mrodoc

I've searched, but can't seem to find a definitive answer. I just completed an LE2 build. I have TPIS LT headers, true duals all the way back, cat delete, no x pipe. It seems everyone runs an x pipe. What is the reason? Should I install x pipe and why? Thanks

aklim

IIRC, the idea is to balance the flow to maximize scavenging effect for the low to mid range. Open headers are great for WOT.

Tom400CFI

Good question. I think the number one reason why people install an xpipe is in search of better sounding exhaust. I think the number two reason is because it's "cool"; the thing to do, in exhausts now days.

The functional reason why you'd install one is that it behaves like a "termination point" in your secondary piping -the piping after the collector. In a properly designed exhaust, the secondary piping would be a specific length, tuned to enhance torque at a specific RPM (likely the RPM that your engine makes peak tq). You can terminate that pipe a number of ways: have it open (that would be the end of your exhaust system, but wouldn't be street legal). Have it dump into a large box, install a cross over ("h-pipe") at that point, or install an X at that point.

The functional problem with H and X pipes in exhausts in most street cars is that there is a catalytic converter upstream of the H or X, and that converter acts as the termination point of the secondary pipe. So, if you've designed a system with specific length primary (header tubes) and specific length secondary tubes, then you can install your X at the termination point of your secondary tubes. Otherwise, you can install one for sound.

aklim

Is there any proven gain with the true duals besides the fact that it was the old way muscle cars were?

Tom400CFI

Are you asking me? Gains vs. what? The stock LT1^ exhaust is effectively "true dual", so, I'm not sure what your wanting to compare...

aklim

You or anyone. I see a lot of home made true duals for the L98 but no actual results as to how it compares to the larger 3 in

mrodoc

I didn't install an x or H pipe just because I wanted to keep it simple, and that's what I was used to from the "old days." My cam is .227/.235 and .565/.579 at .050. But here's the kicker, it has 110 LSA. I've have a kind of popping sound, at idle which is 900rpm. This is not the cam lope, of which there is plenty. I'm thinking that with that amount of overlap and the firing order and no X pipe, that's what's creating the exhaust note that I don't like. It almost sounds like a miss, but it smooths out, and runs to redline like a beast, with no hesitation. There is no surging unless I get under 2000rpm in 4th gear(4L60E with 3000 converter).
Do you think an X pipe help this sound?

TheMongoose

The X pipe will give you a different sound. Usually a higher pitched exhaust note, not a deep rumble. It will scavenge the cylinders better at low rpm. May make your popping sound worse - can't say for sure but I thi nk the popping has to do with the low backpressure you have, I wasn't sure if You had any mufflers? If no mufflers, adding a resignator rather than a muffler may clear it up. That was my experience with a firebird i raced which sounded horrible from idle to 1500.
The H pipe changes the sound, more rumble. It only balances the pulses, that's what hanges the sound, it doesn't improve hp/tq like the X.
On a related note i always wondered if the X pipe craze started with the nascar circuit. Those guys run X pipes.

TheMongoose

I should also mention if you decide to add one or the other where to put it. Paint your exhaust pipes downstream of the collector, start the car watch to see where the paint burns off. This is the hottest spot in the pipe and you put the H right where the paint is still present. Doesn't always match with other parts of the car that are in the way...like the tranny or cross braces, etc. the X goes as close to collectors as possible.

aklim

Could be. Kinda why they say "Win a race on Sunday, sell a car on Monday" or "Monkey see, monkey do". Might be the right thing or might be the wrong thing but if the race cars do it, I want to do it. Never mind that the motor and circumstances might not be what I am doing. Kinda like the sound you are talking about. Old muscle cars sounded like this, I got to make my car sound like it. Might be because they had no choice due to the technology hasn't caught up but I want to make it sound like the old muscle cars so others think I am powerful.

cv67

your popping may need to be diagnosed esp if it goes away with throtttle doubt its the exhaust

If youre hoping put one in will make it faster it wont

As posted it can tone down some of the brappiness, little smoother note

What works for a purpose built NASCAR motor doesnt always do anything or is needed on the st as they are after every last hp;thats why we dont need 260cc heads

Does your motor really need more scavenging? There is such a thing as overscavenging; really just splitting hairs is all
Id say figure out why its missing which is probably something minor go from there.

ive used true duals, H, X on various cars other than a slight pitch change never felt one bit of difference one way or the other regardless of "theory" or some mag article

Like having none just makes working on the car easier

Going to 3" over 2.5 will just make it louder inside

aklim

Why is why I have been asking if it makes a difference or it is just "Monkey See Monkey do" when it comes to duals. I have read that scavenging does make some difference at low to mid range on a dyno but not whether true duals make a difference on the dyno or just doing what the old timers do because it made sense then but might not today.

Kevova

Shelby put the H pipe with the 289/302 mustangs to help with torque Ford brought it back for the Fox body 5.0 off road exhaust. It really has to be in the right place to get the benefit . With the C4 layout; I think the crossover is to far back for a large gain. If it is put where it belongs there would be a 21/2 inch pipe hanging down behind bell housing. Chevrolet did such a good job tucking everything into the floor, and designed the engines to have plenty of torque.

aklim

Behind the bellhousing is kinda far back so if you are right, probably not worth it. So any idea how the duals help? I don't see too many people making kits for it and being able to brag that it does better than a larger tube with about 3 inches. I agree that 2 tubes at 2.5 can flow more than 1 at 3 inches but is it just there to be there or does the dual help?

Kevova

There is a science to exhaust flow and there is way more to it than I know. Biggest thing true duals does is reduces back pressure compared to a factory exhaust which usually increases horsepower and torque. The factory looks at 1 big cat per car is cheaper than 2 smaller cats, everything is a compromise between cost and benefit. Cost tends to be deciding factor. Some cars layout limit what can be done with out modifying the floor pan. The Gen 3 F body snaked the mid pipe under the floor pans actually allowing for a large single exhaust pipe, and makes running 2 pipes is PITA There are those who believe the all in to one is the best. In NASCAR you can find headers feeding 1 big oval exhaust pipe or headers,H pipe, and 2 exhaust pipes.

Tom400CFI

http://www.superchevy.com/how-to/exhaust/0505phr-exh/

aklim

Yes, over stock, perhaps it works out but is it worth the hassle of having to build your own over any of the other 3 inch systems already in production?

Tried it with having the Y pipe removed. No appreciable difference.

Perhaps so but their engines are completely different from ours and they don't have to worry about how much it costs to replace or how often. All they car about is to win the race today.

Kevova

I think it depends on what you have to start with. The lt1 exhaust flows better than the l98. IMO 21/2" is the largest diameter pipe for a normal street driven car. You do want to "fit" the application, from my experience manuals do better with larger pipes than automatics. Bigger isn't always better it can make for bigger talk and a slower car. Pro Streeters or other forms of race cars with licence plates are another matter.

aklim

I heard that too but I am not sure. Are they talking about the cat back that flows better or the exhaust manifolds? Exhaust manifolds, well, it doesn't take much to get better than the crap ones the L98 has.

Does it make a difference as to what the exhaust is? I know my 3 inch is post cat.

Tom400CFI

Every part of the LT1 flows better than every part of the L98 exhausts. From the heads to the tail pipes.