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+--- Thread: Lowering compression ratio with special 'glow' plugs? (/showthread.php?tid=6915)
Lowering compression ratio with special 'glow' plugs? - NZScott - 12-08-2015
In the process of my NA 617>turbo conversion, been reading another thread with bent rods problems.
I was after boost at low RPM but I'm probably asking for trouble with a 5cm turbine and more than enough fuel to match it.
I'm thinking (hoping!) reducing compression will preserve my conrods.
Don't want to go to the expense of custom rods of machining anything, don't even want to take the head off...so got me thinking about using the glow plugs to reduce the compression. Idea being, take some old loop GPs (this engine originally had them) and machine them down enough to reduce the compression, 18:1 seems to be a popular number.
While I'll be sacrificing the glow plugs themselves, it doesn't get too cold here and I'll have enough fuel to make it splutter into life in a few seconds. You could probably make something that held the GP further away from the prechamber but that's starting to get tricky...
Thoughts?
RE: Lowering compression ratio with special 'glow' plugs? - Petar - 12-08-2015
Depends really on how much the combustion chamber volume is increased with new glow plugs. 21:1 compression with 600cc per cylinder means 30cc chamber volume if i've done the math right. If you manage to increase the combustion chamber volume to 35cc that means (600+35)/35=18.15 compression.
If we assume that the glow plugs cylindricall, 12mm in diameter then the combustion chamer volume would increase by 1cc for every ~9mm of the plugs removed, so to reduce the CR to 18:1 you would have to remove about 45mm of the glow plugs. Not sure if it is physically possible.
I'm on the boost it and f*ck it side. Just keep the boost below 1 bar and stay conservative with the fuel and you should be fine
RE: Lowering compression ratio with special 'glow' plugs? - MFSuper90 - 12-08-2015
Im with petar, boost it and f*ck it
but in all reality, lowering compression will also make it harder to cold start. Like petar said 1 bar of boost really isn't that much, I would be worried about it if you were going to try to push 2-4 bar.
RE: Lowering compression ratio with special 'glow' plugs? - barrote - 12-08-2015
this is diesel.... lowering compression wont help anything , diesels dont have pre detonation/detonation issues...
more the boost the better more compression ratio = more pressure definetly more power
hehhe... but if someone is intending to reduce compression ratio use a thicker gasket MB makes them till 2.5mm and the idea behind is to keep those numbers and avoid colisions in highly opened engines
regards
RE: Lowering compression ratio with special 'glow' plugs? - Volker407 - 12-08-2015
(12-08-2015, 05:36 PM)barrote this is diesel.... lowering compression wont help anything , diesels dont have pre detonation/detonation issues...
more the boost the better more compression ratio = more pressure definetly more power
i think the idea is to lower compression to have the possibility to run more boost.
Gruß
Volker
RE: Lowering compression ratio with special 'glow' plugs? - Druk - 12-08-2015
(12-08-2015, 05:51 PM)Volker407(12-08-2015, 05:36 PM)barrote this is diesel.... lowering compression wont help anything , diesels dont have pre detonation/detonation issues...
more the boost the better more compression ratio = more pressure definetly more power
i think the idea is to lower compression to have the possibility to run more boost.
Gruß
Volker
And what would be the point of that? It's a compression ignition engine. Lower the CR and it might not start.
RE: Lowering compression ratio with special 'glow' plugs? - Duncansport - 12-08-2015
This thread.......
High performance diesels lower the CR all the time to improve durability of the engine.
RE: Lowering compression ratio with special 'glow' plugs? - MFSuper90 - 12-08-2015
(12-08-2015, 07:46 PM)Duncansport This thread.......
High performance diesels lower the CR all the time to improve durability of the engine.
But, most are not daily driven, or even street legal for that matter. If your into a build deep enough to lower compression, most engine at that point are running 70psi(5bar) and above boost pressures and need lower CR to cope with outrageous boost.
We are still talking about a 617
RE: Lowering compression ratio with special 'glow' plugs? - NZScott - 12-08-2015
Yes, I've heard of a 245hp OM616 with 18:1 compression, and it probably had NA rods, so thinking I should be good for 150+ region provided my rods stay together and pistons don't melt -I was trying to go "high" boost with this engine to keep as lean as practical, barrote built my pump to 160cc but can dial back to 100/120. Probably still need a block under the juice pedal!
Thanks for the calcs Petar, was wondering how the hell I could work the volume out. Figured I could dip the end of the GP in water to get that volume
Guess I can try this anyway. If the engine won't start or is too difficult to start then I'll just swap back to the normal setup.
RE: Lowering compression ratio with special 'glow' plugs? - Petar - 12-09-2015
You should be more conservative with the fueling
I would go with 70-75cc max. A bolt limiting throttle travel on the pump or a bolt on the stop lever will take care of that.
