Rear end ratio / power transfer
 

I'll keep this simple and to the point. If you look at my signature, you can see what I have done to my motor. This was a 290 horse crate, and I added the intake manifold, carb, exhaust, etc.

My question is this: Even with a 2.73 rear end gear ratio, should I, theoretically, still be able to spun tires if I punch it from a stop? They are brand new tires, so they are sticky, but still... I would think with a 290 horse crate with my add ons, I should be able to spin these things.

Something just doesn't feel right in my truck and I wanna make sure it's not just my imagination.

Re: Rear end ratio / power transfer
 

2.73? Maybe not, but 3.73 definitely. What tranny? torque converter?

Re: Rear end ratio / power transfer
 

Man I know EXACTLY how you feel.

For a truck with 2.73's yes you should, I base that statement on this...

Our stock 84 with 305 h.o. and 2.73 rearend with a th350, everything stock as far as I know and if non of it has changed, you can break them loose god with it.


Now I went through the same thing with my monte carlo. The motor in it was a stock 350 4 bolt, 2.02 iron gm replacement heads, weiand intake dual plane, edelbrock 600 cfm carb, comp 268 cam and lifters, hei dist., flowtech ful length headers. it had a stock th350 and stock convertor, also had stock non ss monte rearend with a 2.29 gear ratio.

I took that motor from my old 76 truck, back then it had a bigger cam, old holley dual plane and had a holley 600cfm vac. sec. mech. choke carb, same as my edelbrock, but it was backed by a stock 3 speed standard shift, and what we think was 4.11's and I know for sure it was posi.

The truck would absolutely smoke tires, you could barely get a chirp, they's just start spinning. We ran 31x10.50's on it and it still smoke the mud tires off. it was freakin awesome, mean as hell, very, VERy quick, but on the highway about 60-70 you let off and it was like gearing down, almost.

Same motor just with the stuf mentioned above in my monte, with the 2.29's, no way I could smoke em. I could barely, BARELY break them loose. I changed the gears to a set of 3.42's added a shift kit and a 2000 rpm stall to it. it will break them loose from a dead stop about half down on the pedal.

I haven't done much else, but with the shift kit when I hit 2nd it'll chirp the tires really good. As for as smoke tires I haven't tried it much. I don't feel like it do it that good, like it not do it as good as the 84 with the 2.73's, but I'm not sure since I haven't tried. I was just stabbing it down halfway in the carport playing around with it. I also have not really dropped it at the stall speed, but from what I've done playing a stall is nice, great launches out of it.

Everyone told me it was my rear gears, but I'm not sure, I think like you, maybe something isn't quite right in the motor, it did run great, but it sat for awhile and only started every couple weeks, and wasn't driven for about 5 years.

Our 86 k10 4x4 had 3.08's factory or so it said, and I know for sure somebody changed the rear because it was a 12 bolt, and the only 12 bolts wer earlier years, but still, it would break them loose good too about half pedal or so, and we ran 33's. I found a gear ratio/tire size calculator online and 3.08's with 33's compared to 235/75's factory put the final ratio at about 2.72.

SO I'm in the same boat as you, everyone says get a stall and gears to keep your motor in it's powerband, like say it tops out making power at 6k, you don't want something that makes the motor run past 6k alot or any at all.

I'm just as lost on it as you are though, maybe now with warm weather I'll take my monte out more and play with it to see how big of an improvment the new gears are compared to before.

Re: Rear end ratio / power transfer
 

I have a couple things for this one. My old man had an 84 1/2ton 2wd, 305/350C, 2.73 open rear, with 235s on it. Motor ran like crap, so dumped that and got a 350 out of another truck. Have no clue what the motor was, but it was a GM Goodwrench motor. Anyways, if you hit the gas too much, it would spin the tire till you let off. It would just keep going, would rev to the moon. Swapped in 3.73s with a Govlock, and would spin them effortlessly, but not as much as with the 2.73s. Miss that truck. Other one was my old car. 200k 400, 400 trans, 2.73 open 10 bolt. That would spin the tire aboot 50 yards or so. Put in a 468, manual v/b 400, 9" rear with 4.10s, so tire spin was pretty easy after that.

So go by what you did to your truck, you should be able to get some nice pinstripes on the road.

Re: Rear end ratio / power transfer
 

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 :(

Re: Rear end ratio / power transfer
 

Hey Extreme just a guess/theory here. How tall are your tires? That could effect your ratio, if you have say 28-29" instead of 26"-27" it could make a difference in your launch capability. In other words if you have shorter tires, that would effectively give you lower rear end gear ratio to make the truck launch faster, if you had taller tires say 30" it could make it more sluggish off of the line.

