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Engine Specific Info and Questions => IDI Engine => Topic started by: fspGTD on November 09, 2004, 09:43:18 pm
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I have a somewhat whacky idea to get more high-rpm power and efficiency on our IDI VW-Diesels.
I was browsing the IDI diesel patents, and I came across US Patent number 3,965,872. It's a patent about the design of the recess that is machined into the tops of the pistons. Check it out - you can pull it up on http://patft.uspto.gov/netahtml/srchnum.htm - enter in patent number 3965872.
It basically presents 2 pre-existing designs, one that looks a heck of a lot like the VW IDI-Diesel piston (with the 2 "leafs" or circles), which it says has good combustion efficiency at low and mid RPM, and then a "slotted" design, which it says has good combustion efficiency at high RPM. It then presents a "hybrid" design, which looks like our VW IDI Diesel piston tops with a slot machined partway in, which it says offers efficiency over a broad powerband. It says depending how deep the slot is machined in, high RPM or low RPM can be biased. So machining it deeper in would then bias the high RPM efficiency more.
It looks like it might be a do-able modification to just take a VW IDI piston, and machine in one of these slots, thus converting it from a "low and mid RPM only" efficiency design into one that supposedly handles high RPMs better. To do this, one might remove some material below the white paint indicated here...
(http://www.imagestation.com/picture/sraid146/p8f475b79c18580b59cba5a4eb86981ff/f64f5758.jpg)
The author says on a test engine that was converted, both torque and power increased more than 8%, and smoke level was reduced as well as a result of the modification. He makes it sounds like it could be promising perhaps, on a VW IDI-Diesel.
What do you guys think - is this crazy or what. Are there any diesel combustion chamber design gurus lurking on this list who might be able to chime in?
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wow Jake, that's something! I almost wish my project engine's pistons weren't ceramic coated, otherwise I'd give it a shot! Perhaps it'd be worth trying on a stocker with a modded pump.
That's really interesting, as I've felt how willingly an IDI can rev the tach off the deep end given the right mods. I wonder how much improvement your slotted piston would give.... hmmmmmmmmmm......
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I don't really think I understand why you guys are so interested in high rpm power. It's a diesel and it's just not going to rev like a gas engine.
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I don't really think I understand why you guys are so interested in high rpm power. It's a diesel and it's just not going to rev like a gas engine.
This thread from the old forum should help bring you up to speed on the high-RPM performance potential of the VW IDI-Diesel motors:
http://www.hostboard.com/cgi-bin/ultimatebb.cgi/ubb/get_topic/f/4037/t/242
In the future, please use the "search" feature of the forum to try and find the answer before posting. Thanks.
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I don't really think I understand why you guys are so interested in high rpm power. It's a diesel and it's just not going to rev like a gas engine.
There are 2 ways to make power from any engine. The first is to increase BMEP (Brake Mean Effective Pressure) which directly increases torque. This entails using more boost (or better flowing ports on an NA engine) and more fuel to increase the combustion chamber pressure. It works well, until you start blowing head gaskets and bending rods, which is where some of us have hit a wall. The second method of increasing power is to keep the same BMEP (and torque) but increase the frequency of the power strokes by raising the RPM. This is just as effective as increasing BMEP but is easier on engine parts, unless of course you get carried away. See the thread about fspGTD's over-revved head :D.
fspGTD's reasons for increasing the rpm range of the engine go beyond just the power advantages. Modifications that permit greater rpm allow the driver to hold a gear longer without shifting, very important in autocross. Also, governor mods, unlike boost mods, are permitted in the autocross class in which fspGTD is competing.
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I don't really think I understand why you guys are so interested in high rpm power. It's a diesel and it's just not going to rev like a gas engine.
You are SO prejudiced. Think outside the box, man. We do, and it's brought us (especially Jake) amazing results.
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I don't really think I understand why you guys are so interested in high rpm power. It's a diesel and it's just not going to rev like a gas engine.
This thread from the old forum should help bring you up to speed on the high-RPM performance potential of the VW IDI-Diesel motors:
http://www.hostboard.com/cgi-bin/ultimatebb.cgi/ubb/get_topic/f/4037/t/242
In the future, please use the "search" feature of the forum to try and find the answer before posting. Thanks.
I've read that before....besides, what I was referring to was the speed at which the diesel combustion process actually happens. Don't treat me like an idiot just because I don't have a big post count.
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Please guys, stick to the subject, we are all here to learn and share what we know.. There's no 'stupid questions. I will write a 'Please read first' that i will stick on the top of the section..
Marc/
Admin.
