engine gurus 2.3L big bore, need help, math isnt checking out... maybe

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gumby510
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engine gurus 2.3L big bore, need help, math isnt checking out... maybe

Post by gumby510 » 08 Jul 2019 19:40

Hello everyone,

I feel kind of dumb asking another question so soon. Im in the process of building a big bore 2.3L.

Big Bore 2.3L
KA24 pistons into a bored Z20/Z22/L20B block. The small 2.8cc dish area of the KA24 pistons helps to preserve compression ratio even with the low piston deck height. Compression ratio with a open chambered U67 head is 9.9:1 or use dished Z24 pistons and peanut chambered head for 8.9:1 compression ratio.
Parts: Z22 crank, KA24 pistons, Z22S/ L20B rods in a +2mm bored Z22 block or +4mm Z20/L20B block.
s/2+r+p= 92/2+145.9+34.0= 225.9 mm
piston deck height: -1.55mm below deck



Here is are my questions. with the KA24 piston I believe a KA24E piston was used for the math. in the 240sx world if you want to bump up the compression of your ka24de you put ka24e pistons. when you look at ka24 aftermarket forged pistons they will have 2 cr listed. ka24de 9:1 ka24e 8:1.

I purchased a z22s engine so I can use the block crank and rods. I want to use this with my A87 peanut head (currently on my l18).

so my math puts using a ka24de piston 9:1cr 22cc dish gives a 8:1cr. with a ka24de 10.5cr piston with a 9cc dish giving a 9.3cr.

These numbers are based on a z24 headgasket assuming its 1.5mm compressed. I dont know if this is right ill probably end up buying the nismo L series big bore headgasket.

1. If anyone can confirm what ka24 piston was used

2. what the compressed z24 headgasket measures at (im looking at the apex headgaset on rockauto, it states that it is mls I dont know if thats correct)

3. if my math checks out.

I dont want to end up ordering the wrong pistons and end up with a compression ratio that is "unusable"

Thank you in advance

Gumby
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datzenmike
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Re: engine gurus 2.3L big bore, need help, math isnt checking out... maybe

Post by datzenmike » 09 Jul 2019 06:09

KA24E pistons. I have an on going project (never finished) using them. S13 car pistons are 'floating' pin while truck KA-E are press on. A carefully honed out the Z22/L20B rod small ends to allow '89 240sx pistons to 'float'.

The first 3 ? months production of the KA24E in the 240sx were domed pistons and 9 to 1 compression. Unlikely you will come across these. The rest of the KA24E in the car or truck were 2.8cc dished pistons. These are '89 2.8cc dished pistons. After market ??? Who knows what they will be. Even the makers don't advertise proper numbers.
Image

I use 1.2mm compressed gasket thickness in my calculations. It's not going to make that much difference which you use. KA and Z24 are both 89mm cylinder diameter. The coolant flow through a Z 'cross flow' head will not be exactly the same as for an L head which has both manifolds on the same side. Lay the old L series gasket on top of the Z series and compare the openings.

A Z22 or L20B block bored to 89mm with stock 2.8 cc dished KA24E pistons, with Z22 or L20B rods on a Z22 crankshaft will have a 9.84 compression with an open chamber L head and 10.48 used with a closed chamber (p-nut) head.
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gumby510
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Re: engine gurus 2.3L big bore, need help, math isnt checking out... maybe

Post by gumby510 » 10 Jul 2019 09:28

So if I believe arias, for their ka24e 8.7cr piston they state 9cc dish. So with the nismo headgasket 1.5mm compressed and using 40.5cc for my a87 pnut chamber volume my cr should be 9.34cr

I also have a z20e engine in my garage, So hear me out on this. For the people that have run LZ setups.

If you were to choose which would you go with between the big bore 2.3L and the 2.1L long rod with 89mm pistons. Custom forged pistons used for both setups, rods will have arp fasteners.

What kind of hp and tq difference would there be will all specs being the same (cam, head, compression, intake and ex)

With the 2.1L I like the idea of a fully counter weighted crankshaft. With the 2.3L I like the idea of more low to midrange tq.

Cc difference between the 2 motors is approx 145cc (2.1L=2138 and 2.3L=2283)

This is a 95% street car (I have other cars for track duty)
Looking to have a 7k redline
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Re: engine gurus 2.3L big bore, need help, math isnt checking out... maybe

Post by datzenmike » 11 Jul 2019 06:36

I get 9.5 .... Closed chamber heads are 41cc unless milled down.