Re: Rear end ratio / power transfer
 

I've got 225/70/15's on it right now, so it's not a big tire at ALL. And with my old engine, I could smoke the 30's that were on it when I got it. They were by no means bald either...

Re: Rear end ratio / power transfer
 

weird, is your kickdown cable working right? Is there a chance your not starting out in first gear for some weird reason?

Re: Rear end ratio / power transfer
 

2.73 and tire spin are not a common mix. If you want to get something that is more apt to do what you want go for a 3.42 or 3.73 geared rear end. What you have for a tranny is also involved in this mix.

The horsepower don't mean much if it is being lost on the way to the ground. Your buddy is kicking your butt, because he has a 5.3 that is a quicker response style motor with fuel injection, with a lower geared rear end and a better power range capability. Have you considered how you have your engine set up? What carb, what is your timing set at, and how is your air cleaner and exhaust set up? As you can see, just adding an engine that is supposed to be 290 HP doesn't make it so, the other items make it do what it is supposed to do. The tire size is another factor, the 225/70/15 is a 27.40" diameter tire, that is a fair size but with a 2.73 geared rear end that is pretty high and is robbing your acceleration. Do you run a tach? What is your RPMs at 70 MPH---my guess is that they are realitvely low.

Re: Rear end ratio / power transfer
 

Thanks for the responses guys. piecesparts, Im currently using a TH350 tranny. I plan on doing 3.73 gears in the rear, but it's so expencive right now!

As for how it's set up, the carb is an Edelbrock 1400, 600cfm elec. choke. Should be more than enough for this engine. The exhaust is pretty much open. Stock manifolds and stock cats, but they are straight pipes with no mufflers. I'm not sure what you mean about the air cleaner. It's a chrome 14" air cleaner.

Also, I was reading up on some things today, and I think my engine is running a little too rich. I'll get some black smoke out of the exhaust when I'm cruising, and at idle, it smells very rich. Since I have no way of checking the actual AF ratio, I'm just going to buy a carb calibration kit from our speed shop here and start leaning it out with new jets or metering rods. Hopefully this can help me out, because after messing with the idle adjustment for about an hour today, I actually have it idling REALLY good finally.

Any thoughts?

Re: Rear end ratio / power transfer
 

Man you don't need rods and jets, the mixture screws are right on the front of your carb, they'll lean it out or rich it up whichever you need.

Also you maybe getting black smoke from the cats if you have no mufflers, and they might even be clogged up, if you don't have to pass a sniffer test I poke them out, just gut the cats out and then you'll have no worrys of them ever plugging up. However it'll be ALOT louder with gutted cats.

We drove our 86 down to get gutted cats and nw pipes with just headers, and cats, no mufflers and it was quieter then my monte carlo which has gutted cats and glasspacks.

As for expensive rear gears your should find some in a junkyard or on here who is parting one out, then swap the whole thing or swap the gears and carrier out. I did that on my car, first one I ever did, bought the guts online shipped for $75.

Re: Rear end ratio / power transfer
 

First off; the air mixture screws are for the Idle circuit only. It has nothing to do with the fuel metering circuit after the transition from the idle slots to the power circuit. That is where the rods and jets come into function. HOWEVER, be careful that you do not take the engine too lean and burn a valve. You will need to spend time looking at your exhaust pipe color and your spark plugs to see if you are going to far. I skipped the purchase of a tuning kit and just bought a collection of rods and jets that went two to three steps on both sides of my factory installed parts. I now have a full set of rods and jets from over the years, but I can figure a fuel adjustment to a gnat's tail, if I want to. Do you have the original carb install book from Edelbrock? It gives the rods and jets that were in it for assembly and it gives you directions that you can go to improve on that. If not then borrow one or go to a store and copy one from a box on the floor.

Setting your idle mixture is definitely best done with a vacuum gauge connected to the intake manifold instead of by ear. Take one of the idle mixture screws in to a point that the idle drops off to a stutter and then start opening up until the idle stops increasing. Now turn the screw back inward an 1/8th of a turn. Do the opposite screw the same way. repeat this a couple times to ensure that the settings are at their best point.

Take a look at your timing and see where it is set at. If you advance initial timing some it will pick up your acceleration and take away some of the doggyness that you hate. Listen closely for detonation sounds on acceleration and also watch for "dieseling" when you shut the engine off. I timed my truck and my Son's truck with a timing light that has the advance feature on it and set them up for a TOTAL advance setting around 36 degrees. Not all engines can be set there, but you can get close.


