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Wastegate Pops w. Flame at High RPM Shift?

I took a couple of "parade" laps at a PCA event a couple weeks ago. I [and all the fans in turn one] noticed that my car consistantly popped and blew a good sized flame [2 feet] out of the wastegate at shift from 2nd to 3rd. This occured 5/5 times as I rounded this corner under acceleration... Usually at 5.5k RPM shift...

I have a digital AFR meter and run 10.5 AFRs under boost. I use an Andial fuel enrichement dial and am locked in at 1.0 bar of boost.

I'm thinking this is a result of rich fuel hitting the turbo and re-igniting then passing through the wastegate... Is this possible?

Or, is it rich fuel/exhaust hitting the hot exhaust headers and re-igniting then taking the shortest path through the wastegate?

Either way, should this "flame/pop" be happening? I've included a pic of my exhaust routing...



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LIVN80S - - Red '79 Porsche 930 Steel Slant Nose Conversion [in 1987] w. 46k miles 3.3L; 964 Cams; K27HF @ 1.0 BAR, with Garrettson Intercooler; Rarly Zork; CIS Flowtech Fuel Head & BL-WUR.
Old 12-07-2008, 07:09 AM
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You have raw fuel igniting in the turbo all right.
An AFR of 10.5 is a little rich and possibly the cause of the flamethrowing behavior.
I'd be worried about raw gas washing the cylinder walls and reducing lubrication for the piston rings.
How often do you check you oil? If it seems that your engine never uses oil or the oil level increases then I'd suggest that that excess gas is diluting your oil too.
Can you tell us about the condition of your WUR? Have you attempted any tuning of your AFR? Is your engine stock or modded?
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Old 12-07-2008, 07:34 AM
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I would say its completely normal... My car also dumps flames through the wastegate between shifts. That is why Porsche from the factory had a muffler/ spark arrestor on the back of the wastegate... You have that same thing that I do, A very small exit pipe on the wastegate. I would not worry about it..... unless you are seeing a flame come out of the wastegate at all times.... then you have problems... LOL

and yes...10.5 is a bit rich under boost... possibly 11.8 to 12.4 or so.... would be better
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Brad...930 gt-1 racecar, increased displacement to 3.6L, JB racing Cylinders, JE 8 to1 pistons, stroked crank, Carrillo rods, extrudehoned 3.2L intake, full bay Bell I/C, GT-2 EVO cams, Rarly8 headers, GTX-3584RS turbo, twin plug, P&P heads, Link G4 EFi system, G-50/50 with LTD slip and oil squirters/oil cooler, zork tube, full race coilover system, with carbon fiber body, full cage, E-85 sippin drunk
Old 12-07-2008, 07:37 AM
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911Nut and Turborat,

I think you're right about 10.5 being a little too low. I only have about 500 miles on an engine rebuild and am trying to keep the engine/exhaust as cool as possible under boost.

I have not done anything with the WUR. I guess I should look at tuning it.

I have followed the digital WUR thread and see a lot of potential there. But, after seeing Alan struggle with it, recently, I realize it might be a little out of my league.

What would someone like me [a novice] use to get my WUR tuned? Thanks...
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LIVN80S - - Red '79 Porsche 930 Steel Slant Nose Conversion [in 1987] w. 46k miles 3.3L; 964 Cams; K27HF @ 1.0 BAR, with Garrettson Intercooler; Rarly Zork; CIS Flowtech Fuel Head & BL-WUR.
Old 12-07-2008, 11:06 AM
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Hi Shannon,
Sounds like your 930 runs "Normal" ;-)
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---Les Garten---85 930, Andial IC, GHL Headers, Fabspeed Dual, K-27 HF2, 3.4 JE Full Finned 7.5:1 CR, 964 CAM'd, Carerra 3.2 Manifold Cut/Flipped, Tec3r, Siemans 55#, GSF Fuel Rails, Clewett Crank Trigger, Clewett Cam Trigger,Dual Plugged, ARP Head Studs/Rod Bolts, Clewett Wires.Tial 46mm WG, Tial 50mm BOV, WEVO Shifter,934 Boost Gauge, Wideband EGO Sensor/Gauge, C2T Head Gaskets, '88 MB 300TE,BMW R100RT
Old 12-07-2008, 11:39 AM
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Upon further investigation...

I took three freeze frame pics of video of my car rounding the corner. On the first two, the flame is coming out of the left side, only. Prompting me to believe that the flame was exhausted thru the wastegate [on left side].

However, on the third video's freeze-frame, I noticed the flame on "both" sides. So, now I realize the flame is coming out of the exhaust.

Here's the picture... Makes me think about a flame-broiled-whopper!

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LIVN80S - - Red '79 Porsche 930 Steel Slant Nose Conversion [in 1987] w. 46k miles 3.3L; 964 Cams; K27HF @ 1.0 BAR, with Garrettson Intercooler; Rarly Zork; CIS Flowtech Fuel Head & BL-WUR.
Old 12-07-2008, 11:51 AM
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Quote:
Originally Posted by mooney265 View Post
Upon further investigation...

