Funny question BUT........Shifting RPM Range

[TJ's GMC]

So what's a good shifting RPM for my 305? I been shifting at around 3000 rpm but it sounds like its screaming its lungs out. I recently hooked up a tach(hillbilly style) and have been reading my rpms. So far it seems 3k is the best to shift as it keeps from lugging the engine all the time because of the wide ratio tranny. Don't get me wrong...that thing begs to be lugged. But sometimes I like to Go. haha. I made a mistake of giving the throttle to a friend and next thing I new, I saw the tach at almost 5000 rpms.....needless to say he was booted out of the driver's seat in a heart beat.

[bigblockv6]

For the most I drove my 68 when it had the 305 in the same manner but a more suitable rpm to shift would be around 2200-2500.

[TJ's GMC]

Thanks. Yeah, I have shifted at those rpms several times but it seems to lug when I do it from 2nd to 3rd.

[bigblockv6]

What gear ratio is your truck? Mine is 4.56 so I can definitely be comfortable shifting at 2200-2500 rpms. I suspect your truck has either 3.07 or 3.54 gears and that may very well explain why it lugs when shifting below 3000 rpms.

[TJ's GMC]

Mine is 4.10 I'm pretty sure judging by the fact 55 is about 2500 rpm with 31 inch tires. I may be underestimating this beast again though as I can easily recognize that lugging it makes you get up to speed quicker than screaming it. haha. My experience anyhow with it.

[bigblockv6]

Mine being a 4wd with 4.56 gears that came stock with 33 inch tires. In my experience the truck would run like a bat out of **** if I shifted from 2nd to 3rd at 4000 rpms, that really launced and carried the momentum for the 3rd to 4th shift and had no problem keeping up with a friends 96 GMC 350 with fuel injection. Things will be different now with the 478M, I made one mistake in the build not realizing until later that the hoollow stem sodium filled exhaust valves snap from over reving, those are going to have to come out.

[jagarra]

Well with the 420 tranny, I guess we should determine what we are calling 1st, granny or 2nd? Since I start out in the gear up from granny I will say that is 1st. What I have noticed is that I can shift from 1st to 2nd at a lower RPM and not have it lug than I can from 2nd to 3rd. Seems to like the shift to high gear when I am going around 35 MPH. I have a 3;54 rear end and the tires are about 29".

[TJ's GMC]

Originally Posted by bigblockv6

Mine being a 4wd with 4.56 gears that came stock with 33 inch tires. In my experience the truck would run like a bat out of **** if I shifted from 2nd to 3rd at 4000 rpms, that really launced and carried the momentum for the 3rd to 4th shift and had no problem keeping up with a friends 96 GMC 350 with fuel injection. Things will be different now with the 478M, I made one mistake in the build not realizing until later that the hoollow stem sodium filled exhaust valves snap from over reving, those are going to have to come out.

I've never had mine up to 4k yet. 3k seemed high enough. lol Its a cruiser for me so I like to be easy on it. Yeah, my 305 would out pull a 350 if we were loaded down. The way it pulled my load of manure. Wow! lol I'm still impressed. 55 going up a grade at 1/4 throttle.

Originally Posted by jagarra

Well with the 420 tranny, I guess we should determine what we are calling 1st, granny or 2nd? Since I start out in the gear up from granny I will say that is 1st. What I have noticed is that I can shift from 1st to 2nd at a lower RPM and not have it lug than I can from 2nd to 3rd. Seems to like the shift to high gear when I am going around 35 MPH. I have a 3;54 rear end and the tires are about 29".

I usually start in 2nd if I not loaded down. Course...I don't have a 3.54 ratio either so I understand starting in 1st. I have the 420 as well.