Overcome with Frustration!

[savatreatabvr]

My 1973 Chevy c/20 454 has never had the power I think it should, I've replaced plugs, wires, cap, rotor, vacuum advance, centrifugal weights, carburetor kit, vacuum hoses! I've adjusted the valves, timing and carburetor so many times I actually thought I had power and then I drove my friends 1974 c/10 454! His truck is bone stock just like mine but it will roast the tires through intersections! Not saying all I want is to do burnouts, I just want it to run the way it's supposed to run! It's always seems to sound like and run on 7 cylinders but all 8 are firing, I've done compression test with no significant differences throughout all 8 cylinders! I know there can't be much of a difference in horsepower from 1973 to 1974, if any, so what am I doing wrong?

[INSIDIOUS '86]

There can be a diff in power between 73-74. remember back then the EPA and insurance company's were cracking down on Detroit hard. A truck motor and passenger motor usually are prepped diffrent. It may be possible that he has a passenger engine in his truck with some more ponies.
A higher stall converter, rear gearing and trans differences can make his feel stronger
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[tucsonjwt]

I drove a 73 C20 454/TH400 for 21 years. That was the fastest vehicle I have ever owned. I know this is not popular with DIYers posting here, but I would take your truck to a shop with an engine analyzer. Not many mechanics have this old school equipment now, since everything is computerized, but I found a shop working on old classic cars here in Tucson who had one and they made the proper adjustments and tracked down/fixed my problems in 30 minutes. I initially went there because I could not pass emissions (just barely) in my current 83 C20/SM465. Also, don't let any mechanic touch your truck unless they have a lot of gray (preferably white) hair, or no hair at all. Unfortunately, this shop no longer works on old classics - just BMWs and Minis, so I guess I will have to find some other knowledgeable old guys.

On a side note, early 454s were noted for having "soft" cams - lobes wore out and caused pushrods to bend/break. This happened on my 73 and a new cam and replaced pushrods fixed the problem. It also happened on my brother's 73 Caprice wagon with a 454, back in the day when it was purchased new and only a few years old. I don't think this is your problem, because the symptoms of this condition were everything was fine until the engine stumbled and refused to run one day.

Also, rear axle ratio makes a big difference in acceleration. Some PO may have changed the rear axle to a low number, like 2:73, in an effort to improve gas mileage - so you might check that. I don't think low ratios help much on 3/4 ton pickups with gas engines since you are hauling around that 1000 lbs. of extra dead weight all of the time, compared to a 1/2 ton.

I did have a 350/350 76 C20 which was in top mechanical condition but was a complete dog. I think a TH400 transmission would have helped on that truck. My current 83 454 C20 will never move very fast with its SM465. This raises the question of whether your transmission is shifting properly.

[LEEVON]

It sounds like you've probably tried it all, but just for kicks what are the specs on your timing? How much initial, mechanical advance and vacuum advance? Are you running manifold or ported vacuum?

[savatreatabvr]

My truck runs best at this timing mark! When I time it the way it's supposed to be it runs bad! I switched to manifold vacuum because of the pedal response but it doesn't seem to help now!

Originally Posted by LEEVON

It sounds like you've probably tried it all, but just for kicks what are the specs on your timing? How much initial, mechanical advance and vacuum advance? Are you running manifold or ported vacuum?

[INSIDIOUS '86]

Originally Posted by savatreatabvr

My truck runs best at this timing mark! When I time it the way it's supposed to be it runs bad! I switched to manifold vacuum because of the pedal response but it doesn't seem to help now!

Timing looks almost right it should be about 12 -14 though. See what it shows when it's at about 3500rpm and tell us if the timing mark still moves past that rpm
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[savatreatabvr]

Really I thought the timing mark had to be within the marks on the timing tab? I'll check the timing after it stop raining here in Phoenix, (I know crazy), when this happens it's more like an event, lol! Last time I had the cap off I checked the weights and they seemed to move freely but I'm still considering replacing the whole HEI distributor! Heck I've tried everything else, if that doesn't do the trick I'm replacing the cam! But if I do that I may as well replace the lifters, timing chain and water pump right?

Originally Posted by INSIDIOUS '86

Timing looks almost right it should be about 12 -14 though. See what it shows when it's at about 3500rpm and tell us if the timing mark still moves past that rpm
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[Firebirdjones]

Originally Posted by savatreatabvr

Really I thought the timing mark had to be within the marks on the timing tab?

Nope, you really need a dial back timing light. With that you simply use the mark on the balancer and "zero" on the tab,,,that's it. Then use the dial to see exactly where it is.

Most of your factory tabs won't go past 12 or 14 degrees. I've found in most all performance applications, and even stock applications, that an initial setting higher than that makes for a smoother, snappier, more vacuum, and all around better performing engine. It also helps engines with camshafts that have a ton of overlap,,they simply won't idle correctly with very low stock like timing settings.

