|
Improving cnc ported heads
#2420102
12/18/17 12:17 AM
12/18/17 12:17 AM
|
Joined: Jan 2003
Posts: 11,718
Portage,michigan
B3422W5
OP
I Live Here
|
OP
I Live Here
Joined: Jan 2003
Posts: 11,718
Portage,michigan
|
Down the road i am thinking about buying a set of cnc smallblock heads.
The "as delivered" numbers seem decent, but not earthshattering.
Can a good head porter typically improve the numbers on a cnc ported head?
I know there are lots of variables.
69 Dart GTS A4 Silver All steel, flat factory hood, 3360race weight
418 BPE factory replacement headed stroker, 565 lift solid cam
Best so far, 10.40 @127 1/4
1.41 best 60 foot
6.60 at 103.90 1/8
|
|
|
Re: Improving cnc ported heads
[Re: B3422W5]
#2420106
12/18/17 12:24 AM
12/18/17 12:24 AM
|
Joined: Feb 2005
Posts: 20,184
PA.
pittsburghracer
"Little"John
|
"Little"John
Joined: Feb 2005
Posts: 20,184
PA.
|
Down the road i am thinking about buying a set of cnc smallblock heads.
The "as delivered" numbers seem decent, but not earthshattering.
Can a good head porter typically improve the numbers on a cnc ported head?
I know there are lots of variables. I have never had a set of cnc'd heads in my hands that I couldn't improve but you never know what tomorrow may bring
1970 Duster
Edelbrock headed 408
5.984@112.52
422 Indy headed small block
5.982@112.56 mph
9.42@138.27
Livin and lovin life one day at a time
|
|
|
Re: Improving cnc ported heads
[Re: B3422W5]
#2420179
12/18/17 02:13 AM
12/18/17 02:13 AM
|
Joined: Oct 2007
Posts: 4,209
New York
polyspheric
master
|
master
Joined: Oct 2007
Posts: 4,209
New York
|
All true.
The CNC surface finish is typically very good but not nearly what an owner would do for himself.
Boffin Emeritus
|
|
|
Re: Improving cnc ported heads
[Re: B3422W5]
#2420185
12/18/17 02:22 AM
12/18/17 02:22 AM
|
Joined: Jan 2003
Posts: 11,718
Portage,michigan
B3422W5
OP
I Live Here
|
OP
I Live Here
Joined: Jan 2003
Posts: 11,718
Portage,michigan
|
Looking at the new trick flow small block head. They come cnc" street ported", hence ny question.
69 Dart GTS A4 Silver All steel, flat factory hood, 3360race weight
418 BPE factory replacement headed stroker, 565 lift solid cam
Best so far, 10.40 @127 1/4
1.41 best 60 foot
6.60 at 103.90 1/8
|
|
|
Re: Improving cnc ported heads
[Re: B3422W5]
#2420528
12/18/17 07:05 PM
12/18/17 07:05 PM
|
Joined: Jan 2003
Posts: 16,376
dogdays
I Live Here
|
I Live Here
Joined: Jan 2003
Posts: 16,376
|
I asked this question a while ago and someone answered thinking I meant smoothing out the ridges left by the cutter. duh! A wet intake port may even benefit from the roughness left by the cutter. That's not where I was going.
I am chagrined by the sheer number of folks, real car people, who keep alive the phrase "ported and polished". In my opinion, the only engine that should be fitted with "ported and polished" heads would run a "3/4 race" cam, or maybe a Purple Shaft!!!
Here's the issue, a good CNC program has to be a one-size-fits-all program. The issue is core shift, casting inaccuracies.
If the cnc program was based on a max ported head, then there would be several heads per batch that would have holes in the port walls.
IMHO: A really good CNC program should be able to get within 5-7% of a pro ported head, meaning 15-21 cfm on a 300cfm CNC head. What do you think of those numbers, pro porters?
R.
|
|
|
Re: Improving cnc ported heads
[Re: dogdays]
#2420548
12/18/17 07:38 PM
12/18/17 07:38 PM
|
Joined: Feb 2005
Posts: 20,184
PA.
pittsburghracer
"Little"John
|
"Little"John
Joined: Feb 2005
Posts: 20,184
PA.
|
I'm not a "pro Porter" by any means BUT when you hand port a head you can port the head in a way to work with a customers combo better. No sense reaching for the "high number" when he or she is going to run a 600 lift cam or smaller. You can do different things to the short turn so you get some very nice mid lift numbers earlier so his combo works perfectly. Port CC and valves angles come into play to if its not a fits all, out of the box, here you go cnc'd head.
1970 Duster
Edelbrock headed 408
5.984@112.52
422 Indy headed small block
5.982@112.56 mph
9.42@138.27
Livin and lovin life one day at a time
|
|
|
Re: Improving cnc ported heads
[Re: dogdays]
#2420635
12/18/17 10:14 PM
12/18/17 10:14 PM
|
Joined: Jun 2005
Posts: 6,257
gulfport, ms, west mi
rowin4
master
|
master
Joined: Jun 2005
Posts: 6,257
gulfport, ms, west mi
|
I asked this question a while ago and someone answered thinking I meant smoothing out the ridges left by the cutter. duh! A wet intake port may even benefit from the roughness left by the cutter. That's not where I was going.
I am chagrined by the sheer number of folks, real car people, who keep alive the phrase "ported and polished". In my opinion, the only engine that should be fitted with "ported and polished" heads would run a "3/4 race" cam, or maybe a Purple Shaft!!!
Here's the issue, a good CNC program has to be a one-size-fits-all program. The issue is core shift, casting inaccuracies.
