3K Head On 4K Worth It?

[Gtr rolla]

Hi guys as heading states is it worth putting a 3kc head on a 4kc is there any benefit or compression increase and is there a difference in valves and ports . Or just leave the the 4k head alone?? Cheers guys

[Evan G]

No get the 4kc head shaved unless its a 3kbp. 4kc havebetter valve stem seals aswell

[Willis]

I think 3k bigport heads give an increase in compression when put on a 4k block. But I think they're Hard to find. If I were going to pull the head off a k motor, I'd just buy a 5k block and stick my 4k head on it. But that's me..If you think it's worth doing then it is.

[Evan G]

have a look in my build thread to see what I done for compression and ports

[Evan G]

5k block with 4k head will lower your compression.

[Spencer[RL]]

5k block with 4k head will lower your compression.

 

Yup commonly used for turbo/supercharger setups.

[Gtr rolla]

I just wanted to get a little cheap power out of it until I drop another engine in . I've got a pair of 40mm solexes manifold extrators and 2in exhaust I might lighten the flywheel' and I thought I might get some more comp out of it by swapping heads of just shave the 4k one

[Willis]

Evan, I wasn't implying that the 5k combo would give an increase in compression. Just saying that i think if he's going to the trouble of pulling the head off an engine, he may aswell drop a 5k block in and put the 4k head on it or a complete 5k. Sorry for the confusion

[FOOMAN]

What would happen if a 3k head was put on a NA 5k?

[philbey]

I agree with evan; just do the work to the 4K head.

 

I see no advantage to playing with the 3K bigport head. For 150-250 bucks, you could have any head cleaned up and the ports opened to bigger than the 3KBP sizes. The 3k bigport is 40 years old, they're at the end of their life and there're a number of cases of people blowing the welsh plug out the back of the head and killing a motor. Plus they don't have decent the valve stem seals.

 

There is no simple 'put X head on Y motor' formula. Unless you know all your engine specs (piston size, ring height, crown to deck height, piston volume, gasket thickness, head volume etc) you wont know what compression you have until you open the engine.

 

If you can get away with having the car off for a couple of weeks, I'd pull the head that you have off, measure up, calculate and then send it to get skimmed, ports opened up etc.

[altezzaclub]

....and all this 5K confusion depends on which pistons are in the 5K, the deep "D" dish or the shallow "round" dish.

 

The 5K block with shallow dish pistons and a 4K head is a great idea, but then you have the hydraulic to mechanical pushrods conversion on top of that.

 

Cheapest to stick with the 4K. If you haven't measured head volumes and areas before, just ask. Its in here-

 

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

 

 

 

 

 

[GJM85]

c... c... ca... camshaft!

 

...bless you!

[Evan G]

+1^^^ engine is a air pump. no point giving tons of compression without a decent camshaft/weber/porting/extractors!