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Ambient air temperature and car performance


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#1 arttidesco

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Posted 16 November 2011 - 12:34

On December 2nd 1962 Peter Arundell driving a Lotus 22 Formula Jr car beat his Monza Lotteria 30 lap race time and set a new FJ lap record to settle a bet between Colin Chapman and Richard von Frankenberg about an allegation against Team Lotus of running oversized Ford Cosworth FJ engines that seems to have arisen from rumours in the FJ pitlane in 1962.

More about the background can be read on the L'affaire Lotus/von Frankenburg TNF thread.

One of the striking things about Peter's achievement is that he won the Monza Loteria on June 24th 1962 with a time of 56'40.8 secs and that his fastest time was 1'50.9 seconds and that on December 2nd 1962 with 'cement put down over patches of ice in the Lesmo Corner', Peter completed the 30 laps 17 seconds to the good of his June race time with a best lap of 1'50.4".

My technical questions are these :-

The two situations were not identical because the car was running with a partially blanked of radiator in December, could this have significantly enhanced the aero dynamic performance of the Lotus 22 ?

I have seen in NASCAR 'go or go homers' often qualify with completely blanked of radiator and brake ducts in the quest for top speed at tracks like Talladega.

In all other respects the Lotus 22 appears to have been in more or less the same condition with similar all weather tyres in both events.

Perhaps more interestingly I am curious to know how much engine performance might have been gained through the drop in ambient temperature ?

Here are a couple of links showing recent average temperatures at Monza for June and December.

We know the temperature at Monza was somewhere around freezing in December and the average maximum temperature at Monza in June in 30 degrees.

How much difference in engine performance would a conservatively estimated 20 degree difference in temperature between the two dates have made to the nominally 100 hp rated Ford Cosworth FJ engine ?

I imagine grip from the tyres would have been reduced by the temperature reduction can we estimate by how much ?

Can we then formulate an approximation of how much better, or worse the whole Lotus 22 package should have preformed between the dates in question ?

Relevant answers may be credited and used in a forthcoming blog.

Thanking you in anticipation of your answers.

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#2 cheapracer

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Posted 16 November 2011 - 16:07

Old rule of thumb used to be 1% for every 10 degrees F change.

Can't see that being any different today.

#3 MatsNorway

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Posted 16 November 2011 - 19:39

Old rule of thumb used to be 1% for every 10 degrees F change.

Can't see that being any different today.


awww.. sucks for metric users.. C*

#4 saudoso

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Posted 16 November 2011 - 20:57

awww.. sucks for metric users.. C*

Roughly 1% every 5c

My rule of thumb conversion is F = 32+2*C. The correct formula is F=32+(9/5)*C

#5 Lee Nicolle

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Posted 16 November 2011 - 21:46

Probably too many questions and hypotheticals. Engines make more power with cold air, which varies widely on the fuel used and the cold air intakes.Taping up the intakes will help a little with straight line speed though aero can and always will be very subjective.

Interestingly diesel engines and LPG engines absolutely love cold air and hate hot air. Normal petrol engines do not have the same power gains or losses. Methanol seems to like cold air also, though on a really cold night sometimes will ice up throttles, defenitly intake manifolds. I believe it is similar on E85 also. Probably not a good fuel for cold climates!

#6 arttidesco

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Posted 16 November 2011 - 22:07

Thanks Cheapracer, this afternoon I unexpectedly received a copy of the report from Auto Motor und Sport it gives the ambient temperature on the day of the event in Dec as 4˚C and on the day of the Lotteria as 30 ˚C so my estimate of 25˚ in temperature between the two events was not too far out.

A corrected difference of 26˚C x 1.8 = 46.8˚F equal to a 4.68% increase in power after this my maths breaks down what other information do I need to work out if this increase in power is equal to the decrease in race time and and lap times ?

ams also reports that Peter completed the test race distance in 55'48.7" a full 52 seconds faster than the actual race distance in June, not the 17 seconds reported above.

Another magazine Motor Rundschau reported that after the test race distance was completed Peter did one more lap lowering the FJ record to 1'49.8".

Edited by arttidesco, 16 November 2011 - 22:08.


#7 saudoso

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Posted 16 November 2011 - 22:32

Probably too many questions and hypotheticals. Engines make more power with cold air, which varies widely on the fuel used and the cold air intakes.Taping up the intakes will help a little with straight line speed though aero can and always will be very subjective.

Interestingly diesel engines and LPG engines absolutely love cold air and hate hot air. Normal petrol engines do not have the same power gains or losses. Methanol seems to like cold air also, though on a really cold night sometimes will ice up throttles, defenitly intake manifolds. I believe it is similar on E85 also. Probably not a good fuel for cold climates!

You got this right. During the early days of ethanol here in BR (late 70's and on) those cars used to have a small gas tank in the hood. The driver was supposed to pump some in the the carburetor for cold starts. By cold starts I mean tropical cold starts, below 15c.
I'm not sure how it's handled today (haven't had an ethanol car in 2 decades), I guess the fuel is heated pre injection.

Edited by saudoso, 16 November 2011 - 22:33.


#8 arttidesco

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Posted 04 December 2011 - 11:57

Thanks to everybody on this thread who contributed to my Lotus 22 blog :up: