91 Sub 2500???'s

[91 Rust Bucket]

Hey there guys new to the forum and Suburbans.

I have a 91 GMC Suburban 2500, with the 454 and 4L80E combo. What I want to do is either rebuild the engine or put another one in its place. The engine has seemed to start lacking power and is in consideration for a refresh. It has 245K on the clock not sure if they were highway or street driven daily. I do know that since I inherited this truck it has slowly started showing signs of loss of power and poor fuel mileage. Before I R&R the engine I want to know a few things about it first. I am a Ford Diesel guy as long as I have been driving. This is my first Suburban, so I will have several questions about it.

1. How do I go about getting better fuel economy from it. Other then the simple cold air box tricks.

2. Would anyone know what rearend gears are in this truck? It is 3/4 ton 2wd with the tow package.

3. Is there any good exhaust upgrades out there for this old of a truck?
I want to retain the stock exhaust manifolds and do a new exhaust from the Y-pipe back. The cat had a hole in it, I replaced it with one from Summit Racing.

4.Do you think just adding a 4" exhaust all the way back would benefit the fuel economy a little?

5. Are then aftermarket sources for body panels and other performance goodies?

6.If I take apart the engine for rebuild what kind of tricks can be done to upgrade the engine in the form of oil system tricks? I will do a some bowl blending on the head and port matching the intake and possibly do a cam upgrade. I plan on using it it to haul small tractors for the local John Deere and Case New Holland dealers. The most weight that goes on this truck has been 7500 pounds with no issues.
I had estimated the fuel economy did drop off a bit, I was getting about 13 mpg and it seems to have gone down to around 9 mpg. here is what I have done so far:
I changed the spark plugs due to being fouled, plugs wires with a set of MSD wires I had in my shop, I have changed the fuel pump, filter and pickup inside the tank as well as adding new lines in case of any fuel line blockage. I saw that the spark wasnt up to par so I put on a new ignition coil, rebuilt the distributor top to bottom. I still get about 9 mpg on a good day. Lately I have gotten a little bit of a sputter when the engine is cold. Only thing I can think of is that timing is out of whack, so I put a timing light on it and there is no timing pointer. What next?

 

[Molson02536]

Hey there guys new to the forum and Suburbans.

I have a 91 GMC Suburban 2500, with the 454 and 4L80E combo. What I want to do is either rebuild the engine or put another one in its place. The engine has seemed to start lacking power and is in consideration for a refresh. It has 245K on the clock not sure if they were highway or street driven daily. I do know that since I inherited this truck it has slowly started showing signs of loss of power and poor fuel mileage. Before I R&R the engine I want to know a few things about it first. I am a Ford Diesel guy as long as I have been driving. This is my first Suburban, so I will have several questions about it.

1. How do I go about getting better fuel economy from it. Other then the simple cold air box tricks.

2. Would anyone know what rearend gears are in this truck? It is 3/4 ton 2wd with the tow package.

3. Is there any good exhaust upgrades out there for this old of a truck?
I want to retain the stock exhaust manifolds and do a new exhaust from the Y-pipe back. The cat had a hole in it, I replaced it with one from Summit Racing.

4.Do you think just adding a 4" exhaust all the way back would benefit the fuel economy a little?

5. Are then aftermarket sources for body panels and other performance goodies?

6.If I take apart the engine for rebuild what kind of tricks can be done to upgrade the engine in the form of oil system tricks? I will do a some bowl blending on the head and port matching the intake and possibly do a cam upgrade. I plan on using it it to haul small tractors for the local John Deere and Case New Holland dealers. The most weight that goes on this truck has been 7500 pounds with no issues.
I had estimated the fuel economy did drop off a bit, I was getting about 13 mpg and it seems to have gone down to around 9 mpg. here is what I have done so far:
I changed the spark plugs due to being fouled, plugs wires with a set of MSD wires I had in my shop, I have changed the fuel pump, filter and pickup inside the tank as well as adding new lines in case of any fuel line blockage. I saw that the spark wasnt up to par so I put on a new ignition coil, rebuilt the distributor top to bottom. I still get about 9 mpg on a good day. Lately I have gotten a little bit of a sputter when the engine is cold. Only thing I can think of is that timing is out of whack, so I put a timing light on it and there is no timing pointer. What next?

