Gross valve lift
03-14-2005, 02:55 PM
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No, but it is specific to each engine. You can measure the total distance from the valve to the piston using the valve drop method. Subtract the minimum piston to valve clearance and that should be your max gross valve lift that you can run.
03-14-2005, 02:57 PM
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Originally Posted by tdrumm
No, but it is specific to each engine. You can measure the total distance from the valve to the piston using the valve drop method. Subtract the minimum piston to valve clearance and that should be your max gross valve lift that you can run.
03-14-2005, 03:20 PM
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Originally Posted by tdrumm
No, but it is specific to each engine. You can measure the total distance from the valve to the piston using the valve drop method. Subtract the minimum piston to valve clearance and that should be your max gross valve lift that you can run.
Actually, let me throw my numbers out there so you can tell me what you think. I got a G5 cam:
http://www.lmperformance.com/4945/43.html
Cam has .581/.572" lift (I assume this is with a 1.7 rocker ratio). Also have stage 2 heads (2.02" valves), heads not milled.
I'm thinking of adding 1.85 ratio rockers which could give me a gross valve lift of .632/.622". Anything over .6" makes me wonder
What do you think? .632/.622" sound like too much?
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03-15-2005, 05:53 AM
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My guess is that is too big and you will have p to v problems if you use those rockers.
But like was stated above, max lift is not the only variable. Your cam duration also plays a role. The closest the piston gets to the valve is not at max lift, but actually around 10 degrees before and after TDC. That is why you need to take the measurements to be sure.
But like was stated above, max lift is not the only variable. Your cam duration also plays a role. The closest the piston gets to the valve is not at max lift, but actually around 10 degrees before and after TDC. That is why you need to take the measurements to be sure.
03-15-2005, 06:52 AM
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Originally Posted by tdrumm
My guess is that is too big and you will have p to v problems if you use those rockers.
But like was stated above, max lift is not the only variable. Your cam duration also plays a role. The closest the piston gets to the valve is not at max lift, but actually around 10 degrees before and after TDC. That is why you need to take the measurements to be sure.
But like was stated above, max lift is not the only variable. Your cam duration also plays a role. The closest the piston gets to the valve is not at max lift, but actually around 10 degrees before and after TDC. That is why you need to take the measurements to be sure.
gotcha, thanks!!
03-15-2005, 07:46 AM
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[QUOTE=EATAZ06MMM]Does anyone know what the maximum allowable gross valve lift that you can achieve without having to change/modify the stock pistons in an LS1?[/QUOTh
if you have a stock head you yous a 216/220 525/532/ on a 112 or a 114 lsa
if you have a m6 a 112 if you have a 4 aol then go to a 114 lsa.
if you have a work head the big is with out / modify the pistons.
thunder/ racing [ feel the thunder] 224/224 / 563/563/ on a 114 lsa.
ckn hwk. yo can you dig.
if you have a stock head you yous a 216/220 525/532/ on a 112 or a 114 lsa
if you have a m6 a 112 if you have a 4 aol then go to a 114 lsa.
if you have a work head the big is with out / modify the pistons.
thunder/ racing [ feel the thunder] 224/224 / 563/563/ on a 114 lsa.
ckn hwk. yo can you dig.
03-15-2005, 07:57 AM
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[QUOTE=cknhwk1] I appreciate your comments, but......
if you have a stock head you yous a 216/220 525/532/ on a 112 or a 114 lsa
I'm pretty sure I can get a cam w/ more lift than that. Actually, the one I have now is .572/.581 lift as stated in the previous post, w/ stage 2 heads, theres no problems.
if you have a m6 a 112 if you have a 4 aol then go to a 114 lsa.
What does lobe seperation have to do w/ gross valve lift?
Originally Posted by EATAZ06MMM
Does anyone know what the maximum allowable gross valve lift that you can achieve without having to change/modify the stock pistons in an LS1?[/QUOTh
if you have a stock head you yous a 216/220 525/532/ on a 112 or a 114 lsa
if you have a m6 a 112 if you have a 4 aol then go to a 114 lsa.
if you have a work head the big is with out / modify the pistons.
thunder/ racing [ feel the thunder] 224/224 / 563/563/ on a 114 lsa.
ckn hwk. yo can you dig.
if you have a stock head you yous a 216/220 525/532/ on a 112 or a 114 lsa
if you have a m6 a 112 if you have a 4 aol then go to a 114 lsa.
if you have a work head the big is with out / modify the pistons.
thunder/ racing [ feel the thunder] 224/224 / 563/563/ on a 114 lsa.
ckn hwk. yo can you dig.
if you have a stock head you yous a 216/220 525/532/ on a 112 or a 114 lsa
I'm pretty sure I can get a cam w/ more lift than that. Actually, the one I have now is .572/.581 lift as stated in the previous post, w/ stage 2 heads, theres no problems.
if you have a m6 a 112 if you have a 4 aol then go to a 114 lsa.
What does lobe seperation have to do w/ gross valve lift?
