Rebuilding L20b (ex racing engine)

[Engy]

So I recently picked up this engine from another ratsun member and I need some help in rebuilding it. He used it in the 70s and I think 80s as well as early 2000s I think. It has an a87 head, domed pistons, 0.040" bore, a turbo zx oil pump, and a 270ish duration cam. It needs a slight rebuild, timing chain, probably gaskets, and he suggested getting flat tops from a 280z. The crank and cam both turn but I haven't been able to try and turn it over since I don't have a transmission to use on it yet since the 5 speed I have needs a rebuild. I'm not 100% sure what I'm going to do with it yet as I strayed from the thought of putting it in the 710 since it's 100% original. All I know is I want to finish it with my 5 speed dogleg and find a car that needs a heart and guts. My plans so far are to get either a single weber was thinking a 38 or 45 and MAYBE if I get more funds and the opportunity I would get an old pull through turbo that I've read alot about.

 

 

 

So right now I need to find a place to rebuild the transmission so I can test for compression and I need to find a timing chain kit for it. I looked on summit racing for a kit but came up empty handed(Guessing this isn't what I'm looking for http://www.summitracing.com/parts/slp-222-3dr102/overview/make/nissan ) if they don't have one where else can I find a timing chain kit for it.

 

Also would it be a terrible idea to keep the domed pistons or should I go for the flat top? It's going to be in a street car hopefully(If I can find one :D )!

[izzo]

I don't know the MM on the pistons, but I thought the 280z flat tops worked on the L18... not 20? Could be wrong... wait for a more clear answer.

 

 

Goto rock auto or your local parts place for the timing chain kit / guides / gaskets etc. Felpro has good gaskets, beck arnly is good parts mfg.  Good luck.

[Engy]

I've read a ton of build threads on L20bs and it seems people use flat tops in them. As I stated the engine has a .040" bore or 1 MM, so it would bring it from 85MM to 86MM which I believe is about the size of a ZX piston. I also found some dished pistons on summit racing( I got a nice gift card for summit) http://www.summitracing.com/parts/uem-9048-1-0mm/overview/make/nissan , I want the car to be streetable and run on pump gas (Don't care if its higher octane as long as I can get pump gas)

 

As for rock auto, forgot about them and found the timing chain kit quickly, thank you. Will check out those gaskets too.

[izzo]

Cool man! I've never built up a motor, so never searched for the info :D  Good for you for doing so.

 

I'm sure you also saw the Jason Grey sticky in here too yeah?

[Xnke]

You need to know the volume of your combustion chambers before you can determine if you can run the domed pistons on pump gas. Also keep in mind that lowering the compression will change the characteristics of the cam; it may not run well if you don't have enough squish.

 

As a general rule, long duration cams (270 degrees total duration and up) will need higher compression to keep from being a total dog down low. Up to about 270 degrees duration, the engine will run decently well on stockish compression.

 

If the engine was built with a well-ported head with good valve unshrouding, and a long-duration camshaft, the domed pistons may be necessary to make the engine responsive enough down low.

 

"former race engine" kinda points to long-duration cams...

[Dawa]

from what ive read, redline recommends the 32/36 for the best of fuel economy and performance,

where as the 38 is more for race only? that is the impressions but perhaps someone with real world

experience will chime in.

 

my L20b had to be bored out to .75mm/.030 and luckily rockauto had the pistons for it, at the time of

purchase it bought 4 of 4 (all they had.)

 

i just checked rockauto for L20B pistons. they have 1 .020 piston and 1 .030 piston.

 

but besides that, hit up rock auto for just about all your other needs.

[Dawa]

and yes, L20b pistons are 85mm (3.346")

and L28s 86mm (3.386")

 

so with your that bore you have,

so you should be able to run the L28s, its been done before

you just need to research harder, a-hole :)

 

the L20b stock piston and L28 stock piston have the same pin height,

[Engy]

You need to know the volume of your combustion chambers before you can determine if you can run the domed pistons on pump gas. Also keep in mind that lowering the compression will change the characteristics of the cam; it may not run well if you don't have enough squish.

 

As a general rule, long duration cams (270 degrees total duration and up) will need higher compression to keep from being a total dog down low. Up to about 270 degrees duration, the engine will run decently well on stockish compression.

 

If the engine was built with a well-ported head with good valve unshrouding, and a long-duration camshaft, the domed pistons may be necessary to make the engine responsive enough down low.

 

"former race engine" kinda points to long-duration cams...

The head is an a87 peanut that doesn't appear to have been ported past stock. Say the cam was 270(it's in that ball park) with the current head and valves, would I want to keep the domed pistons or should I get a 260 duration cam and dished pistons(the ones I linked) to "dumb" it down a bit for road use? Or does none of that matter?

 

I have no problem using domed pistons as long as I would be able to use it on the road.

 

 

 

from what ive read, redline recommends the 32/36 for the best of fuel economy and performance,

where as the 38 is more for race only? that is the impressions but perhaps someone with real world

experience will chime in.

 

I've seen that too but in a few cases I've seen people use 38 on their road cars, but I'm no expert by far.

 

I'm in no rush to build this engine, I have the funds but I want to take my time and make sure I like what I'm doing. Infact I've had the engine for 2-3 weeks and I just got the engine stand today.

[Engy]

and yes, L20b pistons are 85mm (3.346")

and L28s 86mm (3.386")

 

so with your that bore you have,

so you should be able to run the L28s, its been done before

you just need to research harder, a-hole :)

 

the L20b stock piston and L28 stock piston have the same pin height,

 

:rofl: I knew that they would fit but my question would be would they work.

[Dawa]

just google it, you dodo bird!
 

googled "L28 pistons in l20b"

http://performanceforums.com/forums/showthread.php?67273219-Bang-for-buck-L20b-build-L28-flat-top-piston-to-valve-clearances

http://community.ratsun.net/topic/17486-l20b-w-l28-flat-tops-and-a87-peanut-head/

http://community.ratsun.net/topic/40769-pistons-for-l20b/

[Xnke]

You need to pull the head and measure the chambers..."former race engine" could mean anything from "I got all these parts let's slap them together and make them work" to "shave the head, dome the pistons, run the most aggressive cam the rules allow" to "this engine is totally stock, marshall, no modifications were made"

 

The aluminum retainers on top show that some money was spent, and the cam lobes have been cut heavily. The cam should have some info engraved or stamped on the back end, should tell you the maker and the grind number. You can figure out what the cam is like, and set the compression appropriately.

 

L28 stock pistons come in two flavors...10cc dish and flat-top. Only 81.5-83 non-turbo engines came with flat top pistons in the US market cars. There are aftermarket pistons available, but not very many. Not a real high-volume item...

[Stoffregen Motorsports]

You need to do some engine math to figure out the compression ratio. It's really easy. I could spell it out, but it's so easy to find engine math calculators on google these days. Just google "engine math calculator", and either havean engine shop cc the head or buy a cheap burette and do it yourself.

[banzai510(hainz)]

domed oistons on a L20 is going to be bad news for a street motor or you got really good gas.

 

if sprockets are not sharp just get a Jap chain and tensioner and slack side guide.

 

Most kits I see now are the USA made sprockets type sold thru Melling or Cyloyes. This not the good set . One waty yo tell is they have the 3 holes. The jap sets will have a 4 hole sprocket.

OS Giken sells a multi hole set. I seen at Napa.

 

Tsubaki sold the best complete sets along with beck Arnley but they seem to be drying up.

Nissan can get them if you need parts numbers.

 

Rock auto sold out most of the better sets now unless you buy in pcieces.