What the process to convert from CIS to PMO??
 

Hi,

Been contemplating switching out my CIS to PMO carb or EFI. In searching on here, it looks like there hasn't been a write up from start to finish? There was a how to for removing the CIS (http://forums.pelicanparts.com/porsche-911-technical-forum/700716-removing-cis-engine-car-writeup.html), but no step by step for the PMO side of things? Is it because it is straight forward?

Does the PMO kit provide instructions on the process? Just curious to gauge to see if this is something that is doable without needing to drop the engine and how much effort it will take to do the actual conversion?

Thanks!

It's very straightforward, you take the old intake manifold off, put the PMO manifold on, and everything bolts to the manifold or the carb bodies.

Tuning them? THAT'S a different story;)

I don’t know the conversion process but a more important question is why are you converting? If you are seeking a performance bump, you need to also replace your cams and possibly your pistons.

If you go with carbs, In return you will get poorer fuel mileage, a harder to start car etc. a decent EFI can address these issues but the cost is not cheap.

I’m contemplating the same thing for my 82 SC. Our host sells them and you give them the spec of your engine and they will spec the Pmo carbs for you. It’s recommended to re curve the distributor for the carbs. Plug the Cis return line to the fuel tank, buy an appropriate fuel pump for the carbs.
I just purchased new euro spec P/c from our host. Yes they are Cis pistons but will work just fine. I am backdating to SSI’s. I’m told the distributor will work as it is but a recurve will enable a higher rev. I’m looking at the cost of reviving my old Cis unit. New fuel lines, injectors etc etc. To me from what I’ve priced I can get new PMO’s. My Cis unit has sat for over 20 years. Is the fuel distributor still usable after sitting for 20 years, don’t know. I live in a warm climate ( Phoenix) so cold start is not an issue.

When I had the engine rebuilt a couple three years back, I had sport cams similar to the 964 grind placed in. The reason I'm contemplating a swap is that my 911 is something I bought to work on as a way to get some me time. The other reason is that I heard the sound that a 911 with PMOs can make and sounds incredible.

How did you handle FPR and fuel lines? Did you use your stock fuel pump too? Did the PMO provide instructions on which fittings to use?

I replaced the fuel pump and lines with what they recommended I use, used their regulator, and it was fairly easy to do , except for running the new fuel lines through the tunnel. I eventually replaced the gas tank as well but that was mostly due to contamination.
As I recall, they did recommend fittings. I don't recall what they are though!

Highly recommend the swap. I did on my ‘77. PMO supplies a lot of good info to help get it all correct. Fuel line fittings are available from BAT (British American Transfer).

The CIS FPR is built into the Fuel Distributor, so you cannot use it for either the ITBs or carbs. You will need to check with PMO on whether a new FPR comes with the kits, or you buy it separately. You can reuse the fuel pump for ITB's, but it pumps at a lot higher pressure than carbs need. Carbs typically use fuel pressures of 5 psi, not 75 psi), so follow PMO recommendations on what pump and FPR to use for the carbs.

You don’t need to change your cams. PMO’s work great with CIS pistons, but performance can be gained with cams.
You don’t need to change your fuel pump or plug the return line, PMO has a regulator that bleeds of pressure.
Tuned properly you can get excellent fuel mileage, up to or even better than 26mpg.
Tuned properly you can start without issue, cold or warm.
The stock distributor curve works fine with carburetors and you can hook up the vacuum from a secret port on the PMO’s.
You can change them out without a full engine drop, a partial drop is recommended.
Plug and play… yes, but it’s not plug and perfect. Perfect tuning will require an expert.

Right, no need for FPR or new pump with PMOs. Great kit.

