Next NSX (HSC) to be SOHC?
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From: Bluffton/Hilton Head,SC / Ft. Lauderdale, FL, usa
Re: Next NSX (boondockgtr)
i dought it.. i can see where the plug would go.. u can see the long sliver tube to the far right sitting diangnal in between the roller rocker and valve spring (where the spark plug goes into)...u can even see the plug wire on it!
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From: funktown, Wa, usa
Re: (aznxphreak)
too bad honda is still in the stone ages. and havent gone Shim under bucket yet. like a Toyota or even alfas from the 70's. that setup is much more lighter than a rocker or roller setup.
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From: Norwalk, CT
Re: (deepgreengsr)
I fail to see how using shims for valve adjustment is an advantage over a tappet screw adjustment . . . .
Besides, not using a rocker arm setup would make VTEC somewhat unfeasible. Not to mention a rocker arm setup makes your cam placement a lot more flexible, which improves spark plug location & head port design.
Besides, not using a rocker arm setup would make VTEC somewhat unfeasible. Not to mention a rocker arm setup makes your cam placement a lot more flexible, which improves spark plug location & head port design.
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From: Surrey, BC, Canada
Re: (aznxphreak)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by aznxphreak »</TD></TR><TR><TD CLASS="quote">I see rollers instead...</TD></TR></TABLE>
I'm talking about the 'arms' that are speared by the 'rollers'... that's a lot of mass to be wiggling up and down at 8k rpms. Shorten those arms by half and you'll save a LOT of wear and tear on the cam. Rockers, rollers, whatever
deepgreengsr, you haven't tried to do a valve "adjustment" on a Nissan, have you? *shudder*
I'm talking about the 'arms' that are speared by the 'rollers'... that's a lot of mass to be wiggling up and down at 8k rpms. Shorten those arms by half and you'll save a LOT of wear and tear on the cam. Rockers, rollers, whatever
deepgreengsr, you haven't tried to do a valve "adjustment" on a Nissan, have you? *shudder*
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From: Norwalk, CT
Re: (mmuller)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mmuller »</TD></TR><TR><TD CLASS="quote">everybody knows that dohc is better for high revs.sohc's HAVE more mass.</TD></TR></TABLE>
Well, that depends on the application.
For instance, on a boxer 4, the cams are so short that a SOHC design reduces mass.
Well, that depends on the application.
For instance, on a boxer 4, the cams are so short that a SOHC design reduces mass.
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From: TX, USA
Re: (raene)
Good news! That is NOT an NSX engine. I was mislead/misunderstood the original poster in this thread https://honda-tech.com/zero...age=1.
The promotional papers from Honda state DOHC V6 with more than 300 HP
The promotional papers from Honda state DOHC V6 with more than 300 HP
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From: Norwalk, CT
Re: (raene)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by raene »</TD></TR><TR><TD CLASS="quote">Short cams have nothing to do with the length of the arms.</TD></TR></TABLE>
I never said it did . . . . I said it reduces valvetrain mass. Cams are included in that - there's a reason we see weight reduction by using hollow cams & such, it's rotational inertia. Rocker arms are important too, but the difference in rocker arm length between SOHC & DOHC is really pretty minimal.
I never said it did . . . . I said it reduces valvetrain mass. Cams are included in that - there's a reason we see weight reduction by using hollow cams & such, it's rotational inertia. Rocker arms are important too, but the difference in rocker arm length between SOHC & DOHC is really pretty minimal.
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From: Surrey, BC, Canada
Re: (Daemione)
Your valvetrain isn't going to fly apart because your cams have too much mass. There's only so much metal you can put into a lobe on a camshaft, and they're relatively balanced, by default. People never have problems with their cams jumping out of their holders. People DO have problems with the rockers floating, though (except for rollers). Also, put weights on the ends of your roller/rocker arms and you'll have problems, too. That's what I'm getting at.
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From: Norwalk, CT
Re: (raene)
Okay, mass may be the wrong word.
I'm going to try & summarize my thoughts:
Say we change a high-revving inline 4-cylinder from DOHC to SOHC. In doing so, we double the amount of stress on the cam because it now has to compress twice as many valvesprings as it did before. And if we bulk up the new cam so it doesn't snap under the extra stress, we're increasing rotational inertia and restricting the engine's revvability. This, of course, is counter-productive to the original goal.
So the main reason you don't often see high-revving SOHC inline 4-bangers is because of the extra stress that's placed on the long(er) cam. Longer rocker arms certainly wouldn't help, since you need stiffer springs to manage them, but again, there shouldn't be a big difference between rocker arm length in a SOHC & DOHC engine.
