IcemanG17

Can a euro S CIS fuel a 5.0L hybrid? Rick's 5.0L engine has been done for a bit, but his car runs stock CIS fuel system. Rick has the full euro S parts from and 80 euro S, but will it be enough to fuel the extra 300cc of displacement with higher compression....

I know this question has been asked before and I recall the answer being "maybe"...but nobody has tried it..... L jet can be modified to fuel a 5.0 properly and is well proven..... We have a full L jet setup on the spare engine, but don't have the harness or brains-AFM....

Of course I want a 5.0L euro as well, but my budget is so sad its not gonna happen anytime soon....

Jadz928

In ~1974, Porsche developed a 16V 5.0L, fueled via CIS... used in an Audi 100 prototype.



FWIW, I'm building one right now.

IcemanG17

Interesting...but a couple concerns.......back in the day engines were fairly low compression to make emissions standards...hence the 8.5 CR in the 1st gen 928 (still high compared to american iron garbage) Of course fuel economy concerns were low as well.....but once Porsche switched to L jet in 1980 things got much better......so they bumped compression to 9.0 and dropped the "cams" a bit for an overall gain in HP with better drive ability....since the L jet allowed better control of the AFR across the board....the greatest weakness of CIS is idle vs high load fueling....want more fuel up high.....gotta run stupid rich down low.....

GlenL

Compression is immaterial. How much more air is going into the engine? Well, the displacement is 7% more. Yeah, that's all. I'll bet Porsche built in 7% tolerance in the fuel flow rate. Go for it with a new fuel pump. Run it on a dyno and look for leaning at high RPM and WOT. I did that with my 4.8 Euro S and there wasn't a hint of it.

Jadz928

Also, there's ways to setup the WUR for better WOT richness, while leaving idle setting relatively the same.

bronto

Jim, I was just thinking about this. How, and would it work on my '79?

IcemanG17

guys CIS is a simple mechanical system.....if you bump one end of the spectrum you bump the other even MORE....its simple.....

I tried tuning Ricks racer last year.....we bumped fuel and all it did was make idle stupid fat 10.5....while still running out up high....granted a dying fuel filter was part of it.... CIS can NOT adjust more than mechanical.....its not possible....there is no O2 loop...how could it work...02 by nature are electrical.....nothing on CIS is.....unless they pull spark like crazy.... CIS is a simple lever just like a carb.....an arm pushed by air pressure pushes another arm to determine fuel.....its insanely simple

GlenL

You really....don't get...how complicated...CIS is....

svpmx83

CIS is adjustable its a two part system with the WUR being the adjustment point for temperature and load. if you are adjusting only the metering plate at the shoe then you are missing out on 90% of the tuning possibilities of the system.
If you want to go really wacky there is an electronic programmable WUR out there too http://unwiredtools.com/utcis.asp
but honestly the standard system is more than capable of being tuned to whatever you need from it.

17prospective buyer

LOL, why not just bump mixture up at using the cold start injector... i know this is a less than ideal way of altering mixture, and hard to get an even mixture to all cylinders but you could know what effect it is having by getting a wideband O2 to watch in the cabin.

Jadz928

Agreed, you're over-simplifying, Iceman. However, the reason I like it IS it's simplicity.

Dave928S

There is a 5.0 litre CIS Auto car here in Tas. It was a standard CIS 4.7 litre Euro 83S which had a failed block. The block was replaced with a 5.0 litre without any other alterations. I've looked at the piston crowns with an endoscope and valve reliefs weren't even cut in the pistons, but this has definitely made it an interference motor. It's a strong motor used as a DD, and has had a few floggings at track days.

Jadz928

You just blew my mind, Dave. Really.

Dave928S

Jim .. to clarify re valve reliefs ... they were standard S4 and not enlarged to 16V size.

checkmate1996

+1

They don't dedicate a couple of manuals for CIS for nothing!! hahaha