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Engine build ideas, need some help (looooong story)


bajango

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Oooook. I just bought a $500 1980 720 for the L20 and 5spd to swap into my 521. So out with the L16 and 4spd, yay. Anyway I want to build a rev happy engine (7-8k rpm). I really want to build the long rod 2.1 setup BUT I CANT FIND Z20e RODS ANYWHERE! My other ideas are L18 pistons or L28 flat top on a stock rotating assembly. If I ran flat tops I would try to find myself a closed chamber head for the anti-detonation combo properties.

Here is what I would like to do (in preference order)

A-

2.1 long rod

L28et valves

Open head/closed head no preference

Isky l490 and 7005 valve springs

B-

Stock rotating assembly w/ l28 flat tops

L28et valves

Closed head

Isky l490 and 7005 valve springs

C-

Stock rotating assembly w/ l18 pistons

L28et valves

Open/closed head no preference

Isky l490 and 7005 valve springs

 

Here is where I have some questions. I've read that flat top pistons in any head combo has too high of compression for 91oct, but can I use that cam's long duration (290*) to my advantage to lower the cylinder pressure and run 91oct? Also, will unshrouding the valves open the chamber enough to effectively lower the compression ratio? These questions pertain to any combination I have floating in my head. I guess I could run a thicker headgasket too...

 

Also I would love to run some bike carbs. Particularly R1 carbs, however the Weber book recommends 46mm venturis @ 8000 rpm on a 500cc per cylinder engine (L20b). I was gonna throw some 85-87 gsxr 34mm carbs on my rock stock L16 but never got around to doing it before shipping to boot camp... Anywaayyy, would the 40mm R1 carbs be able to handle that setup? I swear I saw another user here use R1 carbs on a mean L20 but now I can't find the thread (or was it a 12v KA?). I thought I might've seen 45mm bike carbs too, but I can only find 45mm bike throttle bodies now.

 

Lastly, is there another cam that I can get the same lift, or a little more lift, and a little less duration? I've read that the isky l490 is streetable, however I did also read that another user had the l480 and said it sucked driving in traffic. It might just be someone's different opinion on what "streetable" means. I'm just a little leery of that much duration, though it may just be an ignorant concern of mine.

 

Any other input is appreciated ☺️

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A 40mm bike carb will out flow a larger Weber or Solex or Delorto due to less garbage hanging in the bore.

 

What are the specifications on the Isky l490 ?

 

If you decide on going the L18 rod idea, I have a set that are yours for the shipping.

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Kidding...with your given options...I would run L18 pistons w/a CC head.

 

Do whatever you want to the head. Add some side drafts and you're good.

 

 

Friend of mine was rocking an L20B with L28 flattops on an open head with cam. Screamer. Little pingy when hot. Maybe 5° of advance to aid in calming it down.

 

 

Motor I will be piecing together over the winter...L18 crank, L16 rods, Z20S flattops in an L16/18 block. Closed head, springs, mild cam with SUs. Decent little winder from what I've researched.

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A 40mm bike carb will out flow a larger Weber or Solex or Delorto due to less garbage hanging in the bore.

 

What are the specifications on the Isky l490 ?

 

If you decide on going the L18 rod idea, I have a set that are yours for the shipping.

 

 

Isky cam

.490" lift

290* duration

242* @ .050"

 

I'm not going for l18 rods though, just the pistons.

 

 

Kidding...with your given options...I would run L18 pistons w/a CC head.

Do whatever you want to the head. Add some side drafts and you're good.

Friend of mine was rocking an L20B with L28 flattops on an open head with cam. Screamer. Little pingy when hot. Maybe 5° of advance to aid in calming it down.

Motor I will be piecing together over the winter...L18 crank, L16 rods, Z20S flattops in an L16/18 block. Closed head, springs, mild cam with SUs. Decent little winder from what I've researched.

That's what I wanna do too. I'm trying to snag the Z pistons for the thinner rings for longevity in high RPM. I just want a little displacement too. I might consider a build like yours too though... How much is .2 or .3L gonna really lose me when I'm trying to build a screamer. It's not like I'm gonna have torque anyway...

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No one drives 7-8K. The L20B red lines at 7K, do the math. Piston speeds above or nearing 4000 feet per minute is too close the the structural strength limit of the steel rods and the rod bolts. The rod is accelerating and decelerating 116 times a second and the G forces so high they will stretch, and the bolts fail.