Like I said in post above, 16-18 initial is a good to start with, but you'll have to modify your distributor breaker plate with a larger stop bushing to limit the total advance. HEI's are extremely easy to do this with if that is what you are running. If so I can put up a couple pics of a very simple breaker plate limiter that I've used on them since the 70's. Works like a champ.

[savatreatabvr]

One more question, did my 1973 come factory with an EGR valve? The truck didn't have one when i bought it.

[Firebirdjones]

Originally Posted by savatreatabvr

My truck runs best at this timing mark! When I time it the way it's supposed to be it runs bad! I switched to manifold vacuum because of the pedal response but it doesn't seem to help now!

That pic tells me a few things. To find out exactly where that is you need a dial back timing light or timing tape on the balancer but a ballpark guess to me that looks like about 16-18 degrees initial.

Keep in mind this has to be checked with the vacuum advance disconnected so I have to ask,,,,is this the timing you have without vacuum assist? If so,,,then 16-18 initial is what I always shoot for. Then I modify the breaker plate to limit 18-20 degrees centrifical.

But here is what I think is going on since you mentioned it runs poorly at the factory timing setting. I'd bet your balancer ring has moved. So you are going to need to verify top dead center with a piston stop and remark your balancer. Even if it hasn't slipped, this should be done on every engine to get your timing "SPOT" on.

Use a simple piston stop that screw into the #1 spark plug. Rotate engine gently until piston touches the stop,,,mark balancer. Rotate engine opposite direction until piston touches the stop,,,,mark balancer.
The exact center of those 2 marks is "ZERO" (top dead center) on the balancer,,,make a perminant mark here and use this as your new indicator to set your timing. I'm betting you'll find that it's several degrees off the original mark and that is probably the beginning of your running problems.

My SCJ was 9 degrees off

Worse case scenario you have a sloppy chain which retards timing and makes the engine sluggish down low, hard to set timing if it's jumping around, but this is a completely different subject. I'd verify that balancer first and foremost, then go from there.

[savatreatabvr]

Yes the vacuum advance is unhooked and plugged when timing is checked. I think it's time to invest in a vacuum gauge, I was told a vacuum gauge will tell me alot?

Originally Posted by Firebirdjones

That pic tells me a few things. To find out exactly where that is you need a dial back timing light or timing tape on the balancer but a ballpark guess to me that looks like about 16-18 degrees initial.

Keep in mind this has to be checked with the vacuum advance disconnected so I have to ask,,,,is this the timing you have without vacuum assist? If so,,,then 16-18 initial is what I always shoot for. Then I modify the breaker plate to limit 18-20 degrees centrifical.

But here is what I think is going on since you mentioned it runs poorly at the factory timing setting. I'd bet your balancer ring has moved. So you are going to need to verify top dead center with a piston stop and remark your balancer. Even if it hasn't slipped, this should be done on every engine to get your timing "SPOT" on.

Use a simple piston stop that screw into the #1 spark plug. Rotate engine gently until piston touches the stop,,,mark balancer. Rotate engine opposite direction until piston touches the stop,,,,mark balancer.
The exact center of those 2 marks is "ZERO" (top dead center) on the balancer,,,make a perminant mark here and use this as your new indicator to set your timing. I'm betting you'll find that it's several degrees off the original mark and that is probably the beginning of your running problems.

My SCJ was 9 degrees off

Worse case scenario you have a sloppy chain which retards timing and makes the engine sluggish down low, hard to set timing if it's jumping around, but this is a completely different subject. I'd verify that balancer first and foremost, then go from there.

[geezer#99]

Sounds like you've thrown a bunch of parts at it.
Have you:
1. Put on headers and 2 1/2 inch pipes. Headers are the biggest hp adder on a bbc.
2. Recurved your distributor.
3. Advanced your cam after deegeeing it in.
4. Better intake.
5. Adjusted the apt and secondary air valve on your carb.
6. Properly gapped plugs in the right heat range.
7 Lightened the whole truck. Don't haul more than what's necessary.
8. Perfect wheel balance and alignment.
9. Tires. Narrow are better. Less rolling resistance.
That said you never know what you're gonna get in a stock truck!
Buddy and I bought identical chev short boxes in 1980. 350 turbo 400 3.08 gears. Exactly the same truck. Only difference. Mine was red/white. His was black.
My truck ran circles around his. In a 1/4 mile mine won by 200 feet. I got better gas mileage and never had any warranty work done on it. His was always in at the dealer.
You and your buddies truck both share the 454 motor but his is a c10 and yours a c20.
His is lighter. Wheels, tires, springs etc add weight to yours. His is tuned different from the factory.
You can make yours faster. Just takes a different approach.

