Pfc D-jetro Needs Aftermarket Plenum/single Throttle?

[saliya]

Hey folks,

looking at ditching my PFC + stock AFMs for a PFC D-Jetro

edit: see below for reasons

Can anybody running a PFC D-Jetro add to this thread or PM me with info about:

* performance of your car changed before/after fitment (and how )

* drivability of your car changed before/after fitment (and how: better/worse generally, at particular RPMs?)

* who installed it / how long it took

* who tuned it / how long it took

* you have changed your plenum/throttles from standard (and if so, what changes were made?)

* if you have a different plenum, and added it at a different time to the D-Jetro, what difference (if any) it made?

I'm told by some knowledgeable tuning houses that a single throttle + aftermarket plenum is essential

to getting the D-Jetro to run right. I'm also told by some well-respected sources that the D-Jetro will

run fine on standard plenum and throttles.

I'll summarise responses in the first post.

Thanks guys/gals,

Saliya

edit: Thanks for everyones responses so far. Anyone had a BAD experience

with a D-Jetro? Please PM me, if you don't want details like your name or the

installer/tuner published then I of course won't.

As per suggestion from jonn: Someone in the Sydney, NSW area with a d-jetro

that would be willing to take a fellow SAUer for a drive? PM me (don't post here )

MAIN POINTS SO FAR:

* tuning time is large, compared to 'standard' or l-jetro == expensive

- I don't know whether the PFC tuning software has the ability to just map several points, then join-the-dots so

to speak (similar to the way that the Haltech MAP ECU software works)but I suspect this could be used to

cut down tuning time. Perhaps an enhancement for FC-Datalogit?

* driveability and outright performance of d-jetro is as good as l-jetro

* installation of the MAP sensors is a PITA, slow, fiddly == expensive.

- nothing I can do to avoid this other than install them myself.

* D-Jetro works fine for people with standard plenums/throttles (so far!)

- this kind of puts the kybosh on the theorem that a single throttle/different plenum is _required_...

any more information about this INCLUDING bad experiences would be good!

* MAP sensors possibly affected by pressure waves and proximity to opening/closing valves

- You'd think that Apexi would have run into this, and made the software handle it. My guess

would be that this is the purpose of the dual sensors - that is, when one sensor is affected by

a wave the other one won't be...

Keep those responses coming...

SW

edit: response from Gav

who installed: unknown, but MAP sensors take a long time and are fiddly

who tuned: unknown, but takes a long time. Perhaps tune time costs more than std PFC?

plenum/throttles: standard

performance/driveability: excellent. Would use again

edit: response from SydneyKid:

who tuned: unknown, tuning time is high

plenum: unknown

raised point about pressure waves affecting MAP sensor readings

edit: response from Willo:

who tuned: unknown, finding a tuner was hard? update: Mark Jacobsen at Godzilla Motorsport (Brisbane)

plenum/throttles: standard

performance/driveability: excellent, fuel economy update: rephrased no problems

edit: response from jonn:

who tuned: Hyperdrive (Perth)

plenum/throttles: standard

performance/driveability: excellent. Would use again.

Edited October 5, 2006 by saliya

[paulr33]

i guess the question is, why do u want to change to djetro?

there is no reason whatsoever it should make more power over the traditional ljetro powerfc. the powerfc faq (in my sig) covers the djetro vs ljetro topic quiet a bit, you should have a read of it before you make your decision. there are known compatability issues with using djetro or map sensor based ecu's on mutlitple throttle bodies like the sr20 gtir and the rb26 gtr and things like different plenum, throttle body changes may workaround it, but is it really worth it? thats like $5k+ of crap to change, all for what?

[saliya]

i guess the question is, why do u want to change to djetro?

Looking to change because I'm about to run out of resolution on the stock AFMs;

I have a couple of Z32s that I was going to use but if the D-Jetro is "as good"

as the standard PFC then the inlet piping will be substantially simpler without

the AFMs (there is not a lot of room between my T04Z and air filter).

