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Join Date: Feb 2002
Location: Atlanta, GA
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Question Excess gas consumption & bucking

Hello all,

I notice that there is another thread involving bucking but I have a 1989 Turbo 911 that has an interesting problem.

First off the modifications:
• GHL header & muffler
• Kokeln intercooler
• 1 bar boost spring
• Andial fuel enrichment system
• Modified K27 7200 turbo

I’ve also installed additional gauges to show the A/F ratio and the boost levels (replacing clock).

The car ran great when I was using the standard K27 7200 turbo putting 389HP to the rear wheels. But not being satisfied and forgetting my car is a “street” car, the turbo was modified to flow more air. It works very nicely and now puts out close to 422HP to the ground.

But the car is in no way as pleasant to drive. It’s a gas hog now and can buck like crazy when under partial boost. Of course it doesn’t always buck everytime. The shop that worked on the car says I need to drive it full throttle to avoid the bucking syndrome but to be honest that isn’t my style of driving. According to the A/F gauge the car is running much too rich but again my shop states it is better to run rich than run lean. True I suppose but my thinking is I have the Andial system in place to prevent running lean when under heavy boost. When not in boost, the enrichment system isn’t on and I thought I should get pretty good gas mileage.

So to my questions.

1) I was told that part of the Andial system was to replace the size of the CIS injector. And that even when the enrichment system was not in use (boost less than 0.65 bar), the bigger injectors would put more gas in than the old “stock” injectors for the same period of time. In effect the CIS injection pulses are can only be made so small in duration, and with bigger injectors I’ll always have more fuel in the motor. The metaphor given was it’s like pulsing a garden hose vs. a fire hose. The pulses can only be made so small and the fire hose will therefore dump more gas in to the motor. Is this true? Is this how the system works?

2) I’ve asked numerous times to have my engine leaned out and was always told its part of owning a Turbo. But according to the new boost gauge I’m not in boost all that often, and when I do go on boost black smoke comes out the rear of the car. Do I need to always run rich?

3) Why did the car run so much better with no bucking when it was using the “stock” K27 7200?

I realize it is hard to diagnose a car remotely but I’d appreciate any suggestions. I keep thinking I need to unmodifiy the K27 but I don't know if that is really the root of the problem. Maybe a faulty wastegate or a wastegate that can't keep up to the new turbo?
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C.H.
Boost Addiction - honestly, I have it under control
1989 911 Turbo Cabriolet
Mods include: Kokeln IC, GHL Headers, Hooligan muffler, Modified K27 7200, BL WUR, LC-1 & XD-16, Bilstein Sports (4), TRG sway bars, Oversize torsion bars, Strut brace
Old 07-20-2007, 11:39 AM
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Crotchety Old Bastard
 
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Time for Don to come visit you.
The "C" in CIS stands for continuous. There are no pulses.
At the power levels you are at you need to junk the Andial unit and get a modified fuel head such as what iA sells.
There is no reason to run more rich than 11.5:1 under boost. As you know 12.2:1 is likely the limit. When off boost you should be in the 14s:1. I asume you have an adjustable WUR.
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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 07-20-2007, 01:05 PM
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Rarly8,

WUR standing for?

I was actually very happy with the Andial - it worked well enough before. And most of my time is spent off-boost according to both the Andial indicator (wired to the relay) and my fancy vacuum boost gauge. So I don't understand the reason for the needing to be so rich.
__________________
C.H.
Boost Addiction - honestly, I have it under control
1989 911 Turbo Cabriolet
Mods include: Kokeln IC, GHL Headers, Hooligan muffler, Modified K27 7200, BL WUR, LC-1 & XD-16, Bilstein Sports (4), TRG sway bars, Oversize torsion bars, Strut brace

Last edited by BlkBird; 07-20-2007 at 02:30 PM..
Old 07-20-2007, 02:25 PM
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Crotchety Old Bastard
 
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Warm Up Regulator.
The WUR along with your fuel head are the main components to the CIS.

The Andial unit is a band-aid, and in my opinion not a very good one. There are proven modifications to your Fuel Head and Warm Up Regulator that will support your level of power without auxiliary fueling. A good mechanic will know this, yours doesn't sound so good. There is no reason to run your engine rich. Excess fuel will wash the cylinders diluting the oil and shorten the life of your engine.

