Boosted Engines and CIS

awjens · 04-24-2016, 12:12 PM

I have spent hours on here reading threads, CIS manuals and other web pages regarding CIS fuel limitations. It seems 930 owners as well as 911 owners with boosted engines have visited and re-visited this topic.

I have read abut "shimming" the head, modifying it by cutting fuel slots bigger etc. Isn't it possible to increase the fuel system pressure and fuel volume to these heads to make them flow more? Is the fuel injector itself limiting the volume? Some threads say it is a limiting factor, some say it isn't. I have the ability to modify any of these injectors to increase their flow based on a specific pressure if the volume isn't limited to the injector.

Will the increase to the -044 pump 5 (8) bar have any impact on the amount of flow thru this head. Right now I have two 0-580-254-967 pumps running to my head.

Can it be increased by a % by turning the adjustments next to each injector line across the board while monitoring each one to maintain equal flow? With my stock injectors I am within 3% from high to low running this flow test multiple times. I have six bottles, with the injectors in them. It doesn't matter if I hold the sensor plate wide open or vary it up and down. All six are still within 3% by weight on a gram scale.

kenikh · 04-24-2016, 01:24 PM

Yes to all of the above, but it is all trade offs. The more open the orifices in the fuel head, the harder it is to control fuel flow at low rates. Edelweiss can get a CIS motor running well at 700HP. The question is: is the cost worth the effort?

Jeff NJ · 04-24-2016, 01:36 PM

What kind of power are you looking for? I have stock fuel head, pumps and injectors and do not run out of fuel. I have k27hfs turbo, turbo kraft IC, rarlyl8 headers and muffler, TiAl WG at 1.0 bar and a leask wur. I'm guessing close to 400 hp at the crank. From what I've read, I probably couldn't go much further with mods though without modifying the fuel delivery though.

RarlyL8 · RarlyL8's Garage

You don't say what your goals are or the current AFRs. The stock Euro system can be adjusted to support 400HP to the wheels before more in-depth methods are needed. The stock USA system needs modification to hit that number. Fuel injectors are not the limiting factor.

awjens · 05:19 PM

I am capable of delivering 1.5 bar + with a supercharger. I will probably set it to run at 1.0 bar with a water/air intercooler. It has SSI's, 8.5:1 JE pistons, aftermarket rods, Mile Miglia exhaust, Custom airbox, MSD with boost retard, FrankenCIS WUR, All raceware bolts/studs, stock fuel pump, lightweight flywheel. Heads were cc/d and it was set up with an effective CR of 8.6:1. Everything was polished, balanced etc. Really looking for 350 reliable horsepower without going EFI. This can easily be switched back to stock CIS at a later date. It was assembled years ago and on the high end it ran lean. The head was adjusted to get even flow from all 6 injectors and verified with the O2 and EGT readings. I had additional injectors running on it after the test results. I have a exhaust system with 14 sensors, O2 or EGT. That was done to make sure the additional fuel was evenly dispersed and no single cylinder ran lean. This is a stock 911 SC -097 Euro fuel distributor currently flowing around 250-260cc/min. It ran fine until it had a airbox mishap. Now its freshened up and I'm looking for more fuel without running the additional injectors. When I found the thread from DKUBUS I decided to try to try this again using some newer technology and their digital WUR. So its presently wired with a Microsquirt, MAP, coolant sensor, control pressure sensor, Air temp sensor and the FrankenCIS block with the injector. I am ordering a Bosch -044 fuel pump tomorrow if I cannot find the 8 bar version. When it was running before I adjusted the head at idle to 12.0 AFR. At 4500 RPM it was at 16.0 AFR with 5 PSI boost, 130 degree inlet air temp. At that point I turned on the other injectors. It ran below 11.7 AFR. I did not have the data logging capabilities that the MS gives me today. The engine is out of the car running on a test stand. This was to dial in the FrankenCIS, hot/cold starts, check for air leaks etc. Now I am back to fuel delivery. The Franken CIS will attempt to hold AFR but unless I can find a way to flow more fuel it wont be able to keep up using control pressure. So right now I'm at 260cc/min. I have done compression tests and leakdown tests. 2-3% leakdown and all cylinders within .75 pounds on the compression. The engine runs and starts fine, solid idle. Less than 4000 miles since it was completely rebuilt. I was hoping the Digital WUR could make control pressure changes after I fire the additional injectors and target AFR better. Even better I would like to eliminate the additional injectors if I can get more flow thru this head.