 

 

Use this handy formula... RPM X stroke in inches (86mm = 3.3884") / 6 must = less than 4K.

 

To go higher you need to use stronger lighter materials. Special titanium rods and special bolts.

 

If running stock parts stick to the 7K red line if you want it to stay together. 

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No one drives 7-8K. The L20B red lines at 7K, do the math. Piston speeds above or nearing 4000 feet per minute is too close the the structural strength limit of the steel rods and the rod bolts. The rod is accelerating and decelerating 116 times a second and the G forces so high they will stretch, and the bolts fail.

 

 

Use this handy formula... RPM X stroke in inches (86mm = 3.3884") / 6 must = less than 4K.

 

To go higher you need to use stronger lighter materials. Special titanium rods and special bolts.

 

If running stock parts stick to the 7K red line if you want it to stay together.

 

Thank you datzenmike. I knew you'd save me from blowing stuff up. That's the kind of input I need. I tend to ever look that kind of stuff. So now my question is: why is the long rod 2.1L build considered a high RPM build? Is it only because of the 1.5mm rings on Z pistons vs the 2mm rings in L pistons? Would the Pistons need to be a special material as well?
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Here is some info I found somewhere years back:

 

Pin heights:
Nissan:
L16/18/20b --------------- 38.1mm
LZ20S ---------------------- 35.56mm
LZ22S ---------------------- 35mm
LS22E ---------------------- 32.5mm
FJ20  ------------------------ 32.5mm
SR20  ----------------------- 32mm
VG30 ------------------------ 31.88mm  (87mm bore)
LZ20E ----------------------- 31.75mm
RB26 ------------------------ 30.3mm
CA18------------------------- 30.0mm
ROSS custom pistons - 31.4mm (L14 rods in L18 )
JE  88mm pistons ------- 29.15 - 2mm dish
 
Honda:
B series -------------------- 30mm
FT500 cycle---------------- 29mm Honda p/n PT# 13101-MA0-000 (LD rods in L18)
 
Rods:
L18, L28, L26--------------------130.2mm
L16, L20, L24-------------------133.0mm
L14 ---------------------------------136.7mm
L13----------------------------------139.9mm
LD28--------------------------------140.0mm (oversize wrist pin)
L20B, Z22S, early Z22E-----145.9mm*
Late Z22E-------------------------149.5mm*
Z20E--------------------------------152.5mm
Z24, KA24------------------------165.0mm*
CA18-------------------------------133.0mm
FJ20--------------------------------140.0mm
 
Block heights:
Block deck height, (crank centerline to top of deck)
L13, L16, L18, L24, L28: 207.85mm
L20B, Z20, Z22, L28diesel: 227.45mm
Z24, KA24: 247.45mm
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Here is some info I found somewhere years back:

 

Pin heights:

Nissan:

L16/18/20b --------------- 38.1mm

LZ20S ---------------------- 35.56mm

LZ22S ---------------------- 35mm

LS22E ---------------------- 32.5mm

FJ20 ------------------------ 32.5mm

SR20 ----------------------- 32mm

VG30 ------------------------ 31.88mm (87mm bore)

LZ20E ----------------------- 31.75mm

RB26 ------------------------ 30.3mm

CA18------------------------- 30.0mm

ROSS custom pistons - 31.4mm (L14 rods in L18 )

JE 88mm pistons ------- 29.15 - 2mm dish

 

Honda:

B series -------------------- 30mm

FT500 cycle---------------- 29mm Honda p/n PT# 13101-MA0-000 (LD rods in L18)

 

Rods:

L18, L28, L26--------------------130.2mm

L16, L20, L24-------------------133.0mm

L14 ---------------------------------136.7mm

L13----------------------------------139.9mm

LD28--------------------------------140.0mm (oversize wrist pin)

L20B, Z22S, early Z22E-----145.9mm*

Late Z22E-------------------------149.5mm*

Z20E--------------------------------152.5mm

Z24, KA24------------------------165.0mm*

CA18-------------------------------133.0mm

FJ20--------------------------------140.0mm

 

Block heights:

Block deck height, (crank centerline to top of deck)

L13, L16, L18, L24, L28: 207.85mm

L20B, Z20, Z22, L28diesel: 227.45mm

Z24, KA24: 247.45mm

 

Yeah. Jason Grey info. It's pinned in the engine sub-forum here. You're missing lime 80% of the info.

 

EDIT: I see what you added in there. Chances of finding L13 rods though?

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Yeah. Jason Grey info. It's pinned in the engine sub-forum here. You're missing lime 80% of the info.

