NA Motor Discussions regarding N/A KA24E, KA24DE, and SR20DE

Alt. to High C/R Pistons

Old 02-19-2008, 09:42 PM
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Alt. to High C/R Pistons

So I've been told that High C/R pistons aren't always the best way to achieve a High C/R. I have also been told that High C/R pistons may increase emissions not allowing me to pass smog and what not. So I've been thinking bout it and came up w/ 2 other ways that I have heard of.

1. Thinner HG, though it wont up the C/R much maybe ~ > .1

2. Welding the head (adding mat. lowering head volume)

3. Bigger valve face? (Bigger valves in general?)

4. Mill/Shave the head

I was wondering how well the KA would react to these and if they are a smart choice instead of going High C/R Pistons.
I see alot of honda guys doing these things but I dont use them as reference for they have such high efficiency heads that the KA dosent even come close too. Though from what I have read is the Best head to it's years that nissan had produced at that time.

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Old 02-23-2008, 02:28 PM
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wouldnt the increase in emissions be due to the increased C/R and not the high comp pistons themselves?
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Old 02-23-2008, 08:18 PM
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Higher compression raises NOX, and in order to lower temprature usually more fuel is added increasing both CO and HC.
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Old 02-23-2008, 09:45 PM
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So an increased C/R period increases emissions? Could I get by w/ say an 10:1 C/R?
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Old 02-24-2008, 03:34 PM
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At the most a 10.5:1 but then you have to use a really good 3way converter from an OBD2 vehicle. Possibly from a Honda s2000... The egr system also has to be capable enough to allow enough emission to run back into th intake mani.
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Old 02-25-2008, 12:33 AM
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So Let's say, I run; 10:1 C.R, BC 264 Cams, DC Header, Hi-Flow Cat, Invidia G200 3" Exhaust. Would that be possible to pass?
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Old 02-25-2008, 03:23 AM
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Originally Posted by 240-kid View Post
So Let's say, I run; 10:1 C.R, BC 264 Cams, DC Header, Hi-Flow Cat, Invidia G200 3" Exhaust. Would that be possible to pass?
I wouldn't know the answer to that. You would have to test it through trial and error. The rod/stroke ratio of the KA is pretty solid on passing emissions.
You would have to worry more about allowing the egr system to intake more of the exhaust emissions, which means you would probably be better using the OEM exhaust header manifold and actually making the port sizes larger to the egr in the runners , as well as using a 3way cat such as random technology, or magna flow to allow enough back pressure for the intake system to feed the exhaust emissions through the egr system.
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Old 02-26-2008, 09:17 PM
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Would a leaner tune help w/ passing smog or does that make it worse?
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Old 02-27-2008, 01:28 PM
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idk. but a couple things to keep in mind.
when you talk about emissions, you're not concerned with only HC (raw fuel)
a lean running engine increases cylinder temps which increases NOx emissions.
rich running engine increases CO emissions.
the EGR system routes exhaust gases to the intake to create a rich condition to lower cylinder temps in order to reduce NOx.
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Old 02-27-2008, 07:36 PM
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^You just cant win lmao

So the best thing would be 3" Magna Flow 3-Way OBD-2 Cats?
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Old 03-01-2008, 08:46 PM
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Originally Posted by 240-kid View Post
^You just cant win lmao

So the best thing would be 3" Magna Flow 3-Way OBD-2 Cats?
Actually you would probably have to use a more restrictive CAT that would be found on a high compression 350z or Honda s2000 those CATS are designed to lower the high NOX levels from high compression, as well as aid in enough back pressure for the EGR system to run back the CO, and HC emissions.
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