Any hp advantage to a good 3 angle valvejob on stock lt1 heads?
Banned
Joined: Oct 2002
Posts: 6,518
Yes, there is always an advantage to a good valve job over stock. Problem is not too many shops understand what the difference is. The valve job is the most important part of the cylinder head.
It doesn't have to be a 3 angle VJ either, you can have 4, 5, 6 just depends on the valve, the chamber and the port.
Bret
It doesn't have to be a 3 angle VJ either, you can have 4, 5, 6 just depends on the valve, the chamber and the port.
Bret
Registered User
Joined: Aug 2002
Posts: 1,509
From: Red Oak Texas
The answer is YES, a GOOD valve job (not just a 3 angle valve job with generic cutters) will definitely help flow and power on a stock LT1 head.
3 angle just means that other than the valve sealing angle (usually 45 degree) there is an angle above that (called a top cut and usually 35-39 degree) as well as an angle below that (called a bottom cut and usually 55-65 degree). It is basically the way that you can direct flow around the valve and into the cylinder.
The # of angles is not as important as the angles used and the widths of these angles. The average shop uses a 30/45/60 valve job that leaves ALOT on the table. A good valve job means a world of difference of how the air exits around the valve and into the chamber. The more efficient this is, the harder the valve job will "suck" on the port and how much air you pull through the port.
Most machine shops buy a "performance cutter" from a catalog thinking they have the best angles ever created by man but different heads like different valve jobs and most people that work with a flow bench will get their own recipe on all of these angles. A valve job is just what allows the valves to seal in the minds of most machine shops. Use 3 angles and run it out the door. What ever it flows, great, just make sure the valves seal.
The valve job to someone that does portwork is much different. First it must seal but they also have their recipe on what the venturi diameter as well as what angles, how wide the angles are, how many angles there are and how it all blends into the chamber.
On LT1 and 23 degree SB Chevy heads, I start with a 90* cut on the throat to set the venturi diameter and then use 2 bottom cuts, a 45 degree sealing angle and then a wide top cut into the chamber. I do the portwork top the 90* throat cut and then blend the top cut into the chamber.
LS1 and SB Ford like something way different though.
All of that talk is about intake valve job and the exhaust is pretty much a radius valve job on every set of well working heads I have seen.
If this info is over the head of the shop doing the 3 angle valve job, find another shop to do the work.
3 angle just means that other than the valve sealing angle (usually 45 degree) there is an angle above that (called a top cut and usually 35-39 degree) as well as an angle below that (called a bottom cut and usually 55-65 degree). It is basically the way that you can direct flow around the valve and into the cylinder.
The # of angles is not as important as the angles used and the widths of these angles. The average shop uses a 30/45/60 valve job that leaves ALOT on the table. A good valve job means a world of difference of how the air exits around the valve and into the chamber. The more efficient this is, the harder the valve job will "suck" on the port and how much air you pull through the port.
Most machine shops buy a "performance cutter" from a catalog thinking they have the best angles ever created by man but different heads like different valve jobs and most people that work with a flow bench will get their own recipe on all of these angles. A valve job is just what allows the valves to seal in the minds of most machine shops. Use 3 angles and run it out the door. What ever it flows, great, just make sure the valves seal.
The valve job to someone that does portwork is much different. First it must seal but they also have their recipe on what the venturi diameter as well as what angles, how wide the angles are, how many angles there are and how it all blends into the chamber.
On LT1 and 23 degree SB Chevy heads, I start with a 90* cut on the throat to set the venturi diameter and then use 2 bottom cuts, a 45 degree sealing angle and then a wide top cut into the chamber. I do the portwork top the 90* throat cut and then blend the top cut into the chamber.
LS1 and SB Ford like something way different though.
All of that talk is about intake valve job and the exhaust is pretty much a radius valve job on every set of well working heads I have seen.
If this info is over the head of the shop doing the 3 angle valve job, find another shop to do the work.
Registered User
Joined: Aug 2005
Posts: 4,405
From: Kantuckee Yo'
The answer is YES, a GOOD valve job (not just a 3 angle valve job with generic cutters) will definitely help flow and power on a stock LT1 head.
3 angle just means that other than the valve sealing angle (usually 45 degree) there is an angle above that (called a top cut and usually 35-39 degree) as well as an angle below that (called a bottom cut and usually 55-65 degree). It is basically the way that you can direct flow around the valve and into the cylinder.
The # of angles is not as important as the angles used and the widths of these angles. The average shop uses a 30/45/60 valve job that leaves ALOT on the table. A good valve job means a world of difference of how the air exits around the valve and into the chamber. The more efficient this is, the harder the valve job will "suck" on the port and how much air you pull through the port.
Most machine shops buy a "performance cutter" from a catalog thinking they have the best angles ever created by man but different heads like different valve jobs and most people that work with a flow bench will get their own recipe on all of these angles. A valve job is just what allows the valves to seal in the minds of most machine shops. Use 3 angles and run it out the door. What ever it flows, great, just make sure the valves seal.
The valve job to someone that does portwork is much different. First it must seal but they also have their recipe on what the venturi diameter as well as what angles, how wide the angles are, how many angles there are and how it all blends into the chamber.
On LT1 and 23 degree SB Chevy heads, I start with a 90* cut on the throat to set the venturi diameter and then use 2 bottom cuts, a 45 degree sealing angle and then a wide top cut into the chamber. I do the portwork top the 90* throat cut and then blend the top cut into the chamber.
LS1 and SB Ford like something way different though.