 

EDIT: I see what you added in there. Chances of finding L13 rods though?

 

Never know....

I did find a new set of L14 rods :-)

Probably never use them :-(

And I do have a set of 140mm FJ rods, that I already bushed to fit the L-series wrist pins.

Have a new set of LZ pistons also, but I would have to find where they are hiding, in order to figure out which ones they are.

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Rod length is just plain not that critical and almost meaningless on a street engine. Lets face it, you are not going to be holding the engine between 6,200 and 7,000 RPMs for any amount of time. A longer rod allows the piston to approach, hover and leave TDC more slowly than a shorter rod so acceleration/deceleration stresses are less. Remember the engine red line formula above? Long rods would be a way to reduce the stresses on the rods but I still would not advise going above this 4000 ft/min limit. Longer rods position the piston higher in the cylinder than a short rod when the crank angles are the same. ATDC the cylinder pressures would be higher and pushing harder on the piston top. Long rods have less side loading on the piston approaching and leaving BDC so there will be reduced frictional losses.  

 

These are esoteric discussions... arm chair hair splitting suitable for race engines where a win is often measured in split hairs. For everyone else you won't feel a thing.

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Not sure where the 4000 ft/sec limit was derived from, but I try to stay close to it, just to be safe.

On my Toyota 7M, that is about at 8200 rpm, and I've been using 8500 for the rev limit, without any problems, but it has aftermarket rods & pistons in it.

 

Went through all the figures to see if longer rods would help, even if going to a single compression ring pistons, to be able to use 4mm longer rods, the theoretical limit only went up a couple hundred rpm, so wasn't worth dropping another $2k on more custom parts.

 

In the mean time, there is a 7M rail dragster in Malta that runs 10,500 through the lights on over 50 psi boost, using stock length rods.....

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Rod length is just plain not that critical and almost meaningless on a street engine.

 

These are esoteric discussions... arm chair hair splitting suitable for race engines where a win is often measured in split hairs. For everyone else you won't feel a thing.

Mike... (sigh)

 

Long rod engines have much better power curves, at least when speaking in terms of Datsun L motors.

 

Smooth power delivery from just off idle to redline. That's meaningless?

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4,000 feet per minute is the average piston speed and naturally there are points where the piston speed is below this and exceeds this so it gets scary. The acceleration/deceleration on a 145.9mm long rod L20B rod and piston is 98190 ft/second2. at 7,000 RPMs. One gravity is about 32 ft/sec 2 so this works out to over 3,000 Gs!!! One acceleration and one deceleration of 3,000 Gs 115 times a second. 

 

My KA pistons are in the 50gr range and I think the L20B rods were 130gr?? Lets round up to 200rg at rest. At 3,000 Gs they decelerate with a weight of 1,320 pounds. That's way over half a ton tugging up on the crank  at TDC 115 times a second. (a small amount will be absorbed by the compression and another by pushing the exhaust out.... but not much)

 

 

(I've made some assumptions and guesses here so If you work with accelerations and gravity calculations and see fault in this say so it won't hurt my feelings. Actually I thought it would be higher)  

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Mike... (sigh)

 

Long rod engines have much better power curves, at least when speaking in terms of Datsun L motors.

 

Smooth power delivery from just off idle to redline. That's meaningless?

 

I notice you don't say 'more' but 'better' and 'smooth'. Long rod engines tend to produce their power slightly higher in the RPM range than a short rod, so maybe this would 'smooth out' the power curve? If so great, why are not all Datsun engines with longer rods? Probably because no one drives them at speeds where any advantage is helpful. It simply does not matter.

 

At any rate, we were discussing red lines and 'rev happy'- ness. That long rods like to rev. I don't think they can alter metallurgical properties of them selves or the pistons and are still subject to the 4,00 ft/min red line. As mentioned, they do slow down more gradually towards TDC and add a safety margin. 

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Wait, I think I just answered myself on the 2.1L build. Thinner rings and lower rod angle. I want to overbuild a little for longevity. It's a lesson I learned a little while back... Where can I do some more research on better internals?

 

Go for increased displacement.

 

Z22 block and crank/rods and KA pistons and U67 head, L16 cast exhaust manifold. Bore to 89mm and fit the pistons to Z22/L20B rods. You have a 2.3 liter torque monster. Red line is 6,500 and you get there sooner than a 2.1 that still has to keep revving with less.

 

Z24 with a U67 head, bam simple.

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