Porting experts
06-07-2002, 12:59 PM
#1
Member
Thread Starter
Porting experts
I read an article in the February CarCraft by Marlan Davis
about Budget Iron Heads. In the article he states
with respect to the Vortec L31 head...
(From Installation Notes sidebar)
As-delivered, the GM factory valve job is virtually
impossible to improve-so don't try
Unfortunately nothing in the article explains why
this is so "perfect".
Any of you porting specialists had achance to analyze
these heads...
about Budget Iron Heads. In the article he states
with respect to the Vortec L31 head...
(From Installation Notes sidebar)
As-delivered, the GM factory valve job is virtually
impossible to improve-so don't try
Unfortunately nothing in the article explains why
this is so "perfect".
Any of you porting specialists had achance to analyze
these heads...
06-07-2002, 01:07 PM
#2
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Vortec heads deliver a very high airflow for what is reletivly a very small port. What that means basically is that the port is just about perfect, or closer to it than even most profesional shops will ever get it. Other stock GM heads with similar port volumes have flaws. sharp edges....dirty contours..rough spots, etc, that hurt flow. Not only due to design flaws but limitations of the casting process. Vortec heads don;t as much.
06-07-2002, 01:17 PM
#3
Member
Thread Starter
Not exactly what I was looking for...
The article further indicates ...
"We've seen 10-12 cfm flow decreases in Vortech
heads when a generic three-angle rebuilder valve job
is used in place of GM's production valve job"
So a "cleaner" casting process isn't the answer.
What I was looking for is something of interest
in perhaps radiusing of the seats, seat width, angle etc
I think the big "hint" is in how well they seem to flow
between .050 and .200 in valve openings...
The article further indicates ...
"We've seen 10-12 cfm flow decreases in Vortech
heads when a generic three-angle rebuilder valve job
is used in place of GM's production valve job"
So a "cleaner" casting process isn't the answer.
What I was looking for is something of interest
in perhaps radiusing of the seats, seat width, angle etc
I think the big "hint" is in how well they seem to flow
between .050 and .200 in valve openings...
06-07-2002, 01:50 PM
#4
Supreme Member
What they are telling you is that unless you have access
to a flow bench and lots of head porting experience
you are best to leave the intake port and valve job as is.
The exhaust port is a different story. It will respond nicely to
basic mild porting technics and polishing.
The intake port will only be significently improved with a pro-
fessionally done full port job and a bigger valve. With flow bench verification.
Just about every thing I do to other chevy heads when I port them is already done for ya on Vortecs.
to a flow bench and lots of head porting experience
you are best to leave the intake port and valve job as is.
The exhaust port is a different story. It will respond nicely to
basic mild porting technics and polishing.
The intake port will only be significently improved with a pro-
fessionally done full port job and a bigger valve. With flow bench verification.
Just about every thing I do to other chevy heads when I port them is already done for ya on Vortecs.
06-07-2002, 06:01 PM
#6
Supreme Member
Originally posted by urbman
Hmmm...
So you don't know anything about the
seat architecture either
Hmmm...
So you don't know anything about the
seat architecture either
06-08-2002, 12:08 AM
#7
Member
Thread Starter
Hmmm....
Well maybe I can't write ...
Roughly...
If the CarCraft data is reasonably accurate then I think there is
something to look at here. What I had read about the Vortec
head is that it was similar to the LT1 head in most respects.
The article is the first one that I had seen that put one on a flowbench.
CarCraft reported that at 28 inches....
Valve lift (in) Intake Flow (cfm) Exhaust Flow (cfm)
0.050 40 25
0.100 70 48
0.200 138 101
0.300 190 129
0.400 227 140
0.500 239 147
According to ...
http://www.malcams.com/legacy/misc/headflow.htm
Stock LT-1
Valve lift (in) Intake Flow (cfm) Exhaust Flow (cfm)
0.050 no data no data
0.100 60.2 46.1
0.200 119.1 93.6
0.300 170.9 123.5
0.400 198.9 141.2
0.500 206.4 153.2
The remarkable thing is the low lift numbers. Fairly competent
porters Vizard, Myron Cotrell et al. barely get there with
highly refined efforts.
So the Vortec isn't a cast iron LT1 head by any stretch. Further
GM seems to be able to do this "by the thousands" my guess
is that these low flow numbers point the way to the "ideal"
seat shape.
