assistance needed in building a forged L20bet

[matto1kute]

Hi everyone. I'm building up a L20b turbo. I'm using forged pistons, L20b block which has been bored out and since reading about L series turbos it seems the stock conrod bolts are a weak link. Is this true? Should I go ARP bolts? Also I have a u67 stock head but would it be any advantage to goto a z or ka head? Is it very hard to chuck on a L series?

[datzenmike]

The stock rod bolts are good to 6,500-7,000 at least. Haven't heard they are 'weak' but if revving higher or running longer at maximum there's no harm in using something stronger. Then the problem becomes the next 'weakest' part... are the rods strong enough???

 

There's a guy in Vancouver, his name is Kieth Law and he's mostly on  .the510realm  who has a blow through carb turbo L20B with 250 RWHP and he has forged pistons and rods. He easily runs to 130+ MPH on a 4.625 differential and turns 8,500 RPMs. Engine is 13 years old! But has everything needed to keep this engine alive... oil cooler, alcohol injection, EGT gauge, boost control, air fuel gauge, inter cooler.. you name it, he has it. The car is extremely hard core.

 

He's often posted on this... http://www.the510realm.com/viewtopic.php?f=30&t=407&hilit=turbo+forum+questions+and+answers

and is known as bertvorgon http://www.the510realm.com/memberlist.php?mode=viewprofile&u=93

 

HEADS...

The U67 is a good choice and the easiest.

 

The Z series are a poor design for good flow. It does have cross flow, hemi combustion chambers and dual plugs but this won't make up for it.

 

The KA24DE can be done but the dual timing chain is a nightmare. There is one in Australia that was a turbo L20B block and KA head.

The KA24E would be simpler. Both KA heads have an oil drain back hole that needs welding up because it opens into the L series cooling system. 

 

 

 

The L series have 5 very large main bearings supporting the crank and will support huge amounts of power. The L20B crank is fully counter weighted and is smooth revving

[Stoffregen Motorsports]

Do you already have the pistons? If not, use long Z20 rods. Better rod/stroke ratio.

 

Stock rods can be massaged to get better longevity (polishing, shot-peening, metal-lax, cryo treating, etc), but I might consider Carillos or equivalent.

 

If you do use stock rods, definitely use ARP bolts and torque them using their guidelines and their lube. You tighten them to proper torque and loosen them 3 times. The third torque is the final tightening.

 

Also, I would have the block o-ringed for better head gasket sealing.

[scooter]

You could put head studs in too, lots of people run the stock bolts and stock main bearing bolts but I don't like the idea of running 40 year old used fasteners inside my expensive motor.

 

The stock rod bolts are pretty strong but I'd put arps because it's the highest stressed bolt in the engine.

[datzenmike]

Age won't hurt the L head and rod bolts. They are not like the 'torque to yield' bolts used once and throw away used today, however you are limited by the strength of the old bolts and stronger ARP won't hurt for sure.

[matto1kute]

OK I've got some more goodies coming in so now I can elaborate a bit more. The bottom end I'm using is a L20b that's been bored and had Mercedes full floating forged pistons fitted. Using a u67 head the compression was setup to 8:1 but now I'm fitting a Z18et head and I couldn't find the combustion chamber size for a z18 head so I'm not sure what the compression will be now. I know the z head won't flow as good but I'm using it because I like the idea of cross flow plus it was easier to get a turbo and efi manifold. I will be using ARP rod bolts and most likely a megasquirt computer. Can anyone tell me what's a good turbo that will fit the stock z18et manifold, what throttle body I should run, what my compression is and what sort of power I should be making? Its going in a 620 Ute btw

[datzenmike]

I've found two Z head combustion chamber sizes.

 

I have measured the Z20E (from an S110) a Z22(S) from a 720 and the Z24 that only comes in the 720. ALL were 57cc, checked them all twice. Compression ratio for all are about 8.5

 

Over here there is a 'Mileage Option' 720 truck with a Z20 engine that has a compression of 9 to one. As the pistons are flattops identical part number to the Z22E (S110) then the 57cc head won't work. I reverse engineered that and found that the mystery Z head size must be around 45cc. Several years pass.

 

Someone posted a picture of a Z20 head from a 720. Low an behold the chamber is subtly smaller.and while the regular combustion chamber is perfectly round the 'smaller' one has two small quench areas on either side.

 

Round 57cc combustion chambers

 

Z20 Mileage Option 45cc? combustion chambers. Note the flattened left and right side quench areas.

 

 

 

 

The point is that a 57cc head in a tiny 1.8L engine will have a compression in the low 7s and will barely drag it's ass around. I assume the Z18 is basically an L18 bottom end? If so, then a 45cc combustion chamber gives an 8.5 compression.... perfect!!!

[matto1kute]

So if it's 45cc and so is a u67 head then my compression should stay at 8:1. The head I'm getting is a z18et head so still not sure of combustion size :/

[datzenmike]

If the Z is about 45cc then yes 8.5 (ish) compression. Can't see any engine, turbo or otherwise being 7 to one compression. Please post a picture of what you get. I only have two of that Z20 head and would like to have a 'for sure' Z18ET head picture.

[matto1kute]

Will do when it rocks up.