RE: Lowering compression ratio with special 'glow' plugs? - barrote - 12-09-2015
the 617 engine holds pretty well the 100cc out of a 7.5mm element pump, with minimal smoke.
the rods wont bend unless the engine is abused, i mean using a Holset 40 crap in the 6k power band, with the full output 160cc. apart from that is kind of safe.... beware that the N/A 617 has a lot of diferences in the head assy, it might boil coolant , at least is everybodys problems is heating dissipation....
get us posted with results
BTW without 3BAR absolute pressure 140cc in that engine will resemble a IIWW tank making a curtain of defense.
RE: Lowering compression ratio with special 'glow' plugs? - NZScott - 04-17-2016
I keep thinking about this through my head. I don't have a lathe nor access to one at the moment, so this idea may never leave paper with me for while.
Some maths for anyone who cares
2998cc /5 = 599.6cc
599.6cc /21 = 28.5cc (for 617.912, 617A was 21.5)
599.6cc /19.5= 30.7cc (the 1978 230hp C111-IIID record car had this ratio supposedly)
599.6cc /18= 33.3cc (18:1 being a random figure to aim for not chosen for any particular reason)
So to go from 21:1 to 18:1 is a 4.8cc increase.
The loop GP has a volume of about 1.4cc and pencil one about 0.85cc.
So if I bought 5x M18x1.5 bolts and drilled a 12mm hole about 30mm long it would do the trick but...
Big thing is whether to try keep the glow plugs (maybe go for the smallest glow plugs available - maybe from a Kubota etc) and calculate volumes for that or abandon having glow plugs and try a different means of starting. Don't really want a intake grid heater, a thermostart plug looks interesting though.
It would be interesting to find out how this extra prechamber space affects the charge air swirl, combustion etc. Also reduction in compression ratio usually has a decrease in power/torque off boost.
RE: Lowering compression ratio with special 'glow' plugs? - [486] - 04-17-2016
Reduce your timing (more like set your timing up on the dyno rather than trying to bump it in by the seat of your pants) and you'll probably be just fine. Guys run way the hell too much timing to compensate for a tiny injection pump's long duration and then wonder why their engine lets go.
If you're dead set on the GP thing, metered ether starting has been a thing for a long time. It's set up to put in just a tiny amount while cranking and therefore doesn't damage the engine like dumping half a can in the intake and then cranking it. Could do the same thing the low-buck way with a propane plumbing torch in the cupholder, hook it up to your boost gauge line, start cranking and then open the valve.
RE: Lowering compression ratio with special 'glow' plugs? - NZScott - 04-18-2016
Yea, I plan on having a visit to the dyno sooner rather than later. I would hope my timing wouldn't be too far ahead...
Lol I actually thought about that. I wouldn't be a big fan of ether due to cost, but damn good idea about the LPG
RE: Lowering compression ratio with special 'glow' plugs? - NZScott - 08-14-2016
This idea just isn't going away...did a whole heap of calculations using the smallest GP I could find, Bosch # 0250201032
Looks like I can get down to at least 18.8:1...interference with oil filter on #5 being an issue but can always chop the glow plug terminal off and just start on the other 4.
Seems like a lot of effort for little gain I know, however being able to use common glow plugs makes it worthwhile, likes of what this guy did
http://www.peachparts.com/shopforum/diesel-discussion/282022-glow-plug-adapter.html
RE: Lowering compression ratio with special 'glow' plugs? - barrote - 08-14-2016
why do u want to lower compression ratio on a diesel like 617 engine?
People in the gasoline tunning do that cause, to beguin with the gas engine is has a lot lower comp ratio like something between 12 and 9 in some cases. When they turbo the engines the chamber pressure easily achieve the detonation conditions, (press and temp) so in order to increase AFM they have to do something: higher octane fuel, running extreme rich , decrease compression ratio, inject water or alchool , basically any solution that lower´s chamber pressure and temp.
well in a diesel , unless u intend to run stupidilly high intake press, u dont need to worry with compression ratio being 20/1.
but its up to u...
RE: Lowering compression ratio with special 'glow' plugs? - NZScott - 08-14-2016
Just trying to preserve my engine a bit longer
Reduce peak pressures.If my clutch holds up to it (which I'm not too hopeful on) it would be nice to have 180hp+from the old girl, which normally would stress the hell out of it.
Would prefer to keep the boost high (2 bar) and EGT low rather than vice versa.
And with this adaptor, I can chop the end off bit by bit to raise the CR back up again if need be, if the engine runs like crap with low compression then that will probably end up happening
RE: Lowering compression ratio with special 'glow' plugs? - barrote - 08-15-2016
U dont need to worry about that , that engine will hold 2.5 bar and 700ºc continuous operation, if the coolant is in the 90ºC region and oil temp at 80ºC. that is good for 300+ HP. Beware the pump u have can do that!!!
Anyway as said before, is up to u...
BTW , removing the glow plug, will increase the chamber by 5% wich i dont think is a great impact in the Comp ratio.
PS be ware with playing in the glow plug holes, if they happen to leak the plug may be fired through the hood!!! i heard about that!!!
RE: Lowering compression ratio with special 'glow' plugs? - NZScott - 08-16-2016
Oh well, lets see if my clutch holds
Certainly makes a racket with a GP taken out lol