[tucsonjwt]

Meaning no disrespect to others posting here, but my experience is that a stock 454 truck engine is very powerful, and needs no modifications to have plenty of acceleration, assuming you don't have a granny 4 speed behind it like I do.
I think the best first step is to pay a true professional with the proper equipment to check out the engine and transmission first. I am one of those "poke around and see what works" guys myself, but sometimes it is best to go right to a pro - at least to get some (often free) advice. My guess is less than $100 will get you enough professional diagnosis to get you farther to where you want to go than a lot of guesswork. A few phone calls to a few shops in your area would be time well spent, IMHO. If everything checks out OK, some shops promote a Motor Vac, other shops say it only removes soft carbon so it is not worth the money, but you can evaluate - some shops offer money back guarantee if there is no improvement.

[johnnyclack]

Have you thought about running it on a Dyno ? It'll provide some decent information if your concerned about the make up of your motor

[savatreatabvr]

No but it would be nice knowing exactly how much HP and torque I have!

Originally Posted by johnnyclack

Have you thought about running it on a Dyno ? It'll provide some decent information if your concerned about the make up of your motor

[tinydb84]

My 454 c20 is gutless too. I bought headers, a recurve kit, new carb, and supercharger lol. I'll let know how it runs when I get it all on there
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[Firebirdjones]

They are decent runners with alot of grunt when tuned properly.

I'd guess you have something going on you just haven't found yet. If the engine has never been opened up I'd suspect it could also be a little tired. Weak valve springs, worn cam lobes, loose valve guides, etc etc... If the engine has an oil control issue that might be a clue to some of the things I mentioned.

But again, tuning is everything. Using a wideband is a must to dial in the fuel curve, and the distributor has to be spot on. As long as it's in good shape (dist shaft bushings not worn) then I like to dial in about 16-18 initial and run about 20 centrifical for a total of 36-38 should be fine on todays crap pump gas on a low compression engine like this.
I then like to dial in the "adjustable" vacuum advance to add about 10-15 degrees more timing under light load conditions and hook that to intake manifold vacuum only. Some of these numbers may vary depending on rear gear, transmission, weight of vehicle, octane you prefer to run etc....On a side note, BBC with these dinasour combustion chambers like as much as 42 degrees of timing on the dyno to make max power,,,,but I find that's hard to get away with on the street once in the vehicle, in the heat, crap gas etc....

If everything else is in proper working order it should squirt around nicely for a truck.

My 79 454 1 ton with headers and exhuast, performer cam and intake, along with a sharp tune,,, otherwise unmolested, went 14.70's and it weighs 5300 lbs. It was just as quick as the camaros and mustangs that were coming out in the late 80's

Knowing more about the truck would help. Difficult to diagnose anything on the internet without having it right in front of me.

[thesickc10]

First what gears do you have in the rear? If you have a high gear back there your truck isnt gonna move right now matter what you throw at it.

[savatreatabvr]

You're right, great answer! I'm not sure what gears I've got but it cruises fine down the freeway so I'm guessing there pretty high!

Originally Posted by thesickc10

First what gears do you have in the rear? If you have a high gear back there your truck isnt gonna move right now matter what you throw at it.

[savatreatabvr]

Since the 454 has high miles on it the cam could very well be worn down and the valve springs could be weak to! I replaced a few valve seals recently and the few push rods I checked were straight. Is there a way to check how worn down a camshaft is? A flat camshaft lobe would make it act like it's running on 7 cylinders correct? Now if I put a new camshaft in it won't it wear out everything else faster?

[RPOZ11]

I feel your pain....

I was troubleshooting my 73 C/20 454 Truck for a while.
I first determined that the distributor that was in my truck was not the original distributor GM installed into it.
The correct one I believe should be stamped : 1111213
I have several of these distributors now; all have distributor cam pieces ranging from 718 to 726.
My guess is that GM either changed it over the year, or different vehicle uses.
The same 1111213 may have been installed in factory 454 El Camino's, Chevelle's, Monte Carlo's, and maybe even Impala's and wagons.
Anyways....
Once I obtained the correct 1111213, I cleaned it up, new vacuum advance, and double checked that the advance weights etc were all working properly prior to installation.
Mine has a 718 cam piece.
I dialed it in at 6* BTDC, and left the factory advance springs and weights as they came from GM.
I did grease up the weights on the pole shaft where the weights land and move.
My cam is straight up at TDC.
My truck is a bit sluggish from a stop but once I get into the 45-80 MPH ranges, it really pulls well.
My truck has 120,000 miles on it.
I assume my compression has dropped from cylinder and ring wear.

Thats a start for you.

