Hks Crank Question

[Nismo_Boy]

I have N1 block with HKS 2.7lt pistons and HKS rods, but only a R33 GTR crank;

Can I simply upgrade to a HKS 2.7lt crank, or do I need to buy a 2.7lt crank/rod combo?

No chat, just yes or no - If no tell me why.

Thanks.

[Beer Baron]

there is no such thing as an HKS 2.7 litre crank. and as for the '2.7 litre pistons' in what way are they 2.7 litre pistons? pistons size doesn't equal capacity. it's bore X stroke which is the deciding factor in the CCs (yes obviously head combustion chamber size makes a difference but we are not changing heads). HKS use the same pistons in 2.6 litre kits and their 2.8 litre kits.

if you want an 2.8 litre then you will need new crank and new rods. your current pistons should be fine (just make sure you match the pin size - ie don't get 22mm rods if you don't currently have 22mm pins which is unlikely).

[Nismo_Boy]

there is no such thing as an HKS 2.7 litre crank. and as for the '2.7 litre pistons' in what way are they 2.7 litre pistons? pistons size doesn't equal capacity. it's bore X stroke which is the deciding factor in the CCs (yes obviously head combustion chamber size makes a difference but we are not changing heads). HKS use the same pistons in 2.6 litre kits and their 2.8 litre kits.

if you want an 2.8 litre then you will need new crank and new rods. your current pistons should be fine (just make sure you match the pin size - ie don't get 22mm rods if you don't currently have 22mm pins which is unlikely).

I know piston size dont = capacity. Interesting info though, the owner of the motor/car asures me it has "oversized HKS pistons". quote "it's now 2.7lt" Maybe i'll get the sump taken off and have someone look in there before I exchange cash

Edited May 11, 2007 by Nismo_Boy

[bnr#@]

Its close to 2.7 if the pistons are 88m which is what he most likeley means

[2gceffy]

definetly get someone to see whats exactly in there

[djr81]

Well how much oversize are they? Oversize pistons can make a bit of a difference to the engine capacity.

Remember stock GT-R

Bore: 86mm

Stroke: 73.7

Capacity: 2.568 litres

If you overbore the thing by 1mm (Not that you would necessarily want to straight up)

Bore: 87mm

Stroke: 73.7mm

Capacity: 2.629 litres.

So a 1mm overbore doesn't make it a 2.7 litre motor - you need a longer throw crank.

If you go to 2mm

Bore:88mm

Stroke: 73.7mm

Capacity: 2.689 litres.

Which can be claimed as 2.7 litres.

Remember though, if you bore the block out to its limit (2mm or whatever it is) it will be a throw away item the next time you need to rebuild it. All that for 60cc's?

Edited May 11, 2007 by djr81

[R31Nismoid]

88mm isnt the best either if you ask me, it shows the motor was fair worn when it was rebuilt, and you might not get another build out of it should it fail

[Beer Baron]

I know piston size dont = capacity. Interesting info though, the owner of the motor/car asures me it has "oversized HKS pistons". quote "it's now 2.7lt" Maybe i'll get the sump taken off and have someone look in there before I exchange cash

yes! definately get the sump off before handing over any decen cash for it. 88mm bore is not a positive selling point, it's a negative. and off the top of my head the largest pistons HKS make atm is 87.5mm I can check later as I have the 2007 goods master at home.

increasing the bore but leaving the stroke does not get the same result as the stroker kits. sure they may both be 2.7 litre or 2.8 litre but the capacity does not tell the whole story. further increasing the bore whilst leaving the stroke the same will reduce some of the low down punchiness of the engine but yes it should make more power high in the rev range. this is why when you want more capacity in an RB26 you go longer stroke.

also 88mm bore is the absolute limit of what you can bore a 26 to safely and at 88mm bore the engine is no longer really suitable for big revs or big power as the cylinders are now quite thin (weak). for big power you want to be using 86 or 86.5mm.

[djr81]

Well, back in the day people used to overbore motors in increments of 10 thousands of an inch ie 0.25mm. If you had (for example) a Cleveland V8 you binned it after 40 thou. Which is why you have to be careful with going too much over size too quickly. Like the Baron says a block out to 88mm is on its last rebuild - so why pay extra coin for something in that condition?

Anyway, to anyone looking for a stroker crank & larger capacity from their RB26 - be careful about which size pistons you order.

Oh, and by the way. Combustion chamber volume has nothing to do with motor capacity. But piston diameter certainly does!

[Adriano]

Overboring will always increase low down torque, not as much as a stroker, but still will none the less. I wouldnt discount the car if its been bored that much, as if the motor does need rebuilding in the future, you can always get a second hand block, they are around, and worth bugger all($2-300). I doubt taking the sump off is really an option in a gtr just to check the bore size, it would be a $1000 job. How do you know its only got an r33 crank. I would be buying the car more based on the rest of the car, and its bolt ons. Preten it doesn't have the pistons and look at the rest of the car on its merits.