Downpipe Bracing - What Works and What Doesn't?
12-06-2011, 11:37 PM
#41
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My current system that has worked for a number of years now. Diving board support off the motor mount to the turbine outlet. This is very similar to what Mazda does on every B6/BP OEM factory install.
1” wide band clamp holding the downpipe to the transmission.
The two failures I have had.
1) Bell housing bolts holding the transmission bracket came out. Forgot to tighten them after a transmission swap. One track session later and the nuts holding the downpipe flange to the turbine outlet were loose and two of
the studs broke off.
2) The single bolt connecting the diving board to the to the turbine outlet flange broke off once. A few sessions later and the manifold became cracked near the turbo flange. Also the first diving board I made out of mild steel and it cracked. current one is made of 4130 plate and hasn't cracked.
I have since added a 1” long spacer to the single bolt on the diving board. It gives the bolt a longer length and ability to stretch some without yielding and it hasn’t snapped since. Using 10mm Inconel studs with Nord locks seems to have almost cured the turbine flange to header problems as long as my two other supports on the downpipe stay functional.
My prior experience with Using U-bolts around the downpipe to secure it were not good. A U-bolt doesn’t have enough bearing surface on the pipe and you can’t keep it securely tight without it crushing the tube after some heat cycles it loosens up as it crushes the pipe.
Bob
1” wide band clamp holding the downpipe to the transmission.
The two failures I have had.
1) Bell housing bolts holding the transmission bracket came out. Forgot to tighten them after a transmission swap. One track session later and the nuts holding the downpipe flange to the turbine outlet were loose and two of
the studs broke off.
2) The single bolt connecting the diving board to the to the turbine outlet flange broke off once. A few sessions later and the manifold became cracked near the turbo flange. Also the first diving board I made out of mild steel and it cracked. current one is made of 4130 plate and hasn't cracked.
I have since added a 1” long spacer to the single bolt on the diving board. It gives the bolt a longer length and ability to stretch some without yielding and it hasn’t snapped since. Using 10mm Inconel studs with Nord locks seems to have almost cured the turbine flange to header problems as long as my two other supports on the downpipe stay functional.
My prior experience with Using U-bolts around the downpipe to secure it were not good. A U-bolt doesn’t have enough bearing surface on the pipe and you can’t keep it securely tight without it crushing the tube after some heat cycles it loosens up as it crushes the pipe.
Bob
I would also like to add a "diving board", but I struggle with the same issue as hustler - how does one mount a diving board to a v-band housing? Using the CHRA bolts, given the problems hustler had, seems like a poor choice. But the diving board concept seems like a logical idea - its always good to mimic OEM setups! And I agree with JKav about the changing the natural frequency of the system with a solid brace versus a crane.
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04-01-2013, 12:53 PM
#45
I keep seeing these and I know I'll be pulling at least 1.5G constant with the hoosiers on, and just thinking about the amount of force on the exhaust where it mounts to the engine. Do we know how much the PPF can twist? I mean, what if we take the trans brace and combine it with the husterl brace, basically hard mount the exhaust to the PPF on both ends of the PPF. Then we wont get the folcrum effect that bundy is legitimately concerned with, and wont get significantly more NHV. I dont see a downside here.
I want to know what bundy used as his wide strap clamp. Shaft collars were looking like a good idea, but they're 60 bucks a piece for 1" wide steel or 7/8" wide 304 stainless. And the 5 dolla exhaust strap clamps on ebay only have 1 bolt and thats not gonna fly for a solid mount.
I want to know what bundy used as his wide strap clamp. Shaft collars were looking like a good idea, but they're 60 bucks a piece for 1" wide steel or 7/8" wide 304 stainless. And the 5 dolla exhaust strap clamps on ebay only have 1 bolt and thats not gonna fly for a solid mount.
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04-01-2013, 02:19 PM
#49
Because the engine, tranny, PPF, and diff all move relatively together with some flexing in the PPF (I have no idea how much though, could be completely minor). Assuming the PPF doesnt flex much, hard mounting the exhaust to the front and back of the PPF would basically eliminate any movement of the exhaust with respect to the engine. IE the exhaust would exert minimal force on the turbo manifold and related bits.
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04-01-2013, 03:05 PM
#50
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Because the engine, tranny, PPF, and diff all move relatively together with some flexing in the PPF (I have no idea how much though, could be completely minor). Assuming the PPF doesnt flex much, hard mounting the exhaust to the front and back of the PPF would basically eliminate any movement of the exhaust with respect to the engine. IE the exhaust would exert minimal force on the turbo manifold and related bits.
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04-02-2013, 12:39 PM
#51
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I'm thinking getting the FM brace and welding a thin ban of SS around the down pipe effective increase the pipe thickness. I'll make a flexable test pipe for track days.
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04-02-2013, 06:50 PM
#54
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I welded a tab onto the rear muffler that bolts to one of the rear towhook bolts using an OEM (from a ford falcon intercooler) rubber bolt thing. Its a cylinder of runner with threads each end constructed the same way an OEM miata engine mount is.
The exhaust cannot swing left and right more than 1mm at the rear btu can twist along with the engine, its braced on the DP and has a flex at the start of the exhaust.
The downpipe brace Ive done will probably fatigue and snap off you really need the full circle exhaust clamp style brace.
Dann
The exhaust cannot swing left and right more than 1mm at the rear btu can twist along with the engine, its braced on the DP and has a flex at the start of the exhaust.
The downpipe brace Ive done will probably fatigue and snap off you really need the full circle exhaust clamp style brace.
Dann
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06-12-2015, 12:06 AM
#59
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Exhaust brace setup. Seems to work ok as tested by unbolting both Tial V-Bands and having it keep things stable. Time will tell.<br />
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<br />I would make some sort of support to hold that clamp, instead of a single bolt.
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