CIS or PMOs
 

I'm panning the build of my engine in my 3.0l SC. I've had quite lengthy discussions with the builder and have all elements planned and agreed except the induction choice, which he says is my choice. The builder has experience of modifying the CIS system as he supports race cars that have to use the CIS system as part of the rules of the class. So he effectively has a recipe he can follow for my car. The car is not for the track but spirited occasional road use. It's one of 4 non daily driving cars I've got so by no means a daily driver. I'm somewhat mechanically minded but don't swing spanners myself and really I will want the car to start without having to open the engine lid and fiddle around. I don't mind a bit of a routine (pumping the pedal etc), but if flooding etc is regular and I'm stuck when I need to get going I'm going to get frustrated quite quickly.

As those responding to this thread will know there are pros and cons to each choice and here is how I see it

CIS

• Factory standard
• Reliable starting
• Good cold driving characteristics
• Cheap
• Good fuel consumption
• No fuel smell in the cabin and area where the car is stored

PMOs

• They're cool!
• They're something different - carbies vs EFI. It was 25 years ago since I had a carby car
• Sound
• Throttle response
• Tunability
• Ultimate power and torque

My heart wants the PMOs, but I'm concerned that they're going to be harder to live with than I think. Clearly it's a big decision to make so I'd be interested in feedback from those who have made this choice or lived with PMOs and what your experiences have been.

Many thanks.

CIS is not EFI. EFI with ITB's is the way to go!

Why would you choose carbs over EFI? EFI:

• Cooler than CIS or carbs!
• In 25 years you have forgotten what a pain carbs are!
• Sound better than CIS or carbs.
• Have better throttle response than CIS or carbs.
• Are more tunable that CIS or carbs.
• Have more ultimate power than CIS or carbs.

OK, thanks for that perspective. I'd heard that it is quite an expensive set up and PMO carbs are already what I call expensive.

Would you care to list the main parts you need for an EFI / ITB set up and the approx cost of each part. Or direct me to a recent thread where this information already exists? Is this a good yardstick? http://www.clewett.com/index.php?main_page=product_info&cPath=2_56&produc ts_id=14

Still interested in the living with carbs feedback.

You've been PM'd

regards,
al

I would imagine $7500+ would be a reasonable budget for ITBs using new parts complete with a decent pump.

A 'Bitz' Racing type conversion may be more economical if you don't want a major performance increase.

Im looking for a decent efi system what do you guys recommend?

Thanks for posting this question. I am looking to build a 3.4 next year- any different recommendations based on motor?

I was leaning towards 46 PMO's.... appreciate input by the experts

Why do people want to do carbs??????????? They suck compared to EFI and ITBs.

I understand the "cool" factor re carbs. But I got over that about 30 years ago when my last Six had carbs and I had to always fiddle with them and it popped and backfired and stumbled when it would start. Ever since I have gone with the factory Porsche injection and have never had an issue. My current car has an essentially stock, (we did swap out the stock cams for 964 cams and added a Steve Wong chip) fresh 3.2 going in it with Motronic. I look forward to driving it everywhere I want without issues.

I'm with Scott Winders, ITBs with EFI beats everything.
*Incredible throttle response.
*Incredible sound.
*Better fuel milage (than CIS)
*Reliable starting
*No fuel smell.

If you would change only ONE thing on your engine you should choose this over anything else.
I went to ITBs with EFI on my bone stock 3.2. That engine went from docile to monster. Totally different engine.

Save the CIS in a box if someone in the future would like to return it to stock.

EFI is always better, the only issue is the cost....that's the reason I went with some good carbs.

If EFI was cheaper and closer to the price of carbs, it would be a no-brainer.

Taking off the CIS stuff hopefully this weekend, anyone need a 2.7 CIS system :D

I can provide an effective/economical EFI/ITB alternative to carbs

X-Faktory - Home

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I've never had much problem with carbs...and I'm a EFI guy. But then I kind of know what I'm doing.

I have webers on my 3.0, if I feel they are too much of a PITA I'll build a intake set out of Triumph or GSXR TB's and do a SDS or MS EFI system.
Selling my webers should recoup most of my cost.

That's what I did on my '67 bug.
http://www.914world.com/bbs2/uploads...1385565263.jpg

http://i197.photobucket.com/albums/a...psevdf7fwl.jpg

Our system is slowly taking shape and the first set of throttle bodies are being assembled.

I have a couple of pairs of Rowlands (South Africa) Intake Manifolds which I don’t need as we have made 911R Style manifolds as an alternative.

They have a closer spacing than Weber manifolds and may work with Motorcycle parts – For sale at a very good price.

http://i197.photobucket.com/albums/a...psomkgcx44.jpg

ITB / EFI feedback is interesting, especially if the costs are not out of control. I'll add this to the list of topics to discuss with my engine builder but I think my chosen builder's understanding and knowledge and ability to support them will be a big factor in which way I go.

