I'm rebuilding my 5k engine I have 3k head and a 5k head.

What is the best to use on a 5k? 

I have heard that the 3k head has higher compression but is it a better head?

Would i be better modifying my 5k head?

Got photos? There are several 5K heads depending on the type of piston. Do you think the combustion chambers are bigger on the 5K or the 3K?? You might have to measure them for volume with a burette.

Actually, the first thing would be to check if they are both straight and free of cracks!

The engine has D dish pistons 

The 5k had a blown head gasket. I haven't found any cracks in the head.

The 3k head is in a working car. I haven't removed it yet.

 

The 5K head will have a very flat combustion chamber if it has D-dish pistons.

The 3K is 1166cc, the 5K is 1486, so its 27% bigger in capacity. The 3K runs about 29cc in the combustion chamber, the 5K's D-dish piston holds 22cc and about 12cc in the head, so you might go from a combustion chamber of about 34cc to one of 29+22=51cc.  You gain some from having a bigger cylinder in the 5K block, but I'd say using the 3K head and the D-dish piston will drop the compression markedly.

If you're not using the 3K motor, pull the head off and measure everything yourself, its the only way to know.

Should i use O dish pistons to get a higher compression?

Can i even use a O dish piston in a D dish engine?  

Sure, they should all be interchangeable.  Is the 5K due a rebore and a rebuild?  Its a much bigger job than just doing the head!

Don't rush to buy pistons until you've measured the volume of the 3K combustion chamber, you'll need to decide the best way to get the compression ratio you want. Without touching the block you could use the drop in compression from the 5K pistons & the 3K head and turbo it!   Also a much bigger job than just doing the head!

It still ends up too low for turbo. 3k head on a 5k with D's will give you about 7.5:1 CR. Take 100 thou off it and you still won't get it above 8.5:1. If you're using the D's just use the 5k head. Get it surfaced and give it a freshen up. 

 

Edited January 12, 20206 yr by Taz_Rx

I decided to get o dish piston and use my 3k head.

can i use 5k lifters and pushrods with the 3k head ?

8 hours ago, chris76 said:

I decided to get o dish piston and use my 3k head.

can i use 5k lifters and pushrods with the 3k head ?

Nope the head height is pretty different. 

It'll either need custom pushrods or a non hydraulic cam with solid small block chev lifters datsun A12 pushrods and 4k rockers.

Edited January 20, 20206 yr by kickn5k

What’s the difference between 3k,4K and 5k rockers? Is it the height?

would I need to get my cam reground to suit solid lifters?

2 hours ago, chris76 said:

What’s the difference between 3k,4K and 5k rockers? Is it the height?

would I need to get my cam reground to suit solid lifters?

3 and 4k rockers are adjustable, 5k aren't. Not sure if 3k and 4k are different, only ever had 3k's for the bigport heads(everything was scrapped).

The ramp rate on a hydraulic cam is different to a solid cam, so unsure if you can change the rate. Probably best to start with a 4k cam. Where are you located I may be able to help with parts.

2 hours ago, kickn5k said:

3 and 4k rockers are adjustable, 5k aren't. Not sure if 3k and 4k are different, only ever had 3k's for the bigport heads(everything was scrapped).

The ramp rate on a hydraulic cam is different to a solid cam, so unsure if you can change the rate. Probably best to start with a 4k cam. Where are you located I may be able to help with parts.

 

I'm from  Newcastle NSW.

2 hours ago, chris76 said:

 

I'm from  Newcastle NSW.

Ok, once you've decided which path you want to take, I can point you in the right path to someone closer than Vic. I only have a spare set of 4k rockers, I thought I'd kept the new lifter and a12 pushrod combo but I must of gone with one of the 2 5k's I had sold a while ago.

BUT FIRST, you'll need to make sure the 3k head is a "bigport" or not. Does it have a welsh plug in the back of the head or is it a 4 bolt plate? If it's a plate it really isn't worth your time messing with a cylinder head that really isn't any better than what you have. 

 

18 hours ago, kickn5k said:

Ok, once you've decided which path you want to take, I can point you in the right path to someone closer than Vic. I only have a spare set of 4k rockers, I thought I'd kept the new lifter and a12 pushrod combo but I must of gone with one of the 2 5k's I had sold a while ago.

BUT FIRST, you'll need to make sure the 3k head is a "bigport" or not. Does it have a welsh plug in the back of the head or is it a 4 bolt plate? If it's a plate it really isn't worth your time messing with a cylinder head that really isn't any better than what you have. 

 

It's not a bigport head .

the rockers are adjustable they look the same as 4k rockers.

maybe i  could use A12 pushrods, 202 lifters and use my 3k cam.

 

This is my opinion but why stuff around changing heads, rockers, cams etc

Get your existing cam reground to whatever specs you want, port match the head to the manifolds or get it ported if you want, add decent carburation/exhaust and go have fun.

 

This is what I did with one of my 5ks - Wade 169 grind cam, 3k-b carbs, extractors and 2" exhaust (plus a few other things 😉 ). This engine would spin to over 7500rpm all event with bursts to over 8000rpm  where the tacho stopped.  Without the issue of adjusting valves all the time.