Lvangundy

I'm still absorbing Jbrady's reponse...

in the meantime I have ONE question..

why converge into a single 3" pipe? Why not keep it separate from the cats?

Just thinking 'visually' 2 Y's would just add to flow restriction.

TomWahjudi

Lvangundy,

It's another version of X-pipe. This is how stock exhaust system is. Joining the flows or at least equalizing the pressure between the two pipes will help with scavenging. That's why we know H-pipe and X-pipe.

John also wants to create a variable-area system. At low rpm, he will only use one "branch" and exhaust gas will exit only from one rear muffler and at high rpm band (or high load), the pressure valve will open and exhaust gas will travel through both rear mufflers. I would like to see a drawing on this too, John, can you scribble something roughly ? Mine is a little simpler.


John,

$500 will be cheap if it includes 3 mufflers, Y-pipes, piping and hardware My mufflers and X-pipe or 2 Y-pipe bill is already at ~$500.

Lvangundy

Someone mentioned that's how Ferrari exhausts work.. something similar I think.

Isn't that a mechanical function? Not just dependant on how much flow is going thorugh?

Like a little metal gate that opens and closes..this is getting confusing on trying to figure out HOW to make it.

If it isn't done another way won't the gas go through both ways?

JBrady

Lee, as the flow moves down the 2.25" sections it has inertia due to its speed and mass. The more speed and the more MASS the more inertia. Lots of enertia resists reversion and increases scavenging. If the Y-pipes are carefully formed, the inertial energy from each feed will be joined into the center section and the total mass energy of the combined gases will create a longer, heavier mass force. This longer heavier mass will resist reversion even more. Splitting the column into 2 parts is only necessary if you wish to have the exhaust exit at 2 places. Otherwise, you would just continue the one main tube. As far as the X vs Y is concerned, my design is basically a long X. Some say the diverging Y of the X or long X layouts creates a slight loss vs a single Y system but in the case of our cars lends itself to other attractive options like the dual path idea.

Another variable is the fact that as the gas is in route from valve to tailpipe it is cooling. This cooling reduces the energy available and lowers the pressure. Some designers slowly reduce the pipe area as you move away from the engine down the system in an attempt to maintain velocity. Could be some merit to that idea but then again the area restiction could ad more loss than is gained...

As far as the dual path concept, Nissan uses dual path mufflers with spring loaded valves that pop open under pressure to relieve the pressure. On the Q45 they use a mechanically operated valve. Both work, both have advantages and disadvantages. I have more than one idea on how to do this...

Lvangundy

This is becoming ming boggling.

I'l be reading this over and over.

TomWahjudi

So, I visited a race car fabricator to ask about the exhaust for my '95. Parts bill came up $800 with 2.25" stainless steel piping, x-pipe and 4 mufflers. Add hangers, flanges, tips and gaskets. Add labor. Oh well, I guess I will be better off learning how to weld and buy myself a nice welder and I'd come up cheaper John, I want to see your $500 or so prototype now

Lvangundy

Post is back from the dead.

I feel I understand this all MUCH better now.

Still, I am stuck on why we need to converge to a SINGLE pipe - which also happens to be 3/4" bigger than the rest of this proposed system. I'm talking about the 2-into-1 Y.

Here is a cheap paint drawing of how I understand the system. I hope nobody takes the time to re-draw another one of these..it took too long for something so simple.

After I got halfway through I realized I was missing the variable flow gate, oh well.

Lextreme

I would recommend 2.5" instead of 2.25". Two 2.5" to one 3" Y to two 2.5". According to Corky Bell's Book on exhaust. Each 3" exhaust can handle 500 rwhp.

TomWahjudi

Lvangundy,

Why converging to a single pipe ? To mimic an X-pipe. An elongated x-pipe that is. My fabricator believes in x-pipe so he wants to put that in and as the result, instead of one 3" resonator, two extra 2.25" mufflers are needed.


Lextreme,

It can be done too, I just want to keep low end torque intact.

JBrady

Guys, I have been working with a guy that builds race type Y pipes and full 180 degree headers for his Porsche 928 and other performance cars. He has a high end computer modelling program that predicts flow and dynamics. We have been playing with various sizes, venturi's, main pipes etc. The results have been surprising.

