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RarlyL8 RarlyL8 is offline
Crotchety Old Bastard
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Join Date: Jan 2000
Location: Huntsville, AL
Posts: 13,525
How much power loss from heat soak?

I had a disappointing morning.
Late last night I finished fitting the stock bumper to my car so I could mount one of my new mufflers for some dyno testing. I was concerned about the forecast for today - very hot. My baseline runs were done when it was 60F, today it will be near 100F.

I know from the butt dyno that I gain a lot of lag and loose a lot of HP when the intercooler sits and heat soaks. I have a nice shroud that I made which eliminates the problem - when the deck lid is shut . The deck lid is open and there is no fan on the intercooler during a Dyno run at this shop.

On the trip to the dyno the car felt like it had gained 20HP. Quicker spool, revved easier, big improvement over the stock muffler. When I arrived at the shop the car had to sit for at least 30 minutes. By the time I got it on the Dyno the intercooler was too hot to touch. I knew I was doomed. The run showed the same typical issues I have seen in the past, before the shroud was added. Greater lag and reduced power. The run still produced more power than stock but I know there is a ton left on the table due to the heat.

So after that long winded deal the question is - does anyone have similar dyno data showing the loss of power due to heat?
Any guess as to how much loss?

My only recourse is to spend more money (and time) and re-mount the stock muffler for another baseline run in 90F heat. I've got to compare apples to apples.

RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 06-23-2007, 08:33 AM
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