Piston puzzle

[frankendat]

In determining the pistons and rings that I should order, some confusion. The goal, to order KA24E pistons for my Z24 in the 1.00mm over (90mm) size. On summit racing site, given my budget, there are two contenders,https://www.summitracing.com/parts/uem-9115-1-0mm/make/nissan  andhttps://www.summitracing.com/parts/uem-9116-1-0mm/make/nissan  aside from cost, what is the difference between the two options?

[datzenmike]

These are for S13 KA24E engines in the 240sx... https://www.summitracing.com/parts/uem-9116-1-0mm/make/nissan 

 

These are for the Truck KA24E engines... https://www.summitracing.com/parts/uem-9116-1-0mm/make/nissan

 

As you will probably press them onto your Z24 rods it doesn't really matter.

 

ONE THING.... check the width of the small end of the rod. I think the KA rods are narrower. The Z24 rods are wider and the KA piston is narrower inside. If insufficient side to side clearance the rod bottom end can't sit over the rod bearing properly.

 

 

I'll go out to the shed and measure them.

 

OK false alarm the KA are wider than the Z so Z24 rods should work on KA pistons.

 

 

[frankendat]

2 hours ago, datzenmike said:

These are for S13 KA24E engines in the 240sx... https://www.summitracing.com/parts/uem-9116-1-0mm/make/nissan 

 

These are for the Truck KA24E engines... https://www.summitracing.com/parts/uem-9116-1-0mm/make/nissan

 

As you will probably press them onto your Z24 rods it doesn't really matter.

 

ONE THING.... check the width of the small end of the rod. I think the KA rods are narrower. The Z24 rods are wider and the KA piston is narrower inside. If insufficient side to side clearance the rod bottom end can't sit over the rod bearing properly.

 

 

I'll go out to the shed and measure them.

 

OK false alarm the KA are wider than the Z so Z24 rods should work on KA pistons.

Thank you for the prompt reply, the two links above are the same link. I was under the impression that the truck pistons are preferred for use in the Z24. Is this correct? And to clarify, the 9116 is the truck piston and 9115 is the piston for the 240sx, right?

 

 

[frankendat]

20 hours ago, datzenmike said:

hese are for S13 KA24E engines in the 240sx... https://www.summitracing.com/parts/uem-9116-1-0mm/make/nissan 

 

These are for the Truck KA24E engines... https://www.summitracing.com/parts/uem-9116-1-0mm/make/nissan

 

As you will probably press them onto your Z24 rods it doesn't really matter.

 

ONE THING.... check the width of the small end of the rod. I think the KA rods are narrower. The Z24 rods are wider and the KA piston is narrower inside. If insufficient side to side clearance the rod bottom end can't sit over the rod bearing properly.

 

 

I'll go out to the shed and measure them.

 

OK false alarm the KA are wider than the Z so Z24 rods should work on KA pistons.

 

Did some more reading and the piston question is sorted. The difference between the two linked pistons, one is press fit and one is free floating (or press fit). Curious the the pistons that include wrist pins are cheaper. Onward and forward.

[datzenmike]

S13 KA24E were floating pin. Truck were press in.

[butter fingers]

hey guys down the road I plan on rebuilding my z24 also . is the big attraction of fitting ka pistons to a z24 for the added compression and slight power increase ? butter fingers

[datzenmike]

Pretty much the compression increases efficiency. They also use newer thinner (less drag) rings. On a stock engine maybe a 5% increase. Hardly worth the bother for 5 hp unless you plan on some head work, carburetor(s) better exhaust system, cam. 

[frankendat]

21 hours ago, butter fingers said:

hey guys down the road I plan on rebuilding my z24 also . is the big attraction of fitting ka pistons to a z24 for the added compression and slight power increase ? butter fingers

 

For me the deciding factor is the KA24E pistons and the Z24 pistons are the same price and I am not planning to run a turbo

[frankendat]

On 7/6/2020 at 4:33 PM, datzenmike said:

Pretty much the compression increases efficiency. They also use newer thinner (less drag) rings. On a stock engine maybe a 5% increase. Hardly worth the bother for 5 hp unless you plan on some head work, carburetor(s) better exhaust system, cam. 

 

Datzunmike and other engine masters, I have a noob question, I was set to purchase the Silvolite cast pistons https://www.summitracing.com/parts/uem-9116-1-0mm/make/nissan when I noticed a potentially cost effective alternative https://www.summitracing.com/parts/uem-3422hc-1-0mm/overview. To save time, I am attaching a word document  with the  two pistons  specifications listed side by side, all differences are in a bigger font and in bold type. There is a $52 dollar difference in cost between the cast piston and the hyper whatsit piston.

Thank you for your time

 

pistons.docx

[Stoffregen Motorsports]

Pin height - you need to figure out which pin height you need before ordering. Pin height is the distance from the top of the piston to the center of the wrist pin. Longer rod engines use shorter pin height.

