Rear end ratio / power transfer

[68Stepbed]

Originally Posted by xtreme80

Man something can't be right here! My buddy has an 07 sierra classic style with a 5.3 and 3.42 rears. Stock tires. We raced from about 55 to about 80, and he pulled on me the whole way. Left me like I was standing still. I don't see why I shouldn't have kept up with him, seeing as his truck only has like 280hp stock with 305 ft/lbs of torque. I'm roughly 315hp/330ft/lbs. And at that speed, I should have hung with him better.

Im so stumped on why this wont run right

Here is something to remeber. Your engine was rated at 290HP with an Edelbrock 2101 intake, 600 Edel. carb, and 1 5/8" open headers on an engine dyno. GM crate engines are dynoed in the old gross hp ratings with no accessories. Newer engine are dynoed in net hp ratings with all accessories. I hate to be the one to burst your bubble, but I learned the hard way myself.
Your engine after you add the water pump, alt., power steering, and A/C if you have it, your engine only makes about 200-220 hp at the flywheel. Your buddy's 07 5.3 is rated at 280hp at the flywheel WITH all accessories and A/C. If you took his accessories off, it would make close to 360 hp. Don't let this discourage you. You will actually be surprised what 220 hp will do. Big hp numbers are so commonly boasted and thrown around today, that anything less than 300 hp sounds like child's toys.

When I first installed my GMGoodwrench engine that claimed 260 hp, I thought I was actually running more by the time I got it tuned out. I finally figured out I was only pushing about 190 at the flywheel. I could still outrun some stock Mustangs and almost every import in town.

My setup was basically this:
GMGoodwrench engine (part # 10067353)
Edelbrock EPS intake
Holley Street Avenger 570 cfm
stock HEI dist.
stock pulleys with swp (which are actually smaller dia. than lwp pulleys)
TH350 tranny with shift kit
3.73 rear gears
28" tall 275/60/15 tires.
This was in my 68. It also only weighed in at 3500 lbs. Your truck may be a little heavier but not much.

Once you get your carb tuned out and a set of 3.73 gears, I would recommend a set of aluminum pulleys if you don't have a set already. you would be surprised what they will do. How and where exactly are you setting your timing? Are you disconnecting the vacuum advance? Where is your vacuum advance connected, to ported or full vacuum? On your vacuum guage, you should be reading 18 to 20" of mercury. Any less than 15", you may have a vac. leak.

I personally prefer Holley carbs over Edelbrock for performance use, but the Edelbrock should do fine with a tuning kit. BTW I would keep the 12 bolt rearend and change gears in it if you don't like the 4.11's. The 12 bolt is stronger with bigger 30 spline axles than the 10 bolt's 28 spline. If you are willing to wait, I may be switching my 3.73's to a set of 3.42's in my 68 when it's done. I may sell them to you cheaper than new ones. They are in good shape. If not, 3.73's are very easy to find for 12 bolts.