Ad: VTT Tech: N54 Head Flow

Oct 24, 2016
1,111
Scottsdale, AZ
Hey guys, wrote up some of our test results of an N54, a VTT/Rebello ported N54, and an N53 head. Check it out!

We'll have stock on VTT/Rebello N54 heads in the next month or so -these will be full PNP, Supertech valves, springs, titanium retainers, locks, and keepers. $3799, +$2000 core if you don't send one in.

PDF of document attached, below are screenshots for those who don't want to download the PDF.

Chris

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Panzerfaust

Lieutenant
Jul 3, 2018
634
Chicago
Good info to have out there for sure! It'd be useful to know more about the extent of PnP'ing done to each head but I understand sometimes companies like to be secretive about that stuff for good reason.
 

fmorelli

Brigadier General
Staff member
Aug 11, 2017
2,864
Virginia
@[email protected] posted this about a year ago, which gives some insight on the work being done.

Filippo

Rebello ported N54 heads are only available through VTT. Rebello is proven in the I6 community for many years

Break down:
  • Complete Disassembly & Cleaning
  • Leak, Crack & Pressure Test
  • Multi-angle Intake, Radius Exhaust Valve Job
  • Unshrouding of Valves
  • Supertech valves
  • Supertech single spring design specifically designed for use in turbo engines
  • Supertech retainers
  • Full Port and Polish Work by Rebello head specialist
  • CC’ed Chamber
  • New Valve Guides
  • New Stem Seals
  • Trueness Checked & Resurfaced Mating Surface
Price is $3799 exchange lead time 30 days, We can provide a head $1000 core charge.
 

mikeseli

Corporal
May 23, 2017
106
I’m questioning the exhaust port flow data that is posted. I’ve also tested a stock cleaned N54 head on my bench and I got these numbers. At 0.300” lift it was 142cfm and at 0.400” lift it was 145cfm. On the intake side I got the same numbers as your graphs. The test I had performed was 2 years ago on the same bench and same settings. The N54 exhaust ports are terrible and very small, you can do all the magic in the world the port size at 32.5mm is too small for a 500cc cylinder.

The N53 exhaust port is 35.5mm, those extra 3mm equate to 18% increase in area.
 

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Oct 24, 2016
1,111
Scottsdale, AZ
I’m questioning the exhaust port flow data that is posted. I’ve also tested a stock cleaned N54 head on my bench and I got these numbers. At 0.300” lift it was 142cfm and at 0.400” lift it was 145cfm. On the intake side I got the same numbers as your graphs. The test I had performed was 2 years ago on the same bench and same settings. The N54 exhaust ports are terrible and very small, you can do all the magic in the world the port size at 32.5mm is too small for a 500cc cylinder.

The N53 exhaust port is 35.5mm, those extra 3mm equate to 18% increase in area.

Sounds like you should post your own flow results! We actually would have more to gain by undervaluing the stock head numbers to try to sell ported heads. Rebello has nothing to gain from any of this testing except the hours to do the testing. We dropped heads off to them and paid them to flow them. Once they finished they gave us a call and we came down to get the data sheets. This is not something these guys began doing last week; they are one of the most respected machine shops across more than one platform. The numbers they gave us are the numbers they got, period. If you have different data, sounds like you should possibly post it. Thanks!

Chris
 
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The Convert

Captain
Jun 4, 2017
1,343
Sounds like you should post your own flow results! We actually would have more to gain by undervaluing the stock head numbers to try to sell ported heads. Rebello has nothing to gain from any of this testing except the hours to do the testing. We dropped heads off to them and paid them to flow them. Once they finished they gave us a call and we came down to get the data sheets. This is not something these guys began doing last week; they are one of the most respected machine shops across more than one platform. The numbers they gave us are the numbers they got, period. If you have different data, sounds like you should possibly post it. Thanks!

