IDI engine, there IS a future...

[TDIMeister]

Mine and many wastegated TDIs have quite a pronounced torque hump at the low end

More broadly, if you look at the vast collection of DI and IDI Diesels over the years, VNT or wastegated, the torque curves look distinctively different.  IDI has a lower peak that is held in a narrow torque range over a wider speed range, and extends to a higher RPM.  Most DI I've seen have very big torque peaks at low RPM, have nearly constant HP over the last 500-1000 RPM before the peak, and drops off steeply at a lower RPM than IDI.

There are many contributing factors for this, but I can't guess as to which one or two are dominant.

[malone]

If a hypothetical TDI could produce 211 lb.ft of torque at 5000 RPM (not saying it has or can be), you know that you can make the rest of the torque curve almost look like anything you want (within limits).

Definitely.

A few months ago a US resident with an ALH TDI contacted me about driving up to BC this Summer to get custom chipped. With a VNT-20 turbo he wants good driveability and drivetrain reliability so he requested a maximum of 275 wheel torque. I took an existing TDI dyno graph and drew dotted lines to simulate his request:


(the final torque curve will not be exactly the same)

The VNT-20 is a good choice in this case because not only it is still capable of producing his requested torque below 2,500 RPM, it will continue to flow more air than smaller VNTs. Good for retaining a little more torque (and HP) up until redline. Lower EGT, too.

If a hypothetical TDI could produce 211 lb.ft of torque at 5000 RPM

A 211wtq @ 5,000 RPM IDI is still more plausible than a TDI performing the same. The IDI has higher combustion efficiency at higher engine speeds with lower amounts of air required per cycle at the same smoke level. 10-15% more power at the shaft according to the document quoted in the first post.

While it is easily proven that a modified IDI can produce enough low-RPM torque to cause initial wheelspin, who said that must be sacrificed for more HP in the top end? That's where compound turbocharging becomes useful to cover a wide RPM range, if not a VNT.

A gasser-like transmission could be used for a 6,000 RPM IDI and the close gear ratios will amplify low-RPM torque. An IDI's powerband seems more manageable for a FWD vehicle and it will help be more competitive against gassers. Some people overlook the importance of RPM and HP. Regardless, like you said:

At the end of the day, it's a preference thing of the driver, and as I've always championed, you make your choices on what suits your preference.

I agree totally. I will be buying a 2006 MKV Jetta TDI soon for daily driving while my IDI goes under the knife. I'll enjoy the fuel economy and if I want to modify it further I intend to make it torque monster

If I had to choose between a TDI and IDI, both with limited redlines (5,000 RPM).. I'd probably lean towards the TDI. Otherwise a high-RPM IDI theoretically has more HP potential.

Nice, I look forward to see some dyno numbers.

Me too.. after the IDI goes back on the road I will definitely go on a chassis dyno

After all the hearsay, a dyno plot -- for all its questionable-ness -- is still the one way we can compare apples-to-apples.

Agreed.

I posted a long time ago expressing my interest to see what Giles could do with the electronic VE TDI pump.  I have a brand-new AHU pump with one of Marc's 12mm heads that's sitting 7000 km from me in Gerry's garage.  The offer now is the same as it was before: I'd gladly donate that pump to Giles (or anyone for that matter) as his development mule for him to work his magic on it. Between Gerry and I, the cost will not be in issue when it actually does something.

Perhaps I can talk to him about that after he finishes my IDI pump.

If Giles raises the physical max. timing in the VE TDI pump, and if Gerry needs adjustments in his ECU to take advantage of the new timing range, then let me know as I believe I'm capable of doing that.

Cheers,
Mark

[malone]

Mine and many wastegated TDIs have quite a pronounced torque hump at the low end

More broadly, if you look at the vast collection of DI and IDI Diesels over the years, VNT or wastegated, the torque curves look distinctively different.  IDI has a lower peak that is held in a narrow torque range over a wider speed range, and extends to a higher RPM.  Most DI I've seen have very big torque peaks at low RPM, have nearly constant HP over the last 500-1000 RPM before the peak, and drops off steeply at a lower RPM than IDI.

There are many contributing factors for this, but I can't guess as to which one or two are dominant.

1) There are a fair number of 1.9 IDIs with K14 and T2 turbos that are larger than the wastegated turbos found on 1.9 TDIs. The larger turbo builds boost more slowly. However, I have not seen a dyno plot of a stock 1.9 IDI with a K03 turbo so you could still be right.

2) The TDI's higher injection pressure likely contributed to the low RPM combustion performance, although stock IDIs with low injection pressures are irrelevant in this type of discussion. There may be a difference in an IDI's low RPM torque:smoke ratio if its pump is upgraded to 10mm or 11mm, and perhaps have its camplate upgraded as well.