Z22 crank and 89mm bore is both longer stroke and larger displacement which equals torque. The 2.1 can and will need to rev higher to make it's power.

Red line is the limit below which an engine can reliably and safely rev all day. Above this, metal begins to stretch from the insane g forces and bolts fail. The red line on a Z22's 92mm stroke is 6,500. Special rods and fasteners might get you to 7K but it's a stretch. (pun intended) If you are arbitrarily picking an upper limit on the red line then select an engine with a stroke of 86mm.... or less.
Last edited by datzenmike on 11 Jul 2019 18:10, edited 1 time in total.
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Re: engine gurus 2.3L big bore, need help, math isnt checking out... maybe

Post by Chadsinto510s » 11 Jul 2019 15:15

I run the 2.1L long rod in my street wagon. It's pretty fun. Z22 block bored for Z24 pistons (89mm), Z20(E?)(S?) conrods (whichever one is longer, I can't remember anymore), L20B crank.

The head is a U67 only slightly shaved with a 490/290 cam, mild port and bowl work and oversized stainless valves. Z car SU's for induction. Fun all around street car that surprises people. Not entirely sure what compression ratio is. I do have to run 91 octane year round though.

I have pics but can't get them to attach. Not sure why yet...

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Re: engine gurus 2.3L big bore, need help, math isnt checking out... maybe

Post by gumby510 » 11 Jul 2019 16:51

So if im deem the 7k redline important enough and im having custom pistons made anyway. Would this be a good compromise between the 2.

Z22 block bored to 89-90mm (90mm would make it a 2.2L)
Z20e rods with arp hardware
Z20e crankshaft
89-90mm Custom pistons with a 9cc dish for a 10:1cr

Ill be running 91-93 non eth gas

With the 2.3 having a max 6k redline with my z trans and rearend gearing wouldnt be a great match.

So it would be an over square vs under square set up.

I know there are tons of variables to play into this but for tq numbers can someone ball park the difference between a long rod 2.1L vs big bore 2.3L.

Sorry if it seems like im all over the place. I just want to sort this out so I can order pistons and start building.
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Re: engine gurus 2.3L big bore, need help, math isnt checking out... maybe

Post by datzenmike » 11 Jul 2019 18:31

Chadsinto510s wrote:
11 Jul 2019 15:15
I run the 2.1L long rod in my street wagon. It's pretty fun. Z22 block bored for Z24 pistons (89mm), Z20(E?)(S?) conrods (whichever one is longer, I can't remember anymore), L20B crank.

The head is a U67 only slightly shaved with a 490/290 cam, mild port and bowl work and oversized stainless valves. Z car SU's for induction. Fun all around street car that surprises people. Not entirely sure what compression ratio is. I do have to run 91 octane year round though.

I have pics but can't get them to attach. Not sure why yet...
The deck height on an L20B/Z20 or Z22 is 227.45mm. Your 1/2 stroke + rod length + piston pin height muse equal this number or less or the piston will extend above the block. You have about 1.2mm of crushed gasket which will elevate the head above the block this amount. Your numbers provided total 229.5mm or 1.95mm above the deck. You can go about 0.33mm above the deck safely. How did you get the piston 1.95mm above the deck and not hit the head???
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Re: engine gurus 2.3L big bore, need help, math isnt checking out... maybe

Post by datzenmike » 11 Jul 2019 18:48

gumby510 wrote:
11 Jul 2019 16:51
So if im deem the 7k redline important enough and im having custom pistons made anyway. Would this be a good compromise between the 2.

Z22 block bored to 89-90mm (90mm would make it a 2.2L)
Z20e rods with arp hardware
Z20e crankshaft
89-90mm Custom pistons with a 9cc dish for a 10:1cr

Ill be running 91-93 non eth gas

With the 2.3 having a max 6k redline with my z trans and rearend gearing wouldnt be a great match.

So it would be an over square vs under square set up.

I know there are tons of variables to play into this but for tq numbers can someone ball park the difference between a long rod 2.1L vs big bore 2.3L.

