4K Modification Query

[AstralSky]

Hi guys! I've been browsing this forum site for information. I'm from the Philippines and I'm planning on building a "project" car. I already read the wiki about the 4k engine mods and it has given me a lot more information and started taking up notes. I would like to build my own engine because I am the one using it anyway. My question is about a 4K engine. I want a engine modification take can take going uphill at ease and much more on a acceleration power. But still have a good fuel efficiency and a bulletproof one. I don't care less running on top speed because it's not my style of driving. As far as I recall, the bottom end modification is the way to go. how about the transmission? should I go for a 5 speed or rally inspired 4 speed tranny? And about the differential gearing? what would be best? Lastly, anymore tips and suggestion for this kind of modification? Thanks in advance! :)

[altezzaclub]

I've just pulled the 4.3 auto diff out and am fitting a 3.9, so I can't tell you if it is more fuel efficient at 100kph yet. With the K50 box it runs at 3500rpm around 100kph, which I though was too much. If you are not cruising at 100kph much, then the 4.3 from an auto is great.

 

You are stuck with the K40/K50 ratios unless you go to a T, which is a lot of hassle for a very small improvement. The 5th down to 4th is handy on a hill, but only adds 300rpm odd at 3000. Then sadly if the hill is steep and you need 3rd you will suddenly go up 1000rpm, so it starts screaming... I haven't found a box with a higher 3rd or a lower 4th to spread those 3 gears.

 

The mods we did have made The Girl's KE70 go up hills much much better than when we bought it. It is no 6500rpm screamer, but has good pulling power between 3000-4000rpm, which is where it is most useful. The 270deg cam is better than a 280deg for that.

 

The next KE70 I get will have the crank lightened, be bored to 1500cc with 5K pistons and have the bottom end balanced. I'll either get inch and 1/2 SUs to try them, or bike quads. This one is great and I hope the 3.9diff will drop the revs at cruising without ruining the pulling power.

 

Take a read through the build if you haven't

 

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

[ke70dave]

its pretty much the same as any engine you want to go better.

 

easy: extractors and exhaust

medium: upgraded carby

more advance: higher compression, different camshaft, head porting

custom: turbo charged

 

but if you go stuff around with any of this, be sure to tune the carby for whatever you do.

[AstralSky]

Thanks for the idea. The thing is the car will be used in city driving and on the weekend maybe bring it to the mountains. And I don't drive that fast to on the open road. I do roughly 80 to 90 kph. So the 4 speed will do I think. And as for the differential, maybe a 4.1 will do. And do I need to change the flywheel to a lightweight one? Or the stock will do?

[altezzaclub]

4-speed will do, but 5speed is better and a quick bolt-in if you find one.

 

4.1 is fine, it will suit a 5speed well. I had the flywheel lightened a couple of Kg by the engineers while they were doing other stuff. It makes 1st and second accelerate faster, but the effect gets less as you go up the gears.

 

It depends on how worn the motor is right now. Do you need to rebore it? or just whip the head off for a valve grind? Do a compression test, then squirt a spot of oil down each cylinder and do it again. That will show you how worn the rings are. Once you decide what needs doing to get the motor back to factory spec you can decide what mods to do along the way.

[AstralSky]

4-speed will do, but 5speed is better and a quick bolt-in if you find one.

 

4.1 is fine, it will suit a 5speed well. I had the flywheel lightened a couple of Kg by the engineers while they were doing other stuff. It makes 1st and second accelerate faster, but the effect gets less as you go up the gears.

 

It depends on how worn the motor is right now. Do you need to rebore it? or just whip the head off for a valve grind? Do a compression test, then squirt a spot of oil down each cylinder and do it again. That will show you how worn the rings are. Once you decide what needs doing to get the motor back to factory spec you can decide what mods to do along the way.

 

The motor is somehow still on good condition though. Our local machinist said that the block is still good and no need to rebore it and it just needed some balancing. As for the head, it needed to be ported and polished. And I was advice to change my cams, valves and spring. And to make it a bottom end mod to suit the driving condition we have here. And a friend told me that lightweight flywheel have a faster acceleration but also tend to strain the engine internals if its too light. Any suggestion for a lightweight flywheel on a bottom end mod engine?

 

And I will stick to the 4 speed. what gearing then should I choose for the differential? a 4.10 or a 3.90?

[altezzaclub]

And I will stick to the 4 speed. what gearing then should I choose for the differential? a 4.10 or a 3.90?

 

I can tell you in a week when I get mine running with a 3.9. I expect you would want the 4.1.

 

I don't think you can lighten the flywheel much, they are 8kg stock and they made mine 6kg. I have never heard of a lightened flywheel affecting the engine in a bad way. The balancing is more important, but to do that you have to have the pistons, con-rods, crank and clutch all out to be balanced. So are you going to just hone the bores and fit new rings or put the same rings back in?? You could always ask filfrederick what he did, he build a 4K bottom end that ran to 9000rpm with a lightened crank.

http://www.rollaclub.com/board/topic/51097-4k-twin-cam/

 

If you pick a cam with max lift of 0.4" then you can use stock springs unless you want 7000rpm.

[AstralSky]

I can tell you in a week when I get mine running with a 3.9. I expect you would want the 4.1.

 

I don't think you can lighten the flywheel much, they are 8kg stock and they made mine 6kg. I have never heard of a lightened flywheel affecting the engine in a bad way. The balancing is more important, but to do that you have to have the pistons, con-rods, crank and clutch all out to be balanced. So are you going to just hone the bores and fit new rings or put the same rings back in?? You could always ask filfrederick what he did, he build a 4K bottom end that ran to 9000rpm with a lightened crank.

http://www.rollaclub...97-4k-twin-cam/

 

If you pick a cam with max lift of 0.4" then you can use stock springs unless you want 7000rpm.

 

A stumbled with my friend mechanic earlier and he told me that before I change a lightweight flywheel, I need to balanced out first the motor internals. And just like you said, pistons, con-rods, crank and clutch needs to be balanced well to go with the lightweight flywheel. Its like a love hate thing he said because fitting one in will have a great accelerating but also looses some torque. He told me that the stock flywheel will do. I just need to balanced the internals so it can run more smoother so I need to bore it and change some new parts and run in between the stock compression up to 10:1. One the other hand, he told me to focus more on the heads and cams.

 

And I don't want a screamer revving up to 9k. I think 7k rpm will be just fine. Thanks for the link. :) I'll read it from time to time and give me news on your differential gearing. But I think your right. I would want the 4.1 :)