First off, 2.50" primary pipes are too large for the engine displacement and power range of our 4.0 liter NA V8s. 2.25" is probably one size too large for optimum but 2.125" piping is not readily available. Eric used 2.25 on his 250+hp engine and is reporting a boost in low speed torque. I recommend 2.25".

BTW, I worked for Corky Bell when he was writing Maximum Boost... even read some in pre-book form. At the time Corky would rarely build anything larger than a single 2.50" exhaust. I wanted a 3.00" on my turbo car and built it myself. A turbo car is a different animal and should not be used to compare. That engine made apx 250hp so a single 3" was viable. On a 4.0 liter engine making 250hp dual 2.5s will reduce velocity and low end torque will suffer.

Lee, regarding the Y pipe. By joining the gasses into one column (assuming it is done properly and without restriction or turbulance) the total energy in the one pipe is more than in either single pipe. This energy is moving one direction. The higher energy in one direction creates inertia and resistance to reversion. This effectively purges the pipes and promotes flow and scavenging. If you keep both pipes separate you do not capitilize on this effect. This demonstrates the importance of the Y pipe design. A poor design or installation can ruin this effect. This one pipe MUST be larger than the 2 feed pipes as it carrys MORE total mass flow. Think of 2 small steel ***** rolling down a hill vs one large steel ball of the same mass as the 2 smaller... which would be easier to stop?

Tom, do what you want but I can supply you with a mild steel racing Y pipe in the size of your choice for $125 or $175 in stainless. This would only require the one center resonator. You will also want a splitter Y and that would be $100/$150 or buy both for $200/$300 (mild steel/stainless).

Coated mild steel should work great for most cars for MANY years.

BTW, a full length professional SS system with 4 mufflers for $800 sounds VERY reasonable. Of course it would not have the dual path feature that I plan.

Parts list so far for my system: part, number required, retail est $
Pricing is for stainless. Price for mild would be apx 30% less.

flanges at catalyst outlet, 2 required, $80
o2 sensor bungs, 2 required, $40
mandrel pre-bent 2.25" pipe sections, 4 required, $200
racing Y pipe, 1 required, $175
center resonator, 1 required, $100
splitter Y pipe, 1 required, $150
pressure activated 3.00" valve, 1 required, $80
3.00" high flow muffler, $100
3.00" piping connecting splitter to muffler, $100
2.25" turbo muffler, 1 required, $30
2.25" piping connecting turbo muffler to splitter, $25
2.25" piping connecting turbo muffler to stock LS400 muffler, $25
hangers, fabrication and connectors as needed, $50
labor, $100
Total retail estimate, $1255

Lextreme

John,

You work with Corky Bell? He is like God in the turbo world. I read his book a ot the time while i am in the John. Not you. You know. lol. If I remember correctly, Corky stated that "NO EXHAUST IS THE BEST EXHAUST". He was refering to turbo cars. For turbo cars, one 3" can handle 500 hp. Therefore, in my exhaust setup, is good for 1000 hp. As for NA, that would be a different story. JB is very knowedgeable in this area. Listen to him and save yourself some money, headaches, heartache and time.

SCV8

Do you guys have a way to tune the fuel curve again after changing the exhaust?
I had to replace the exhaust on a car with dual webers,and the fuel requirement was way off from the original system, just from changing the header design slightly.
It took months of tuning to get it back again with the six areas(jets) of adjustment that those carbs use.
An adjustable fpr might work,if the exhaust design was the same,but only had slightly larger pipes.

JBrady

SCV8, unlike carbureted engines, our cars have MAF meters, o2 sensors and various other sensors... the computer can compensate for the change in air flow with a better exhaust system. A way to fine tune the A/F ratio and ignition timing would allow a small increase in power in the hands of a true tuner but I would not suggest this for a simple exhaust and or intake modification, just not cost effective.

SCV8

I don't care how many sensors our cars have,it's not enough to keep up with even minor mods like a bigger airbox.
Good luck

Lvangundy

In theory (or lack of education on my part) I agree that the sensors can't even adjust to such big changes..

But I don't think anyone here is a factory lexus programmer so there's no real way to say if the ECU can compensate.

However, there is proof that changing the intake/exhaust systems does make a difference in HP. Maybe the ECU can't adjust, but in osme cases it's helping flow..at least so far on the exhaust. No intake yet has seen to gain HP.