Member Contributer YoshiHNS Posted February 29, 2016 Member Contributer Share Posted February 29, 2016 The staggered setting is almost personal preference. I've put mine even and staggered. Even is a little better IMO. Link to comment Share on other sites More sharing options...
Member Contributer maxredline Posted March 1, 2016 Member Contributer Share Posted March 1, 2016 The staggered setting is almost personal preference. I've put mine even and staggered. Even is a little better IMO. Ya, I don't understand why honda would want staggered vacuum readings. Can anyone explain this? Link to comment Share on other sites More sharing options...
Member Contributer Terry Posted March 1, 2016 Member Contributer Share Posted March 1, 2016 Yeah I'm puzzled by that one too. I always believed that a good even balance was essential for smooth idling on an inline four, and that if the balance was out you could get rattles/vibes from the crank speeding up and slowing down. The VFR does have a a very uneven firing order compared to a conventional flat-plane in-line four, and I wondered if the vacuum level offset was to encourage some crank speed variation to make up for the gaps in the firing order. If so....why isn't the same thing specified in the 6th or 8th gen bikes, or 2nd-4th gen carbed bikes? Which would force me to conclude that, as the 5th gen is the first FI model, the vacuum stagger is intended to compensate for something in the FI system that they were unable to tune out in the software. Link to comment Share on other sites More sharing options...
Knight Posted March 1, 2016 Share Posted March 1, 2016 Anyone have the Common Service Manual? I think it has a comment about this, but mine is currently away. I thought it said the variance is due to different exhaust runner lengths, but we really shouldn't rely on my memory. The relative pressure from intake to exhaust is important methinks, if in fact it differs by cylinder. Link to comment Share on other sites More sharing options...
Member Contributer maxredline Posted March 1, 2016 Member Contributer Share Posted March 1, 2016 Knight, the manual and other good things are on the download page, gotta love that! I initally thought about the exhaust lenghts also but I really don't know anything about their length.Terry's explanation sounds interesting reguarding the firing order. Once I get all my gaskets and put my viffer back together I will first go by the manual and if I don't like the sync I try the vacuum even. Link to comment Share on other sites More sharing options...
Knight Posted March 1, 2016 Share Posted March 1, 2016 Knight, the manual and other good things are on the download page, gotta love that! I initally thought about the exhaust lenghts also but I really don't know anything about their length.Terry's explanation sounds interesting reguarding the firing order. Once I get all my gaskets and put my viffer back together I will first go by the manual and if I don't like the sync I try the vacuum even. I found (?) one Honda Common Service Manual in the downloads but it is circa 1988. I presume starter valves began with the fuel injection. (?) Yes, you should see some idle difference and can decide for yourself the settings to keep. A neat method would be iterative tuning. Tweak one way, then the other, re-measure idle, rinse repeat. Would need a machine to do that repeatedly among the 3 valves though, and an extremely accurate tach would be desirable to measure incremental changes. But I dream... Link to comment Share on other sites More sharing options...
Member Contributer MaxSwell Posted March 2, 2016 Member Contributer Share Posted March 2, 2016 Do dream on Knight. Much good can come from it. Link to comment Share on other sites More sharing options...
GreginDenver Posted December 24, 2016 Share Posted December 24, 2016 The answer to the question: Why does the 5th gen Service Manual specify a slightly lower vacuum pressure on the starter valves for cylinders #3 and #4? Because cylinders #3 and #4 experience slightly better exhaust scavenging. The 5th gen exhaust system is a 4 into 2 into 1 type. The 4 into 2 section of the exhaust is as follows: Cylinders #1 and #2 are merged and cylinders #3 and #4 are merged. Then these two merges proceed to the 2 into 1 section merge then on to the exhaust pipe. The difference in exhaust scavenging effect between the #1 and #2 merge set and the #3 and #4 merge set is caused by the 90 degree "V" engine configuration. The 90 degree V causes the firing order to be (shown in 90 degree increments) is: 1-0-3-0-0-2-0-4, which means that cylinder #1 fires only 90 degrees after cylinder #4. This close-coupled exhaust pulse causes the #3 and #4 merge set to experience better scavenging than the #1 and #2 merge set. Link to comment Share on other sites More sharing options...
