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Flirty Wheels and other Flirty Bits


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Claire,

I note in another thread I can across that Mr Revhead posted on the 2nd February that you were considering upping the compression ratio on your 4K by possibly putting on a 3K head.

 

I think a little homework here might pay off here. From the picture you posted earlier in this thread, the pistons you have are "D" shaped dished pistons. That makes your 4K probably a 4K-U, which was different to other 4K series engines, which basically have flat topped pistons.

 

To compensate for the larger swept volume of the dished pistions in the 4K-U the head is also different to other 4K series engines. The "Heron head on the 4K-U has a different combustion chamber shape and depth to keep the compression ratio correct & better gas flow. The head itself is about 4-5mm deeper than a standard 4K head, and has head bolts & pushrods that are again about 5mm longer than those on standard 4K engines.

 

The problem is that if you plop a 3K head on top of your 4K-U with dished pistons you'll probably have more than a little compression increase. As someone else has calculated, when I matched a Heron head from a 4K-U with flat top pistons on a std 4K-C, the compression ratio would prbably be about 15 or 16:1.

 

The same result would occur if you place a 3K head on top of dished pistons. The larger swept volume of the cylinder compressed into a smaller combustion chamber in the head would probably finish up with a compression ratio that would be undrivable.

 

Someone might be able to correct me, but I think my theory is correct.

 

Someone else might have tried a 3K head on a 4K-U block with dished pistons: so I'd be glad to be corrected.

 

As the Heron head is 5mm thicker through, it should take a nice surface grind, which should give you the extra compression you require.

 

I'm doing up a 4K-U also at present, and I am sending my "Heron" head off next week for a overhaul & shave.

 

=)

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  • 2 weeks later...

that doesn't seem to make sense to me; if you have a flat top piston that generates 9.5 to 1 copmpression ratio with a certain cc head and then take that head and put it on dished pistons.......wouldn't that make lower compression?

I have a kc head, a 3kc head, 2 4kc heads, 2 4ke heads; the kc and 3kc have HUGE ports and the combustion chambers are identical

the 4kc's have smaller ports, heart shaped combustion chambers.

the 4ke's have TINY ports and the same cumbustion chambers.

now, you guys have some wierd stuff out there(5k's?) so i don't know how much of this is true out there.....i have never seen a dished piston on any "k" engine

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  • 2 weeks later...

**UPDATES**

 

heheheh i got my cam back today from Kelford Camtech :dance:

 

don't understand the spec sheet tho....

 

kelfordcams5lc.jpg

 

i don't know what any of it means tho :blinks: if someone wants to explain, please feel free :D

 

me & Mr Revhead are putting the engine back together this weekend.... well, I'm going to put it back together, warwick is going to sit there and drink coffee whilst telling me what to do :dance: hahaha ;)

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wow, that's an interesting cam profile, it's very similar to a sprinter cam

 

it's pretty much the best cam you can put in a 3k. it will give you lots of torque in a 4k/5k, and peak power at 6500rpm, instead of a little less torque but a bit more power and peaking at 7500rpm like mine or teddy's cam would. our cams open and close about 5 degrees later

 

your cam could have about 050 more lift, but at least you can use that cam with stock valve springs no worries

 

it's very nice to see a camshaft in a K motor which isn't stupidly large and a waste of time and petrol. i've often contemplated putting a cam with specs almost identical to yours in my motor, to pick up the torque down low, which is what makes a street car quick

 

overall it's a very good cam which will make your car nice and torquey to drive, without having to rev the tits off it to make its peak power, your guy at kelford sure knows what he's talking about, good stuff! :dance: :D

Edited by Super Jamie
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