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Not to worry, Mike. Most of us used to think the same way about diesels as you used to... :wink:
But the truth is that diesels are inherently capable of revving as high as a gas engine of similar architecture. The primary restriction is that diesel has a relatively fixed ignition delay, but the flame front speed itself is pretty much as fast as that of gasoline.
The bottom line is that many of the tricks applied to raising the RPM, power and torque of a gas engine will work as well with diesels.
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Let me some time to arrange something.. Ok, back to the crazy idea of Jake :P
Marc/
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Well if I was going to cut up any pistons in research those would be my first candidates :wink: , I would say tha tif it was worth the time effort and money to patent it it probablyhas some good merrit. In fact the next time I have the head off the old motor I will try it myself, or even on the "new motor" when ever it gets started or finished (another long story). My only consern here is how much CR are you going to drop by cuting that piston material away, and I didn't see any refrence (though I only quickly skimed it and the images wouldnt load on my comp) to the size, angle, or depth these cuts should be made. Other than those few things I am all for it and will have my die grindeer ready the next time I blow my head off :roll:
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This would be a "correct" way of adding volume to the combustion chamber to achieve a drop in compression ratio. I would expect it to give much, much better results than thickening the head gasket, which adds volumne to the squish area.
I haven't run any calcs yet to see what the compresion ratios would drop to, but it would depend how deep and long the pockets are made.
There is one thing I noticed that might throw a monkey wrench into the idea, and that is on the VW IDI diesel combustion chamber design, I noticed in between the valves there is a semi-circular relief already machined into the head... you can see them in this picture:
(http://www.imagestation.com/picture/sraid146/p35aaaff82edf04732656953a3664e359/f64f5756.jpg)
In the combustion chamber, this relief is in the same general area as where the groove would be machined into the piston, except the VW IDI groove is in the head rather than in the piston top. So I wonder if VW has already incorporated this functionality into our engine's design, but just in a different way (by putting the void in the head rather than the piston?)
The patent papers don't show if they expect the surface of the head at this location to be flat or not, and nothing is mentioned about it that I saw. But it might be assumed. Since it's patented by someone working for Toyota in the mid 70's... it makes me wonder what the diesel engines Toyota produced in this era looked like... anyone know if Toyota made any diesel engines in this period (maybe Japanese market only type deals?) and if so how we might find out what their combustion chambers looked like?
I tried out filing and dremeling grooves into the edge of a scrap chunk of aluminum by hand just to experiment a bit, and I just wasn't happy enough with the results to warrant trying doing this on my pistons with them installed in the block. I think to give it a decent shot, I'd need to remove the pistons and take them to a milling machine, which could machine in the slots precision-style and repeatable from one piston to the next.
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For those of us running greater then stock boost lowering the CR will probably quite quickly become a advantage and mabey even a necessity, however in your app, I see this more as a hinderance then a help, as you arn't able to fill the added voulme wiht extra pressure. But I maybe wrong and I sure some one will fill me in if I am :wink:
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Oh I just thought of some more infoi, the only three road vehicals that toyota imported into north america in the 70's were the corona, the corolla, and the p/u none of which had a diesel avalible until the early 80's.... oh scrap that thought the Landcrusier had the toyota 3b as i recall and that might have been as early as '76, but through further research the diesel engine wasnt an option until '81 dont know of any mediium or heavy duty toyota trucks from the '70s that were imported, the only other thing that I can come up with is forklifts, or somthing on the JDM.
Also now that I am on a role they said the deeper or was it bigger the cut in the piston the more it moved the rpm scale up. So even if VW has already taken in some account in the semi cirlces in the head they were never forseeing, or designing for some one to be racing this motor and wanting to extend the rpm band further, so there is a good posibilty that there are still some benifits to doing this.
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"Balancing" the shape of the piston tops exactly so the combustion patterns and power from each piston to the next is also important. Figure 24 of the 1.6lTD SAE paper shows a cross-section of the piston. The piston crown is a solid chunk of aluminum from the piston top to the cavity inside, it's a half inch or thicker. (The cavity starts at about the same depth as the top ring.) So it looks like it could take a little machining into it's top to me, no problem.
Dvst8r - the CR for optimal efficiency is significantly lower than what VW went with at 23'ish:1... at least that's what they have stated in the SAE Papers (here we go... 1.5D SAE paper, p.83 states "The compression ratios which permit attaining optimal fuel combustion in small swirl-chamber engines range between 16:1 and 18:1." Therefore if it were to get dropped down the correct way (IE: by enlarging the pre and/or main combustion chamber, not by enlarging the squish area which is what happens when you install a thicker headgasket) this means we might expect to see an increase in power and fuel efficiency. The downside is that cold starting would be harder.