[datzenmike]

KA24E and Z24 use a compression or pin height of 34mm which brings the piston about 0.45mm below the block deck. You can usually extend about 1/3 mm above the deck safely because there is a 1.2mm thick gasket. So on a stock Z24 crank the maximum possible rod length would be 165.75mm stock are 165mm OR the pin height can be increased to 34.75mm. Better to mill the deck this amount if you want to maximize the compression.

 

BTW Hypereutectic pistons 12-19% silicon and are cast. So what are 'cast pistons' then????  The only other piston is a forged. These are not cast but billet and pressed into shape. They are most definitely NOT hypereutectec but a superior strength aluminum alloy

[frankendat]

1 hour ago, Stoffregen Motorsports said:

Pin height - you need to figure out which pin height you need before ordering. Pin height is the distance from the top of the piston to the center of the wrist pin. Longer rod engines use shorter pin height.

 

44 minutes ago, datzenmike said:

KA24E and Z24 use a compression or pin height of 34mm which brings the piston about 0.45mm below the block deck. You can usually extend about 1/3 mm above the deck safely because there is a 1.2mm thick gasket. So on a stock Z24 crank the maximum possible rod length would be 165.75mm stock are 165mm OR the pin height can be increased to 34.75mm. Better to mill the deck this amount if you want to maximize the compression.

 

BTW Hypereutectic pistons 12-19% silicon and are cast. So what are 'cast pistons' then????  The only other piston is a forged. These are not cast but billet and pressed into shape. They are most definitely NOT hypereutectec but a superior strength aluminum alloy

 

Thank you both for responding.What to add or subtract in the compression height has me confused. As Datzenmike listed, the compression height of the Z24 is 34mm (33.705); the compression height on the mystery pistons is 30mm (29.718). The mystery pistons decrease (shorten) the pin height by 4mm (3.987). Stoffregen Motorsports comment above "Longer rod engines use shorter pin height."  Then is it true, if the mystery pistons were used, to maintain compression, rod length would need to be increased by 4mm (3.987) to169mm (168.987) AND since the maximum rod length for this motor is 165.75, the mystery pistons are not viable.

 

Did I get it?

[datzenmike]

You got it right. The stock Z24 piston being 4mm lower in the cylinder at TDC makes the combustion chamber almost 25cc larger which will drop the compression to 6.57

 

A stock KA24E piston that is 4mm too low will make 7.28

 

The other piston is 33.7mm and still short of 34mm. Also the piston dish is not specified. Largrt dish, lower the compression. The Z24 is 15cc while the KA24E is 2.8cc.

 

These pistons are probably for some other application and just happen to be close.

[Stoffregen Motorsports]

It may be best to go to the manufacturer's website and punch in the part number to get more accurate specs, like piston dish.

 

 

[frankendat]

There is an engine builder out there (deviousKA)who bored his KA block to 91.1 to use Mazda B2600 pistons. All info on the swap was interesting, but the build threads are very old and the email deviousKA is no longer viable. 

Here is a summary of deviousKA's piston plan, written by deviousKA:

the car has been running for a week now, and running strong. i picked up my 90 fastback with 105k for 900 and decided to build up the knocking but clean ka24e. i decided to go with a n/a setup because of my type of driving, price, and just plain coolness. the prices for any kind of custom forged pistons are outrageous from my standpoint. i did a little researching and brainstorming and ordered myself some mazda b2600 91.1 bore 36.1 compression ht. flat top pistons with a 22mm press fit pin (very, very cheap ). obviously the pistons will come above deck ht, the bore is HUGE (especially for ka24e), and the pin is 1mm larger. i view all of those as positives . okay first i tackled the deck ht. problem. the edge of the piston (where compression ht is measured) was machined down to allow relief for the headgasket and combustion chamber. the mazda pistons have much lower ring lands then the ka24e as well as 2 2mm compression rings. once the piston was modified to clear up top i noticed the piston skirt came extremely close to the counterweight on crank. after a little die grinder work and piston weighing was finished it has plenty of clearance. the rods were honed out to 22mm (some of the copper bushing is left in) and the pins were pressed in. After many calculations and double checking my c/r is right where i wanna be 10.5:1. my crank was full of plastic shavings due to a shredded timing chain guide, and due to the factory installed ball plugs impossible to clean. the ball bearings plugs were drilled out and allen plugs installed, nice. during this whole process i had been dreading the fact of having to fly cut my pistons (myself most likely ) to accomidate the tall compression ht. as well as my pdm c.404 cam. well after a little rediscovered fun with some modeling clay, i find out i have over .080" of piston to valve clearance (exhaust valve, intakes clear by a mile) so that really cheers me up. the rest of the engine was rebuilt and had performance grind on the valves, no porting, stock exhaust manifold. i had to buy 3 headgaskets to get the fit that i wanted and finally settled on the ROL. i bought new headbolts and a steel-backed timing chain kit. i put it in last week with some new injectors and super-nice k&n filtercharger system. i hope to get it on the dyno soon with some ecu and fuel tuning. i am mixing my own gas. i have a 90 coupe that was rebuilt recently and i thought it was fast. this engine pulls so hard from 4000-6000rpm is is unbelievable it is ka24e. total cost ~700 including cam, pistons, machine work, and the rest of rebuild kit.

