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mccuistion

L18 +.030 pistons vs L28 flat top 86mm for budget rebuild

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Hey guys, i'm fairly new here but as some of you know i'm in the process of planning/buying parts for my KA24DE-T swap for my 620.  Since i want to drive my truck in the mean time i purchased an L18 and 5spd swap. Well i decided to freshen up my L18 before installing and it turns out it probably needs a rebuild.

 

The photos show that not only is there poor cross hatching, cylinder wall galling,  and cylinder wall rusting, but it looks like #4 piston got in a fist fight with a valve.

 

 

I found a set of new old stock NPR +0.75mm L18 pistons for $90 that will make it a 85.75mm bore for pretty cheap, but i'm wondering..... if i'm getting it bored and honed should i step up to a set of 86mm L28 flat top pistons to add some performance? or is the difference not worth the extra money?  I only plan to use this engine for a year or so until my KA swap is sorted so i'd like to keep it cheap, but if the L28 pistons are about the same price why not get the performance gain?

 

Also as a sidenote, can anyone recommend a person or shop in the Seattle/PNW area that can bore and hone my block for a good price? 

 

Thanks guys!

 

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Edited by mccuistion
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Don't assume those L-18 pistons are really L-18 pistons with the 4 cc dish.They could be L-20b pistons with the 11 cc dish.Id go with the Z pistons.

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Thanks for the part number Doctor, that confirms what i found but wasn't sure it was correct. 

 

I believe i read DatzenMike said he had these L28 86mm flattop pistons with a closed chamber 41cc head and was around 9.66:1 compression.... that isn't a bad place to be for a daily driver..... i'm just wondering if its worth the extra $100 since i'm only using it for a year or so.

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2 minutes ago, john510 said:

Don't assume those L-18 pistons are really L-18 pistons with the 4 cc dish.They could be L-20b pistons with the 11 cc dish.Id go with the Z pistons.

Really? is there an obvious way to tell from seeing them? or only measuring?

 

This is the ebay link i'm thinking of purchasing:  https://www.ebay.com/itm/L18-NPR-Piston-Set-NOS-0-75-Datsun-1973-74-1129-4/382297849105?hash=item5902ba3d11:g:Z-oAAOSwdJ9aHvcQ

 

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The dish isn't that deep so most likely L18 pistons. If you are buying them anyway and the cost is comparable get the L28 flattops and bore 1mm over.

 

That last piston has FOD (foreign object damage)

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Anyone have a suggestion on where to buy the ITM L28 flattop pistons? I tried rockauto but its forcing me to purchase 6..... I only need 4 and don't want to waste $70 on un-used pistons!

 

Also DatzenMike, did you use any special thickness headgasket for your setup or will a standard one be fine for me?

 

I also might get the block and head surfaces trued/milled a bit to bring the compression ratio up a little. If I'm spending money to increase performance I might as well get all that I can. I'm fine with buying 93 octane gas so a 10:1+ ratio is fine by me. 

 

Also, if I'm adding the L28 pistons an increasing compression ratio, are there any oem cams that better suit the build? I don't want to spend big bucks on a custom cam but if an OEM cam from a different engine can help my performance I will find that and use it. ill do some searching.

Edited by mccuistion

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Stock L18 with open chamber head................................................................... 8.43

 

The L18 with stock 4.36cc dish pistons and a closed chamber head.............. 9.000 compression

Above L18 block bored to '86mm and fitted with L28 flattop pistons............... 9.85

Above with open chamber head........................................................................... 9.19

 

This is theoretical and assumes a crushed gasket thickness of 1.2mm, open chamber head volume of 45.2cc and a closed chamber volume of 41cc. A thinner gasket will give higher numbers as will a head that has been shaved making the combustion chambers smaller. Pistons on the L18 do not come up to the top of the block and stop 0.55mm below it, making the combustion chamber larger by 3.119cc.... this has all been added into the calculation.

 

 

 

The L18 and the L20B (IIRC) are the same 0.413" lift at the valves as the L16SSS cam. If you measure the cam across it's thinnest point and across the highest part of the lobe and subtract, you should get 0.275" This is the cam lobe lift. Multiply by the rocker arm ratio of 1.5 you get 0.413" at the valve. Theoretically. (there's 0.010" or more of valve clearance) I think some L16 cams are around 0.389" valve lift????

