FGT Weather Sensitivity


sahlman

Ford GT Team Alumni
Jul 21, 2011
329
Verona, WI
The following is intended to give some background on my comments regarding the FGT air temperature sensitivity in the OEM tire article. I have tried not to get too technical here, but show some fundamentals on the differences causing the FGT to be more weather sensitive than turbocharged (or normally aspirated) counterparts. I will not try to discuss other tradeoffs between turbocharging and supercharging like lag versus instant power from low RPM upward.

The GT engine performance sensitivity to weather/air temperature I mentioned are due to efficiencies as some posts mention. Engine architecture, cooling system and intercooler efficiency primarily. Engine system inefficiency means lost energy typically in the form of heat. Heat is obviously bad for performance. An engine system that has more waste energy benefits most or is penalized the most by weather conditions that help or hurt the performance. This is the case of the supercharged FGT and supercharged engines in general versus turbo charged (or naturally aspirated).

A supercharger is a lot less efficient than a turbocharged or naturally aspirated system. A turbocharged system utilizes waste energy/exhaust to turn the compressor for higher density intake air. EcoBoost’s (turbocharger) advantage is real. A supercharged engine runs directly off of the crankshaft. The FGT creates about 650 HP in the combustion chamber, but it takes about 100 HP to drive the supercharger, for a net gain of 550 BHP at the crankshaft. The FGT has to cool for 650 HP while the same BHP naturally aspirated engine has to cool for only 550 HP and the turbo charged engine is similar. So the FGT engine has to cool for nearly 20% more power it cannot use.

Forced induction engines (turbo and super chargers) use intercoolers (now mostly “aftercoolers”) to cool the intake charge because higher density air heats more when compressed, so the intercooler attempts to maintain the gains of the increased air intake density. As discussed by a few here, intercooler efficiencies can vary a lot and are critical to performance and efficiency. The FGT cooling pack with intercooler is at a big disadvantage to an equally rated turbocharged system because of the extra 100 HP the supercharged engine has to cool.

Exterior air of 75 deg F plus and the FGT cooling system and intercooler are far more taxed than equally rated turbocharged or naturally aspirated engine in which the FGT performance drops from “ideal” quickly. Many here have experienced the very noticeable power drops with a little heat soak at the mile events or spirited driving on the road course as you watch the engine water temp reach 225 deg F+ quickly.

However, the FGT cooling and intercooler perform well when it is cold out and the car is just being driven slowly on the street with short bursts of acceleration. The FGT engine benefits greatly from this cold air and sauntering pace to reach its “full potential” plus with the cold dense air.

The FGT cooling pack (radiator, A/C condenser and intercooler) up front is challenged to maintain cooler intake and engine temperatures on a warm day, but has little trouble on a 40 deg F day on the street. So engine architecture (supercharged) and intercooler inefficiencies cause the FGT to have much wider swings in performance due to weather conditions than its turbo charged and naturally aspirated counterparts of similar BHP.


Scott
 

fjpikul

GT Owner
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Yeah, yeah, and the tires are not up to the challenge at those temps. I know.
 

AJB

GT
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Scott - very good. thanks for this explanation. When at the Texas Mile (Rally 3 or 4 ?) I did notice how at around 150 MPH on that very hot day (and I made the mistake of keeping my A/C running) , The FGT just "went completely LIMP" no matter how hard I pressed the accelerator.
Part of that may have been the Engine computer 'protecting ' the engine but not sure.

If this is the case, why then would a Supercharger be used vs a Turbocharger? Is it just to offset the lag?
(although Superchargers do look and sound cool)
andy (ajb)
 

Xcentric

GT Owner
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Jul 9, 2012
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Where is Mullet? 226 in the Texas mile with a TT/SC/NOS engine.

SAE Tech Paper on the GT cooling system: http://rudelere.com/buuk/1179/

Ford already had a lot of experience with supercharging. Not so much with turbocharging. Given the compressed development cycle, emissions, drivability, cost, etc., maybe part of the decision was to go with what you know.
 
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Brombear

GT Owner
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May 16, 2013
1,396
Frankfurt Area, Germany
I for myself am quite happy about supercharging. My daily Audi S6 (TT V6 with 430HP automatic) has such a terrible lag, if you try to slowly accelerate from a standing car it is quite difficult to modulate the power pedal without the car suddenly accelerating too much (this really sucks when dealing with difficult parking situations). The GT on the other hand doesn't have that problem. IMHO TT is the only way for car manufacturers to solve emission regulations and others. From a driving point of view, a naturally aspirated engine is of course the best :)
 

nota4re

GT Owner
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this really sucks when dealing with difficult parking situations

This has to be attributed to some other mis-matched calibration as there is no turbo/boost capability at parking (near idle) speeds.
 

nota4re

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The FGT just "went completely LIMP" no matter how hard I pressed the accelerator.
Part of that may have been the Engine computer 'protecting ' the engine but not sure.

If this is the case, why then would a Supercharger be used vs a Turbocharger? Is it just to offset the lag?
(although Superchargers do look and sound cool)

Unfortunately, no little blue pill to keep the GT from being "limp". Yes, the GT ECU will protect it's motor when it gets too hot. The two major ways it can do this is by pulling timing and/or activating the SC bypass valve so that boost cannot be achieved. The ECU can actually go into limp mode (I'll run just enough to get you to a safe place), but formal limp-mode would also illuminate the CEL.

