Variable H pipe?
Thread Starter
Race Director
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From: Camp Verde AZ
C1 of Year Finalist (performance mods) 2019
2017 C1 of Year Finalist
Variable H pipe?
Looking at the two RW dyno charts below, you can see the first one with no H pipe and the second one with H pipe added, no other changes.
The H pipe gained me a ton of torque below 3000 RPM and lost me 30 ft-lb between 3000 and 4000 RPM and also over 5500 RPM.
I was thinking about getting a cutout valve, like Quick Time Performance makes, and adapting it into the middle of my H pipe, so the H pipe can be turned on or off., them using an extra output on my EFI ECU to activate/deactivate the valve starting about 2800 RPM, thus closing the H pipe over 3000 RPM, giving me both my increased low end torque when teh valve is open/H pipe operational and restoring the midrange and top end torque with the H pipe closed.
Anybody know of any other exhaust pipe valves that may work?
Thanks,
Doug
The H pipe gained me a ton of torque below 3000 RPM and lost me 30 ft-lb between 3000 and 4000 RPM and also over 5500 RPM.
I was thinking about getting a cutout valve, like Quick Time Performance makes, and adapting it into the middle of my H pipe, so the H pipe can be turned on or off., them using an extra output on my EFI ECU to activate/deactivate the valve starting about 2800 RPM, thus closing the H pipe over 3000 RPM, giving me both my increased low end torque when teh valve is open/H pipe operational and restoring the midrange and top end torque with the H pipe closed.
Anybody know of any other exhaust pipe valves that may work?
Thanks,
Doug
Team Owner
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From: Beach & High Desert Southern California
A vital consideration is how fast the valve actuator operates? Will the expected relatively slow actuation speed only benefit cruise operation, or will it be fast enough to react before the end of a WOT pass down the quarter mile?
The concern is much like issues I had when I ran an Old's switch pitch T400 in my GTO. The torque converter slip varied from 4% with a 1600 rpm stall (on the tight end) to 12% and a 3200 rpm stall (on the loose end). The full pitch change took about ten seconds, too long for actuation in 3rd gear. I ended up using a second brake light switch to power the solenoid for the loose pitch, a switch that held the solenoid during staging and then released to allow the TC to switch to cruise pitch as I barreled down the track. I took a few more seconds than normal staging, and I gained a reputation for being the last to trip the second staging light.
It worked well, very well with a N2O trigger off a second trans kick down switch on the throttle linkage, but it was not consistent enough for serious bracket racing (what I was into at the time). I could cruise and get 18 mpg (with 3.73 gears), and still run 14 second ET's on street tires with the 400 (significantly under 13-second ET's with the N2O).
How fast do you need (or want) the valve to close?
The concern is much like issues I had when I ran an Old's switch pitch T400 in my GTO. The torque converter slip varied from 4% with a 1600 rpm stall (on the tight end) to 12% and a 3200 rpm stall (on the loose end). The full pitch change took about ten seconds, too long for actuation in 3rd gear. I ended up using a second brake light switch to power the solenoid for the loose pitch, a switch that held the solenoid during staging and then released to allow the TC to switch to cruise pitch as I barreled down the track. I took a few more seconds than normal staging, and I gained a reputation for being the last to trip the second staging light.
It worked well, very well with a N2O trigger off a second trans kick down switch on the throttle linkage, but it was not consistent enough for serious bracket racing (what I was into at the time). I could cruise and get 18 mpg (with 3.73 gears), and still run 14 second ET's on street tires with the 400 (significantly under 13-second ET's with the N2O).
How fast do you need (or want) the valve to close?
Thread Starter
Race Director
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From: Camp Verde AZ
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2017 C1 of Year Finalist
Valve should close in 1/4 second or so.
I suspect the motorized gear drive ones are slower, i will contact manufacturers for info.
I can always build a simple valve with a couple bushings welded to the pipe, a shaft and a throttle plate,and use a lever actuator and put a solenoid on it. It doesn't heve to be absolutely air tight as exhaust will be on both sides, it just needs to shut off 95% or so of cross flow.
