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Rebuilding L series motor - Worth it?


adam

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Hi all, 

Thought I'd be a little old fashioned and use forums instead of modern age Facebook social media.

Those of you who have rebuilt your L series motors, whether it be L24, 26 or the L28, has it been worth the effort?

Let's be honest, in this day and age, you can buy much quicker cars and motors.

I'm currently running a stock L28 with triple carbs and a full exhaust, it does the job and love the fact I can squirt it around town without breaking speeding fine records. It's a little tired, chewing through oil, leaking a bit here and there.

Was thinking of a standard rebuild, possibly flat tops and mild cams but the question, did you take it a bit further? Was it worth it?

If you could do it all again, what would you do differently? Original L series is my goal but should I waste my time?

Keen to hear from those who have done it.

 

Thanks, 

Adam

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You question is a bit "How long is a piece of string", Adam.
And it depends on what your expectations are...

The big $ is in the cylinder head - if you want performance that's where the bulk of the $ go.
If you are aiming for under 250hp (flywheel), then a standard bottom end is fine.

Have a read of this thread if you haven't already - it cost the owner, all in with a new Scorcher Dizzy ,$6,000


 

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Apologies, quite evident that I didn't elaborate enough.

The zed I have wasn't built to go fast, it's predominately a weekend twisties car. It has plenty of go at the moment to be fun.

Although it has plenty of go, it's at the point where, 'it could do with a freshener'. By that, it's losing a bit of oil in it's usual places and blows some smoke (could be from running a tad rich also).

I have another car which is tracked and is the 'go fast car' so I don't necessarily need another. But in saying that, if I were to go and build a motor, those that have spent the little extra coin for head work, oversized pistons or even going to flat tops from the standard dished, has it been worth it? 

Should I spend the extra coin on a cam, new pistons, head work, etc. For an additional... 20hp gain? Or if I was to do new rings and a hone, do I just leave it at that because the extra $500 per horsepower isn't worth it?

Obviously the response would vary from person to person but I am just curious to hear thoughts, create conversion and activity on the forum social media platform again.

Also thanks for the link, I have read it before, definitely to the level of something I would consider doing. 

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In a word Adam :YES

Yes it is worth it.

I have been lucky enough to have belonged to a Zed Club for 35 years and have seen, not all of it but most of it.

In my experience the Lseries engine stacks up well against all comers . It may not have it over all transplants but they have to work hard to put a L series down. The Barra transplants are hard to come to terms with as they are a cheap motor and look at home in a s30 engine bay.

But I am old sckool. A  S30 without an L-series  engine is just an other modified car.    

Edited by Bonkers
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Thanks, Bonkers, that's the kind of response I was expecting..

No intentions on doing a motor swap at all. I have a spare L28 here that's stripped and ready to go in for a rebuild but was on the fence about going that little more or a stock standard build.

As mentioned, completely understand that everyone's responses will be different but I was hoping to create conversation. Was actually expecting someone to say, 'dont even waste your time on small/minor modifications, go hard or do nothing at all'.

And Cracker, already dyno'd current motor. Would be nice to compare before and after's but it's another complete motor going in.

Original intention was to sonic test bores, go largest flat top pistons possible, standard stroke, just cleanup ports of the head with mild cams and call it a day. Didn't know whether it was worth going over bore if there was minimal gain. Now I'm thinking of just fresh bearings and rings lol 

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Adam you sound as if you are happy with the configuration of your power plant .

But would like a little more drive ability from it.

So if you have a L28 sitting around and don't wish to spend big dollars. I would look at this .

The 42 and 54 blocks both have there pro's and con's pending on who you speak to. If the bore is standard put in 240Z pistons. If the bore is worn and you will need over size pistons . You can take a number of paths here. 1mm over size is common but pistons are becoming hard to find. 

A lot of us put in Z24  or KA24 pistons. A few install the LD28 crank with 240Z rods with 2 or more head gaskets.

Or stay with the standard L28 or L26 crank with 240Z rods. But you may want to deck 1mm off the block and slot the holes in the chain guides to take up the slack in the timing chain. In this configuration with a n42 head and Z24 pistons give around 9.6:1 and KA24 gives around 10.4 :1 from a 2990 cc engine.

This is standard machining and off the shelf parts. This is only a sample starting point for a weekend warrior with a few K to spend and wants some change in their pocket . But it won't buy much at MacDonald's 

  

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Not an L28, just a little L18.

Old engine, pretty much worn out after 20 years (stock bottom end, unknown mild cam, minor head work and 38mm SU's) - 69hp at the rear wheels

Same engine carefully rebuilt with 87mm flattops, bit more head work, 72 degree cam and 1 3/4" SU's - 102 hp at the wheels.

No, its not the most powerful engine around, but the difference pre and post rebuild was considerable. I rebuilt it myself, total cost of all parts and machining was well under $2K for that extra 33hp. Would the next 33hp gain be just as cheap ? I doubt it....

 

Edited by 1600dave
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2 hours ago, adam said:

 

84rwkw from memory

To me that makes a rebuild worth it. I was getting 84rwkw from an old L24 with a cam and an exhaust.

For a fresh L28 you'll get 110rwkw+ and it'll make a huge difference with a lightened flywheel. You'll love it.

There's a certain charm about a bone stock zed, but if it's not the original motor you might as well go for it. I love my L28 with triples (I also love my original zed, but it's a different kind of love :P)

For a cheap alternative, make sure your diff ratio is fun enough, and if you have a WR box, go to CR and get your flywheel lightened. Will add 30% fun for not much cash at all.

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3 hours ago, cracker said:

To me that makes a rebuild worth it. I was getting 84rwkw from an old L24 with a cam and an exhaust.

