Why EFI?, maybe excellence was expected and they came as close as they could.. Options

[JFJ914]

Thanks Jeff.

Now I throw out the challenge to someone running a stock 2.0L with FI (NOT MODIFIED) in any way and running well, to go do a dyno run and post a print out of HP v AFR and we can all see the differences between Carb & FI in black & white once and for all.

Hi Darren,

Thanks for the info. Regarding the original question, the answer is EMISSIONs. What would your setup have provided in the way of HC's and NOx? US requirements starting in 1968 screwed up everything we held dear in performance cars. I know we can get away with non emissions HP mods with our 40 year old cars today, but it was far different back in the day.

[Darren C]

Very Nice info Jeff, but it doesn't show AFR which is what we need to compare eggs with eggs.
Maybe i can convince a fellow UK 914 FI owner to visit the same dyno and then we'll get a fair comparison. However at $150 an hour for dyno time it may prove a big ask.
The data I just shared on here cost me 4 hours to obtain!

We all know the real answer was emissions, my input to this thread was to make it a little more constructive. As regards HC's and NOx, in UK we have an emission tests each year. Older cars are exempt but I still get mine tested for kicks. The 914 on a carb conversion likes to run rich (hence less mpg when you convert) at 3%CO it runs but pops and farts. 4% CO and its fine, but would barely pass the modern UK emissions test.
If you look at my graph the ideal AFR is 14.7:1, with carbs you will see they run between 13:1 and 9.5:1 in the jet range. Lower than a 115 main jet in a 2.0L carb car will get you close to 14.7:1 but you loose power & driveability (I tried it)
Bosch state that most spark ignition engines develop their maximum power at air/fuel ratios of 12.5:1 - 14:1, maximum fuel economy at 16.2:1 - 17.6:1, and good load transitions from about 11:1 - 12.5:1. However, in practical applications, engine air/fuel ratios at maximum power are often richer than the quoted 12.5:1,

This is the reason modern FI triumphs over carbs, because it can finitely vary the fueling to meet emissions.

[brant]

We all know the real answer was emissions, my input to this thread was to make it a little more constructive.
If you look at my graph the ideal AFR is 14.7:1, with carbs you will see they run between 13:1 and 9.5:1 in the jet range. Lower than a 115 main jet in a 2.0L carb car will get you close to 14.7:1 but you loose power & driveability (I tried it)
Bosch state that most spark ignition engines develop their maximum power at air/fuel ratios of 12.5:1 - 14:1, maximum fuel economy at 16.2:1 - 17.6:1, and good load transitions from about 11:1 - 12.5:1. However, in practical applications, engine air/fuel ratios at maximum power are often richer than the quoted 12.5:1,

ideal AFR for a 914 isn't 14.7
I think your own research shows that
and a DJet tuned for a more rich mixture does help
I've always done this to all of my F.I. cars

14.7 may be a goal in a laboratory... looking for emissions and theoretical burn
but with an air cooled motor, other traits come into play such as intake charge cooling, max power, etc...

in short, these cars like a more rich mixture under load (any time your not cruising at light throttle or idle)

its long been my belief that the historic valve seat problem with stock 914/4 motors was due to the factory setting up the fuel injection too lean in an effort to improve emissions/fuel economy.

empirically.. it is my observation that a lot less carb'd cars dropped valve seats due to running a more rich mixture and the cooling effects of a rich mixture on the heads

brant

[ConeDodger]

Thanks Jeff.

Now I throw out the challenge to someone running a stock 2.0L with FI (NOT MODIFIED) in any way and running well, to go do a dyno run and post a print out of HP v AFR and we can all see the differences between Carb & FI in black & white once and for all.

Except that would be a pretty much worthless comparison. Unless the two were compared on the same Dyno with the same base settings and ambient conditions you still aren't comparing, how did you put it? Eggs to eggs?

I'm certainly not saying you can't make more HP (which is a worthless number because you don't use HP when you drive, you use torque) with carbs. I also said the reason for the change was emissions in a previous post. Carbs are so much cheaper to use than EFI that the bean counters would never have allowed them unless they were necessary for some other reason. That reason was emissions. But coincidently, EFI is far superior as far as flexibility, resolution, dependability...

We agree, but the scientist in me can't allow a worthless experimental model.

Keith Franke, a retired Lawrence-Berkeley Laboratory scientist and Lotus enthusiast once told me that carbs make up for a multitude of sins by being run "butt-ugly-ass rich." He redesigned the jetting on the dcoe Webers because he wasn't allowed to put EFI on the Lotus race car he enherited from his father. His Hypojets made the dcoe an almost civilized set of carbs. I ran a set of three of them on my 240Z for years. But, they can't compare to the control even rudimentary programmable EFI like SDS can give. You mention Stochiometric A:F and that is the magic emissions number but slightly richer is where the power and torque is made. The problem with carbs is that one step down from too lean on the jets is often way too rich.

