Pelican Parts
Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help



Go Back   Pelican Parts Forums > Porsche Forums > 911 Engine Rebuilding Forum


Reply
 
LinkBack Thread Tools Rate Thread
Author
Thread Post New Thread    Reply
Wer bremst verliert
 
JohnJL's Avatar
 
Join Date: Jan 2005
Location: Toronto, Ontario
Posts: 4,767
Can the CIS airflow sensor/plate be upgraded with MAF?

This might be a stupid question and I know there are a lot of strong opinions (bordering on religion?!?!) about the merits/limitations of CIS. My question is very narrowly-focused -

Has anyone successfully replaced the CIS airflow assembly (plate) with another properly-calibrated sensor, such as a more modern MAF, and successfully overcome the "reversion" issue I've heard and read about? I am planning out my next build whch will initially retain the CIS. WOuld such a modification work and if so what kind of effort is involved?

Thanks,
John

__________________
2007 911 Turbo - Not a toy
1985 911 Cab - Wife's toy
1982 911 3.2 Indiash Rot Track Supercharged track toy
1978 911 3.0 Lichtbau toy "Gretchen"
1971 911 Targa S backroad toy
Old 03-06-2005, 01:03 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #1 (permalink)
Somewhere in the Midwest
 
MotoSook's Avatar
 
Join Date: Oct 2001
Location: In the barn!
Posts: 12,499
If you could wire the the MAF sensor to a processor which controls a solenoid that raises and lowers the fuel distributor plunger, you can get rid of the air plate/meter.

It's more trouble than it's worth, but it would be a fun project. A Megasquirt EFI conversion would be easier.
Old 03-06-2005, 01:25 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #2 (permalink)
Wer bremst verliert
 
JohnJL's Avatar
 
Join Date: Jan 2005
Location: Toronto, Ontario
Posts: 4,767
Souk,
Thanks. For me, going to carbs is the next stop, but I may be forced to keep the original induction setup due to racing class rules. I'm not even sure this modification would be allowed but I am curious if it would work.

Couldn't you simply remove the plate assembly, tap and thread the intake and screw in/epoxy/mount , wire it to a converter chip/resistor or other such electrical device to set the reading range correctly, and wire that into the CIS harness? The point of this would hinge on whether or not the MAF would be better able to deal with the "reversion" feedback better than the plate.
__________________
2007 911 Turbo - Not a toy
1985 911 Cab - Wife's toy
1982 911 3.2 Indiash Rot Track Supercharged track toy
1978 911 3.0 Lichtbau toy "Gretchen"
1971 911 Targa S backroad toy
Old 03-06-2005, 01:42 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #3 (permalink)
Somewhere in the Midwest
 
MotoSook's Avatar
 
Join Date: Oct 2001
Location: In the barn!
Posts: 12,499
The CIS harness has nothing to do with fuel flow rate. Well, the Lambda circuit on the 80-83 CIS does fine tune the flow rate a bit to get the right exhaust gas reading (O2 sensor feedback to mildly richen or lean the mixture). The circuit controls the frequency valve, but it alone does not control fuel flow. The primary fuel flow is mechanically controlled by the fuel distributor plunger moving up and down as the air meter is moved up and down as air flows through the venturi of the meter.

Although I think it'll be more effort than it's worth, you can proportion the output of the MAF to a solenoid's travel such that fuel rate increases with increase signal output from the MAF, but the air meter is not exactly linear. If you could get a solenoid to react fast enough, you would still need to process the MAF signal to make up for the lack of linearity in the air meter to plunger travel of the normal CIS. You'll need a lot of tuning time if you can get the equipment to perform per spec.

Like I said, it would be a fun project, but I would just go to carbs or EFI.

The MAF would handle reversion better.

Something else that might work, is a damper on the air plate lever arm. But that's a crazy idea too as the damper would prevent free motion of the air plate.

Last edited by MotoSook; 03-06-2005 at 01:58 PM..
Old 03-06-2005, 01:55 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #4 (permalink)
Registered
 
blue82coupe's Avatar
 
Join Date: Oct 2003
Location: Louisville KY
Posts: 493
JohnJL. Pat Williams Racing is inthe process of building a CIS to EFI conversion. It retains the manifolds, air filter housing and some other existing parts, and replaces the WUR, AAR, fuel distributorand God knows what other Rube Goldberg contraptions on the existing CIS system. I'm planning to use his kit in my 3.0 build -up. Dan
__________________
I have plenty of lead for my pencil... just not enough paper to write on..

82SC with 95 993 engine
2004 Ford Powerstroke
Old 03-06-2005, 04:29 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #5 (permalink)
Just a big kid really...
 
