Turbo Charade Pistons Into 4k

[Rolla__Boy]

What sort of diff does that car have in it?

[love ke70]

1971 alfa romeo berlina lsd

4.3:1ratio

[Rolla__Boy]

See these are standard corolla diffs I have been breaking, If you are careful with that one, I am sure you wont do any damage.

[love ke70]

pfft careful, theres a fair bit of oil around one side of it tho, gonna have to look into that.

but yeah, this car was used for drifting with this diff so I'm pretty sure itll hold up to a fair bit of punishment

I'm tempted to put my spare ke70 diff in once its running, and drop the clutch...fun to see the result :P hehe

[Boost+k]

pfft careful, theres a fair bit of oil around one side of it tho, gonna have to look into that.

but yeah, this car was used for drifting with this diff so I'm pretty sure itll hold up to a fair bit of punishment

I'm tempted to put my spare ke70 diff in once its running, and drop the clutch...fun to see the result :y: hehe

 

 

weld up the sstandard one then go find a closed road and go for a real spin... its quite surprising how fast a car will spin on the spot with a locker.

 

23/16 LOL i havent blowen any boxes yet just a few diffs... i'm only running a 4spd haha i have a 5spd for when it blows :P

 

my clutch is still the standard one that came with the car so who knows what condition it was when i started... i got a new one sitting there but havent been bothered to do it yet

[Rolla__Boy]

I would change it, and I doubt you will have any issues once you do :y:

 

 

When you say closed road, of course you mean on someone's private property :) :P Don't ya

[love ke70]

yes of course, private road :P

[Dan]

Postwhores.

 

Will 4k/5k rods fit a 3k, and is there a difference in piston bore?

[Teddy]

Lets do some maths..

 

3K = 75mm Bore, 66mm Stroke

4K = 75mm Bore, 73mm Stroke

5K = 80.5mm Bore, 73mm Stroke

 

If you have a 3k, with some work (Re: :cool:) you can put a 4k Crank and Rods into a 3k

~ 3k and 4k have the same bore, but by putting 4k stuff into it, you bump up the compression. I'm not sure how much displacement you end up with tho.

 

i think I'm headed in the correct direction?!

[irokin]

4K stuff in a 3K block should have the same dimensions as a 4K...why you'd bother doing it except for complying with rally regs is beyond me. Compression will be the same as a 3K head on a 4K...

[Dan]

Reality is I'm trying to get more power and reliability out of my engine illegally (according to junior sedan specs i can only race 1200s). As long as it looks like a 3k on the outside, once those seals are done baby I can do whatever i want :cool: .

 

Actually, on recollection, I think I didn't explain it correctly. The reason why I want to know about the K rod interchanges, is because I read earlier in this thread that the 4k commercial/5k rods are good for 10,000rpm, rather than the 3k which I have read elsewhere is good for 8,000rpm. This certain mod I want to do for reliability. No one will notice, its not as if I'm going to go out there and blitz the competition or anything. Just more fun for me, and not have to worry so much when I thrash my car.

 

Thanks for the help!

Edited January 19, 2006 by Dan

[Felix]

not quite.

 

a 4k block is around 10.5 mm taller than a 3k block (3k and 4k share the same pistons). if you were to put a 4k crank and rods in a 3k the pistons will poke 10.5 mm out of the top of the bore at top dead center.

 

the 4k crank has 7 mm more stroke. ie, the crank has 3.5mm more throw above and below the crank centerline.... also 4k rods are ` 7mm longer.

 

if you were to build a 3k blocked cheater motor with a 4k crank and rods, you would need pistons with a lower 25mm pin height as compared to the standard 35.5mm pin height to account for the 10.5 mm extra from the longer stroke crank and longer rods.. with a 4k crank and 3k rods you would need pistons with a pin height of 32mm.

 

:cool:

Edited January 19, 2006 by Felix

[Dan]

Another thing I'd like to ask, is whether the 4k rods will bolt up to the 3k crank. This is essentially what I was asking in the first place. I should have simply asked whether the stroke was made up in the rod, or in the crank, or both. I want a beefier rod, in other words.

 

God damn it, Felix, your a bloody legend; you answered my question before I even asked it!

 

Hang on, one more thing; will the 4k rods bolt on to the 3k crank?

 

Fark this is the third edit!

 

I take it that if 3k rods will bolt to 4k crank it would work vice versa? Then I would need pisons with a pin height of 32mm, correct?

[Felix]

yes, both a 3k and a 4k (and 5k too) use the same rod and crank bearings. they all run 18mm little ends on the rods.

 

you would just have to relieve the 3k block with a die grinder to clearance the crank and rods.

 

 

I take it that if 3k rods will bolt to 4k crank it would work vice versa? Then I would need pisons with a pin height of 32mm, correct?

 

yes, as you only have to account for half the extra crank stroke. :cool: not as strong as a 5k rod though.

[Dan]

From what I understood, 4K commercial rods and 5K rods are both the same?

 

If not then 5k rods would be the way to go for me, providing that the rod is the same length as the 4k rod (dreams that the crank makes up the stroke) well i can dream.

 

If I were to chase the 32mm pin height for the pistons they would have to be custom made, yes?

 

Dan.