[DBCooper]

Interpret this data as you will, it shows the pros and cons of fitting carbs over the whole rev ranges.
It’s not heated opinion its hard fact.

This information is worth far more than the 4 pages that proceed my post.

Sorry to disagree, but I don't think this information lends anything to the discussion. You were jetting carbs for power. So were any of your dyno runs done at part throttle? Then the results are applicable for full throttle situations, and how often do you drive your car at full throttle, what percentage of the time? So how is that related to "drivability"? And except at full throttle how does it shed any light in any way on "the pros and cons of fitting carbs", or any comparison of fuel injection vs. carburetors?

The reason no manufacturer uses carburetors any more is that carburetors are primitive and only fuel injection will give them the control they need to meet emissions standards. Fuel injection will meter the correct fuel/air mixture for ANY driving situation. Carburetors can't do that, simply can't, and that control isn't only emissions, it gives the same control over every aspect that affects "drivability". That was as true back then when Porsche/VW installed injection on these engines as it is now. Fuel injection is better today than it was then, but it's always been better than carbs. That's not a baseless "claim" because empirical evidence is easy enough to find, just do a google search of "performance comparison fuel injection vs. carbs" or anything similar and look for actual test results. For peak power, as in the dyno charts above, once jetted there's little difference between carbs and F.I., but for every other measurement that affects "drivability" fuel injection is better.

Excuse me for being undiplomatic but this isn't secret information, and to imply that Porsche "effed up" by choosing fuel injection is simply ridiculous.

[stugray]

This information is worth far more than the 4 pages that proceed my post.

You mean it would have been (more useful) if you had presented any FI data to compare it to.

[gereed75]

Thanks Darren for the post. Wish it had been started in a separate thread for open discussion about carb tuning.

I have a wide band O2 sensor and gauge on my 6. After much research and consultation with very experienced folks to get jetting right, I see very solid 12.3 - 13.5 AFR's under pretty much the entire RPM range under driving loads (heavy throttle and acceleration and pulling hills etc).

However under partial throttle steady state cruising, I see AFR's in the 10's - way too rich for economy.

There may be ways to correct this, but they will require some carb mods not easily done (changing of idle air correction jets, that in the IDA 3C are not changable).

My point is, the triple throat Weber is a pretty sophisticated carb (PMO's are a bit better). Mine are tuned relatively well. They are fun and make good power when being romped on - otherwise they pretty much stink. They just don't carburate cleanly everywhere and probably never will..... short of doctorate level fiddling.

Am currently putting together an EFI system based on MFI throttle bodies. Really looking forward to seeing how well this engine can run!!

[brant]

Thanks Darren for the post. Wish it had been started in a separate thread for open discussion about carb tuning.

I have a wide band O2 sensor and gauge on my 6. After much research and consultation with very experienced folks to get jetting right, I see very solid 12.3 - 13.5 AFR's under pretty much the entire RPM range under driving loads (heavy throttle and acceleration and pulling hills etc).

However under partial throttle steady state cruising, I see AFR's in the 10's - way too rich for economy.

There may be ways to correct this, but they will require some carb mods not easily done (changing of idle air correction jets, that in the IDA 3C are not changable).

My point is, the triple throat Weber is a pretty sophisticated carb (PMO's are a bit better). Mine are tuned relatively well. They are fun and make good power when being romped on - otherwise they pretty much stink. They just don't carburate cleanly everywhere and probably never will..... short of doctorate level fiddling.

Am currently putting together an EFI system based on MFI throttle bodies. Really looking forward to seeing how well this engine can run!!

changing your emulsion tubes and float level would likely get you in the direction you want to go.... Also, the air correction jets have a profound effect on part throttle
Smaller primary venturi's also have a huge impact on part throttle and lower rpm/velocity mixtures...

more parts, more money, and more tuning could solve your part throttle NON PROBLEM.. that is easy to live with

[gereed75]

Thanks Brant, First let me say that I also consider it a non-problem. Partly just illustrating the point about how deficient even well tuned carbs can be...but I would also like to get it better.

The engine is a 2.4 with some head work done, DC 30 cams and 9.5 CR, single plug.

I have played a bit with emulsion tubes and am running F26's with 32mm venturi's.

Idle AFR's are around 12 (hard to tell, they vary alot).

From everything I have read and all I have talked to, the idle airs seem to be a definite factor. But, as you know they are pressed into the IDA 3C body.

