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Frankenstein L18


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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.

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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.

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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.

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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.

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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.

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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

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