Auspanglish Posted December 24, 2016 Share Posted December 24, 2016 The answer to the question: Why does the 5th gen Service Manual specify a slightly lower vacuum pressure on the starter valves for cylinders #3 and #4? Because cylinders #3 and #4 experience slightly better exhaust scavenging. The 5th gen exhaust system is a 4 into 2 into 1 type. The 4 into 2 section of the exhaust is as follows: Cylinders #1 and #2 are merged and cylinders #3 and #4 are merged. Then these two merges proceed to the 2 into 1 section merge then on to the exhaust pipe. The difference in exhaust scavenging effect between the #1 and #2 merge set and the #3 and #4 merge set is caused by the 90 degree "V" engine configuration. The 90 degree V causes the firing order to be (shown in 90 degree increments) is: 1-0-3-0-0-2-0-4, which means that cylinder #1 fires only 90 degrees after cylinder #4. This close-coupled exhaust pulse causes the #3 and #4 merge set to experience better scavenging than the #1 and #2 merge set. OK, so why does the 6th gen have all equal levels? It too is a 90° V4. Link to comment Share on other sites More sharing options...
GreginDenver Posted December 24, 2016 Share Posted December 24, 2016 1 hour ago, Auspanglish said: OK, so why does the 6th gen have all equal levels? It too is a 90° V4. Ok... (in spite of your use of "OK" as a conversational qualifier) I'll give you some thoughts on why the 5th gen exhaust and 6th gen exhausts might have different scavenging characteristics (this will be nothing definitive, just pointing to differences that may individually or together result in different exhaust scavenging characteristics between the 5th gen and 6th gen): 1. Unless I'm mistaken (my only hands-on experience with VFRs is the '99 5th gen I just bought) the routing of the 5th gen and 6th gen exhausts is slightly different. I can't provide you with exact measurements but the Honda engineers seem to have made subtle changes in the the routing of the 6th gen exhaust system and it's fair to assume that they may have done this to change the overall length of the piping into each of the two primary "Y" merges which could easily change the way the engine is scavenged. 2. Each of the 6th gen primary "Y" merges have an oxygen sensor protruding into them. I know from working with and configuring fuel injection systems that installing an O2 sensor can cause a change in the way an exhaust system scavenges, specifically affecting the gas velocity and how quickly that velocity drops between exhaust pulses (the Delta-V). 3. The 6th gen has a catalytic converter installed in the position where the 5th gen has a "clean flowing" 2-into-1 merge joint. If I had to point a finger at any particular item in the 6th gen exhaust that might affect exhaust gas scavenging it would be this item. From working with track cars about 30 years ago I can tell you that taking a catalytic converter out of a crossplane V8 engine's exhaust will significantly change the individual cylinder's exhaust scavenging, making 2 of the cylinders, one in each bank, run leaner (can't remember which 2 though). Overall I'd guess that the difference you're pointing out, the fact that the 6th gen Service Manual directs you to set all of the Starter Valves to identical vacuum while the 5th gen has a different vacuum specification, is merely a side-effect of the Honda engineering team working hard to overcome the addition of emissions equipment (catalytic converter and O2 sensors) with a goal of delivering horsepower and torque ratings for the new (at the time) 6th gen that compared favorably with the (outgoing) 5th gen (it certainly would have negatively affected sales volume if the 6th gen produced less horsepower/torque than the 5th gen). As they did what was necessary to compensate for the negative effects of the catalytic converter and O2 sensors they ended up with the (purely side-effect) result that equal vacuum settings on all 4 of the Starter Valves gives the 6th gen engine its best idle and off-idle throttle characteristics. Link to comment Share on other sites More sharing options...
Auspanglish Posted December 24, 2016 Share Posted December 24, 2016 Thank you for a highly detailed hypothesis. Much appreciated. You surely have gone to great lengths. It wasn't my intention to challenge or refute you, just thinking out loud as I've always wondered why they are different and I understood you had put it down exclusively to the 90°V4.I used to own a 98-99 5th gen VFR, came from factory non-catted, at the same time I owned a 6th gen (obviously catted)... There is also a catted 5th gen 00-01. If I'm not mistaken the workshop manual does not give different baseline values for catted and non-catted 5th gens. I believe I read on here years ago that Hispanic Slammer opted for synching his 5th gen as per 6th with maybe a small twist... Not sure, my memory fails me... He swore it felt and behaved better. Food for thought! Link to comment Share on other sites More sharing options...
