3.0 switching to carbs...questions...
 

I am putting a 3.0 into my 914-6. It is an early US 8.5 comp. ratio big port motor. The engine has real good leak down and should not need any sort of rebuild. I could just plug this thing into the 914 and run the engine with it's CIS as-is. Using the stock 914 heat exchangers and a 2-in, 2-out exhaust should give the engine about a 10hp bump (vs the SC exhaust in a 911 installation) if my reading is correct. Or.... I can put my 40mm Webers on the engine and re-curve the dizzy. Maybe another 10-15 or so hp there. I know the stock 3.0 SC cams will work ok...but...it looks like the 964 or Web Cam 20/21 cams might add yet a little more sparkle without tearing too deeply into the engine. I realize a bump in compression would also be nice but now we are really starting to get into a top-end job on a motor that doesn't need one. My goal for this is to have a super reliable engine capable of revving to say 6800 or 7000 rpm.

Thoughts??

Which exhaust / header system do you intend to run? Frankly, given the decent engine you have, I'd leave it alone and install it in the 914. 914/6 headers / heat exchangers will help wake up that engine. Get it running and assess how you like it. If you want more power, then do it right... higher compression, Mod Solex / S / Mod S cams, and 46 Weber / PMO.

I'm in the middle of doing a Carrera 3.0 engine for my 914 GT conversion. 9.5:1, Mod S cams, PMO 46, 1 5/8" headers. I went into the build knowing what I wanted and just did it. You have the option of running a good engine immediately.

I have stock 914-6 heat exchangers and a 2-in, 2-out "sport type" (brand unknown) muffler. I am just trying to maximize this 3 liter without changing the Ps and Cs or splitting the case. So we're basically talking exhaust, intake, ignition, and cams.

Retrofit required to low pressure, high volume fuel pump, high volume fuel lines, high micron full flow fuel filters (lots of them) and a fuel pressure regulator set up

The 2.3 (that's a 2.0 with 86mm Ps and Cs) in the car now already runs carbs so all that plumbing is already in place. The plan would be to use the 40mm Webers from the 2.3 and swap them and the existing exhaust over to the 3 liter.

Post this on 914World. You'll get a lot of comments.
Leave the current cams in, stick on the (correctly jetted / venturis) Weber 40's, regulate the fuel pressure, and have the distributor re-curved. You'll need excellent fuel filtering.

I put it here because this is really more about the 3.0 liter engine...not so much about it going into a 914-6. I would really like to hear from folks who have the early low compression, big port motor as to which cams they like with carbs without increasing the compression ratio.

I have done exactly what you are contemplating.
I have a 3.0 with big port heads, SSI, 40 PMO's, with 964 cams. I believe it is best to not use the 964 cams. These are better for using the CIS. The Cam doctor will have a much better cam for you. I also am using MSD ignition and a Clewette Distributor. Also a 2 in 1 out Dansk Sport.
I love the way it sounds and drives. Definitely a lot more spirited, actual increase in HP....IDK, I have never dyno'ed.

Cam doctor??

IMO, the CIS cams really suck. There are much better alternatives. Changing cams is low hanging fruit and one of the best returns on investment for drive quality and engine character. Your -6 conversion will be light enough that a trade off for loss of low-end torque can more than be made up with overall area under the curve.

Call any of the good cam grinders (Dougherty, Elgin, Web) and tell then what you want to do. Stuff as much cam as you can fit on stock pistons.

The issue is exhaust side clearance. You can play with lobe separation, lift and duration on the exhaust side to really maximize your current (stock) internals. There are a few options.

Dougherty Racing Cams

Anybody running a Web Cam 20/21 with carbs and the 8.5 cr pistons??

Yes, 20/21 can be done.

However, You have low static compression. You want high dynamic compression. Seriously, Call a good cam supplier or engine builder and get a recommendation. Worth the effort.

Not a bad idea...

Paging Steve from Rennsport!

A stock early SC engine gets pretty wheezy after 5k RPM, especially in a fully optioned (read: heavy) 911. Cams will help a bit but you're pigeonholed by 8.5:1 CIS pistons. There's only so much a cam grinder can do to wake it up, and the benefit of carbs come from the allowed higher compression which you wouldn't be able to take advantage of.

It depends on what you plan to do with it. If it's strictly a point A to point A hotrod, I'd suggest biting the bullet and swapping in higher compression pistons with big reliefs. Then you can run big cams and spin it up.

If you want a car that you can road trip, I'd stick with CIS. When dialed in, it's super reliable and gets decent mileage. I was all about ditching CIS a few years ago for carbs or EFI and the more I get comfortable with it, the happier I am that I stuck it out and didn't write a big check for PMOs.

The 914-6 is a bit lighter than the 911...plus the 901 trans has a pretty short 1st and 2nd gear. I wonder if re-timing the cams toward the retarded side of the range of allowable cam timing might wake it up some at higher rpms. The lighter weight and short gearing plus the extra cubic centimeters should offset any loss down low.

Anybody remember what setup the old 911 spec class ran? I think they ran stock compression and cams but with carbs in place of the CIS.

You might also find some info in Bruce Anderson’s book, but with stock P&C, I think you’re limited in your gains. The CIS system should work fine and should be a lot of fun in a light 914-6. I don’t think the Weber’s will add much more than sound to the engine.

I would really consider 1.625 heat exchangers or stepped 1.5 to 1.625 heat exchangers for optimal performance.. And yes we make them but not the stock 914-6 heat exchangers are 1.5" which are fine for daily driver but all out performance stepped or straight up 1.625 would allow for the most power potential..

I used 964 cams...needed some machine work to remove the end lobe.