Of course, on a VTEC engine we've got that extra rocker arm which necessitates stiffer springs than a "normal" engine, so camshaft stresses are even higher.
On a boxer-4 or V6, not only is your cam shorter, but it has fewer valvesprings to manage, so you can theoretically get away with higher rpms.
I'm going to try & summarize my thoughts:
Say we change a high-revving inline 4-cylinder from DOHC to SOHC. In doing so, we double the amount of stress on the cam because it now has to compress twice as many valvesprings as it did before. And if we bulk up the new cam so it doesn't snap under the extra stress, we're increasing rotational inertia and restricting the engine's revvability. This, of course, is counter-productive to the original goal.
So the main reason you don't often see high-revving SOHC inline 4-bangers is because of the extra stress that's placed on the long(er) cam. Longer rocker arms certainly wouldn't help, since you need stiffer springs to manage them, but again, there shouldn't be a big difference between rocker arm length in a SOHC & DOHC engine.
Of course, on a VTEC engine we've got that extra rocker arm which necessitates stiffer springs than a "normal" engine, so camshaft stresses are even higher.
On a boxer-4 or V6, not only is your cam shorter, but it has fewer valvesprings to manage, so you can theoretically get away with higher rpms.
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From: Surrey, BC, Canada
Re: (Daemione)
Good explanation 
However, I don't believe the cams get longer between the DOHC and SOHC engines. They're nearly the same length, to keep up the strength. The SOHC's limitation is that the VTEC system requires double the usual number of lobes, and on the SOHCs, there's just not enough room for that. But again, I don't consider the cam the weak point. The valvespring stresses are eensy compared to the stress on the crank - the crank also has to grow in length to match the cam, you see. And the crank sees MUCH more force through accelerating/decelerating the rods + pistons than the little bit of force applied by the valvesprings to the cam. So I think it's to avoid a flexy crankshaft that the cam is kept shorter, which limits the amount of space available for more lobes on the cam, which in the end is why the SOHCs have only intake VTEC.
If you actually compare the rocker arm length + mass between the SOHC and DOHCs, you'll see the SOHC rocker arm is about a third as large again as the DOHC, at least. That will only grow as you cant the valves more, so you have to shrink the rocker length by shrinking the cant, which causes a less direct flow path to the head, which restricts breathing.
However, I don't believe the cams get longer between the DOHC and SOHC engines. They're nearly the same length, to keep up the strength. The SOHC's limitation is that the VTEC system requires double the usual number of lobes, and on the SOHCs, there's just not enough room for that. But again, I don't consider the cam the weak point. The valvespring stresses are eensy compared to the stress on the crank - the crank also has to grow in length to match the cam, you see. And the crank sees MUCH more force through accelerating/decelerating the rods + pistons than the little bit of force applied by the valvesprings to the cam. So I think it's to avoid a flexy crankshaft that the cam is kept shorter, which limits the amount of space available for more lobes on the cam, which in the end is why the SOHCs have only intake VTEC.
If you actually compare the rocker arm length + mass between the SOHC and DOHCs, you'll see the SOHC rocker arm is about a third as large again as the DOHC, at least. That will only grow as you cant the valves more, so you have to shrink the rocker length by shrinking the cant, which causes a less direct flow path to the head, which restricts breathing.
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Re: (Daemione)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Daemione »</TD></TR><TR><TD CLASS="quote">Okay, mass may be the wrong word.</TD></TR></TABLE>No, I think mass is exactly the right word. But you're confusing rotational mass with reciprocating mass. Reciprocating mass is all the stuff that moves back & forth, like the valves themselves & the lifters... That contributes to valve float.
The camshafts themselves are rotational mass, but since they're small & spin at 1/2 speed, it's not such a big deal. You get more bang for the buck by lightening your flywheel vs. lightening your camshafts.
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Daemione »</TD></TR><TR><TD CLASS="quote">So the main reason you don't often see high-revving SOHC inline 4-bangers is because of the extra stress that's placed on the long(er) cam. Longer rocker arms certainly wouldn't help, since you need stiffer springs to manage them, but again, there shouldn't be a big difference between rocker arm length in a SOHC & DOHC engine.</TD></TR></TABLE>And the main reason we don't see many high-revving pushrod engines isn't because it can't be done, it's because of the cost. Sometimes, some racing rules make it worthwile to do that. It just costs lots of money.