I don't think there is anything wrong with your wastegate, if so you would be over boosting. What you are describing sounds like turbo surging. What exactly was done to the turbo?

If your mechanic told you this is normal and you have to live with it you need to find another mechanic immediately. He is fixing to cost you a whole lot of money. I wouldn't drive this car until it is tuned properly or until you put it back the way it was. 390RWHP is very respectable for a CIS engine.
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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 07-20-2007, 05:03 PM
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Which shop did you take it to? (just curious)

Bucking under partial throttle means you are way to rich, probably something like 10:1 for it to buck that bad. The Andial unit is setup wrong. (not a good long term solution) I would persoanlly ditch the microfueler and go with a modified WUR (Warm Up Regulator) such as the ones Brian Leask provides...

I would also highly suggest a wideband O2 meter to keep an eye on your ratios... a few hundred bucks well spent. Here is what I picked up ==>

http://www.bmotorsports.com/shop/product_info.php/cPath/103_107/products_id/357

Remove the cheesy sticker on top, tape off the front with blue painters tape and spray paint the unit wrinkle finish matt black and it will look great.
Old 07-20-2007, 05:12 PM
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Wow - run from that mechanic/shop. Bad advice, or more specifically, wrong. They might be a Porsche shop, but not a turbo shop.

With the mods you list, you don't need anything more than a tuned WUR. Properly tuned, it will dump plenty of fuel and as stated above, the Andial is not a very good unit for what you are doing.

Another good piece of advice above is to get a good wideband meter ASAP.

Where are you in Atlanta?
Old 07-20-2007, 05:46 PM
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Rarlyl8,

My day for questions it appears. What is "turbo surging" and what causes it?

Quick update. I spoke with Pete @ Andial and he tells me that their kit doesn't include any change to the injectors. Therefore it's not a garden hose vs. fire hose comparison even if the system did pulse fuel. Which I should have remembered it doesn't. Pete also suggested the warm up regulator might have been badly setup.

So is the stock WUR fixed or are they all adjustable? Where does one obtain a good adjustable version (eg. contact info for Brian Leask)?

As to the turbo, it was sent to Florida for modification. I believe they changed one side of the housing so that it would flow more air using the K27 as a basis. It does this well reaching full 1 BAR boost by 3800 rpm.

But it isn't the on-boost performance that bugs me. I used to love my five speed transmission for the way I could moderate throttle & boost. Now it feels like I have an off/on switch for boost. Almost like the stories I've heard about four speeds.
__________________
C.H.
Boost Addiction - honestly, I have it under control
1989 911 Turbo Cabriolet
Mods include: Kokeln IC, GHL Headers, Hooligan muffler, Modified K27 7200, BL WUR, LC-1 & XD-16, Bilstein Sports (4), TRG sway bars, Oversize torsion bars, Strut brace
Old 07-20-2007, 06:26 PM
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Crotchety Old Bastard
 
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3800? Are you kiddin' me? That guy is hosing you. You should have full boost by 2800rpm.

WURs are not adjustable from the factory. Contact Brian Leask at bleask@cox.net
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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 07-20-2007, 08:11 PM
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I read up on turbo surging and it sounds like it's a possibility, especially with a modified turbo housing. Anybody else experience this surging and did you discover the root cause?
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C.H.
Boost Addiction - honestly, I have it under control
1989 911 Turbo Cabriolet
Mods include: Kokeln IC, GHL Headers, Hooligan muffler, Modified K27 7200, BL WUR, LC-1 & XD-16, Bilstein Sports (4), TRG sway bars, Oversize torsion bars, Strut brace
Old 07-21-2007, 04:36 AM
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Crotchety Old Bastard
 
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Turbo surging is caused by pressure pulses. Those pulses are generally created by uneven pressures before and after the turbo. The uneven pressures can be created several different ways. One way is by a grosly over-rich condition. The cylinders are fighting one another because the flame is periodically being doused in one or more cylinders. It upsets the air flow through the engine among other things.
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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 07-21-2007, 06:26 AM
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