what is the ultimate aaz?

[RabbitGTDguy]

Haven't been over here on the IDI boards for a while as at the current moment I don' t have an IDI in my arsenal anymore. However, having had experience with both motors, inside and out...modified and stock I think I can offer some insight here. Many of the comments already made here are very true and will hold up, others need some reinterpretation...
I currently have a heavily modified 1z/AHU based mTDI motor in my mk1 that I built from the ground up and is documented elsewhere here on the forums.

In addressing the reliability of the DI motors vs. the IDI motors....

Both motors have been proven to be very reliable, especially when you look at it from the strictly mechanical ends of the motors. Electronics do give the TDI a bad name (mostly in the form of MAF's and n75 valves), but the motors on a whole, mechanically are just as reliable as the next IDI. There are many TDI owners that have racked up 200K + on there cars without issue and paying attention to regular maintenence.

As far as efficiency goes. The DI motor by design is far more efficient than the IDI motors. It was one reason that so many manufacturers have moved from the IDI motors to the DI motors. Think about the design of the head and means of injection alone. In your IDI motor their is a pre chamber where the fuel is injected, combusted and then the energy is then transferred out of the prechamber through the blast ramp and finally making power when it meets the piston...in simplistic terms....
The DI motors on the other hand don't have "big scary dishes" in the pistons...that is actually a specially designed combustion chamber. Injection, combustion and power all happen RIGHT HERE at one time.
The biggest thing about these two difference is the energy loss/efficiency factor. The IDI motors waste a considerable amount of energy in the "prechamber" design. This heat is lost to the head translating in one way or another to power loss. Also, the design and direct injection of the DI motors does translate to more power/torque just by design.
I can go on...but, I could do that for quite a while...

Hope that helps?!?!

The mTDI, or mechanically controlled TDI can be created quite easily but it isn't as easy as building a "Franken pump" from many different pumps and just flying with that. There are considerations to be made in the size of hydraulic head you want to use on the pump and more importantly the design of the camplate profile and timing advance mechanism that you have in the pump. mTDI's LIKE THERE ADVANCE, and even on the eTDI's (electronics involved) one of the biggest liimitations is the amount timing advance that the ECM is able to pull, etc. Look over on TDIclub.com and you'll find that many reach this wall. Chip programming and reflash, etc. gets expensive (in this persons opinion) and I like the simiplicity of the mechanical control I have. If I have to lose a little bit of "economy" when transitioning between altitudes and super finely controlled advance (controlled by the eTDI pump), I'll take that as it; I believe, pays back in the end somewhere else. A mTDI also sounds alot more like a IDI motor...or a cummins motor if you really want to be specific do to the lack of PRECISE electronic control of timing and advance.
There are a variety of pumps out there that are good for building your base pump, or to send to Giles and have done. These include the cummins 4bt pump, Croma pumps, Perkins pumps to name a few, as well as your other parts pumps (IDI and TDI pumps).

On revving. This is not limited on the DI motors because of the design of the DI engine itself. Rather, it is a bore/stroke issue. The 1.5 is the most rev. happy motor, the 1.6...not too shabby as has been proven on the site here and elsewhere...and the 1.9AAZ....hmm, not too far off from the TDI. If the bore/stroke issue could be addressed with the TDI, you could pull more revs out of it. I remember a topic/discussion not too far in the past that discussed the feasibility of using a 1z/AHU head (same basic bolt pattern, coolant passages, etc) on a 1.6 IDI block... the biggest issue to address here would be finding pistons to fit this configuration. It would def. be a fun project....but one that involves some reverse engineering.

Anyways...my .02.

I'd love to see an IDI motor make that kind of power...even a 4cyl TDI make that... but I think displacement and overall size (as already mentioned) would limit that. Remember...there is no replacement for displacement and TORQUE, not HP wins races...
I suppose if money wasn't limited and you didn't mind cutting into your motor every few months, BIG huge power could be done...but not reliable. There has to be a balance somewhere.

I'm a mTDI guy now, building my second motor here this winter for my daily driver (b3 variant) with a proper blend of economy and power in mind... the MK1, was and continues to be just all out performance...it is fun and the TDI's are just as reliable as anything else and are a more efficient design.
Cost wise...they are more expensive but those prices are slowly starting to creep down a bit as more become available and more diesels for that matter are coming in on the market.

Have a good one!

Joe

[rabbid79]

For that kind of power, I think the four biggest issues are reliability of the swirl chamber, piston strength, exhaust back pressure, and block flex.  Some of these are IDI-specific, and some are not.

One:  That is a high volume of hot combustion gasses going into and out of that little swirl chamber hole.  I have heard of some people enlarging the hole, and others who have considered coating the whole chamber with a thermal barrier.  These both sound like good ideas to me.  As far as I know the swirl chamber is made of Inconel, so that's a good start.

