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F350Lawman's Avatar
 
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Overboost

.8 spring w/ BB headers and Tial 46mm,w/ Zork tube.

With the below listed mods, the most recent being the B6 intercooler, fuel solenoid and Zork, I am overboosting in 3rd and even 4th. I am sure 2nd will be even easier to overboost I just haven't rung it out in 2nd recently. It is also a factor of the weather, when it's cold it happens easy.

Yesterday (25F), 4th gear WOT it overboosted at about 115. Later when it warmed up (35F) at about 120 or so. Now I am glad I am getting full boost and the car is pulling well....but it is causing me to short shift or run one gear higher so I don't overboost.

I am thinking of going with a softer spring and installing an EBC set right at 1 bar....any thoughts. By the way AFRs are good (safety wise) IMO. I run 13.5 -14.00 at a nice speedy highway cruise and drop into mid-high 11's real quick under full boost.
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1987 930 - K27 7200 / DAS Full Cage / Blownsix Intercooler / BB Headers / Zork Tube / Tial 46mm / Adjustable WUR / RPM Activated Solenoid / Open Element Air Intake / Smart Racing 27mm Sways / 24 and 33mm Torsion Bars / Adj. Spring Plates / Wevo Strut Brace / Monoballs / Tow Hooks / Oil Cooler Scoop / Brey Krauss Harness Truss / Race Seats / XD-16 AFR Guage/ 17" Kodiak Racing Whees and Nitto NT-01 255/315s
Old 03-31-2008, 07:17 AM
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There was problems in the past with the header waste gate circuit being too small. I believe it was on GHL headers. Could this be it?
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Old 03-31-2008, 07:59 AM
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Turbo Hooligan
 
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I have the old GHL headers, I used to overboost all the time in 3rd and 4th. modified my headers with a bigger wastegate pipe and twin tial 46's and no more problems.
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Old 03-31-2008, 09:44 AM
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I don't think B&B has that issue, but I could be wrong. however, it does seem like something isn't reacting quick enough to avoid a spike that shuts me down for an instant. I think with the Zork/bigger intercooler and maybe junking the air box , I am spoooling much easier so that gate may not dump in time to keep me below the threshold. Either that or something is amiss in the system.

When we added the B6 intercooler We got rid of the stock valve and replaced it with the included Forge blow-off unit, we also change some fittings and tubing so who knows? The overboost swith is now right on the cooler instead of on the housing that contains the blow off valve on the original Porsche setup. I will get my mechanic to test it. The car is fine to drive for now unless it's cold and you get crazy...hopefully it will warm up
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1987 930 - K27 7200 / DAS Full Cage / Blownsix Intercooler / BB Headers / Zork Tube / Tial 46mm / Adjustable WUR / RPM Activated Solenoid / Open Element Air Intake / Smart Racing 27mm Sways / 24 and 33mm Torsion Bars / Adj. Spring Plates / Wevo Strut Brace / Monoballs / Tow Hooks / Oil Cooler Scoop / Brey Krauss Harness Truss / Race Seats / XD-16 AFR Guage/ 17" Kodiak Racing Whees and Nitto NT-01 255/315s

Last edited by F350Lawman; 03-31-2008 at 11:24 AM..
Old 03-31-2008, 11:17 AM
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Did you confirm the over-boost switch works by comparing it to what the readin gis on the boost gage when it kicks in?
Are you using the clock VDO boost gage or the POS tach gage to monitor boost levels?
Make sure the wastegate hose to the TIAL unit is securely mounted and not leaking.
The vent to atmosphere for the TIAL unit is not blocked?
Try to check simple things first before changing out parts.
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1979 930 Turbo....3.4L, 7.5to1 comp, SC cams, B&B intercooler, Snow Perf water/meth injection, Rarlyl8 headers, Garret GTX turbo, 36mm ported intakes, Innovate Auxbox/LM-1, custom Manually Adjustable wastegate housing (0.8-1.1bar),--running 0.7bar max
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Old 03-31-2008, 12:23 PM
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OK,

Help a new 930 owner out here. All this talk of overboost has me concerned I am going to grenade a really solid running motor.

I drove my 3.2 hard. I would hit the rev limiter with abandon.

Just got a 930. It has two boost guages. One is in the tach, standard equipment. The other is in the traditional clock slot. Seller said it came of of a 935? Anyhow, it has a tattletale and knurled key to reset the tattletale.

When I want some thrills, I get rolling in 1st and hit the boost . I let her rip up to about 7,200 RPM at times cuz the high revs come on so fast in low gears, then a quick shift to 2nd.