03-15-2005, 08:03 AM
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I need to repost the last one. Forgive me, I'm a "newbie"
I appreciate your comments, but......
"if you have a stock head you yous a 216/220 525/532/ on a 112 or a 114 lsa"
I'm pretty sure I can get a cam w/ more lift than that. Actually, the one I have now is .572/.581 lift as stated in the previous post, w/ stage 2 heads, theres no problems.
"if you have a m6 a 112 if you have a 4 aol then go to a 114 lsa."
What does lobe seperation have to do w/ gross valve lift?
I appreciate your comments, but......
"if you have a stock head you yous a 216/220 525/532/ on a 112 or a 114 lsa"
I'm pretty sure I can get a cam w/ more lift than that. Actually, the one I have now is .572/.581 lift as stated in the previous post, w/ stage 2 heads, theres no problems.
"if you have a m6 a 112 if you have a 4 aol then go to a 114 lsa."
What does lobe seperation have to do w/ gross valve lift?
03-15-2005, 09:14 AM
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1. If you have a pair of lobes regarding intake and exhaust duration and lift for each lobe and everything else stays the same such as:
a. rocker ratio
b. you don't mill the heads (making the valves closer to the pistons) or
c, anything like that and
2. you increase the lobe separation angle by 10 degrees. We'll split it half and half making the intake open 5 degrees sooner and the exhaust closes 5 degrees later.
3. Then the intake and exhaust valves are sticking out closer to the piston as the piston is in the vicinity of top dead center.
There are some other important issues here regarding improved performance other than simply putting in a cam with a bigger lift. I'll try to name a few:
1. If your heads have not been ported to take advantage of the increased lift, the big cam may perform much more poorly than a smaller cam. The reason is that the big cam may not perform well at the mid-lift flow range where your heads are performing well in their existing state.
2. If you go to a higher lift cam (let's say above about .540 lift) and are operating above 5,800 RPM's, you really need to upgrade your whole valve train . . . not just the cam but the timing set, the push rods (especially the push rods), roller tip rockers regardless of the ratio because the higher lifts exert higher side loads on the valve stems.
3. A much bigger cam will require bigger injectors
4. A bigger cam and all that it requires to operate properly will demand proper tuning as it will really out strip what the PCM is set up to do.
5. Disregarding the milling of the stock pistons and valve to piston clearance, will the stock pistons be up to the task. They are Eutectic or Hypereutectic cast pistons, not forged which are much stronger.
If you want to do something with bang for your buck, get your stock heads ported in the bowl area and a good three angle valve job. You want something that preserves the swirl ramp and the majority of the mixture dam on the intake side and gets rid of the intake valve stud boss in the intake port. You want the bowl blended into the throat/venturi of the valve seat inserts and preserve velocity and swirl, not a hog out job. They need to make sure that the short side radius in the intake and exhaust chambers are smooth like a baby's behind and not have ripples and ridges. Look for a head porter that can spend a few hours on your heads and replace your push rods.
Then get a proper tune, that's my advice for the day. Don't worry about a mega cam.
All my best,
Steve
a. rocker ratio
b. you don't mill the heads (making the valves closer to the pistons) or
c, anything like that and
2. you increase the lobe separation angle by 10 degrees. We'll split it half and half making the intake open 5 degrees sooner and the exhaust closes 5 degrees later.
3. Then the intake and exhaust valves are sticking out closer to the piston as the piston is in the vicinity of top dead center.
There are some other important issues here regarding improved performance other than simply putting in a cam with a bigger lift. I'll try to name a few:
1. If your heads have not been ported to take advantage of the increased lift, the big cam may perform much more poorly than a smaller cam. The reason is that the big cam may not perform well at the mid-lift flow range where your heads are performing well in their existing state.
2. If you go to a higher lift cam (let's say above about .540 lift) and are operating above 5,800 RPM's, you really need to upgrade your whole valve train . . . not just the cam but the timing set, the push rods (especially the push rods), roller tip rockers regardless of the ratio because the higher lifts exert higher side loads on the valve stems.
3. A much bigger cam will require bigger injectors
4. A bigger cam and all that it requires to operate properly will demand proper tuning as it will really out strip what the PCM is set up to do.
5. Disregarding the milling of the stock pistons and valve to piston clearance, will the stock pistons be up to the task. They are Eutectic or Hypereutectic cast pistons, not forged which are much stronger.
If you want to do something with bang for your buck, get your stock heads ported in the bowl area and a good three angle valve job. You want something that preserves the swirl ramp and the majority of the mixture dam on the intake side and gets rid of the intake valve stud boss in the intake port. You want the bowl blended into the throat/venturi of the valve seat inserts and preserve velocity and swirl, not a hog out job. They need to make sure that the short side radius in the intake and exhaust chambers are smooth like a baby's behind and not have ripples and ridges. Look for a head porter that can spend a few hours on your heads and replace your push rods.
Then get a proper tune, that's my advice for the day. Don't worry about a mega cam.