All of that talk is about intake valve job and the exhaust is pretty much a radius valve job on every set of well working heads I have seen.
If this info is over the head of the shop doing the 3 angle valve job, find another shop to do the work.
3 angle just means that other than the valve sealing angle (usually 45 degree) there is an angle above that (called a top cut and usually 35-39 degree) as well as an angle below that (called a bottom cut and usually 55-65 degree). It is basically the way that you can direct flow around the valve and into the cylinder.
The # of angles is not as important as the angles used and the widths of these angles. The average shop uses a 30/45/60 valve job that leaves ALOT on the table. A good valve job means a world of difference of how the air exits around the valve and into the chamber. The more efficient this is, the harder the valve job will "suck" on the port and how much air you pull through the port.
Most machine shops buy a "performance cutter" from a catalog thinking they have the best angles ever created by man but different heads like different valve jobs and most people that work with a flow bench will get their own recipe on all of these angles. A valve job is just what allows the valves to seal in the minds of most machine shops. Use 3 angles and run it out the door. What ever it flows, great, just make sure the valves seal.
The valve job to someone that does portwork is much different. First it must seal but they also have their recipe on what the venturi diameter as well as what angles, how wide the angles are, how many angles there are and how it all blends into the chamber.
On LT1 and 23 degree SB Chevy heads, I start with a 90* cut on the throat to set the venturi diameter and then use 2 bottom cuts, a 45 degree sealing angle and then a wide top cut into the chamber. I do the portwork top the 90* throat cut and then blend the top cut into the chamber.
LS1 and SB Ford like something way different though.
All of that talk is about intake valve job and the exhaust is pretty much a radius valve job on every set of well working heads I have seen.
If this info is over the head of the shop doing the 3 angle valve job, find another shop to do the work.
You ported my heads up to LE2 spec a year ago, did my heads get any kind of valve job like what you are describing?
Banned
Joined: Oct 2002
Posts: 6,518
wrd1972, yes.
ZL1, depends on who you go too. A valve job sounds like a simple thing to do, but done right it's time consuming. A well done valve job can be $300-$450 easy, the best valves are relative to who is doing the work. I know on some things I work on we buy a larger valve for it's shape, then cut it down to a smaller size, cut the seat and backcut we want on it and then do a little work to cut mass out of it. You can also find some guys that will give you something decent for around $150, it's just not going to be as labor intensive and detailed out as the more expensive ones.
Litterally there is as much to write about valve jobs as there is about head porting, the more you learn/know about it the more complex and interesting it is. Especially applying theories and concepts from one type of racing/heads to another and seeing it work. Pretty cool stuff. Valve jobs are like cam specs in some reguards, they are easily represented by numbers, but it's the combination and exicution of them that makes them work.
I've had some recent work with LS stuff that is pretty cool, there is a lot of air flow and quality in those heads with a stock port in just the valve job shape and angles. I have a spare set of LT1 heads laying around that I should apply some of these things too and see what just a valve job can do to a set of stock castings.
Bret
ZL1, depends on who you go too. A valve job sounds like a simple thing to do, but done right it's time consuming. A well done valve job can be $300-$450 easy, the best valves are relative to who is doing the work. I know on some things I work on we buy a larger valve for it's shape, then cut it down to a smaller size, cut the seat and backcut we want on it and then do a little work to cut mass out of it. You can also find some guys that will give you something decent for around $150, it's just not going to be as labor intensive and detailed out as the more expensive ones.
Litterally there is as much to write about valve jobs as there is about head porting, the more you learn/know about it the more complex and interesting it is. Especially applying theories and concepts from one type of racing/heads to another and seeing it work. Pretty cool stuff. Valve jobs are like cam specs in some reguards, they are easily represented by numbers, but it's the combination and exicution of them that makes them work.
I've had some recent work with LS stuff that is pretty cool, there is a lot of air flow and quality in those heads with a stock port in just the valve job shape and angles. I have a spare set of LT1 heads laying around that I should apply some of these things too and see what just a valve job can do to a set of stock castings.
Bret
Last edited by SStrokerAce; Dec 1, 2007 at 06:27 PM.
Registered User
Joined: Nov 2005
Posts: 646
From: PA
i would love to see what type of gains can be had by getting a valve job and larger valves on stock heads...
if it yields good results i may just get that done as well as the custom grind cam... Good to me would be ~20rwhp
Registered User
Joined: May 2004
Posts: 2,001
From: Bay Area, CA
Lots of good info here - like Bret said, there is tons of R&D that just goes into the VJ, for example, I have seen our valve jobs pick up 15-30 CFM with just seat work, no porting - for no porting rules race motors.
FYI: The factory LT1 valve job is a 3-angle. So if you are not getting them rebuilt with at least a good 3-angle VJ, you are loosing power.
FYI: The factory LT1 valve job is a 3-angle. So if you are not getting them rebuilt with at least a good 3-angle VJ, you are loosing power.
Banned
Joined: Oct 2002
Posts: 6,518
I would just need something to run them on! ;-)
Banned
Joined: Oct 2006
Posts: 4,970
From: Goochland, Va.
I got something you can test them darts on
The valve job is a major key in your flow. I have seen a big profiler head gain 35 CFM by changing the angle on the valve job. Same thing you do in stock class racing. And its not always a 3 angle......the more angles the easier it is for the air to flow around the valve
The valve job is a major key in your flow. I have seen a big profiler head gain 35 CFM by changing the angle on the valve job. Same thing you do in stock class racing. And its not always a 3 angle......the more angles the easier it is for the air to flow around the valve