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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.
Old 10-02-2016, 09:51 PM
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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.
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Old 10-02-2016, 10:32 PM
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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&products_id=14

Still interested in the living with carbs feedback.

Quote:
Originally Posted by winders View Post
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.

Last edited by Pork Chops; 10-02-2016 at 11:03 PM..
Old 10-02-2016, 10:52 PM
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You've been PM'd

regards,
al
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Old 10-03-2016, 08:12 AM
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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.
Old 10-03-2016, 09:07 AM
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Im looking for a decent efi system what do you guys recommend?
Old 10-03-2016, 04:20 PM
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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
Old 10-03-2016, 08:42 PM
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Why do people want to do carbs??????????? They suck compared to EFI and ITBs.
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Old 10-03-2016, 09:24 PM
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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.
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Old 10-04-2016, 06:35 AM
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Quote:
Originally Posted by Pork Chops View Post
CIS
  • Factory standard, YES
  • Reliable starting, NO
  • Good cold driving characteristics, MAYBE
  • Cheap, MAYBE
  • Good fuel consumption, Compared to what?
  • No fuel smell in the cabin and area where the car is stored, MAYBE

Many thanks.
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.
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Old 10-04-2016, 06:57 AM
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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
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Old 10-04-2016, 07:35 AM
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Quote:
Originally Posted by Pork Chops View Post
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? Individual throttle body kit - single plug [9007-03] - $6,650.00 : Clewett Engineering, The complete solution for ignition & fuel injection

Still interested in the living with carbs feedback.

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

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Old 10-04-2016, 07:50 AM
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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.
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Old 10-04-2016, 09:32 AM
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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.

Old 10-04-2016, 10:20 AM
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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?
Old 10-04-2016, 02:53 PM
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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.

Quote:
Originally Posted by Pork Chops View Post
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?
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Old 10-04-2016, 04:15 PM
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Quote:
Originally Posted by Pork Chops View Post
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.
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).

Last edited by clutch-monkey; 10-04-2016 at 05:20 PM..
Old 10-04-2016, 05:18 PM
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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.


Last edited by 3literpwr; 10-04-2016 at 06:53 PM..
Old 10-04-2016, 06:44 PM
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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
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Last edited by Gordo2; 10-04-2016 at 07:19 PM..
Old 10-04-2016, 07:15 PM
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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
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Last edited by al lkosmal; 10-04-2016 at 07:33 PM..
Old 10-04-2016, 07:25 PM
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