L18 build.

[RetroRocket]

One-off engine design. Long-rod engine. L18 block & crank (five-bolt, fully counterweighted). Overbored from 85 to 86mm. Rods: L13 with Arp bolts (yes I have them in hand) c-c 139.9mm, 21 pin. Rod/stroke = 1.79.

Pistons: Genuine GM fitment 1999 Cadillac Catera, also used in Saturn engines and others, same part #. I have two; need two more. Compression ht 1.079" [27.4mm], pin dia .8268". The pistons have a very slight symmetric dome which I may need to bring flat to comply with deck ht and quench with head table; or not.

 

It should work out just right. Stock L18 has pistons below deck with 78mm stroke. You can just crunch the numbers using L18 rod c-c and piston c,ht [38.1mm] and do the math against those numbers. So, 130.2mm + 38.1 = 168.3. In L18 this combo lies 0.50mm down below deck because it uses same c.ht and rod length as L28 but has a 1mm shorter stroke (78 vs 79), so add back 0.5mm distance, now 168.8 length to zero deck. 168.8 - 139.9 = 28.9mm..The GM piston is 27.4 c.ht and therefore should be below deck by 28.9 - 27.4 = 1.5mm dome and all.

I'll have to mock it up and check it. My past calculations brought it to deck and I thought I had to shave the slight dome...maybe not. The Catera c.ht. spec I'm using might be off slightly (low) can't find my notes. Compression ratio with the closed chamber head should be reasonable. I want to keep it below 10:1. It is an engine for street use and occasional autocross.

 

I have a five-bolt aluminum flywheel for it. I have Electomotive crankfire on the car now but I want to configure an optical L28ET distributor with wasted spark for ignition. I thought up this engine design about 30 years ago, bought the L13 rods ordered from a local Nissan dealer and they've been in storage since. I've built the taller block engines in various configurations but I want a five-bolt sohc low block engine for my 510. 

 

Thoughts?

[datzenmike]

The L18 piston is 0.55 below the deck... close enough.

 

I get 8.96 and because the dome volume is unknown I treated these pistons as flattops. I also assumed the crushed gasket thickness to be 1.2mm. If you keep the dome the compression will be higher.

 

L18 stroke is 78/2=....... 39mm

L13 rod length............. 139.9mm

Compression height..... 27.4mm

total............................ 206.3mm

 

The deck height on an L18 block is 207.85 so your pistons stop 1.55mm below the deck. 

[RetroRocket]

Yeah, I'm getting about 1,5mm below deck too. The dome is slight, it reminds me of a roadster piston with a curve to the top. Maybe I'll search for another piston source with a bit more c.ht. I haven't searched for a long time so there might be something interesting in 86mm available now.

I'm having difficulty finding my last two pistons after having great luck at first (brand NOS Genuine GM with rings for $13/each). They are discontinued and some online dealers want full price.

To the back-burner for now....although I could deck the block down...

[RetroRocket]

What do you think re the optical feed LD28ET distributor as a crankfire (it is directly gear driven off of crank rather than any timing chain involvement) and it works on the same ht block L18 = L28. This is a budget build. I have a homemade f.i. manifold available which I've bought but never installed. Or I have SSS twin SU's that I have dual Patton injectors kit for conversion. 

Is a camshaft angle sensor timed off of a cam sprocket-attached trigger wheel, with sensor attached through valve cover, something that is done?

[datzenmike]

All L series 4 or 6 cylinders are worm gear driven off the crankshaft. 

 

 LD is a diesel engine, I'm sure you meant L28ET from the 280zx. It's a six cylinder so not sure how that would work on a 4 cylinder. The later Z24i in the 720 truck has a CAS crank angle sensor or is it a cam angle sensor? distributor. 

 

The block height has nothing to do with the L series distributor choice.

 

Usually a trigger wheel is fitted to the crankshaft.  

 

 

I would just get an EI matchbox distributor from a '78-'80 L20B and run the SU carbs.

