Frankenstein L18

[AceOfDiamonds0]

Ok so here's an odd one.

 

So a couple weeks ago I picked up a '77 KC 620 that looks and sounds pretty decent and all but the guy I bought it from told me the motor is a rebuilt L18 with an L20 head and L16 rods. To top it off its got a holly 350 carb on it. It's quite gutless and gets maybe 17 or 18 mpg on the freeway. I did some research and found that the head is a U67 open chamber head.

 

He also put in a pretty beefy electric fuel pump because he said with the previous electric fuel pump the float bowl would go dry.

 

I picked the 620 up from out of town and it was then that I realized just how gutless the motor is. Going up any kind of incline it doesn't do so good. I guess I should mention it has a long tail 5 speed.

 

So my question is, what would be the purpose of sticking L16 rods in an L18 and would a 32/36 weber do me any good? It doesn't idle very even but seems to do ok when driving other than having no balls at all.

 

Oh and I did switch it from points to a matchbox dizzy and it still runs about the same. Definitely not any worse.

[AceOfDiamonds0]

Oh and I'll post some pics as soon as I get the chance.

[ggzilla]

The purpose of L16 rods is to lower compression. Top that with a carb too big and it will run like a dog

 

Maybe the PO took the L20B and pieced together this frankenmonster to sell the truck.

[flatcat19]

How does switching rods decrease compression? 

 

And since there is a difference in rod length, which pistons did he use? Which crank?

[ggzilla]

Good point. L16 rods are longer so I was wrong

 

I'd give the engine a compression test just to make sure. If it is low no point in changing carbs.

[flatcat19]

If L16 rods on L18 pistons, pistons aren't even hitting top deck. 

 

If L16 rods AND pistons-stroker motor. 

 

 

Who knows whats going on without a teardown. 

Lots of unknowns here. 

[datsunaholic]

L16 rods on an L18 crank would push the pistons past deck height unless they were custom pistons.  L16 rods are 2.8mm longer, so the pistons would pop out 2.3mm (stock L18 rods had 0.5mm understroke), which is more than head gasket crush depth.

 

The purpose would be to increase compression, but it only works with custom pistons.

[flatcat19]

Ah.

[RTB]

possibly flat tops with the timing off?

[ggzilla]

Holley 350 should run very well floored at high rpms. But run poor in normal driving

[AceOfDiamonds0]

Yeah at higher rpms it does alright but still not a whole lot of power.

 

All I know about the motor is what he told me. I'll do a compression test and that might give me a little better idea what I'm running.

 

I do have to run the timing a bit advanced. It won't run unless it's above 20 degrees BTDC and it runs the best between 28 and 32.

[flatcat19]

I wonder if the dizzy is even clocked properly. 

[datzenmike]

Look on the top edge of the iron block just behind the dip stick handle. The engine size is stamped there. If and L18 it can't have any L20B parts in it but pistons, and who would do that???? you'd have 7.6 compression

 

1/ That timing is crazy and won't run at that level. 12 is the normal static advance. When revved up another 20 degrees is added by mechanical advance. You're reading the timing scale wrong, mechanical advance is frozen or the pulley is from an L20B on an L18 crank.... something.

 

2/ 18 MPG says the carb is totally wrongly set. You should expect 50% better mileage if running the right mixtures.

[ggzilla]

Its a Holley 350 carb from a V8

[AceOfDiamonds0]

I tuned the holly 350 according to the book for that specific carb.

 

I read that the holly 350 was originally supposed to go on a Ford or Chevy 302 or something like that. I don't do V8's I only do datsun's lol.

 

I looked on the motor and it's stamped with L18.

[AceOfDiamonds0]

[AceOfDiamonds0]

 

[AceOfDiamonds0]

Mike, I don't think it has any L20B internals just the U67 head.

[AceOfDiamonds0]

With this current setup, does anyone think putting a 32/36 on it would be at all beneficial?

 

I don't like how this motor was built at all.

 

I was originally planning on finding an L20B to do just a full stock rebuild and swap this POS out but I'm thinking about doing a KA or an SR just because fuel injection is looking mighty enticing. I don't plan on racing it because personally I don't think trucks are for racing, cars are. But I think a stock KA n/a or a stock SR n/a would make for a good daily driver if done right.

[ggzilla]

Not enough information

 

If it has good compression, it is worth troubleshooting to find the cause of the problem .could be spark. Could be a lack of fuel. Could be the brakes are partially stuck.

 

Start with a compression test. Always check the basics.

[datzenmike]

L18 with U67 head will have stock compression so that's good. U67 has nice large ports and valves.

[AceOfDiamonds0]

I know it has good spark and is getting fuel. How could the brakes be a factor in how the engine runs though?

[datzenmike]

Brakes that are dragging will slow it down but mostly ruin the mileage. If you have a power brake booster the hose could leak vacuum and affect the idle.

[AceOfDiamonds0]

Oh gotcha. It's still early for me here.

 

No the brakes aren't dragging. I've checked for vacuum leaks on the booster and I just rebuilt the brake MC and bled the brakes last week and they work just fine.

[Russell]

Yeah at higher rpms it does alright but still not a whole lot of power.

 

All I know about the motor is what he told me. I'll do a compression test and that might give me a little better idea what I'm running.

 

I do have to run the timing a bit advanced. It won't run unless it's above 20 degrees BTDC and it runs the best between 28 and 32.

 

 

if your having to run this much timing i belive that your compression ratio is pretty low