l20a rod length

[pauly_adams]

hey all I'm in the process of planing to build a stoker motor and was wondering if any one could help me with some info.

 

i been doing my research and i though i came up with the perfect stroker for me but the problem i have is that there are different sizes listed for the L20a rods from a skyline, what i can gather the sizes stated the are 135mm in length which would be perfect for my application but then it is said elswhere they are 128mm in length.

 

so does any one out there actually have a set they could measure or does any have experience with them that could tell me the size.

 

cheers Pauly

[NZeder]

Hi Pauly,

 

Well given I have had and owned some 4 L20a over the years (well either me or Dad) I can give you the correct answer

 

1. There is no 128mm L20a rods

2. There are 2 type of L20a rods

3. The early pre 79 are the one you are after they are 133mm long have the same big and little end as the L24/26/28 rods and have the 9mm bolts

4. Post 79 ie Skyline L20a are what you want to avoid as they are 135mm long, have the incorrect big and little ends - however I believe in Japan a few workshops have used these with mods to the crank to make the big end smaller. They then install larger little end bush that is installed offset from the stock position to make a length of 137mm. However all the $$ in machining = purchase some custom H or I beam rods and be done with it.

 

Also another NZ guy I know has supplied a few sets of L20a rods to people in 133mm length and I know he striped a few also and he confirms the above about the pre and post 79 differences.

[gav240z]

Mike,

How easily can you obtain Pre-79 L20A rods in New Zealand?

 

I have 12 L14 rods, but am considering selling them to fund a custom rod set.

[NZeder]

Mike,

How easily can you obtain Pre-79 L20A rods in New Zealand?

 

I have 12 L14 rods, but am considering selling them to fund a custom rod set.

Like finding L14 rods these days (no, not quite as bad but getting close) we are talking about a 30+ year old engine and most L20a were fitted in Fairlady Z imported from Japan in the 80's most of the L20a were removed and replaced with either L26 (from 260c) or L28 and the L20a were just binned as people did not know or care about building strokers back in the 80's so like the L14 just about long gone.

 

There is a pre 79 L20a listed on trademe currently but guy is asking $500 for the complete engine - crazy when only the rods are of use (unless you wanted to de-stroke a L28 and build a 2.5L that would rev more than a L24 due to the shorter stroke of 69.7mm vs 73.7mm for the L24

[C.A.R.]

When you can get a company like Argo to make you a set of custom H or I beam conrods,

why would you even bother looking at 30+yo factory rods?

I'm not saying Nissan L6 rods are crap (far from it), but if your going to spend all the extra $ on a 'stroker' you might as well get some custom rods as well...

 

BTW Pauly, I would still blow you away with a stock bore/stroke L28 built to the same specs - strokers aren't worth it unless you spend 12k+ on the build & use the LD block...

[NZeder]

When you can get a company like Argo to make you a set of custom H or I beam conrods,

why would you even bother looking at 30+yo factory rods?

I'm not saying Nissan L6 rods are crap (far from it), but if your going to spend all the extra $ on a 'stroker' you might as well get some custom rods as well...

I agree and having had one set of L20a rods modified to take a RB30 bush at the little end (very good bush for an OEM item) and machine costs and $$ involved I could have had some custom units for only about $20-30 a rod more.

 

BTW Pauly, I would still blow you away with a stock bore/stroke L28 built to the same specs - strokers aren't worth it unless you spend 12k+ on the build & use the LD block...

LD Block = longer rod/stroke ratio options but to get a good bore out of one = more machine costs so like Lurch states a good well setup L28 is cheaper to build. Having owned a L32 the torque is great but it comes at a cost the engine cost the PO (I did not build - just fixed the issues) over $20K and I added $4K to that with better carbs, headers to match the internals (and a new metal 1.0mm head gasket as the stock unit was too small for the 90mm build - why did they spend all the $$ then cut cost on the head gasket, I suspect this was the PO that did that after he blew a head gasket after the engine was built)

[pauly_adams]

i was actuly after the 135mm rods due to it making everything so neat and tidy. hear are the specs of the engine im going to build not theres no ld28 crank

 

L28 block bored 0.120" (89mm bore)

L20a conrods 135mm

n42 head

std head gasket

L28 or L26 crank

ka24 pistons flat top preferable

 

 

engine bore 89mm

engine stoke 79mm

deck height 0.630mm

deck cc 3.919

rod stoke 1.71

 

compression with -ka24e dished piston 10.53:1

                -ka24e flat top pistons 11.2:1

                -LZ24 pistons 8.79:1

engine cc 2.949 cc

 

 

this engine should reve quite hard but it looks like im going down the path of using L24 conrods if i cant get the l20 or if they just wont work. it says on the ozdat engine disign utility the Lengine program and also atlantic z car engine builder state that the big and little end on the 135mm L20a rods are the same as the L24, 26 and 28 either way im not too fussed but it would have worked out perfectly.

 

cheers pauly

[NZeder]

The ozdat engine builder application has incorrect information about the L20a rods. The 135mm version of the L20a ie post 79 don't have the same big and little ends. The little end is 20mm not 21mm and the big end is 48mm not the 53mm of the L24/26/28/LD28/L16/18/20B.

