BlkBird

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?

sand_man

I'll just throw a few things out:

It's better to run "rich" over "lean" in that you might be saving yourself the disastrous affects of detonation and/or melting stuff, but too rich and you are washing the cylinder walls of precious oil and contaminating that oil (with gas). Additionally, too rich and acceleration becomes sluggish and the car will fight you, to to get to higher RPMs.

It is better to run right and continue to tune it. What are your AFRs and at what RPM? For example cruising around town, very little boost, my AFRs hover around 13:1. However, on a WOT run to to about 6,300 RPMs from third to fourth gear, I'm at about 11.5:1.

I also think there are better methods for adding fuel beyond the Andial unit. I run the IA fuel head, Brian Leask fully adjustable WUR, and Brian Leask RPM solenoid trigger.

Can you tell us more about the turbocharger?

Also there have been lot's of discussions regarding CIS, AFRs, WURs, tuning, etc.

sand_man

I wonder what your WUR cold, warm, and enrichment fuel pressures are?

JFairman

Nobody can know what your mechanics did along with changing or modifying the turbo, and it sounds like they did something to make it run too rich.

CIS injection does not pulse, whoever told you that is wrong.
CIS stands for "constant injection system" meaning the fuel is constantly injected or spraying if the motor is running.
Only the fuel pressure and volume sprayed is changed.
It sprays continuously at the injector, and if there was any minute pressure pulsing coming from the fuel pumps the accumulator would absorb those pulses and smooth out the fuel pressure. The accumulators purpose is to hold some fuel pressure at the injectors after the engine is turned off so it will start quicker next time.

I would try disableing or disconnecting the andial frequency valve inline injector and see if it runs better and go from there.

If you don't work on your own car, I think you need to find a different mechanic.

BlkBird

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. There were also extensive dyno runs made to ensure the air/fuel ratio would product maximum HP.

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.

sand_man

Brian Leask:
http://members.***.net/930wur/

Some threads on WURs:
https://rennlist.com/forums/911-turbo-930-forum/297546-a-crazy-little-thing-called-a-wur-warm-up-regulator.html
https://rennlist.com/forums/911-turbo-930-forum/347113-brian-leask-adjustable-wur.html

Some threads on the Andial enrichment unit
https://rennlist.com/forums/911-turbo-930-forum/301562-disconnecting-andial-fe.html
https://rennlist.com/forums/911-turbo-930-forum/236395-andial-fuel-enrichment-adjustments.html

nathanUK '81 930 G50

Please post your AFR readings as suggested.

Need to know the AFR at all loads & rpms.

ferraripete

my car does this as well...blackens the sky at partial trottle and them whap! clean running on wicked boost!!!

nathanUK '81 930 G50

Sounds like you could do with an adjustable WUR from Brian Leask.

ferraripete

nathan, can you please explain the function of the wur? where is it located and how much is it priced at?

is it a tough install?

ferraripete

nathan...disregard. i saw the prior post w/ the web link.

it does indeed sound like the ticket to fixing my car. how much is the wur priced at?

nathanUK '81 930 G50

Not sure exactly, but it is sensibly priced.