I have just completed a PMO ITB conversion on my 3 litre. The throttle response is night and day. Admittedly I did install a aluminium pressure plate at the same time. I can’t believe the induction noise and the way the revs climb now. It is as different car from the CIS. It performed well and was always reliable but always felt like it was holding the engine back. I am happy with the change @nd it looks great also.

The internals are good for 7200 rpm in my opinion and that is what I have been taught.

It is how I drive my car . ..............It is the 3.2 rod bolts that need an upgrade .

Also my M1 cam will pull 7,000 in fourth, 6400 in fifth @ 146 mph.

Almost all SC cams will pull to 6700-6800 rpm , just rev it until the power gets soft.

Ian

Ian, I ask because I'm seriously considering with the clutch/gearbox check/removal to tweak things up a bit, just for fun over winter, not this next year but the following, but I don't want a rod bolt or valve guides wearing to shreds. I see the videos online of bat guys selling their cars, or tedward and I'm like, why did you buy the car if it sits at 3000rpm? But... I want it to last say 25k miles if it's sitting at higher rpms, daily before a rebuild. Is this possible?

I'm not happy with my springs, (machinist picked them out but they're not true), rod bearings are good, there is no machinist nearby that can do work and I don't want to send across countries just to have some fun, too much cost and risk. You said stock, but how does one know without blowing up the engine?

Phil

Phil , give me a call and i'll talk you through it

Ian

I don't think you have priced them lately. Don't forget to include manifolds, intake plenum, filter, snorkel, linkage, etc. Improving the stock CIS or Motronic is way cheaper and more reliable than carbs will ever be.

Or go Holley 350 cfm 2bbl NASCAR carb with electric choke..
Starts instantly, one pump of the gas peddle.. I mean on the first cog of the fly wheel.

http://forums.pelicanparts.com/uploa...1670204609.jpg
Now I am changing out the electric choke for the mantle type so I can have old school cruise control..

Wow
Some serious good information and input from everyone. Our host sells the PMO carbs and they are around $5 grand. But some good points were brought up about my pistons. I’ve already purchased new Mahle euro spec CIS pistons/cylinders from our host and I’ve already had the valves done. The car is just a weekend cruiser but everyone has given me a lot to think about right now, I appreciate everyone’s input.

That almost looks like the top of a Chebby!

For the carb crew: Do you have access to ethanol free fuel?

I'm switching from Webers to EFI shortly. My reason is two-fold: Shops around here will work on air-cooled cars or carbureted cars but not many will work on both (or at least do the tuning/carb rebuilding aspect), which means the one that do are always backed up. Second, I don't have reliable access to ethanol-free fuel and in just a year and a half, my carbs started leaking from everywhere.

MrBonus - I've seen more than one video on YouTube showing how to remove ethanol from gas. Also videos of the damage ethanol does to carbs. I drive 21 miles to get 93 non eth. 25 gals in 5 gal containers. Add fuel when needed at home. Never use ethanol fuel.

I only fill up with Ethanol-free fuel. Costs a bit more, and it's only available at the lowest RON, but worth it to not have issues IMO.

Unfortunately, access to ethanol-free fuel is spotty near me. There is a place but it's 45 minutes away in a busy corridor, and with my current fuel mileage, I would be making that drive all too frequently. I guess I could store some for future use but I wouldn't even begin to know the safest way to do that.

So EFI it is for me.

I have a lot of personal experience with CIS being a very stable system that reliably deliver great power. I also have a great network of some very highly regarded Aircooled engine builders.

At the end of the day, I feel that this literally comes down to personal preference, driven by how deep you're willing to dig into your pockets...

From my experience and the experience of the professionals I am very well connected to:

CIS is a robust and stable system that (as stated) will support a wide range of applications and up to a stout horsepower number... It's not sexy and doesn't necessarily sound the motorsport part.

Carbs, make basically the identical power to CIS, they can be finicky, there is no way to tune carbs 100% perfect across the entire RPM range, but they sound amazing, provide a different expereince, and certainly look the part. The fuel mileage takes a hit and their best application is go fast...they like WOT the best. Add 5-6K to your budget to get everything sorted.

ITBs...For the performance return on the money, they're your worst option. There are literally only a handful of people in the country that can actually properly tune them. They have great response and can make power gains, on certain engines, only if they're perfectly tuned. 3.2L and smaller applications are where ITBs are best utilized. They certainly look the part, provide the sound, once tuned are rock solid, and "finicky" is a thing of the past. A Rasant style set-up will cost you $40k, for about a 10% gain on a stock application. $2000/hp is just astronomical IMHO.

I have a close friend who was "sold" on ITBs on a shorthood hotrod with a 3.6. After $31k all in, he has been chasing his tail for 4 years, sending the car up and down the east coast trying to get it tuned properly. The best result was 43whp LESS than the motor made with the OEM system. The only reason he hasn't put the VRam back on is his frustrated desire to get his "investment" to function.

I have 2 close friends who are a couple of the original RGruppe members with very heavily built twin plug 3.0 based motors, both carb'd, they both love the set-up, the attitude, and will tell you that the cars love to live wide open.

I have a CIS 3.0 that makes 215whp with cams/exhaust and it's rock solid. It rev's like a switch but that is directly related to the lightweight clutch/flywheel.

As for those accomplished Engine Builder/Race Team friends... They either use CIS or Carbs, on both street, club, and race applications. They recommend highly against ITBs based on cost/hp ratio and difficulty tuning.


....ultimately, the choice is yours...

Responses to this should be pretty entertaining.

Where in Delaware are you?

North Wilmington.

I'm sorting through my carb setup now on my 10.7:1 SC and getting the kinks out. Icarp has been a big help as we've chatted through the setup and so far, it's going well. As for ITB's, the $$$ quoted seems really out of whack, but I have not bought a system for a 911. I did however have them on previous rally cars, and while they took some dyno sessions to tune, once I have it dialed, I just needed to fiddle with getting cold enrichment.

If you are referencing the $40k for ITBs mentioned earlier, I am scratching my head on that one, too.

It is interesting how polarizing CIS can be in the community. From my own experience owning/driving an SC for over 20 years, I could not be any more impressed. I have had zero issues. Always starts up right away and settles to a nice, predictable idle quickly. I have too found that many of the respected shops and engine builders in SoCal are very complimentary towards CIS -- not what I had expected. Parts are becoming increasingly difficult to find from what I hear (I have luckily not needed to replace anything on my SC). To compare my SC with my MFI hotrod - well, certainly the MFI is sexier, sounds better and has an even better throttle response -- but it was challenging to dial in and extremely expensive to build. What I like about both options is the ability to drive from the beach to the mountains with no issues from altitude changes -- and in SoCal, this type of driving is common for those that like these driving experiences. Not sure if you will encounter a lot of elevation changes and how that might impact carbs.