pulley on the sc to create more airflow, and performance while maintaining a lower boost level than if the exhaust restriction had not been removed.

I think what you are really trying to get at here is that if one improves the exhaust flow and drops boost pressure, and then puts on a smaller pulley on the supercharger to force in more air and bring the boost back up, then the higher airflow will most definitely bring the power up more in line to what one might expect. With an NA engine, this happens “automagically” after improving VE via the better flowing exhaust because “nature’s boost” (atmospheric pressure) doesn’t change.

:cheers