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Crotchety Old Bastard
 
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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.



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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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I know my car feels lethargic after sitting on a hot day - heat soak sucks.

For the dyno, why not pack some ice on the IC between runs? (The intent is to bring to back to ambient temp, not bring it to unrealistic ice-cold temps between runs.)
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Old 06-23-2007, 10:47 AM
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The car and motorcycle magazines always use a conversion formula to adjust for heat, if you think that will help, I can try to dig that up.

40 degrees makes a HUGE difference when your intercooler isn't working.

60 degrees is about 2 degrees from the absolute ideal temperature of 58, I think, that they use in their formulas.

Actually those formulas might not be for hp, but for elapsed time, now that I think about it. But there has to be a formula out there!

You can't really compensate for the intercooler effect, but you really ought to be able to get an estimate of hp change by temperature. In fact, the lack of using your intercooler may just make the conversion formula more accurate, because an intercooler doesn't do much at 60 degrees, maybe?

Your exhaust weighs less as well, and even if your overall horsepower is similiar, did the spool up happen faster? That is just as important.

Look, if you increased horsepower on a 100 degree day, you did good.

No exhaust is magic, but a much lighter, faster spooling, cool sounding exhaust is a good start if it makes more power on a hotter day.

Last edited by DDDD; 06-23-2007 at 08:40 PM..
Old 06-23-2007, 01:26 PM
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Here is what I noticed about heatsoak on my car.

It takes about 4 mins of run time to get back to ambient temps after sitting for an hr while hot. That is with the deck lid down and a well shrouded intercooler.

So my advice is to shut the lid and idle for 4 mins while you set the car up on the dyno. That should get you close to ambient.

You should dyno with the lid down.
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Old 06-23-2007, 03:45 PM
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Crotchety Old Bastard
 
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Unfortunately the deck lid has to be up during the run in order to get data from the ignition system.

The runs need to be set up identically in order to have an accurate comparison. It won't be hard to repeat today's fiasco now that it is nearly July in Alabama. The ambient temperature on my dyno sheet states 93*F and that was at 10:00 this morning. The humidity didn't help either. I've pulled the bumper back off and will put the stock muffler on when I put it all back together.

The shop owner has a huge fan that he points toward the radiator of "normal" cars. A tripod of some sort would be needed to accommodate the 930 style intercooler.

I was hoping that one of you fellas had experienced a similar problem during a dyno tuning session and might know approximately how much power I have left on the table.
Once I reset the baseline with another heat soaked dyno run I'll have my numbers.

My dyno results are not going to be impressive by 930 standards. I am doing this strictly to measure the HP increase of a free flowing exhaust on a 930 engine with typical mild modifications. The engine has been locked down at 0.7bar; it's a great test mule.

What won't show up on a dyno graph is the free-revving characteristics and the kick ass sounds this thing makes! It is a cackle monster during decel and the turbo spool sound is as orgasmic as the muscle car idle.


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'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, 07:39 PM
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Quote:
Originally posted by RarlyL8
What won't show up on a dyno graph is the free-revving characteristics and the kick ass sounds this thing makes! It is a cackle monster during decel and the turbo spool sound is as orgasmic as the muscle car idle.
Nope, for that we have youtube
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Old 06-23-2007, 11:46 PM
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Quote:
Originally posted by Emission

For the dyno, why not pack some ice on the IC between runs? (The intent is to bring to back to ambient temp, not bring it to unrealistic ice-cold temps between runs.)
Heh. That should work.

Or, I remember reading a magazine article in the 70's about some US drag racers @ Santa Pod using a fire extinguisher to get a six pack to what they considered a drinkable temperature.

Which gives me an idea....

A CO2 extinguisher wouldn't leave a mess, would get all through the core finning (as opposed to just sitting on top), and you could do it gradually, allowing temps to lower slowly, so there wasn't too much thermal shock to the I/C (don't even know if this is too much of a concern, but you'd hate it if you cracked something, I'm sure).
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Old 06-24-2007, 03:13 AM
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Crotchety Old Bastard
 
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Consistancy is key.
The baseline runs need to be done under the same conditions as the muffler test runs.
The conditions are now a 30 minute heat soak and 93*F ambient temps. Talk about a conservative dyno number! HA!
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'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 06-24-2007, 07:22 AM
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Brian, head down to your local WalMart and pick up a medium-sized box fan - it is an absolute must for dyno runs.
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"930 is the wild slut you sleep with who tries to kill you every time you "get it on" - Quote by Gabe
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Old 06-24-2007, 11:08 AM
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Or one of the industrial chromed steel fans will do:

http://home.comcast.net/~craigcarolann/trackvideos/930_November_11_2006_dyno_009.mpg
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"930 is the wild slut you sleep with who tries to kill you every time you "get it on" - Quote by Gabe
Movie: 930 on the dyno
Old 06-24-2007, 11:10 AM
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When my IC outlet temp reaches 120-130 degrees at the track, I can feel a 'seat of the pants' power decrease.

