Can someone help me make sense of the differences in JTD engine outputs and mapping? - Alfa Romeo Forum
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(Post Link) post #1 of 12 Old 11-01-15 Thread Starter
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Can someone help me make sense of the differences in JTD engine outputs and mapping?

I've been looking into the various tuning - mapping options for the JTD engine and put together the table below.

I've loved my 147 JTDm-140 for the last year. As we grow up () things change and the 147 wasn't suitable for the trip to scouts with a handful of kids, so I've had to bite the bullet and have gotten an 06 Multipla 120 JTDm. Apologies for bringing this up on the Alfa forum but I'v found the technical knowledge here fantastic.
I haven't gotten or driven the Multipla yet but assume that the drop from 140BHP-305Nm to 120BHP-205Nm is going to hurt.

Assuming that the data below I've picked off the internet is correct, why would the Alfa 115JTD and fiat 115JTD have such different torque outputs. 205 Fiat Vs 275 Alfa. If it purely is mapping, then why would the mappers not be able to bring the Fiat engine to the same as the Alfa without actually "tuning". And when mapped the Alfa and Fiat engines, one would logically think, should have the same torque outputs, but appear to be different - 263 Fiat Vs 325 Alfa.
The same goes for the Opel "JTD" versions. They seem to have similar outputs to the Alfas.

I suppose what I'm coming to is that I can't see any reason why my soon to be "90 mile a day overtaking artics on country roads" Multipla 120-JTDm (8V) daily ride can't achieve the same as a 147 120-JTDm (8V), including after mapping.

Hopefully there will be someone on here with knowledge to explain this.


nM Mapped
Std-BHP Std-Torque BHP Torque Turbo
Fiat Bravo/Brava JTD-105 105 200 132 260 GT1544
Bravo/Brava JTD-110 110 200 GT1749V
Marea JTD-110 110 200 138 260 GT1749V
Multipla JTD-115 115 203 139 263 GT1749V
Multipla MJ-120 120 210 GT1749MV
Stilo JTD-100 100 200 GT1749V
Stilo JTD-115 115 255 145 300 GT1749V
Stilo MJ-120 120 255 GT1749MV
Stilo MJ-140 140 305 170 365 GT1749MV
Stilo MJ-150 150 305 GT1749MV

Alfa 156 JTD-105 105 255 140 315 GT1749V
JTD-110 110 275 140 330 GT1749V
JTD-115 115 275 145 325 GT1749V
MJ-140 140 305 170 365 GT1749MV
MJ-150 150 305 175 360 GT1749MV
147 MJ-120 120 280

Opel Astra 1.9CDTi 120 280 150 330 GT1749MV
150 320 180 380 GT1749MV
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(Post Link) post #2 of 12 Old 11-01-15 Thread Starter
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OK, that table did not come out like it looked in the submission page!
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I don't think any of the stilo or 147 had the 1749mv turbo, I think these are the cast manifold and turbine together the astra are and saabs might be as some of the later jtdm like 159.
the mv has larger internals in the turbo so that helps.
and 1749 has many different turbine and compressor wheel variances in its family so its not really that helpful, (one may only be safe to 160hp 1.4bar boost one to 200hp 1.7bar boost for example)
the astra has a better clutch that supposedly doesn't slip anywhere near what our fiats and alfas do, this is main reason for larger torque output.
other car to car variances could be down to what componants are fitted as a whole package.
inlet piping, airbox, turbo internal size, intercooler effectiveness, exhaust size, cats size and numbers, dpf's , injectors fitted, fuel pump fitted ,std rail pressure, driveshafts, clutch, dmf. even gearbox and diff.
most tuners will map to a percentage increase over standard, if asked they may map to maximum safe value ?
also from there previous experience they have learnt what they can get for each car, then most probably compare to other tuners sites for cars they havnt tuned.
best advice is take figures with a pinch of salt best search if you can find someone who had there multipla tuned and what figures they ended up with.
205nm seems low double check figure and then find why, they may have fitted a really weak dual mass flywheel or clutch or something else they were trying not to stress.
or it may have been an eco attempt to hit emmisions targets.
hopefully someone like alfatuner or ahm have done one in the past.
if nothing else take a figure of 30-40% so no reason yours shouldn't be able to go to 260-280nm at least.

