[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"detail-sidebar-cat-0-en-105":3,"doc-seo-399918-105":59,"doc-detail-399918-en":131},{"code":4,"msg":5,"data":6},0,"success",[7,13,18,23,28,33,38,43,48,51,55],{"id":8,"doc_module":4,"doc_module_name":9,"category_name":10,"show_sort_weight":11,"slug":12},1,"Document","Story & Novel",90,"story-novel",{"id":14,"doc_module":4,"doc_module_name":9,"category_name":15,"show_sort_weight":16,"slug":17},2,"Literature",80,"literature",{"id":19,"doc_module":4,"doc_module_name":9,"category_name":20,"show_sort_weight":21,"slug":22},4,"Exam",70,"exam",{"id":24,"doc_module":4,"doc_module_name":9,"category_name":25,"show_sort_weight":26,"slug":27},5,"Comic",60,"comic",{"id":29,"doc_module":4,"doc_module_name":9,"category_name":30,"show_sort_weight":31,"slug":32},6,"Technology",50,"technology",{"id":34,"doc_module":4,"doc_module_name":9,"category_name":35,"show_sort_weight":36,"slug":37},7,"Healthcare",40,"healthcare",{"id":39,"doc_module":4,"doc_module_name":9,"category_name":40,"show_sort_weight":41,"slug":42},8,"Research & Report",30,"research-report",{"id":44,"doc_module":4,"doc_module_name":9,"category_name":45,"show_sort_weight":46,"slug":47},9,"Religion & Spirituality",20,"religion-spirituality",{"id":46,"doc_module":4,"doc_module_name":9,"category_name":49,"show_sort_weight":46,"slug":50},"World Cup","world-cup",{"id":52,"doc_module":4,"doc_module_name":9,"category_name":53,"show_sort_weight":52,"slug":54},10,"Lifestyle","lifestyle",{"id":56,"doc_module":4,"doc_module_name":9,"category_name":57,"show_sort_weight":24,"slug":58},19,"General","general",{"code":4,"msg":60,"data":61},"ok",{"site_id":62,"language":63,"slug":64,"title":65,"keywords":66,"description":67,"schema_data":68,"social_meta":124,"head_meta":126,"extra_data":128,"updated_unix":130},105,"en","manifold-pressure-sucks-quiz-time-understanding-manifold-pressure-mp","Manifold Pressure Sucks! - Quiz Time - Understanding Manifold Pressure (MP)","","Article explains how the manifold pressure (MP) gauge works on normally-aspirated piston engines and why pilots often misunderstand its readings. It challenges common power-setting assumptions after takeoff using a series of quiz questions about throttle/RPM changes, takeoff roll, sensor location, and how suction versus pressure is measured. It covers expected MP indications at different altitudes and conditions, engine idle warming effects, and interpreting abnormal MP drift, culminating in troubleshooting an audible whistle.",{"@graph":69,"@context":123},[70,84,106],{"@type":71,"itemListElement":72},"BreadcrumbList",[73,77,79,82],{"item":74,"name":75,"@type":76,"position":8},"https://docshare.wps.com","Home","ListItem",{"item":78,"name":9,"@type":76,"position":14},"https://docshare.wps.com/document/",{"item":80,"name":20,"@type":76,"position":81},"https://docshare.wps.com/document/exam/",3,{"item":83,"name":65,"@type":76,"position":19},"https://docshare.wps.com/document/manifold-pressure-sucks-quiz-time-understanding-manifold-pressure-mp/399918/",{"url":83,"name":65,"@type":85,"image":86,"author":91,"headline":65,"publisher":94,"fileFormat":97,"inLanguage":63,"description":67,"dateModified":98,"datePublished":99,"encodingFormat":97,"isAccessibleForFree":100,"interactionStatistic":101},"DigitalDocument",{"url":87,"@type":88,"width":89,"height":90},"https://docshare.wps.com/thumbnails/manifold-pressure-sucks-quiz-time-understanding-manifold-pressure-mp/399918.png","ImageObject",300,407,{"name":92,"@type":93},"jayni","Person",{"url":74,"name":95,"@type":96},"DocShare","Organization","application/pdf","2026-11-04","2026-09-27",true,{"@type":102,"interactionType":103,"userInteractionCount":105},"InteractionCounter",{"@type":104},"ViewAction",11,{"@type":107,"mainEntity":108},"FAQPage",[109,115,119],{"name":110,"@type":111,"acceptedAnswer":112},"Why can MP rise slightly when RPM is reduced after takeoff even if manifold pressure is expected to fall?","Question",{"text":113,"@type":114},"A coordinated throttle/RPM change can produce a brief increase in the MP reading during the RPM reduction, and the article prompts readers to understand why that rise occurs in the gauge’s measurement behavior.","Answer",{"name":116,"@type":111,"acceptedAnswer":117},"What does the MP gauge really indicate on a normally-aspirated engine?",{"text":118,"@type":114},"With the engine running, the instrument is effectively reading suction (lack of pressure), even though it is labeled with manifold pressure numbers.",{"name":120,"@type":111,"acceptedAnswer":121},"What MP indication should you expect when the airplane is at rest with the engine not running at sea level, and how does altitude affect it?",{"text":122,"@type":114},"At sea level on a standard day it should read about 29.92 inches (near 29.9). At higher elevations, the article states the gauge will show roughly one inch less per thousand feet above sea level, with other conditions also affecting the reading.","https://schema.org",{"og:url":83,"og:type":125,"og:title":65,"og:site_name":95,"og:description":67},"article",{"robots":127,"canonical":83},"index,follow",{"doc_id":129,"site_id":62},399918,1790852881,{"code":4,"msg":5,"data":132},{"doc_id":129,"user_id":133,"nickname":92,"user_avatar":134,"doc_module":4,"category_id":19,"category_name":20,"doc_title":65,"doc_description":67,"doc_content":135,"file_id":136,"file_url":137,"file_type":138,"file_size":139,"view_count":105,"is_deleted":4,"is_public":8,"is_downloadable":8,"audit_status":8,"page_count":140,"language":141,"language_code":63,"site_id":62,"html_lang":63,"table_of_contents":142,"faqs":143,"seo_title":144,"seo_description":67,"update_tm":145,"read_time":146,"preview_page_count":4},3985747859343,"https://ap-avatar.wpscdn.com/davatar_276721f389ce27ea32af1340a28f341c","Manifold Pressure Sucks!  \nFirst appeared March 21, 1999, [www.avweb.com](www.avweb.com)  \nIf you fly behind apiston engine with a controllable-pitch propeller, the manifold pressure gauge plays an important part in the power settings you use. Few pilots, however, have any real understanding of what the instrument actually measures or what its readings truly signify. Pelican to the rescue! Read this column by AVweb's John Deakin and you'll be able to teach your CFIandA&P a thing or three about MP.  \nThe manifold pressure (MP) gauge is a very simple instrument, but what it does is a mystery to many pilots. Simply put, if you do not fully understand what that instrument is telling you, you cannot possibly understand the engine, engine management, power settings, or troubleshooting.  \nQuiz Time  \nFirst, allow me to pose a few rhetorical questions to help you understand why there's more to this subject than meets the eye. You might be uncomfortable with the thought of actually doing some of these things to your engine--and that's fine--but I ask that you visualize them as a mind exercise and think about them, please.  \nThis entire column will deal only with normally-aspirated engines--those without superchargers or turbochargers. I'll be dealing with the fire-breathers in another column.  \nQuestion: Assume that someone--perhaps a CFI quoting a poorly-done old POH, or perhaps just regurgitating what his CFI taught him--has told you that the first power reduction after takeoff should be to 25 inches and 2,500 RPM. Leaving aside the issue of whether this is really a good procedure, let's assume you take off and dutifully pull the throttle back from about 29 inches, to exactly 25 inches. Then you pull the prop control back from 2,700 to 2,500 . Are you surprised to see the MP rise to 26 inches or so as the RPM comes down? Do you understand clearly why that slight rise occurs?  \nQuestion: Suppose you leave the throttle wide open after takeoff, and just reduce the RPM from 2,700 to 2,500 (usually a better choice in the big-bore flat sixes). What would you expect to seethe MP do, and why?  \nQuestion: Suppose you do a full-power runup in position before releasing the brakes (another bad procedure, but never mind) . You note the MP and release the brakes. What will the MP do during that takeoff roll and the early climb, and why?  \nQuestion: Do you know (in general) where the \"sensor\" is for the MP instrument, and how it works? Which would you think is more stressful to the engine's intake manifold plumbing: a power setting of 12\" MP (in a power off descent, for example), or 30\" at takeoff power? Why? How is that pressure transmitted to the instrument you're reading?  \nQuestion: Your airplane is sitting at rest, engine not running, at a sea-level airport. What should the MP show? Suppose you're parked at an airport at 5,000 feet above sea level; what MP indication would you expect? What else can affect that reading? Suppose you know what it is supposed to show, but its two inches low in an airplane you've never flown before? What effect would that have on your flight? Would you depart with it showing that error? Could you correct for it? How?  \nQuestion: Suppose you start the engine and idle at 1,000 RPM to warm the engine. What will the MP show at sea level, or at that 5,000-foot elevation? Suppose you just happen to know the answers to these two questions in your own airplane, and one fine day you notice the MP is three inches higher than normal at 1,000 RPM while warming up? What would you think? Suppose the MP was lower than normal; can you think of a possible cause for that?  \nQuestion: Suppose you're cruising at 10,000 feet, full throttle, 2,500 RPM, and you cycle the prop between 2,700 (redline), and the lowest it will go, perhaps 1,200 RPM. What would you expect to see the MP do during this huge variation in RPM?  \nQuestion: Finally, suppose you're sitting in the runup area, ready to go, and you notice an audible whistle coming from","cbCaiqjcLbXGzXtw","https://ap.wps.com/l/cbCaiqjcLbXGzXtw","pdf",1741387,56,"English","# Quiz Time\n## Key MP questions and scenarios\n# Suction, Not Pressure\n## What the MP instrument actually shows\n# Not Started, Yet\n## Ambient pressure and expected readings","[{\"question\":\"Why can MP rise slightly when RPM is reduced after takeoff even if manifold pressure is expected to fall?\",\"answer\":\"A coordinated throttle/RPM change can produce a brief increase in the MP reading during the RPM reduction, and the article prompts readers to understand why that rise occurs in the gauge’s measurement behavior.\"},{\"question\":\"What does the MP gauge really indicate on a normally-aspirated engine?\",\"answer\":\"With the engine running, the instrument is effectively reading suction (lack of pressure), even though it is labeled with manifold pressure numbers.\"},{\"question\":\"What MP indication should you expect when the airplane is at rest with the engine not running at sea level, and how does altitude affect it?\",\"answer\":\"At sea level on a standard day it should read about 29.92 inches (near 29.9). At higher elevations, the article states the gauge will show roughly one inch less per thousand feet above sea level, with other conditions also affecting the reading.\"}]","Manifold Pressure Sucks! - Quiz Time - Understanding Manifold Pressure (MP) | PDF",1790505344,141]