So, I went ahead and upgraded my old cam-only (MTI C1) to a h/c set-up (PRC 2.5 5.3l 2.04/1.585 valves, 228/232 112+0 XE-R)

At the same time I picked up some 28" MTDR's for a little bit of highway milage assistance. Turns out I didn't gain any mpg, just spinning the motor a little lower, haha.

So I went to the local 1/8mi track and ran it a few times... Old set-up netted a 7.8 @ 89 w/ 1.70 60' (26" ET Drags). New set-up netted a 7.9 @ 91 w/ 1.82 60'. Other than the tires, my suspension set-up remains the same.

Would 2" more tire really be slowing me down slower than my old times even making more power? I figured I'd run about the same, probably just a hair quicker.

I've got a similar thread in the dyno section, but there I'm mainly making sure my engine's making the power it ought to. Here's a link to that one if you're curious: https://ls1tech.com/forums/dynamometer-results-comparisons/576262-set-up-issues.html

 

2"'s makes a big difference both in 60' and ET. The final ET is very similar so everything else being equal (weather) I'd say the power is there but it's gotta fight through those extra 2".

 

so you think that 28in tires are making him run slower than 26in tires even though he should have about 40 more rwhp??

 

I personally think he has two things working against him:
1) too much tire(although the mph is tricky, considering his old time was on ET drags, and this last time was on MT radials)
2) with the extra 2", you're shooting yourself in the foot with running a 4.22 gear. If you went up in gear, i think it'll really help your e.t's

 

Cam the tire might be hurting you. If you weren't at a point where you were gonna run out of gear with the 26's I'd go back to them when the 28's are worn out. The dyno results aren't really adding up either, I would have suspected results much like the other car you tuned. The 9 inch and steel driveshaft are probbly eating 15 to 20 hp over stock stuff.. but that's not enough to make all the difference. I'd do a leakdown test just to be safe.

The other thing too is the mt radials are probably alot heavier then the et streets you were on before, which I would bet isn't helping any either. I knwo everyone says that the tires work and it doesn't matter, but ever now and then I see someone that has the same problems that you are right now that makes me think otherwise.