Please tell me more about float levels. Mine are set "stock". I guess lowering them might effect the idle circuit towards lean???

Thanks man, now this thread is getting constuctive!

PS.... love your car

[SirAndy]

My latest task was to see what happens when you fit carbs to a 2.0L FI stock engine.

So basically, you lost some 5 HP by switching to carbs.

A stock euro D-Jet 2.0L FI engine is rated at 100HP @5000 rpm ...
(IMG:style_emoticons/default/popcorn[1].gif)

[914werke]

(IMG:style_emoticons/default/agree.gif) (IMG:style_emoticons/default/first.gif) (IMG:style_emoticons/default/aktion035.gif) Bravo, that is awesome info. Fuel delivery can only do so much to develop power, irregardless of the delivery method.

(IMG:style_emoticons/default/blink.gif) (IMG:style_emoticons/default/chair.gif)

[Jake Raby]

Either system works fine, IF the user can tune it. The stock system is very analog, can't really be altered, or tuned, and the parts are hard to find. That said, my '76 is bone stock with EFI.

For a period of 3 years I went exclusively to PEFI for all my engines. The problem that I found was people thought that EFI didn't need anything, even though I told them the system would need baseline tuning for different elevations and weather conditions. I even had to fly to Lake Tahoe to support one engine that had been to 3 different shops after an install. Guess why the engine ran like crap? The installer (Porsche shop) installed the TPS backwards, so the engine would only idle. It pulled fuel as the engine increased RPM. I diagnosed it in 10 minutes, and fixed it in 5, but wasted two days traveling.

What we fight are complexities with installs, and the more wires, lines and etc an engine has, the better the chance that a human is going to screw something up that was perfect when it left here.

Thats why my engines come with carbs, at most someone sets the fuel pressure too high, or low. There's not much to screw up, and thats what matters most to me. Once someone gets to an advanced level they can add EFI themselves, and by that time I have been forgotten about, and my engine has proven it's self. That means they don't call me, which is the best case scenario.

This post has been edited by Jake Raby: Jun 13 2016, 01:18 PM

[worn]

[
See all the made up Shit Below

"Will your engine make more peak power with EFI??
More than likely the answer to this is NO. At high RPM and wide open throttle carburetors really work well; so well that it has been hard for us to make more power with EFI on the dyno than a well tuned set of craburetors. The benefits to EFI occur at lower speeds in the form of drive-ability enhancements and torque boosts. This may defy what you've read somewhere else, but it is the fact concerning our own engine program.

I think this answers your own question. Very few people want to run WOT near redline most of the time. Passing another car, maybe. You don't use full throttle most of the time. Drivability is really important, especially when a buyer is out for a test drive. Even with a Porsche.

[Darren C]

Hold on guy’s, I know the OP has got everyone hot under the collar….

Brant. I never said 14.7:1 is ideal specifically for a 914. It’s the best ratio for max power from burning gas. I agree totally with you, our cars run much richer.

Conedodger. I agree entirely with you, like I said in my earlier post the best comparison test would be an other UK members FI car on the same Dyno. The lower data in the graph show barometric pressure, relative humidity and temperature at the time of the testing if you want to get real picky with comparisons.

DBCooper, check the lower scale on the graph, its RPM, so you see the full AFR & HP across all throttle settings. Each of these dyno runs took 20 minutes over the full rev range against the force of the rollers, the Dyno’s computer takes the data and produces the graph. The rollers offer a resistance to the car so that you get a true representation of driving underload through the whole rev range. It's the only sure fire way to get meaningful data and a feel for driveability while plugged into the machine.

I’m not agreeing or disagreeing with the OP, just posting some data so that everyone can make up their own minds. Jeez even with hard data you guy’s still want to pick a fight as you only see what you wanna see.

Stugray, I agree with you, that’s why I said we need to compare eggs with eggs and welcomed an FI data post by someone else. Although I do disagree with you when you say its not as useful as the first 4 pages :-)
So as a fair comparison with all I can offer, lets look back at Jeffs equally informative graph of factory specs. His graph has Torque v Horsepower for the FI 914.
As I indicated earlier I have around 50 various data graphs from the 4 hours on the Dyno. Here’s the equivalent graph to Jeffs, showing HP & Torque but on a carb 914 through 3 jet sizes.

For info The dyno is at sea level in Portsmouth UK, the car is timed at 27 BTDC as per standard with stock cam, NO modifications other than just bolting on carbs.

