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peterd

5K Head 4K Block

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I picked up my head today from the engine builders and was told that it was a 5k head. I thought it was 4k as it sits on a 4k block.

From what I've read, 5k on a 4k block increases the compression and isn't a good idea.

The car is a ke35 with a gm trimatic and is quite spritely around the city. Most people say that the 4k auto combination is a dog and with a 5k head, it should be horrible, but its not.

There is a 2mm spacer with the head gasket. The bore is 75mm. (4k)

I have no idea what cam is in it. When I get it back together, I'll see what the compression is.

Has any one else tried this combination?

I've added some photos of what I have.

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Edited by peterd

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It all depends. I've seen 4k's with flat and dished pistons. Same with 5k's. Looks like you have flat pistons and a dished piston head so your compression should be quite high. Someone's tried to lower it a bit with the 'head spacer'. Though don't know what you mean by that, I'd assume they're just using two head gaskets?

 

 

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That's definitely a 5k head, you can tell by the lugs under 1 and 4 spark plug holes. Your pistons also appear to have a bit of a dish in them. Maybe you actually have a 4ku!?

A 5k head on a flat top 4k would normally raise the c/r far too high.

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While the head is off, measure the volume of the combustion chamber, then you can calculate the compression ratio. All you need is a pipette or burette, or at the worst a couple of syrnges, such that you can measure about 25-32ml accurately.

 

Then you can decide how thick the spacer should be to run it at whatever compression you want.

 

The head surface looks very uneven.. did someone use a grinder on it? It doesn't look like it was skimmed flat.

 

Why was the head taken off?? Head gasket blown from too much compression?

 

There is a picture of a head with the plastic over the combustion chamber and the pipete I used in here-

 

http://www.rollaclub.com/board/topic/42407-the-girls-ke70/

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Well I did my homework today and came up with these figures.

 

bore 75mm, stroke 73mm, gasket diameter 78mm, gasket thickness 1mm plus 2mm shim = 3mm, combustion chamber volume 17.5mm, dished piston volume 6mm ( a figure I got from a forum)

 

using http://www.csgnetwor...m/compcalc.html

 

I get the awesome compression ratio of 13.5:1, which corresponds to the 14:1 mentioned here. http://www.rollaclub...head-vs-4k-head

 

The car was running fine on 95 octane, but I think I might change to 100 octane. (or methanol!)

 

My mechanic mate looked at the motor today and couldn't find any damage to the pistons or cylinder bore from the high compression and said to make sure I properly warm up and cool down the motor each time I use it.

 

The head was off because my 13yo son blew the head gasket by starting the car with full throttle. The head reco guy said that apart from the gasket going, there was a hole in the water jacket which needed welding and said it had been leaking for a while. The head had already had a lot taken off it. There's a mark which looks like a grinder mark on the surface which my mate thought was a burn mark. (from memory)

 

The head spacer (shim) is a 2mm piece of sheet steel cut to match the gasket.

 

A few weeks ago I asked on this forum if there is much advantage in changing the auto to a manual. The car goes really well as an auto, and now I know why. I'm not a burnout type of guy, so I think I'll leave it as it is and see what happens.

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don't look very dished to me? I thought dished pistons looked like this.

 

post-9116-1272432042_thumb.jpg

 

They're what are commonly referred to as the "D dish" pistons which have a volume of about 22cc. The OP has "O dish" pistons which are normally around 6cc.

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combustion chamber volume 17.5mm,

 

Lol! That is TINY! Around 30cc is normal for 4K. Go for it, if it runs just use it.

 

Imagine it with a DCOE Weber and extractors on a hot cam!! Then it could really breathe.

 

The manual gearbox would make it a lot more direct and involving to drive, much more fun and it gets the power down better while using less fuel. You've still got to go through the hassle of changing it tho'.

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Its got extractors and a rejetted aisin carb. It goes great so I think I'll wait until it blows up and then do the manual trannie swap when a new engine goes in. I've got no idea what cam is in it. I wondered if it was a speedway engine or just a bits and pieces in the shed engine for fun. Lets see how long it lasts.

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Has the head been skimmed flat this time? Checked for flat?

 

It looks like another head we had where someone had used a flapper wheel or some similar abrasive disc to clean the gasket off. It rounded all the edges slightly and groound a few shallow grooves into it.

 

I wondered if this contributed to blowing the gasket.

 

The guy that built it was no dummy- if he did the 3K head with a spacer and extractors on a stock carb he built the cheapest neat mod he could. I would've put a cam in it if it was me...

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yes the head was skimmed and reco'd by a popular place in Perth, but I don't know it's history.

 

The end result might be the perfect solution to adding power to an auto car. I can see the head gasket blowing every week if it was in a manual with the higher revs.

Time will tell how long it lasts. I'll let you know when it blows up!

 

The car is just some fun for me to learn about mechanics and have some fun. I'm not relying on it. I've got a gas guzzling, extremely reliable Kluger as a daily, with no user servicable parts. (14.5L/100km average)

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(14.5L/100km average)

 

My old ute struggled to get 18l/100km on the highway. 14.5 sounds good to me :)

 

Back on topic, can you get copper head gaskets for 4k's. Used to see 5k copper head gaskets advertised in the past. Just thought you may be able to use a copper gasket instead to the standard gasket and spacer.

Edited by coln72

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