How easy is it to switch induction systems? PS and an MFI questions?

82SC · 03-03-2002, 10:02 PM

Well as i build my SC motor the damn smog laws really get in the way of a kick ass motor...

Is it a simple bolt on/bolt off if I want o for example switch between CIS and Carbs?

I would probably run 964 cams...since anything hotter is not going to work on CIS

The engine would be a 3.4L SC double plugged 10.3 CR 3.2L ported heads...

I really don't mind every 2 years dropping the motor...doing valve adj and other maintainence...and switch the systems...

But my question is...is it a simple matter of unplugging injectors...remove carbs...slap on the CIS...plug everything back in???

As long as there are not permanent changes (machine work) etc...that would not allow the switch I would be willing to do this every 2 years...then after I am exempt ditch the CIs...swap to S-cams and my engine would be kick ass....

Or do you think the 964 cams/CIS vs 964 cams/carbs is not worth the trouble...and S-cams are really needed to optimize...???

Thanks...

MJ

What about MFI...I think these are not swappable with CIS because of different setups on the heads for each...

but what would it take to convert a MFI setup from an earlier car (are they compatible with 3.4L SC???)
and how much...

I have a decent novice understanding of most engine components, but FI is absolutely a mystery to me...

Thanks again...

Formerly Steve Wilkinson · 03-04-2002, 05:35 AM

I have exactly the engine you're planning to build--twin-plug 3.4 in an '83 SC, PMO carburetors, headers, etc. Switching from CIS to carbs is a piece of cake: you simply unbolt eveything induction-system from the heads up, substitute the far simpler carbs and their intake runners. (Plus the different cams, of course.) Then you strip out all the DME wiring--which is like just about everything that comes back to the engine compartment other than two or three sensor wires.

I think it would be far more difficult to go the other way, however, even if you left the DME and its wiring in place. I'm not entirely sure how you'd do it. And I'd wonder if the thing would pass the emissions testing anyway, with the CIS workign through valves controlled by the reground cams.

Bottom line, I don't think it makes any sense to assume you'll be able to do a re-conversion to pass smog testing every two years. I, fortuantely, live where there is no such testing.

Stephan

82SC · 03-04-2002, 06:06 AM

well what I was envisioning was keeping all wiring...
running 964 cams....

and switching carb/CIS every 2 years...

The reason is that I am getting great heads that flow well...
and my induction system chokes all $1500 of labor!!!

so my other option is get a early CIS system with better flow...but why not just get Carbs and do the switch...

But what would a Carb with 964 cam be like...worth the trouble? or is the CIS 964 combo decent...

hmmm...well what about if I have the Carbs + 964 cams and plug up a mainjet and de jet the carbs a bit would that pass emissions? especially with the double plug.... (this was suggested by a BBS member who will remain nameless)
Maybe that will pass emissions....

CIS!!!! the bane of my exsistence...then again noah p. is has good info on sticking with CIS...

I am sure EARLY-S-MAN must have a solution to my dilema???
I think many CA P-car owners can benefit from this!!!!

MJ

CamB · CamB's Garage

Don't forget the different fuel pressures of the two systems - may need to change fuel pump or somehow regulate from very high pressure (CIS) to ~4-6psi.

emcon5 · emcon5's Garage

Quote:

Originally posted by 82SC
..well what about if I have the Carbs + 964 cams and plug up a mainjet and de jet the carbs a bit would that pass emissions? especially with the double plug.... (this was suggested by a BBS member who will remain nameless)
Maybe that will pass emissions....

Amount of tailpipe emmissions is irrelevant. If it has carbs instead of CIS, it will fail the visual.

The sticker on the engine lid has a few abbreviations, which corespond to what smog equipment should be on the car. My 82 has FI-EGS-TWC

FI = Fuel injection (gasoline)
EGS = Exhaust gas sensor (oxygen sensor)
TWC = Three-way catalyst system (includes systems combined with oxidation catalyst)

There is a list of the acronyms and what they mean on the CA smogcheck info site here.

Remember, they are the government, they are there to help, and they know what is best for you.

Tom

StuttgartDavid · 03-04-2002, 01:05 PM

The CIS itself is not the flow limit on a stock motor - the cam is. I assume this is why you chose the 964 cams, which I understand to be the most aggressive possible to run with CIS. The real issue here is whether the CIS can keep up with your 10+% increase in displacement and other changes.

If your CIS can keep up (sorry, I just don't know if it will ), changing to carbs will cost you power in addition to losing smoggability. Carbs give absolutely no advantage over CIS other than the ability to run a longer duration cam. Worse, they actually cost power relative to injection when used with a mild cam. That complex induction system may look restrictive and mysterious to the naked eye, but it is not. It is literally "just what the Doctor ordered" (think about it . . . ) to match the stock engine, which is a pretty high performance peice of gear. It will breath to the limit of the cam. Porsche used it for the turbo, so clearly it can be made to flow more air and fuel. Porsche, Bosch and I all guarantee you that the CIS will make greater overall power than carburators due to more precise fuel metering and better atomization. It also will have better power throughout the rpm range, because it doesn't sacrifice midrange mixture control to avoid leaning out the top end, as carbs do. Drivability will be significantly better in corners, as fuel is not sloshing around the float bowl, alternating rich and lean when you are trying to accelerate on corner exit.

Finally, the engine will last much longer with CIS than with carbs due to increased cylinder washdown effect from the poor fuel control inherent in carbs, better temperature and detonation control throughout the powerband, etc. Note that engine longevity on the 3.0 and 3.2 cars is vastly greater than the early carb engines of 2.4L and below. Neither have heat issues like a 2.7, so that isn't the main factor. Yes, the newer engines benefit from better metalurgy, etc. But the later fuel injection gives much more precise mixture control, which has all sorts of benefits for engine longevity as well as overall performance.

Skip the carbs with the 964 cams and save your money for a good aftermarket injection system for when you finally do get to run those 'S' cams.

82SC · 03-04-2002, 08:55 PM

Thank you for that GREAT explaination...

I think you are going to join the few on this borad who really know what they are talking about (unlike me) and can explain it clearly (unlike me)

But so the main advantages of a carb system is the ability to run hotter cams...and if I am going to run the milder cam I might as well stick with CIS....

good enough for me....thanks

I think the CIS can keep up...andial was telling me how their boss' car is a 3.7L SC on CIS...and he says he loves it...
But I think I will try to souce a cheap euro or early SC setup since the intake runners are larger and flow a bit better then the later CIS....