IDI engine, there IS a future...

[rabbit_tdi]

Oh, I forgot to mention earlier there is another reason that I lowered the compression ratio.

Initially, I did run the engine at the stock compression ratio (with high boost and a heavy fueling rate).  After 10-20 hours of hard use I noticed dried coolant at the head gasket joint.  I interpreted this as the peak cylinder pressure being enough to lift the head just enough to let a little coolant out during operation.  There was no leakage during the weeks the engine was not running.

After reducing the compression ratio, and keeping the same boost and fueling rate, I had no more dried coolant at the head gasket joint.  :-)

[Alcaid]

Did you ever answer the question on how you lowered compression while still running 1.6 head?

[carrizog60]

Did you ever answer the question on how you lowered compression while still running 1.6 head?

nope

[CrazyAndy]

Did you ever answer the question on how you lowered compression while still running 1.6 head?

He probably just ran the next notch up head gasket.  His logic on his reason for doing it does seem sound; I would have tried hylomar and head studs, but as long as he didn't have hard starting, smoke at cold idle, or noticeable power loss then he found a way to solve his problem cheaper than the route I'd take, and just as effective.

[R.O.R-2.0]

Did you ever answer the question on how you lowered compression while still running 1.6 head?

He probably just ran the next notch up head gasket.  His logic on his reason for doing it does seem sound; I would have tried hylomar and head studs, but as long as he didn't have hard starting, smoke at cold idle, or noticeable power loss then he found a way to solve his problem cheaper than the route I'd take, and just as effective.

its been proven many times that running the wrong head gasket does not effectively lower the compression while still retaining good power and low smoke at cold idle...

[rabbit_tdi]

According to the manual, the piston protrusion calls for a 2-hole head gasket, which would give a 23:1 compression ratio.  My calculation indicated that a 3-hole gasket would give a 22.4:1 ratio.

Realize that initially I had no idea how low the compression ratio could be, and the engine still be able to start.  So, I did not want to make any expensive changes, and only changes that could easily be undone; this eliminated my considering machining the pistons or the head.  The cheapest thing I could think of was to increase the distance between the head and the block, so I did; the original head gasket was .059", the replacement was/is .110".  My calculation indicates the resulting compression ratio is 17.5:1.  As it happens, the timing belt was just barely able to slide on to the sprockets; it needed very little rotation of the idler to properly tension the belt.

I recommend AGAINST the 17.5:1 compression ratio for use on the street.  This engine of mine is NOT used on the street, and does not need to start below freezing.  When starting it, I keep the timing advance knob pulled out until the engine temperature is up to about 140-160*F or so, in order to smooth the idling and reduce the white smoke.  Also, the engine does have an electric block heater, which I use if the temperature is below about 45*F.  Of course, the glowplugs are necessary.  When the engine is up to operating temperature, it runs nicely and does what I expect.

When I remove this 1.6 TD engine and then put it in a street-use car, I will restore the compression ratio to 23:1, and reduce the fueling rate to something from which I will expect a reasonably long life.  :-)

[gldgti]

My dad has a well used 1.5D is his mk1. He has rebuilt it a couple of times and the pistons have been out on numerous occasions... anyway, basically he's using on it a 4 notch gasket (which is pretty uncommon in the states I believe) but you can get them... anyway its very thick. Not necessarily the correct thickness.

Anyway, he has a lot of trouble starting the car compared to all my VW diesels - and he blows a lot of white smoke when cold (Actually just a lot of the time).

All my engines have the right headgasket :-)

I ran the calcs on rabbit_tdi's numbers and I would agree you compression must be down around 17.2:1. Pretty low for an IDI but not unheard of by any means for a standard engine. There are some older toyota precombusiton chamber diesel that have a 17:1 compression ratio as standard. Those engines go forever but they are not at all powerful and they get poor economy.

With your static compression ratio so low, I think you could afford to advance the timing a lot more than you otherwise might.

[carrizog60]

on the other side how could i increase the compression?
using a 1.5 guts on 1.6 block and 1.9 head.

[RabbitJockey]

on the other side how could i increase the compression?
using a 1.5 guts on 1.6 block and 1.9 head.

Only thing I could really think of is having the precup areas filled and remachined to fit 1.6 cups.  Or just run a 1.6 head that's ported.  Or just do a 1.6 with 1.9 head haha.  I think that small amount of displacement is more valuable than any gained rev ability from 1/8" shorter of a stroke.  How ever the weird factor makes some setups more desirable

[R.O.R-2.0]

on the other side how could i increase the compression?
using a 1.5 guts on 1.6 block and 1.9 head.

Only thing I could really think of is having the precup areas filled and remachined to fit 1.6 cups.  Or just run a 1.6 head that's ported.  Or just do a 1.6 with 1.9 head haha.  I think that small amount of displacement is more valuable than any gained rev ability from 1/8" shorter of a stroke.  How ever the weird factor makes some setups more desirable

why does everyone want to build a 1.5/6/9 now all the sudden?

the 1.6 bottom end is good for whatever RPM we can throw at them..

THERE ARE NO GAINS TO BE HAD WITH A 1.5 ROT. ASSY.

[theman53]

Also as I found with my last engine being a 1 notch but still not in the range it should have been the fuel doesn't burn right. The compression is lowered, but I think the flame travel is elongated and what gave me the EGT issue I had. It compression retards timing, so you throw more to it to mask the problem and then you get hot spots. This is all theory, but my engine grenaded because of precup failure and I have traced it back and guessed/reguessed and this is the best answer I have. What is safe compression ratio??? I don't have a concrete answer, but I think if you had around 19 even you would have the best of both worlds.

[RabbitJockey]

I think the pre cup has to be the right height from the piston for combustion to work properly

[theman53]

I think the pre cup has to be the right height from the piston for combustion to work properly

yes...at least that is what my feeble mind has came up with and I call it flame travel. When it is too far away instead of swirling in the precup and then to the piston and then out the ex. valve. It has room to leave and go to the space between the head and piston. Leading to incomplete portions of the diesel not burning as it isn't compressed or quenched enough. So you advance it to help the problem and you get more of the same just hotter hotspots. Right now it is just my theory and I cannot accurately prove it 100%, but I won't mess around with it ever again theory or not.

[carrizog60]

wanted that combo for werd factor lol
what is the diference in adding the 1.5 equation to the 1.6+1.9 engine?what cause the compression to lower even more?

[libbydiesel]

Compression ratio is swept volume / un-swept volume.  The rotating assembly determines the swept volume.  The shape of the piston crown, the space between piston and head and the shape of the combustion face of the head determine the un-swept volume.  Because there is a considerable volume to the combustion chamber in the head (un-swept volume), changing to a head from a larger displacement engine increases un-swept volume and lowers compression.  Changing the rotating assembly to one from a smaller displacement engine lowers compression as well.  Going to a 1.9 head and a 1.5 rotating assembly will result in the lowest compression using stock IDI parts.  Because in stock form the pistons come darn close to hitting the valves already, your options for increasing compression are limited to decreasing the pre-chamber volume or increasing swept volume (goodbye 1.5 rotating assembly).