If found a figure in the 1.5lD SAE paper (figure 8, p.82) that shows a cross-section of the VW IDI Diesel combustion chamber. It clearly shows the semicircular "blip" in the cylinder head between the valves and the relationship of this feature with the "clover leaf" recess in the piston tops. Interestingly, at TDC, there is not a very open connection between the two volumes except through the thin clearance between top of piston and bottom of cylinder head! As the piston moved down slightly, it seems like the gasses may be channeled upward and into this relief in the head however. Make me wonder what's going on in there... IE: is it a feature that comes into play only after the piston moves down somewhat... (kind of like the high-rpm piston channel described in the patent paper we are discussing...)
Studying some figures in the 1.5D SAE paper (Fig 9, p.83) of the cylinder pressure over crank angle, it looks like most of the combustion (the pressure rise) happens between TDC and 40 degrees crank angle. At some RPMs though, it looks like some combustion trails off until around 60 crank degrees. It would be interesting to do a study and see what shape the combustion chamber is when combustion is happening...
PS - to the guy who said that combustion in a diesel was too slow for it to be able to revv high... here in the 1.5D SAE paper there is a comparison (in figure 9, p. 83) of the 110HP GTI motor vs the diesel... and in the GTI motor, the combustion is spread over about a 80 crank angles. This is much broader than with the diesel, which is concentrated more narrowly, like over more like a 40-50 crank angle area. Just goes to show that with a diesel, combustion happens fast! A big challenge for the diesel engine designers indeed seems to be trying to get the combustion to slow down and getting it controlled, not trying to get it to speed up... This explains the existence of pre chambers in diesels, and also of the significance of the pilot injection feature (which is what VW pioneered, with Bosch's help, for their TDI motors.)
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Great post, Jake! One thing though...
This explains the existence of pre chambers in diesels, and also of the significance of the pilot injection feature (which is what VW pioneered, with Bosch's help, for their TDI motors.)
I read somewhere (TDI Forum?) that the pilot injection's function is to raise the temperature and turbulence so as to achieve more complete fuel burning during the main injection phase, and hence raise their overall efficiency.
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I don't know if that's accurate... it doesn't jibe with what I remember reading in the TDI SAE papers. (I don't recall anything about pilot injection increasing efficiency, but it did cause a more gradual pressure rise during combustion. By starting a "little fire" burning early in the combustion chamber before the main injection happens, the ignition delay time main fuel injection is reduced (it atomizes and begins burning quicker), and this reduces the otherwise sharp pressure rise and noise of the burning of the main injection, so pilot injection thereby "tames" the more efficient DI combustion process enough to make it suitable for use in passenger cars.)
I'll dig up that SAE paper (based on development of VW's first TDI engine...) and see what it says.
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Jake, please do let us know what comes out of the SAE paper. As I said, I can't even recall where I read that, much less how accurate it might be... :wink:
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Just wanted to add to this topic that while I was browing the grant piston & rings web site, I stumbled across their "piston designs" page,
http://www.grantpistonrings.com/products/pistons/piston_styles.htm
which had this picture of various piston designs:
(http://www.grantpistonrings.com/images/pistonStyles_n2.jpg)
Notice at right, third up from the bottom is the piston that looks identical to the toyota patent, I'll bet it's from some toyota diesel engine but I'm curious to learn anything more about it. Maybe someone up here who has a toyota diesel could look underneath their head sometime and see if this is the kind of piston it has. (Feel free to take some detailed pictures and measurements. 8) ) And IDI VW Diesel piston is pictured by the way at left in the bottom row.
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Maybe someone up here who has a toyota diesel could look underneath their head sometime and see if this is the kind of piston it has. (Feel free to take some detailed pictures and measurements. 8) ) And IDI VW Diesel piston is pictured by the way at left in the bottom row.
I have a couple sets of 86-88 "2LT" (2.4L turbo IDI inline-4) pistons out, I will have a look at them and take some pictures if I have a chance.
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here's a picture with some rough measurments.
The piston top is just like described in the patent paper.
(http://toy4x4.free.fr/passiont/photos/meca/2LTpiston0.jpg)
'85-90 2LT engine stock specs :
63kW / 86hp @ 4000rpm
139lbs.ft /188Nm @ 2400rpm
92mm bore x 92mm stroke
20:1 or 21:1 CR
8psi max. boost
4000rpm max. governed speed
OHC with rocker lifters
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Nice!! Thanks for your contribution, 2446
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Wow - thanks for the info, 2446! It's amazing the kinds of resources that can come out of the woodwork on this board. :D
It seems like the 92mm toyota diesel bore is too big to consider swapping it into a VW Diesel block (considering VW Diesel pistons are usually under 80mm). But it could be feasible to machine this pattern into a VW piston top. Your measurments would prove very useful for anyone trying this.