If the D-Jetro is _not_ "as good" as the AFM PFC then I'll have to remake

the split/join part of the inlet tract. I'm not looking for 'more' out of the D-Jetro,

I'm looking for 'the same, but without the AFMs'... yes, there will be a

restriction removal but I'm not expecting it to make a huge difference.

edit: I've read the FAQ; but it doesn't really help me all that much. It's an

overgeneralisation to imply that MAP-sensored cars will inherently run badly

(the Toyota 1JZ seems to refute this pretty well) but it _may_ be true that

MAP-sensored cars with multiple throttles will run badly - hence this thread

Regards,

Saliya

Edited October 4, 2006 by saliya

[Swiper the Fox]

im going single throttle body aftermarket plenum and still retaining my STD Power FC with twin Z32's. I don't see a reason to worry about changing unless the compressor surge is a problem with AFM reversion.

[paulr33]

as dirtgarage have said more often than not its much better and easier to keep the ljetro setup and use that. even if the cost to change to djetro was $0 (which its not) i still would stay with ljetro.

[bnr#@]

I have read that the D-jetro gives better throtle response and some people claim better fuel economy, how true is any of this?

[paulr33]

i cant see it giving better throttle response, there is no logic behind it why it would, if anything it would be worse. as the djetro looks purely at pressure. the ljetro measures airflow directly into the system, which says to me it would logically (at least) give better response and accuracy. i also can not under any logic whatsoever see how the djetro would give better fuel economy. theres no magical button or feature that would make fuel economy better

pressure != air volume

[Adriano]

I fitted a d-jetro to a r32 gtr, to do this it uses two map sensors, both in the runners after the throttles.Installing them is a bastard of a job, as it requires removal of the plenum, throttles etc, i didn't have any dramas with tuning, although the car is running standard cams. Neuther fuel ecomomy or response would be improved over a standard pfc.

[Gav]

I will provide a contrary opinion to paulr33.

This is a debate that that has been running for some while and while paulr33 is extremely knowledgeable in his coverage of the PFC, he has a bias towards the standard L-jetro PFC. His opinion is one based on theory and research and not on personal experience with GT-Rs.

I have run L-jetro PFC, Wolf3D (Map sensor) and D-jetro PFC on my GT-R. Although each upgrade has brought with it engine mods, the D-jetro is by far MY preferred option for large low mount turbos. The D-jetro has delivered very good drivability and almost eliminated turbo shuffle. Back to back I have seen 2 GT-Rs gain power by converting to the D-jetro PFC. As paulr33 has stated there is no obvious reason why this system should gain power, but I have seen it done with my own eyes. I guess this aspect will be debated for a time to come.

The D-Jetro has the benefit of measuring pressure directly at the plenum. This does indeed improve response where there is a significant volume in the intercooler and associated pipework. The L-jetro does not take into account the existing pressure within the induction tract and therefore the instantaneous engine load can vary depending on how much pressure is present when you first open the throttle.

Th D-jetro also does a good job at dealing with turbo shuffle - particularly where air reversion back through the AFMs is a contributing factor.

There are downsides as previously stated above including the need to fit the map sensors (a fiddly job) and the requirement to splice into the ECU harness. Tuning is also more involved and will most likely cost you more than a std PFC.

I realise that my comments are contrary to some (many) posters here on the board, but I guess that's what forums are all about - hey? Please feel free to PM me with questions.

Cheers

Gav

[paulr33]

thanks gav, at least we have some real world experience.

why one would make more power is beyond me, could it be the tuners who do the djetro setups spend more time on the tune, thus tuning it better? how much did the djetro tune cost? i guess the difference of pipework and inlet can make a difference, but i wonder if you relocated a single q45 as an example you would see the same throttle snappy response. this sounds like it would also eliminate the compressor or afm shuffling or chuffing.

good thinkin 99

[Sydneykid]

I will start off by saying that I have never personally tuned a car using a DJetro, but I have sat by when one was done. Plus I have compared a DJetro with the Motecs and Autronics that we use all the time and I can’t see why they would be any different.