Aside from that, seems like a lot of negatives on carbs (which is fine) but are there any comments on the for side to try and get some balanced feedback?

carbs
 

I know that I'm an EFI guy and this is blasphemy....but carbs are cool too! One of the pros is that they are more readily understood by more DIY peeps and mechanics as a proven method of extracting more power out of CIS based engines. That, combined with the (seemingly) shorter learning curve, lack of intimidation, availability of high quality carbs from PMO........makes carbs still an attractive alternative.

I like them....but obviously I've been there and done that (MFI too) and have personally taken a large drink of the EFI kool-aid...............try it...you'll like it.

i'll give you some feedback based on my own (local) experience:
1. fuel economy: not much in it, the webers did not use that much more when tuned and jetted properly, my experience is that the increase in fuel consumption is from a) incorrect setup, or b) you start mashing the throttle more due to the great noise.
With regards to tuning webers.. i never had to touch mine, again, if you are using new parts they shouldn't really go out of tune like people say. If anything i'd say maintaining a CIS system is on about par with webers.
Cold start has also never been an issue, i don't even have a choke on mine. I drove my carb'd bmw 2002 to melbourne and back twice, and through the victorian alps, never let me down, and surprised some newer bmw's.

2. Cost: PMO's are expensive, EFI/ITB's are more expensive. about 50% more expensive when it's all done and tuned. close to 8.5-10k AUD when it's all said and done, whereas the PMO's are easier to setup after the initial sting and will be in for 6k or thereabouts. Try and do as much as you can yourself, but the cost saving of cobbling together your own system over an off the shelf kit is often offset by the pain of making various parts work with each other.

3. I have a few carb'd cars that work fine, and some that just never ran properly, had flat spot, nothing under 4000rpm etc.. my efi cars tend to have minor niggles and generally ran nicer overall. it is definitely worth getting a good workshop to set them up.

If it was me, try to get some seat time or even passenger in a carb'd 911 and get the owner to run you through how it runs, how it is to live with. You don't save money going carburettors if you then discover you don't like it and have to redo it all.
If you are up my way i can give you a carb vs efi/ITB run through (triple carb'd 240z vs EFI/ITB 3.6 longhood).

I battled with this topic myself for my rally build. I built a EFI system for my last Mitsubishi rally car and had little issues besides getting a good cold weather map. In the end, the car ran good but I did end up taking it to a tuner and getting it on a dyno for load based tuning.

When I started building my SC, I bought a bunch of triumph parts and designed a system in CAD for the car. While I was doing this I was tracking cost on all the setups and I decided that my home brew EFI setup was going to run me nearly 4k and that did not include dyno time. With the cost of PMO 46's @ $4200 and a 12 plug about $1200, the total package was not much more. The biggest thing for me was people seem to have little interest in second hand EFI setups, especially homemade ones...contrast this is 46mm PMOs which sell in a day.

Also, they look the business.

http://forums.pelicanparts.com/uploa...1475631771.jpg

Carbs vs CIS vs EFI
 

Kind of depends, but based on the sounds of your interests - I would stick with the CIS and your guy who knows the system.

I wrestled with Carbs vs EFI for my engine.

I'm a DIY'r so my decision finally came down to the idea that with EFI, I might end up having to bring my vehicle to a tuner to get it configured right. I found plenty of DIY EFI projects (using kits like vs. assembling various parts/components) ending in frustration and handing off to a pro.

I went with PMO carbs and have loved them. Setting them up to optimize them for my engine was a steep learning curve - but I was into it. I had multiple conversations with Richard Parr and Paul Abbott, who I found extremely helpful and incredibly knowledgable - and more than willing to share their knowledge and experience to help me. The whole experience is part of what I enjoy about this car - the interaction and exchanges with an excellent community who surround and support the 911...

My carb'd engine takes a few pumps and it's started. It has a few spots that could be better (slight hesitation when stomping off of low RPM), but in general they are exceptional. In comparison with a finely tuned EFI system, the carbs will always have some form of trade off in how they are configured, whereas an EFI system can be incredibly efficient and effective across all driving conditions.

Why CIS... In the right hands it can be a great system, as your builder has proved in some of the engines he's worked on. Additionally, unless you plan significant engine upgrades, I don't think you will get the bang for buck on going to carbs or EFI.

My 2 cents.

Good luck, Gordo

EFI................is a good thing

https://www.youtube.com/watch?v=pxXwaL_TdmY&feature=youtu.be
https://www.youtube.com/watch?v=xaj0FyEmc68
https://www.youtube.com/watch?v=enRgZ4FUNB4&feature=youtu.be
https://vimeo.com/128026936

LJK Setright who was the Technical Editor of CAR magazine once wrote 'A carburettor is an instrument that has been specifically designed to produce the wrong mixture under all conditions'.

