Engine and Transmission Tech

Guys,

My TR7v8 project is getting close to bolting the engine into the car.
It is a B&B RangeRover 3.9L, with 9.35:1 pistons, 4L ported heads, a Woody Erson cam, Edelbrock carb and intake, and a set of Ted's headers. These headers end in a 2"ID collector.

I want to go with a two-into-one exhaust, as I plan on recessing the battery into the RH side of the trunk and a muffler there would prevent that. I plan on a resonator and a muffler in the system, to keep it to a muted roar. :)

I was wondering what was the collective wisdom was on pipe diameter for the single pipe portion of the exhaust. I've been told to keep it at 2" though out, go to 2.5", 3" and even 4". So, I'm a bit confused and am trying to figure out what will give me the best power across the entire rpm range.

Any suggestions?

Martin

The problem you will find witht he Rover heads and the 4-2-1 headers is the power dies off at 6200rpms and this is with dual exhaust. I have a single big bore rally exhaust I am going to use which is 2-1/8 inch OD (2 inch ID) from the headers going back to the rear muffler and coming out of the rear muffler is 2-7/8 inch OD (2-3/4 inch ID).









I will warn you that it is EXTREMELY loud! 100+dbs and most track will turn you away. You will need a middle muffler or glass pack to deaden the sound. Do you need the pipe diameters?



Edited 1 time(s). Last edit at 05/03/2010 10:05PM by WedgeWorks1.

I'd run a 2.25 inch or maybe a 2.5. You won't be able to fit much more than that. I did twin 2.25 on the last car that got a 4.9, and it worked out well. I'm doing a single 2.5 for the 4.0 turbo project. Mathematically, a single 3" pipe has more cross sectional area than does 2- 2" pipes. You will also encounter a problem sinking the battery in the rear, because the frame rails run right under the battery location. Maybe you can make a box out board of the rail, but it will be tight.

Here are some pics of my slightly used headers. A bit of surface rust I'm about to get blasted off, then some high temp silver paint and exhaust wrap, like in Mike's 3rd pic..



Each header starts with 1.5" primary pipes, into 1.75" secondaries, into a 2.5" collector, which then is reduced to 2". The headers came with 1.75" OD stub extensions that were swaged to fit onto the 2" outlets (they are somewhere in a box now).



My guess is they reduced it to 1.75" OD with the extension pipe to connect to a stock cat back exhaust.
What I don't understand is why they reduced the collector from 2.5" to 2".

I was also reading that the largest pipe shouldn't be bigger than 2.5" for the Rover engine, but I wasn't clear if that was for single or dual exhaust pipes.

I plan to make a Y-pipe similar to:



And use two 90's to link from the pass side to the drivers side.

So what do you think, should I make a Y-pipe with dual 2" in and 2.5" out, or cut the collectors back to the 2.5"OD and make a Y-pipe with 2.5" in and 3" out? Either way, I'm going to run a single exhaust out.

Re the battery box, I plan on cutting and making a box to sit outboard of the frame rail and as tight to the lower, outside panel as I can get. The panel already has rust holes, so I'd have to work on it anyhow. Need to leave as much room in the trunk as I can for the wife's luggage, you know........ !!

Martin



Edited 5 time(s). Last edit at 05/04/2010 12:26AM by bsa_m21.

Mike,

Your first, 3rd and 4th pics looks like a Rimmers 2-1 exhaust set up. Yes? How does it perform?

I believe the 2nd one is from a UK Rally car build I read about last year or so. Yes? Simply gorgeous fab work. Way beyond my skill levels. :(

Todd,

Sounds like you are suggesting I go 2" from the headers to a Y-pipe and then 2.5" the rest. Yes?

M.

Martin-The exhaust is Rimmers single big bore rally system. The y-pipe pisture is from another forum and that car turned out great! Perfromance is great but not the best. True dual with a balance pipe (H-Pipe) isthe way to go and a 4-1 header. What you have for headers is typical so make up for that on the rest of the exhaust side.

Yes. 2 into y into 2.5 the rest of the way. Anything larger than that and it gets tough to get the pipe over the axle. Had a 3" pancaked side exhaust on the race car once. Sounded great until I drove down the straight up against the wall and the sound reverberated back into the car. Scared the crap out of me the first time it was so loud. Needless to say, I didn't keep that exhaust for long.

Martin, there are many brands of compact/light weight, batteries now, "Braille", etc., to open-up some space options. I think well done, side pipes could be a consideration,(less resonances), under the car. No one has mentioned the benefits of "X" pipe ? Many warmed-up Rovers, can take advantage of 1 5/8" primary pipe,(also helps with "anti-reversionary step"), at head juncture.Good Luck, roverman.

