BREAKING NEWS! Complete Exhaust Stack Re-Design

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TXFlyGuy

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Here is what we have learned...

There is a major loss of power, both torque, and horsepower, using the Titan short stack exhaust. This starts to occur at 3000 rpm and above. Hutter Performance was really scratching their heads on this one, and it is purely due to the design. Titan purposely blocked off part of the exhaust port in order to reduce the power output from the LS3.

After a long conversation with Trevor (Hutter Performance), and Ron Dalin, we have decided to fabricate an all new exhaust, with the correct port sizing to match the exhaust manifold. In addition, Trevor wants to increase the diameter of the pipes, and add just a little extension from the current length.

As the Titan exhaust is actually a but undersized, we feel the new design will actually improve the looks from a cosmetic standpoint.

And Trevor is certain that we can regain a good amount of the lost power from the LS3. Hutter will be making an all new stainless steel exhaust. And keeping it true to appearance for a P-51 look.

The increase in power will allow us to cruise at altitude at a reduced rpm setting, while still getting the power we desire. This will result in added engine longevity, quieter cockpit, and reduced fuel burn. If you want to go all out, and race your Mustang, having the high performance exhaust is what you will want. If you want to fly at slower rpm settings, and still have good power, the high performance exhaust is what you want.

Anyone currently flying a T-51 Mustang with an LS3 might want to look into this.
 
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BJC

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Darn, Tex, I read the first part of the thread title, and thought, “Tex flew the T-51.”


BJC
 

TXFlyGuy

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So why would they constrict the flow rather than optimize power output?
This header will flow much better, with larger diameter pipes, and with zero exhaust port blockage. The Titan header blocks off the ports.
We will know next week after they do another dyno run with this new exhaust.

It would appear that the original design was not properly engineered, according to Hutter Performance. Titan was under the impression that by blocking off the exhaust ports at the head, and restricting the pipe size, you could get more torque at low rpm. Hutter does not agree. And Dale Earnhardt won back-to-back championships running engines built by Hutter.
 

TXFlyGuy

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Found this...some good reading on exhaust design, and header pipe diameter:

Exhaust Design Comments:
The concept that maximum power is obtained by zero pressure in the exhaust is only partially true. There should be absolutely
no back-pressure from the collector rearward, but the diameter of the system beginning with the exhaust valve is a compromise. The highest efficiency for the system requires a minimum speed for good exhaust gas velocity to insure that
gas does not "back up" into the chamber during overlap at low engine speeds, and that the "suction" (negative pressure pulse) effect of a resonant (tuned length) and/or collector (overlapping exhaust pulses) system is optimized.

To predict what primary size will be best for a specific motor, you must know where you want the engine to develop peak torque. If the existing torque peak is at bit lower RPM than you prefer (typical in under-cammed or stock motors), it can be "bumped" a bit by increasing the primary diameter. If the torque peak is too high (motor is "peaky", with no range and poor recovery from
gear changes), the peak can be adjusted down by using a smaller pipe. A change of 1/8" in the primary diameter will raise or lower the peak torque RPM by 500 or so.

This factor slightly overlaps the effect of primary pipe length, but the pipe length generally will not change the peak torque or the RPM at which it occurs. A length change has the effect of improving the torque on only 1 side of the peak by "borrowing" it from the other side. A shorter pipe improves the torque after the peak (reduces it at lower RPM), preventing the curve from
flattening out so quickly as speed increases.

A longer pipe extends the torque curve backwards to improve the engine's flexibility, at the expense of after-peak torque. Less stall speed is required, and the motor will pull taller gears; this re-tunes a 4-speed motor for better operation with Torqueflite, etc.
For best effect, the gas speed in the primary tube at the peak torque RPM should be about 240 feet per second. The formula to calculate pipe size is:
Area of Primary Pipe = RPM ? Cylinder Size ? 88,200

This determines the pipe's cross-sectional area, from which we can calculate the ID. Typical exhaust pipes are 18ga. (wall thickness of .049"), so the OD will be .098" larger. From this we can construct a formula for an 8 cylinder motor, and factor in the 18ga. wall thickness:

Area of Primary Pipe = RPM ? Motor Size ? 705,600
Pipe ID2 = RPM ? Motor Size ? 705,600 ? .7854
Pipe ID2 = RPM ? Motor Size ? 554,177
ID = (RPM ? Motor Size ? 554,177).5
OD = (RPM ? Motor Size ? 554,177).5 + .098"

Remember that your peak torque RPM will always be lower than your peak HP
RPM. The separation between peak torque and peak power is roughly
proportionate to your range of useable power (wider is better). Be realistic in your
estimates and plans - peak torque @ 7000 RPM sounds good, but is almost certainly
beyond the breathing ability of even a professionally-built race motor, and if
true will make the car impossible to launch. Note that 1-1/2" pipe is large
enough for a 273" motor with max torque @ 4000 RPM. A 360" only needs 1-3/4"
for 4200 RPM. A 440" is fine @ 4500 RPM with 2" primaries.

If choosing pipes for a 4WD, van, towing, etc. keep the size small to
improve torque where you need it most - the lower RPM ranges, typically 2500-3500.
One exception where use of a larger pipe (than indicated by the above
formula) will help power is, of course, motors using nitrous oxide, supercharger
or turbocharger. In these cases, size the pipe for the expected peak torque,
not the motor size.

Another instance where a slightly larger pipe may help is where the
departure angle of the pipe from the flange is very sharp (typically downward). The
added cross-sectional area immediately after the flange apparently helps
reduce the restrictive effect of a small radius after the port. This partially
explains why some header models or brands work better than others with similar
dimensions.

As far as ability of an exhaust system to flow enough air for a given amount of horsepower without causing significant back pressure, this is from one of David Vizard's books:

1. For avoiding significant restriction from back pressure, the pipe should flow at least 2.2CFM per horsepower produced.

2. A straight pipe will flow ~115CFM per square inch of area (using inside diameter of the pipe)

Recommended Header Primary Tube Diameter:

Horsepower / Primary Tube Diameter
200-325 hp. - 1 1/2 in.
275-425 hp. - 1 5/8 in.
400-500 hp. - 1 3/4 in. or 1 7/8 in.
500-Plus hp. - 2.0 in. or larger

It would appear that Hutter Performance is right on the money with the choice of a 1.75" diameter header pipe.
 
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TXFlyGuy

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Just got the results in from Trevor. There is a substantial power gain, mostly above 3600 rpm. This would be a benefit to those with the 84 inch prop and the standard gearbox. Your max limit for rpm is over 5000. This would allow you to cruise at altitudes above 8000 feet, and get more power from your LS3. While easily staying at or below the 300 hp limit. The advantage of the smaller prop is you can turn it faster and the tips will remain subsonic.
The other big advantage will be in climb performance. This is a safety issue as you might want or need to climb through a cloud layer quickly in order to avoid icing. Or simply get on top above the weather.
Note: There is no such thing as too much climb Performance.

3800 rpm = +5 hp / +6 torque. 305hp / 421 lbs
4000 rpm = +16 hp / +20 torque. 336hp / 440 lbs
4200 rpm = +31 hp / +38 torque. 371hp / 463 lbs
4500 rpm = +42 hp / +49 torque. 412hp / 480 lbs
 
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TXFlyGuy

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The owners of LS376/495 engines are thrilled with this data. More power than we ever thought we would have.
This will really pay off at high cruise altitudes.
 

Voidhawk9

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Did you switch from the 376/480 to the 376/495 at some point? My impression was the 495 gained more power at the top, but sacrificed it lower down.
 

TXFlyGuy

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Did you switch from the 376/480 to the 376/495 at some point? My impression was the 495 gained more power at the top, but sacrificed it lower down.
No changes made, other than GM changed the nomenclature to LS376/495. The Hot Cam puts out more power than they first thought (or wanted anyone to know). We got 525 hp on the dyno.

The difference mainly is above 2800 rpm for the benefit of the Hot Cam. Perfect as our settings will not be below 3600 rpm most of the time. 4000 rpm for high speed cruise. That keeps the prop tips in the sweet-spot, at .65 Mach.

For those wondering about specific fuel flow, here is what we have right now:

29 inches manifold pressure / 4000 rpm = 336 hp / 28 gallons per hour fuel flow.

That is in line with what Holley stated, .5 lbs per hour, per hp.
 
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