The above is probably the simplest for install,as I already have a V-band clamp removable H pipe,and adding a some bearing bushings at one end for the cross shaft wouldn't change any dimensions or require a bunch of exhaust welding. (plate would be at one end of the H pipe to allow access to install the throttle plate, I do not think a larger dead area on one side of the pipe vs the other, when the plate is closed, will make a difference between one bank of cylinders vs the other bank, as we are taking about 3" on one side and 12" on the other)
Doug
I suspect the motorized gear drive ones are slower, i will contact manufacturers for info.
I can always build a simple valve with a couple bushings welded to the pipe, a shaft and a throttle plate,and use a lever actuator and put a solenoid on it. It doesn't heve to be absolutely air tight as exhaust will be on both sides, it just needs to shut off 95% or so of cross flow.
The above is probably the simplest for install,as I already have a V-band clamp removable H pipe,and adding a some bearing bushings at one end for the cross shaft wouldn't change any dimensions or require a bunch of exhaust welding. (plate would be at one end of the H pipe to allow access to install the throttle plate, I do not think a larger dead area on one side of the pipe vs the other, when the plate is closed, will make a difference between one bank of cylinders vs the other bank, as we are taking about 3" on one side and 12" on the other)
Doug
Le Mans Master
Joined: Oct 2000
Posts: 8,897
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From: Santa Ana CA
I was thinking about getting a cutout valve, like Quick Time Performance makes, and adapting it into the middle of my H pipe, so the H pipe can be turned on or off., them using an extra output on my EFI ECU to activate/deactivate the valve starting about 2800 RPM, thus closing the H pipe over 3000 RPM, giving me both my increased low end torque when teh valve is open/H pipe operational and restoring the midrange and top end torque with the H pipe closed.
Thanks,
Doug
If you were to "plug" the H-pipe "in the middle," would it really give back this hp?
For all we know, perhaps the hp loss is not due to the intermixing of L/R gas, but from the turbulance at the intersection of the "H." Adding a "restrictor" at the center of the H-pipe does little/nothing to alleviate these turbulances so may not give the "payout" you are hoping for.
Pro
Joined: Oct 2001
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If you were to "plug" the H-pipe "in the middle," would it really give back this hp?
For all we know, perhaps the hp loss is not due to the intermixing of L/R gas, but from the turbulance at the intersection of the "H." Adding a "restrictor" at the center of the H-pipe does little/nothing to alleviate these turbulances so may not give the "payout" you are hoping for.
For all we know, perhaps the hp loss is not due to the intermixing of L/R gas, but from the turbulance at the intersection of the "H." Adding a "restrictor" at the center of the H-pipe does little/nothing to alleviate these turbulances so may not give the "payout" you are hoping for.
Thread Starter
Race Director
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From: Camp Verde AZ
C1 of Year Finalist (performance mods) 2019
2017 C1 of Year Finalist
You can't do an X pipe on a C1 (sorry, Tom), the frame is in the way.
You actually don't get that much turbulence from a plugged side passage, at least in process plant piping.
If turbulance was an issue, I would think that the 4000-5000 RPM range would be lower as well with the H pipe, instead it is the same as no H pipe.
You don't actually get gas intermix from left to right with an H pipe, instead, you get pulse pressure alleviation, scavanging and reversion effects, most of which is not really understoood by about anybody, even me.
Doug
You actually don't get that much turbulence from a plugged side passage, at least in process plant piping.
If turbulance was an issue, I would think that the 4000-5000 RPM range would be lower as well with the H pipe, instead it is the same as no H pipe.
You don't actually get gas intermix from left to right with an H pipe, instead, you get pulse pressure alleviation, scavanging and reversion effects, most of which is not really understoood by about anybody, even me.
Doug
Last edited by AZDoug; Apr 27, 2009 at 01:56 AM.
Racer
Joined: Nov 2005
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From: LIFE IS GOOD Along the Strand New Jersey
The position of the H or X crossover is important. Think of the exaust gasses as a wave on the ocean, where the peaks of the waves are, are the pressure points. Now at different RPM's the waves will be closer together at the higher RPM's than the lower RPM's.