(IMG:http://www.914world.com/bbs2/uploads_offsite/i265.photobucket.com-18255-1465851457.1.jpg)

Hopefully this’ll be a starting valued comparison for you Stu. Jeff or someone more computer literate than me can maybe post the two graphs side by side (Jeffs and the one above)

Gereed, Thanks for your post, I agree, the only way to truly optimise AFR is to go FI. You can pull the lean/rich issue slightly changing air correctors, but imagine the AFR graph line is a see-saw (pivoting in the middle, say around the 3500rpm point in the lower scale) if in your case your running too rich at part load changing to a smaller air corrector will tip the graph up a little at low revs but down at high revs. The pay off in trying to fix your issue with air correctors alone will be richer running at higher revs. This is where a lot of messing about and testing on the Dyno is needed, but as we all agree, FI makes this easier to control. Carbs are great but crude in this respect. However carbs can be fiddled with by any home mechanic, not many have the tools or knowledge to re-map FI. It’s horses for courses. As Brant says by changing more than the air correctors you could eventually get close to a perfect set up, but it will always run richer than an FI equivalent.

Sir Andy,
My car is a US California car, so its stock wasn’t 100HP. US spec GA 2.0 engine: 91 HP @ 4900 rpm is the figure measured by the U.S. standard SAE
In Europe the HP figure is measured by DIN which is 95 HP @ 4900 rpm for a U.S. spec GA 2.0 engine.
As I’m in Europe our Dyno measures HP in DIN, so I haven’t lost any HP at all, but thanks for asking!

So tin hat back on, I try and be helpful, offer facts not opinions, have no bias to FI or Carb and the guns point my way yet again?

[brant]

Thanks Brant, First let me say that I also consider it a non-problem. Partly just illustrating the point about how deficient even well tuned carbs can be...but I would also like to get it better.

The engine is a 2.4 with some head work done, DC 30 cams and 9.5 CR, single plug.

I have played a bit with emulsion tubes and am running F26's with 32mm venturi's.

Idle AFR's are around 12 (hard to tell, they vary alot).

From everything I have read and all I have talked to, the idle airs seem to be a definite factor. But, as you know they are pressed into the IDA 3C body.

Please tell me more about float levels. Mine are set "stock". I guess lowering them might effect the idle circuit towards lean???

Thanks man, now this thread is getting constuctive!

PS.... love your car

thanks for the compliment

the float level will change which emulsion tube holes are exposed and have a big impact on part throttle mixture.

might be worth playing with (its free) and checking its effect with an AFR

but like you said....
not a big deal really... not an issue
that sounds like a fun motor!

we play with air corrections depending on certain corners at certain tracks.. that cause certain RPM/gearing outcomes
so If I have a flat spot as I transition to mains in a certain corner (lower rpm), that is causing me problems on the track, I can often move that transition point with air corrections to benefit one certain corner.... plus humidity and temp change through out the day
I often run different jets in the afternoon or different jets on sunday... than I did on Saturday morning. This is due to running too large of primary venturi's and essentially over carbureting a 2.0 motor. (loss of air speed/velocity for correct atomization at 4,000 -5,000 rpm)

but I only care about redline output so this is the way it is for a race car

right now I'm running 35mm venturi's on a 2 liter at 6,000 foot of elevation.
mains are usually around 175 or 180mains depending on the weather of the day
I carry everything up to around 215 mains for lower altitude tracks

I'm also running IDS carbs on this motor, and the 2ndary enrichment tubes really benefit mixture above 7,000rpm. You can literally see them kick in on the AFR gauge. They have to prime themselves, and are very noticeable on the mixture when they aren't working the first 3 times you run up to redline. The factory installed them for a reason on the S cars.... even though it was a one year change, right before they went to MFI (they even made the 2ndary enrichments in 3 different jetting sizes... but impossible to find)

brant

[SirAndy]

My car is a US California car, so its stock wasn’t 100HP. US spec GA 2.0 engine: 91 HP @ 4900 rpm is the figure measured by the U.S. standard SAE
In Europe the HP figure is measured by DIN which is 95 HP @ 4900 rpm for a U.S. spec GA 2.0 engine.
As I’m in Europe our Dyno measures HP in DIN, so I haven’t lost any HP at all, but thanks for asking!

Since you're in Europe, thanks for leaving out the (somewhat important) detail that your car has a US spec engine ...
(IMG:style_emoticons/default/rolleyes.gif)

PS: Do you still have the CA smog equipment installed? Are you using the stock exhaust and stock heat exchangers?
Because if not, the 95HP @ 4900rpm is not a correct baseline to measure against. To quote your own words "eggs with eggs".

[somd914]

Thanks Jeff.

