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Closed chamber hp gains?


KamakSun

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...and 80 seconds to get into PB, then wait and wait and fail to load, and wait and load image and go and try to find it in your album. I can go to Imgur, then find an image in my computer, load and copy it and post it in Ratsun in less than a minute..

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...and 80 seconds to get into PB, then wait and wait and fail to load, and wait and load image and go and try to find it in your album. I can go to Imgur, then find an image in my computer, load and copy it and post it in Ratsun in less than a minute..

Really? Imagur is that easy? You can upload from your PC directly to a forum?

 

Sounds like you know your PB. That's exactly what happens, every time.

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...and 80 seconds to get into PB, then wait and wait and fail to load, and wait and load image and go and try to find it in your album. I can go to Imgur, then find an image in my computer, load and copy it and post it in Ratsun in less than a minute..

 

Not so fast. :lol:   I can go there, find an image in my computer that I want, load it (into imgur) copy it and post in Ratsun. (make that 80 seconds fro sure)

 

 

 

 

I'd say it's working. The A87 has 33.75mm intake ports so not quite as large as the U67's at just under 35mm. The intake valves are almost 42mm and the exhaust valves are 33mm or 35mm. I'm guessing the 33mm were on the heads used on the L18 and the 35mm were for use on the L20B. I've never seen an A87 on a stock L20B but I hear it was only the very early ones. If that's the case the '74 610 may be the one. After 40+ years one could have been swapped on to any L20B.

 

rICEyZb.jpg

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Can't work out the compression without knowing the volume of the piston dome, the piston pin height and the volume of the closed chamber head. Often they have been previously milled down.

 

A stock L20B with a closed chamber head would be... 8.9

Above with flattop pistons........................................... 10.68 anything with a dome will be much higher.

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So L20B and closed chamber head. Well compression will be about 8.9.The advantage of a closed chamber head will not be fully utilized as the pistons are dished. You do have the compression.

 

The tighter you squeeze the fuel and air the faster it burns, the stronger the explosion and the more energy that can be put to work moving a piston. You are simply making more efficient use of your fuel. For an engine with 8.4 compression (a stock L20B) increasing it upwards one point will generally get you about 4% more hp. The next point is a little less than 4%, the next point a little less and so on. This is because you are getting closer and closer to the ideal efficiency. Going from 8.4 to 8.9 is worth about 2-3 hp. 

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The machinist said that not a lot of gains are to be had unless the head is ported, valves and springs changed and a hotter cam installed. Is this correct?

Additionally, he wants me to switch to headers and this board told me to keep the cast manifold.

He is correct.

The board is correct.

 

I had 4-2-1 header and like the cast manifold better.

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So L20B and closed chamber head. Well compression will be about 8.9.The advantage of a closed chamber head will not be fully utilized as the pistons are dished. (Quote)

 

With the engines that came with a closed chamber or peanut head did they come factory with flat top piston?

 

I see a bunch of motor builds with dished pistons and a peanut head... even coming from engine builders....

Why would that combo be chosen if flat top pistons are the better choice with a closed chamber head?

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The whole point of a closed chamber head is to induce swirl and turbulence of the air and fuel. This homogenizes the mixture (no rich or lean spots) and cools the combustion chamber piston top valves and spark plug reducing hot spots that can auto ignite the mixture. This is why (all things equal) a closed chamber head is more detonation resistant that an open chamber head with the same compression.

 

To get the swirl/turbulence, a combustion chamber must be smaller than the bore below it. This means that when a flattop piston is at the top of it's travel there are areas where it is up against the head surface, being separated only by the head gasket thickness. (about 1.2mm or less than 0.050")  As the piston approaches TDC the air caught in this area is violently pinched out into the combustion chamber. The area where the piston and the head almost touch is also called the quench area.

 

As you can see having a dished piston negates most of this pinch effect. People who build with them either don't know better,  don't have the resources to get flattops or it doesn't matter as higher compression is all that they want.

 

There may be a few closed chamber heads around but likely these came here on import engines in the '80s. The '70s was all about lowering compression and emissions. I find it exceedingly unlikely that Nissan randomly sent some engines with higher compressions than advertised. What pistons the import engines used with them, I don't know but the L16SSS and L18SSS used in the 510 coupes were flattops.

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Knowledge is key....

Got lucky when I assembled my L16 with the w53 head.. I wasn't paying attention just buying parts not understanding how everything interacted....

In the end it all worked out, barely..

Higher compression than what I wanted, but was able to utilize the head to its fullest....

Proper planning definately helps....

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Probably....

I'll say this.. with the money I put into my L16 I could have done a motor swap and bought a spare motor.... and I still wanna spend more and have the head ported and what ever they do with the flow bench...

But I'm that fool that likes the matching chassis and motor #....

Was it worth it probably not, do I love the motor i built and what I've accomplished.... hell ya...

The biggest thing I learned was proper planning before I bought things, what intended to build was not what I ended up with..

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