I often hear that the cis fuel pump is just fine to use with a carb set up.
I do NOT agree, it makes 77 psi , the ideal pressure for most carbs is less than 4 psi. Oh that's ok I'll just run a fuel pressure regulator , yikes !! , ok a proper FPR like the PMO, will happily cut 65 plus % or more with great efficiency , this is the regulated return type .
This the ONLY type I would ever use. This regulator is ESSENTIAL on a PMO- Weber set up.
But asking the system to regulate down to 4% of the standard pump pressure is not fair to the float system in a carb. You are just asking for trouble . What is aeration or entrained air? For the most part the fact that PMO says you can run a cis pump with their carbs is just for marketing reasons .
Saving $$$$ . lower cost .
I say the right part for the job . High volume low pressure pumps are the correct pumps to use , $65 from jegs or summit .
The red plastic housing Eddelbrock is what I put on snbush67's car . It produces 4-6 psi.
The PMO regulator is set to 3 psi and no problems , plan for the outcomes ,
Positive outcomes.
Or do what you like
Just my thoughts
Ian

https://www.jegs.com/i/Edelbrock/350/17303/10002/-1?gclid=CjwKCAiAuOieBhAIEiwAgjCvcqHiPPT8ZtiS87RBLm SLnolRPlpw9oPWDq8P_6rx45qs8iI_W0bm0xoCfsUQAvD_BwE#

This is all good to know. I've been running a stock '88 pump with my PMO's with no issues but I never really thought about it. While the car is down for major service, I might just change the pump.

In regards to harder to start, my engine barely makes a half a turn and fires right up. I just give it a little squirt before turning the key.

Awesome, a lot of great info. I'm leaning towards carbs because despite the lower mileage I think any decent mechanic can do a "good" tune. I think going the EFI route you would need to source a tuner that is familiar with the ECU you decided to use?

Charlie, find the man who will jet your carbs and engine tune before you start .
He must be a 25year plus expert on carbs , quiz him on tools and AFR numbers he wants at what rpm and throttle position, elevation, Baro, air filter system, ports, cam, comp ratio, .

Find out first then start the process

I think there are fewer than 50 people in the country that are real carb experts
except for american v8 fans , though not the same system

Paul Abbott was our true champion , but he had to retire , maybe he can recommend someone.

most carbs are just tuned to an OK level , this is far from fantastic !!!!

Ian

You’ll get a lot more “me” time with EFI by learning to tune it yourself! :)

I really enjoyed the change up. I decided to do it in phases.

1. Phase 1, take the CIS off, add carbs (Stock 2.7) and use PMO regulator

I had a lot of issues, but most of them were dealing with vintage webers. New PMOs would be much easier.

My CIS fuel pump could be regulated no lower than 4.5psi ish. That seemed to be OK.

2. Phase 2 Swap to low pressure CIS pump. This was more involved for me as my car came with the fuel pump in the back (1975) so as part of this phase, I relocated it to the front like later cars.

I cover some of the headaches of converting in my build thread.

Some other things to consider:

- Breather setup
- Fuel filter, low pressure carb fuel pump, new lines etc.
- Ignition changes (you should change to a hotter fatter spark),
- I did an RS curve on my distributor. It's not cheap.
- linkage geometry, I had to change the throttle rod from the bell housing on the trans to carbs. I had to make the hole in the engine tin bigger. The CIS bell housing crank is different angles than the mfi/carb angles. Though not 100% necessary, getting the right one on there can help with WOT and linkage issues.

3. Phase 3 will be cam/piston change up. But that's full motor rebuild time.

He must be a 25 year plus expert on carbs?? Quiz him on tools? Where do you come up with this stuff?? Have you ever owned a 911 with Webers? Have you ever torn down and rebuilt a set of Webers?? Ever tuned a set?
They’re carbs not space shuttle guidance systems. Shouldn’t be so quick to discourage someone. Carbs get a bad reputation because a lot of them are worn out and not properly restored, can’t tune crap carbs no matter how good you are. Yeh EFI is great if you have the money.

I've found more shops are comfortable with EFI than they are with carbs and, at least theoretically, once tuned should require no adjustment going forward.

In addition, if you go with an ECU from a company like Haltec they can remotely access your car and ECU while running to run diagnostics and help tune it provided all the mechanicals are in order. Pretty cool.

In my search to find tuners who were familiar with Megasquirt I had no problem, vintage Porsches on the other hand were for some reason super intimidating and several tuners/shops said no.

WRT the conversion, the mechanicals are fairly straightforward; remove CIS, install ITBs. There isn't a set instruction manual as every car and owner are slightly different and will have to figure out where to put components, how to run hoses and wires all based on their wants/needs and those of the car.