Two:  Piston strength.  As I understand it, stock IDI and TDI pistons are cast.  It might be necessary to round up some forged pistons for it.  I read one of TDIMeister's posts where I think he said he knew where to get some forged TDI piston blanks that didn't have the bowl machined into them.  If these are available, perhaps they could be machined with the funny little IDI swirl design on the top instead.

Three:  Exhaust back pressure.  As was mentioned earler, you would want to go with a huge exhaust and turbo, and have the head extensively ported.  Possibly even bigger exhaust valves and different cam profile would be necessary.

Four:  Block strength.  400 HP at 6000 RPM is 350 ft./lb.  I don't think the stock AAZ block is up to the challenge.  It is true that the TDI blocks have more webbing and internal bracing than non-TDI blocks.  You could beef the block up with a girdle available from Eurospec for about $500.  If you're installing this engine in a MK1, MK2 or MK3, you could make it easier by using a 1Z or AHU (TDI) block since these engines have have the proper mounts for the older cars, but are compatible with the older IDI style heads.  You may still want to internally brace the block though.

Of course all of this assumes you already have lightweight forged crank and rods, upgraded clutch, stronger transmission, axles, high flow intake, intercooler, etc.  The high HP TDIs also have these same issues, so no advantage there.

Obviously there are many other issues that need to be resolved, but as was mentioned by other members earler, you can fortunately leave those problems to the experts.  For example, how to get the fuel and advance timing you need.  This should definately be left to Giles.

[jtanguay]

with diesels forget HP.  you want the TORQUE!  :twisted:

hp sells cars and torque wins RACES

[RabbitGTDguy]

Two:  Piston strength.  As I understand it, stock IDI and TDI pistons are cast.  It might be necessary to round up some forged pistons for it.  I read one of TDIMeister's posts where I think he said he knew where to get some forged TDI piston blanks that didn't have the bowl machined into them.  If these are available, perhaps they could be machined with the funny little IDI swirl design on the top instead.

This is only true of EARLY TDI engines... the 1z TDI motor has cast pistons... AHU, ALH and later motors have Forged pistons with brass truions and quite a bit beefier construction than the 1z units. Also, ring lands are thicker and the top ring location on the 1z vs. AHU/ALH, etc. pistons is different.

with diesels forget HP.  you want the TORQUE!  :twisted:

hp sells cars and torque wins RACES

HP indeed with diesels does not give insight into overall power. It is all about torque...and to say again what I said again in my previous post is summed up again by jtanguay.

Joe

[subsonic]

When I wrote to Kolbenschmidt about doing a 1.7TD, The concern they raised was not the strength of the piston crown but rather the strength of the side of the piston where the pin was connected.  They said that High HP long term would cause cracks in this portion of the piston.

[oldskool rich]

sorry if i sound stupid but exactly what is an M-TDI is it just a TDI with a cable throttle instead of a fly by wire? and im guessing it has the hole knock sensor advance thingy?

so pre combustion chambers are bad, IDI pistons are good, so why cant u just use IDI pistons in a TDI?

so what head and what block?

why can IDIs hit higher revs?

im seriously thinking of moving on to TDI but keeping sum of the idi features

the car im building this engine for is a rear engined mk1 scirocco that wen finished will weigh 500kgs so i dont want to mess this up, i had the chance to hav an audi 4.2 twin turbo v8 but turned it down because everyone does that, i want to do sumthing never done before, its mainly for the quater mile but will also be "road legal" ish

as soon as caddy cums to life ill start a progress diary

[RabbitGTDguy]

sorry if i sound stupid but exactly what is an M-TDI is it just a TDI with a cable throttle instead of a fly by wire? and im guessing it has the hole knock sensor advance thingy?

so pre combustion chambers are bad, IDI pistons are good, so why cant u just use IDI pistons in a TDI?

so what head and what block?

why can IDIs hit higher revs?

im seriously thinking of moving on to TDI but keeping sum of the idi features

the car im building this engine for is a rear engined mk1 scirocco that wen finished will weigh 500kgs so i dont want to mess this up, i had the chance to hav an audi 4.2 twin turbo v8 but turned it down because everyone does that, i want to do sumthing never done before, its mainly for the quater mile but will also be "road legal" ish

as soon as caddy cums to life ill start a progress diary

No offense on my part either, but go back through a re-read what others have said and also what I tried to draw together.
Sounds like you are really new to diesels...
mTDI is a mechanical TDI, mechanical in the fact that the pump utilized on these motors is a fully mechanical pump. The "throttle" if you will is operated by cable and the ONLY electrical connection needed is a simple ignition on/off signal to acutate the fuel stop solenoid on the pump. This is the same type of pump that was used on the IDI motors. Same TYPE...not entirely internally as there are several things that need to be taken into consideration when building an "m-pump" for a TDI motor.

"Knock sensor" ignitions are reserved for gasoline cars...not diesels. They detect "knock" indicitive of fuel/air mixture in the engine....
Diesels always sound like we are "knocking"
(Though...I can tell you stories about what diesel "knock", if you want to call it that...more pre-combustion than anything though....sounds like from my experience with propane on my old IDI motor...which I did run successfully).

