Effects of Lobe Seperation Angle on Tq/HP
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Effects of Lobe Seperation Angle on Tq/HP

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    Distinguished Member David 519's Avatar
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    Default Effects of Lobe Seperation Angle on Tq/HP

    OK, maybe this is to broad a subject for the kind of generalizations necessary for conversation, but I'd like to try...
    The basic concept I'm curious about is; does widening the LSA move the power band upward in the RPM? Some background on why the questions:
    When we ran our 4" stroke combination (BBC), we seemed to make the best power (compromise between torque/HP/RPM) for a flat with cams using a 110 degree LSA (usually installed 3-4 degrees advanced). When we tried wider LSA's it seemed we gave up to much in the lower RPM for the benefit of a bit more HP up top.
    In our last build we used a 110 LSA (installed straight up) on our 4.5" stroke deal. After dyno'ing it, I'm thinking we may have given up some HP since the TQ was already over 800 by 3500 RPM but peaked by 5000 RPM. I'm leaning towards trying a 112 LSA to get it to move the Tq peak up a bit higher in the RPM. So, am I even close to correct in my thinking???
    OBTW, cams I've tried were generally around 285*@.050", around .78" valve lift using conventional heads (Dart 355's /Brodix -2's), nothing trick.
    Thanks

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    Senior Member stix818's Avatar
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    Quote Originally Posted by David 519 View Post
    OK, maybe this is to broad a subject for the kind of generalizations necessary for conversation, but I'd like to try...
    The basic concept I'm curious about is; does widening the LSA move the power band upward in the RPM? Some background on why the questions:
    When we ran our 4" stroke combination (BBC), we seemed to make the best power (compromise between torque/HP/RPM) for a flat with cams using a 110 degree LSA (usually installed 3-4 degrees advanced). When we tried wider LSA's it seemed we gave up to much in the lower RPM for the benefit of a bit more HP up top.
    In our last build we used a 110 LSA (installed straight up) on our 4.5" stroke deal. After dyno'ing it, I'm thinking we may have given up some HP since the TQ was already over 800 by 3500 RPM but peaked by 5000 RPM. I'm leaning towards trying a 112 LSA to get it to move the Tq peak up a bit higher in the RPM. So, am I even close to correct in my thinking???
    OBTW, cams I've tried were generally around 285*@.050", around .78" valve lift using conventional heads (Dart 355's /Brodix -2's), nothing trick.
    Thanks
    By far I'm no cam expert but the way I kind of understand it and been told is if you widen the LSA to say 114 you make more power but have a shorter powerband, that's where a tranny helps offset the short powerband. Just the opposite with 110, they have a wider power band and make a little less power and a trans doesn't become as beneficial. Most motors until this pontiac I built had a 110 with similar #s as yours!! My old man's Olds that I currently have in the boat has a 114 and my Pontiac that's getting put back together has a 114 but I do run a trans also.
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    Senior Member ol guy's Avatar
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    Quote Originally Posted by David 519 View Post
    OK, maybe this is to broad a subject for the kind of generalizations necessary for conversation, but I'd like to try...
    The basic concept I'm curious about is; does widening the LSA move the power band upward in the RPM? Some background on why the questions:
    When we ran our 4" stroke combination (BBC), we seemed to make the best power (compromise between torque/HP/RPM) for a flat with cams using a 110 degree LSA (usually installed 3-4 degrees advanced). When we tried wider LSA's it seemed we gave up to much in the lower RPM for the benefit of a bit more HP up top.
    In our last build we used a 110 LSA (installed straight up) on our 4.5" stroke deal. After dyno'ing it, I'm thinking we may have given up some HP since the TQ was already over 800 by 3500 RPM but peaked by 5000 RPM. I'm leaning towards trying a 112 LSA to get it to move the Tq peak up a bit higher in the RPM. So, am I even close to correct in my thinking???
    OBTW, cams I've tried were generally around 285*@.050", around .78" valve lift using conventional heads (Dart 355's /Brodix -2's), nothing trick.
    Thanks
    Good Subject. Not well understood by many. Simple terms, Shorter degree on lobe separation, more on top. Wider sread on lsa more on bottom and smoother idle. Advance a cam to build torque, retard a cam to bring up the rpm range. M

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    Quote Originally Posted by ol guy View Post
    Good Subject. Not well understood by many. Simple terms, Shorter degree on lobe separation, more on top. Wider sread on lsa more on bottom and smoother idle. Advance a cam to build torque, retard a cam to bring up the rpm range. M
    I think you have to factor in Cubic inches. The bigger the engine particularly the longer the stroke the opposite of what you said is true.

    The 565 uses the 4.25" stroke to make trq. it uses the 112* lobe sep to stretch the power to 7,000 rpm's.