Now I throw out the challenge to someone running a stock 2.0L with FI (NOT MODIFIED) in any way and running well, to go do a dyno run and post a print out of HP v AFR and we can all see the differences between Carb & FI in black & white once and for all.

From an engineering analysis perspective doing what you suggest above would be meaningless. What needs to be done is swap carbs to D-Jet on the same engine. Otherwise you cannot account for wear, build quality, etc. that differ between the engines and effect HP and AFR.

As for the above pages being useless, so is the original question. Just about any aspect of the 914, or any other consumer car, can be debated like this thread. One must keep in mind the goal is not ultimate performance, the goal is to sell cars and make a profit. And with that comes compromises in countless aspects of a car's design; these compromises include such considerations of reliability, cost, emissions, fuel mileage, safety, comfort, etc.

[Darren C]

My car is a US California car, so its stock wasn’t 100HP. US spec GA 2.0 engine: 91 HP @ 4900 rpm is the figure measured by the U.S. standard SAE
In Europe the HP figure is measured by DIN which is 95 HP @ 4900 rpm for a U.S. spec GA 2.0 engine.
As I’m in Europe our Dyno measures HP in DIN, so I haven’t lost any HP at all, but thanks for asking!

Since you're in Europe, thanks for leaving out the (somewhat important) detail that your car has a US spec engine ...
(IMG:style_emoticons/default/rolleyes.gif)

PS: Do you still have the CA smog equipment installed? Are you using the stock exhaust and stock heat exchangers?
Because if not, the 95HP @ 4900rpm is not a correct baseline to measure against. To quote your own words "eggs with eggs".

Sir Andy,
I'm not looking for a fight here.
As I said earlier my car is stock apart from the carbs, including stock exhaust and heat exchangers. The smog equipment came off the car as part of the FI removal.
That's all.
As for neglecting to to say it is a US spec car, it was you who assumed it was european, then chastise me?
My build thread and introductions on this forum show quite clearly it's a US car, photos of it in Desert Hot Springs CA and its importation to UK are well documented and it's listed on the register on here.
Why do I have to keep on making justification for every post I make on this forum?
It just creates fear to post by those who are less thick skinned than me.
Somd914, I agree with you, that would be the best comparison ever.
My reason for posting in this thread was to try and add some fact on why emissions drove the carb to FI move in our 914 and to in some way satisfy the OP without all the tit for tat that ensued over the first 4 pages.
Like anyone breaking up a fight, seems both sides have turned on me now and any good intent and good information is lost in the fractious. Hey ho.

[jd74914]

FWIW: Using the factory measurements from 30 years ago (taken on who knows what equipment and averaged over a number of engines) and comparing to new measurements is really irrelevant. Heck, dynoing your car on one dyno then driving down the street to use another isn't even a good comparison. The only relevant comparison is against a single dyno because no two share the same calibration, etc. The only thing you are really guaranteed is repeat-ability, assuming you are using a quality device. When dynoing a car you really should be looking at the shape of the curve and relative comparisons between changes, not the peak HP/torque number

To me it's quite impressive [and lucky] that Darren's plots are anywhere close in magnitude to the factory numbers. Note that the Dyno Dynamics one that Darren is showing plots from is an extremely well-regarded eddy current device which is very repeatable. It can also hold engine speeds/loads constant to produce really nice curves unlike inertial dynos which are much more common (at least in the USA).

It shouldn't be surprising that you can get better peak numbers on a carbed car than D- or L-jet car when just thinking about fuel mixing. Assuming both allow the exact same amount of fuel at a given time, fuel atomization from the carb will be much better. The Bosch fuel injector nozzle design is archaic compared to modern injectors.

[Darren C]

To me it's quite impressive [and lucky] that Darren's plots are anywhere close in magnitude to the factory numbers. Note that the Dyno Dynamics one that Darren is showing plots from is an extremely well-regarded eddy current device which is very repeatable. It can also hold engine speeds/loads constant to produce really nice curves unlike inertial dynos which are much more common (at least in the USA).

Thanks Jim,

That's probably why it's $150 an hour for roller time!
I agree it was extremely lucky considering my car has 119,000 miles (1 owner with full history which shows no engine rebuild in it's life) Also it hadn't run for about 6-7 years before I bought it. All I did was pull the engine to change a couple of leaking oil seals and fit the carbs. All in all I am extremely pleased with this result. I bought it blind late one night off ebay, for a low price based on 6 thumbnail pictures and two bottles of wine.

(IMG:http://www.914world.com/bbs2/uploads_offsite/i265.photobucket.com-18255-1465860566.1.jpg)

(IMG:http://www.914world.com/bbs2/uploads_offsite/i265.photobucket.com-18255-1465860566.2.jpg)