 

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On 8/23/2018 at 3:31 PM, mccuistion said:

Really? is there an obvious way to tell from seeing them? or only measuring?

 

This is the ebay link i'm thinking of purchasing:  https://www.ebay.com/itm/L18-NPR-Piston-Set-NOS-0-75-Datsun-1973-74-1129-4/382297849105?hash=item5902ba3d11:g:Z-oAAOSwdJ9aHvcQ

 

I can't tell from the picture.I bought some L-18 pistons for my L-20b and compared the pistons (new and old) next to each other.It's obvious if you can get the two side by side.For that price you can't go wrong.

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fUjxrJl.jpg

 

My Z24, Z22, Z20E and my L20B pistons

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On 8/23/2018 at 6:56 PM, mccuistion said:

Anyone have a suggestion on where to buy the ITM L28 flattop pistons? I tried rockauto but its forcing me to purchase 6..... I only need 4 and don't want to waste $70 on un-used pistons!

 

Also DatzenMike, did you use any special thickness headgasket for your setup or will a standard one be fine for me?

 

I also might get the block and head surfaces trued/milled a bit to bring the compression ratio up a little. If I'm spending money to increase performance I might as well get all that I can. I'm fine with buying 93 octane gas so a 10:1+ ratio is fine by me. 

 

Also, if I'm adding the L28 pistons an increasing compression ratio, are there any oem cams that better suit the build? I don't want to spend big bucks on a custom cam but if an OEM cam from a different engine can help my performance I will find that and use it. ill do some searching.

Aftermarket Datsun parts aren't as plentiful as other engines (like SBC), so you are definitely at the mercy of what's out there. The pistons, for example. You may be able to talk your local machine shop into selling you just four, but I doubt it.

 

The head gaskets aren't really available in different thickness, unless you go with a custom steel composite or copper gasket. Just make sure whatever stock type gasket you use is graphite coated.

 

I would be wary of having a skim cut taken off your head or block. Seems like a lot of machine shops don't cut a squared surface anymore, unless you spec it and pay extra. The blocks generally don't need a skim cut, but if you do cut the deck of the block, be sure to factor this into the new piston height. With a stock head gasket, your pistons should be a maximum of .015" above deck.

 

The best ever L4 cam was the U20 casting found in L20Bs. They were stamped "A, B or C" on the back and if I recall, the best one is the one stamped "B".

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Also, depending on how much you cut off the head and/or block, you may have to file the slots in the curved timing chain guide to get the correct chain geometry.

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Thanks for the info guys! So as you probably know, once you get into a block and start buying parts its a slippery slope from budget refresh to all out performance build...... and after a few beers lastnight and an ebay shopping spree this went down the performance slope haha.

 

I purchased the following:

New old stock nissan OEM L28 flattop pistons 86mm

Matching quality rings

New L18 rods

Main and rod bearings

Intake and exhaust valves

Valve seats

Full rebuild gasket kit

Clutch kit

Water pump

 

Im going to have the machine shop hot tank, magnaflux, and bore/hone. Also going to have the head gone over, port/polish, new valves and seats, and have it checked for warpage or true it up.

 

So after going this far i might as well get a get a decent cam.

Stoffregen, is that U20 cam a sizeable upgrade? Or is there a decent aftermarket cam you would suggest that is a good value? I have a weber 32/36 and its a street car. 

 

 

I found this but $260 seems steep for a single cam? Ill search more.

https://zcardepot.com/camshaft-comp-cam-racing-l16-l18-l20b.html

Edited by mccuistion

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$260 doesn't seem to bad for a new cam.... it's about 130 to 150 to get a regrind done, you send them your cam...

Dont over look that you'll have to recondition or replace your rocker arms... also you may need new valve shims.. the springs and retainers optional...

 

Also just because I've made similar purchase for my L16 and made mistakes.....

What type of rods did you buy?

With Stock rods the piston pin is pressed into the rod and floats the piston....  if you bought h-beam rods they float the pin in the rod and piston would need clips, so just be aware of how the pistons and rods will be assembled.