You want the cross-sectional area of the single pipe to be at least
as large as that of the combined area of the two header outlets.
Area is equal to the radius squared times pi. With a radius equal
to one, the math is trivially easy. The combined area is equal to
approximately 6.28 square inches. For a single pipe, the required
diameter would be approximately 2.818 inch. The next largest standard
pipe size is 3" so you'll want to use a 3" diameter. Your muffler
should flow 2.2+ CFM per HP (the point at which there is a 1%
difference between mufflers and open pipes. A section of straight
pipe the length of a typical muffler flows around 115 CFM per square
inch at 1.5" Hg. The very best mufflers flow nearly as well as straight
pipe so use that as an upper limit. A 3" diameter is approximately
7.068 square inches. (7.068*115)/2.2 = 369.5 so a single 3" inlet
3" outlet muffler like a Magnaflow can support up to 370 HP before
becoming a restriction. There are a few manufacturers like Dynomax
that put there muffler's flow rating on the box.

David Vizard wrote a couple of good articles ("Exhaust Science Demystified"
Popular Hot Rodding, May 2005 and "No Loss Exhaust", Drag Race Monthly) in
which he presents simple design equations for header and muffler sizing.
I use his equations as starting points for Dynomation iterative simulations
so I wrote a little routine to calculate the parameters. The equations are
based what the exhaust port flows at your maximum exhaust valve lift:

OID = SQRT (Ex_CFM * 1.27/FD)
CDiam = 1.75 * OID

where:

OID = optimal internal diamter (inches)
Ex_CFM = exhaust port flow (CFM) at 28" H20
FD = flow density (around 80 CFM/square inch @ 28" H20)
CDiam = collector diameter (inches)

I have tested several sets of Buick 215 and 300 aluminum heads on a local
flow bench and ran the exhaust flow numbers through Vizard's equation:

Buick 215 unported 85 CFM (1.3125" exhaust valve)
Primary ID (inches) = 1.16
Collector ID (inches) = 2.03

Buick 300 unported 116 CFM (1.3125" exhaust valve)
Primary ID (inches) = 1.36
Collector ID (inches) = 2.38

Buick 215 home ported 129 CFM (1.48" exhaust valve)
Primary ID (inches) = 1.43
Collector ID (inches) = 2.50

Buick 300 pro ported 153 CFM (1.5" exhaust valve)
Primary ID (inches) = 1.56"
Collector ID (inches) = 2.73

The above CFM numbers are exhaust flow at 0.5" lift and the diameters are
ID's (internal diameters). You have to add your tubing thickness. Vizard's
rules reflect bank separated 4-into-1 headers on 90 degree V8's with dual
plane crankshafts. For most applications, primary lengths should fall
between 24 to 36 inches with shorter lengths favoring higher RPM. Likewise
collector length should fall between 12 and 20 inches (good for up to 8000
RPM). On engines like ours, longer collectors are generally better.
To not pose a serious restriction, mufflers should flow 2.2+ CFM per HP
(the point at which there is a 1% difference between mufflers and open
pipes). In my own limited experience, mufflers can have a big effect.
I dyno tested a 475 HP small block Ford V8 street motor (made peak power
at 5500 RPM) that lost 50 HP through the stock mufflers compared to open
headers with an 18" extension. Installing a pair of 3" inlet/outlet
Magnaflow mufflers, it got all but 1 or 2 HP of that back. Interestingly
enough, there was little difference in peak power on that engine between
headers with 1 3/4" and 2" diameter primaries but the smaller primary
headers (which also had longer collectors) made a bit better torque below
3000 RPM.

You may want to discuss this with Woody. I believe he runs a single
muffler to combat drone in his coupe.

Dan Jones

Woody is running the single bore exhaust from Rimmer that I have pictures of above with 1-3/4 primary tubes on the 4-2-1 headers.

Fantastic info. What a great list.

M.

I hereby nominate Dan as our resident, Professor. Thanks again Dan.

Outstanding information. I'm looking to see if there's any of this information that explains why the 4-2-1 headers seem to make more torque.

As a side note; 5.0HO Mustangs like my 86 GT came from the factory with dual exhaust that had different sized mufflers on them. That is to say that the left muffler was a different size than the right muffler. This was done to eliminate the drone from resonating mufflers. I had a tough time convincing my muffler shop that I wanted this same setup when I needed new exhaust. The SOB who ran the shop insisted that the mufflers wouldn't drone. I wasn't ready to take his word for it.

I pulled the following from the site of a firm that specializes in circle track exhaust systems:

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Header Design

The header has the greatest effect on the power band and ultimate power production of a non-turbo car. There are MANY factors that go into a properly designed header. One factor is the way you join the pipes together. The two possible configurations for a V8 cylinder are per side, 4-2-1 and 4-1. Basically a 4-2-1 design joins two primaries together into a secondary pipe, and then joins the two secondaries together. A 4-1 design joins all four at the same time. Both have advantages, but the 4-1 design allows the gas pulses to interact in a way that makes better torque.

Primary Pipe Diameter
Smaller diameters keep velocity higher with smaller exhaust volumes. The more exhaust you are trying to push out the larger the primaries need be. The volume of gasses that you need to flow depends on displacement, RPM, and load. The more displacement you have per cylinder the larger the primaries need to be. The same is true for RPM, the more RPM you will be turning, the larger diameter you will need, as you will be pushing out a lot of volume over time. Higher loads on the motor also create a higher volume of gasses. As with every other variable there is a balance to be kept. If you are not flowing enough gasses for the pipe diameter (pipes are too big) the gasses will loose their velocity If the gasses get too slow you loose torque, and if you go way to large you can even loose top end power as well. Get it right and you get the best of both worlds, good low end torque and good top end power.