GreginDenver Posted January 1, 2017 Share Posted January 1, 2017 On 12/24/2016 at 9:40 AM, Auspanglish said: Thank you for a highly detailed hypothesis. Much appreciated. You surely have gone to great lengths. It wasn't my intention to challenge or refute you, just thinking out loud as I've always wondered why they are different and I understood you had put it down exclusively to the 90°V4. I used to own a 98-99 5th gen VFR, came from factory non-catted, at the same time I owned a 6th gen (obviously catted)... There is also a catted 5th gen 00-01. If I'm not mistaken the workshop manual does not give different baseline values for catted and non-catted 5th gens. I believe I read on here years ago that Hispanic Slammer opted for synching his 5th gen as per 6th with maybe a small twist... Not sure, my memory fails me... He swore it felt and behaved better. Food for thought! I think I've found the evidence we're looking for: I was reading through my copy of the 19980-2001 Honda VFR800 Service Manual and when I got to Chapter 21, which is titled "Technical Features", I found a surprisingly detailed description of the bike's PGM-FI system. On page 21-10 the Service Manual description of the PGM-FI system there's an explanation of how the ECM (the Engine Control Module, located in the tail of the bike) operates. Specifically, page 21-10 shows three-dimensional graphs of each individual cylinder's MAP signal (Manifold Absolute Pressure) during low RPM operation. Here's a screen-shot of the page: You can see from this screen-shot that at low RPM the individual cylinders experience different amounts of vacuum (and as a result they each require a different level of fueling from their respective injector: No. 1 INJ, No. 2 INJ, No. 3 INJ, No. 4 INJ). I still can't explain exactly why the Service Manual procedure for Starter Valve Adjustment on page 5-68 tells us to adjust (to "drop") the vacuum on cylinders No. 3 and No. 4 but I'm pretty sure that this is the basis for it. Link to comment Share on other sites More sharing options...
Member Contributer JZH Posted January 4, 2017 Member Contributer Share Posted January 4, 2017 On 12/24/2016 at 4:13 PM, GreginDenver said: Ok... (in spite of your use of "OK" as a conversational qualifier) I'll give you some thoughts on why the 5th gen exhaust and 6th gen exhausts might have different scavenging characteristics (this will be nothing definitive, just pointing to differences that may individually or together result in different exhaust scavenging characteristics between the 5th gen and 6th gen): 1. Unless I'm mistaken (my only hands-on experience with VFRs is the '99 5th gen I just bought) the routing of the 5th gen and 6th gen exhausts is slightly different. I can't provide you with exact measurements but the Honda engineers seem to have made subtle changes in the the routing of the 6th gen exhaust system and it's fair to assume that they may have done this to change the overall length of the piping into each of the two primary "Y" merges which could easily change the way the engine is scavenged. 2. Each of the 6th gen primary "Y" merges have an oxygen sensor protruding into them. I know from working with and configuring fuel injection systems that installing an O2 sensor can cause a change in the way an exhaust system scavenges, specifically affecting the gas velocity and how quickly that velocity drops between exhaust pulses (the Delta-V). 3. The 6th gen has a catalytic converter installed in the position where the 5th gen has a "clean flowing" 2-into-1 merge joint. If I had to point a finger at any particular item in the 6th gen exhaust that might affect exhaust gas scavenging it would be this item. From working with track cars about 30 years ago I can tell you that taking a catalytic converter out of a crossplane V8 engine's exhaust will significantly change the individual cylinder's exhaust scavenging, making 2 of the cylinders, one in each bank, run leaner (can't remember which 2 though). Overall I'd guess that the difference you're pointing out, the fact that the 6th gen Service Manual directs you to set all of the Starter Valves to identical vacuum while the 5th gen has a different vacuum specification, is merely a side-effect of the Honda engineering team working hard to overcome the addition of emissions equipment (catalytic converter and O2 sensors) with a goal of delivering horsepower and torque ratings for the new (at the time) 6th gen that compared favorably with the (outgoing) 5th gen (it certainly would have negatively affected sales volume if the 6th gen produced less horsepower/torque than the 5th gen). As they did what was necessary to compensate for the negative effects of the catalytic converter and O2 sensors they ended up with the (purely side-effect) result that equal vacuum settings on all 4 of the Starter Valves gives the 6th gen engine its best idle and off-idle throttle characteristics. And has kindly been pointed out to me by CandyRed on VFRW, the 8th gen exhaust configuration is completely different again. I wonder which configuration is "best"? Ciao, Link to comment Share on other sites More sharing options...
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