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Thanks for the heads up crashtd, i stumbled upon that info last week on ratsun luckily so i purchased rods that are press fit for the pin.

 

I just found this schneider cam and think this will be a better value at $139, is it odd to see longer exh duration than intake duration?

Intake Duration (gross): 284
Exhaust Duration (gross): 294
Intake Duration (.050”): 240
Exhaust Duration (.050”): 244
Intake Valve Lift*: .480"
Exhaust Valve Lift*:

.480"

 

 

A 480/284 is probably the upper limit of streetable, but the near 10:1 compression ratio ill have should help. You dont think valvesprings are mandaroty when going with a bigger cam? I assumed i would have to upgrade them to stronger ones or get new oem at the very least.

 

Im also wondering if the 32/36 will be able to keep up after all these upgrades.... ill have to do some research. So much for my budget refresh haha.

Edited by mccuistion

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Ya I went down this worm hole with my L16, which is now 10.7-1 cr.. ... I have the 260/270 cam regrind from Schneider.. I did get the springs and retainers and lash pads from them also.... you need their retainers with their springs.... 

I think they should be done, but that's me.... others may say different that's why I said optional... plus budget... also depends on how far you wanna rev the motor.... 

As far as the carb, dont know.... 

I'm currently running a single weber 40dcoe...

 

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How do you like the 260/270 schneider? That was the other one i was looking at but i like the power range schneider listed for the 284/294. I didnt see they sell springs and such, ill call them tomorrow and make an order. 

 

Really, A single 40dcoe? I thought most people running built L`s are running dual 40dcoes. How does your engine do at high rpm with that carb and cam?

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I like it , it makes the motor sound different. I wasnt trying to go to crazy with cam because my truck is a daily driver, i told them it was basically a mild street motor and that's the one they recommended....

 

And they did sell the springs retainers and pads when I had my cam ground..

 

And ya a single 40 on a lynx intake.. I was going for something between a 32/36 and dual 40s hoping for decent fuel economy and still make some power... I'm happy with the way it performs,  I've ran the engine to just over 6000 with no issue and even felt like it had a little more, my motor only has about 1500 miles on it now since I built it.... it doesnt seem to like the lower rpm if I'm in a higher gear or just putting along but from 2500 on up it's great... im not sure if that's because of the carb or the cam, or possibly even my  pistons.  I think I can improve that but I'm not to knowledgeable on tuning so I'm still trying to learn  so I can get things running 100%..... 

 

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It'll be mostly the cam. You've changed the closing and opening points of the valves around. It favors higher RPMs now where there is less time to draw air in and get exhaust out so the doors are held open wider and longer. What you can do is drop a higher differential ratio in.

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It's the rob Peter to pay Paul scenario, you rob torque at lower RPMs to make more HP at higher RPMs, that is why big cams are not street friendly.

I like stock cams because I like having power when I start out normally, and I do not run it up past 4500rpms anyway, so there is no point in having a lumpy cam.

When I was a kid my 65 Nova had a strip engine, but I drove it like I stole it and got about 7mpg, but it was a fun car for a kid.

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I love low speed torque wayno. It's the most used and most appreciated when driving. I think third is my favorite gear around town now with the 4.11s.

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20 hours ago, mccuistion said:

So after going this far i might as well get a get a decent cam.

Stoffregen, is that U20 cam a sizeable upgrade? Or is there a decent aftermarket cam you would suggest that is a good value? I have a weber 32/36 and its a street car. 

 

 

I found this but $260 seems steep for a single cam? Ill search more.

https://zcardepot.com/camshaft-comp-cam-racing-l16-l18-l20b.html

The U20 cam is not big. It's a stock L20B cam.

 

My favorite cam for a mild street car with a DGV is called a 27c. It is pretty mild with small gains across the entire RPM range. You can get them from Rebello Racing. The main reason I like it is because it is very easy on the valvetrain and doesn't require very stiff valve springs.

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I second Doctor 510's post of American custom cam - I run an 056 (going from memory) grind from them and it is great - super fun and didn't rob enough of the low end torque to notice.  

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