I took three freeze frame pics of video of my car rounding the corner. On the first two, the flame is coming out of the left side, only. Prompting me to believe that the flame was exhausted thru the wastegate [on left side].

However, on the third video's freeze-frame, I noticed the flame on "both" sides. So, now I realize the flame is coming out of the exhaust.

Here's the picture... Makes me think about a flame-broiled-whopper!



Now that is PERFECTLY normal!!! I used to drive my car on I-75 in Atlanta, and when in the Carpool lane, I would get people driving up along side of me and tell me that my car is on fire.... I would just punch it a bit, and immediately after I release the gas petal... There would be a big ball of fire.. even better now that I run the Zork tube as an exhaust!!!
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Brad...930 gt-1 racecar, increased displacement to 3.6L, JB racing Cylinders, JE 8 to1 pistons, stroked crank, Carrillo rods, extrudehoned 3.2L intake, full bay Bell I/C, GT-2 EVO cams, Rarly8 headers, GTX-3584RS turbo, twin plug, P&P heads, Link G4 EFi system, G-50/50 with LTD slip and oil squirters/oil cooler, zork tube, full race coilover system, with carbon fiber body, full cage, E-85 sippin drunk
Old 12-07-2008, 11:55 AM
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A better pic...
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LIVN80S - - Red '79 Porsche 930 Steel Slant Nose Conversion [in 1987] w. 46k miles 3.3L; 964 Cams; K27HF @ 1.0 BAR, with Garrettson Intercooler; Rarly Zork; CIS Flowtech Fuel Head & BL-WUR.
Old 12-07-2008, 11:58 AM
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EFI will get rid of that...
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---Les Garten---85 930, Andial IC, GHL Headers, Fabspeed Dual, K-27 HF2, 3.4 JE Full Finned 7.5:1 CR, 964 CAM'd, Carerra 3.2 Manifold Cut/Flipped, Tec3r, Siemans 55#, GSF Fuel Rails, Clewett Crank Trigger, Clewett Cam Trigger,Dual Plugged, ARP Head Studs/Rod Bolts, Clewett Wires.Tial 46mm WG, Tial 50mm BOV, WEVO Shifter,934 Boost Gauge, Wideband EGO Sensor/Gauge, C2T Head Gaskets, '88 MB 300TE,BMW R100RT
Old 12-07-2008, 12:21 PM
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Those flames are par for the corse- dont worry about them as much as enjoy them
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Old 12-07-2008, 12:35 PM
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looks like your car works perfectly!
Enjoy!
Old 12-07-2008, 12:51 PM
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We're lucky the manufacturers off the various exhaust componenets don't charge us extra for the flame option! I get teenagers in ricers pulling alongside and laughing and pointing in appreciation when my car does that
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Old 12-07-2008, 01:12 PM
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Quote:
Originally Posted by mooney265 View Post
. . . I have a digital AFR meter and run 10.5 AFRs under boost. I use an Andial fuel enrichement dial and am locked in at 1.0 bar of boost. . . .
You really should adjust your AFR's upwards. 12.5 max for safety. And, you're probably going to pick up 20/25HP.
See below technical discussion.
--------------------------------------------------------

