L-jet Q, cams... Options

[bd1308]

912E engines were 2.0 914 engines with L-jet fitted to them. Intresting point that someone brought up was the fact that the engine was fitted with a carb cam....at first thought, I was like huh?

but it kinda makes sense....the whole reason that carb cams couldnt work with D-jet was because the vaccuum signals at idle weren't what the mps wanted or was looking for...so the idle was rough to say the least (a pure guess).

So, in L-jet you have this intresting change....an air flow meter, designed to match the amount of air entering the plenum with the "correct" amount of gasoline, which is running a tad rich--due to the displacement difference. But it doesnt matter how choppy the vac signal is, as long as the engine draws in air, the AFM will know and will give the air some fuel to mix.....


so my Question: could a carb cam be used in a L-jet system for a little extra pep?

1.7L 72 engine.


It's late, so if im way off, just lemme know.

b

[rick 918-S]

(IMG:http://www.914world.com/bbs2/html/emoticons/idea.gif) (IMG:http://www.914world.com/bbs2/html/emoticons/popcorn[1].gif) (IMG:http://www.914world.com/bbs2/html/emoticons/wavey.gif)

[John]

I would doubt that you could use too radical of a cam with the L-jet. Similar to the problems with the djet vacuum issues with a hotter cam, you would be introducing rougher pulses into the intake manifold due to the cam. (This is just my own theoretical opinion).

The 911 Carreras (1984-1989) used a similar vane type air flow meter to measure air flow and to my knowledge did not use a real aggressive cam.

My opinion is that you may gain a little from a slightly warmed up cam, but I don't think it is worth the headaches if your AFM is damaged due to a backfire or being subjected to the more harsh intake pulses generated by a more aggressive cam. (That's what dual Weber carbs are for)

[Maltese Falcon]

Hey Rick, how's that little green alien doing ? There were no alien sightings at SEMA this year- sorry he doesn't get a brother.
Now back on topic...
Marty

[Jake Raby]

In 1999 I spent about 4 solid months trying to optimize both D jet and L jet for better stoock performance as well as to sustain a larger engine. Through all that testing and data gathered I came up with 4 solid rules concerning the limitations.

Now, remember that Plenum volume has a great deal to do with idle choppiness with cams and vac signals and since there are one each plenum (4 in all if you count the Bus Plenum) the results one attains depend upon the plenum used, the cam used, the set up of that cam (advanced or retarded) CR and operating elevation (air density)

What I'm trying to say is the same engine with just a traded out plenum can run significantly better than the same cam did with another plenum, and thats heavily impacted by cam....

SO before I could go any further what plenum do you plan to run?

And YES L Jet is just as impacted by cam as D Jet and NO the same cam will not work optimally for either arrangement. The L Jet system has issues with leaning out @ peak torque while D Jet has issues with lean out in the upper midrange, generally right after peak torque but just before 5,300 RPM- Yet again this range will move a bit based upon the plenum being used.

The big differences are at idle and up to about 1750 RPM..

Remember that the 912E used AFM with L jet AND a 2.0 D Jet plenum... Hmmmn- start thinking.

[rick 918-S]

QUOTE (Maltese Falcon @ Jan 10 2006, 09:25 PM)

Hey Rick, how's that little green alien doing ? There were no alien sightings at SEMA this year- sorry he doesn't get a brother. Now back on topic... Marty

Still holding air (IMG:http://www.914world.com/bbs2/html/emoticons/wavey.gif)

[Mueller]

QUOTE (bd1308 @ Jan 10 2006, 10:13 PM)

912E engines were 2.0 914 engines with L-jet fitted to them. Intresting point that someone brought up was the fact that the engine was fitted with a carb cam....at first thought, I was like huh? but it kinda makes sense....the whole reason that carb cams couldnt work with D-jet was because the vaccuum signals at idle weren't what the mps wanted or was looking for...so the idle was rough to say the least (a pure guess). So, in L-jet you have this intresting change....an air flow meter, designed to match the amount of air entering the plenum with the "correct" amount of gasoline, which is running a tad rich--due to the displacement difference. But it doesnt matter how choppy the vac signal is, as long as the engine draws in air, the AFM will know and will give the air some fuel to mix..... so my Question: could a carb cam be used in a L-jet system for a little extra pep? 1.7L 72 engine. It's late, so if im way off, just lemme know. b

"carb" cam can be misleading...there is more than just one carb cam, some are just as mild or tame as the stock FI cam......

when are you going to just give up on trying to make the D-jet or L-jet fuel injection work with a hot rodded engine??

people have been trying for 30 years and it's not worth the hassels when MS or other better options are out there.......

[Trekkor]

I'm still waiting for someone to tell me VW/Porsche used a differant cam on each of their stock FI/Carbed type four motors... (IMG:http://www.914world.com/bbs2/html/emoticons/dead horse.gif)


KT

[McMark]

Mike, Ray Greenwood has done a lot of work to make D-Jet work with hot motors successfully. But for the amount of work he's done it would have been easier to do MS or something else.

[type47]

.... SDS is $1100-1300 for 914 (roughly)... just think, modern FI system......

looking for solutions to their (SDS's) mounting of crank sensor for magnets and/or mounting of their signal pick ups for the distributor-less system....

interested in discussions of cam applications compatible with SDS systems.

[bd1308]

I like being the underdog....I guess.