I have found a std file of multipla 120hp , is your cf4 ?euro 4 ?(should be on v5 log book)
looks like it has 1600bar rail setup
looks like it has 2300mbar max boost with 2500mbar limiter not sure on svbl
looks like the torque limiter has been set very low , as you say 200nm odd ?
and fuel limiters set low to match
yet drivers wish look like 300nm plus

start looking for a reason this may be a detuned version? is it badged eco in any way?

Last edited by sussexa; 12-01-15 at 09:19.
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Second time sending this reply, computer crashed yesterday.

Thanks for your reply.
I don't have the Multipla yet so can't see what engine it is yet. Hoping that because it is a Multijet it should have better ancillaries than the older models. Presumably similar to the lump put into the Croma, which has 280Nm. Surely it would just cost more to make different versions in the factory? Although the croma does have the GM 6-speed box which might allow a stronger clutch.

That's interesting about a family of 1749 turbos being very different. How does that work when there is generally one CHRA sold to fit the family? When the turbo died on my 147 16V, I used the CHRA from a scrapped Marea 110JTD 8V I had and it fitted and worked great.

In terms of Fiat purposely detuning the Multipla, I can offer two reaons:- 1) They are generally driven by mothers who probably don't want a torquey car. 2) they don't want the Fiat to be similar in performance to an Alfa, which is supposed to be the sporty member of the family.

One reason I'm doing this investigation is that I have all the suspension and running gear from a Fiat Coupe 20VT which will all fit on the Multipla. So I could have a solid flywheel which can take a 3.2 GTA Clutch, viscous coupling LSD, hugely improved suspension and 4-pot brembos up front with rear discs. Air intake, intercooler and exhaust off the Coupe should fit as well.
All of this is on a wish list - whether it will ever make it onto the Multipla we will have to wait and see.
Suffice to say I wouldn't be too afraid of the torque an 8V JTD can produce.

Thanks, Dave
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alfa's often get stronger (and heavier) clutches. sometimes different gearboxes aswell.

does the multipla use the same type gearbox as the coupe 20 VT? I doubt it somehow. the lsd won't fit if the gearbox is a different type.
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I've been told, by someone who has worked with Fiats & Alfas for the last 25 years, that there is a good chance that the differential and the LSD from the 20VT can be swapped with the one on the JTD.
No guarantee obviously, but worth a look.
At the very least, from reading on this forum, the 20VT flywheel with a GTA clutch kit can be fitted to handle any increased torque that I may end up getting.
Should have the multipla next weekend and will take things from there.

The problem is that it could be all or nothing!
To put on the 4-pot brembos I need to use the 20VT struts and hubs. This might mean that the 20VT driveshafts need to be used. If this is the case then I might have to fit the diff and LSD - and so these things go on, and on etc!
I just happen to have all these things and it would be a shame for them to sit in the shed.
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I think the 20VT uses a C530 gearbox, but I don't think the multipla does with the least performant engine. it might be more like the twin spark box which explains the torque limit.

Lift up reverse, that's the key...
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Quote:
Originally Posted by Cuore_Sportivo_155 View Post
I think the 20VT uses a C530 gearbox, but I don't think the multipla does with the least performant engine. it might be more like the twin spark box which explains the torque limit.

Lift up reverse, that's the key...
So, a six speed box from a 16V JTDm would solve that?
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yes, if it fits the subframe....
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There's always something!
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I don't know, it could be compatible, but it could not be... Mostly the center support on the subframe might be troublesome
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There's always something!
Sure there is! Would be boring if not.
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