As far as pistons....what we were essentially saying is that IDI pistons tend to be weak, especially without modification for HIGH power applications since they are cast units. Hence the quest for "forged" units... blanks namely so you guys could have the valve reliefs and ramp cut into them...
TDI pistons are stronger (namely your FORGED units from the AHU, ALH and later motors that also utilize coatings as well).

Why can't you use IDI pistons in a TDI block? THEY ARE TWO TOTALLY DIFFERENT TYPES OF INJECTION/COMBUSTION.
The IDI head contains the "combustion chamber" essentially for the most part for the IDI motor, it is contained in the prechamber. On a TDI, the combustion chamber is in the pistons themselves!
Putting IDI pistons in a TDI block? Ok, that could work if you used AAZ IDI 1.9 pistons...but you'd still need to use a IDI head to make the motor work. TWO different types of combustion...

IDI's themselves don't make "higher revs" Its the displacement and stroke of the motors that lend to this. Namely with the 1.5 and 1.6 motors that are pretty rev happy. The 1.9 AAZ TDI has its limitations in revving just as the 1.9 TDI motors...
It has nothing really to do with IDI vs TDI in revving...

Heads?
DI heads belong on DI blocks  and IDI heads on IDI blocks. There are your exceptions (for instance, the AAZ block and the 1z/AHU 1.9 TDI block are essentially the same...minus their internals...one could use a AAZ block and build it with TDI pistons, a head, etc. and have a TDI motor)...someone on here is building one of these right now. It won't make a difference, etc. power wise...just a place and item that can be interchanged.

I'd love to build say a 1.6l or a 1.7l mTDI motor, that'd be fun... you could use the 1.9 TDI head on a 1.6 block but you have to consider the problem in finding pistons that are DI specific to do this. That would be a happy little revving monster that could be alot o' fun.
Not to mention...and I already said it above. TDI's and mTDI's especially (since you can mod your pump to allow it) LOVE their timing advance! Alot! Substantially more than you can throw at the IDI motors.

Anyways...

Joe

[rabbid79]

I don't mean for this to become a TDI vs. IDI debate, but IDIs don't rev higher simply because of their shorter strokes.  Plenty of gassers have 95.5mm and 100mm strokes, and rev to 8000 RPM.  It's not about the stroke.  It's about the swirl chamber in the IDI and its ability to burn the fuel faster than DI.  If you want RPMs, which is essential in making HP, go IDI.  That's what I intend to do.

[jimfoo]

Gassers aren't a fair comparison however as their pistons weigh considerably less than a Diesel piston, which makes a very big difference as to max rpm.
That is probably the main reason they can rev higher.

[jtanguay]

if you're looking for around 400hp then maybe the 2.0 twin cam PD engine is what you're looking for.  IMO that would have no problem reaching 400, just bigger turbo, DP, intercooler, and a re-map.

how much was the audi twin turbo V8? if it was cheap it would have probably cost you more since they like to drink gasoline...

[RabbitGTDguy]

I agree...it is hard to compare a diesel to gassers just from a shear design aspect. Stroke doesn't have everything to do with it...but it does play in.



Joe

[oldskool rich]

ok sorry for my beginer questions, im not much of a computer wizz it might take me months to find the answers im looking for, so please bare with me guys im trying my hardest.

i want to rev like a gasser so idi is what im going with, what can i do? i also want to maintain a large cubic capacity. wud it just meen lighten everything?

if i ran a 1.6 crank in a 1.9 wud i not get enough compression to combust?
what if i cut my block down ?

[jimfoo]

You won't get a Diesel to the same rpm's a gasser can attain, period. Too much stresses on everything. A 1.6 has a shorter stroke, but I don't know you'd be able to reduce the block height enough. You probably would also need custom rods, plus I'm not even sure that a 1.6 crank has the same main bearing size. With a ton of torque and the correct gearing, you could keep pulling in one gear while they will have to keep shifting to stay in the powerband. That's the beauty of the Diesel. You don't need the high rpm's. The Audi R10 won the LeMans getting up to just 5000 rpm.

[jtanguay]

lower rpm's means a longer lasting engine.  i laugh at honda's that rev to 8000 or even 9000 rpm.  imagine something broke at those speeds?  :shock:

IDI's make their torque down low, and TDI's make it even lower (some as low as 1500 rpm or so??? with VNT turbo's)

i'd say custom tall ratio 6 speed tranny to take full advantage of the torque.

AND since it revs lower, it consumes less fuel through more efficient combustion.

[oldskool rich]

in my quest to build the ultimate idi ive found a pump that i was thinking about using, has anyone herd of a bosch vp44? its a raidal pump that aparently can deliver 1600 bar :shock: , loads more than any VE pump

has anyone come across raidial pumps?

surly this cud be adapted to fit?