Join Date: Mar 2005
Location: Gippsland Gourmet Country, Australia
Posts: 1,233
Why don't you fit an after market EFI to your engine, with a 3.2 inlet manifold and throttle body? The other option is of course is a Triple throttle body set up( rules allowing) There are many options as you would know for EFI systems.
Regards Mike
__________________
Lisa Gregory
www.spyderautomobiles.com.au
blog: http://spyderauto.net
Old 03-07-2005, 03:57 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #6 (permalink)
 
Irrationally exuberant
 
ChrisBennet's Avatar
 
Join Date: Aug 2001
Location: Nashua, NH USA
Posts: 8,164
Garage
I really doubt any race class that requires you to retain the CIS is going to allow you to remove the CIS throttle plate and replace it with something else.
-Chris
__________________
'80 911 Nogaro blue Phoenix!
'07 BMW 328i 245K miles!
http://members.rennlist.org/messinwith911s/
Old 03-07-2005, 04:48 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #7 (permalink)
Registered
 
Elombard's Avatar
 
Join Date: Jul 2002
Location: Atlanta
Posts: 7,125
I amnot sure the MAF would be better on Reversion??? seems like the air going back over the sensor would mess it up..... also the connected intake runners is a problem too because the pulse back up the runner from the one cylinder effects other cylinders. Although Mazda made this work to their advantage on the rotary.
__________________
erik.lombard@gmail.com
1994 Lotus Esprit S4 - interesting!
84 lime green back date (LWB 911R) SOLD
RSR look hot rod, based on 75' SOLD
73 911t 3.0SC Hot rod Gulf Blue - Sold.
Old 03-07-2005, 09:16 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #8 (permalink)
Registered
 
KobaltBlau's Avatar
 
Join Date: Mar 2004
Location: City of Seattle, WA
Posts: 3,374
Quote:
Originally posted by Souk
If you could wire the the MAF sensor to a processor which controls a solenoid that raises and lowers the fuel distributor plunger, you can get rid of the air plate/meter.

It's more trouble than it's worth, but it would be a fun project. A Megasquirt EFI conversion would be easier.
well said, Souk. normally the metering plate is a purely mechanical "sensor", acting on the fuel distributor plunger as Souk said.
__________________
Andy
Old 03-07-2005, 10:34 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #9 (permalink)
Wer bremst verliert
 
JohnJL's Avatar
 
Join Date: Jan 2005
Location: Toronto, Ontario
Posts: 4,767
The Aussie historic class rules are pretty vague...allows for modifications "within the technology available at the time of manufacture...

Since I'm building for lower-speed (read:twisty) courses and events, perhaps my choice of a lower-overlap cam will negate the reversion issue anyway. Just pokin' around for potential issues.

Maybe this needs another thread, but I'll ask anyway: Given a choice of euro heads (larger intake ports) and US heads, am I better served with the US heads? Faster intake velocities at lower RPMs and the ability to later port out if needed sounds like 2 good reasons to go with the narrower-intake US heads. Sound reasonable? Assume comperable shape and the goal is to build torque quickly at 2000 rpm and up. I'll rarely have the chance to go WOT on a straightaway...

thanks!
__________________
2007 911 Turbo - Not a toy
1985 911 Cab - Wife's toy
1982 911 3.2 Indiash Rot Track Supercharged track toy
1978 911 3.0 Lichtbau toy "Gretchen"
1971 911 Targa S backroad toy
Old 03-07-2005, 10:39 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #10 (permalink)
Somewhere in the Midwest
 
MotoSook's Avatar
 
Join Date: Oct 2001
Location: In the barn!
Posts: 12,499
Carbs would be legal as "available at the time technology." That is one reason why I'm developing carbs for my car. Yes boys, I'm getting rid of CIS eventually and installing my slide valve carbs! I still love CIS, but for a race car it's obviously not the best.

As for 2000+ torque, that's a pretty tall order. You may be better off to consider gearing, instead engine work, if you will be running the tight courses.
Old 03-07-2005, 12:05 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #11 (permalink)
Wer bremst verliert
 
JohnJL's Avatar
 
Join Date: Jan 2005
Location: Toronto, Ontario
Posts: 4,767
Souk, you are right, gearing is under similar development...

__________________
2007 911 Turbo - Not a toy
1985 911 Cab - Wife's toy
1982 911 3.2 Indiash Rot Track Supercharged track toy
1978 911 3.0 Lichtbau toy "Gretchen"
1971 911 Targa S backroad toy
Old 03-07-2005, 12:47 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #12 (permalink)
Reply


 


All times are GMT -8. The time now is 12:10 PM.


 
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2025, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2025 Pelican Parts, LLC - Posts may be archived for display on the Pelican Parts Website -    DMCA Registered Agent Contact Page
 

DTO Garage Plus vBulletin Plugins by Drive Thru Online, Inc.