Believe it or not a motor works a little better if there is some slight back pressure. I never like a straight pipe, but many do. So that is your choice, but the cats may be plugged and causing you some grief on your acceleration. Dispose or replace as necessary. Headers are a must for horsepower building. I figure your system is just enough to make it work well, but you have a ways to go, just my .02 worth.

The air cleaner is important, the more air in, the more power to work with. What height of filter element, preferrably a 4" tall one. The little short filters and a chrome cleaner assembly may be causing a turbulance issue above your carb and making you loose Horsepower. Look into a quality filter and set it up to work for you.

The 3.73 gears is a hard step for a TH 350 tranny, that will kill any highway mileage that you want. I would consider a set of 3.42 gears at the lowest and may a set of 3.08 for every day would be better. When we took my son's 86 SWB truck to 3.73 gears, we had already changed it out to a 700R4 tranny and that works well with his combination. I have a complete 10 bolt 3.08 rear end sitting by my garage, with the drums. brakes, cables, hoses, housing, and fluids still in it.

This can be done with time and a little creativity.

Re: Rear end ratio / power transfer
 

hmm on my edelbrock it ran rich, after driving, I pulled the plugs and they were black, I tuned the mixture screws as stated in the book and then they burned clean.

They are IMS though, Idle mixture screws, I forgot that.

My edelbrock book tells you what to do and to test for a lean or rich driving mix and what to do about it.

Like one was be up to speed and stomp it and if it done this then it's way one way or the other and this was needed to correct it, and so on.

Re: Rear end ratio / power transfer
 

I see what you mean, but what I don't understand is where the vacuum gauge comes into play? What would I look for on the gauge to help me with this?

As for the exhaust, I'm sick of it. It's way too loud and raspy, and the shop that did it did a horrible job on it. I've got a set of headers sitting in the garage, but they aren't expencive ones.

As for rear ends, I don't really do much highway driving at all, and I'm not worried about the gas mileage, yet. (wait till prices come up more)

I've got a 12 bolt that I'm gonna go look at this weekend. It's a 4.11 ratio in the rear. It's a little higher than I wanted to go, but the price is so dang cheap that I'm going to just give it a try and see where I can go with it. If it's too much, I'll just resell it and find something geared higher in a junk yard.

Re: Rear end ratio / power transfer
 

Other then the high rpm's while driving around town and highway I bet you'll love the power transfer and tires smoke you get from the 4.11

You'll probably never keep tires on it with a 4.11

When he says vacuum guage he means when you have it hooked up and are tweaking the idle mixtues screws you set them to get the HIGHEST reading/vacuum possible. That's the optimum air/fuel idle mixture setting, can't get much better then that.

Re: Rear end ratio / power transfer
 

The vacuum gauge is a telltale meter for reading your vacuum as you adjust the idle mixture. Most vacuum gauges measures vacuum in inches/mercury (0" to 30" with 0" being atmospheric pressure and 30" being a near perfect vacuum) and the higher numbers are readings of a better vacuum. Once you turn one of the mixture screws, on the carb, inward to get the intial setting the truck engine will stumble and run poorly, also at that time the vacuum reading will be really low (bad vacuum). As you turn the screw outward, the idle will improve and the vacuum reading will get higher. The idea is to turn the screw outward until the vacuum gauge numbers quit climbing and stay at one point on the dial. (do this slowly so that you do not overshioot) That is the point that you turn the mixture screw back in 1/8th of a turn from. That will be the OPTIMUM vacuum/fuel mixture setting for your carb. The vacuum reading is actually a readout of your fuel metering and the engine's response to the mixture. This should be done on both fuel mixture screws to get them set exactly the same.

Many carb specialists have been using vacuum gauges for setting idle mixtures and balancing multiple carb setups for years.

You will not get the setting any closer by using your hearing. Try it and you will see what I mean. Vacuum gauges are not that expensive at many parts stores and they are useful.

For your exhaust, may I suggest a set of dual exhaust pipes from the headers, with an "H" pipe or "X pipe crossover at the tail end of your tranny's output shaft. Then run 2 1/2" exhaust pipes to the outlet points through your mufflers. That would about the most optimium exhaust pipe size for your engine's size.

The 4.11 rear end is pretty steep for any daily use and will make your truck a City block SPECIAL. After a city block the other guy will kick your proverbial butt, because your engine will be topped out.

Re: Rear end ratio / power transfer
 

Thanks pieces and benoit454 for the information. I already have a vacuum guage, so I'll give that trick a try tomorrow and see what I can come up with.

