carburetors vs CIS

[Eagledriver]

Our spec 3 litre engines are indeed limited by the cams. Infact that is why we specify stock SC cams and CIS pistons. It keeps things from going crazy in the engine spending catagory. They guys that have dynoed their engines have found that the torque curve is skewed toward the higher RPM range with a race exhaust system and Carbs. This is a big reason why the HP numbers are so high. The exhaust and carbs work together. With a better exhuast the CIS becomes an even bigger limitation to the overall breathing of the engine.

-Andy

[RoninLB]

anyway, CIS is a great reliable street induction.

To dump CIS for carbs better mean you really want them.
" The theoretical advantages of an IR system are more accurate calibration, no inter-cylinder distribution problems, a tuned intake length working on the second wave reflection, better drivability and significantly better low and mid-range torque. Add to this, the engine's ability to tolerate a longer duration cam and you can see a lot of things fall in favor of an IR setup."

fwiw, it's a Carb eat MFI world imo.

[}{arlequin]

at the end of the season I'll be switching from CIS to carbs and I'll have something worthwhile to contribute. I've driven w/ CIS for the past 2 years.

I haven't had any CIS-related problems, my non-starts always dealt w/ issues inside the dizzy, so I'm looking forward to seeing whether properly setup carbs can give me similar reliability.

[svonkampen]

I had TRE drop a 3.0SC engine into my '68 SWB............Had I wanted to keep CIS of SC....the install would have been much costlier......

So just using my existing Weber's and running them rich saved me thousands.

So....In conclusion, if your looking for the most inexpensive way to get a 3.0 into an old SWB....carb's are the way to go.

Sounds awesome by the way ;-)

SvK

[dd74]

Thousands saved? How's that? It might depend on the car a CIS engine is dropped into, no? With mine, it took more time cleaning up all the oil and soot spewed from the old 2.7 than it did dropping the 3.0 in. And anyway, if the additional cost is for the Lamba (or however it's spelled) unit, that doesn't need to be part of the install.

[Tyson Schmidt]

The higher compression afforded by the 80-83 cis 3.0 motors work well with carbs. We have had lots of real world experience with clients and our cars with the installation and back to back comparisons. Without any doubt if you want more power, removing the cis and installing carbs are probably the easiest thing for thr diy to do. Sure there are several efi systems out there and this board has members that have gone the diy route. I cannot speak as to what hp gains those have with using the cis tubing and single throttle body, but i am guessing they do not have the total gains that the carbs would yield. Notice that all other items being equal: SSI's or headers, cams- most of our previous installs were on stock cammed motors, recurved distributor to match the induction used.
As others have noted here, throttle response is much better over a cis using carbs too. Net gains on an otherwise stock internal motor, about 35-40 hp.
To answer the original post's question "Is there any instructions on install?" I am sure some one has outlined the procedure here and can help
Now to the caveats:
1) installing carbs will defeat your emmissions specs. Your car will not pass smog tests anymore
2) Carbs will require more tuning depending on conditions. You may end up with a small collection of jets to accomodate the various altitude and humidity changes
3) You will experience drastically reduced mileage (if you don't then you have not jetted your carbs properly for more performance)
4) With a open air filter arrangement, noise levels are increased (though it sounds great!)
5) Your engine will run a little cooler due to the inherent nature of carbs being a little on the rich side when jetted for performance
6) If competing in a series, you may be bumped into a much more competitive class thereby invoking the "slippery slope rule", whereby large amounts of money are rationalized on being spent to be competitive in the new class

Finally, Porsche was looking for a induction system that would yield performance and good emmissions. CIS was developed by Bosch to fit those requirements. As the specs were tightened from country to country, so did the further modifications and improvements to the CIS. They are good reliable systems when all is in spec. But you really have to think hard about spending a couple thousand on rebuild/replacement of the system (there are only so many used parts left that are any good!) in the quest for more performance.

Posted by TRE Cup (i did not know i was on tyson's acct!)

[dd74]

TRE- any experience with PMOs? Or are they more or less the same as Webers?

[Brother]

Switching to carbs!

[dd74]

Originally posted by Brother
Switching to carbs!

I just called TRE...

[Brother]

I just got some headers off the classifieds on this board so I'm gonna hook it all up with an M&K Specialties muffler and then start saving for some PMO's.

[dd74]

Oh Brother!

[Mysterytrain]

listen, I've been doing the 'no carb' diet thing and lost 30 lbs does anyone know what the horsepower gain is? lol, loved this post! There ain't nothing like passion.

[}{arlequin]

now if we could only get Henry's input on this too, this thread would be a "perfect 10"!

Dave B,
Thanks for the input.

[dd74]

Originally posted by }{arlequin
now if we could only get Henry's input on this too, this thread would be a "perfect 10"!

Dave B,
Thanks for the input.

If you're writing about the same Henry, he's assured me several times that 230-240 hp is possible out of a CIS-equipped 3.0. I trust Henry immeasurably. Fintstone has a Supertec-built 3.0 that has CIS, and according to him, the engine screams.

The idea, I think, is bolting a newer 3.0 bottom end to an older 3.0 top end, setting in some 20/21 cams and doing distributor work. I'm not certain if that's all of it, but Henry knows his stuff...

Of course, the one person who should chime in here is Noah. He's got the most powerful CIS engine on the board IIRC...

[}{arlequin]

Originally posted by dd74
Noah. He's got the most powerful CIS engine on the board IIRC...

I thought that was Rdane

[dd74]

Originally posted by }{arlequin
I thought that was Rdane

...in a running car. Dane's engine is out, I thought. Plus, Dane's motor is stroked-out to 3.4. It's nice, but for the amount of money the engine cost him, I would have opted for an induction system other than CIS.

[}{arlequin]

Noah's car is running t-bitz so it's not exactly CIS either

[dd74]

Originally posted by }{arlequin
Noah's car is running t-bitz so it's not exactly CIS either

Noah's car before it ran TBitz had 240 hp. Search it out.

[Jeff Alton]

I am putting together a 3.4 with PMO's. Yes, scrapping the 3.2 Motronic and going crankfire twin plug and carbs! Old school! Yipee.

Jeff

[}{arlequin]

Originally posted by dd74
Noah's car before it ran TBitz had 240 hp. Search it out.

oh that... gotcha