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911tracker85's Avatar
 
Join Date: Feb 2009
Location: Park Hills, KY
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boost popping intake hoses

at Putnam Park this past weekend, and for the second time, I had the boost pressure pop off one of the intake rubber hoses. fortunately it was about 10 min before the end of the last session on Sun, so no big loss of track time.

first time this happened last year it 'blew' 1 1/2 days of track time.

in full disclosure, in both cases I had turned up the boost a bit. frist time from stock to around 12lb. this second time from 12 to 14lb.

so if you ever have your car start stuttering and die under throttle, first thing to check is all of the intake hoses on the pressure side of the intake.

my first was at the output side of the turbo. this time the hose to the ISV.

what is happening is the air is being sucked in after the AFM, so the fuel deliver never reacts when you give it throttle. just goes lean and dies. I was told sometime the car will start and idle, but die as soon as you touch the throttle. in both of my cases when cranking it would sputter but never start and idle.


first time took me quite a while to figure it out.

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Bob Cox
84 928S, Ruby Red linen/brown interior - preferred DD
87 924S resurrect and gut and another track car...
86 944 turbo my new DE/track car.
78 930 clone project car.
Old 05-01-2018, 06:42 AM
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In the Fires of Hell.....
 
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Been there, done that.....
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NASA/PCA Instructor: '88 951S - with LBE, Guru chips, 3Bar FPR, 1.3mm shimmed WG, 3120 lbs, 256 RWHP, 15 psig boost
1987 924S 944 SPEC racecar - '88 pistons/DME, short 5th
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Old 05-01-2018, 10:08 AM
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your average wrencher...
 
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Lol you oughta hear it when she pops off at 28lbs! It's brutal.
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1986 951 Garrett turbo, Rogue Tuned.
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Old 05-01-2018, 07:47 PM
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Did the same thing at Putnam last year in April coming down the front straight into turn 1. Not that fun with people behind you on the fastest part of the track. I had a pretty good idea thats what it was, so wasn't too worried. Mine came loose at the turbo to pipe connection. Are you using factory clamps? I upgraded to T-bolts a number of years ago and this was the first time I had a T-bolt connection come loose.
Old 05-04-2018, 01:05 PM
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probably need to get better hose clamps.

mine started coughing and sputtering between 7 & 8. made it to the pits but had to be towed from there to the trailer.

regarding turn 1. earlier that weekend was threshold braking into 1, downshifted, and came off the clutch too quick the revs did not get matched. caused the car to get totally loose. kept from spinning, but as I got control I realized I had lost so much speed I just drove into the grass. was not sure how close the traffic was behind me and did not want to try to save it and end up a road block between 1 & 2 and cause an issue.

Midohio in June.

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84 928S, Ruby Red linen/brown interior - preferred DD
87 924S resurrect and gut and another track car...
86 944 turbo my new DE/track car.
78 930 clone project car.
Old 05-04-2018, 01:16 PM
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you have a few options, All of which are upgrading your clamps

If you are using standard worm gear style clamps, get some T bolt clamps on there, they provide a larger and more even clamp load, 100 % necessary for silicon hoses, as they dont stick like rubber does to the pipe.

If you dont have beads welded or pressed into your IC pipes, do that,


Worst case scenario, you can pop for something like this, which will be $$$ but these will not blow off unless the clamp fails

Vanjen clamps. They use 2 O ring grooved weld fittings for the pipes, a sealing sleeve, and a clamp that physically prevents the assembly from moving past the point of sealing, plus they allow up to 12* of misalignment or so.

as a plus, they are super easy to remove, one push lock pin and the joint comes apart.


https://vibrantperformance.com/catalog/advanced_search_result.php?fc=POLISHEDHD&fcdesc=Po lished+HD+Clamps

https://www.youtube.com/watch?v=PDIjevlgN6k

Last edited by SDFla7Nose; 05-04-2018 at 11:56 PM..
Old 05-04-2018, 11:53 PM
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Just one other thing. Make sure your recirculating valve is functioning properly. Since this relieves pressure in intake tract when throttle plate closes it certainly can cause intake hose to come off.
Old 05-05-2018, 06:01 AM
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Quote:
Make sure your recirculating valve is functioning properly.
I suspect you meant the blow off valve?

it is newer but good idea to check that too.

in both cases the hose popping off followed a 2-3 lb increase in boost. so really suspecting I need to get better hose clamps and/or tighten them.
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Bob Cox
84 928S, Ruby Red linen/brown interior - preferred DD
87 924S resurrect and gut and another track car...
86 944 turbo my new DE/track car.
78 930 clone project car.
Old 05-07-2018, 06:20 AM
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Actually no I meant recirculating valve. On the 951 Porsche designed the valve to simply dump the waste charge air back to the intake tract for the compressor. This is an efficiency measure as the air is redirected to the turbo and not "wasted" to the atmosphere as it would be in a "blow off" setup.
Old 05-08-2018, 04:47 AM
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The factory recirculating valve is a bosch one made out of plastic. I am now running an aluminum one and some come with different springs. I am running 16 psi and have never had any issues like you describe.
Old 05-13-2018, 05:43 PM
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I am running an alum one I got from Lindsey Racing when building this car.

recirculating or blow off valve. a rose by any other name.... and mine also dumps back to the intake track. on the 930 I am building, will probably vent the blow off to the air.

this time it is the hose from the ISV up under the intake. but looks like I will be able to get to it without removing the intake ... I hope.

after a couple weeks of 'honey do' for our family to all come to our house for Mother's day, will get to fix the car tomorrow. Midohio in June.

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Bob Cox
84 928S, Ruby Red linen/brown interior - preferred DD
87 924S resurrect and gut and another track car...
86 944 turbo my new DE/track car.
78 930 clone project car.
Old 05-15-2018, 08:42 AM
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Nice colors, just missing the white
Is that the permanent state of your air filter or just off to show the banjo bolt ?
Sox
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Old 05-15-2018, 09:16 AM
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LOL... forgot the reason I took this was to show someone the location of that banjo.

no it usually has the cover on the air cleaner.
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Bob Cox
84 928S, Ruby Red linen/brown interior - preferred DD
87 924S resurrect and gut and another track car...
86 944 turbo my new DE/track car.
78 930 clone project car.
Old 05-16-2018, 07:18 AM
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I thought you had discovered a way of increasing the air flow

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"Little problems always come back and bring bigger friends with them".
1986 951"MADDOG" black with maroon interior
All stock with shimmed WG
Old 05-16-2018, 10:23 AM
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