For a fresh L28 you'll get 110rwkw+ and it'll make a huge difference with a lightened flywheel. You'll love it.

There's a certain charm about a bone stock zed, but if it's not the original motor you might as well go for it. I love my L28 with triples (I also love my original zed, but it's a different kind of love :P)

For a cheap alternative, make sure your diff ratio is fun enough, and if you have a WR box, go to CR and get your flywheel lightened. Will add 30% fun for not much cash at all.

Awesome! So no matter what route I go with the rebuild, it should be a huge difference. I actually didn't think the power was all that bad power wise; good to know there should be a bit more in it!

 

Will definitely try and strive for Lurch's build on that customer's car minus head work I think at this stage. 

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  • 11 months later...

Just wanted to report back because of iso boredom.

Ended up getting the spare motor built, standard crank, aftermarket H beam rods, 1mm oversized dished pistons and your usual ARP bolts, fresh seals, etc. Got machine work done, bearings to suit from machine shop so it was just a matter of slapping it all together at home. Was going to go flat top pistons but supply and concerns around detonation with stock cams, i decided it wasn't worth the effort.

Before Victoria/Melbourne went into our first lockdown, I managed to get the motor finished and installed. Did a few drives to run the motor in and what can I say, even standard build, the motor has so much more torque than the old motor.

Blows less smoke, mid range pickup is amazing. This was literally no changes to carbs or cams as these were swapped out and over into the new motor.

Would be interesting to dyno this motor and see what power it makes now after run in. To answer my own question of whether it was worth it, with my goal, this was enough. More than enough power to blast through the hills or cruise through it in 4th gear.

The power drops off dramatically from around 5krpm though (so did old motor), so I'm currently looking into a new cam to open it up a bit. A 72 with high lift (which will require new springs and retainers) is looking like the choice at the moment as I don't intend on revving it any higher than 6.5krpm.

Also got the spare flywheel machined and lightened too but didn't install it as it's a 240mm item while the HD clutch I had and transferred over was only a 225mm. Will hopefully get this in at some point.

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Edited by adam
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2 hours ago, adam said:

The power drops off dramatically from around 5krpm though

What size chokes have you got in your triples?

EDIT: I read your wordpress blog and see you have 34mm chokes so that is not the issue.

Maybe a trip to see Richie at Allcraft Automotives is needed to sort it out?

Edited by AndBir
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12 hours ago, AndBir said:

What size chokes have you got in your triples?

EDIT: I read your wordpress blog and see you have 34mm chokes so that is not the issue.

Maybe a trip to see Richie at Allcraft Automotives is needed to sort it out?

Yep, 34mm is still accurate. 

I've done a heap of reading and experiences of hitting a wall and just making noise from 5krpm isn't unusual it seems.

I will give the cam upgrade a go, it will eventually happen anyway and if that doesn't improve it, I'll definitely go see a pro.

Loving the car though, if only we could go for a drive!

IMG-20191226-WA0030.jpg

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1 hour ago, adam said:

I've done a heap of reading and experiences of hitting a wall and just making noise from 5krpm isn't unusual it seems.

I will give the cam upgrade a go, it will eventually happen anyway and if that doesn't improve it, I'll definitely go see a pro

Is that a typical characteristic of the L28 or is it likely cam related? I have never driven an L28 but definitely don't have that problem in my L24. Between 3.5k-6.5k the L24 just wants to keep going.

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  • Administrators

In my experience all L-series L6 tend to run out of puff around 5,500rpm. My own 72 240z makes good power all the way up to that point then starts to feel flat, I don't think it's the carbs, rather I think it's the cam doesn't offer enough room to breathe further.

I find the stock SU's are also quite restrictive at higher rpms.

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3 hours ago, adam said:

I've done a heap of reading and experiences of hitting a wall and just making noise from 5krpm

From your AFR plot you are going too rich at higher revs so you might need to change your emulsion tube.

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43 minutes ago, AndBir said:

From your AFR plot you are going too rich at higher revs so you might need to change your emulsion tube.

I believe the plots on my blog are all out of date. I've since tinkered with the jets some more and AFRs in top end are at 12 -12.5 now (from memory) which shouldn't be far off the mark.

Believed I could do with one step up in air jet but wouldn't have thought it'll give that flat feeling Gav's also referred to.

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4 hours ago, gav240z said:

In my experience all L-series L6 tend to run out of puff around 5,500rpm. My own 72 240z makes good power all the way up to that point then starts to feel flat, I don't think it's the carbs, rather I think it's the cam doesn't offer enough room to breathe further.

I find the stock SU's are also quite restrictive at higher rpms.

We'll, this discussion is very interesting. 

When I had triple webers ( 40mm ), I had this exact issue ( my first experience of the L6 engine ) . I looked around the Web, obviously not well enough, and found no obvious answer. I even have a post on here somewhere, where I mentioned this. It started bothering me because I thought there was an issue with my engine / webers. 

Fitted the HS6 conversion, and it will now pull all the way to the top, no issues. And it gets stronger as the revs build. 

But my bottom end has suffered greatly. 

Edited by RAP260
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Is your motor L24, L26 or L28? 40mm isn't really big enough for an L28 IMHO. At least not for making power at higher rpms.

Camshafts also make a difference. My 72 240z has a very mild duration cam. When I had SUs it really struggled to keep up with the engine which is high compression, ported with cam.

On Triple Mikuni 44s it really improved driveability and mid range, too end is good, but at 5,500rpm-6000rpm the power feels like it gets a bit flat. I haven't played with jetting, venturis, chokes etc.. or looked at advancing cam timing or duration but that would be my next step..

 

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