The tuning is what gets most people but it's not all that hard once you start to understand the process and what you're trying to do and with what tools.

DP
I have been tuning carbs on racing engines for 50 years , similar to the time you have been active with cars. I have been on dynos 200 times . I have re-tuned too many carbs to remember .
This is where my thought process comes from

Ian

I have huge respect for the people that can tune, maintain, and rebuild carbs. I know there are some really impressive engines out there running them flawlessly, but they aren't for me. I read the various manuals, books, and watched the YouTube tutorials. I just didn't have the patience, time, and perhaps talent to manage them myself, so I went EFI, and I do not regret it for one second. Turn key, start engine, drive off. No funny starting procedures, ongoing diagnosis, or jet swaps with weather change.

I’m trying to teach Ian my secrets about carburetors but I’m not sure I’m getting through to him.

Tip in
Tapping on butterflies.
Silent Float leveling.
Vacuum porting
Pump jet bleed holes.
pump jet diaphragms and hatchets.
Eliminating Black Magic from the floats.
Float inlet valves.
Synchronized balance and air flow.
Precise adjustments of linkage to be equal through full throttle.

And much more.

Seriously, Ian has gained about 95 HP on my car from ignition, timing and carburetor adjustments over the last year. I thought I had it tuned, was I ever wrong.

PMO tuning question.

I keep hearing how carbs are difficult to tune, is the difficulty getting them to run as close to 100% as possible?

For example: If you are at 95%, is it the final 5% that's difficult? Wouldn't the car run great at 95%?

I've been wanting PMOs for a long time but I keep getting discouraged from threads like this. I've had muscle cars and dirt bikes all my life and doing some simple tuning wasn't all that difficult on a street car and dirtbikes are fairly easy with only one carb.

Sorry if I'm high jacking the thread.

I’m leaning toward a set of PMOs and if carbs are what you want you shouldn’t be discouraged. Appreciate that the cis system is 30+ years old. I personally would never try to regulate a fuel pump designed to deliver 70-80 down to 5-7. You are asking for trouble! Just because you were told it’s ok and that currently it works for you, well when you have an engine fire then that’s on you. I’ve spoke with our host about a set of PMO’s, they will spec them for you based on info you give them about your engine. I’ve looked at refreshing my current cis system and it’s not cheap. Fuel lines, regulator, fuel pump, fuel distributor etc etc.

The difficulty is knowing what perfect is. If you’ve never been there then you don’t know what can be achieved. I think that most people don’t realize how the smallest adjustments can make an incredible difference, both in smoothness and power.

I put carburetors on and ran them for years thinking I had them perfect, I wasn’t even close. But they felt better to me then the CIS I replaced. Then Ian did some small adjustments to the linkage, then the mixture and probably increased the smoothness and horsepower by 50 or so. Then I purchased an AFR gauge, and a 123 distributor and we started dialing in perfection. There are a few other things we did to increase air flow and timing. But mostly it was experimenting with jetting and finding the right plugs.

You need to use all your senses and the right tools. You could just bolt the carbs on and tune to best lean mix, and think you got the right jetting. But you won’t know until you’ve checked your AFR’s, plugs, and timing etc. it’s really the same with any intake system your using, with carburetors it’s in the jetting. There is no standard jetting, every motor is different.

One of the hardest things to do is to get the linkage dead on synchronized. But there is a way. I’ll share it later. I’ll probably have to make a video.



http://forums.pelicanparts.com/uploa...1675297451.jpghttp://forums.pelicanparts.com/uploa...1675297545.jpg

Thanks and yes, I totally understand what your saying, just because it's good to me doesn't mean there's not a lot left in the tank. I've already decided that CDI+ or 123 will be done before I would do the conversion and already plan on having O2 bungs installed on my SSIs so that I can run a AFR guage on each bank.

My Thoughts
 

I've enjoyed my PMO carb experience.

http://forums.pelicanparts.com/911-engine-rebuilding-forum/821976-gordos-pmo-carb-tuning.html

Favorite quote from this thread:


Agree - thank goodness it's a set it and forget it process, unless you need to remove the carbs and linkage brackets for some reason.

Parting shot - installing and tuning carbs or aftermarket EFI requires considerable interest, study and patience / that or a good chunk of $$ to have someone knowledgeable do it for you.

