I am looking for some input. I have 99 silverado (4600 lbs with me in it) with a mild lq4. It has .020" milled 243's with a 225/229 .580 .590 lift cam, truck intake, 44lbs injectors, 1 3/4" LT's a 3600 yank converter and 28" slicks. I had a 3.73 gear but I recently swapped it out for a 4.56 It was running 13.20's at 101 N/A with a 1.8 60 ft. in a 3000 ft. DA. I have been researching a while now and I'm finding alot of people claiming that a 3.42 to 4.10 swap is good for .3-.4 in the 1/4. My math figures that to be about a 17% reduction change and I'm sitting at a 19% reduction. I was shifting at about 6300 when i ran the 13.24 now I'm gear'd way lower and shifting at 6800. I am planning another trip to the track next weekend. I'm hoping to go 12's but I'm a little scared I over gear'd. What do you guys think? It feels like it pulls way harder in 2nd and in 3rd now. I know I will probably see less MPH, but is a .3 to .5 second drop in E.T. realistic with the added 500 rpm in each gear and the 4.56? It was crossing the traps at 4600 rpm, my calculations say if I run the same mph it will cross at about 56-5700 rpm now. Just looking for input, thanks.

 

take it for what its worth, i now cross the traps at 6500 rpms, reason i do gear swaps is cause of my powerband, i know where it falls off and i know where it peaks and i know where it begins without this knowledge you know nothing about what your truck can do ie: speaking of mine, realistically gears are your friend, i gain in mile per hour for each gear swap i have done and also cross the traps at a higher rate of rpms reason being the powerband on my setup is so wide and so far up in the rpm range.. personally i dont think you went wrong with 4:56s, maybe not even on spray, me on the other hand its possible, but i am trying to achieve something this coming fall.BUT i will try and spray my truck with such gears before i make anymore changes!!

 

My power peaks and flatens out at 6400 on the Dyno sheet but it still feels like its pulling strong at 6800...

I'm sure its not really spinning to 6800 I had it set the other night to shift at 6600 and the snap on tool that we were using for data logging said it was shifting at 6475. Whats that all about?

 

Yep. Get your truck onto the dyno, and get some track logs to compare it against. I just put in an order for 4.30 gears. I am planning a healthy dose of nitrous though. my tires with 4.30 gears should put me at 126mph at peak hp which is roughly what I expect to trap in the ¼. If I was an all motor guy, I would be all over the 4.56 gears.