intake duration
Mar 17, 2005 | 03:07 PM
#41
TECH Addict
Joined: Oct 2003
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From: Central, MA
Originally Posted by BADMOFO
This is something that I believe Lingenfelter started doing in the LS1 motors. Some of their early "secrets" was running a fairly mild duration with a higher lift and custom rockers in the 1.8 and 1.9 ( 
) range. This kept the motor "drivable" and able to make necessary vacuum, yet still have the advantages of higher lifts.
) range. This kept the motor "drivable" and able to make necessary vacuum, yet still have the advantages of higher lifts.
Mar 17, 2005 | 03:26 PM
#42
Jay Allen of Cam Innovations did a profile similar to what you are referring to for a F-body.
Good read on that here w/ a good debate from a bunch of top notch cam grinders.http://bbs.hardcore50.com/vbulletin/...&highlight=ls1
----
The x-er lobes that are listed in comp's catalog are not the only lobes with x-er profiles available. I think they run down to a 216 lobe @ .05 exc. Comps catalog lists 3720-3734
Good read on that here w/ a good debate from a bunch of top notch cam grinders.http://bbs.hardcore50.com/vbulletin/...&highlight=ls1
----
The x-er lobes that are listed in comp's catalog are not the only lobes with x-er profiles available. I think they run down to a 216 lobe @ .05 exc. Comps catalog lists 3720-3734
Mar 17, 2005 | 11:42 PM
#43
Originally Posted by SportSide 5.3
Jay Allen of Cam Innovations did a profile similar to what you are referring to for a F-body.
Good read on that here w/ a good debate from a bunch of top notch cam grinders.http://bbs.hardcore50.com/vbulletin/...&highlight=ls1
----
The x-er lobes that are listed in comp's catalog are not the only lobes with x-er profiles available. I think they run down to a 216 lobe @ .05 exc. Comps catalog lists 3720-3734
Good read on that here w/ a good debate from a bunch of top notch cam grinders.http://bbs.hardcore50.com/vbulletin/...&highlight=ls1
----
The x-er lobes that are listed in comp's catalog are not the only lobes with x-er profiles available. I think they run down to a 216 lobe @ .05 exc. Comps catalog lists 3720-3734
Mar 21, 2005 | 09:55 PM
#45
Mar 21, 2005 | 09:57 PM
#46
another fyi:
The most important point in the four-stroke cycle is the intake closing point. While this is not part of overlap, the timing of intake opening and closing determines total duration. The intake closing point is a big determiner in where the engine makes power. A later intake closing point improves top-end power. Combine that with more overlap and you have a cam designed to make power at high rpm. However, it’s possible to decrease overlap by using a shorter-duration intake lobe and retard the intake centerline (which spreads the lobe separation angle) to improve midrange power.
The most important point in the four-stroke cycle is the intake closing point. While this is not part of overlap, the timing of intake opening and closing determines total duration. The intake closing point is a big determiner in where the engine makes power. A later intake closing point improves top-end power. Combine that with more overlap and you have a cam designed to make power at high rpm. However, it’s possible to decrease overlap by using a shorter-duration intake lobe and retard the intake centerline (which spreads the lobe separation angle) to improve midrange power.
Mar 21, 2005 | 10:05 PM
#47
after researching this for some time, I'm going to have to say the intake lobe has more to do with powerband placement than exhaust.
btw, I pm'ed a couple of Sponsers to comment on this, as you can see, none did......
oh well, I feel like I found the correct answer, cheers!
btw, I pm'ed a couple of Sponsers to comment on this, as you can see, none did......
oh well, I feel like I found the correct answer, cheers!
Mar 21, 2005 | 11:22 PM
#48
Originally Posted by moregrip
... I'm going to have to say the intake lobe has more to do with powerband placement than exhaust.
Sorry for the long delay. I've been busy lately. I have typed up a reply a couple of times, mostly directed replies to earlier statements, but decided not to post them.
Anyhoo... I agree with your intake lobe statement. IMO - the intake lobe design and duration have the most effect on the placement of the powerband. There are so many factors involved in this. Common .050 lift duration numbers are a small part of the puzzle. You need to keep the intake valve open to give your cylinders a complete fill. The higher rpms, the more open time (duration) will be needed. Yet the design of the cam lobe itself will alter the needs for a specific duration. Getting a lobe with a higher peak lift and more duration at points higher than .050 will give your cylinders more air, than a less aggressive lobe. Along with the size and shape of the intake lobe, opening and closing it at the correct time will maximize power. The correct opening and closing of the exhaust valve will alter the range some as well as define the curve. Open the exhaust too early, you bleed off torque. Open it too late, you don't get all the exhaust out soon enough, which hurts scavaging intake charge. Close the exhaust valve early, you lose the same scavaging, but close it too late and you lose low end torque because you allow fresh miox to go out the open exhaust valve at low rpms. You have to decide what power level you want, how many rpms you want to spin it, where you want your power to come on, and determine if thats realistic with your complete setup. Ideally you'd want to pick out your opening and closing points for the valves, which would determine your durations, LSA, and ICL. Then decide what lobes you want to use and order it up.