I agree that better casting methodology certainly explains
the numbers above .200 inches but as I understand it
below that the primary influence is the seat itself and the valve.
The point of my query was, as there seems to be a lot of guys
goofing around with Vortec head combinations, that maybe
someone has done the work and I had missed it.
And as is always the case to spark some debate as to why
this seat combo works, provided someone had some
reasonable measurements regarding the seat, angle,
radiusing, valve back angle etc.
If this is unremarkable then its even cooler than I thought...
F-dude the smiley was to indicate a friendly jab as opposed
to an insult.
Well maybe I can't write ...
Roughly...
If the CarCraft data is reasonably accurate then I think there is
something to look at here. What I had read about the Vortec
head is that it was similar to the LT1 head in most respects.
The article is the first one that I had seen that put one on a flowbench.
CarCraft reported that at 28 inches....
Valve lift (in) Intake Flow (cfm) Exhaust Flow (cfm)
0.050 40 25
0.100 70 48
0.200 138 101
0.300 190 129
0.400 227 140
0.500 239 147
According to ...
http://www.malcams.com/legacy/misc/headflow.htm
Stock LT-1
Valve lift (in) Intake Flow (cfm) Exhaust Flow (cfm)
0.050 no data no data
0.100 60.2 46.1
0.200 119.1 93.6
0.300 170.9 123.5
0.400 198.9 141.2
0.500 206.4 153.2
The remarkable thing is the low lift numbers. Fairly competent
porters Vizard, Myron Cotrell et al. barely get there with
highly refined efforts.
So the Vortec isn't a cast iron LT1 head by any stretch. Further
GM seems to be able to do this "by the thousands" my guess
is that these low flow numbers point the way to the "ideal"
seat shape.
I agree that better casting methodology certainly explains
the numbers above .200 inches but as I understand it
below that the primary influence is the seat itself and the valve.
The point of my query was, as there seems to be a lot of guys
goofing around with Vortec head combinations, that maybe
someone has done the work and I had missed it.
And as is always the case to spark some debate as to why
this seat combo works, provided someone had some
reasonable measurements regarding the seat, angle,
radiusing, valve back angle etc.
If this is unremarkable then its even cooler than I thought...
F-dude the smiley was to indicate a friendly jab as opposed
to an insult.
Trending Topics
06-08-2002, 04:09 AM
#8
Supreme Member
The remarkable thing about it is that there is nothing high tech
or any hokis pokis in the seat angles. they are pretty
standard. But they work ON THIS HEAD.... Up to a point.
Take away the chamber or the floor and generous short side radius and it will want something else. Get beyond .500"
and it starts to want something else. There is no radius seats
or other super narrow seats or any witchcraft here.
This is a production truck head made to last 100,000miles
between valve jobs.
Put the hot rod books down and get ahold of an actual head
and you'll see that it's a complete system that makes the port good. I had the benefit of chatting with one of the GM engineers
who worked on the production (casting plant) end of the project.
Very interesting. The casting is very accurate, not smooth
but a consistant texture. There is little or no core shift at all.
This is called "Cast Port" technology. A lot of the research was done here in St. Catharines Ont. The chamber is designed to
unshroud the valves for good low lift flow, yet promote
swirl and tumble along with high quench energy (Fast Burn).
This promotes high torque, low emissions, good fuel mileage.
and better the usual throttle response. The plug is centrally located, requiring less ignition timing and high detonation
tolerance.
1960's Cadillac and Buick motors used a simular design, so there really is nothing new under the sun.
My friends and I have messed a bit with these heads and flow tested and dyno tested and raced 'em a bit. I can tell you
that the car magazines are right. Try it stock first cause it's
almost idea out of the box for the intended purpose. "Street Performance". If you get in there and start carving away you are
more likely to kill over all performance than help it.
No magic here just good engineering and manufacturing.
Resulting in a better than average and/or better than most, reasonably priced high performance street head. Hope I haven't disapointed you too much....
Previously I said that he ports cannot be improved much
with professional porting and bigger valves. I ment the average
person can't improve it much without a full professional job and
flow testing. This head like other small block heads responds
to all out max porting and big valves but you'll need a .650+ lift roller and a Big tall single plane intake to take advantage of the high lift flow.
Have a good day.....
or any hokis pokis in the seat angles. they are pretty
standard. But they work ON THIS HEAD.... Up to a point.