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Daemione »</TD></TR><TR><TD CLASS="quote">Of course, on a VTEC engine we've got that extra rocker arm which necessitates stiffer springs than a "normal" engine, so camshaft stresses are even higher.</TD></TR></TABLE>The extra rocker isn't the only thing that necessitates the stiffer springs; it's also the higher redline of the VTEC engines.
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Daemione »</TD></TR><TR><TD CLASS="quote">On a boxer-4 or V6, not only is your cam shorter, but it has fewer valvesprings to manage, so you can theoretically get away with higher rpms.</TD></TR></TABLE>There's lots of other stuff, too. Like twice as many cam-drive sprockets, more belts (or chains), etc.
The camshafts themselves are rotational mass, but since they're small & spin at 1/2 speed, it's not such a big deal. You get more bang for the buck by lightening your flywheel vs. lightening your camshafts.
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Daemione »</TD></TR><TR><TD CLASS="quote">So the main reason you don't often see high-revving SOHC inline 4-bangers is because of the extra stress that's placed on the long(er) cam. Longer rocker arms certainly wouldn't help, since you need stiffer springs to manage them, but again, there shouldn't be a big difference between rocker arm length in a SOHC & DOHC engine.</TD></TR></TABLE>And the main reason we don't see many high-revving pushrod engines isn't because it can't be done, it's because of the cost. Sometimes, some racing rules make it worthwile to do that. It just costs lots of money.
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Daemione »</TD></TR><TR><TD CLASS="quote">Of course, on a VTEC engine we've got that extra rocker arm which necessitates stiffer springs than a "normal" engine, so camshaft stresses are even higher.</TD></TR></TABLE>The extra rocker isn't the only thing that necessitates the stiffer springs; it's also the higher redline of the VTEC engines.
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Daemione »</TD></TR><TR><TD CLASS="quote">On a boxer-4 or V6, not only is your cam shorter, but it has fewer valvesprings to manage, so you can theoretically get away with higher rpms.</TD></TR></TABLE>There's lots of other stuff, too. Like twice as many cam-drive sprockets, more belts (or chains), etc.
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From: Norwalk, CT
Re: (raene)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by raene »</TD></TR><TR><TD CLASS="quote">However, I don't believe the cams get longer between the DOHC and SOHC engines.</TD></TR></TABLE>
Whoops - I worded that poorly. When I said "long(er)", I meant longer cams than in a V6 or boxer-4, not that a single overhead cam would be longer than it's DOHC counterparts.
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by raene »</TD></TR><TR><TD CLASS="quote">So I think it's to avoid a flexy crankshaft that the cam is kept shorter, which limits the amount of space available for more lobes on the cam, which in the end is why the SOHCs have only intake VTEC.</TD></TR></TABLE>
I don't think that's the case - I mean BMW makes an I-6 crankshaft that's fine at high rpms, but they're not crazy enough to try & run it SOHC, even on the lower revving 2.5 I6 . . . . If I'm not mistaken, the last time they used SOHC on an inline 6 it was on the old E30 2.5's. But they only had 2 valves per cylinder, and weren't terribly rev-happy.
I think that's indicative of what's going on in an inline-4. Crank strength on a 4-banger is rarely a concern these days, but if you try & run a SOHC at high rpms, cam strength can be.
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by raene »</TD></TR><TR><TD CLASS="quote">If you actually compare the rocker arm length + mass between the SOHC and DOHCs, you'll see the SOHC rocker arm is about a third as large again as the DOHC, at least. That will only grow as you cant the valves more, so you have to shrink the rocker length by shrinking the cant, which causes a less direct flow path to the head, which restricts breathing. </TD></TR></TABLE>
Do you have any more information on this? From the SOHC & DOHC heads that I've seen, rocker arms are pretty comparable in size. After all, a SOHC is plopped right inbetween the valves, so as long as the valve stems aren't ridiculously long or approaching a horizontal angle or something, the rocker arms are pretty small - the V6 pictured in this thread is a good example. Any smaller and there's no room for the pivot point . . . .
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JimBlake »</TD></TR><TR><TD CLASS="quote">No, I think mass is exactly the right word. But you're confusing rotational mass with reciprocating mass. Reciprocating mass is all the stuff that moves back & forth, like the valves themselves & the lifters... That contributes to valve float.</TD></TR></TABLE>
Well, it was the wrong word for the point I was trying to get across at the time (that a SOHC boxer-4 or V6 will do better than a SOHC inline-4 at high-rpms)
Whoops - I worded that poorly. When I said "long(er)", I meant longer cams than in a V6 or boxer-4, not that a single overhead cam would be longer than it's DOHC counterparts.
