True Top Speed for the A6M Zero

[Old Crow]

There seems to be a rather large variance in top speed claimed for the Zero. For the A6M2 I've seen anywhere from 309 mph (Saburo Sakai) to 332 mph. The lower numbers come from here: http://yarchive.net/mil/zero.html and higher numbers can be found in any modern book you pick up. (Fire In The Sky by Eric Bergerud being one of many). The A6M5 top speeds range from 335 mph (TAIC Report No. 17, Nov. 1944) on up to 358 mph (William Green - Famous Fighters of WW2). Koga's A6M2 Zero recovered in the Aleutian Islands in 1942 upon being repaired displayed a top speed of 326 mph with American fuel.

I realize we used 100 octane fuel for our tests here in the USA compared to the 91-92 octane the Japanese used during the war. I am no fuel/engine expert by any means but another website pointed out that if the engine was tuned to use 91 octane, simply using 100 octane wouldn't do a thing to increase performance without tuning the engine for it. If that is the case, I would think we adjusted the engine to get optimal performance out of the 100 octane fuel but I don't know for sure.

According to some on the yarchive site above, the Wildcat wasn't inferior to the A6M2 as many history books and TV shows have told us over the years. I tend to agree with the lower mph numbers being more representative of what American pilots faced in the Pacific but would appreciate any other info/opinion anyone else might have on this topic.

[DaveBB]

It was either a Ki84 or Ki100 that was captured and tested after the war.  With high octaine fuel, it added a significant amount of speed to the aircraft (20-30mph).

[RODBUSTR]

the data I have from jiro hirokoshi's data from Mitsubishi is top speed 331.4 mph@14,760 feet.. one of the books it is published is the great book of ww2 airplanes. author of this chapter isrobert c. mikesh.....with a 940 hp sakae engine....type 32 1130 hp sakae 21 top speed 338mph at19,690 feet....  type 52 with 1130 hp sakae 21 engine.....351mph @ 19690feet al though the 52 was about 500 pounds heavier and had the same engine it was faster mainly because of the jet effect of the redesigned exhaust stacks.

[Wmaker]

Well, AH's A6M2's weight and top speeds match the data aquired during the testing of the Akutan Zero. The speed on the deck was especially low (270 mph) on the Akutan Zero compared to Japanese literature sources that I've seen. And the weight was reported as roughly 200 lbs higher than for example Francillon mentions.

[Devil 505]

I realize we used 100 octane fuel for our tests here in the USA compared to the 91-92 octane the Japanese used during the war. I am no fuel/engine expert by any means but another website pointed out that if the engine was tuned to use 91 octane, simply using 100 octane wouldn't do a thing to increase performance without tuning the engine for it. If that is the case, I would think we adjusted the engine to get optimal performance out of the 100 octane fuel but I don't know for sure.

I find it highly unlikely that any modification was made to the engine to make use of 100 octane fuel. It makes no sense to do so since the purpose of testing the aircraft is to see what the enemy can do with it. Also, it would be just plain stupid to mess with an engine you can't get replacement parts for easily.

[icepac]

Devil is correct.

Funny is that I posted the exact same thing in another thread just 2 minutes ago.