Take away the chamber or the floor and generous short side radius and it will want something else. Get beyond .500"
and it starts to want something else. There is no radius seats
or other super narrow seats or any witchcraft here.
This is a production truck head made to last 100,000miles
between valve jobs.
Put the hot rod books down and get ahold of an actual head
and you'll see that it's a complete system that makes the port good. I had the benefit of chatting with one of the GM engineers
who worked on the production (casting plant) end of the project.
Very interesting. The casting is very accurate, not smooth
but a consistant texture. There is little or no core shift at all.
This is called "Cast Port" technology. A lot of the research was done here in St. Catharines Ont. The chamber is designed to
unshroud the valves for good low lift flow, yet promote
swirl and tumble along with high quench energy (Fast Burn).
This promotes high torque, low emissions, good fuel mileage.
and better the usual throttle response. The plug is centrally located, requiring less ignition timing and high detonation
tolerance.
1960's Cadillac and Buick motors used a simular design, so there really is nothing new under the sun.
My friends and I have messed a bit with these heads and flow tested and dyno tested and raced 'em a bit. I can tell you
that the car magazines are right. Try it stock first cause it's
almost idea out of the box for the intended purpose. "Street Performance". If you get in there and start carving away you are
more likely to kill over all performance than help it.
No magic here just good engineering and manufacturing.
Resulting in a better than average and/or better than most, reasonably priced high performance street head. Hope I haven't disapointed you too much....
Previously I said that he ports cannot be improved much
with professional porting and bigger valves. I ment the average
person can't improve it much without a full professional job and
flow testing. This head like other small block heads responds
to all out max porting and big valves but you'll need a .650+ lift roller and a Big tall single plane intake to take advantage of the high lift flow.
Have a good day.....
06-08-2002, 04:14 PM
#9
Member
Thread Starter
>>The remarkable thing about it is that there is nothing high tech
>>or any hokis pokis in the seat angles
Any chance you know what these are ?
>>Put the hot rod books down and get ahold of an actual head
>> and you'll see that it's a complete system that makes the port
>>good
Well, I blew my chance. Assuming I knew what I was looking
at was a mistake ( A nice Iron version of an LT1 head).
Also my eyeball calibration is off. Without another pair of seats
right next to them I can't look at a head and tell you that the
seat is .060 vs .070 or that the angle is clearly 45% vs 40%.
More power to ya !
>>The chamber is designed to unshroud the valves for good low
>> lift flow
The numbers seem to indicate that, that is the case.
At any rate the goal is/was to see what I could learn from
the success of the L31 head and apply it to other heads
namely the LT1 heads on my bench...
And a good day to you sir...
>>or any hokis pokis in the seat angles
Any chance you know what these are ?
>>Put the hot rod books down and get ahold of an actual head
>> and you'll see that it's a complete system that makes the port
>>good
Well, I blew my chance. Assuming I knew what I was looking
at was a mistake ( A nice Iron version of an LT1 head).
Also my eyeball calibration is off. Without another pair of seats
right next to them I can't look at a head and tell you that the
seat is .060 vs .070 or that the angle is clearly 45% vs 40%.
More power to ya !
>>The chamber is designed to unshroud the valves for good low
>> lift flow
The numbers seem to indicate that, that is the case.
At any rate the goal is/was to see what I could learn from
the success of the L31 head and apply it to other heads
namely the LT1 heads on my bench...
And a good day to you sir...
06-09-2002, 10:19 AM
#10
My iron LT1 heads responded very favorably to 2.02/1.60 valves, deep valve bowls, shortened radii on the near side of both intake and exhaust valves, general port straightening and raising the ceilings, and a radius on the FRONT side of the intake valves (from the margin outward). I'm sure the Comp cam didn't hurt either.
SLP used to have some flow numbers on these modifications somewhere on their site. Intake flow on the cast iron LT1 heads increased from 230SCFM @ .500" to 261SCFM @ .500", before teh 1.94 valves were replaced. Oddly enough, the iron LT1 heads outflowed the aluminum ones in the CHP tests from 1998: http://www.malcams.com/legacy/misc/headflow.htm
SLP used to have some flow numbers on these modifications somewhere on their site. Intake flow on the cast iron LT1 heads increased from 230SCFM @ .500" to 261SCFM @ .500", before teh 1.94 valves were replaced. Oddly enough, the iron LT1 heads outflowed the aluminum ones in the CHP tests from 1998: http://www.malcams.com/legacy/misc/headflow.htm
06-09-2002, 11:30 AM
#12
Member
Thread Starter
>>why question perfection?