[RetroRocket]

Typo on the LD28, I meant L28. I'd use the optical plate from a Z24i into the L28ET distributor. By block ht I';m referring to the distributor shaft/housing length, i.e., can't use a Z24i distributor because it is too long.  But L28 is correct length/height distributor to fit L16/L18. I have Electromotive crank trigger now on my L18 in the car now but I think it is squandered on my engine compared to an engine (like my '75 20R toyota chinook) where distributor mounted on the cyl head gets signal from a flopping timing chain drive. The L engine is basically right off of the crank coupled by helical gear with little slop/spark scatter. On the toyota I could adapt the cyl head distributor to become a cam angle sensor and take the crank angle directly from the crank with a trigger wheel (the electromotive setup) and get a lot more bang for the buck vs using it on the L18.

 

I'm thinking that 1mm cut from the deck would solve the low c.r. easily. 

 

I do like the elegant simplicity of the SUs. I've used them before and tuned by changing springs and carefully sanding needle valves to eliminate flat spots in acceleration. I disconnect the choke actuation so that the jet isn't moved around and instead configure a cold-start system using an antique aircraft primer pump for cold-start. Plus auxiliary air valve with thermal spring actuation can be adapted for fast idle.

[datzenmike]

Well 1.55mm deck and 1.2mm for the head gasket, that's 2.75mm. That dome is bigger than I thought. Do you have a volume for the dome? 

[banzai510(hainz)]

one made in USA one made in Germany(Opel ?) same part number.

Edited July 8 by banzai510(hainz)

[iceman510]

The Catera was basically an Opel.  Box with "made in USA" is probably a lie.

[RetroRocket]

Yeah, it is a European engine but it's good because there is a Euro Quality conformity standard that applies to such parts. I don't understand the details but it's good for quality assurance.

 

I don't know the dome volume and haven't seen any specs for it anywhere. I'd rather have it flat for a better quench to the closed chamber head but this is a budget build and I can live with the baby dome. List price is about $300/each for that GM part#. I think that they are available aftermarket but for more than I want to spend on them. I'll keep searching the part # on Ebay. That is how I stumbled on two for ridiculously low $13/each.

[RetroRocket]

Here's a source for $50/each:  https://www.gmpartsonline.net/oem-parts/gm-pistons-90571284?srsltid=AfmBOorfUboZcD10q9pqP7SpHliHdiklU0vw7kMPgqOaX0tmor_3Oi8R

 

Otherwise I'm seeing them for about $160-$180/ea. I may pay the $100 for the pair I need for the set because half a set is useless and they are getting scarce.

They are floating pin pistons but the rods aren't oil hole drilled and I'll just go with fixed pins.

 

 

[RetroRocket]

I went ahead and ordered the two @ $50/ea but I'll likely get a response that they are NLA in spite of their Ebay ad.

BTW, the same log rod approach would work with L28 and FJ20 or L13 rods but with 79mm stroke they wouldn't be so far below deck.

The photo makes the dome look huge but it is really subtle. It could be machined flat for L28 use.

[datzenmike]

52 minutes ago, RetroRocket said:

 ...I don't know the dome volume and haven't seen any specs for it anywhere. I'd rather have it flat for a better quench to the closed chamber head but this is a budget build and I can live with the baby dome. ...

 

 The flattop piston should be as close to the deck height as possible when used with a closed chamber head. This means the piston is basically separated from the head by the thickness of the head gasket about 1.2mm. At TDC the air is violently squeezed out from between them and into the combustion chamber maximizing swirl and mixing of the fuel/air. Adding 1.55mm to the piston top will reduce this affect.

 

[RetroRocket]

yeah, I know. I've been working on Volvo redblocks, datsun L's and mercedes inlines for a long time. Yes everything you said and that's why the piston top should be in one plane, parallel to the flat of the head. Did you see my design for 0.060" overbore L28 to 87.5mm and use of eyebrowed Toyota v6 sohc same side pistons? For use with P90 head (closed chamber like A87 shape)...here, image:

 

The flat table locates at the flat quench pad on the head. Due to datsun asymmetric pairing of valve ports the valve pocket cuts on piston tops only line up half the time. I am cutting valve reliefs (project) to make the eyebrows symmetric Int. and Ex. on every piston. Here; I need an actual piston vice to accomplish what I'm doing..