Based on Motec and Austronic experience, tuning the DJetro will take shit loads longer than tuning an LJetro. Many tuners take short cuts when tuning LJetro, because the AFM lets you "get away" with “close enough is good enough” tuning. The DJetro DEMANDS perfect tuning, there aren’t any “shortcuts” and it’s either right or wrong. There is no AFM measuring the airflow to save yo ass and fill in any gaps in your tuning.

If you spend half as much time tuning a LJetro than you do tuning a DJetro, then you will get the same (if not more) horsepower. The comparison falls over when the tuner spends less than 1/10th the time tuning the LJetro. So don’t look to the DLetro tune as being BETTER, it’s far more likely that the LJetro tune was CRAP in the first place.

I have heard the “measuring the pressure close to the engine” reasoning before. I believe it is erroneous. The truth is, if you have a decent boost controller, the pressure is constant (once boost is stable). So the MAP sensor proximity to the engine is IRRELEVANT.

The big problem with DJetro is the multiple throttle bodies on RB26’s. Getting a stable pressure means dampening it, using a large reservoir to even out the 6 cylinder pulses. A dampened pressure signal is hardly RESPONSIVE. If I was building an RB with a single throttle body and really large (drag use) turbo, then a DJetro might get a look in. But multiple throttle bodies and road/circuit sized turbo/turbos means the LJetro will still be on top of my list.

cheers

[Gav]

thanks gav, at least we have some real world experience.

why one would make more power is beyond me, could it be the tuners who do the djetro setups spend more time on the tune, thus tuning it better? how much did the djetro tune cost? i guess the difference of pipework and inlet can make a difference, but i wonder if you relocated a single q45 as an example you would see the same throttle snappy response. this sounds like it would also eliminate the compressor or afm shuffling or chuffing.

good thinkin 99

Cheers Paul - I actually expected to raise the hair on your back by my response

I think that you may be right - since the tuner does spend more time perhaps that's where the extra power comes from. I suspect that it may also be that the D-jetro is replacing an L-jetro where the AFMs are already out of resolution so the gain in top end may have been possible by swapping to larger AFMs anyway?

One other comment that I remember reading from the Datalogit forum. One of the Datalogit developers is adamant that the D-jetro only uses pressure for the load calculation axis. As you have stated this would mean that at constant manifold pressure the map essentially becomes 2 dimensional (i.e. no movement along the load axis).

I am absolutely certain that I have movement along the load axis even when the boost is rock steady (as shown by both the Apexi sensors and the Blitz BC sensors). My gut feel is that it takes reference from the revs and probably the TPS when calculating the load value of each point.

Thoughts?

[paulr33]

nah its fine, no problems from me at all. we are all here to learn and discuss. after dicussing this on the datalogit forums and writing up the ljetro vs djetro in the powerfc faq it was clear where the load axis calculation comes from, and its only map sensor signal. so once you are on max boost it will be stagnant from there on, so yes it should shoot across the horizontal axis after that. that is load will never increase anymore. the calculation to work out load on the djetro powerfc is simply

Appexi Djetro Load Calculation:

LOAD = Map Sensor Offset * Map Sensor(PIMV)

so it doesnt care about rpm, tps or anything. there are corrections applied to the map around TPS and rpm but they don't apply load offsets, such as making it move down more in higher rpm or tps load. if it is in fact moving diagnoally on max boost then there must be some explanation for it, we just dont know what it is. it would be great to see a djetro "map trace" of say a 3rd gear run from idle to redline, an extra bonus would be datalogit logs of the same run or sequence.

with afms maxing, if they hit the ceiling value of 5v they can still flow more air, well logic says they can, it just can't show any more "resolution" to the ecu, so the load will never change, which is the same as map sensor. i am unsure when z32s would become a bottleneck due to physical size.