All my best,
Steve
03-15-2005, 09:43 AM
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Originally Posted by Steve Bryant
1. If you have a pair of lobes regarding intake and exhaust duration and lift for each lobe and everything else stays the same such as:
a. rocker ratio
b. you don't mill the heads (making the valves closer to the pistons) or
c, anything like that and
2. you increase the lobe separation angle by 10 degrees. We'll split it half and half making the intake open 5 degrees sooner and the exhaust closes 5 degrees later.
3. Then the intake and exhaust valves are sticking out closer to the piston as the piston is in the vicinity of top dead center.
There are some other important issues here regarding improved performance other than simply putting in a cam with a bigger lift. I'll try to name a few:
1. If your heads have not been ported to take advantage of the increased lift, the big cam may perform much more poorly than a smaller cam. The reason is that the big cam may not perform well at the mid-lift flow range where your heads are performing well in their existing state.
2. If you go to a higher lift cam (let's say above about .540 lift) and are operating above 5,800 RPM's, you really need to upgrade your whole valve train . . . not just the cam but the timing set, the push rods (especially the push rods), roller tip rockers regardless of the ratio because the higher lifts exert higher side loads on the valve stems.
3. A much bigger cam will require bigger injectors
4. A bigger cam and all that it requires to operate properly will demand proper tuning as it will really out strip what the PCM is set up to do.
5. Disregarding the milling of the stock pistons and valve to piston clearance, will the stock pistons be up to the task. They are Eutectic or Hypereutectic cast pistons, not forged which are much stronger.
If you want to do something with bang for your buck, get your stock heads ported in the bowl area and a good three angle valve job. You want something that preserves the swirl ramp and the majority of the mixture dam on the intake side and gets rid of the intake valve stud boss in the intake port. You want the bowl blended into the throat/venturi of the valve seat inserts and preserve velocity and swirl, not a hog out job. They need to make sure that the short side radius in the intake and exhaust chambers are smooth like a baby's behind and not have ripples and ridges. Look for a head porter that can spend a few hours on your heads and replace your push rods.
Then get a proper tune, that's my advice for the day. Don't worry about a mega cam.
All my best,
Steve
a. rocker ratio
b. you don't mill the heads (making the valves closer to the pistons) or
c, anything like that and
2. you increase the lobe separation angle by 10 degrees. We'll split it half and half making the intake open 5 degrees sooner and the exhaust closes 5 degrees later.
3. Then the intake and exhaust valves are sticking out closer to the piston as the piston is in the vicinity of top dead center.
There are some other important issues here regarding improved performance other than simply putting in a cam with a bigger lift. I'll try to name a few:
1. If your heads have not been ported to take advantage of the increased lift, the big cam may perform much more poorly than a smaller cam. The reason is that the big cam may not perform well at the mid-lift flow range where your heads are performing well in their existing state.
2. If you go to a higher lift cam (let's say above about .540 lift) and are operating above 5,800 RPM's, you really need to upgrade your whole valve train . . . not just the cam but the timing set, the push rods (especially the push rods), roller tip rockers regardless of the ratio because the higher lifts exert higher side loads on the valve stems.
3. A much bigger cam will require bigger injectors
4. A bigger cam and all that it requires to operate properly will demand proper tuning as it will really out strip what the PCM is set up to do.
5. Disregarding the milling of the stock pistons and valve to piston clearance, will the stock pistons be up to the task. They are Eutectic or Hypereutectic cast pistons, not forged which are much stronger.
If you want to do something with bang for your buck, get your stock heads ported in the bowl area and a good three angle valve job. You want something that preserves the swirl ramp and the majority of the mixture dam on the intake side and gets rid of the intake valve stud boss in the intake port. You want the bowl blended into the throat/venturi of the valve seat inserts and preserve velocity and swirl, not a hog out job. They need to make sure that the short side radius in the intake and exhaust chambers are smooth like a baby's behind and not have ripples and ridges. Look for a head porter that can spend a few hours on your heads and replace your push rods.
Then get a proper tune, that's my advice for the day. Don't worry about a mega cam.
All my best,
Steve
Thanks for the post. Nice post by the way...
Already have the polished and ported heads (stage 2). And I'm happy with the G5 cam (see original post for specs). I'm not looking to change the cam. I also realize that changing anything on the fuel intake or exhuast will pretty much require a PCM retune.
The reason for the post was I'm considering the 1.85 ratio rocker arms and am concerned that with my existing cam, I may be too much lift for my engine and cause valve to piston interference.
Since I'm not much of a risk taker, I think I might take it to MTI to get a measurement of the total valve lift since I don't have to proper tools to get a precise measurement. Then just install the rocker arms (if there's enough clearance) myself.
These rocker arms look attractive because it looks like an easy mod (I've replaced rocker arms before, pretty much a no-brainer). And are not outrageously expensive (can pick some up more $400). I'm thinking I can get an easy 18 hp for $400 w/o too much effort (I'm lazy in other words)....
But thank you very much for your post.....