RarlyL8 · RarlyL8's Garage

The Euro -097 will flow more than the USA models but nowhere near 350HP. You really need to get a V8 or 930 FD to feed the engine you have. FrankenCIS should have something that will flow those numbers.

T77911S · 04-25-2016, 02:58 AM

increasing system fuel pressure leans it out.
when you increase fuel pressure that puts more pressure on the lower chambers which puts more force closing the "valves" that let fuel goto the injectors.(very crude explanation)

talk to larry at flowtech.
there is not anyone out there that knows more about the heads.

JFairman · 04-25-2016, 06:45 AM

Quote:

Originally Posted by T77911S

increasing system fuel pressure leans it out.
when you increase fuel pressure that puts more pressure on the lower chambers which puts more force closing the "valves" that let fuel goto the injectors.(very crude explanation)

talk to larry at flowtech.
there is not anyone out there that knows more about the heads.

Correct, and Larry Fletcher is the man for CIS fuel head rebuilds and modification.

When raising overall fuel system pressure CIS control pressure goes up too. Raising control pressure forces the control plunger down in a 930 fuel head lowering the amount of fuel sent to the injectors. At the same time the airflow sensor plate raises restricting more of the intake air supply.

If you raise system pressure with shims in the fuel head fuel pressure regulator than you have to use an adjustable control pressure regulator to lower the fuel head control pressure so the control plunger will raise higher in it's chamber uncovering more of the fuel metering slits so more fuel is sent to the injectors.

It's complicated so a cross section diagram of the fuel head with arrows showing fuel flow through the chambers and valves helps to explain whats going on.

T77911S · 08:36 AM

I had always thought the CP went up/down with system pressure. funny, as much as I have played with all this I have never verified it myself.
anyway, I was talking to larry last week about this. he said the CP does not move much when system pressure changes, (not sure what larry had in mind as far as system pressure changes).
I would still like to test this myself because I don't think the WUR is really much of a "regulator" even though it has a spring and diaphragm basically.

I was also thinking more along the lines of higher sys pressure in the lower chambers pushing up on the diaphragm making ir harder for the fuel entering the top to open the valve

to the OP,
if you want a 930 euro head, I am sending mine back to larry for an aluminum head.
mine has been rebuilt and opened up about 10%.

awjens · 04-25-2016, 09:15 AM

JFairman

I understand what you are saying, that is why I purchased the FrankenCIS WUR. If I shim the head to increase system pressure and lower the control pressure with the Digital WUR won't that increase flow to some degree?

awjens · 04-25-2016, 09:17 AM

Quote:

Originally Posted by T77911S

I had always thought the CP went up/down with system pressure. funny, as much as I have played with all this I have never verified it myself.
anyway, I was talking to larry last week about this. he said the CP does not move much when system pressure changes, (not sure what larry had in mind as far as system pressure changes).
I would still like to test this myself because I don't think the WUR is really much of a "regulator" even though it has a spring and diaphragm basically.

I was also thinking more along the lines of higher sys pressure in the lower chambers pushing up on the diaphragm making ir harder for the fuel entering the top to open the valve

to the OP,
if you want a 930 euro head, I am sending mine back to larry for an aluminum head.
mine has been rebuilt and opened up about 10%.

I have an SC head.

Ken911 · 04-25-2016, 11:42 AM

Having been down that road with CIS and the associated rebuilds each time it decides to go lean on you. You would probably be way ahead financially to just swap it to EFI and put all the cis stuff in a box to put back on if you decide to sell your car. Not trying to be a turd in the punchbowl just trying to save you heart ache and aggravation.

kenikh · 04-25-2016, 11:50 AM

Quote:

Originally Posted by Ken911

Having been down that road with CIS and the associated rebuilds each time it decides to go lean on you. You would probably be way ahead financially to just swap it to EFI and put all the cis stuff in a box to put back on if you decide to sell your car. Not trying to be a turd in the punchbowl just trying to save you heart ache and aggravation.

My experience exactly. I just got tired of having one eye on the road and one eye on the AFR meter every time I wanted to do a power pull.

I already travelled this path. My heartache and aggravation has dollar signs associated with it. You have a choice to minimize those dollar signs now.