What is the purpose of a Y pipe, as far as performance is concerned? One would figure that since two separate exhaust pipes is proper for increased exhaust flow, a team of engineers would choose to go with dual versus Y. Whether it be reasons of manufacturing costs or just poor design, from what I know-dual is better. Why am I wrong or right, in your opinion?

 

There are different opinions about the exhaust system. Some say the system as it is, is perfect for these engines, due to the fact that they are not high output, high flowing engines.
I personally like the idea of small tube headers with true dual system connected by cross pipe or equalizer pipe.

 

Seperate dual exhaust with a connector is definitely the best way to get max HP from a V8, specially if using a higher lift & duration cam.
But I am sure that wasn't what land rover had in mind for a off-road vehicle, they most likely wanted more torque in lower to mid range of RPM, & for that purpose Y-pipe system works best, also less plumbing means less weight & takes less space.

 

Thank you for the input, gentlemen.

 

I'm currently running high flow cats and a borla (straight through) muffler back to duals and it's great, though I also have a cam/port and polish/intake to match. That said, I will be doing headers, de-cat with resonators in place of cats, and 2.5" pipe y-d back into the Borla with a single 3" out the back. On a stock engine, my current setup would be about perfect even with 32" tires and regular wheeling, though I'd go for a single 2.5" out the back. The dual 2.5" on mine is purely cosmetic because the exhaust is already bottlenecked at the end of the y-pipe.

 

I am definitely going to address the complete exhaust system in time. I also am getting together the parts for the cold air intake mod that Alex_M has posted. I am firm believer in improving the total air flow.
I really like the idea of headers into Magnaflow stainless steel exhaust, which eliminates the resonator.

 

For trucks like these a properly designed exhaust needs to have a certain amount of flow with a certain amount of exhaust velocity. It doesn't matter if it's a single or dual exhaust if it meets the needs of the engine.

The main gains to a dual exhaust for these would be more weight, more expense, more complication.
And, if not engineered correctly, more detriment to good cylinder scavenging, more fuel use and greater reduction in power.
Having both banks feed a single muffler and exit the muffler in dual pipes doesn't benefit the engine at all and is likely worse if not properly engineered.

On the topic of CAI's, every one I've seen photos of in a Discovery look like they are actually HAI, hot air intakes, when compared to the stock filter setup. Drawing more air from the engine compartment, rather from the front of the vehicle.
Then there's the proven fact they pass more dirt to the engine. Seems like a lot of money for something that's worse for your engine.

 

Everything stated here is correct. The duals don't benefit the engine at all, I did it for looks and am quite fond of the asthetics, though it was too much trouble and I will not be doing it when I redo my exhaust again.

On the intakes, it does seem that way. However, I've compared temp readings and actually the CAI I have made up pulls cooler air than the stock setup did pulling air out of the fender. Strange, I know, but it's true. None the less, there were performance gains. You are correct though, they do allow more dirt in and some people are more OK with that than others.

 

I would save the money it would cost to go dual flow for other things down the road. If you want to improve air flow then buy a snorkel kit. It will get the intake up high and out of the stock fender location for cooler cleaner air. If you go with that "Cold Air" option you are just going to be sucking in hot engine compartment air, not all that great of an improvement from the stock location if you ask me. Besides the snorkel kit looks COOL so it must be COOL

There are all kinds of kits out there online but this is the one I'm currently looking at buying. Its the best price I've found by far.

Snorkel Kit for Land Rover Discovery Series 2 II Diesel Petrol TD5 V8 99 Onward | eBay

 

i think with Alex's engine setup, he will see a difference, because he does have a more aggressive cam and porting. Too many people do not realize just adding a cam will not be that beneficial, if they do not increase the breathing capabilities to match the increase in flow created. The same goes with just adding free flowing exhaust, or intake. The idea is to increase the volumetric efficiency of the engine. The only way to truly match the intake, ports, cam lift/duration, valve cut angles, and exhaust is with a flow bench. Obviously, this is not something we have in our garage, so we have to rely on the manufacturers (cam, headers,etc.) recommendations on what works best with their products.