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Closed chamber hp gains?


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#41 Crashtd420

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Posted 14 September 2017 - 04:55 AM

[quote name="datzenmike" post="1515966" timestamp="1504932158"]

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?

#42 datzenmike

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Posted 14 September 2017 - 05:32 AM

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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#43 Crashtd420

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Posted 14 September 2017 - 05:59 AM

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....

#44 Stoffregen Motorsports

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Posted 14 September 2017 - 07:05 AM

I've run 12:1 on the street in a long rod L 2200 (my street car for many years) and it ran on pump gas. It also had a big cam which used up all that cylinder pressure.

 

10:1 is ideal for the street, but if you go over, it's not the end of the world.



#45 distributorguy

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Posted 14 September 2017 - 07:13 AM

The spare race motor I built was 12.5:1, and I plan on eventually assembling our parts truck, possibly using that as a street motor.  It was quite tame and controllable with a set of SU carbs on it.  

Knowledge IS key!



#46 Crashtd420

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Posted 14 September 2017 - 07:21 AM

When you say pump gas what octane?
I'm at 10.7:1... mild cam, initial timing at 14.... running 93 in the tank?
Was definately fun on the street...

#47 Stoffregen Motorsports

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Posted 14 September 2017 - 08:08 AM

Pump gas here in CA at that time was around 92 octane.

 

When I say big cam, I mean it was big. It idled like a big block Chevy.



#48 Crashtd420

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Posted 14 September 2017 - 08:45 AM

Well since 87/89/93 are my choices.... I'll stick with 93.... I can hunt for stations and maybe get 91/92, but I'll just be wasting gas to do it....

#49 racerx

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Posted 14 September 2017 - 08:50 AM

So after reading peoples input, its not worth it unless you will race it. Could this be the reason why peeps say fuck it and install a KA motor?

#50 Crashtd420

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Posted 14 September 2017 - 09:42 AM

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..

#51 racerx

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Posted 14 September 2017 - 09:45 AM

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..

....that lesson is priceless.

#52 Stoffregen Motorsports

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Posted 14 September 2017 - 10:04 AM

Projects evolve though. It's like famous painters always saying that the canvas "told me what to do." Sometimes you just don't know how it's going to play out.



#53 Crashtd420

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Posted 14 September 2017 - 10:09 AM

Projects evolve though. It's like famous painters always saying that the canvas "told me what to do." Sometimes you just don't know how it's going to play out.

I always thought it was the voices in my head.... glad to know it been my datsun talking all a long....

#54 racerx

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Posted 14 September 2017 - 10:16 AM

Projects evolve though. It's like famous painters always saying that the canvas "told me what to do." Sometimes you just don't know how it's going to play out.

...true, but it starts from the beginning, how you plan, how much money you got, being real about your skills, a place to work on, time, etc.

#55 Stoffregen Motorsports

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Posted 14 September 2017 - 10:19 AM

True, very true.

 

I don't work that way, or I more accurately, I start with a rough outline but I always try to innovate on every job. As long as the customer's willing to pay for it, they usually end up with something other than what everybody else is doing. I think they appreciate that.