    The 512" engine I had that I wanted to only rev to 6,000 with a 4.14" stroke ran a 108* lobe sep to help build as much trq and hp possible to 6,000. Shorter power band.

    I think the IHRA Mountain Motor's use lobe sep's beyond 115*.

    Just my .02 and I might be 180 out, but someone that knows more than me might correct me. Hey Straub where are you ?

    To the point of the original post, you didn't say how high you wanted to rev it ? With your 4.5" stroke I'd try a 112* in a heart beat maybe even 114* depending on the rpm range and compression. Just my .02

    Edit: my bet would be the 1,000 Hp pump gas 588" that Cyclone has and CS19 1,000 hp engine both run cams with lobe sep's at or bigger than 114*.( just a wild ass guess) based off of no fact's.

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    Last edited by Sleeper CP; 07-24-2008 at 04:07 PM.

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    Just another Wannabe Wannabe's Avatar
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    *just a little side note*
    I purchased a ton of cams from NHRA pro stock teams when everyone went to 4.9 bore spacing way back when. I went through about ten or 15 of them last night looking for something to throw in a little Pontiac I am throwing together out of spare parts. I think the average lobe separation of the ones I dug through was 116.5. A few were 117.5 and one at 118. And these babies were getting run in the very late 80's and early 90's.

    With fairly standard performance cams and overlap, I have seen the wider the lobe separation, the more it will run up top, all other things being equal. But you can retard the cam a little to lose some down low and gain a little up high if that is what you are looking for.

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    Senior Member stix818's Avatar
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    Quote Originally Posted by Wannabe View Post
    *just a little side note*
    I purchased a ton of cams from NHRA pro stock teams when everyone went to 4.9 bore spacing way back when. I went through about ten or 15 of them last night looking for something to throw in a little Pontiac I am throwing together out of spare parts. I think the average lobe separation of the ones I dug through was 116.5. A few were 117.5 and one at 118. And these babies were getting run in the very late 80's and early 90's.

    With fairly standard performance cams and overlap, I have seen the wider the lobe separation, the more it will run up top, all other things being equal. But you can retard the cam a little to lose some down low and gain a little up high if that is what you are looking for.
    Wannabe, what kind of duration and lift where some of those cams if don't mind me asking?

    I guess I was a little off on the powerband also. Makes since on what you said!!
    Last edited by stix818; 07-24-2008 at 04:33 PM.
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    Size does matter look at small super stock engine ,those are on 104 in at 102 and small block that runs good are 106,they make a bunch more cylinder pressure at a tighter lobe center.The big engines can handle wider lobe centers,also wider centers help bleed off some cylinder presure.Pro stockers are 116 118 and are very spikey power bands but have 5 speeds to keep the rpm in that range.My first 540 had a 108 in at 108 2nd time has a 112 in at 110 made a bit more power.But us river racers hardly ever see 7000rpm ,so I wonder sometimes for us if a tighter lobe center would be good ,more torque.Unless you have a huge shot of nos.Pro stockers see 9800 or more and are beyond normal thinking.I heard guys boreing the block a few degrees minus on 1 side and few plus on the other so when thing twisting down the track its back at a 90 degree wedge.I have not been around those engines since 2001 when I worked for the mopar team in Houston.THe engines that were even bader were PS truck ones 10,000 every dyno pull.

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    Distinguished Member David 519's Avatar
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    Quote Originally Posted by Sleeper CP View Post
    I think you have to factor in Cubic inches. The bigger the engine particularly the longer the stroke the opposite of what you said is true.

    The 565 uses the 4.25" stroke to make trq. it uses the 112* lobe sep to stretch the power to 7,000 rpm's.

    The 512" engine I had that I wanted to only rev to 6,000 with a 4.14" stroke ran a 108* lobe sep to help build as much trq and hp possible to 6,000. Shorter power band.

    I think the IHRA Mountain Motor's use lobe sep's beyond 115*.

    Just my .02 and I might be 180 out, but someone that knows more than me might correct me. Hey Straub where are you ?

    To the point of the original post, you didn't say how high you wanted to rev it ? With your 4.5" stroke I'd try a 112* in a heart beat maybe even 114* depending on the rpm range and compression. Just my .02

    Edit: my bet would be the 1,000 Hp pump gas 588" that Cyclone has and CS19 1,000 hp engine both run cams with lobe sep's at or bigger than 114*.( just a wild ass guess) based off of no fact's.

    Sleeper CP
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    My thinking is along the same lines as you, but I don't know enough to be sure. As far as how high I want to rev it, in a flat I like enough torque to burn the prop, but if you can pull a higher RPM, it will pull farther down track. I doubt a cam will move the HP peak up say a 1000 RPM, but may be wrong.
    As our combo is now, we are done at half track. We're still messing with gears//props, but since we are reworking our engine during this racing break, we have an opportunity to adjust the motor tune up a bit...