Things to check :
Compression
Fuel Pump
Vacuum advance piece
Distributor is fulling advancing
Spark Plug Wires
Cap
Rotor
Plugs
Coil
Vacuum hose leaks, brittle &/or cracked hoses

One thing that I have always considered is is whether or not my timing chain is original GM issue.
Those were plastic press on gears over a steel core.
Those plastic gears can :
A: wear
B: break plastic teeth
C: jump time

I initally was of the thought that my power loss could have been from a timing chan that had jumped time.
I am convinced now from my above fixes that this was not the case.
However: I am still going to change to a Cloyes True Roller soon.
One : for reliability
and
Two : to prevent permanent damage or future engine failure from occurring.

Another note :
I determined that the carb (Quadrajet) installed onto my 454 was not the original unit.
I took it off of the 454 and cleaned it as best I could.
At that time I checked all of the securing bolts throughout the carb.
I discovered that the whole thing was loose.
I gently tightened all of the screws that keep it together.
Once reinstalled, that greatly improved the idle, rpm pull, and created a more smoothly operating engine.

I have not done much to it since.
It runs well on a single point, coil, as the factory delivered it.

By the way,
I belive that the factory LS-3 cam is having a 434/434" lift on 112* duration.
I might be wrong.
But, the 434 #'s seem correct in the lower performance it should act like; and it does act accordingly.

Remember,
Back in the early 70's, car manufacturers were up against fuel economy and HP to weight ratios placed upon them by the US Gov't.

I love my C/20.
Rides a bit rough for a daily, but it is ALL Truck!

Hope this is all useful....

[LEEVON]

I can't remember the last time I found an engine with TDC at the correct spot on the timing tab. Balancers slip, timing covers are replaced, you name it. I'd invest in a piston stop (Summit has them) and start there. I put a stock replacement cover on my 350 and it was still 8 degrees off. I degreed it with the head off and again with the piston stop, which was pretty accurate. You don't necessarily need a dial-back light if you buy some 360 degree timing tape at the same time as the stop. These are (2) invaluable tools.

You could be at 8 degrees initial and who knows where on advance. If you're not hitting 34-36 degrees you're leaving power on the table.

[savatreatabvr]

I've got one of those old chrome PENSKE 244.2115 timing lights I bought at a flea market for $10, I've always assumed it was accurate but how accurate can it be after 20 years?

Originally Posted by LEEVON

I can't remember the last time I found an engine with TDC at the correct spot on the timing tab. Balancers slip, timing covers are replaced, you name it. I'd invest in a piston stop (Summit has them) and start there. I put a stock replacement cover on my 350 and it was still 8 degrees off. I degreed it with the head off and again with the piston stop, which was pretty accurate. You don't necessarily need a dial-back light if you buy some 360 degree timing tape at the same time as the stop. These are (2) invaluable tools.

You could be at 8 degrees initial and who knows where on advance. If you're not hitting 34-36 degrees you're leaving power on the table.

[Firebirdjones]

Originally Posted by savatreatabvr

I've got one of those old chrome PENSKE 244.2115 timing lights I bought at a flea market for $10, I've always assumed it was accurate but how accurate can it be after 20 years?

Could be okay, I've got some really old timing lights here that go with my Sun diagnostic machine and I know that's from the late 50's early 60's. Even that one has dial back adjustability. Still works fine but I prefer to use a more modern timing light with a dial back that is probably 15 years old and works on every ignition system, been great for me. I have a newer digital timing light but I've found it works a little funky when you mess around with high energy systems like MSD Digitial 6 and 7 boxes,,,so I always tend to fall back on my trusty 15 year old analog piece

You don't need the dial back as mentioned, I also mentioned you could get away with timing tape for about $10 and accomplish the same thing,,,providing your balancer hasn't slipped that is....

You really should verify top dead center on the balancer and remark it if necessary before you install timing tape, otherwise the tape will be off too since you will use the "zero" mark to line the tape up.

I'll get you a couple of HEI pics,,,,hang on.

[Firebirdjones]

Here is a spare HEI I modified years ago.

The outer holes are used to hold the rotor button down. The inside holes are not used for anything. You can use either side. I tap this hole with a 10/32 and install a screw upside down (with a little loctite).

Then as the breaker plate moves it contacts this screw and acts like an advance stop. Cheap, simple, easy, and it will never wear out like the cheesy plastic bushings that GM puts in there (throw those in the can).

This trick gives you exactly 18-20 degrees of centrifical advance (it varies a couple degrees from one distributor to the next) but allows an initial setting of about 16-18 degrees so you will have about 34-38 degrees total depending on where you want to be.

Here is the breaker plate at zero advance.....


Here is the breaker plate at full advance contacting the screw....


As you might be able to see in these pics, I've actually filed the side of the screw down a bit where the breaker plate makes contact to allow more centrifical advance ( I don't remember why as I can't remember what engine I had this in last) but this can be done if need be so you can then set your intitial timing down a little lower if you prefer. If you go too far, simply remove the screw and install a new one and start over. Really very simple setup.