If the cnc program was based on a max ported head, then there would be several heads per batch that would have holes in the port walls.
IMHO: A really good CNC program should be able to get within 5-7% of a pro ported head, meaning 15-21 cfm on a 300cfm CNC head. What do you think of those numbers, pro porters?
R.
I was at a seminar years ago , Jack Roush was the speaker. He talked about porting heads and leaving the intake rough for a wet flow. Thinking back now , I think that was before CNC machines were invented.LOL
it's ok to butt heads, just don't do it with a butthead
|
|
|
Re: Improving cnc ported heads
[Re: rowin4]
#2420813
12/19/17 03:44 AM
12/19/17 03:44 AM
|
Joined: Aug 2003
Posts: 43,218
Bend,OR USA
Cab_Burge
I Win
|
I Win
Joined: Aug 2003
Posts: 43,218
Bend,OR USA
|
I know a good shop in SO CA that had ordered a set of very expensive CNC ported Dart BB Chevy heads for a customer for his heads up PSCA car on a unlimited budget, the customer saw the heads and ask about smoothing out the CNC ridges in the intake ports to make them better. That shop had a new Super Flow 600 flow bench at that time so he flowed one port before and afte smoothing it out, no measurable improvements doing that on the flow bench   That may be one of those mods that needs to be done after dyno testing the motor and racing it at the track and then do the smoothing and retest it again with similar weather conditions
Last edited by Cab_Burge; 12/19/17 03:46 AM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
|
|
|
Re: Improving cnc ported heads
[Re: B3422W5]
#2420931
12/19/17 02:12 PM
12/19/17 02:12 PM
|
Joined: Oct 2007
Posts: 4,209
New York
polyspheric
master
|
master
Joined: Oct 2007
Posts: 4,209
New York
|
heads are only so thick, once you get them thin, seats start to move around
This^^^
Vizard reported on intake valves that didn't seat properly because the seat itself moved laterally when hot. The cure: weaken the valve head so it bends to conform. !!!
Boffin Emeritus
|
|
|
Re: Improving cnc ported heads
[Re: B3422W5]
#2420942
12/19/17 02:49 PM
12/19/17 02:49 PM
|
Joined: Jan 2003
Posts: 14,504
So. Burlington, Vt.
fast68plymouth
I Live Here
|
I Live Here
Joined: Jan 2003
Posts: 14,504
So. Burlington, Vt.
|
IMO, if the pre/post reworking of the CNC job isn't accompanied by a pre/post dyno session, you can't really quantify what you did.
Then, if it is better, by how much? And what did that gain cost?
68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123
Dealer for Comp Cams/Indy Heads
|
|
|
Re: Improving cnc ported heads
[Re: B3422W5]
#2420954
12/19/17 03:04 PM
12/19/17 03:04 PM
|
Joined: Jan 2003
Posts: 11,718
Portage,michigan
B3422W5
OP
I Live Here
|
OP
I Live Here
Joined: Jan 2003
Posts: 11,718
Portage,michigan
|
Again, talking about the as delivered " street port" cnc the new trick flows will come with
69 Dart GTS A4 Silver All steel, flat factory hood, 3360race weight
418 BPE factory replacement headed stroker, 565 lift solid cam
Best so far, 10.40 @127 1/4
1.41 best 60 foot
6.60 at 103.90 1/8
|
|
|
Re: Improving cnc ported heads
[Re: B3422W5]
#2420960
12/19/17 03:18 PM
12/19/17 03:18 PM
|
Joined: Feb 2005
Posts: 20,184
PA.
pittsburghracer
"Little"John
|
"Little"John
Joined: Feb 2005
Posts: 20,184
PA.
|
Again, talking about the as delivered " street port" cnc the new trick flows will come with Sometimes it comes down to WHO ported the head that the cnc’d Port was copied from. Anyone can Port a head and some guys call a buff & shine porting.
1970 Duster
Edelbrock headed 408
5.984@112.52
422 Indy headed small block
5.982@112.56 mph
9.42@138.27
Livin and lovin life one day at a time
|
|
|
Re: Improving cnc ported heads
[Re: B3422W5]
#2421069
12/19/17 06:32 PM
12/19/17 06:32 PM
|
Joined: Oct 2007
Posts: 4,209
New York
polyspheric
master
|
master
Joined: Oct 2007
Posts: 4,209
New York
|
CNC is not a program that analyzes port efficiency, or determines ideal port characteristics, that's CFD (and few of us can afford it).
CNC is the xerox of porting. It can never be better than the manual porting done on the original modified head to be used as a model.
How to:
1. have a highly rated and successful porting service do a common casting*
2. do an A > B dyno test, then a track test (especially for mph, not ET)
3. digitize the head using multi-axis probes
4. the computer program creates instructions to direct cutting tools to follow the contours identified in 3.
* you may see someone attempt to use a CNC program developed from a specific casting on a different casting... because they interchange on the same engine.
DON'T.
Boffin Emeritus
|
|
|
Re: Improving cnc ported heads
[Re: B3422W5]
#2421071
12/19/17 06:38 PM
12/19/17 06:38 PM
|
Joined: Oct 2007
Posts: 4,209
New York
polyspheric
master
|
master
Joined: Oct 2007
Posts: 4,209
New York
|
There may be differences in result quality between 2 different programs and 2 different CNC fixtures from the same (already ported) head.
How is that possible?
One takes smaller readings with the probe, at more angles, then uses more passes and smaller cutters at more axes (hours longer to complete).
In some castings (not all) the difference may be significant, especially with small ports and 3 dimensional curves.
Boffin Emeritus
|
|
|
|
|