Somewhat objective example:

C6 Z06 has faster acceleration at that temperature and at any mph range - despite a higher RWHP P/W ratio.
Z06 has more torque, but when the 930 IC is cool, it is quicker than the Z06 in a straight line.

No numbers, but a fairly significant difference.

The fan will keep everything cooler - intercooler, intake manifold - but at 90 degrees ambient, trying to correct for and comparing against a 60 degree baseline will probaly prove inaccurate, if not impossible.
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- Craig 3.4L, SC heads, 964 cams, B&B headers, K27 HF ZC turbo, Ruf IC. WUR & RPM switch, IA fuel head, Zork, G50/50 5 speed. 438 RWHP / 413 RWTQ -
"930 is the wild slut you sleep with who tries to kill you every time you "get it on" - Quote by Gabe
Movie: 930 on the dyno

Last edited by Craig 930 RS; 06-24-2007 at 12:13 PM..
Old 06-24-2007, 12:03 PM
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Crotchety Old Bastard
 
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You're right, I'm not going to try and correct for the heat mathmatically. Even using a fan will not eleminate the problem - you can't push 70*F air through an intercooler when it's 93*F outside.
So for now I will stick to my original plan and try to duplicate the conditions as accurately as possible. It'll never be perfect but I can get it close. There is no break in the heat in sight so I've got some time as well.
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'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 06-24-2007, 06:39 PM
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Brian, Eddie and I dynoed his car and he had me use lots of water, ice, and wind to cool his I/C. Your best bet would be to get someone to cool the intercooler between passes with at least water. I thought the ice was over kill as there would be no chance of getting ice to flow over the i/c in real world conditions. You would be suprised how fast the water pulls the heat away when a fan is blown directly over it
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Old 06-24-2007, 07:40 PM
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Crotchety Old Bastard
 
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There are lots of ways to cool and super-cool an intercooler, thanks for the suggestions.

What I don't want to do is get great dyno numbers solely due to or influenced by intercooler efficiency. I must measure only the affect of changing the muffler. The constraints that I have to use must be repeatable and realistic to what you would see while driving down the road in your car. Given those conditions I can use a fan on the intercooler and that's about it.

Thanks all and I'll post my results when I get finished with all of this!
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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 06-25-2007, 06:00 AM
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Well, the good thing is there is no realistic way that you could surpass the 60 degree ambient ideal conditions

Typically the difference between a chambered muffler to a straight through is 12 RWHP - this, according to a local shop that has a bazillion dyno runs from stuff like this -
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- Craig 3.4L, SC heads, 964 cams, B&B headers, K27 HF ZC turbo, Ruf IC. WUR & RPM switch, IA fuel head, Zork, G50/50 5 speed. 438 RWHP / 413 RWTQ -
"930 is the wild slut you sleep with who tries to kill you every time you "get it on" - Quote by Gabe
Movie: 930 on the dyno
Old 06-25-2007, 07:37 AM
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Crotchety Old Bastard
 
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I'm expecting a little more than that Craig.
I assume the resulting increase seen by a free flowing muffler (as compared to stock) would be directly proportional to the level of engine modifications. This 12RWHP figure - do you know what are the level of mods on the engines that saw that specific increase?
Can you imagine what a stock muffler would do to your car?

As for the 60* ideal ambient temperature, you should go for a ride on a sub-freezing day. Hot oil and cold intake air and intercooler. Hollllllllllly ***** hang on to your shorts!
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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 06-25-2007, 08:50 AM
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12 RWHP is achieved even on a relatively stock engine.
I saw sheets showing 15-17 HP on moderately modified cars.

Also, power-wise, a straight through muffler is virtually the same as a Zork!
Turbo engines absolutely do not 'like' the old nemisis, backpressure.

Up here in the Pacific Northwest we have the ideal:
Moist, cool days that really help the HP
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- Craig 3.4L, SC heads, 964 cams, B&B headers, K27 HF ZC turbo, Ruf IC. WUR & RPM switch, IA fuel head, Zork, G50/50 5 speed. 438 RWHP / 413 RWTQ -
"930 is the wild slut you sleep with who tries to kill you every time you "get it on" - Quote by Gabe
Movie: 930 on the dyno
Old 06-25-2007, 12:47 PM
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What about boost pressure @ 90* vs. 50*?

I've noticed a decrease on the gauge of at least .2 bar.

Is it the same to you guys?
Old 06-28-2007, 07:00 PM
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Brian,

You are only 3 hours away from me in Memphis. Let me know if I can assist you with video production/editing or still images and sound. I have a digital video camera, digital audio recording, and professional photography gear. We can put something together and upload it to youtube.com.
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Last edited by JeffreyNMemphis; 06-29-2007 at 10:40 AM..
Old 06-29-2007, 10:38 AM
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Crotchety Old Bastard
 
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I appreciate the offer but with this extreme heat we are having I'd die during the trip. Having an option delete coupe with no sunroof , no A/C, and no pop-out windows seemed like a good idea when I lived in IL.
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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 06-29-2007, 01:01 PM
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