F4U-4 engine question.

[Neil Stirling]

Hi,

I hope you  knowledgeable guys can help me out with a few of questions.

Its my understanding ( Vought F4U Corsair, by M. Bowman and the internet) that the R-2800-18W was fitted to the F4U-4 up to August 1946. From then on this engine could be replaced by -42W, this engine being able to take advantage of 115/145 fuel and deliver an additional 300hp.

1./ Was the -42W required to get the additional 300hp?

2./ If not what was the point of the -42W?

2./Was the date August 46?

Neil.

[SgtPappy]

I'm pretty sure the extra HP comes from the engine. I highly doubt that 115/145 US grade octane (150 grade UK i think) produced an extra 300 HP.

We'll have a whole load of more Hog-dweebs in here soon, so stay tuned to find out some more!

[Stoney74]

If indeed it did run the higher octane fuel, higher manifold pressures could be set without the threat of detonation...

So, indirectly, the fuel can account for the higher horsepower.

[Neil Stirling]

Sorry, I didn't make myself very clear.

The F4U-4 that served during WW2, used 100/130 octane fuel and ran at 60"HG and produced 2,450hp?
Some time later 115/145 octane fuel was introduced and this then allowed 70"HG and the engine produced over 2,700hp.

Marti W Bowman states that the change that allowed increased power (the -42W engine) occured with F4U-4B Bu.No.9748, constructed after 16th August  1946, however, http://www.wwiiaircraftperformance.org/f4u/f4u-4.pdf  gives the -18W and 115/145 octane.

Were any of the WW2 F4U-4 units, using 115/145 fuel and 70"hg? For example, 115/145 octane fuel was made availble to some WW2 Pacific Mustang units, allowing 80"HG. The fuel was not generally available during WW2 as producing this fuel cut 100/130 octane production.

Neil

[gripen]

Checked the White's R-2800 book. There is only minor differences between these engines; the later has longer connecting rods + some strenghtening etc. The -18W being C-series engine and tha -42W being CB-series.

[Neil Stirling]

Thanks guys

It would seem that P&W confirm that the -42W was the engine that could use 115/145 octane fuel.

http://www.enginehistory.org/P&W/R-2800/DoubleWaspIndex.pdf

Neil.

[SgtPappy]

Well, 115/145 grade is just as exchangeable as the 100/130 grade is. You can use them in both P&W engines, but you'd only get the higher boost from the 115/145.

[F4UDOA]

Neil,

I have engine charts for both of these Blocks if you are interested can email them.

[Neil Stirling]

Yes please F4UDOA !

Neil.

[Stoney74]

Originally posted by SgtPappy
Well, 115/145 grade is just as exchangeable as the 100/130 grade is. You can use them in both P&W engines, but you'd only get the higher boost from the 115/145.

Remember, the gas doesn't provide more power.  Higher octane fuels have higher flash points, therefore, they can sustain higher pressures during the compression stroke before they spontaneously combust, or detonate.  It is important to understand the terminology here.

The caveat is, that the same engine using a higher octane fuel can run at higher manifold pressure before the fuel detonates.  The engine parts may not be designed to sustain those pressures (I have first hand knowledge here) but the potential remains.

Just want to make sure you don't draw the wrong conclusions here Pappy...

[SgtPappy]

Oh I know, I think you've told me many a time before
I should say that if the engine has the potential to use higher grade octane than it will always get the higher power settings or more technically, higher boost settings.

With a lower-grade, not all the engine's potential is tapped. The engine always had the potential, but it can only be tapped (not given) by the higher grade octane.

[Scca]

I found this on another web site

There's always a lot of confusion regarding octane, octane-boosters and how they work. Typical misconceptions are evident in blank-statements like:

"Higher octane fuels burn slower, thus their higher octane number"
"Higher octane fuels burn hotter, therefore more power is generated"
"Higher octane fuels explodes with more force, thus their higher power"

Both of which are untrue and are coincidental in effect, rather than causal. In actual practice, an engine has to be tuned specifically for high-octane fuels to generate extra power. If you have an engine fully-tuned and optimized for 91-octane pump gas, adding 100-octane race-gas into it will yield little if any increase. However, if you were to take that engine and increase the compression, advance the knock and/or increase the boost, then you can take advantage of the higher-octane fuel. But this precludes going back to the previous lower-octane fuels.

In short, an engine that is optimized for 87 octane will only see a slight improvement if you change to 105 octane unless other modifications or adjustments are made.  

Often, as witnessed by me in my drag racing days, just advancing the timing is enough to make that difference.   If you advance timing, switching back to 87 with out readjusting the timing will cause engine "ping", which is very damaging to an engine.

There are other adjustments that can be made, including boost pressure from a turbo or mechanical blower to further improve performance when using high octane fuels.  Even if the base mechanicals are unchanged, modifying boost and timing advance will produce more HP.  

From my personal lessons learned, only adding higher octane fuel may sometimes degrade performance unless other adjustments are made.

[joeblogs]

The engine has to be able to take the higher loads associated with the additional manifold pressure and it has to be able to dissipate more heat in the same amount of time...

-blogs

Originally posted by SgtPappy
Oh I know, I think you've told me many a time before
I should say that if the engine has the potential to use higher grade octane than it will always get the higher power settings or more technically, higher boost settings.

With a lower-grade, not all the engine's potential is tapped. The engine always had the potential, but it can only be tapped (not given) by the higher grade octane.