How Does A 3K-B Make More Power Than A 4K-U?

[niland]

I have been doing alot of reading before deciding which k engine I want to overhaul, and according to the rollaclub tech page

 

a 3k-b makes 83bhp@6600 with torque 75@4600 and 1166 displacement bore 75mm stroke 66mm

a 4k-u makes 74bhp@5600 with torque 78@3600 and 1290 displacement bore 75mm stroke 73mm

 

I am scratching my head as to why a 7+ year older engine with less displacement can make more power than the 4ku.

 

I'm assuming its the Big port head, manifold and twin carbs that are making all the difference,

 

so if I put the Big port head, manifold and twin carbs on the 4ku it should make up the 9hp difference and alot more YES?

 

I have a bigport head and manifold

 

but should I go to the effort of sourcing a 4K-u block and use my bigport gear on it, or just port and polish the head on it and use my bigport manifold?

Edited June 23, 2013 by niland

[coln72]

Cam specs were different to.

[philbey]

Go out and buy yourself a 5k,get the 5k head ported to match your manifold and bolt it.onto.that

 

[niland]

Go out and buy yourself a 5k,get the 5k head ported to match your manifold and bolt it.onto.that

 

I much prefer the rev happy 3k and 4k engines.

Is it really worth sourcing the 4k-u block over any of the other 4k blocks?

I guess age of the block comes into the equation as they were the last 4k made. But what is it that makes them have the most power?

[niland]

Cam specs were different to.

so the cam in the 3k-b makes most of the difference, besides the bigport gear?

[rian]

I've never ever seen a 4K-U, did they even come out in Australia?

[niland]

I've never ever seen a 4K-U, did they even come out in Australia?

 

Yeah you can import them pretty easily. They came out in japanese and south african ke70's

[B.L.Z.BUB]

They are Jap spec. There are a few floating around.

[coln72]

 

 

I much prefer the rev happy 3k and 4k engines.

 

A 5k will pull pull 7000 plus with very little mods. Just how many revs do you want. Also,in my experience a 5k revs better than a 4k.

[niland]

A 5k will pull pull 7000 plus with very little mods. Just how many revs do you want. Also,in my experience a 5k revs better than a 4k.

 

Ive always liked the 4k because my 1st Ke10 had one. Ive driven plenty of 5k powered rollas but still have memories of that 4k.

I'm just trying to get some answers before I decide either way.

 

Already having a bigport head and manifold I'm sort of jaded as to whether to insist on using it or maybe just getting a 4ku and then using the manifold.

[philbey]

The main reason for more grunt out of the 3KB will be the compression ration, plain and simple. Alleged 10:1 vs the 4Ku 9:1.

 

There is no point sourcing a 4Ku block over the other blocks. It is the same block, with the same bore and stroke. The only difference for the 4KU is the dished pistons, which will render your 3K head useless.

 

3K bigport heads are overhyped and suffer 'talk it up' syndrome

 

If you're really keen on a 4K buy a good clean running one, pop the head off and have some work done. Up the compression slightly planing it and get the it port matched to your manifold, it will likely cost only 150. You probably need to spend that much on your 3KB head anyway.

 

5K's rev, anyone who says otherwise is talking guff. The reason they feel less revvy is because they've got a rubbish distributor advance curve suited to vans and the like

Edited June 23, 2013 by philbey

[snot35]

From memory the way that actually rate horsepower changed somewhere around that era, you're probably comparing apples and oranges. Everyone is right, 5K is the way to go. Stroke is the same and there's greater potential for bigger valves if you really want to rev it. Plus the port design on the 5K's that I've seen is much nicer. The short turn is actually a turn and not a step. The 4KU manifold might be one of the small port variants, so you wouldn't be gaining much.

[you_nes]

torque is what you can feel and the stock 4ku makes (almost the same) peak torque 1000rpm lower (coincidentally very close to the rpm that it will turn at 100km/h in 4th in most ke's)

[parrot]

As above, a K-B had a more aggressive cam, 10:1 compression and twin carbs to provide more fuel charge.

 

No reason why you couldn't shave a head and put a bigger cam in anything you desire

 

And before anyone jumps up and down. that refers to K-B's and 3K-B's

 

I have a great article from a late 60's Racing Car News with a review of an improved production KE10 Toyota were piloting around at that time. I'll try and put it up tomorrow. Has some good specific engines mod info

Edited June 24, 2013 by parrot

[GJM85]

I have a 5k with flat top pistons and a 4k head shaved and ported to suit a big port manifold. Made 44hp when the cam was 20 degrees out and before i'd sorted fuel and timing. It would easily make twice that and revs cleanly to 6500rpm.