 

Would this option negate the longevity/reliability of the KA?

 

 

 

 

[datzenmike]

Any time you make it work harder you shorten the life. Engine life depends on how hard you drive it also. Tooo late , don't worry about it. Keep the oil full and filter changed and  rad full. Use an oil with high ZDDP level like Shell Rotella T4.

[frankendat]

9 hours ago, datzenmike said:

Any time you make it work harder you shorten the life. Engine life depends on how hard you drive it also. Tooo late , don't worry about it. Keep the oil full and filter changed and  rad full. Use an oil with high ZDDP level like Shell Rotella T4.

 

It wasn't to late when I started this thread, but it's too late now.Piston and rings purchased. $20.12 for a Hypereutectic piston with Hastings rings was a good enough deal to take a chance. I would like to nail down the  compression. The calculators ask for more information than I have. I will keep searching if you do not have the information readily available. The block is Z24, bored to 91.1, the head KA24E.The piston  info: Flat top, 91.1  diameter, Comp. height 1.418.The top edge of this piston will be milled to clear the  head gasket. When the engine is bored, I will have the head and deck blocked. Whether the block should be milled (or how much) is dependent on compression. This engine must be pump gas friendly.

Edited August 4, 2020 by frankendat

[frankendat]

On 8/3/2020 at 12:18 PM, datzenmike said:

Any time you make it work harder you shorten the life. Engine life depends on how hard you drive it also. Tooo late , don't worry about it. Keep the oil full and filter changed and  rad full. Use an oil with high ZDDP level like Shell Rotella T4.

The pistons will not arrive for a couple of weeks and I am just triple checking my data. I am not confident in the compression numbers. The online compression calculators do not inspire trust, but it might be that I am entering the wrong variables. Here is the info that I have (I have not personally confirmed these measurements,but they come from individuals who are experts in this field.)

Block Z24 bored to 91.1mm

Stroke Z24 rods 96mm

Pistons Flat top

Compression height 36.017

Head KA24E

Combustion chamber volume  65cc 

(That cc is taken from an average of three stock KA24E heads. Additionally, there has been professional work on my cylinder head, which might impact volume)

 

What do you get with those numbers for compression? Am I missing important data?

[datzenmike]

Gasket is wrong if there is any chance the piston top needs milling to clear hitting it.  Head gasket must be at least the bore diameter and a little larger is better. If exposed to highly corrosive high temperature gasses, it will erode away. Being tightly clamped between head and block allows it to transfer heat and stay cool. An xposed gasket is also a source of pre ignition.

[frankendat]

Thank you for responding Datzenmike, Do you have a theory that might explain deviousKA's assertion,

"... obviously the pistons will come above deck ht, the bore is HUGE (especially for ka24e), and the pin is 1mm larger. i view all of those as positives . okay first i tackled the deck ht. problem. the edge of the piston (where compression ht is measured) was machined down to allow relief for the headgasket and combustion chamber"?

 

 

[frankendat]

I have been researching compression and am placing some  of the found data here.

Based on the use of a Z24 block overbored to 91.1mm/KA24E head; Flat top pistons (no dome or dish)
Stroke of Z24 96mm
Z24 Connecting Rod length 165mm
Z24 Compression Height 36.1mm
Z24 Deck Height 247.45mm
Z24 Piston Clearance (Stroke/2 = 48mm + Rod length 165mm + compression height 36.1mm = 249.1 – Deck Height 247.45) = 1.65 Above Deck
KA24E Combustion Chamber (Stock) 65cc
Z24 Head gasket .050

Some of the above numbers were taken from stock engine measurements, compression calculator results are 10.8. The original builder/creator of this engine reported compression  at  10.7. It is a bit higher than I would like. I will continue to refine these numbers

[Stoffregen Motorsports]

Even with all the math you've done, nothing beats an actual mock-up. Every custom engine I ever built got a mock-up before assembly. It's the best way to ensure fit and take measurements like deck height, and you can even CC the piston volume with a mock-up.

 

I know, you can't do a mock-up until you bore it, but assuming you go ahead with this combo, once you get it back from the machine shop, stick the crank in it and one rod piston. Take your measurements and determine CR before assembly time.

 

Get yourself an inexpensive burette- https://www.hbarsci.com/products/ch0240g?cmp_id=1997057436&adg_id=76769829288&kwd=&device=c&gclid=EAIaIQobChMIlMTZ-8SO6wIVyyCtBh1yDg-qEAQYBCABEgLgu_D_BwE

 

And make yourself a cc plate for pistons out of deck by bonding a piece of clear tubing to a flat piece of clear plexiglass (you can get both at any plastics shop). Use a flat plate for checking the head volume.

[datzenmike]

You can safely go about 1/3 mm above the deck. The head is a crushed gasket thickness away, about 1.2mm. Speaking of head gasket what are you going to use??? Has to be at least 91.1mm. An 89mm KA or Z24 gasket will not do.