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.

[xtreme80]

Originally Posted by 68Stepbed

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.

Wow, alot of good info here. I also never knew that's how they measured the HP numbers, so that's good to know. I still know that I have more now than I did from the factory.

So here's the thing. You asked what my timing was set at. Well, I don't actually have a way to accurately set it. For some reason the timing mark on the balancer doesn't line up with the mark on the tab. When I try to time it, the mark is nearly straight up, whereas the timing tab is offset to the side a little. When I got the balancer, I went to the chevy dealer, and we looked up the part number for the balancer that was made for this engine specifically, and that's what I got. Still no go though. So for right now, I'll just advance it till it starts becoming hard to start, or till it pings, and then I'll just bump it back a little.

I also don't think I'm gonna do the 4.11's. That's a little too tall for me. Right now I have a factory 12 bolt in the truck, it's just got the 2.73's in it. I'm still not sure when I'll be upgrading, so whenever you do have the parts, let me know and I'll take em off your hands.

EDIT: Also, I have my vacuum advance unplugged and capped off right now. For some reason, when I put a new distributor in the truck, it started running like **** with the advance hooked up. No idea why, and it never did this before. I even replaced the new distributor with another, and it still does it. If I unplug it though, it runs great.

[68Stepbed]

Well, it seems you have the wrong balancer. You should have one with a 2:00 timing mark. You can order one for a 72 pickup with a 350 from any parts store. The easiest way to tell if the balancer is the right one is look and see if the timing mark almost lines up with the crankshaft keyway notch. If they're not close, you have the wrong balancer. This may be the reason your new dist. won't run well and why the vacuum advance won't work right either.

If you have the right balancer, set your timing at 10 deg BTDC with the vacuum advance unhooked and the vacuum line plugged or capped. Hook the vac. advance up to the vacuum port on the right side of the carb(your left if looking straight at it). This will be ported vacuum. Another way to tell is uncap one port at a time while the engine is idling. One will have vacuum, one will not. Hook your vac. advance to the port with NO vacuum. It sounds like you may be hooked to full vacuum and advancing the engine too high at idle.

[xtreme80]

One will have vacuum, one will not. Hook your vac. advance to the port with NO vacuum. It sounds like you may be hooked to full vacuum and advancing the engine too high at idle.

I get what you're saying, but here's the thing: I've hooked both ports on the front of the carb up to a vacuum guage. Neither one holds manifold vacuum. They are both showing no vacuum at idle, with high vacuum when I give it gas. This is the second edelbrock I've had on it, and they both do it, even though the video I have shows different.

I'll take a look at the balancer tomorrow though and see what I can come up with.

[Ivan D.]

Originally Posted by 68Stepbed

If you have the right balancer, set your timing at 10 deg BTDC with the vacuum advance unhooked and the vacuum line plugged or capped. Hook the vac. advance up to the vacuum port on the right side of the carb(your left if looking straight at it). This will be ported vacuum. Another way to tell is uncap one port at a time while the engine is idling. One will have vacuum, one will not. Hook your vac. advance to the port with NO vacuum. It sounds like you may be hooked to full vacuum and advancing the engine too high at idle.

Here's a question - 10*BTDC at what rpms? My truck (uses a stock HEI disty off god knows what vehicle) has a mechanical advance that seems to come into play at 800-900rpms, like I set the timing to 8* at 800rpms and then when I bring it up to 1000rpms (via the idle screw of the carb, so it's steady) I'm looking at 10* at least. So yeah, what rpms are we setting the base timing at?

[68Stepbed]

Originally Posted by Ivan D.

Here's a question - 10*BTDC at what rpms? My truck (uses a stock HEI disty off god knows what vehicle) has a mechanical advance that seems to come into play at 800-900rpms, like I set the timing to 8* at 800rpms and then when I bring it up to 1000rpms (via the idle screw of the carb, so it's steady) I'm looking at 10* at least. So yeah, what rpms are we setting the base timing at?

I usually set it at 650-750 for a stock or mild engine. I actually put the vehicle in gear, chock the wheels, and set it at idle in gear. High hp engines with radical cams are a different story.

Why do you have to set the idle up to 1000 rpm's? Do you have a stock engine? You may want to check into an advance spring kit.

[68Stepbed]

Originally Posted by xtreme80

I get what you're saying, but here's the thing: I've hooked both ports on the front of the carb up to a vacuum guage. Neither one holds manifold vacuum. They are both showing no vacuum at idle, with high vacuum when I give it gas. This is the second edelbrock I've had on it, and they both do it, even though the video I have shows different.

I'll take a look at the balancer tomorrow though and see what I can come up with.

If the left port has no vacuum, you have other problems. Do you have vacuum coming from the large center port? Do you have a fitting in the intake behind the carb? If so, what does it connect to? Do you have power brakes? Where are they connected and how do they work at idle?

[xtreme80]

I do have vacuum from the large center port. I have a fitting in the intake that's for my power brakes. I also have the plug removed from the back of the carb, and in place is my ac vacuum line. Everything is sealed up, I just don't see why that port wouldn't have vacuum

[benoit454]

I think on my edelbrock 600 the driver's side vacuum port on front is the one that pulls all the time.

I might have to hook up my vac. guage to it and run it a little, maybe it's why mine lacks good power. it has good power, but something is missing, something simple.

