-/+ deck height in n/a engine

[DavD3]

OK i did search on this question, and not much came up and i still don't understand it.Can you,please, expain to me is it bad to have negative deck height in n/a engine.I am thinking about combo L28 crank,L24 rods,KA24 pistons and E31 head with 1 mm HKS head gasket. In this case there will be negative deck height of 1.37 mm is this really bad? How it can affect n/a engine work ? Less HP and Torque ? And what about positive deck height is this affects engine performance too? I think that "0" deck height is the way all engines go in production, am i wrong? Can someone clear this for me,please.Thanks a lot.

[datsunlover]

I don't think there's anything 'wrong' with a slightly negative deck hight.. I think that's pretty normal for N/A engines, although it seams you're talking about using 240 rods as they are longer, hence 'stroking' it.. (I'm not 100% sure on this though..don't know anythign about the KA pistons)

But what really maters is what's been done to the head you're using, and where the valves are gona end up. IE; Has it been shaved? Gona run a hot cam? I supose you could deck the block as well..

[olie05]

DavD3,

When dealing with N/A engines, what you want to worry about is compression ratio. You want to go for the ka24 pistons i'm guessing because of the 89mm bore. With your setup you will be at 9.16:1.(according to l-engine builder program) This will result in more horsepower and torque across the power band, but a higher cr will give you a more serious N/A engine. I don't think deck height is as much of a concern here as compression ratio is, unless it is positive deck height and it will hit the head at tdc. Of course, any other piston/rod combo would not let you run such a wide bore (without custom pistons) and such a "low" compression ratio.

-Oliver

[JMortensen]

The problem with negative deck height is that it effectively makes quench 0. So if you have a high compression engine that needs (or would benefit from if you like that better) quench, you won't have any. If the compression is 9.5 or lower, you'd never notice.

 

Any stock L series has a positive deck height from the factory AFAIK. It is a positive height of .003" or something like that, I can't recall off the top of my head. The pistons don't hit the head due to the thickness of the head gasket. Stock is something like .050" and you can get the HKS or Fail-Prone 1mm (.040").