i think after installing headers i am going to take out my resonator and stock H pipe and replace it with a really good X pipe. what size should i get for my 2.75inch pipes? where should it go? as close to the header collectors as possible? further back? its not as loud with headers as i thought. at idle and druising its just as quite as it was before with no mufflers and no cats. it feels like i lost a little bit of very bottom end tq though. i have heard many times that an X pipe will cure this. what are you guys' expert opinion on this?

 

As close to the headers as possible for any performance gain.

I never installed headers on my car with a stock cam so I couldn't really tell you if I lost any torque or not. Also I installed my x-pipe at the same time as the headers.

I drove Brian's car with headers, otherwise stock. I know his has more very low end torque than mine does. Damn his stock cam that lets him just idle down the driveway....

 

The "X" would be most effective if placed at the "burn point", but in a street machine, it is best where ever it fits. How or why would you consider an "X" pipe of a size different than the mating exhaust pipes?

RACE ON!!!

 

If this is determined in the same manner as that used to select optimum
header collector length, then the technique is to apply high temp paint
to the header collectors, operate the vehicle in the intended manner
and examine the collectors to determine how far along the paint burned
from the heat of operation. This is the starting point for collector
length and you tune from there with longer/shorter collectors.

Assuming CFI-EFI is referring to the same approach, the X or H-pipe
goes where the burnt paint ends. However, as he mentions, there
are usually obstacles that prevent installation this far forward on a
street vehicle. Still, it is simple to perform the test.

Not everyone feels that high temp paint (1,400º) is necessary. I hold
the opinion that the lower scorch temp of conventional paint skews
an outcome and results in starting with a too-short collector. If you
tune you eventually get to where you need to be, regardless.

.

 

Paint a strip down each pipe after the collector and see where the burnt area is located. The X should go as close to the center of the burn area as possible.

 

Face it, it's going to have to go where the resonator comes out. You are restricted by transmission placement, it can't go dorectly under the pan of an auto trans.

If everyone is agreed that an X-pipe needs to be placed as close to the header collector as can be fit, then puzzle me this. Why is the X-pipe placed at the back of the car on C5/C6 LG Pro systems?

 

I disagree. The only difference the type of paint makes, is how much heat or time it will take for the "burn point" to reveal itself. For drag cars, we've fired them, done the burn out and made the pass, using crayon. If we'd have used high temp paint, we would still be making 1/4 mile passes.

When you cut the collectors, you want the burn point just beyond the cut, outsde of the collector. With an "X" pipe, you would want the center of the "X" at the burn point.

RACE ON!!!

 

Might have something to do with 'Re-ignition' if the location is somewhere
around 50 - 60 inches from the end of the primaries. To read more,
see pgs 217-218 of the large paperback edition of BDGiT Vol III (Li'l
Skinny Rule Book) by Smokey Yunick. In short, he discusses the effects
of adding ambient air to support secondary combustion for the purpose
of maintaining peak exh gas temp, lowering exh system pressure thru
higher velocity at lower specific wgt. Net result: less overlap required
for a given quantity of exh gas -> higher cyl operating pressure ->
more power from a given quantity of fuel.

Consider that Smokey figured this out and put it into practice over 43 yrs ago.
Next, consider that something similar had been implemented earlier on
motorcycles and aircraft. There is not much that is new under the sun.

You might also want to read
"The High-Speed Internal Combustion Engine" by Sir Harry Ricardo
"Scientific Design of Exhaust & Intake Systems" by Philip H Smith & John C Morrison
"The Design & Tuning of Competition Engines" by Philip H Smith
"Performance Tuning in Theory & Practice" by A. Graham Bell
and I can't find my book by Waddell Wilson but I remember that
I learned about exhaust science from it, too.

.

 

Wish I would have bought what I think was last month's issue of Popular Hotrodding......great article on exhaust system theory..

Didn't get to read it, just scanned it at bookstand, next time I went to buy, but it was gone, but I think it might have addressed this issue...

 

I think you are correct in theory but missed the translation somewhere...High temp paint won't give you a burn (unless you are talking about 43 years). Crayon or plain old masking tape will work like CFI suggested and reveal the burn or "hot spot" where resonance actually occurs. There are a few old guys on the forum that really know what they are talking about, albeit, I doubt CFI wrote any books on the subject

 

Is that so? Well, Smokey had aluminum venturies mounted in 3.5"
OD pipe 56" downstream from the end of the primaries when he did
his initial tests and in one lap, the venturies melted. The remains
were found splattered on the quarter panels. Although the EGT's
1.5" from the head recorded 1,475º, the aluminum venturies some
88" downstream (primary length, plus 56") must have seen temps
of 1,750º+ in order to melt.

Maybe that is just a colourful tale. I hold Smokey Yunick in high
regard, but I wasn't there.

However, back in prehistoric times when I swept floors for a crew
that raced jet boats in events like the Smokey River, Rio Balsas and
one they participated in Australia, the LS7's used for power had polished
stainless headers with large extentions after the collectors through
to the transom. By the end of the first event, this setup had changed
from a mirror polish to a gun-metal blue finish right on down through to
the transom, the only shiny bit left was the last inch or so on the much
cooler outboard side of the transom. If there had been any paint on
these pipes, all that would have been left of it would have been a
crusty bit of charred residue.

Now these are two different situations ('Re-ignition' vs high power
endurance conditions). But I believe they both serve to illustrate
my point.

Take an engine that makes real power, put the spurs to it and see
for yourself whether it takes 43 years to scorch high temp paint. I
believe you will find that it does so quite handily. There's a reason
why Jet-Hot and others have such been so successful with their
coating services.

.

 

Somehow I think you missed the er uh point, post....

 

Actually my memory is going, happens when you get old. The X-pipe is NOT all the way at the back of the car on C5/C6 LG Pro exhausts. It's in the middle of the pipe and probably only a foot farther back than the X-pipe on my own car. These headers have exceptionally long primaries, that's why the X-pipe is wehre it is.

Here's a picture from Lou Gigliotti's web site :



This thread didn't make anybody mad like some discussions so no harm, no foul?