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by raene »</TD></TR><TR><TD CLASS="quote">So I think it's to avoid a flexy crankshaft that the cam is kept shorter, which limits the amount of space available for more lobes on the cam, which in the end is why the SOHCs have only intake VTEC.</TD></TR></TABLE>
I don't think that's the case - I mean BMW makes an I-6 crankshaft that's fine at high rpms, but they're not crazy enough to try & run it SOHC, even on the lower revving 2.5 I6 . . . . If I'm not mistaken, the last time they used SOHC on an inline 6 it was on the old E30 2.5's. But they only had 2 valves per cylinder, and weren't terribly rev-happy.
I think that's indicative of what's going on in an inline-4. Crank strength on a 4-banger is rarely a concern these days, but if you try & run a SOHC at high rpms, cam strength can be.
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by raene »</TD></TR><TR><TD CLASS="quote">If you actually compare the rocker arm length + mass between the SOHC and DOHCs, you'll see the SOHC rocker arm is about a third as large again as the DOHC, at least. That will only grow as you cant the valves more, so you have to shrink the rocker length by shrinking the cant, which causes a less direct flow path to the head, which restricts breathing. </TD></TR></TABLE>
Do you have any more information on this? From the SOHC & DOHC heads that I've seen, rocker arms are pretty comparable in size. After all, a SOHC is plopped right inbetween the valves, so as long as the valve stems aren't ridiculously long or approaching a horizontal angle or something, the rocker arms are pretty small - the V6 pictured in this thread is a good example. Any smaller and there's no room for the pivot point . . . .
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JimBlake »</TD></TR><TR><TD CLASS="quote">No, I think mass is exactly the right word. But you're confusing rotational mass with reciprocating mass. Reciprocating mass is all the stuff that moves back & forth, like the valves themselves & the lifters... That contributes to valve float.</TD></TR></TABLE>
Well, it was the wrong word for the point I was trying to get across at the time (that a SOHC boxer-4 or V6 will do better than a SOHC inline-4 at high-rpms)
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From: Surrey, BC, Canada
Re: (Daemione)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Daemione »</TD></TR><TR><TD CLASS="quote">
Do you have any more information on this? From the SOHC & DOHC heads that I've seen, rocker arms are pretty comparable in size. </TD></TR></TABLE>
I have both sitting at home and I'll pull off the valvecovers tonight and measure
Do you have any more information on this? From the SOHC & DOHC heads that I've seen, rocker arms are pretty comparable in size. </TD></TR></TABLE>
I have both sitting at home and I'll pull off the valvecovers tonight and measure
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Re: Next NSX (powerofdreams8)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by powerofdreams8 »</TD></TR><TR><TD CLASS="quote">CleenSi: Don't ever talk. Again. Ever.</TD></TR></TABLE>
ha ha ha, your killing me
ha ha ha,
your killing me
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From: Surrey, BC, Canada
Re: (Daemione)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Daemione »</TD></TR><TR><TD CLASS="quote">From the SOHC & DOHC heads that I've seen, rocker arms are pretty comparable in size. </TD></TR></TABLE>
Well, on my B16 head, the arm is about 2.5" long, conservatively measured. On my old D16A6 SOHC engine I conservatively measured it at 4" long.
Reason? The roller for the B16 is located at one end of the arm, like so:
O_U_U
The O is the roller. The middle U is the point at which the cam contacts it. The final U is the piece that contacts the valve. The final piece of the arm is built much more lightly than the entire D16 arm, which resembles a crescent.
U____O____U is the D16 arm. The first U is the valve contact, the center O is the roller, the final U is the cam wipe.
By my estimation the D16 piece weighs easily 2x as much as the B16 one. It's way more massive.
Well, on my B16 head, the arm is about 2.5" long, conservatively measured. On my old D16A6 SOHC engine I conservatively measured it at 4" long.
Reason? The roller for the B16 is located at one end of the arm, like so:
O_U_U
The O is the roller. The middle U is the point at which the cam contacts it. The final U is the piece that contacts the valve. The final piece of the arm is built much more lightly than the entire D16 arm, which resembles a crescent.
U____O____U is the D16 arm. The first U is the valve contact, the center O is the roller, the final U is the cam wipe.
By my estimation the D16 piece weighs easily 2x as much as the B16 one. It's way more massive.
I have the D16A6 arm lying around but the B16 one is installed on my car 
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