shaved N47 with flat top

[nico]

How can I calculate compression ratio? F54 block with flat pistons and Felpro gasket. This is stock bottom end. Want to shave the head to be in the 11.5:1 / 12:1 ratio.

 

 

[Xnke]

Hope you plan to run racing fuel.

 

You will need a buret, some simple measuring tools, and some simple geometric formulas, it's high school math.

[nico]

Race fuel like 110 or 112. At the pumps next to my house I have 94. Works well in my Camaro with 11.8:1.

 

I know if I put the N47 on as is should be around 10.4:1 This is what I found with Google.

[Xnke]

That assumes your N47 is from a Z car and not a Maxima, and also that your head has never been shaved/modified.

 

If you don't measure, you will not know.

 

What year camaro? Iron heads? 1970's aluminum heads? Stock cam? Long duration cam? Late intake valve closing? Modern ECU with integrated knock sensors and timing control? I'd have no doubt that such could run 11.8:1 and not destroy itself on pump fuel. The L28 OE design and control systems won't support compression ratios that high on fuel octane that low without causing damage.

 

And unless you live at elevation, it's very unlikely you'll be able to run pump fuel of any kind at 11:1 compression or higher...10.5:1 is REALLY pushing it on an L-series and non-ethanol 93 octane gasoline. Ethanol-diluted, 93 octane behaves differently, even though it shows the same detonation resistance when it's dry and fresh. I'm not convinced that it is better or worse, yet.

 

We have LOTS of threads detailing cylinder head preparation, from several different members and several different styles of building.

Edited December 30, 2015 by Xnke

[Chickenman]

^ Agree 100% with Xnke's  post above. He speaks the truth.  Keep the CR below 10.5 to 1 ( Preferably 10.1 ) for Pump fuel. 

 

I live in BC and have a 1976 280Z with an F54 block ( standard bores ) and  N47 Head ( not shaved ) running  Flat Tops. That should give me around 10.3 to 10.5 to 1 CR. I've raced Datsuns and Chevies for many, many years.

 

I would advise you to leave the head alone. For my 280Z, I run fairly conservative timing, 34 - 35 degrees total mechanical and absolutely have to run Chevron 94. At that I'm on the ragged edge, as I can sometimes detect slight pinging between 4,500 to 5,500 rpm. I also have a fairly big camshaft ( Shneider 280 ) so that helps lower Dynamic Compression.

 

Datsun L-series heads, in general,  are less tolerant of detonation than Chevy Aluminum heads. I had early Edelbrock RPM Aluminium Heads on my Hillclimb, Autocross, Track-Day car with a nicely 420HP 355 SBC. Those particular heads  gave me a realistic 10.3 to 1 CR on a 355CI SBC. Car was Dyno'd at 360 RWHP and was a DD.  

 

Anyhoo... the Camaro, ( and other SBC's  like it ) would tolerate a lot more Ignition Timing than a Datsun L-series ( with comparable CR )  on 91 or 94 Octane pump fuel without detonation..... so you really shouldn't compare the two to decide your Datsun's CR. It's Apples and Oranges.

 

In BC, the guys running street cars on Pump gas try and keep NA L-series under 10.5 to 1. Anything higher and they can't get good enough fuel for it. Chevron 94 is usually the best for Hi Compression and Turbo cars. We can't get the Mohawk 94 Octane with 10% Ethanol anymore, (  thanks to Government Dick Heads ).  That was sweet for Turbo cars. We also can't get Petro-Canada Ultra 94+ out West, which I hear is a bit better than the Chevron 94.

 

And don't forget that if you take a trip South of the Border, the USA fuel is  generally worse than ours as far as Octane quality. Their 93 and 94 Octane seem to be roughly equivalent to our 91 Octanes. So you'll have to de-tune your car some, by dialing out some ignition timing. And that's with CONSERVATIVE CR's.

 

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Edited January 21, 2016 by Chickenman