 

Don't trust the ozdat info when it comes to L14, L20a rods. Now with that said if you want 135mm then take a 133 L20a rod or L24 rod (ie 1 and 1/2 set of L16 rods if you can't find either) and offset bush to make 135mm centre to centre length - this can be done (and has been done in the past ) but again the cost might be the same or close to the same as getting custom rods made.

 

Over to you but trust me if you get the L20a 135mm rods you will be up for some work to get these to fit due the 5mm difference in the big ends (the little end can be dealt to easy enough use a piston that takes a 20mm pin or increase the 20mm bush to 21mm if there is enough meat (which I believe there is))

 

Hope this helps.

[bluerat]

Please, Excuse my stupidity, but other than purchasing the LD crank and finding the longer rods, where's the big money in the stroker build?, and if you were building a high rev engine would you use a normal L28 crank instead? my understanding was that the LD crank was an all round better/stronger crank?? or is stroke length the major issue?

 

All right, there's grout filling the block, the fancy head gaskit and block machining (is going 1mm over dearer than 3-4 mm over?), but everything else you would do to a good engine anyway, wouldn't you?

 

I've seen you mention before Lurch that a std rod will handle 150hp a rod!! So  why go after market? is it the the fact you can get a custom length to suit, or that's it's a new rod not a very old rod or big Rev's. I know a L20 rod will handle better than 8000rpm ( got the dyno sheets to prove it!) Is the extra stresses imposed by the six the problem?

 

Sorry to go off topic, again, but I, and I suspect a lot of people, find this very interesting. Lot of questions i know....

 

Hodgo.

[NZeder]

Big $$ come in for big HP and if you are building a stroker you should be looking for big HP - sure you can build a stroker with truck pistons on the top (ie KA24 - have to seen how big the rings are - does not/will not rev + they are heavy - sorry to all the guys out there that follow the US builds)

 

I have seen guys in the US build stroker and then only put down 200HP at that wheels - WTF - you can and should be able to get this from a L28 without too much trouble.

 

Like you say L28 or LD28 cost should be around the same - and they should be if you do the work were it is needed - the head is were you should put most of the $$ as the bottom ends should be the same $$ ie rod prep, crank prep (apart from you guys in OZ that have to pay $800 for a LD28 crank), machining, balancing and the key to any high power bottom end build some good light weight forged pistons on the top with good size rings not massive truck size oil rings like the KA24 units or even the stock L24/26/28 units)

 

If you build cheap then you will not get good HP and for the same cheap investment in the L28 (ie not spending $800 on the LD28 crank = $800 more on the L28 build) you will get the same or more power for the $$ put in ie $5000 budget is a cheap L28/LD28 build to do either correctly double that and this is before we start adding carbs and headers to match the head work that you will get done.

 

Remember the ICE is just a big air pump - air in - air out. You need your head right to ensure you get the most power you can for the given air numbers. cc does help which is why people go for the stroker the more cc = more air required, more air required the more fuel you can mix with that air = bigger bang = more power/torque that is the theory anyway. But again if any part of the engine is not done right then you will not get the result you require.

 

Ie take my old L32 - N42 block, L14 rods, LD28 crank, cosworth forged units on top, and poor head work with a large cam (the ports looked impressive they were 42mm on the intake - the intake manifold was ported so large that at one point in its life it snapped and was welded back up with extra bracing) and it was a pig below 3500rpm it was top only it made good power up top but you lost soooooooo much power getting their. It had crap weber 48 carbs (there are two type of 48 webers, the good SP ones and the sh!t 48 units were are nothing more than 45 bored but then parts are hard to get due to their oddness) and a custom header that had short primaries. All this made crap power down low. It was loosing so much power trying to clear its throat it could only lay down 180HP at the wheels - and this cost the PO $20K to have built in the early 90's which is a truck load of coin.

 

Anyway - not long after the dyno run the head gasket blew = remove the head and took to my head guy we fixed a few issues with the head (ports were too big = air speed issues = loss of power) and installed larger exhaust valves. I replace the webers with 47 OER with much smaller chokes 37mm not the 42mm in the webers, replace the intake manifold which was ported to 39mm, and I installed some headers that were larger and longer so some $4K later back to the dyno and now 250HP at wheels (on avgas) I sold the car and a new head that my guy build for pump gas (ie lower the CR from 12:1 down to 10.5:1) this new head had a 240/240 cam - yes small but they don't have to be big to make power just match all the other head work. The new owner had this head installed and back to the same dyno and on pump gas 230HP at the wheels and much more driveable down low and it would still making power at 6800rpm which is were we told the dyno guy to stop as the engine still only had a factory balancer on the front - so if that was done right too then more power would be there for sure.

