Hi guys,

As a part of my 800whp project I am planning on getting my heads ported.
Looking at my options and trying to decide between CNC porting or letting an experienced specialist do hand porting.

Recieved some flow numbers from a company offering CNC porting for 996tt. At this point only received flow numbers for the intake side.
See pic below.

How does this compare to flow numbers you guys have seen?
I have seen a couple of posts about McKenzie ported heads and those flow numbers seem considerably higher.. But I dont know enough about flow testing methods to understand and compare.

For example these flow tests seem to be conducted using different vacuum - it says tested @ 25" water vs tested @ 28" water in McKenzie flow tests..

Can someone with experience in this field explain to me if those numbers I received from CNC company are good or bad?
Should I rather have a specialist hand port.

 

No experience on ported 996 heads, but the 25 vs 28 will indeed favor flow numbers for the 28 all things being equal.

The only real difference (that I've ever known from other makes) between hand and cnc is that cnc is programmed to be the exact same everytime, where as hand ported has some bit of variance from one head to the next. Obviously the hand porter would attempt to replicate the same thing each time, but being human and all it wont be 100% identical and will be up to how consistent the human is.

 

Yes obviously the cnc ported head will have identical ports.
But to me these flow numbers above they are not soo impressive..
Or actually the percentage over standard are not so impressive.

 

I'm not sure how 25 v 28 affects the outcome but here are McKenzie head numbers. The percentages are in the two far right colums.. I looked at CNC headwork but in the end felt more comfortable with McKenzies knowledge and ability. Seemed like a real straight shooter. No BS. He was one of the only ones that stressed the importance of port matching the intake manifold to the heads for max gains. None of the other CNC vendors even mentioned that. His 9000 RPM valve train was part of his package. YMMV

[url=https://flic.kr/p/rrzTDr]

OEM INTAKE
[url=https://flic.kr/p/qmbSh5]

MCKENZIE INTAKE
[url=https://flic.kr/p/qYRcon]

OEM EXHAUST
[url=https://flic.kr/p/ri4ABP]

MCKENZIE EXHAUST
[url=https://flic.kr/p/rfSqQ3]

 

Being a guy that does a lot of porting, hand vs cnc is always a hard discussion. I do hand porting. Hand porting, I'd you know what your doing, can actually do a better job than many cnc because of the machines limitation. You will have a small difference in in port though.

as John said though, a huge thing is port matching. Lots of guys port stuff but overlook that actual port matching. Not doing so can create lots of turbulence and can offset a great deal of the gains from porting.

 

Thanks for the McKenzie flow numbers.
It was actually those that I have seen before and was referring to.
When comparing flow numbers from McKenzie with numbers from the CNC company, the base numbers (pre porting flow test) are very different.

McKenzie seem to get much lower numbers. That makes the end result (% flow gained) looks much better.
Impressive how the McKenzie hand porting can gain over 100% flow..

See below

 

For 800whp there is no reason to do more than just light manual porting of the heads, our heads are proven even over 1000hp, even some 1200hp.. I have seen very fast setups on stock heads and just some mild cams. My gtx30 GT-R I have just did 1111.9 hp, full OEM heads and cams, save your time and ditch your money somewhere else if you dont want to squeeze the last drop of power, but remember you can address that with a bit more boost anytime, so unless you want a high hp car running on pump gas for some unknown reason, I dont see why you would want that expensive porting as thats not a limiting factor for you

 

^ that is a good point. Depends on how much your paying and long term goal. For a guy like me, doing it myself costs basically nothing. If you're paying big bucks for it, money could be better spent elsewhere.

 

For my latest heads, the heads are hand ported for optimal flow, then the ports and chambers are digitized and then cnc machined on a5 axis. This ensures every port and chamber is identical.

Far more efficient then hand porting the entire heads every time. you get the best of both worlds!

 

If not running at least GT35 turbos I wouldnt touch the heads exept manual porting, same idea for adding cams only for turbos bigger than GT30s or similar or very specific setup/needs. Expect maybe 30-40whp more from heads at high boost (30+ psi) and maybe the same from cams running big turbos

 

The saying is God fills the cylinder and man empties the cylinder. That's for a N/A engine. This in some way justifies a bit of port work on the intake side at least, with less justification for any exhaust port work, other than port matching, of course.

For a turbo-charged engine man both fills and empties the cylinder thus this makes a case against any porting other than perhaps some smoothing and of course port matching.

Plus consider this: The engine putting out 800whp means the engine making that kind of HP is going to be running hot, hot, hot.

I'd be tempted to leave the ports alone leaving the wall thicknesses as thick as possible especially on the exhaust side to avoid possibly head cracking.

Port to manifold matching would be ok and maybe a bit of smoothing up but that's about all I'd do.

 

I question those flow numbers,the number I personally have for a stock head at .400 is 260 on the flow bench...

Anyone else flow bench a stock head? I'd love to see more comprises with stock flow numbers.

 

I'd disagree with some of this. On a turbo motor, air volume is more important than air velocity. Because the air is under pressure you are trying to create the ability to maximize the volume of air that can get through the head, around the valves, and into the cylinder. Large gains can be made in the valve area on almost every head. Also reducing turbulence and overall flow with port matching and enlarging the runners produces more go at lower boost pressures. Also on the exhaust side, maximizing flow out of the head helps reduce drive pressure and reduces max egts under full load.

overall when porting, you have to take about a full system. Porting matching everything going in and out of the engine and increasing the engines ability to move larger air volume produce hp. You need to think about everything though. Just doing heads but not matching the intake and exhaust manifolds will lower gains. Then have to think about the turbine housings as well.

the cost though is what you have to consider. For me it basically only costs time. For other is may cost thousands.

for example on my Sti. Everything in the whole system ported. My car vs another running the same turbo on same dyno. My car makes 10whp and 25wlb more at 21psi compared to the other car at 25psi

 

Remember, boost is a measure of restriction! This was brought home to me hard when I had an intake swapped and heads heavily ported on a Mustang I owned. I was quite confused to have a noticeably faster car that was "down on boost" by quite a bit. The airflow had gone up but because it was belt driven centrifugal the blower still pushed the same air. Once I understood this I used to chuckle at guys who felt they made more power because they saw higher manifold pressures...

On a turbo car the wastegate makes up for lower boost within the capacity of the turbo to make it. If you port everything and dyno at the same boost level the increase is airflow through the motor but higher turbine speeds to get there. In extreme cases you can push a turbo out of its efficiency range if it already been on edge.

Given a choice and opportunity I'd port for sure. CNC should duplicate a known good port job if it was digitized from one and be far less labor intensive after the first run. Looking at pictures of our heads vs Porsche NA heads it seems ours got less attention - they hit their number and saved the effort. I think a mild cleanup at least should be done - $ willing!

 

Thanks for all inputs!
I am upgrading from GTX3071 to EFR7163.
I want to reach my 800whp goal at 1,5bar while retaining fast spool.
I believe doing head porting and upgrade exhaust cams will help me achieve this.
Considering also upgrading intake cams but the exhaust cams seems to be where most is picked up.. Probably because of the variocam plus on the intake side.

Was planning on having my heads CNC ported, can have that done at a really good price, but seeing that McKenzie flow numbers are considerably higher much of the way, made me reconsider.

However the fact that these two flow tests show very different base numbers, I am unsure how much I can actually compare the two.
McKenzie are showing some very high % gains vs much smaller gain numbers in the CNC test.
I am leaning towards differences in the flow test procedure / equipment being the main reason for this..

@ nitro - your 260cfm at 0,400 lift does back up my feeling that McKenzies base numbers are loooow.