Skyman,
If he's running mid 13s (taking his word for it) on 245s, in a stock GT, I can't see it improving ANY in the quarter unless more mods or gear change. For reasons stated earlier such as tire bulge (not good on tire), b/c of such a large tire on an 8" rim,
I would at least get a bigger wheel first.
The main thing though is that that wide of a tire will hurt his trap speed. Especially if he's running 101 mph with the 245s.
Yeah, it's more traction on the launch, but after that, he's gonna have to pull them things down the track.
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'79 Mustang Coup
4" Cowl
Weld wheels (15x6;15x8)
Stock 5.8L
C4 w/ shift kit
1.5" MAC full length headers
Holley 750 CFM
Edelbrock intake
2.5" Off road H-pipe, 2-chamber Flowmasters
8.8" Rear end w/ 3.55 gears (Now that's more like it!!)
Front: 225/60/15 Rear: 255/60/15 Eagle GT II
14 x 4” K&N air filter (getting the Xtreme setup soon)
"Red, thou art my companion. Hasten now your quickened metamorphosis to Green that I may conquer all who dare abide there beside me. May they be left thither behind burnt black." ---Fox Body