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Nismospek

Mystery Big Valve Ported N42 Head.

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With all the recent postings I was hoping to get some help trying to read out my Flow sheet. I picked off this head from Yahoo Auctions Japan. It was completely bare missing cam towers and about everything else. All I could tell from the photos was that it had been ported and that it had welded chambers. I decided to risk it and put a bid in knowing full well I might have just bought a new paperweight. I finally got it back from a reputable builder with new seats, Datsun Spirit Big valves and some unfurling of the valve area. I was told that different flow benches are like dynos. It seems that the flow bench used for this head maxes out at 160 cfm at 10 inches of water. Not sure how this coverts to newer type flow benches that read at 20 inches etc. Also not sure how this relates to max lift on the cams? 

post-928-0-37701300-1504048992_thumb.jpg

Edited by Nismospek

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I'd get it flowed somewhere locally at 25 or 28 inches. If you have a stock head, get them to do that as well for a baseline. Then at least you can have numbers on a comparable scale to what others do.

 

I'd expect the head to perform well though, fingers crossed for you!

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Found a nifty calculator. Decided to convert everything to 25 inches which is what I believe Rebello uses. 

 

 

100 lift  58 cfm

200 lift  117 cfm

300 lift  158 cfm

350 lift  178 cfm

400 lift  189 cfm

450 lift  192 cfm

500 lift  200 cfm

550 lift  205 cfm

600 lift  213 cfm

650 lift  219 cfm

 

 

 

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On 8/30/2017 at 7:26 AM, Nismospek said:

Going to use a thicker headgasket to lower cr. This head has been shaved a couple times over its life. Hopefully 10.5 or 11 to 1. Hope to run 91 octane.

 

You mention that the chambers were welded, how much quench pad is there? If a lot, then a thicker gasket might be hindering more than helping. Google quench pad and quench distance to learn more. Also, pics are always nice. :wink:

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The converted numbers are similar to my Rebello ported p90a head.  The port is what Rebello called a "mild port."

  • Custom Isky Turbo cam
    • Intake: .535 lift, 278 duration, 114 lobe center
    • Exhaust: .535 lift, 278 duration, 114 lobe center
  • Ported head with 1 mm over sized stainless intake valves
    • Intake: 201 @ 25" water
    • Exhaust: 151 @ 25" water
Edited by rossman

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4 hours ago, rossman said:

The converted numbers are similar to my Rebello ported p90a head.  The port is what Rebello called a "mild port."

  • Custom Isky Turbo cam
    • Intake: .535 lift, 278 duration, 114 lobe center
    • Exhaust: .535 lift, 278 duration, 114 lobe center
  • Ported head with 1 mm over sized stainless intake valves
    • Intake: 201 @ 25" water
    • Exhaust: 151 @ 25" water

 

.535 is a lot of lift!

 

For NA cams it's typically only seen on racy cams. (Maybe because it requires some skill to get right? Notched pistons valve train stability?)

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3 hours ago, turbogrill said:

 

.535 is a lot of lift!

 

For NA cams it's typically only seen on racy cams. (Maybe because it requires some skill to get right? Notched pistons valve train stability?)

 

Not really. I'm running an Isky L6 grind (.540" lift, 270 duration) with flat-top pistons and a Rebello "street ported" P90 on an OEM HG. From memory, my measured piston-head clearance is 0.023", piston-valve is ~0.080", and compression is 11:1. Runs great on 91, even with MBT timing @ 35* all in if I remember right.

Edited by Leon

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7 minutes ago, Leon said:

 

Not really. I'm running an Isky L6 grind (.540" lift, 270 duration) with flat-top pistons and a Rebello "street ported" P90 on an OEM HG. From memory, my measured piston-head clearance is 0.023", piston-valve is ~0.080", and compression is 11:1. Runs great on 91, even with MBT timing @ 35* all in if I remember right.

 

Interesting, so how come a lot of the other  260-290 duration NA cams have such moderate lift? 

Edited by turbogrill

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2 minutes ago, turbogrill said:

 

Interesting, so how come a lot of the other  260-290 duration NA cams have such moderate lift? 

 

There's no point in running high lift when the rest of your system can't make use of it, you have to see the big picture. I'm also running triple 45s with a ported intake and a 6-1 header into a 2.5" exhaust. I sized my cam based on a conversation with Ron Iskenderian about my use case. Most cams you see advertised online are the tip of the iceberg, just bulk items sold to people that want to say they have a "Stage III cam". Talk to a cam grinder and expand your horizons.

 

I will say with the .540 lift cam, there was little room for error during setup due to it using a lot of the lash pad.

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Rebello built my entire long block. He used notched flat top pistons with a metal head gasket. Compression is 8.5:1 according to him. The cam is a regrind but all the lash pads are stock height. I guess he compensated for the difference in cam base circle by adjusting the valve heights.

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