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    Quote Originally Posted by David 519 View Post
    As our combo is now, we are done at half track. We're still messing with gears//props, but since we are reworking our engine during this racing break, we have an opportunity to adjust the motor tune up a bit...
    Wow you got to fix that. Good luck with the combo.

    Sleeper CP

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    Look to the cylinder head. The bigger the motor...the quicker the cylinder head is used up. I could tell you stories....but that is the bottom line.
    I wish I had the money back it cost me to learn that.

    Ok...carry on.

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    just a ski boat with bark Carnivalride's Avatar
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    Quote Originally Posted by David 519 View Post
    OK, maybe this is to broad a subject for the kind of generalizations necessary for conversation, but I'd like to try...
    The basic concept I'm curious about is; does widening the LSA move the power band upward in the RPM? Some background on why the questions:
    When we ran our 4" stroke combination (BBC), we seemed to make the best power (compromise between torque/HP/RPM) for a flat with cams using a 110 degree LSA (usually installed 3-4 degrees advanced). When we tried wider LSA's it seemed we gave up to much in the lower RPM for the benefit of a bit more HP up top.
    In our last build we used a 110 LSA (installed straight up) on our 4.5" stroke deal. After dyno'ing it, I'm thinking we may have given up some HP since the TQ was already over 800 by 3500 RPM but peaked by 5000 RPM. I'm leaning towards trying a 112 LSA to get it to move the Tq peak up a bit higher in the RPM. So, am I even close to correct in my thinking???
    OBTW, cams I've tried were generally around 285*@.050", around .78" valve lift using conventional heads (Dart 355's /Brodix -2's), nothing trick.
    Thanks
    David,

    Was this a 10.2" deck height block and what rod length did you go with 6.7" long? I think the R/S ratio plays a little part in the lobe seperation as well as the cubic inch and heads.

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    steelcomp was here
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    The way I've always understood LSA which is overlap, in general terms, was that the closer the lobe centers, the more overlap you have. The more overlap you have, the longer the intake and ex valve are open at the same time, which makes it harder to build cylinder pressure at lower rpm. As has been mentioned, it's difficult to generalize between different combinations, though. Cyl head plays a huge role in the decision. Big, high flowing ports are going to make it hard to build low end cyl pressure, so may require more LSA (less overlap) that a smaller more effecient head on the same engine. Longer rods don't have quite the piston acceleration and may require the same to help get the cyl pressure up quicker. Tunnel ram with a pair of dom's vs, single four. Again, it all depends on the combination.
    Last edited by scott foxwell; 07-25-2008 at 07:21 AM.
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    As posted by many, what is needed is determined by a bunch of factors in the combination used.
    Typicaly, a tighter LS will produce a narrower, more pronounced torque curve in the mid-range. A wider LS will give a flatter curve lending it self to more of upper mid-range to high speed. As said before this works hand in hand with the duration used as it governs overlap. As mentioned, this is "typical" trend, but can vary with engine size, compresion ratio, duration ect.
    In our little engines (limited to 12.1cr) we used to run a fairly wide LS when turning 10,000+ rpm's (and allot less aggressive lobes). Since the gear rule (about 9500-9600 rpm's max at most tracks) we have narrowed this quite a bit to pack more into the midrange engine speeds (along with shorter, more violent lobes).
    You see a bunch of big engines running over 120* of lobe seperation these day's, but then again they are spinning these big engines 10,000+ and are using lobes in the 300+ degrees @ .050.

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    This came up on another board and my thoughts go along with Fiat:

    use to fall into the lobe sep "sliding scale" of narrower for more low end and wider for more top end arguement. I dont' anymore as I have learned over the years if you cam and engine for a given rpm range let the lobe sep fall where it needs to be. I have cammed 496 CID BBC with 112 lobe sep and some in the 107 lobe sep. I have found the 2 things that will determine lobe sep is "How much air can we get in and out and what rpm we are going to run.
    Two equal engines, 496's, going to 6400 rpm. One is under headed and the other is properly headed. The underheaded engine is going to need to have the valve open a little sooner to fill the cylinder. The properly headed engine can have the valve open a little later because of good fill. The camshaft profile will be different for both engines but the powerband will mirror each other fairly closely.

    Select a camshaft based on what you want YOUR engine to do. Build a combination then cam it.

    Another thing is cam for powerband. If the damn engine is going to see 7500 but in all reality maybe 6800 then cam for that. Don't worry about running in the "Dream RPM" lets make power in the "reality RPM".
    Chris Straub
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