Primary Pipe Length
This has a huge effect on the powerband. Generally longer primaries make better low end while shorter lengths move the powerband up in the RPM range. The length affects the powerband by timing when pressure waves reach the cylinder. To put it as simply as possible, the pressure wave comes out of the cylinder and travels down the primary pipe until it hits the collector. There it gets reflected back down the primary pipe as a negative wave. When it hits the cylinder it helps pull more exhaust gasses out of the cylinder and pull more air in to the cylinder. Since power is made by mixing air and fuel and then exploding it, more air and fuel make more power. This effect is known as scavenging and is one of the main goals of a well designed header. Equal length primaries help each exhaust pulse pull the one behind it, helping to create more suction. Instead of just relying on the pressure of the exhaust stroke of the motor to get the spent gasses out, the suction of the pulse in front of it helps pull it out. One factor some header designers forget when trying to design an equal length header is that the length of the exhaust port is effectively part of the header and needs to be accounted for.

Collector Type
The collector merges all of the primary pipes together. There are designs ranging from cheap and simple to incredibly complex and costly. If you just joined the pipes in the simplest possible way you would have something that resembled the picture on the right.

The dead space in the middle of all of the pipes would cause a lot of turbulence and hinder flow. Eliminating the dead space is the main advantage of the merge collector. This is a more cost effective way to make the pipes join smoothly. Not quite as elegant as the merge collector, but still very good.

The bad daddy of all collectors is the merge collector. These pictures are from Burns Stainless and are some of the finest collectors you can buy.



Collector Length
The length of the collector also plays a role in determining the powerband of the motor. Generally the longer the collector the more the powerband is shifted up. You also want enough length in the collector to smoothly join the gasses coming from the primary pipes. If the junction is too abrupt they do not interact very well causing turbulence, and again hindering flow. This is also another area of a lot of testing. The volume of the collector has a fairly big effect on the powerband of the motor.

Collector Width
The width of the collector helps control how well the exhaust pulses interact with each other. Make it too big and one pulse cannot help pull the next very well and the gasses can stagnate hurting flow. Make it too small and you hinder flow by causing too much backpressure. Yet another area to test.

Taper Angles
Basically you want the least amount of abrupt changes as possible. This mostly applies to the collector where it necks down to the diameter the exhaust will be. You do not want an abrupt angle as it will hinder flow.

Notes
The entries into the primary pipes from the head also have to be as close to the diameter of the exhaust ports as possible. This is so that you do not get yet another area for turbulence to get in the way of things. Protrusions into the gas flow should be avoided here most of all, as they have a much larger effect than in any other point in the system. According to many experts that do not play the marketing game, the stepped header designs are an attempt to cure other problems inherent in the design. The steps also add complexity and cost.
The lay-out of the car dictates a lot of how the header is made.

Remember, you will only flow as well as the greatest restriction. If you have a poor cat or muffler design then it will choke the flow no matter how good the rest of the system is designed. Fortunately straight through mufflers and newer high flow cats flow very well. Having a cat is not only good for the environment, but we have seen very little power difference in levels in excess of over 350 h.p. Why be dirty when you can make just as much power while keeping tree hugging hippies happy? Also, a cat tends to quiet things down a little.

Pipe diameter does have an effect on flow rates as well, but again it is not the major factor in most cases.
o 2.5" may flow enough for 300-350 h.p. without being a restriction.
o 3" is usually capable of flowing 500-600 h.p. before becoming a restriction.
This is assuming that you have designed the rest of the system up to par.

Unless you are making over 500-600 h.p. anything over 3" is a case of diminishing returns and in most cases has no advantage. There is more to gain going from 2.5" up to 3" than there is going from 3" to 3.5". A 3" system will not loose torque compared to a 2.5" system if designed properly. In fact if designed properly 3" may be capable of making better low end torque than 2.5".

The only reason to reduce the size towards the end of the pipe is for packaging, cost, and noise reasons. Having smaller pipe towards the end has less effect that having smaller piping at the beginning. In other words a system that has 3" pipe for the majority, and necks down to 2.5" at the end will flow enough for more power than a complete 2.5" system. The further downstream you neck down the exhaust the better……..if you decide to neck it down.

-----------------------------------------------

Martin



Edited 1 time(s). Last edit at 05/05/2010 09:11AM by bsa_m21.

On Dan's calculations, it's interesting to see that the calculated primary pipe size is close to the size of the exhaust valve, and smaller than you would guess.

I wonder if try-y's work better because they allow a longer primary length in a smaller package. With a 4-1 collector, you would have four pipes that are 1.625" each, or a square package of 3.25" x 3.25" at the collector. Kinda bulky. With a 4-2-1, you'd get two 2" pipes, or a 2" x 4" package at the final collector. That would be easier to fit under the chassis, so you could go longer without having clearance problems.



Edited 1 time(s). Last edit at 05/05/2010 10:14PM by pcmenten.