Sorry if it seems like im all over the place. I just want to sort this out so I can order pistons and start building.
An 89mm bored Z22 block, with L20B/Z20 crank shaft, 45.2cc open chamber head, 152.5mm Z20 rods will need a custom 9cc dish piston with a pin height of 31.95mm to have a zero deck height (you could go 0.3mm taller reasonably safely and any amount shorter to lower the compression. I calculated the compression at 9.91 with the zero deck height and an engine size of 2,138cc. B&S 89mm X 86mm


Option 2
Buy four 1mm oversize VG30 pistons and bore to 88mm. With 152.5mm Z20 rods and L20B/Z20 crank the compression is 10.555 and the displacement 2,091cc. Pistons and ring sets are reasonable and cheaper than custom made pistons. You can always open up the 45.2cc combustion chambers around the valves to unshroud them and drop the compression. B&S 88mm X 86mm

Larger bore than stroke is an over square engine. I wouldn't read too much into over or under square engine.
Last edited by datzenmike on 11 Jul 2019 18:56, edited 1 time in total.
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Re: engine gurus 2.3L big bore, need help, math isnt checking out... maybe

Post by gumby510 » 11 Jul 2019 19:21

datzenmike wrote:
11 Jul 2019 18:48

An 89mm bored Z22 block, with L20B/Z20 crank shaft, 45.2cc open chamber head, 152.5mm Z20 rods will need a custom 9cc dish piston with a pin height of 31.95mm to have a zero deck height (you could go 0.3mm taller reasonably safely and any amount shorter to lower the compression. I calculated the compression at 9.91 with the zero deck height and an engine size of 2,138cc. B&S 89mm X 86mm.

For this option if I were to use my a87 closed chamber head. To compensate for the increase in comp, would it be more beneficial to go from 9 to 12cc dish or move the pin height to 32.55mm and 5cc dish? (If thats right)

Lastly is boring a z22 out to 90mm a good option to gain another 50cc in displacement, or is there minimal gain from that?

Thanks again for responding to my questions
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Re: engine gurus 2.3L big bore, need help, math isnt checking out... maybe

Post by datzenmike » 12 Jul 2019 06:11

Going to a smaller closed chamber head will raise the compression.

The 31.95mm pin height brings the piston up and even to the top of the block. Going up to 32.55mm will push the piston even higher and hit the underside of the head. A shorter pin height will lower the compression.

A larger dish will lower the compression.

Boring an 87mm cylinder to 89mm is ok. The difference between an 89mm and a 90mm bore is just 12cc or 3cc per cylinder. Going more and boring through the cylinder wall isn't worth the risk.
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Re: engine gurus 2.3L big bore, need help, math isnt checking out... maybe

Post by gumby510 » 12 Jul 2019 06:48

Alright, keep it 89mm bore it is. So keep the 31.95mm pin height (center of pin to the top of the piston correct)
And a 9cc dish.

The calculator im using gives me this
Bore. 89mm
Stroke. 86mm
Head volume. 41cc
Dish/dome cc. 9cc
Deck clearance. 0mm
Compressed hg. 1.5mm

Gives me 10:1cr and 2139cc

Lastly can I bore out my z20 to 89mm and still be safe (are z22 just a bored out z20?). If I can that saves me from cracking open my z22 and save that maybe for another future build.

Thanks again
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Re: engine gurus 2.3L big bore, need help, math isnt checking out... maybe

Post by datzenmike » 12 Jul 2019 19:38

I get 10.01 with a 1.5mm compressed gasket. Stock gaskets are closer to 1.2mm which would be 10.3. I use a hand held calculator, pen and paper. After a while you get a 'feel' for small changes.
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Re: engine gurus 2.3L big bore, need help, math isnt checking out... maybe

Post by Chadsinto510s » 15 Jul 2019 16:29

datzenmike wrote:
11 Jul 2019 18:31

The deck height on an L20B/Z20 or Z22 is 227.45mm. Your 1/2 stroke + rod length + piston pin height muse equal this number or less or the piston will extend above the block. You have about 1.2mm of crushed gasket which will elevate the head above the block this amount. Your numbers provided total 229.5mm or 1.95mm above the deck. You can go about 0.33mm above the deck safely. How did you get the piston 1.95mm above the deck and not hit the head???
Shaved the pistons a bit:
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Re: engine gurus 2.3L big bore, need help, math isnt checking out... maybe

Post by datzenmike » 15 Jul 2019 17:23

Of course, that will work also.
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