 

So the point - any engine needs to be done right and matched to make good power = $$ with a good guy that knows his stuff - not $20k with a guy who is going on rep (he does know his stuff but the PO would not spend all the $$ on the right stuff as this guy was $$$ for labour). I forgot to say one of the reasons for the $20K build is that engine blew up twice and when I go the car - the head gasket went on me and then I started to look into why. The fuel pump was not up to the job (F'n holy reds - get a carter pump much better) the fuel press reg the PO had was faulty so $$ on a good unit and the fuel issues delivery issues were over = no more detonation but damage was done already

 

I know of another stroker but only on a 87mm bore and it make a lot more power than my 3.2 (90mm bore) again because everything matched and $$ were put into the right places.

 

I know Lurch you have a thing about the rod/stroke ratio of the typical LD28/L28 build but 1.5 is ok look at the V8's with around this that rev to 8000+rpm that is not the issue the long crank and load on #6 bearing is bigger issue with the incorrect flywheel setup (a little hint right there about the LD28 cranks)

[bluerat]

Thank's for that Mike, so go as light as possible where you can in the bottom end, to get it to say together and run some rev's. So your also saying to build it properly, weather it is a l24, 26, 28 or big banger 3.1 there should be minimal cost differences other than the crank etc costs? So Lurch why is the non stroked L28 a better option in your eyes? You've made some pretty big statements up there? I'm about to build a race motor should I throw my LD crank away??

 

 

 

 

/

 

 

[tbscobraZ]

Are you sure you want to use the standard head gasket? Also highly agree with the custom pistons advice definately the go. Also highly agree with the work on the bottom end advice as it is your base and sets the tune for the build, if you want a really nice build make sure the bottom end is sweet, maybe get it cryo'ed. Because if you have and awesome top end and a terrible block you will do damage because the block needs to take the abuse. Also the reason for the higher price of the stroker is the extra care, treatments and precision required eg whats the point of a stroker that drives like a truck and only puts down 200hp - 250hp.

[NZeder]

If the bore is under 88mm then the stock gasket is fine just o-ring the block for a good fire-ring/seal.

 

All this stuff is covered in the book

 

"How to modify your datsun OHC engine"

 

Nothing new really just do it correctly and the cost of a good build be it L28 with a LD28 crank or stock crank should be the same bar the extra for the LD28 crank you have to buy (+ the different rods)

 

My last L28 which I sold before it was finished as I decided to go RB. Was using L20a rods on L28 crank and some light weight postion I got from Japan. So that bottom end cost the same as a stroker due to all the perp work hmmm should have kept it.

[bluerat]

What I'm trying to say Cobra is shouldn't "the extra care, treatments and percision" be put into any engine you build? and what are the extra care and precision if needed?  The fact is the old L series is a pretty simple thing, and the only real problem with them is the crank can crack in the six cylinder when pushed hard. Like most things worth doing, good info can be hard to find and like most people I'm just trying to work out the facts from the BS before I spend my dough.

[pauly_adams]

well im waiting on a price for some z24 pistons i have decided to go L24 rods and z24 pistons mind you im going to need a new hks 89mm head gasket. by the way im not after huge amounts of power im looking at 200hp nothing huge and maybe a turbo down the track to pick up a little bit of slack thus me building it with low comp and slighty thicker pistons as i dont wont to use forged pistons good luck with your build bluerat.

 

cheers pauly

[bluerat]

Thank's Paully, sorry about the major Hijack!! For a street/sometimes race engine the extra cubes and torque of a 3.1 are magic. It will give you plenty of yippty-do-dar off the line and be very nice to drive.

[DatZed]

I am building a 3.1 ATM with custom rods and so on. Does anyone know where to get quality custom forged pistons from in Australia? Don't say SPS because they have gone down hill recently, their items are too heavy and they don't listen.

I am using 3s rods and custom pistons, ported and sleeved N42, SM4 and stepped headers. Also looking for a crank girdle if anyone has any leads on that.

Cheap altenative to L14 rods, SR20. Grind the big end and use a piston with the correct PE size to keep it centred. Cheap 136mm, 22mm pin.

Cheers

[NZeder]

I am building a 3.1 ATM with custom rods and so on. Does anyone know where to get quality custom forged pistons from in Australia? Don't say SPS because they have gone down hill recently, their items are too heavy and they don't listen.

I am using 3s rods and custom pistons, ported and sleeved N42, SM4 and stepped headers. Also looking for a crank girdle if anyone has any leads on that.

Cheap altenative to L14 rods, SR20. Grind the big end and use a piston with the correct PE size to keep it centred. Cheap 136mm, 22mm pin.

Cheers

it is a bit of work but there is another Nissan engine with a crank girdle that can be made to fit hint - they are a Nissan inline 6 share the same bore spacing and head bolt pattern but use a belt drive for the cam timing

[DatZed]

That sucks, I just gave away an RB25! If I get really exited I might CNC one, but that's not all that high on the 'to do' list. Getting the ex ports to flow is my next task, time to fire up the TIG!

[pauly_adams]

the l series and rb series realy arnt that different after all.

 

[NZeder]

the l series and rb series realy arnt that different after all.

 

No they aren't that different, and one does think this was by design ie keep the history and a link to the good old, strong, well respected L Gata engines but sharing the same bore spacing and head bolt location. Also take a look at the S20 engine and you can see how the RB looks a little like these also so again a bit of connection only if it via some visual similarities.