Gordo is a great example of an owner being committed to the process of tuning his carbs .
Look at the time line , he stuck to the plan of learning , writing down the data and building a plan. ...... More than 12 months of diligent work and research.
It is a worthwhile endeavour , and takes persistence , Good on you Gordo.
I'm not trying to scare people away from the idea, just trying to help them understand the process.
Give it a shot , all you can do is learn.
Ian

Back in the stone age all we could do was make runs, read plugs and exhaust pipes

Off the wall question.

Does anyone know if a Holley Sniper EFI could be fitted to a CIS System?

I could see it being a sweet option. Cut the CIS Air box to allow attaching the unit to the base of the CIS Air box, Block the injector holes, tune and go!

Replaced the stock CIS fuel pump with a low pressure pump;

http://forums.pelicanparts.com/uploa...1662850103.jpg

This is a L shaped bracket I had on hand, just drilled a couple holes and it mounted in the stock location perfectly.

http://forums.pelicanparts.com/uploa...1662850103.jpg

Anything is possible however the cis intake runners would be a poor choice for sending atomized fuel to the heads.

OP. If you keep the CIS pump with the PMO regulator, then you can keep the accumulator. The accumulator is meant to manage the volume and pressure pulses from the CIS pump. If you go to the low pressure pump then bypass/remove the accumulator. You can keep the stock filter.

No matter what system you choose, use the PMO fuel pressure regulator and keep the return line.

The bottom line is that the high volume low pressure pump is the best system for carburetors.

Jess P,

When you say you spoke with the host, I'm assuming you mean Pelican Parts? Reason why I ask is I don't see PMO carbs available for sale on their site. Do they need to special order it from PMO?

There are authorized EMPI dealers of the artist formerly known as PMO. I think Rothsport racing, Patrick Motorsports and their ilk could be suppliers now. Expect a 20% increase in what they cost unfortunately.

My bad, PMO appears on Pelican if I search for it without entering a specific 911 model and just do a generic search. It looks like its $6200 starting
https://www.pelicanparts.com/More_Info/PMO8030.htm?pn=PM-O803-0&SVSVSI=911M

I wonder if the PMO EFI systems are going to become available.

What the heck, everyone else has an opinion on this...

Listen to Ian. He knows of what he talks. Maybe a bit of hyperbole thrown in ("at least 25 years"), but either building your own experience with tuning carbs, or finding someone with that experience, is not trivial. I've been cleaning, setting, tuning carbs for 50 years.

Did I mention cleaning? Yeah, with the introduction of ethanol-contaminated fuel, the problems with carbs getting gunked up internally has increased dramatically, ESPECIALLY with cars and equipment that are not used regularly. Any fond memories I have of tuning carbs have been displaced with unending frustration with cleaning and resetting them due to ethanol gunk. That applies to everything from chainsaws to big V8's. Full disclosure: I have a Kawasaki KLR 650 with a SINGLE carb. That I can deal with cleaning once in awhile. A single 4-bbl carb, maybe. Multiple carbs? Fuhgeddaboudit.

And the amount of ethanol contamination is already set to increase further, from 10% to 15%. This will exponentially increase problems.

So for me, there's only one real answer now--EFI. I still run CIS on my SC 3.2 engine because it works very well and I have become a CIS aficionado (I keep a 3mm long Allen wrench in the glove box), but if it craps out, I'll be replacing it with ITBs and EFI, and I will use a fixed distributor with a programmable curve, or I will just go all-in for an integrated engine management system with coil-on-plugs, etc. Why screw around with anything else?

And about the idea of grafting an EFI onto the CIS intake system--forget about that too. Carbs and intake manifolds had to be carefully designed to minimize changes in mixture to different cylinders due to the differences in "wet flow" versus "dry flow" inside the manifolds. I won't go into it, except to say that the CIS manifold was designed for air only (dry flow). It will not work well with a throttle body style EFI system. There's good reason why manufacturers replaced throttle body injection with port injection several decades ago.

The really good news is , PAUL ABBOTT is back in the biz of weber recreation

Paul Abbott
Weber service specialist
Performance Oriented

Ian

Pete , that conversation was lots of fun!!

Ian