L18 Long rod or L20b motor?

[datsun4dsc]

Will a L18 Long rod perform as good as a standard built L20b?

Trying to decide which route to take given that I already have both L16 and L18 components to build a L18 long rod less the pistons.

 

 

 

Long rod L18

flattop Z20S pistons and peanut chamber head for 9.7:1 CR, better rod/stroke ratio for higher RPM.

Parts: L18 crank, L18 block, L16 rods, Z20S pistons

s/2+r+p: 207.66mm

piston deck height: -0.29 (below deck)

[datzenmike]

I would think it would run like an L18 with 10 to 1 compression. I doubt that would beat an L20B BUT.........

 

IF a big valve, ported head with hairy cam with multi carbs were on it, it would be just right for 7,500 RPM screamer.

[Dudeman]

I have been dreaming of a long rod l18 for some time now, and when I do finally get the money (who knows when that'll be tho) it's what I'm going to build. I have done a fair bit of looking, however, and haven't been able to locate much in the way of Z20S pistons, most piston manufacturers dont even list the motor. I think they were only in 80-81 510's domestically, and some early 720's elsewhere. It would be a good idea to make sure you know where to find pistons, as a custom made set could be like 500 bucks:eek: Also if anyone knows where to find a set I would be interested to know, as rods and pistons are all i need to start a build

[pl521sss]

I want to build one myself

Z20s pistons are not readily available.

Yup, custom pistons are at least $400

 

Secondly, there's conflicting information whether to use Z20s flat top pistons.

But if you do more research on Z20s pistons, it appears that they are dished.

So the build suppose to be using a flat piston to attain 9.7:1 CR

Have not build one myself so can't say for sure how it should work.

[DISLEXICDIME]

I would think it would run like an L18 with 10 to 1 compression. I doubt that would beat an L20B BUT.........

 

my l18 will smoke most l20b's:p

 

IF a big valve, ported head with hairy cam with multi carbs were on it, it would be just right for 7,500 RPM screamer.

 

my l18 is built like you just described and it is a 8000 rpm screamer;)

 

if i was going to build a long rod engine i would build a long rod 2.1

[jonesy510]

the l18 described is the one i just dropped in my goon

 

i have a set of some su's that im plannin on puttin on it too and i cant wait to drive it :)

[imtb]

jonesy510,

 

lets us know how it runs, I have a L18 in my goon and trying to decide if I want to rebuild or step up to 2.3l.

[pl521sss]

the l18 described is the one i just dropped in my goon

 

i have a set of some su's that im plannin on puttin on it too and i cant wait to drive it :)

 

Yeah, let us know how it runs

I asked that question on Bluebird list and Jason stated that might not be worthwhile if the pistons are dished. Your the only one so far that I know having this setup. Hope it works well

[datzenmike]

.....

Secondly, there's conflicting information whether to use Z20s flat top pistons.

But if you do more research on Z20s pistons, it appears that they are dished.

So the build suppose to be using a flat piston to attain 9.7:1 CR

Have not build one myself so can't say for sure how it should work.

 

Here's the only picture I have of a Z20S piston. It has a 35.5mm piston pin height and a 9.32cc dish. There were flat top Z20S pistons?

 

These pistons give 8.52 compression with pea nut head.

Edited October 12, 2009 by datzenmike

[ggzilla]

Long rod L18 will be more efficient. L20B will have more torque and HP than a the long-rod L18

 

What do you want? Technical formula perfection, or more performance?

[datsun4dsc]

Long rod L18 will be more efficient. L20B will have more torque and HP than a the long-rod L18

 

What do you want? Technical formula perfection, or more performance?

 

Need the build formula to be correct.

Otherwise, will be stuck in the middle of the build cause pistons won't work or not ideal. Nice to have a good L18 for around town with little bit more power.

Coupled with a A87 head and twin SU's

[DISLEXICDIME]

build the bottom end to hold together then port the head and put 44mm z car intake valvs with 35mm exhaust valves and decent cam and comp valve springs

 

but bye the time you pay for all this you could put a ka in your car

[datsunaholic]

Every Z20S I've taken apart had essentially flat pistons with 4 valve recesses that act as a tiny dish. I'm not sure I've ever seen a dished Z20 piston, at least a dish like what you see in a L20B. I've seen dished Z22 and Z24 pistons though.

 

But- one thing to note is every Z20S I've taken apart was rebuilt at some point, usually with a slight overbore. Dunno why that is, as every L-series I've taken apart had original pistons.

[DISLEXICDIME]

napa sells replace meant z20pistons but they are dished.

If you want to see what a slightly built l18 feels like i can take you for a ride i am in tigard .