In the real world I realize its not that easy, which is why most people just buy cams that other guys have had good results with. I suggest you take it a step further and look at the effects certain cams have on the powerband and see if its close to your needs. Once you start comparing several of them, you'll get a better feel for the cam specs you need for your goals. Then instead of buying one of the popular cams, order one custom that suits your specific needs.
Mar 21, 2005 | 11:31 PM
#49
Originally Posted by BigTex
Sorry for the long delay. I've been busy lately. I have typed up a reply a couple of times, mostly directed replies to earlier statements, but decided not to post them.
Anyhoo... I agree with your intake lobe statement. IMO - the intake lobe design and duration have the most effect on the placement of the powerband. There are so many factors involved in this. Common .050 lift duration numbers are a small part of the puzzle. You need to keep the intake valve open to give your cylinders a complete fill. The higher rpms, the more open time (duration) will be needed. Yet the design of the cam lobe itself will alter the needs for a specific duration. Getting a lobe with a higher peak lift and more duration at points higher than .050 will give your cylinders more air, than a less aggressive lobe. Along with the size and shape of the intake lobe, opening and closing it at the correct time will maximize power. The correct opening and closing of the exhaust valve will alter the range some as well as define the curve. Open the exhaust too early, you bleed off torque. Open it too late, you don't get all the exhaust out soon enough, which hurts scavaging intake charge. Close the exhaust valve early, you lose the same scavaging, but close it too late and you lose low end torque because you allow fresh miox to go out the open exhaust valve at low rpms. You have to decide what power level you want, how many rpms you want to spin it, where you want your power to come on, and determine if thats realistic with your complete setup. Ideally you'd want to pick out your opening and closing points for the valves, which would determine your durations, LSA, and ICL. Then decide what lobes you want to use and order it up.
In the real world I realize its not that easy, which is why most people just buy cams that other guys have had good results with. I suggest you take it a step further and look at the effects certain cams have on the powerband and see if its close to your needs. Once you start comparing several of them, you'll get a better feel for the cam specs you need for your goals. Then instead of buying one of the popular cams, order one custom that suits your specific needs.
Mar 22, 2005 | 06:51 AM
#50
It's pretty cool you are finding an interest in this Grip and not just out to buy the fan favorite ots cam.
Here's some info for you. A few threads I would suggest reading; if you have not already, are below the quoted.
https://ls1tech.com/forums/showthread.php?t=101100
https://ls1tech.com/forums/showthrea...aft+discussion
https://ls1tech.com/forums/showthrea...aft+discussion
Here's some info for you. A few threads I would suggest reading; if you have not already, are below the quoted.
The area most cam companies error on is the exhaust. This causes problems with these limited intake designs. The exhaust VE's are the most important on these setups.
Simply put, on an N/A motor the intake aircharge is not assisted.
After the combustion stroke there is tremendous pressure in the cylinder. As soon as the exhaust valve cracks open it flows a LOT of air. It's basically boosted out of the cylinder if you want to look at it like this. Having the exhaust valve open too early not only costs heat (power) & velocity through the exhaust runners, it also empties the cylinder before the intake valve is open enough to take advantage of the pressure differential. (in a limited overlap/smogable camshaft this is especially true) This causes exhaust reversion & is one of the key factors in surging problems. By the airflow reversing course it is loosing a lot of it's inertia. Typically this is overcome before peak torque however. So only low-speed issues are present. At the track these motors are always above 4500rpm so this does not affect track times too much. Stilll....there is significant power lost by allowing reversion. So it makes sense to open the exhaust valve a little later & increase the overlap a bit. By adding advance into the camshaft this makes the problem even worse as now you're opening the exhaust a few more degrees earlier.....& shortening the effectiveness of the intake unless you have significant overlap flow to over come this.
Simply put, advancing a cam makes it more exhaust bias relative to TDC. Retarding a cam makes it more intake bias relative to TDC.
Simply put, on an N/A motor the intake aircharge is not assisted.
After the combustion stroke there is tremendous pressure in the cylinder. As soon as the exhaust valve cracks open it flows a LOT of air. It's basically boosted out of the cylinder if you want to look at it like this. Having the exhaust valve open too early not only costs heat (power) & velocity through the exhaust runners, it also empties the cylinder before the intake valve is open enough to take advantage of the pressure differential. (in a limited overlap/smogable camshaft this is especially true) This causes exhaust reversion & is one of the key factors in surging problems. By the airflow reversing course it is loosing a lot of it's inertia. Typically this is overcome before peak torque however. So only low-speed issues are present. At the track these motors are always above 4500rpm so this does not affect track times too much. Stilll....there is significant power lost by allowing reversion. So it makes sense to open the exhaust valve a little later & increase the overlap a bit. By adding advance into the camshaft this makes the problem even worse as now you're opening the exhaust a few more degrees earlier.....& shortening the effectiveness of the intake unless you have significant overlap flow to over come this.
Simply put, advancing a cam makes it more exhaust bias relative to TDC. Retarding a cam makes it more intake bias relative to TDC.
https://ls1tech.com/forums/showthrea...aft+discussion
https://ls1tech.com/forums/showthrea...aft+discussion
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