Sharing Is Therapy, Right?

[ITSA510]

Here

[Rusty]

most people just say... "hi I'm new... this is my ride"

then check the search box for their questions....but.

 

stand by, I'm sure someone will answer your question, if they get through your intro novel;)

welcome to our Forum, there is no other.

[fisch]

I dig your story itsa510! Nice introduction. Great you are getting back into the Dat maddness.

 

Which I could help you out with your question, but I am more of a design junky than actually knowing what makes these things move! The fact that you've pulled apart a motor puts you way ahead of what I know!

 

But you are in the right place indeed!

[]2eDeYe]

You should be able to measure the pistons and compare them to the stock dimensions. I 'think' the stock sizes are in the haynes manual but I could be wrong.

 

I'm sure 'holic or datzenmike will pipe up shortly with their wealth of knowledge :P

[kiznook]

This should help. Read here first, then see if you still have any questions

http://forum.ratsun.net/showthread.php?t=1011

I think the BEST way to know what you've got is to measure.

[hang_510]

older, wiser & richer ? id be happy w/ 2/3 :lol:

 

 

if you have the part#'s you can easily look them up

if its the cast markings then, wait for the eggspurts and post pix (esp of the carnage :w00t: )

 

id start w/new

 

;) now you have 6 spares (if you remember to tighten em up! :P )

[datzenmike]

The Z22E was used in the '82 and '83 200sx.

 

All Z22E or Z22S pistons were 87mm bore stock. There were two different heights of pistons with their corresponding rods for this motor. The piston height is measured from the pin centerline to the top of the piston. All Z22S, and the Z22E motors made before 12/81 had the same piston height of 35.5mm and a dish of 9.32cm. After 12/81 the Z22E pistons only, were changed to 32.1mm height. (the Z22S stayed the same) This means that all Z22S, and the pre 12/81 Z22E rods, were 145.9mm. (the same as the L20B) But all rods for the post 12/81 Z22E had to be 149.5mm to match the shorter piston pin height.

 

Pre 21/81 piston + rod.... 35.5mm + 145.9mm = 181.4mm for all Z22S, early Z22E piston rod combos.

 

post 12/81 piston + rod.. 32.1mm + 149.5mm = 181.6mm for all late Z22E piston rod combos.

[pope_face]

Hey Mike, the engine would still run if you used two of the old style and two of the new style piston/rod combos, correct? I'd be curious to see how well that would pan out...

[ITSA510]

most people just say... "hi I'm new... this is my ride"

then check the search box for their questions....but.

 

stand by, I'm sure someone will answer your question, if they get through your intro novel;)

welcome to our Forum, there is no other.

 

I am not one for testing the water...I prefer to just jump in. I did spend quite a bit of time looking for answers before I posted but did not come up with any. As for my ride, it is in pieces so I am not overly proud of it right now but give me a few months!!!

[ITSA510]

Thanks Kiznook & DatsunMike. I will get out the yardstick and go to work.

[Rusty]

NICE PLATE!:thumbup:

[datzenmike]

Hey Mike, the engine would still run if you used two of the old style and two of the new style piston/rod combos, correct? I'd be curious to see how well that would pan out...

 

Yes.

 

Two of the cylinders would make power and torque at slightly different RPMs than the other two. Weird idea. Changing the rod length will change the position where the piston reaches it's maximum speed going up or down the bore. You would think that the piston is moving fastest at the halfway point... but you would be wrong. Its point of maximum speed is when the crank throw and the rod are at 90 degrees. (we'll leave piston pin offset out of this) To have maximum speed at 90 degrees, the rod would have to be infinitely long (and the throw infinitely short). As the rod shortens the crank throw will have to turn upward past 270 degrees on the compression or exhaust stroke, or before 90 degrees on the intake or power stroke, in order to keep a right angle. So a longer rod will move the maximum piston speed further from either side of TDC.

 

From the point of max piston speed on the up stroke, the piston is decelerating until it stops at TDC then begins to accelerate on the down stroke until max piston speed. Now think of two ramps the same height but both ending at the same spot and one closer than the other. The closer one will be steeper and faster than at any corresponding point on the less steep one. This means that the two pistons will be moving at different speeds when the cam opens the intake at 16 degrees BTDC and closes the exhaust at 14 degrees ATDC. (L20B)

 

Short rod the good:

A short rod spends less time at TDC than a longer rod and is moving faster before and after TDC and this:

Provides very good intake and exhaust velocities at low to moderate engine speeds causing the engine to produce good low end torque, mostly due to the higher vacuum at the beginning of the intake cycle. The faster piston movement away from TDC of the intake stroke provides more displacement under the valve at every point of crank rotation, increasing vacuum. High intake velocities also create a more homogeneous air/fuel mixture within the combustion chamber. This will produce greater power output due to this effect.

The increase in piston speed away from TDC on the power stroke causes the chamber volume to increase more rapidly than in a long-rod motor - this delays the point of maximum cylinder pressure for best effect with supercharger or turbo boost and/or nitrous oxide.

Cam timing (especially intake valve closing) can be more radical than in a long-rod motor.

 

Long rod the Good

A long rod spends more time at TDC and is moving slower before and after TDC, and this:

Provides longer piston dwell time at & near TDC, which maintains a longer state of compression by keeping the chamber volume small. This has obvious benefits: better combustion, higher cylinder pressure after the first few degrees of rotation past TDC, and higher temperatures within the combustion chamber. This type of rod will produce very good mid to upper RPM torque.

The longer rod will reduce friction within the engine, due to the reduced angle which will place less stress at the thrust surface of the piston during combustion. These rods work well with numerically high gear ratios and lighter vehicles.

For the same total deck height, a longer rod will use a shorter (and therefore lighter) piston, and generally have a safer maximum RPM.

 

 

 

Short rod the bad:

Causes an increase in piston speed away from TDC which, at very high RPMs, will out-run the flame front, causing a decrease in total cylinder pressure at the end of the combustion cycle and a loss of power.

Due to the reduced dwell time of the piston at TDC the piston will descend at a faster rate with a reduction in cylinder pressure and temperature as compared to a long-rod motor. This will reduce total combustion.

 

Long rod the bad:

They do not promote good cylinder filling (volumetric efficiency) at low to moderate engine speeds due to reduced air flow velocity. After the first few degrees beyond TDC piston speed will increase in proportion to crank rotation, but will be biased by the connecting rod length. The piston will descend at a reduced rate and gain its maximum speed at a later point in the crankshaft’s rotation.

Longer rods have greater chance of interference with the cylinder bottom & water jacket area, pan rails and pan - some combinations of stroke length & rod choice are not practical.

[pope_face]

Mike: Very interesting response... I didn't expect to get such a detailed reply, but then again I didn't realize it changed so much. But, say you've got a four-cylinder engine, and you set it up so it has two short rods and two long rods, but all four with the same overall rod/piston length. Assuming they fired alternately (long, short, long, short), would it balance out the torque over all rpms, or would it just reduce the torque overall? What if it were possible to create a "hybrid" camshaft, using lobes from both long and short rod motors? What if this design was applied over more cylinders, say a V8? Would it be like running a good low-end I4 together with a good high-rpm I4, or would it be like running a poorly tuned V8?

 

Sorry for all the hypothetical questions, but I've always been interested on what happens when you modify things or push them past a limit.

[datzenmike]

AFIK the cams are the same for long or short rod motors. There's no way to magically get low end torque AND high end power. Mixing would only blend or compromise everything. You want low RPM torque AND high RPM power design a variable valve timing/ overlap set up for the L series head.