[Sydneykid]

Cheers Paul - I actually expected to raise the hair on your back by my response

I think that you may be right - since the tuner does spend more time perhaps that's where the extra power comes from. I suspect that it may also be that the D-jetro is replacing an L-jetro where the AFMs are already out of resolution so the gain in top end may have been possible by swapping to larger AFMs anyway?

One other comment that I remember reading from the Datalogit forum. One of the Datalogit developers is adamant that the D-jetro only uses pressure for the load calculation axis. As you have stated this would mean that at constant manifold pressure the map essentially becomes 2 dimensional (i.e. no movement along the load axis).

I am absolutely certain that I have movement along the load axis even when the boost is rock steady (as shown by both the Apexi sensors and the Blitz BC sensors). My gut feel is that it takes reference from the revs and probably the TPS when calculating the load value of each point.

Thoughts?

Yep, it's a three dimensional map (MAP sensor, TPS and RPM) and when the pressure is constant, the TPS and RPM are the two axis of the map

cheers

[paulr33]

well that may explain why it moves diagnoally then, if in fact it does once its on max boost. so is there some form of scaling it uses, given that when you are on max boost, tps will be 3.9v or whatever the max is. rpm will keep increasing on the RPM axis so would LOAD move down anymore?

[Gav]

well that may explain why it moves diagnoally then, if in fact it does once its on max boost. so is there some form of scaling it uses, given that when you are on max boost, tps will be 3.9v or whatever the max is. rpm will keep increasing on the RPM axis so would LOAD move down anymore?

Unfortunately I'm overseas at the moment and can't log a run at full throttle and constant boost, but I'd be really interested to see a log of load vs revs under these conditions.

Do any D-jetro uses have such a log handy?

[Willo]

I have a D-Jetro on my 34 and once I found someone who could tune it (long story) have had no problems. I am running standard plenum and throttles and have had no problem with drivability, fuel economy and it is making good power.

My reason for using the D-Jetro was the car arrived without AFMs. Once I discovered the F-Con under the carpet there were no dramas tuning it. As stated above installation of the map sensors is a bitch.

I can't really give a fair comparison before and after as the car was always running without AFMs but I have no complaints.

[jonn]

I've got a D-Jetro on my R32. After the installation the car gained more power over the std ecu. I guess that be attributed to the fact that the D-Jetro was tuned to the car and the std one had a std shitty map in it. The fuel economy was better by miles. I could get over 500k's to a tank with sensible driving round town.

Hyperdrive in Perth installed and tuned the car. It retains the six throttle setup but had I put the Apexi kit on it as the afms were now gone.

All in all I like the way the car drives and runs, the response is great. I've had no problems at all with it. There's always going to be arguments over which one is better but I would happily put another D-Jetro on another GTR.

Best bet is to find someone that has one in their car and get them to take you for a drive.

Jon

[R31Nismoid]

Best bet is to find someone that has one in their car and get them to take you for a drive.

exactly.

What one person calls "perfectly driveable" another person willl call it "shocking"

Its each to thier own, IMO if you dont have issues, dont change it.

Changing can cause issues, sometimes it brings gains...

Although gains can be masked by either the dyno, or the tuner not really doing a good job on the first hit

[Willo]

edit: response from Willo:

who tuned: unknown, finding a tuner was hard?

plenum/throttles: standard

performance/driveability: excellent, fuel economy excellent

Just to clarify, the first tuner I went to had a lot of dramas and I ended up taking it to Mark Jacobsen at Godzilla Motorsport and he had no problems at all. At the time I would say I was one of the first D-Jetros in Brisbane but I would say by now there are quite a few people who can tune them.

And as for fuel economy, I've never referred to any GTR as having excellent fuel economy with any ECU.