[68Stepbed]

Originally Posted by xtreme80

I do have vacuum from the large center port. I have a fitting in the intake that's for my power brakes. I also have the plug removed from the back of the carb, and in place is my ac vacuum line. Everything is sealed up, I just don't see why that port wouldn't have vacuum

Did you get a vacuum guage reading yet?

[69BBsuburban]

Originally Posted by xtreme80

I just don't see why that port wouldn't have vacuum

It's a TIMED vacuum port.......meaning it doesn't pull vac until above idle......

[SSC's76]

Like Josh mentioned its a timed port and doesent see vacuum until the primaries are cracked open. You can play with a full mainfold source and see which one gives you better driveability. Usually a larger cam will want more advance at idle but the 290 crate cam isnt much over a stock smog grind.

Your crate engine should have came with 2 timing tabs sounds like you used the wrong one with the 6" ballancer from the 305.

Gears will help alot. My bird came with 2.73s and even with a 270H cam in it it couldent break the one wheel loose on gravel. When I put a 3.42 axle in it it was instant on power like someone droped a BB under the hood without me looking.

[xtreme80]

Originally Posted by 69BBsuburban

It's a TIMED vacuum port.......meaning it doesn't pull vac until above idle......

I'm talking about the one on the carb that is supposed to be manifold vacuum.

Going to get a reading now for everything, back in a few.

[xtreme80]

Ok, here we go.

Both the left and right ports on the front of the carb hold NO manifold vacuum. Only timed vacuum.

The middle port on the front of the carb holds about 32" of vacuum. This is the biggest of the ports.

The port on the intake manifold for the brake booster holds about 38-40" of vacuum.

[piecesparts]

Originally Posted by xtreme80

Ok, here we go.

Both the left and right ports on the front of the carb hold NO manifold vacuum. Only timed vacuum.

The middle port on the front of the carb holds about 32" of vacuum. This is the biggest of the ports.

The port on the intake manifold for the brake booster holds about 38-40" of vacuum.

Did you say 32" vacuum, that is greater than a perfect vacuum. Are you sure of this number? I would venture that the number is a lot lower than that, even on the PCV connection of the carb. The discussions here are right on, with which port to use, however it centers around how you have your vacuum pot on the distributor set up. I am running a larger profile cam and I use the full vacuum port on my Edelbrock and have the timed port plugged. I also am running my timing more advanced than just 10 degrees. As a matter of fact, I haven't run timing set at 10 degrees for years. Prior to getting a timing light that has an advance setting feature on it, I aways set mine at 12 to 14 degrees and the resulting engine response was good. The timing mark at the 12 O' clock position is the equivalent of the later model GM motors in the 80s model trucks. They timed from behind the water pump, by looking down the front of the motor, and the tab was made on the timing chain cover. To make sure of what you have pull the number one spark plug, bring the piston to the highest point ensure that the valves are closed for this and see just where your timing mark is and then see if the kit had a timing tab for that. If not then get a balancer for the engine that has the timing mark at the 2 O' clock position.
Set the timing at 650 to 750 RPMs and play with the advance degrees to get the snap and performance that you want. Listen for pinging and DIESELING (run on when shut off) for being to far advanced. I would look at getting a spark advance weight and spring set for the HEI dizzy to get it to function better. Also what quality of spark plug wires are you running? They make a seious difference in the performance and gas mileage. Look for a set that is of a large diameter and has avery low resistance in the wiring. I run MSD 8 MM wires, but Taylor makes some great stuff also. If you have a radio or stereo make sure that the wires are shielded.

I time and set my engines using the vacuum gauge to set the idle mixtures (as stated before) and I set my timing at a TOTAL advance setting of around 35 degrees. That gives me the best performance and idle. It just takes time to get there and once you find it, you will like it.

Everyone has their preference for a carb, and whether it is a Holley, Edelbrock, or a Barry Grant, they all work about the same. The real differences come into play on how they open up, whether it is vacuum actuated or mechanical. I presently run Edelbrock and they work well, once you have them tuned to your engine's profile, the changeover to the secondaries is a little harsher than a vacuum actuated carb, but it is a real HOOT when they do transition. I have had problems with both styles of carb, but that is just my experience. The Edlbrock 1406 Performer series carb is actually a 625 CFM carb (the advertisement says 600 CFM). It is an EXACT match to the Carter AFB design carb and the parts are interchangeable--I know, I tuned my carter using Edelbrock's parts, since they were cheaper. I now have the Edelbrock Thunder AVS carb on my truck and it is advertised at a 650 CFM carb, it shows a little bigger than that. It fits my stroked 383 motor real well and the gas mileage is good for a motor set up like mine.

[xtreme80]

Let me take a look tonight, and I'll do what I can to get pictures, and then get back with you. I'm sure of the number, but I'm going to take a picture just to double check.

[piecesparts]

If you are getting 32" of vacuum, then you need to keep that motor for evacuating freon out of systems for refrigeration work. The world of engines is more likely to be around 20" or below, if you have a really lopey cam, then expect that number to be around 12" or less. Take the vacuum gauge (it should read in inches of mercury) and connect it to a vacuum port on the intake manifold (usually the one behind the carb works best).

[xtreme80]

See, the I hooked up the gauge to the manifold vacuum port in my intake manifold. The same one my brake booster is hooked up to. That's the one reading the highest. I wasn't able to mess with it today, but I'll definitely be looking and taking pictures tomorrow of what I'm seeing.