Finally driving again!, Type IV CIS conversion Options

[dlee6204]

I finally got to drive my 914 again! (IMG:style_emoticons/default/mueba.gif) (IMG:style_emoticons/default/biggrin.gif) Back in June I was having fits with the L-Jet system that was on my car so I decided it was time to tackle a project I was wanting to do for some time, a CIS conversion.

I retrofitted a CIS Basic system to my stock 1.8L engine using parts from various VWs and Mercedes and today I fired it up for the first time and was able to take it for a long drive. It felt AWESOME. Smooth reliable power all the way to redline. It has a nice growl to it too. (IMG:style_emoticons/default/evilgrin.gif) I'm quite impressed. I still have to make some small adjustments but at least now I can get back to driving the car daily and the best part, NO MORE JACKSTANDS! I'm going to drive the snot out of the car this week to get the system dialed in and hopefully next weekend I will take it for a day drive in the mountains. (IMG:style_emoticons/default/driving.gif) More details and pics to come later.


The cat is happy too!

[Dr Evil]

There has been proof that CIS actually does fine with radical cams....I need to find where that was. I am putting CIS on my tweaked out corvair engine in the bus (IMG:style_emoticons/default/smile.gif) Already have it in the 914 on the 2.7 (stock).

[ArtechnikA]

There has been proof that CIS actually does fine with radical cams...

There's a whole spectrum of meanings to 'radical'... And 'fine' for that matter ;-) Lift is OK, but when you get into lots of overlap there are going to be issues. Are they issues that have workarounds? probably...

Porsche ran CIS on the 934's because the FIA made 'em do it, and they ran just fine, but not with as much power as the Kugelfisher injection they could run in Group 5. They certainly didn't have 'street-car idle' either. I suspect they gave up a lot in fuel economy at idle and part-throttle - but no one much cares about those in a race car.

...I am putting CIS on my tweaked out corvair engine in the bus (IMG:style_emoticons/default/smile.gif)

this being the bus that weighs half as much as my 5,6-liter Titan but gets just as good mileage?

Never did I say it couldn't be made to work. As Scotty says, it's a dirt-simple mechanical injection system, but it does have a few fundamental underlying principles, chief of which is that the instantaneous position of the metering plate is proportional to the fuel requirement at that moment. If the plate is fluttering (and it does have some hydraulic damping to it) that principle isn't true. 6-cylinder engines have pretty much continuous intake flow - 4's are a little choppier by their very nature. And yes, I ran a Techtonics 268º cam in the ur-GTI and it ran great. That was generally accepted as radical as you'd like in an emissions-rated street engine - and I think it might have given the cat a workout if I'd still had one...

[Dr Evil]

There has been proof that CIS actually does fine with radical cams...

There's a whole spectrum of meanings to 'radical'... And 'fine' for that matter ;-) Lift is OK, but when you get into lots of overlap there are going to be issues. Are they issues that have workarounds? probably...

Porsche ran CIS on the 934's because the FIA made 'em do it, and they ran just fine, but not with as much power as the Kugelfisher injection they could run in Group 5. They certainly didn't have 'street-car idle' either. I suspect they gave up a lot in fuel economy at idle and part-throttle - but no one much cares about those in a race car.

...I am putting CIS on my tweaked out corvair engine in the bus (IMG:style_emoticons/default/smile.gif)

this being the bus that weighs half as much as my 5,6-liter Titan but gets just as good mileage?

Never did I say it couldn't be made to work. As Scotty says, it's a dirt-simple mechanical injection system, but it does have a few fundamental underlying principles, chief of which is that the instantaneous position of the metering plate is proportional to the fuel requirement at that moment. If the plate is fluttering (and it does have some hydraulic damping to it) that principle isn't true. 6-cylinder engines have pretty much continuous intake flow - 4's are a little choppier by their very nature. And yes, I ran a Techtonics 268º cam in the ur-GTI and it ran great. That was generally accepted as radical as you'd like in an emissions-rated street engine - and I think it might have given the cat a workout if I'd still had one...

Um, the bus comment was separated from the radical cam comment for a reason. They are not related. So, no need to argue (IMG:style_emoticons/default/wink.gif) The bis was related to the topic of adaptation, the cam remark was related to the concept that there is more cam variability available with CIS than more people think (IMG:style_emoticons/default/rolleyes.gif)

[ArtechnikA]

...So, no need to argue

twasn't an argument. trust me - if I am arguing with you, you will know it ;-)

...

the cam remark was related to the concept that there is more cam variability available with CIS than more people think...

I agree. So you don't need to argue ;-) ...
But it is something to be aware, especially if you're looking for efficiency (i.e. mileage) or need to be concerned about emissions (some do...). Overlap is the killer. I don't recall all the specs for the Techtonics 268º cam, other tha the signature duration. For 911's the sweet spot is somewhere between the '75 'S' cam and the 964 cam.

But the reality is that it's way easier to change cams in a 911 or Rabbit than a T-IV. I just want people to do their homework, think about what they're doing, and make an informed choice. CIS is a thing of beauty in its ability to provide efficient, smooth idle, broad smooth power band, and decent top end - with a minimum of constant tinkering. I used to go from 6000' to sea level twice a year in a 10,3:1 engine with no other attention paid than running premium gas at sea level - which was pretty much necessary only because I ran so much spark advance at altitude.

If you go in thinking you can run any cam you like because the CIS will adapt, you will probably be faced with driveabilty issues. Just look at the changes Porsche made between the last of the carb/MFI cars to the CIS cars. To be sure, a lot of those were driven by emissions requirements, especially in a leaded-gas no-cat environment.