Can I use CIS heads with carbs?

teachkenpo · 04-27-2010, 05:14 AM

Hi, I just purchased a set of newly rebuilt 73 CIS 2.4 heads. I was planning on using them on a 2.4 rebuild with Carbs. Is there anything significantly different with these heads that could cause a problem when using with the carbs? The build will be a 2.4e with 2.2e pistons and either solex or e cams.
Thanks,
John

Porsche-O-Phile · Porsche-O-Phile's Garage

Shouldn't be an issue AFAIK.

teachkenpo · 04-27-2010, 02:05 PM

Thank you for the reply. Do you know if there are actually any differences to how a CIS head differs from a MFI or carb head?
Regards,
John

Superman · 04-27-2010, 03:18 PM

I don't know. But.....I wouldn't expect them to be different. With carbs, I would use different pistons and different cams. But I doubt the heads would be any different. Unless of course you wish to twin-plug the heads.

rfuerst911sc · 04-27-2010, 03:22 PM

I'm running carbs on two different 3.0's that were CIS originally with no problems.

4sd911 · 04-27-2010, 04:08 PM

There should be a cutout on the intake for the fuel injector. I believe you need adapters from PMO or the cutout can be welded and resurfaced.

SCOTITUDE · 04-27-2010, 05:14 PM

carbs on SC 3.0l, plug and play, direct simple swap. no issues.

RWebb · RWebb's Garage

I guess people are assuming he will keep the CIS pistons also - if true, then sure he can run carbs.

IF he changes to different pistons, then I'm not sure.

teachkenpo · 04-27-2010, 08:48 PM

Thank you again for all the replies. Just to clarify the various questions, here is what I am running.
2.4 crank
2.4 cylinders
2.2 pistons (to give it a little higher compression)
Solex or E cams
73 2.4 CIS heads
weber 40 carbs

I will run it and see how it goes. I will post results here.
Regards,
John

Flieger · Flieger's Garage

Quote:

Originally Posted by teachkenpo

Thank you for the reply. Do you know if there are actually any differences to how a CIS head differs from a MFI or carb head?
Regards,
John

CIS and carburetor heads are similar.

MFI heads have a hole in the intake port where the MFI injector sticks in. CIS injectors are above the head/port area and do not have this cutout.

Courtesy of Hans and Ed at KundenSport:

Steve@Rennsport · 04-28-2010, 12:17 AM

Quote:

Originally Posted by teachkenpo

Thank you for the reply. Do you know if there are actually any differences to how a CIS head differs from a MFI or carb head?
Regards,
John

Hi John,

No worries,......all you need are the proper manifolds that fit the CIS heads.

PMO makes them.

Don't forget to get an insulator kit, too.

pcar9119 · 04-28-2010, 12:37 AM

You can just port you old intakes also. I had mine port matched and they work great. The CIS heads will have the intake port notched out for the injector. I just put on new Gaskets and away I went. There is no need to weld up the head or buy 300.00 intakes from PMO.

E Sully · E Sully's Garage

The 73.5 CIS heads have the injector mount next to the port opening. I bought the PMO insulators notched for these. I had the local shop make aluminum plugs the same size as the injectors to plug the opening.
I ground the intake manifold to match the insulators.

pcar9119 · 04-28-2010, 12:54 PM

Yeah, I was thinking 3.0 heads. They have the notch. Good luck with your carb conversion

teachkenpo · 05-03-2010, 03:04 PM

Ok, now I am really confused. Now that I have unpacked the heads, they look more like MFI than CIS. The heads are dated 1-73 and here is the picture.

I thought the CIS heads had the small groove in the intake. Was a 73.5 CIS different than other year CIS? How do I use these heads with carbs?

Thank You,
John

jbell959 · 05-03-2010, 03:15 PM

Those are CIS heads... the 73.5 engine was the only one with that type of heads. Starting in 74 the CIS injectors were in the intake runners. As Ed posted, you will need to plug those injector ports. Other than that they are the same as MFI or carb heads. The MFI heads have an injector port with threads... CIS is a press-in injector.

teachkenpo · 05-03-2010, 03:21 PM

From what I just learned, the 73.5 CIS did have a MFI looking hole in it for the injector. So, these heads are in fact 73.5 CIS and no one makes a plug for that specific half year application. It was suggested that I tap the hole and put in a plug. Unless someone has a better idea, I will give that a try. Seems like a shame to bugger up these heads by threading the injector holes. Perhaps I can just tap them partially so that they could be used in the future if someone needed original 73.5 CIS heads.
Thanks for listening to me think out loud.
Regards,
John

teachkenpo · 05-03-2010, 03:23 PM

Thanks Jbell. Ed did state this, but I didn't understand it at the time. I do now. Thank you all for your patience with my rather slow learning curve on this topic.
Regards,
John

E Sully · E Sully's Garage

Here is a pic of my 73.5 CIS injector ports. I had the plugs made to fit the injector rubber grommets with a threaded end so that a bolt could be used to pull them out easier. Your heads seem to be missing the metal sleeve that would hold the rubber grommet.

teachkenpo · 05-04-2010, 07:30 AM

Ed,
That is part of what confused me when I saw your pictures the first time. Since these heads were rebuilt, those sleeves seem to have been removed. It was suggested that I just thread the head to take a threaded plug. Your plugs seem to be a press fit, but to do what you did, I would need to re-install those sleeves.
John