When I look at the tattletale, it shows 1.2 - 1.5 boost.

My question ..... is that just inertia from the needle or am I REALLY pumping that much into the beast?

Is there a definitive way to tell if all my checks and controls are in place to keep my money in my wallet and not at my wrench?
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Old 03-31-2008, 01:25 PM
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switch the boost reference for the waste gate to the turbo side of the intercooler- it reacts quicker that way. This may solve the problem- but I think you may have normal "gatecreep", which by the way with B&B's is still a problem. The real problem with the B&B headers along with the rest of the bolt on stuff is not only the small diameter of the waste gate tube, but also the length of it. If you want to really solve the problem, try getting a Tial V-60 or try twin 44 mms on either side. By the way, the v-band 44 mm wastegate does flow more than the F46 series that we use. I think the only reason Tial still makes them is because they are a direct fit for porsche headers. This shouldnt happen with a K-27, but it dosent supprise me- My PT-67 T-4 did the same thing your talking about untill I moved the wastegate under the turbo flange.
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Old 03-31-2008, 01:34 PM
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I am using the POS tach/boost gauge combo. It is due for replacement as it just stopped working a week or 2 ago. It would pin the needle when it worked though. Actually all these dash gauges need to go out and be recalibrated/ fixed. Since the car is hardly stock, I may go aftermarket anyway.

So will the EBC set on a higher number and a soft spring help, if in fact this is just s symptom of the BB / Tial / Zork combo??? I can use a new guage so the EBC w/ readout would serve 2 purposes.
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1987 930 - K27 7200 / DAS Full Cage / Blownsix Intercooler / BB Headers / Zork Tube / Tial 46mm / Adjustable WUR / RPM Activated Solenoid / Open Element Air Intake / Smart Racing 27mm Sways / 24 and 33mm Torsion Bars / Adj. Spring Plates / Wevo Strut Brace / Monoballs / Tow Hooks / Oil Cooler Scoop / Brey Krauss Harness Truss / Race Seats / XD-16 AFR Guage/ 17" Kodiak Racing Whees and Nitto NT-01 255/315s
Old 03-31-2008, 01:58 PM
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I'm running BB headers/Tial 46mm with .6 spring /3.5" open exhaust/ K27HF2/ with Motec ECU controlling boost. FWIW, I can run as low as .7 bar. Mine will over shoot boost by about .05 bar for a second or so until the EBC valve gets control (I'm not much of controls guy, so I can't figure out all the EBC valve settings in the Motec ECU )
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Old 03-31-2008, 02:53 PM
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Even if it is just a momentary boost spike cutting off the fuel, it's very abrubt, causes me to lift, I loose all momentum and most importantly.... it kills the fun ;(
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1987 930 - K27 7200 / DAS Full Cage / Blownsix Intercooler / BB Headers / Zork Tube / Tial 46mm / Adjustable WUR / RPM Activated Solenoid / Open Element Air Intake / Smart Racing 27mm Sways / 24 and 33mm Torsion Bars / Adj. Spring Plates / Wevo Strut Brace / Monoballs / Tow Hooks / Oil Cooler Scoop / Brey Krauss Harness Truss / Race Seats / XD-16 AFR Guage/ 17" Kodiak Racing Whees and Nitto NT-01 255/315s
Old 03-31-2008, 07:54 PM
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Quote:
Originally Posted by F350Lawman View Post
Even if it is just a momentary boost spike cutting off the fuel, it's very abrubt, causes me to lift, I loose all momentum and most importantly.... it kills the fun ;(
If you're seeing fuel cutoff, there's no doubt that you're over 1 bar - prolly closer to 1.2 bar at cutoff. Sounds like boost creep since you're hitting the cutoff in higher gears. Overboost happens in 1st/2nd (maybe 2nd) where fast reving motor/turbo produce boost faster than the wastegate can react. Generally, 1st/2nd gear and high rpms is where I've seen the cutoff kick in.

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Old 04-01-2008, 04:31 AM
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+1 on the B&B overboosting.
my .8 bar spring in a Tial routinely hits 1 bar when I wring it out.

Bill K
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Old 04-01-2008, 11:38 AM
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I have had some overboost issues as well.

On mine the follwing is what I checked:
-made sure the connection to overboost switch was good.
-replaced the wg line (this ended up being the problem, the old one had a crack in it, which was just enought to delay the wg from opening).

Hope this helps,

Bill
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Old 04-01-2008, 11:47 AM
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