I just has a couple of questions.

First, doesn't the y-pipe serve the same function as an x-pipe? Does it balance out pressure from both banks, and serve as a type of crossover? Also, wouldn't the y-pipe into a single, larger pipe be more efficient than separating again into duals?

Secondary to the first question, what size pipe would be optimum for 400-450horsepower? I want to run headers to an aftermarket y-pipe, through a cat and a muffler, and dump in front of the rear wheel. My gut tells me this would be a very efficient system, and lightweight.

I would appreciate any real responses regarding exhaust flow and efficiency, so thanks in advance!

 

The y-pipe is not like an x-pipe. A x-pipe is used to allow each bank of cylinders to use both pipes and if equiped both mufflers to double the flow.
Now you can have a y-pipe lets say Dual 2.5" merge into a 3.5" or 4" single pipe and have the pipe flow but the cat and single muffler has to be able to flow the same in order to min the backpressure. That's why most split back into two mufflers to divide the flow and reduce the backpress.

To support 400-450 hp at the wheels or at the crank. At the crank you'r going to need at least a 3.5" pipe, at the wheels it's going to be a 4" pipe.

 

does anyone make a cat with a 3.5 inlet/ outlet? Also, any muffler recommendations?

 

I don't know of a 3.5" cat but I'm a fabricator so if they don't sell it I'll just make it. As far as the muffler if you want to keep your ground clrnce then size is going to determine that. If sound is not an issue then you could go with a flow through round or oval magnaflow, borla, dynomax, hooker the list goes on as long as they can support your cfm needs.

 

That's crazy talk. 3" exhaust, with cat, supported 500hp for me for a good while. There is a few other guys on here with 3" exhaust running mid 11s at 120mph too.

-- Joe

 

Joe, I would be interested to have seen a pressure gage installed on your exhaust system. I wonder what the back pressure was with the single cat?

 

Also, a properly designed y merge will outflow an x and most certainly an h merge. Most don't run the proper merge so y pipes get a bad reputation.

 

Nothing I'd imagine. single 3" supports 800cfm.

-- Joe

 

My point exactly. There have been tests with a single 3" vs a single 3.5" and 4" exhaust systems. And the motors with the right tune and bigger pipes made more power.
I'm not saying you can't get a motor to make 500hp with a single 3", you can but your losses are going to be extremely high. If my car makes 375hp at the rear wheels with a 3" and would make 395 with a 4" then guess what I'm going to do. Make more power with the better system.

 

800 cfm with a straight 3" pipe. Which is good for about 360 hp before you start seeing some hp loss due to backpressure. Besides our systems are not straight so the power loss will start sooner.

 

Post links to the tests with proven data. Otherwise it's about as viable as witness accounts to the lockness monster.

Kinda like the "the car feels faster" posts.. sure it does..

-- Joe

 

Here is a post on another forum based on numerous dyno pulls. I have seen other posts with similiar numbers. By the way these are pipe inside diameters. So a 3" pipe relates to a 2.875" pipe. Based on this a 3" pipe will support around 400hp at the motor. After that you will suffer loses.

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As requested in the exhaust flow question thread here is an article on my own rules for exhaust system design for primary pipes, secondaries and muffler flow.

All pipe sizes referred to are internal pipe diameter because this is the appropriate measure for determining flow characteristics. The o/d for imperial pipe will usually be 1/8" larger because most tubing is 1/16" wall thickness.

PRIMARY PIPES

For primary pipes (headers) the chart below is based on the power output of a 4 cylinder engine or one bank of a V8. If you want to convert to another engine configuration then divide by 4 to get the power per cylinder.

Header I/D...Power
1 1/8"............125
1 1/4"............150
1 3/8"............185
1 1/2"............220
1 5/8"............260
1 3/4"............300
1 7/8"............350
2 0/0"............390

If the secondary pipes are a 4 into 2 into 1 configuration then the I/D of the secondary pipe should be 25% larger in diameter than the primary and the collector should be 50% larger in diameter than the primary or use the muffler chart below.

If the secondary pipes are a 4 into 1 configuration then the I/D of the secondary pipe or collector, which will also be the exhaust system pipe for a 4 cylinder or one bank of a V8, should be 50% larger I/D than the primary or use the muffler chart below.

For the final system pipe size of a V8 where both banks join together to go through a single muffler or set of mufflers then refer to the chart below or use the rule 50% larger in I/D than the collector on each bank.

SYSTEM PIPES AND MUFFLERS

The chart below shows the maximum flow potential and power potential at various pressure drops of the final system pipe sizes and mufflers. Again sizes are I/Ds. This assumes 100% efficiency for the mufflers which will only be achieved with good internal design.

The rule for pipe or muffler flow is you need between 2.2 and 2.5 CFM per bhp measured at 25" of water pressure drop. In the chart below I've used the average of these which is 2.35 CFM per bhp.