L-jet is great. My engine is great. I'm just wondering what cam the 2.0 912E engine had in it....somebody said a warm cam and then it made me think, thats all.

b

[bd1308]

QUOTE (trekkor @ Jan 11 2006, 02:04 AM)

I'm still waiting for someone to tell me VW/Porsche used a differant cam on each of their stock FI/Carbed type four motors... (IMG:http://www.914world.com/bbs2/html/emoticons/dead horse.gif) KT

it was someone in the 912E vs 914 engine thread.

I guess I trust people too much.


b

[Trekkor]

Britt, I think somebody was zinging you. (IMG:http://www.914world.com/bbs2/html/emoticons/rolleyes.gif)

Again...



KT

[r_towle]

I think you may want to look at waht jake said.
Then look at all the possible combinations.

Its all in the combo...

But seriously...

Which plenum did the 912E have...what was the part number...

I can see the point..If the 912E had a bigger plenum box, it could potentially have had a cam with slightly larger lift, and possibly a little bit more overlap...or even a different cam lobe profile....

Rich

[Bleyseng]

QUOTE (Mueller @ Jan 10 2006, 11:48 PM)

QUOTE (bd1308 @ Jan 10 2006, 10:13 PM) 912E engines were 2.0 914 engines with L-jet fitted to them. Intresting point that someone brought up was the fact that the engine was fitted with a carb cam....at first thought, I was like huh? but it kinda makes sense....the whole reason that carb cams couldnt work with D-jet was because the vaccuum signals at idle weren't what the mps wanted or was looking for...so the idle was rough to say the least (a pure guess). So, in L-jet you have this intresting change....an air flow meter, designed to match the amount of air entering the plenum with the "correct" amount of gasoline, which is running a tad rich--due to the displacement difference. But it doesnt matter how choppy the vac signal is, as long as the engine draws in air, the AFM will know and will give the air some fuel to mix..... so my Question: could a carb cam be used in a L-jet system for a little extra pep? 1.7L 72 engine. It's late, so if im way off, just lemme know. b "carb" cam can be misleading...there is more than just one carb cam, some are just as mild or tame as the stock FI cam...... when are you going to just give up on trying to make the D-jet or L-jet fuel injection work with a hot rodded engine?? people have been trying for 30 years and it's not worth the hassels when MS or other better options are out there.......

Jake's 9550 cam is "warm" and really wakes up my 2056. Runs effin cooler too which is the biggest reason I switched cams. I'll dyno it soon to get some solid numbers to compare to the old setup.

I thought the 72 - 74 bus carb cam and the 411/412 carb cam were really the only different cams VW used although there is something like really 10 different cams used over the years.



(IMG:http://www.914world.com/bbs2/html/emoticons/burnout.gif)

[DNHunt]

I doubt this will help much but, I have tuned 2 different cams in the same engine with MS. The first had more intake lift (0.016") than the second and also a little more duration (about 6 degrees on the exhaust side). The numbers on paper didn't seem that great to me but it made a big difference on the fueling curve. The bigger (1st cam) one was easier because there was more vacuum. The point is for me at least cams are a mystery.

The stock D-jet cam in a 2.0l was a vacuum pig. Sucks like an old whore. Can you say cam porn? (IMG:http://www.914world.com/bbs2/html/emoticons/wacko.gif) (IMG:http://www.914world.com/bbs2/html/emoticons/cool_shades.gif)

Dave

[Jake Raby]

SDS or any other EFI system is also very dependant upon cam at idle with a plenum based system. The engine in my 912E has a 100% CARB cam installed and it was a bitch to tune the idle specs up to 1500 RPM with it. I built the engine for carbs and considered it a challenge to tune it with EFI, a challenge that would prove if SDS could be used with any camshaft with tuning and I do believe the answer is yes.

You guys really are making this way harder than it has to be.......I have played with so many cams with 7 different EFI arrangements in just the past year to have over a dozen cams with known specs for certain "combos"... The variables in each and every combo will lead to a different cam more than likely and there are no general rules.

"Everything is dependant upon everything else"

BTW- My SDS EFI retrofit kit is only 1500 bucks, and it comes with every sensor, TPS adaptors, replacement TPS, all wires labeled for easy hook up and it even has a fuel MAP from an engine similar to yours, that I have tuned, loaded into it (not default numbers)- Or you can buy it direct, save 300 bucks, not get the TPS, adaptors for the T/B for the TPS, nothing is labeled and you get a default MAP and zero support from a TIV specialist.Its your call.

I know many of you want to un derstand the arrangement enough to pick your own cam and while thats great you need to understand the big picture to the level that I do to be effective with such a feat. Pride costs money, blown engines and marriages, so when you get smart- call me and the guess work is removed.

[Brando]

Now here's a question jake... What's the difference between a CIS cam and a carb cam? Can they be the same? CIS is always dumping gas into the intake, waiting for that valve to open and suck it all in...

[Jake Raby]

CIS hates intake duration changes, unlike carbs that love it.

crazy intake duration makes big power with carbs most of the time, BUT with CIS it creates bumpy signals to the flap in the fuel distributor and that flap sets the fuel delivery caharacteristics.

CIS cams have really smooth intake ramps and love exhaust duration, couple that to a head with a tad more intake flow than conventional and you get the best of all worlds with smoothness to boot.

[Joe Ricard]

QUOTE (Jake Raby @ Jan 11 2006, 10:12 AM)

CIS hates intake duration changes, unlike carbs that love it. CIS cams have really smooth intake ramps and love exhaust duration, couple that to a head with a tad more intake flow than conventional and you get the best of all worlds with smoothness to boot.

Jake you just described the cams in a early 928. and up to 85 in the Euro cars.
Tons of torque that was as broad as a picnic table top.
The only thing I didn't like was some throttle lag.