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Brett Foote
Team Owner
Joined: Nov 2005
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From: Beach & High Desert Southern California
Valve should close in 1/4 second or so.
I suspect the motorized gear drive ones are slower, i will contact manufacturers for info.
I can always build a simple valve with a couple bushings welded to the pipe, a shaft and a throttle plate,and use a lever actuator and put a solenoid on it. It doesn't heve to be absolutely air tight as exhaust will be on both sides, it just needs to shut off 95% or so of cross flow.
The above is probably the simplest for install,as I already have a V-band clamp removable H pipe,and adding a some bearing bushings at one end for the cross shaft wouldn't change any dimensions or require a bunch of exhaust welding. (plate would be at one end of the H pipe to allow access to install the throttle plate, I do not think a larger dead area on one side of the pipe vs the other, when the plate is closed, will make a difference between one bank of cylinders vs the other bank, as we are taking about 3" on one side and 12" on the other)
Doug
I suspect the motorized gear drive ones are slower, i will contact manufacturers for info.
I can always build a simple valve with a couple bushings welded to the pipe, a shaft and a throttle plate,and use a lever actuator and put a solenoid on it. It doesn't heve to be absolutely air tight as exhaust will be on both sides, it just needs to shut off 95% or so of cross flow.
The above is probably the simplest for install,as I already have a V-band clamp removable H pipe,and adding a some bearing bushings at one end for the cross shaft wouldn't change any dimensions or require a bunch of exhaust welding. (plate would be at one end of the H pipe to allow access to install the throttle plate, I do not think a larger dead area on one side of the pipe vs the other, when the plate is closed, will make a difference between one bank of cylinders vs the other bank, as we are taking about 3" on one side and 12" on the other)
Doug
The actuator decision will end up much like the H-pipe placement, a compromise, what will work will fit the valve or damper (it's all about logistics and working with what's available).
The project sounds fun.
Melting Slicks
Joined: May 2007
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From: cooper city florida
Where would the best place be,close to motor,or closer to the mufflers? It seems like I remember reading somewhere that the closer to the mufflers,the better. I installed mine on my C2 one foot to the rear of the cross member,but I could of gone back much farther. Thanks for posting Doug. Very interesting,and its the first dyno documentation I've seen on H pipes. I have seen a couple of dyno results on X pipes, and they seem to prove increased power through the entire rpm range.
Le Mans Master
Joined: Oct 2000
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From: Santa Ana CA
Well I wouldn't go that far.
Actually, based on my dyno numbers (I have an H-pipe), I find it hard to believe that you loose a bunch of hp in the range mentioned. Maybe it is the placement of the crossover tube, it's size, the exhaust piping size, or ???
I run headers, mandral-bent 2.5" exhaust tubes (including the tips), and a 2" H-pipe crossover. My H-pipe:
And my dyno pulls. Note how smooth they are and there are no spurious humps or drops in the ranges noted.
Last edited by toddalin; Apr 27, 2009 at 01:40 PM.
Thread Starter
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From: Camp Verde AZ
C1 of Year Finalist (performance mods) 2019
2017 C1 of Year Finalist
The reason your curves are smooth is you have an analog fuel delivery system and an analog distributor, and you can't tune them to take advantage of every engine nuance, you are giving up power, somewhere, in the RPM range of your engine. If I stuck a carb back on my motor,and also a centrifugal distrib, it would have a nice smooth curve also, probably peaking out at about 400-415 ft-lbs
Now, with that H pipe, even though it lost some power from 3-4K RPM, it flattened the torque curve to about as flat as I have ever seen, as in a 90% torque curve from a little over 1500 RPM all the way to about 5600 RPM, on a 9.5:1 CR motor
Without the H pipe, its 90% torque curve was about 2800-5600 RPM.
Doug
Now, with that H pipe, even though it lost some power from 3-4K RPM, it flattened the torque curve to about as flat as I have ever seen, as in a 90% torque curve from a little over 1500 RPM all the way to about 5600 RPM, on a 9.5:1 CR motor
Without the H pipe, its 90% torque curve was about 2800-5600 RPM.
Doug
Last edited by AZDoug; Apr 27, 2009 at 01:16 PM.