Diameter I/D...Flow 20.3"...Flow 25".....Power
1 1/2"................220..............244..........105
1 3/4"................299..............332..........140
2 0/0"................390..............443..........185
2 1/4"................494..............548..........235
2 1/2"................610..............677..........285
2 3/4"................738..............819..........350
3 0/0"................878..............975..........415
3 1/4"...............1031............1044..........485
3 1/2"...............1196............1327..........565
3 3/4"...............1372............1523..........650
4 0/0"...............1562............1733..........735
4 1/4"...............1763............1956..........830

Example. You're designing a system for an 800 bhp V8. The power per bank is 400 bhp so the primary pipe should be 2" I/D. The secondary if it's a 4-2-1 system should be 2 1/2" and the collector should be 3". The muffler flow chart agrees that a 3" pipe will cope with 400 bhp on each bank. The final pipe size if both banks join into one should be 4 1/4"

Example. You're designing a system for a 200 bhp 4 cylinder engine. The primary should be 1 1/2" I/D. The secondary if it's a 4-2-1 system should be 25% bigger which is 1.875" or 1 7/8". The collector should be 50% bigger than the primary which is 2 1/4". The muffler flow chart agrees that a 2 1/4" system should cope with 200 bhp.

Dave

 

LOL! Will have the data as soon as I take this customers car to get re-dynoed. He went from a 3" Dynomax cat back to a bigger custom system.

 

This is an interesting way of putting together the data, but it kind of eliminates the tech. How about this instead:



I think primary sizing by CFM is a better starting point then theoretical max power output. Your data would suggest 1 5/8 ID tube header (roughly 1 3/4" OD) be good for up to a 520hp sbc. I dissagree, most 500hp applications would have an exhaust port flow and cam profile output that would deliver around 190cfm naturally aspirated. A 1 5/8" inside tube won't support that. I'd say a pressure drop as it would only support about 172cfm.


I've seen the 2.2 number used in the past. You can't translate CFM to power that easily though.


-- Joe

 

Good info, thanks Dave.

 

I just want to chime in and say there is some amazing info in this thread. It really helps me feel good that my exhaust plan is the correct way to go and won't lose much/any power. definitely gonna use those 2 posts for future exhaust excursions.

 

I picked up 2mph going from a 3" pipe to a 3.5" with a 400hp NA motor. I haven't proven it due to other variables, but it looks like I picked up over 4mph on the bottle.

3" pipe chokes the top end on a 400hp+ motor, unless it is a small ci one with a turbo or 2 (like an EVo or something).

 

2mph? That's a pretty good increase.

When I went from a ported TPI setup to a singleplane manifold I picked up 10mph. Amazing how restrictive even $1200 worth of TPI is.

-- Joe

 

Hehehehe. I forgot my own car. Anways installed a Mufflex 3.5" catback system to replace my 3" SLP one and at the same time installed a Meizere electric water pump. Picked something like 26rwhp. Same dyno and corrections. So say the water pump was worth 10 that leaves 15+ for the exhaust. I was making around 325rwhp at the time.

 

Very good info. Makes me realize again how much I don't know.

 

Okay there is some great info here thats good, but if you are running a 400-450 hp engine a 3" dual exhaust would be better than any y-pipe setup for several reasons.

BP(back pressure)

1. The BP on a dual is easier to account for and adjust accordingly.
2. Unless your going pure racing setup for the amount of horses shes putting out over 3" is overkill (especially money wise)
3. Y-pipe's have a flaw that in order to fix requires much more BP considerations to take into account = more money to fix

Dont get me wrong a y-pipe setup is not the end of the world, but when you force 2 seperate exhaust pipes into one (you dont think they just immediately start heading down the pipe holding hands) of course not there constantly pushing against each other causing a rippling effect, which restricts the flow, which slows down the flow, now this does dwindle off and eventually the are heading in one direction, but you still have the main slow down point at the y-pipe, which is why if you the most free flowing (just weld pipes from your block out the side of your fendors)...Just kidding, a true dual setup would be the best way

Now I know theres going to be complaints about what I said, but going back to the original question, No a dual setup will always beat a Y-pipe setup, and 3" is all you need for your HP

 

Yes but a y-pipe balances out the exhaust gasses and helps with scavenging. A y-pipe is like a REALLY POOR MANS h-pipe.

No offense, but I think you need to spend some more time reading. A "true dual" setup is not the end all. A dual exhaust setup with an x-pipe, h-pipe, or resonator properly placed is the ideal setup.. A y-pipe works well too, as long as the transition is propper. (i.e, using a flowmaster or hedman Y collector).


In theory..

-- Joe

 

I wouldnt say I need to reading, if you think a true dual setup does not have a x-pipe or h-pipe then you need more reading. (no offense)

Wyo-tech even agrees when building a car it is better to run a true dual setup to allow the car to breathe properly and maintain the correct BP.

 

You are 19 years old. You are younger than most cars I've owned/built

"True duals" do not have an x-pipe, because they are TRUE DUALS. No crossover.

Cool.

How many race cars have you built?

I've been doing this for a while.

-- Joe

 

I have built three race cars do far, 2 scambler class circletrack cars,

One 78 camaro drag car

 

Also lets not forget that dual 3" exhaust under a thirdgen is going to suck HARDCORE for ground clearance. Check out my post on my new exhaust system: https://www.thirdgen.org/forums/exha...0s-t-56-a.html

I went from SLP shorties and a Flowmaster 3" cat back system (no cat) to Hooker longtubes and Mufflex 4" cat back with the restrictive Spintech muffler and I picked up 38 rwhp, and I havent even tuned it yet.

Im running a Minirammed 383 making 475 flywheel hp. (untuned from old exhaust system)