Other than these, I'm not too sure how much the DI combustion process itself contributes to the added low RPM torque.

[jtanguay]

I would think that the lower CR would allow better low rpm efficiency

[TDForNow]

2) The TDI's higher injection pressure likely contributed to the low RPM combustion performance, although stock IDIs with low injection pressures are irrelevant in this type of discussion. There may be a difference in an IDI's low RPM torque:smoke ratio if its pump is upgraded to 10mm or 11mm, and perhaps have its camplate upgraded as well.

Has anyone experimented with higher injection pressures on IDI's and if so, what were the effects, the limits and how much effect on actual timing?

[TDForNow]

Bump for refreshing:.....

[TDIMeister]

I would think that the lower CR would allow better low rpm efficiency

No, it would make it particularly worse.  At low-load and low-RPM, heat losses are especially high, because there's simply more time for heat transfer to occur to the cylinder walls.  Less trapped mass also loses heat faster (compare seasonal temperature variations between Lake Superior and Lake Erie, for example). Therefore the cylinder charge cannot get up to an optimal temperature to combust the fuel, and thermodynamically, heat loss simply represents wasted energy.

In theory, thermal efficiency increases continually with increasing CR, but in practise, the thermal efficiency to CR graph flattens out at a peak and falls off as well due to other losses.  And the "optimum" CR is below what is common practise on most Diesels to offset the need for good cold-start and low-load efficiency.

[mike71ghia]

I haven't used their products, but check out the website... ceramic metalic bake at home coatings..
http://www.techlinecoatings.com/
I also posted in this thread about toyotas notched chamber , I'd be willing to do some machining.
http://www.vwdiesel.net/phpBB/viewtopic.php?p=33214#33214

[dover]

A very enlightening discussion, including the toyota piston digression.

What about anodizing (a thick alumina layer produced with electrochemistry)
prechamber, PC insert and piston
?

It should reduce heat transfer and -I think- is the most durable.
It's probably the most do-able with the least equipment.

[gldgti]

anodizing wont really make any kind of heat transfer difference.... there are some ceramic coating techniques which may be used for this application which would dramaticallydecrease heat transfer through the pre-chambers, and I will be looking into this and experimenting with it in 2007.

[bert]

Hi,no one has mentioned keeping the chambers warmer by activating the heater plugs on say half voltage all the time the engine is running,so adding heat,peugeot diesels here in the u.k have there heater plugs activated for at least 1 minute after starting to stop any smoke.This will cause more drag off the alternator,but if for racing have a slave battery fitted just for the glow plugs post starting,and manually charge it at home or have a switchable split charger,switch on after racing  :twisted:
Might be a crap idea?
Bert

[tSoG-84bit]

All very interesting stuff, even the stuff that was beyond me... As someone with a 1.6N/A IDI that may need a rebuild this is all stuff that could be of some use to me. Am I just waking the dead bumping this post, or has there been progress with improving the efficiency of the IDI in the last few months?

[JetPo]

I juste finished reading the WHOLE POST !!!! :shock:  It took me almost 1h30 but it was worth it !    I am going to be rebuilting a 1.9 TD in a couple of weeks to go in my 1992 Jetta. I wanted to know if someone had tried the ceramic coating ? Because i would be very interested. But some guys talked about ''too much heat for the injectors''??? Is that a probleme Because this motor will be in my daily driver, so i want the motor to be reliable (thought i want it to be powerful  :wink: ). So if anyone as more info on the ceramic coating, i would be interested on maybe testing it on my 1.9 TD. So thanks everyone for this great post, it is very interesting. I'll be waiting for your reply.

Alex

[Mark(The Miser)UK]

Hi,no one has mentioned keeping the chambers warmer by activating the heater plugs on say half voltage all the time the engine is running,so adding heat,peugeot diesels here in the u.k have there heater plugs activated for at least 1 minute after starting to stop any smoke.This will cause more drag off the alternator,but if for racing have a slave battery fitted just for the glow plugs post starting,and manually charge it at home or have a switchable split charger,switch on after racing  :twisted:
Might be a crap idea?
Bert

[/size]

Nothing wrong with a crap idea... Better than no idea at all. Would it be of any benefit? H'mm  Why not raise compression to raise the heat homogenously ?sp!  Both methods add load to the engine... or do they  :wink:  
Would this paint work as a ceramic substitute?
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&ih=003&sspagename=STRK%3AMEWA%3AIT&viewitem=&item=130022011795&rd=1&rd=1

[zukgod1]

Um no, that stuff wouldnt even stay on the outside of the manifold let alone inside the combustion chamber.


dan