 

but if you are planning to build an engine that can really rev. you will have to figure out A distributor. once you start going over 8500 you start sheering the oil pump drive. you might be able to find one of the old brass oil pump drives in the comp catalog. This is the issue i am dealing with. so i only rev short blips to 8000 rpm.s. i was thinking of trying mega jolt and getting rid of the distributor but i have herd that edis brakes up after 7000 rpm's

[Dudeman]

So the Jason Grey data gives a stock L18 piston pin height of 38.1 mm, and the Z20S is 35.56 mm, giving a 2.54mm difference. If it is too difficult to find flattop pistons (want a higher CR than 8.52) with an 85mm bore and 35.56 pin height, could one machine a couple mm off of a stock piston to make the pin height correct for use with L16 rods, or would it weaken the piston too much? Might have to get a set of pistons custom made to do that particular long rod motor...

Edited October 12, 2009 by Dudeman

[jovial_cynic]

if i was going to build a long rod engine i would build a long rod 2.1

 

FYI, if you do build the long-rod 2.1 (which was my original plan), make sure you get the the short z22e pistons. I had everything assembled and realized that I had the tall pistons on the rods, and as I hand-cranked the engine to set it up, the pistons were rising a full 3.4mm above deck. I'm not sure that I'd be comfortable milling the pistons down that much...

 

I ended up using the z22e rods that came with my z22e engine, leaving me with .45mm above deck, and I milled the pistons down another .2mm to keep it safe.

[pl521sss]

So the Jason Grey data gives a stock L18 piston pin height of 38.1 mm, and the Z20S is 35.56 mm, giving a 2.54mm difference. If it is too difficult to find flattop pistons (want a higher CR than 8.52) with an 85mm bore and 35.56 pin height, could one machine a couple mm off of a stock piston to make the pin height correct for use with L16 rods, or would it weaken the piston too much? Might have to get a set of pistons custom made to do that particular long rod motor...

 

You could use a L20b pistons and shaved it down.

But there's a concern

That moves the top ring higher by about 3/32'' which will subject the rings to more heat or damage from detonation.

 

[datzenmike]

RE:

Here's the only picture I have of a Z20S piston. It has a 35.5mm piston pin height and a 9.32cc dish. There were flat top Z20S pistons?

 

These pistons give 8.52 compression with pea nut head.

 

Should have this picture with it:http://i138.photobucket.com/albums/q251/datzenmike/L%20Z%20Heads%20and%20Motors/motorZ20EandZ20S720pistons3-1.jpg[/img]"]

 

For reference, this is a Z20E piston below, 31.75mm piston pin and maybe 2cc of valve relief:

 

http://i138.photobucket.com/albums/q251/datzenmike/L%20Z%20Heads%20and%20Motors/motorZ20EandZ20S720pistons4-1.jpg[/img]"]

 

 

Now if you think about it, these two pistons in the same motor will produce a widely different compression as there is 9cc of dish in one of them and the flat top is from the 200sx which I know is about 8.5 to 1. Which led me on a 2 year search for a mystery Z20/22 head with smaller combustion chamber. If the flattop piston was found in a Z20S then it had the same head as the '80-'81 200sx. If you have a Z20S with the dished piston then you have one of my mystery heads, which I did eventually discover.

Edited October 12, 2009 by datzenmike

[datsunaholic]

The bottom pic is like what was in my '81 510:

 

[datzenmike]

Hmmm the intake side reliefs look deeper on your pistons Doug. Didn't measure the pin height did you?

 

Perhaps there are a third Z20 piston. A flattop and a 9.32 dish, both with 35.5mm pin height for the Z20S?

Edited October 12, 2009 by datzenmike

[DISLEXICDIME]

The bottom pic is like what was in my '81 510:

 

 

i have seen those pistons in a l20b. some one put them in there ! it was a screamer.

[datsunaholic]

I think that's just the grime buildup in the recesses. That one piston was really clean because it had gotten steam cleaned with ethlyne glycol mix. I couldn't measure pin height or anything since I just replaced the head (the engine was just fine except for the banana-shaped cylinder head). All I know is that engine ran really good, right up to the point that I got punted into a freeway divider. Still have the engine.

[Dudeman]

Perhaps there are a third Z20 piston. A flattop and a 9.32 dish, both with 35.5mm pin height for the Z20S?

 

Seems like a flattop with a 35.5 mm pin height would be the only way to build a long rod motor with a decent compression ratio. That motor with a little more cam and dual weber 40's would be the way to go

 

Makes me tingle just thinking about it :lol::lol::lol:

[datzenmike]

Way past tingle all the way to wet!

[ggzilla]

Will a L18 Long rod perform as good as a standard built L20b?

No, a 1.8 liter long-rod L18 motor will not have as much power as a 2.0 liter L20B. Assuming you use the same head, induction, exhaust etc.

 

Or do you mean L18 long-rod bored and stroked to 2 liters? That might be better than an L20B with standard length rods. Perhaps you will gain 3%. I saw a study by Smoky Yunick who got 3% more horsepower (from same displacement) by changing a SBC V8 rod-to-stroke ratio.