 

The point is, quench is going to be far more optimal with a flat top section or area of a piston top than curved (unless the curve of the combustion chamber matches the shape of the dome.  I was hoping in the L18 case for there to be too much overdeck piston ht and that I could machine (lathe) down the dome to be a more flat area for quench. Anyway, the c.ht. on these 3VZE IIRC pistons and the partial dish-top configuration allows for  high quench effect in L28 block without creating a too high c.r.  I can't remember the spec..21cc maybe of dish region but with a functioning flat top region. The clay volume rests above the dish area which creates a distinct combustion chamber combo, no?

 

Back to the L18 build, maybe I'll force induction and not worry the c.r./below deck issue. I'll get a pic of the efi intake I have yet to use.

BTW, anyone know the proper bore finish to best suit the type of OEM piston rings that piston #90571284 comes equipped with?

Edited July 9 by RetroRocket

[RetroRocket]

I ordered two 90571284 GM pistons for $50/each but days later received notice that they are no longer available as the part is discontinued.....How about deleting their own ad if the item is not for sale?? This has happened with several Ebay sources for these genuine GM pistons. They process the payment and then figure out they have nothing available, then refund the purchase price. What a PITA these online dealer/suppliers are.

[banzai510(hainz)]

I was going to say. Opel. People in Germany dont really rebuild Opels or really anything. When I lived there they never keep their old cars. No need to make parts.

 

I thought one can get L18 flattops in Austraila Steward Motor sport?

[RetroRocket]

what do flat top L18 pistons have to do with this L18 build thread about use of 140mm rod c-c have to do with c.ht 38.1mm you are referring to?

Please don't hijack

[RetroRocket]

Now re finding obsolete parts.......that part is relevant. 

 

BTW, if L18 flat top, = L20B flat top and is a good choice for a budget build L20B. An easy way to boost performance on a truck L20B with W53 closed chamber head is to swap in stock L18 (us market) pistons onto the rods. Same dia and c.ht. and pin. The dish volume change is 11.36 -4.36 = 7cc subtracted in c.r. calculation to a nice streetable c.r. I did this on my 720 with SU's but otherwise stock engine and it pulled hard. I could haul a big load of topsoil no problem.

 

Z20E pistons are the lowest c.ht. of those that would fit bore and are commonly available but they are still way too tall to use with the L13 rods. 

 

 

 

[RetroRocket]

RE piston source for GM 90571284 (rare), this set from Enginetech shares the specs. They are $320/set of 6: https://www.ebay.com/itm/363550188284?_skw=Cadillac+Catera&itmmeta=01KX4JK5F5F19WE2KSQCV9HGN7&hash=item54a547a2fc:g:ZOEAAOSwBahVGwca&itmprp=enc%3AAQALAAAA0DKQclQvzFwZQpmMrsO4LuodjIdDq19n%2BrDI78Btm2AXnsjFM4EYrDEDgvOI%2BbrOjscodQWbA0U%2FvmafedYZANrUtwUmtVy6sX89T9RX3LsaLJJ7QvdylBDkVbJLzR9yYBqzl%2BRZRXywvTN2SzJq5JNpIzl4mbqXgUnrL8VO2PVVtjiDn7%2BGaGpCmqQuZoYUoSziDUqnQH0EFlSC6PjbecGbWnLUfnssrxXV%2B3MlRt13lhTrhLwxQBJFbSkBDUqv%2BxfZ2gx8NG0c%2BvsVv%2FBVI7A%3D|tkp%3ABk9SR9bXzJLpZw    free shipping, so $53/each.

Too bad I don't have six of the L13 rods because If I did I'd build a long rod L28 instead. r/s = 139.9/79 = 1.77.  It wouldn't have the 'below deck' issue like the L18 build because stroke is 79 in L28 and only 78 in L18 sharing same rods.