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FASCINATING thread! I'm starting to think I should drop out of college (engineering) and just spend all my time reading posts on this board--I swear I learn more per minute here than I ever could in any of my classes. Amazing how we go from some patent paper that Jake dug up describing a long-forgotten Toyota engineer's brainchild design, to a photo of an actual Toyota diesel piston that uses the very same principle!
Interesting that, despite the piston cut, the Toyota diesel is a pretty low-revver--it's capped at 4000 rpm. However, it is a substantially larger engine; maybe with the right mods, that method could be used to great advantage in a VW diesel. I have a nice 80,000-mile 1.6NA short block sitting on my bedroom floor at home waiting for me to do something with it--who wants to give it a try? (Although, without a turbo, it might prove pointless, as dropping compression down like that without filling it with extra boost won't help anything.)
Also interesting points about the TDI pilot injection. Are you sure they used that on the older rotary-pump TDIs, though? I know the injectors don't have any electronic controls on them, and the pump, outside of its electronic control and higher pressures, works basically the same as our old IDI pumps, as far as I am aware. I wonder how they would have accomplished the pilot injection at all, much less timed it precisely. I thought they didn't use pilot injection until the advent of PD and common rail. However, if they did, that does help explain why it is so difficult to make a mechanical TDI work well--I'm sure the people who do it do without the pilot injection, which, if VW does use it on the older motors, must be an important part of their functionality.
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Interesting that, despite the piston cut, the Toyota diesel is a pretty low-revver--it's capped at 4000 rpm. However, it is a substantially larger engine; maybe with the right mods, that method could be used to great advantage in a VW diesel.
Actually I'm convinced this engine as quite some revving potential. I pushed the accelerator linkage stop a good bit on my all stock NA 2.4, (VE style pump) and it pulls strong almost all the way to 4800 now. The smoke levels at WOT are consitently low all the way (fuel is adjusted at the max. "little grey smoke" level), so I'm assuming the combustion quality at higher revs. is fair.
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Nice!! Thanks for your contribution, 2446
Taking a photo and a couple measurements was the least I could do, given how much I've learnt reading this board so far :wink:
denis
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Let me add my thanks and welcome to the forum, Denis!
I assume that the numbers you added to the photo of the piston top represent the depth of the cut, right? Can you add the width and length, as well?
Thanks! :D
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Interesting you mention the pilot injection. A friend of mine works at www.sturmanindustries.com and they R&D injectors (and more) that are a competitor to the common rail and achieve multiple pilot injection events. (I think the common rail does too). Their injectors are installed on the new ford powerstroke (2004 and on, I think).
And oh yea, v8volvo, stay in school because to work at a place like Sturman you're gonna need it!!!!!! If I knew about a place like that when I was in school I would have made it my goal to work there. It's VERY cool. Check out their web site which is just the tip of the iceberg. I'm an aircraft engineer at Boeing, and Sturman is a million times more interesting and exciting than my job here.
My novice understanding of the benefits of the pilot injection is that it decreases noise and emissions. Not sure about efficiency. The Sturman web site might mention something. I haven't read it recently...
I used to work about 2 miles from Sturman Industries up in the mountains in Woodland Park, CO. Man I miss that...
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Can you add the width and length, as well?
The first cut starts at 16mm wide and finishes at 15mm, and is approx. 24mm long. The second cut starts goes from 14 to 13mm wide, is 21mm long.
The relative positions you can measure on the picture with the provided scale ;)
The beginning part of the first cut curves somewhat roundly just like in fig. 6 in the patent document.
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Can you add the width and length, as well?
The first cut starts at 16mm wide and finishes at 15mm, and is approx. 24mm long. The second cut starts goes from 14 to 13mm wide, is 21mm long.
The relative positions you can measure on the picture with the provided scale ;)
The beginning part of the first cut curves somewhat roundly just like in fig. 6 in the patent document.
are these cuts like radiuses? i hope to get my 81mm pistons this week. because they are totally flat i have to mill these mickey mouse holes into the top and thats the time when i could do some aditional grinding :D
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The bottom of the fist cut is radiused along the length for a smooth gas flow out of the swirl chamber. The second cut is straight. The top and bottom side edges are all straight. Basically it is just like what is described and drawn in the patent paper.
Good luck, when it's done report back and tell us what kind of real-world difference it makes. :wink:
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TTT. I love this thread! :)
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some (ok, a lot) interesting reading here:
http://www.somender-singh.com/
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:oops: I wonder if a vortex creating swirl could be machined in to the piston? H'mm maybe it would need a corresponding but tapered 'male' ridge in the head... taper pointing towards exhaust valve to direct exit gases when valve open? A bit too complex perhaps...