As for the exhaust, it'll be a while. The first thing I have to do is pass emissions in June. What is the purpose of an X or an H pipe? Does that just balance both sides?

The rear end is a little steep for my tastes, and after reading what you're tellin me, I think I may hit a junk yard and try to find one before I go with this one.

Thanks again for the info!

Re: Rear end ratio / power transfer
 

i'm thinking about that same thing with my truck.i did some research online and with my tall rear tires and stock 3.08 rear end.i'm down in roughly 2.73.as 71lowrider said tire size make's a hell of a difference.i could feel it when i put new ones on.also i used to tow a 23 ft. boat with an 02 dodge diesel i had it came with stock with 265(32or33)tires.i put 35's on it and i really felt it.escpecially in the hills we have up here in washington and oregon.i figure a 3.73 ratio with my tires will put me in the 3.50 area.which ought to be about ideal.

Re: Rear end ratio / power transfer
 

Is that why they call you boatpuller? ;) :metal:

No seriously though, I believe I have smaller than stock tires, and when I went from the 30's it had to these 27 inch tall tires, I noticed a hell of a difference. Performance AND looks!

Anyone know of a good final drive ratio calculator that will include the tire size as well?

Re: Rear end ratio / power transfer
 

I've got some experience with 2.73's in my 69 Nova. When I first got it, the engine was a wheezy 307 2bbl with a TH350, 2.73 gears and puny 195/70 14's. Even with the teeny tires that wheezy 307 took a lot of effort to spin the right rear. Pumping the brake, turning right to unload the right rear and such. Swapping in a 4bbl helped but I had bumped up the tires to 205/60 14's. Once I put the 350 in smoke shows came a little easier. Changing to 2 1/2" duals and then an edlebrock intake/holley carb woke it up. Thats where its at now. Even with the 2.73's it can do a wicked peg leg burnout.

It all boils down to the tuning like others have said. Each time I changed something, I had to go back and re-adjust the timing, carb or both. It can be done with 2.73's but you got to dial your combination in better.

Here's a little example of what my Nova does with 2.73's....

Re: Rear end ratio / power transfer
 

I have the calculations for a ratio and it includes tire sizes. I also have a tire size website that take the numbers of tires and gives you the tire sizes. Let me do a little research and I will get them.

Re: Rear end ratio / power transfer
 

This may have already been addressed, but your old engine probably made more low end torque, as opposed to the new engine with the bigger cam, which doesn't make power until higher RPMs.....a slightly higher stall on the converter would help, but probably won't be needed once ya swap in the 3.73's......

My truck would BOIL the tires with 2.76's.....but of course a built 454 helps!:burnout:

Re: Rear end ratio / power transfer
 

yup,bought boats,sold boats......... therefore,...pulled alot of boats.

Re: Rear end ratio / power transfer
 

Try the following formula for calculating gear ratio and speed to different tire sizes. It works real well, If you have a overdrive tranny, the number for that will not be (1), it will be more like 0.68.


NEVER MIND, this dang website won't let a photo into it that is of any size. So here goes :

MPH=
RPM X Tire Diameter
Rear Axle Ratio X Trans output X 336

RPM =
Axle ratio X MPH X Trans output X 336
Tire diameter

Tire diameter=
Axle ratio X MPH X trans output X 336
RPM

Trans output =
RPM X Tire diameter
Axle ratio X MPH X 336



Also attached is a webssite that has a tire size calculator. It can take any tire size and give you dimensions or even comapare to other tire sizes.


http://www.discounttire.com/dtcs/infoTireMath.dos

Re: Rear end ratio / power transfer
 

Well with my 3.42's I can definately turn the tires over alot easier then before.

The 2.73's in the 84 truck sure will smoke them off too, so did the 86 4x4 with 3.08's but 33's.

Re: Rear end ratio / power transfer
 

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.

Re: Rear end ratio / power transfer
 

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.

Re: Rear end ratio / power transfer
 

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.

Re: Rear end ratio / power transfer
 

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.

Re: Rear end ratio / power transfer
 

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?

Re: Rear end ratio / power transfer
 

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. :crazy: 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.

Re: Rear end ratio / power transfer
 

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?

Re: Rear end ratio / power transfer
 

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

Re: Rear end ratio / power transfer
 

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.

Re: Rear end ratio / power transfer
 

Did you get a vacuum guage reading yet?

Re: Rear end ratio / power transfer
 

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

Re: Rear end ratio / power transfer
 

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.

Re: Rear end ratio / power transfer
 

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.

Re: Rear end ratio / power transfer
 

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.

Re: Rear end ratio / power transfer
 

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.