My New 18 GT Auto is Slower Than My Prior 18 GT Auto?

[Ohthatguy]

So I had an 18 auto GT that was bone stock except for wheels and tires. I never dyno'd the car but I ran it against my co-workers' cars (2015 Panamera Turbo and 2015 Jaguar F Type R). My first 18 GT auto pulled away just by a hair against the Porsche and was dead even with the F Type R (both from 40 mph rolls on a closed course).

I traded the GT in for something else then went back to a 2018 GT Mustang auto about a month ago. Both cars were base GTs with basically no options but the new one just felt less potent that I remembered the first one feeling. I swapped the MRR wheels onto the new car along with the 325/30/19 MPSS I ran on the prior car. The only changes are switching from 28 lb Michelin Sport 4S front tires to Pirelli 275/40/19s that probably weigh 32 lbs., the faster car was lowered on Ford Performance Street/ X springs vs stock on the slower car and the new 18 has a resonator delete (replaced with a fabbed up H pipe at a local muffler shop).

I never dyno'd the first car but the second one laid down 413rwhp and 387rwtq (in 6th gear) after the wheels/ tires/ resonator swap. I haven't run against the Porsche in the new car but the Jaguar was pulling a couple of cars on it where the prior 18 hung in there. Same drivers, same S mode punch, same road. The difference in performance has to amount to 20 hp or so. Bummer.

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[w3rkn]

What are the drive ratios..?

 

[Ohthatguy]

What are the drive ratios..?

Not sure. I think both had the same standard base GT ratios.

 

[Ohthatguy]

Checked the window stickers. Both had 3.15 gears.

 

[cgreen5150]

Checked the window stickers. Both had 3.15 gears.

"Had" ?? Did you get rid of the second one, too?

 

[Ohthatguy]

"Had" ?? Did you get rid of the second one, too?

Ha, no. Keeping the one I have.

 

[scrubber3]

Looks like you need a tune.

 

[ihc95]

A 2018 GT shouldn't be keeping up with an F-type R in the first place. Those cars trap 122+ versus ~118 for the GT. Who knows maybe the Jag wasn't running right before. Or your first 2018 was a factory freak.

Also 413whp is perfectly normal and healthy for a 2018 A10.

 

[Vert]

What was the difference in the weather when you ran the races. Im wondering if the Jag SC was heat soaked in the first race and was running cooler when you raced him with your 2nd stang.

 

[keiths2kgt]

Hopefully you didn’t trade away a factory freak and get an engine rattling lemon. Let us know how it sounds after the first few oil changes.

I say all that in humor only lol

 

[brucelinc]

How many miles on each one? My 2018 ran 2.5 tenths better after 3000 miles than it did at 600 miles in the same DA at the same track and using the same technique.

 

[Ohthatguy]

A 2018 GT shouldn't be keeping up with an F-type R in the first place. Those cars trap 122+ versus ~118 for the GT. Who knows maybe the Jag wasn't running right before. Or your first 2018 was a factory freak.

Also 413whp is perfectly normal and healthy for a 2018 A10.

Yeah, my first one also took down a 2015 Panamera turbo from a 40 roll. Those do 12.1 s @ 118.7 mph. I do think the first car was just a freak. I’m starting to believe the stories about some stock 2018s that dyno 435+.

The weather on the first run against the jag wasn’t much different and the cars were only running for 5 minutes before the pull so I don’t think heat soak was a factor on the jag.

My new 18 had 2,300 miles on it for the run, not sure on the first 18.

 

[Furiosa GT]

Unless you have DA corrected trap speed times for both cars and nearly a identical race weight I'm not sure you could accurately make that assessment. Two SAE certified engines making 20HP difference from one another seems kinda crazy to me. Unless the new engine isn't performing at peak. Are you using 93 octane? Engine break in for good piston ring sealing? And yeah the cars you ran might not have been running at optimum performance. Lots of variables. In my racing group boosted cars are having a field day right now with this nice weather. That's another thing to think about.

 

[Ohthatguy]

Unless you have DA corrected trap speed times for both cars and nearly a identical race weight I'm not sure you could accurately make that assessment. Two SAE certified engines making 20HP difference from one another seems kinda crazy to me. Unless the new engine isn't performing at peak. Are you using 93 octane? Engine break in for good piston ring sealing? And yeah the cars you ran might not have been running at optimum performance. Lots of variables. In my racing group boosted cars are having a field day right now with this nice weather. That's another thing to think about.

Yeah, just from driving the new car I felt it was down on power from the first one even before I raced the Jag. Both had similar break in procedures and 93 octane. You may be on to something with the DA and the boosted cars.

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