Chris
For someone who is usually very professional in their responses, this response sounds pretty sour. Since someone else got equal intake results and drastically different exhaust results, on the conservative side, a better response might have been to say that that is interesting data and you’ll doublecheck with Rebello to make sure only one valve was open and that the intake ports were completely sealed off, because it sounds like they may have had a leak. It’s a lot harder to under flow something on a bench than it is to over flow.
 

langsbr

Captain
Apr 5, 2017
1,084
For someone who is usually very professional in their responses, this response sounds pretty sour. Since someone else got equal intake results and drastically different exhaust results, on the conservative side, a better response might have been to say that that is interesting data and you’ll doublecheck with Rebello to make sure only one valve was open and that the intake ports were completely sealed off, because it sounds like they may have had a leak. It’s a lot harder to under flow something on a bench than it is to over flow.
It was probably Tony posting as Chris :p j/k. The stock N54 exhaust numbers do seem high - MMPs are more inline with what @mikeseli got. Granted, what Chris said is true - there's more to be gained by undervaluing stock numbers, BUT, if the stock numbers are janky, and the ported numbers are janky, it gives a false impression of flow. In advertising, flow numbers matter, even if they don't in real world application.

An old thread from PAW Motorsports (now defunct?) had stock exhaust flow numbers more inline with MMP and @mikeseli.
 
Oct 24, 2016
1,111
Scottsdale, AZ
Not sour a bit! Honestly I have no control over what mikeseli did, no way to know where he lands on the spectrum of legitimate expert to internet legend, and just having different results could be the result of any of many causes. No disrespect to mike, he's obviously one of not-very-many people who went through the trouble of flow testing, so hats off to him for that, but an after-the-fact comparison of his data to ours that is meaningful is essentially impossible. All that said, this is why we invest so much up front in choosing partners that have a proven track record of elite performance and capability.

I can tell you this, napkin math suggests the flow numbers we've seen and posted about line up with our extensive dyno time with various heads.

As to the customer relations advice -thanks? One of the things I love about working for VTT is the freedom I have to do my job as I see fit. I know well what the corporate appropriate response is, and there are times I just plain ignore it, as this job is fun. Mostly as it makes me feel like a real person instead of some drone -I get a lot of positive feedback because of that edge. I do get your perspective though, thanks for keeping me honest. xoxo

Chris
 
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DCook

Corporal
May 25, 2018
217
Im sure this probably isnt the place to ask, but what are the limitations on the stock head? Other than flow rate? Springs, valves, retainers etc? Are the valves 2 piece?

At what limit is it needed for port+polish and full valvetrain?
 
Oct 24, 2016
1,111
Scottsdale, AZ
People have made over 800 whp on the stock head, but that doesn't make a it a great idea to try. End use goals really determine what makes sense from an upgrade perspective. I wouldn't bother for less than 600 whp unless you already had a head that was worn and needed some love. For a track car, to optimize a particular turbo system, or if you just want some more efficient breathing, then it starts to make sense. FWIW I'll likely put a ported head on my stock-motor street car (articles forthcoming).

Chris
 
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The Convert

Captain
Jun 4, 2017
1,343
Im sure this probably isnt the place to ask, but what are the limitations on the stock head? Other than flow rate? Springs, valves, retainers etc? Are the valves 2 piece?

At what limit is it needed for port+polish and full valvetrain?
Just from failures people have posted, and conversations with Chris at Motiv, the springs sound like the weak link if you’re not talking about power limiter, but failure point.
 
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DCook

Corporal
May 25, 2018
217
Just from failures people have posted, and conversations with Chris at Motiv, the springs sound like the weak link if you’re not talking about power limiter, but failure point.
Yup thats the answer i was looking for, thank you much! I wanna do away with all weak links in my build, just as a preventative. And its nice to get more info out there for others that are looking for info. As I've done some searching and its hard to find actual answers of defined weak/failure points, that arent power limited/rated. If that makes sense.
 

mikeseli

Corporal
May 23, 2017
106
More flow. Less PSI. Less heat.

Filippo
Less pumping loss especially during the exhaust cycle. This is very important especially on a boosted or nitrous injected engine.

Having the exhaust port flow more or having the exhaust valve open earlier and/or closing later helps allot. You will see gains across the boosted power band (2700+rpms). The gains will increase as the rpms are climbing. As an example, if the ported exhaust port if flowing 20-25cfm (at .25” to .40” valve lift) more than previously, at 3000rpms you may see 10hp more, at 5000rpms you may see 25hp more and at 7000rpms you may see 40hp more without changing the boost curve. Play with the timing and the gains will continue to improve.
 
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