Always question everything
Vader...
My primary interest is in the low lift numbers any chance
you have a pointer to your head data roughly .050 to .200
Could you clarify..
"and a radius on the FRONT side of the intake valves (from the margin outward)"
Did you leave the relative valve heights alone ?
Apparantly I can't read
Always question everything
Vader...
My primary interest is in the low lift numbers any chance
you have a pointer to your head data roughly .050 to .200
Could you clarify..
"and a radius on the FRONT side of the intake valves (from the margin outward)"
Did you leave the relative valve heights alone ?
Apparantly I can't read
06-09-2002, 12:25 PM
#14
Always question EVERYONE. That's the only way anyone can learn, understand, or decide for themselves. Questioning doesn't have to be insulting, just an inquiry. Dumb questions are the ones that are never asked, and there's a huge distinction between "dumb" and "uneducated". One is a condition, the other is simply a process.
As for the valve radii, I contoured the front faces of the intake valves back to the margin. Basically, the theory is that the margin becomes a radius, and there is no sharp corner at the valve face to aid low lift flows. There are already enough sharp angles around the valve perimeter to inhibit flow. The short trackers around the region have been doing this for several years, and getting 5-8 dyno HP out of it. They typically run their 2-barrel 358s between 4,000-7,200 RPM around the oval so the time spent at low lifts would be minimal, but it seems to work on the track and dyno as well as on paper. Oddly, the machinists are saying the modification done to the exhaust valves doesn't hurt, but does nothing to add power either. The speculation is that the higher pressure differential exhaust gasses get around the valve with less of a problem (which is why a smaller diameter exhaust valve can be used in the first place) and the port configuration and sheer volume are far more important than valve angles and edge flow on the exhaust side.
After polling several reputable race engine builders, I/we collectively determined that it wouldn't be a good idea on a street engine where reliabilty is more of an issue. The intakes are not a serious issue since they are a lot cooler than the exhausts, so the face raduis seemed to be a safe bet. If I get even 3-5 HP peak out of it, I'm happy, since it was basically "free". The trick was getting them to set up the valve grinder to touch the "wrong" side of the valve. DuMores and Healds are great for this though, since they set up so easily.
By valve height, if you mean lift, no, it is not stock. The installed heights were taller than stock by about 0.100". I also changed the cam to an eventual lift of .510/.510 from .418/.430 with a lot more ramp, so time at low lifts is minimized. Lots of free area under the curve.
I'll try to get more data on the flow @ lift to you. You might try searching some of the LT1/LT4 fora for data.
As for the valve radii, I contoured the front faces of the intake valves back to the margin. Basically, the theory is that the margin becomes a radius, and there is no sharp corner at the valve face to aid low lift flows. There are already enough sharp angles around the valve perimeter to inhibit flow. The short trackers around the region have been doing this for several years, and getting 5-8 dyno HP out of it. They typically run their 2-barrel 358s between 4,000-7,200 RPM around the oval so the time spent at low lifts would be minimal, but it seems to work on the track and dyno as well as on paper. Oddly, the machinists are saying the modification done to the exhaust valves doesn't hurt, but does nothing to add power either. The speculation is that the higher pressure differential exhaust gasses get around the valve with less of a problem (which is why a smaller diameter exhaust valve can be used in the first place) and the port configuration and sheer volume are far more important than valve angles and edge flow on the exhaust side.
After polling several reputable race engine builders, I/we collectively determined that it wouldn't be a good idea on a street engine where reliabilty is more of an issue. The intakes are not a serious issue since they are a lot cooler than the exhausts, so the face raduis seemed to be a safe bet. If I get even 3-5 HP peak out of it, I'm happy, since it was basically "free". The trick was getting them to set up the valve grinder to touch the "wrong" side of the valve. DuMores and Healds are great for this though, since they set up so easily.
By valve height, if you mean lift, no, it is not stock. The installed heights were taller than stock by about 0.100". I also changed the cam to an eventual lift of .510/.510 from .418/.430 with a lot more ramp, so time at low lifts is minimized. Lots of free area under the curve.
I'll try to get more data on the flow @ lift to you. You might try searching some of the LT1/LT4 fora for data.