Application Note: You CAN be too Rich
By Klaus Allmendinger, VP of Engineering, Innovate Motorsports
Many people with turbochargers believe that they need to run at very rich mixtures. The theory is that the excess fuel cools the intake charge and therefore reduces the probability of knock. It does work in reducing knock, but not because of charge cooling. The following little article shows why.
First let’s look at the science. Specific heat is the amount of energy required to raise 1 kg of material by one degree K (Kelvin, same as Celsius but with 0 point at absolute zero). Different materials have different specific heats. The energy is measured in kJ or kilojoules:
Air ~ 1 kJ/( kg * deg K)
Gasoline 2.02 kJ/( kg * deg K)
Water 4.18 kJ/( kg * deg K)
Ethanol 2.43 kJ/( kg * deg K)
Methanol 2.51 kJ/( kg * deg K)
Fuel and other liquids also have what's called latent heat. This is the heat energy required to vaporize 1 kg of the liquid. The fuel in an internal combustion engine has to be vaporized and mixed thoroughly with the incoming air to produce power. Liquid gasoline does not burn. The energy to vaporize the fuel comes partially from the incoming air, cooling it. The latent heat energy required is actually much larger than the specific heat. That the energy comes from the incoming air can be easily seen on older carbureted cars, where frost can actually form on the intake manifold from the cooling of the charge.
The latent heat values of different liquids are shown here:
Gasoline 350 kJ/kg
Water 2256 kJ/kg
Ethanol 904 kJ/kg
Methanol 1109 kJ/kg
Most engines produce maximum power (with optimized ignition timing) at an air-fuel-ratio between 12 and 13. Let's assume the optimum is in the middle at 12.5. This means that for every kg of air, 0.08 kg of fuel is mixed in and vaporized. The vaporization of the fuel extracts 28 kJ of energy from the air charge. If the mixture has an air-fuel-ratio of 11 instead, the vaporization extracts 31.8 kJ instead. A difference of 3.8 kJ. Because air has a specific heat of about 1 kJ/kg*deg K, the air charge is only 3.8 C (or K) degrees cooler for the rich mixture compared to the optimum power mixture. This small difference has very little effect on knock or power output.
If instead of the richer mixture about 10% (by mass) of water would be injected in the intake charge (0.008 kg Water/kg air), the high latent heat of the water would cool the charge by 18 degrees, about 4 times the cooling effect of the richer mixture. The added fuel for the rich mixture can't burn because there is just not enough oxygen available. So it does not matter if fuel or water is added.
So where does the knock suppression of richer mixtures come from?
If the mixture gets ignited by the spark, a flame front spreads out from the spark plug. This burning mixture increases the pressure and temperature in the cylinder. At some time in the process the pressures and temperatures peak. The speed of the flame front is dependent on mixture density and AFR. A richer or leaner AFR than about 12-13 AFR burns slower. A denser mixture burns faster.
So with a turbo under boost the mixture density raises and results in a faster burning mixture. The closer the peak pressure is to TDC, the higher that peak pressure is, resulting in a high knock probability. Also there is less leverage on the crankshaft for the pressure to produce torque, and, therefore, less power.
Richening up the mixture results in a slower burn, moving the pressure peak later where there is more leverage, hence more torque. Also the pressure peak is lower at a later crank angle and the knock probability is reduced. The same effect can be achieved with an optimum power mixture and more ignition retard.
Optimum mix with “later” ignition can produce more power because more energy is released from the combustion of gasoline. Here’s why: When hydrocarbons like gasoline combust, the burn process actually happens in multiple stages. First the gasoline molecules are broken up into hydrogen and carbon. The hydrogen combines with oxygen from the air to form H2O (water) and the carbon molecules form CO. This process happens very fast at the front edge of the flame front. The second stage converts CO to CO2. This process is relatively slow and requires water molecules (from the first stage) for completion. If there is no more oxygen available (most of it consumed in the first stage), the second stage can't happen. But about 2/3 of the energy released from the burning of the carbon is released in the second stage. Therefore a richer mixture releases less energy, lowering peak pressures and temperatures, and produces less power. A secondary side effect is of course also a lowering of knock probability. It's like closing the throttle a little. A typical engine does not knock when running on part throttle because less energy and therefore lower pressures and temperatures are in the cylinder.
This is why running overly-rich mixtures can not only increase fuel consumption, but also cost power.
Old 12-07-2008, 02:09 PM
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Thanks for the write up!
so the maximum AFR should not exceed 12,5AFR under WOT?
I always tried to tune for 12,0AFR to be on the safe side...
Old 12-08-2008, 02:25 AM
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WOW!

Thanks for the theory/logic behind the 12.5 number!

Q1: What type of WUR / Lambda device should I look at for tuning my AFR's?
Q2: Does anyone know a repututable Dyno shop near me to verify the AFR readings i'm getting with my wideband O2?

Thanks...
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Old 12-08-2008, 04:42 PM
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The Andial will give you wonky AFR numbers due to it's inconsistency and rob Peter to pay Paul design.

I'd burn the Andial (one person here actually did that!) and get an adjustable WUR or the new digital WUR.

Flames are relatively normal. Closing the throttle results in mucho fuel and little air - and it is simply burning once it hits the ambient air outside the exhaust pipe(s).
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Old 12-09-2008, 07:57 AM
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More importantly:

Why doesn't my car do that!?!?!?

and

How can I get it to!!!

8-)

I run a RarlyL8 dual out exhaust, WG stub pipe, otherwise all stock. AFR's looked middle of road during last dyno run.

I watched a bud romp it up / down the block - hoping for flames - nada zilch none.

Do tell!

Yes, I'm an immature giddy little schoolgirl - apparently in good company here...
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Old 12-09-2008, 12:12 PM
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You need short run after market headers ala B&B for the flames.

JP
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Old 12-09-2008, 01:02 PM
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Quote:
Originally Posted by rsrfan View Post
You need short run after market headers ala B&B for the flames.

JP
Damn, was 'fraid that was the answer.

Reason alone to get them 8-).

Those are sosososo far out of my near term reach it ain't funny. Que sera sera!

Thanks for confirming tho.
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| '58 TR3A | '01 S8 | '95 S6 6gang | '88 M5 | '87 190E 2.3-16 |
Old 12-09-2008, 01:10 PM
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Short headers are not a must for the flames - definitely helps as you can see moonie265's. Mine and most 930's with "free" exhaust - where fumes velocity is not restricted - flame some. It depends on what you are looking for.

Old 12-10-2008, 03:34 AM
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