As others have said, Ford had considerable SC experience and at the time little turbocharging experience. This was undoubtedly the main factor when combined with an accelerated schedule to bring the car to the market. There are countless other differences as well, but the "packaging" of a SC is more straightforward with a SC.
 

Indy GT

Yea, I got one...too
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Nice job Scott:thumbsup
 

Vince H

GT Owner
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You have no idea how much I appreciate these layman's term explanations of our GT's. Thank you very much Scott. I continue to learn so much from this forum and it's awesome members.

Vince H
 

sahlman

Ford GT Team Alumni
Jul 21, 2011
329
Verona, WI
Thanks AJB, Indy and Vince.

For sure there were multiple good reasons for choosing the FGT engine vs alternatives including what is noted by Xcentric and Nota4re. Yes, lots of experience with the supercharged engines and little with turbo charging at Ford North America, at the time. Well established supplier relationships were part of that equation. The engine team was confident they could hit the HP and torque targets (and then some) reliably in incredibly short timing with the path chosen. The big flat torque curve and great drivability for every day usage were also reasons for choosing the direction versus alternatives.

For sure the intent of above regards weather/temp sensitivity. Not pros/cons of super charger vs turbo. The resultant answer just points out one difference/deficiency of supercharging versus turbo charging. The list is large of pros and cons...didn't intend for that debate...


Scott
 

twobjshelbys

GT Owner
Jul 26, 2010
6,053
Las Vegas, NV
Hi Scott

I asked a similar question in the tire topic too. Over there it was about how the great amount of work on the Goodyears influenced the decision to use the same tire on the GT500

Here the question is similar. How much info sharing was done between the two teams on superchargers? The FGT used a different one, but underneath the engines were quite similar (yeah, I know, but at least for displacement and probably similar heat generation). Were design considerations on the FGT then leverged into the GT500?

Thanks!
 

jbyrnes

FORD GT OWNER
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Jun 13, 2006
224
Louisville CO
Thanks for the info Scott. On my other point about water injection, it now makes sense that a S/C motor would see more benefits from it than a turbo'd one since it runs hotter (less efficient). Do you know roughly the air temps on either side of the GT's intercooler given say a 70 or 80 deg. outside air temp and under max boost?
 

Specracer

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Great post as always bud!
 

Ed Sims

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NorCal
Anyone thinking about installing the new flat plane V8 from the GT350 into a FGT? What do you think Scott?

Ed
 

mmlcobra

GT Owner
May 25, 2013
1,215
Anyone thinking about installing the new flat plane V8 from the GT350 into a FGT? What do you think Scott?

Ed

I don't think that it would fit.
 

steved57

GT Owner
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Mar 29, 2008
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kilgore tx
Thanks for the informative post Scott

I drove my GT pretty hard at COTA last year(usually six lap sessions) and air temps were high 50's and engine water temps reached up to 220 ish. I then went to Road Atlanta in June with air temps in 90's and doing six lap sessions I think it was 3rd session of day the car went in to limp mode. I will be goint to COTA in two weeks so I am hoping for a cool weekend
 

sahlman

Ford GT Team Alumni
Jul 21, 2011
329
Verona, WI
Hi Scott

I asked a similar question in the tire topic too. Over there it was about how the great amount of work on the Goodyears influenced the decision to use the same tire on the GT500

Here the question is similar. How much info sharing was done between the two teams on superchargers? The FGT used a different one, but underneath the engines were quite similar (yeah, I know, but at least for displacement and probably similar heat generation). Were design considerations on the FGT then leverged into the GT500?

Thanks!

Hi Tony,

Leveraging the FGT work, especially powertrain was SVT's intent, but I do not have first hand knowledge of the level of transfer to the GT500. I was not involved on the project and did not keep tabs on it. Mark McGowan may know.

Scott
 

sahlman

Ford GT Team Alumni
Jul 21, 2011
329
Verona, WI
Anyone thinking about installing the new flat plane V8 from the GT350 into a FGT? What do you think Scott?

Ed

Ed,

I think it would be great and seems like it should fit, but we would have to look at vibration modes and make sure the flat plane crank modes don't line up with other chassis, subsystem and part modes. The wrong modes lining up could cause early failures. Do you know of a good donor car for me to do it?!:wink

Scott
 

sahlman

Ford GT Team Alumni
Jul 21, 2011
329
Verona, WI
Thanks for the info Scott. On my other point about water injection, it now makes sense that a S/C motor would see more benefits from it than a turbo'd one since it runs hotter (less efficient). Do you know roughly the air temps on either side of the GT's intercooler given say a 70 or 80 deg. outside air temp and under max boost?

Glad its a help. 10-4 on water injection. I am sorry, I don't have the detail intake temp data for you.

Scott
 

sahlman

Ford GT Team Alumni
Jul 21, 2011
329
Verona, WI
Thanks for the informative post Scott

I drove my GT pretty hard at COTA last year(usually six lap sessions) and air temps were high 50's and engine water temps reached up to 220 ish. I then went to Road Atlanta in June with air temps in 90's and doing six lap sessions I think it was 3rd session of day the car went in to limp mode. I will be goint to COTA in two weeks so I am hoping for a cool weekend

Steve, no problem. Understood on temps. Yes, use taller gears on hot days. Hope it is cool at COTA and the new coil-overs work well. Looks like an awesome track.

Scott