What about a couple of ridge and sockets squirting the gasses towards the middle :?:
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thats what i was told in the power stroke course i took, it makes the engine less noisey and rough
I don't know if that's accurate... it doesn't jibe with what I remember reading in the TDI SAE papers. (I don't recall anything about pilot injection increasing efficiency, but it did cause a more gradual pressure rise during combustion. By starting a "little fire" burning early in the combustion chamber before the main injection happens, the ignition delay time main fuel injection is reduced (it atomizes and begins burning quicker), and this reduces the otherwise sharp pressure rise and noise of the burning of the main injection, so pilot injection thereby "tames" the more efficient DI combustion process enough to make it suitable for use in passenger cars.)
I'll dig up that SAE paper (based on development of VW's first TDI engine...) and see what it says.
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Before you machine a slot, find out how thick the pison is from face to underside in this area. This can be done on the cheap with a regular 6 inch dial caliper and two trimmings of coat hanger cut to a known length in even inches/mm..deep enough on one end to clear the skirt,and the depth you want to probe on the fixed end Take the coat hanger ya have a caliper just cut and file to size, then hot glue or epoxy to the caliper jaws... close the now extended jaws to touch, zero the dial, and subtract your total extension rod lengths to find the actual thickness at any point you touch, sharpen the one on the fixed end and use it on the piston face...
I've got a mill and lathe if anyone wants to experiment I'll be more than willing to chuck and cut!
The hot glue or epoxy should pop right off the caliper if not degreased first. Poster tack will stick probes wherever you want to put them if you prefer...
mike71ghia<AT>yahoo.com
Google "techline coatings" for bake at home ceramic/metalic low friction coatings... anyone considered nikasil cylinder liners?
Never used their stuff but intrigued
http://www.techlinecoatings.com/
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Very interesting. It seems we need a test mule. :twisted:
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nikasil was big like 20 years ago... porsche used it, but the sulphur in fuel broke the liner down and caused engine damage.
even with ultra low sulphur diesel, the chances of the liner breaking down are pretty good.
very interesting thread indeed!
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i think im going to try this
has anyone tried it yet? are you still even around :roll:
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here's a picture with some rough measurments.
The piston top is just like described in the patent paper.
(http://toy4x4.free.fr/passiont/photos/meca/2LTpiston0.jpg)
@2446: Can you please put the picture online again?
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here's a picture with some rough measurments.
The piston top is just like described in the patent paper.
(http://toy4x4.free.fr/passiont/photos/meca/2LTpiston0.jpg)
@2446: Can you please put the picture online again?
i was checking out my pistons today and im most likely going to have this done. im glad i saw this pic with the depths
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Thanks for putting it online again!
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you're welcome :mrgreen:
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nikasil was big like 20 years ago... porsche used it, but the sulphur in fuel broke the liner down and caused engine damage.
even with ultra low sulphur diesel, the chances of the liner breaking down are pretty good.
Most of the top level sportbikes currently use nikasil to line cylider walls. I know they don't burn diesel but though it was worth mentioning.
This is a sweet thread though.
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This is a sweet thread though.
im pretty surprised more people arent currently interested, maybe its an old thing i just found, haha
but i want to do it now and i know that our pistons arent the same size as the toyotas in the picture, which would affect the size that we would need for our pistons.
why is jake MIA when i need him!!
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guys, this stuff is gold.
my mehc eng final year project is coming along - im developing the performance potential of the idi 1.5 engine ('cos i have one spare) and i'm DEFINATELY going to try this.
my current goal is to look at modifying the injector system to improve its efficiency at higher rpm.... but the project will go further.
as someone noted in another thread, optimum CR for the vw idi is around 17:1. VW also note that they would have preferred to use a longer duration higher lift camshaft.
i would like to turn down the piston crowns, machine the groove and the "flowers" back in to the piston to get a 17:1 CR and then use a standard petrol 1.6 camshaft for the extra duration and lift on the intake.
with the use of a thin head gasket and good studs, the reduction in compression ratio and extra clearance should be more than enough to allow easy application of a supercharger setup.
did anyone get around to machining grooves in their pistons?
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I wonder if this would have a similar result? It does mention diesels.
http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=6237579.PN.&OS=PN/6237579&RS=PN/6237579
There was also a forum I looked at where people had done it on gas engines, mostly Volvo, claiming much smoother running, the ability to lug the engine way down, being able to run more boost, leaner mixtures, and some, better mileage