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I am currently building my motor on my 280z, and I was looking at having the head chambers welded up. The issue I have ran into is everyone wants big money to perform this service. I was was wondering what everyone's opinion was on if should even weld the chambers, or if someone has a reasonable source to have this service done. My current build list is as follows:

 

  • N42 Block
  • N42 Head / Ported & Unshrouded
  • .030" over ITM Flat-top pistons
  • 280z rods w/ ARP rod bolts
  • ARP main studs
  • ARP head studs
  • Triple Weber 45 DCOEs with Cannon intake
  • Advance Distributors re-curved 280zx distributor w/  E12-80 ignition module
  • Schneider factory cam regrind 284-92F grind 
  • Intake Duration (gross): 284 Exhaust Duration (gross): 292 Intake Duration (.050”): 236 Exhaust Duration (.050”): 244 Intake Valve Lift*: .488" Exhaust Valve Lift*: .504" Lobe Separation: 107 Intake Valve Lash: .010" Exhaust Valve Lash:  .012" RPM Range 3250-7250

 

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Might as well to that, the matter of degree - just welding, or welding and shaping, welding/shaping/porting, welding/shaping/porting/flow testing to a specific number, etc.

 

I remember reading about a guy who taught welding and raced L series engines.  He reshaped the intake ports in to the valve cover area via added metal to raise the port floor and give a more direct path to the valve head.  Had to build a new valve cover to fit it, it was that high.  You can go pretty far if you want to.  Might be in the How To Modify book.  

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I think the problem lies in the premise: WHY exactly are you looking to weld the chambers up?

 

It seems like a common thing to do to improve airflow and reduce detonation. The process is described in Frank Honsowetz book, also the Kameari SPL head has welded chambers. I seen it discussed on the forums multiple time as well. I just have never seen anyone say were they have had the work done. I also listed all of my engine specifications so i could get input on whether it would benefit my setup or not. I was mainly looking to improve the burn in the head to reduce the risk of detonation and hopefully pick up a few extra horsepower at the same time from the more efficient burn. If i could decrease my chance of detonation, then I would be able to run more timing and take advantage of the higher compression from the N42 flat top combination. Currently I am relying on the cam to reduce my dynamic compression to avoid detonation, and also the re-curved distributor to take full advantage of the triple Webers.

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I think it's a matter of paying the man or getting a different head . So you find out how much it is to weld but that is just the first part. Did you consider a p79 or p90 and shave?

How about a mn47 and port . An early e31?

Why box yourself in with the 42 head that will need so much work . That work should be left to the professionals

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I'm with Steve. This is nothing a shaved P79/P90 couldn't handle. The list is a very basic L-series setup, nothing that hasn't been done before.

 

If we're talking a 400hp, 9000RPM, 14:1 compression motor then it's a different story. And in that case, if you gotta ask... ;)

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I have two full N42 motors, so i didn't want to source another head. I was just blown away at some of the prices I got, one company wanted $6,000 to weld and and resurface and that didn't include doing the valve job or anything else. I had considered trading someone a N42 head for a P90 head at one point. I just wasn't sure what compression ratio I would be at with a shaved P90 and flat top pistons.I was looking at shaving .080" to get back to 10:1 compression ratio.

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This site has a really useful calculator for our engines http://www.ozdat.com/ozdatonline/enginedesign/

 

Like many have said, if you want the quench pad, go for a later head. P79s are fairly easy to get and the exhaust liners are good for flow. A P79 or P90 head will give you 8.79:1. I'm not sure how much volume is reduced by shaving, but you can play with the head CC in the calculator and then figure out how much you need to remove.

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This site has a really useful calculator for our engines http://www.ozdat.com/ozdatonline/enginedesign/

 

Like many have said, if you want the quench pad, go for a later head. P79s are fairly easy to get and the exhaust liners are good for flow. A P79 or P90 head will give you 8.79:1. I'm not sure how much volume is reduced by shaving, but you can play with the head CC in the calculator and then figure out how much you need to remove.

 

I've noted that the OZDDAT calculator comes up with figures that are different from other established sources, including Hybrid Z.

 

EG: I punched in an L28 with Flat-Tops, stock N47 head and stock L28 head gasket. Calculator came up with a 9.7 CR. However, most other sites all report that combo as being over 10 to 1 CR. Usually in the mid 10's. That's quite a difference.

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I've noted that the OZDDAT calculator comes up with figures that are different from other established sources, including Hybrid Z.

 

EG: I punched in an L28 with Flat-Tops, stock N47 head and stock L28 head gasket. Calculator came up with a 9.7 CR. However, most other sites all report that combo as being over 10 to 1 CR. Usually in the mid 10's. That's quite a difference.

 

I have noticed the same kind of results as well.

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Could be the deck height?? The Oz calculator sticks the deck height at .050mm ( below the top of the deck ) . Calculator does not seem to allow that value to be altered.

 

Was recently reading an article that the L28 Flat top  pistons are .025 mm above block deck . I used a different CR calculator that does allow deck height to be adjusted, and setting it at -.025mm ( -.10" ) gives a CR of 10.3 to 1 with flat tops. Confusing.

 

https://www.rbracing-rsr.com/compstaticcalc.html

 

post-44147-0-41855700-1470464166_thumb.jpg

 

Edit: Found one of the the articles on deck height. It was on Hybrid Z of course. Check out Braap's post at #5. There are also numerous reports that Frank Honsowetz's Datsun Bible has several errors in it pertaining to Piston heights.

 

http://forums.hybridz.org/topic/58658-pistiondeck-height-misinformation/

 

 

Every N/A L-28 built after, (I think it was 8 of 1980 or there abouts, someone else here will have the exact manufacture date the change was made), any how, the engines with the P-79 head and flat top pistons, the pistons pop up OUT of the bore between .020†and .025†from the factory. So long as the head gasket is thick enough that there is approx .016†clearance between the cylinder head and the piston, all is well and in fact, quite good.

Here is an assembled short block with the OE flat top pistons, OE rods in an OE block, and the block was NOT decked. The piston pops up out of the bore .023"

Edited by Chickenman
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Here's an updated calculation using the stock head gasket thickness of .049" ( 1.25mm ) and a positive deck height of .023" as measured by Braap in the article. This makes a lot more sense.

post-44147-0-05539200-1470467230_thumb.jpg

 

The P79/P90/P90a  heads used on late motors with the F54 an has a big combustion chamber of 53.6 CC. Compare that with an N42/ N47  head with a 44.6 cc chamber and you can see why you have issues with detonation with the N42/N47 heads.

 

10.4 to 1 CR is hard to do on 91 Octane pump gas. Add a less than optimal chamber shape, and it's ping-a-ling city!!

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If you would have said they quoted you $6,000 for a welded N42 head in your original post you could have saved yourself whining over no answers, as I would have told you to go elsewhere. I have seen a full on race head (welded) under $3,000.

 

You live in the Middle East, they are not friendly to Furrin' Iron there...

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