LJKS was a firm supporter of Fuel Injection and made some very valid comments.

Carbs, however, make it relatively easy to modify engines and to tinker at weekends without the cost of a bunch of expensive tools and computing.

As technology has become more accessible and the programming tools needed have reduced in price many of the arguments in favour of carbs have become less significant.

Historic Motorsport is one area, however, where EFI systems, at least in FIA Sanctioned events, won't encroach.

It is also useful to understand the basic needs of the ignition/fuelling requirements of an engine which remain constant regardless of how we decide to provide the fuel and the spark.

We still have interest in both systems as well as for a sound conversion of a CIS into a single I

Don't think there is an 'absolute' solution it all depends on the real needs of individual owners.

I have spent many weekends "tinkering" with carbs. Trying to obtain steady AF ratios at multiple throttle angles using carbs is a nightmare. Idle jets, main jets, air correctors etc.

Using wideband O2 measuring equipment is a must during setup, you soon realise carbs are blunt instruments compared to electronic fuel injection.

Saying that, CIS when setup correctly will be tough to beat if using a standard engine on normal road conditions.

I'd say tuning EFI is cheaper. Almost everyone has the tools, a laptop. Even an ipad will work with some systems. With carbs you need a bunch of different neck rings and jets.
With electronic ignition you can change the ignition curve with a few button clicks instead of sending away the distributor for a recurve/rebuild.
Assuming a CIS system in Tip-Top condition (with a bunch of n/a parts) its still a very boring engine...

I don't think a carb is a blunt instrument -it is just what it is and it used to all that was available.

You have to understand that setting up carbs was usually done by ear and by road testing.

When we started Rallying we had a screwdriver, a rubber hose and little else.

Wideband lambda sensors, rolling roads and all the other fancy kit just hadn't been invented.

We seemed to manage and I think it should only take about half a day to set up carbs virtually from scratch.

Everyone had a stock of jets, needles and the like in the same way that everyone has a lap top and a set of jet reams was obligatory.

It really isn't that difficult.

It isn't all that easy either.

A carb is a blunt instrument compared to modern EFI. The difference between pad and pencil versus a calculator is similar! There is no situation were carbs out perform EFI. None. Nowhere. Nohow.

Carbs are less efficient. Carbs don't even come close in tuning granularity. The only place carbs are equal to EFI is possibly no throttle and at full throttle. Anywhere in between EFI is vastly superior.

^Agreed. For the cost of PMO's, you can buy, have installed, and tuned EFI.

Compared to EFI they are. Even large car companies like Audi couldn't get the mixture right when they had carb fed engines.....they were pig rich under heavy load.

I'm sure lots of people "tuned by ear" but then how long did the engine last with the oil being washed from the bores by an overly rich mixture or burnt valves from it being lean.

Anyway....carbs look cool and on some old crappy British "sports car" , then they are acceptable.

It's the same argument with distributors....sure you can set the max advance the same but the curve or trimming odd spots out in the midrange is better left to EFI.

I still look at the condition of the plugs and the colour of the exhaust tail pipe as a guide of a cars overall running though.

You guys must have all been really lousy at tuning carbs. :)

97% of all carb issues I see are owner/novice induced.

NASA put a man on the moon with human calculators... pad and pencil. Many were black women mathematicians like Katherine Johnson and Mary Jackson. SmileWavy

How about a slide rule? :)

I think you miss my point completely.

I just don't think it is a contest.

We run carbs on Period FIA race engines, there is no alternative, we use Solex 40PIs as they are mandatory. We have had to develop an expertise and learn how to make them work.

When you have engines on carbs and make them run well it is rewarding and enjoyable.

I am equally sure that a good EFI will be superior in every respect expect perhaps WOT.

Equally rewarding but why does the comparison have to so black and white.

Some of us old farts still like them :D

I used to read him all the time when he was alive. Things have gone downhill since his departure.

https://www.youtube.com/watch?v=bripeGzQJ_4

https://www.youtube.com/watch?v=2kcaq6eUQgI

First start?

https://www.youtube.com/watch?v=2kcaq6eUQgI

Which triumph throttle bodies are you guys using?

The newer 2000- something 3 cylinder TB's. There a couple of threads in the tech forum on it if you do a search.

I've got the 45mm set you need if you want to explore that route. I was aiming for this direction before I went PMO. This CAD is built off the Triumph parts and was going to use water jet aluminum adapters and off the shelf aluminum tubing.

http://forums.pelicanparts.com/uploa...1476054478.jpg