06-09-2002, 04:53 PM
#15
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Car: Junk
Engine: Junk with nitrous
Transmission: Junk with gears
I really doubt vortec's ports can't be improved upon. If my stock heads flow what you say they flowed, then explain how my new ported heads flowed 272/228 cfm after some extensive home porting (and with help from a professional head porting buddy of mine)???? There is definitely stuff you can do to this heads to improve on them. Basically what was done to mine was MAJOR porting to the exhaust bowls, intake bowl ported within reason (mostly just cut down the pushrod boss almost completely while still leaving the "fin") and reshaping and grinding of the exhaust ports to enlargen them to match fastburn style D shaped exits. Naysayers said it was a waste of time, but flow testing doesn't lie, and MAN does the car haul *** now compared to the old vortecs and smaller cam
06-09-2002, 08:25 PM
#16
Member
Thread Starter
Any chance I could convice you to post some numbers...
(I'd be most interested in what you got between .050 and .200)
Pics if you have em would be a great help
(I'd be most interested in what you got between .050 and .200)
Pics if you have em would be a great help
06-09-2002, 10:20 PM
#17
Member
Thread Starter
Vader says...
>>By valve height, if you mean lift...
I was guessing that you might have had new seats installed.
This would give one a chance to make a slight change in the
position of the valves relative to one another.
Also ...
Just so you know where I am trying to go with this...
My thinking so far is to try to minimize the total number of
head "experiments" ( I really can't afford building up a half dozen heads, time, money, energy,enthusiasm).
I guess a quick logic check is in order...
1. The basic port design of the LT1 is sound
2. Most everyone having success with an LT1 head is either
compensating for the low lift shortcommings with aggresive
ramps, longer rockers or both
3. The use of aggresive profiles requires either lightweight
valve train pieces, full rollers aggresive springs and
attendant strengthening
4. The vortech head, in its primary role as a truck head
couldn't make use of low lsa cams and so had to be a
good low lift flowing head to be "better".
So...
If I could sort out the low lift characteristics of the vortec
apply them to the Lt1 perhaps I could make reasonable
power with relatively modest componentry...
As opposed to getting somebody to cook up
a set of LT4's $$$
I guess its time to mold some ports...
Anybody got a set of Vortecs laying around
>>By valve height, if you mean lift...
I was guessing that you might have had new seats installed.
This would give one a chance to make a slight change in the
position of the valves relative to one another.
Also ...
Just so you know where I am trying to go with this...
My thinking so far is to try to minimize the total number of
head "experiments" ( I really can't afford building up a half dozen heads, time, money, energy,enthusiasm).
I guess a quick logic check is in order...
1. The basic port design of the LT1 is sound
2. Most everyone having success with an LT1 head is either
compensating for the low lift shortcommings with aggresive
ramps, longer rockers or both
3. The use of aggresive profiles requires either lightweight
valve train pieces, full rollers aggresive springs and
attendant strengthening
4. The vortech head, in its primary role as a truck head
couldn't make use of low lsa cams and so had to be a
good low lift flowing head to be "better".
So...
If I could sort out the low lift characteristics of the vortec
apply them to the Lt1 perhaps I could make reasonable
power with relatively modest componentry...
As opposed to getting somebody to cook up
a set of LT4's $$$
I guess its time to mold some ports...
Anybody got a set of Vortecs laying around
Last edited by urbman; 06-09-2002 at 11:35 PM.
06-10-2002, 03:06 PM
#18
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Car: Junk
Engine: Junk with nitrous
Transmission: Junk with gears
Originally posted by urbman
Any chance I could convice you to post some numbers...
(I'd be most interested in what you got between .050 and .200)
Pics if you have em would be a great help
Any chance I could convice you to post some numbers...
(I'd be most interested in what you got between .050 and .200)
Pics if you have em would be a great help
I do remember that the peak flow #'s occured at .520 lift, not .470 or so like the stockers, and the flow #'s at .200 and below were really impressive in comparison to aftermarket aluminum heads.......they outflowed Edlebrocks RPMs #'s by a good margin. I forgot to mention that my vortecs still have 1.94 valves, but 1.6 exhaust. Going to 2.02s isn't going to do anything on vortecs, but uping the exhaust size along with your porting does wonders for the I/E ratio. IMHO vortecs are an awesome head if you can do your own porting work and dont' mind spending a couple bucks and a few weeks at the machine shop getting the screw in studs and better valve springs setup...........because in the end they WILL make more power than most low end Aluminum heads, not to mention they are cast iron and will last practically forever 
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