27" Tyre Help or Hinder

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Well, just in case anyone is still interested, slightly slower ET, slightly more MPH, but close enough that it really made bugger all difference. Crosses the line quite comfortably at 5500 RPM in second gear (peak power with this combo was at 5400 RPM when I had it on the dyno a couple of years ago).

Had a few runs tonight.
Best ET tonight 13.831, previous best  13.779
Best MPH tonight 103.21, previous best 102.62
Best 60' tonight 2.180, previous best 2.162

FWIW, I did cheat slightly, removed the 1" open spacer and put the old 1/2" 4 hole spacer back on, figured I needed all the help I could get.

I was certainly expecting to run quite a bit slower, so the next step is to get those 3.54 gears in.

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WesternRed Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Aug/03/2010 Location: Australia Status: Offline Points: 5799	Post Options Post Reply Quote WesternRed Report Post Thanks(0) Quote Reply Posted: Mar/05/2014 at 8:11am
	Well, just in case anyone is still interested, slightly slower ET, slightly more MPH, but close enough that it really made bugger all difference. Crosses the line quite comfortably at 5500 RPM in second gear (peak power with this combo was at 5400 RPM when I had it on the dyno a couple of years ago). Had a few runs tonight. Best ET tonight 13.831, previous best 13.779 Best MPH tonight 103.21, previous best 102.62 Best 60' tonight 2.180, previous best 2.162 FWIW, I did cheat slightly, removed the 1" open spacer and put the old 1/2" 4 hole spacer back on, figured I needed all the help I could get. I was certainly expecting to run quite a bit slower, so the next step is to get those 3.54 gears in.

jcisworthy Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Jul/23/2009 Location: North Carolina Status: Offline Points: 2805	Post Options Post Reply Quote jcisworthy Report Post Thanks(0) Quote Reply Posted: Mar/06/2014 at 5:34pm
	An open spacer will lean out your engine and a 4 hole will make it richer. Maybe your car is a little rich and the open spacer picked it up because it leaned it out. Either try the open spacer or take some jet out of it and run it again to see what happens.

WesternRed Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Aug/03/2010 Location: Australia Status: Offline Points: 5799	Post Options Post Reply Quote WesternRed Report Post Thanks(0) Quote Reply Posted: Mar/06/2014 at 11:41pm
	Was originally dyno tuned with the 4 hole and did have a habit of backfiring at part throttle with the open spacer, so I suspect it was going lean with the open spacer on due to less signal to the carby. With the tall tyres and tall gears, the 4 hole and split plenum air gap should in theory give it a bit more down low where it needs it. The open spacer might be an advantage after the gears are changed. From what I've seen the open spacer usually works well with the airgap for improving peak power, but with my less than ideal combo I need as much bottom end grunt as I can get. It has effectively gone from a 2.87 to a 2.60 rear by virtue of the taller tires so as mentioned, I fully expected it to be a bit slower and the run at the strip was just to see what would happen. Ideally needs 3.9 or maybe even 4.1 gears for the best performance at the strip, but to retain some degree of streetability 3.54's will be the go, especially since I already have them.