1. Keep the air filter clean

2. There is a PRO code sticker in your glove box, but most likely faded so your going to have to go to the Dealers parts department with your Vin number and have them pull up your PRO code options. This will give you all the information to your Suburban on when options was installed from factory. (Rear end ratio)

3. You can get a Cat back exhaust system from http://www.flowmastermufflers.com/ or http://www.magnaflow.com/ for a better exhaust system.

4. Turning your Exhaust to a 4" system will cause you to lower your MPG and loose your bottom end HP and towing abilities at lower RPMs.

5. There are aftermarket body parts you can get, just look on the net or Parts Source can order them in for you.

6. Here is how to check your timing, there is a connector under passengers side of dash where the wiring harness comes through firewall and you will see a tan with a black striped wire with a connector connecting the wires together. This is the est bypass wire, you need to unplug this connector and set timing to 0 degrees then turn off engine then reconnect the connector.

The other thing also is to give your 454 a http://www.seafoamsales.com/ and add a bottle of http://www.marvelmysteryoil.com/ to clean out your oil passage ways from the years of carbon build ups. Do this for the next few oil changes and then add the Marvel mystery oil about 600 miles before servicing the engine oil and filter after 5 months or when you feel that the engine is internal cleaned.

http://gmcowners.com/gmc-forum/showthread.php?t=13770

Also keep your TBI clean and your EGR valve to give you the most performance and economy your 454 can give. This with the servicing of your transmission oil and filter will help you reach your goals and what ever you do, NEVER GET YOUR TRANSMISSION FLUID FLUSHED. Just have them drop the pan and replace the filter and transmission fluid.

As for your engine, keep it stock for what your looking to do with it. Keeping it stock will give it the most durability and reliability your going to ever get from it with low maintenance as possible to when it was stock. If you want to make it in to a 450hp 454 here is a few things your going to be looking at to change.

1. All New 4 Bolt Main Engine

2. 9.6 to 1 Compression

3. Forged Steel Crankshaft

4. Forged Pistons

5. Chrome Moly Rings

6. Heavy Duty Double Roller True Roller Timing Set

7. Aluminum fast burn Edelbrock Oval Port Heads w/ 110cc Combustion Chambers

8. 2.19/1.88 stainless steel valves, hardened valve locks, chrome moly retainers, Heavy Duty Valve Springs and Screw in Studs

9. Roller Camshaft Duration @ 050 211/230, Lift 510/540

10. Hardened Seats for running Unleaded fuel

11. Hydraulic Roller Lifters

12. Federal Mogul Tri-Metal Bearings

13. New 1.7 Ratio Rocker Arms

14. Melling High Volume Oil pump

15. Race Prepped High Energy Ignition Distributor w/ 53,000 volt coil Pak

16. High torque starter.
This should give you 450 HP at about 5,200 RPM according to me program.

 

[91 Rust Bucket]

Hey thanks Molson (great Beer by the way). I have a set of aluminum Brodix heads that my dad bought new about 15 years ago and never used them. I was thinking along the lines of 550+ HP and I want to see what I can pull out of the torque range. I really like this truck, its cool and all. But as you know Ford didn't make a vehicle like this unless it was an aftermarket deal. I was at Napa today and the parts guy told me the best bang for you buck camshaft is to go with some in the upper .550 lift range to maybe .600 lift range. He did mention that upgrade for the torque converter, I have a guy that builds custom deals for my race cars and I can go with my cam guy also with something to match the torque converter. With the added HP what mods are good for the tranny? I don't want to rebuild the engine and then the transmission come apart. However, I have a great big 482 Olds with a th400 that may find its way in the truck being that it is 2wd. This engine is a rebuilt stroker Olds with aftermarket everything, may consider dropping it in there til the 454 is done.

 

[Molson02536]

Hey thanks Molson (great Beer by the way). I have a set of aluminum Brodix heads that my dad bought new about 15 years ago and never used them. I was thinking along the lines of 550+ HP and I want to see what I can pull out of the torque range. I really like this truck, its cool and all. But as you know Ford didn't make a vehicle like this unless it was an aftermarket deal. I was at Napa today and the parts guy told me the best bang for you buck camshaft is to go with some in the upper .550 lift range to maybe .600 lift range. He did mention that upgrade for the torque converter, I have a guy that builds custom deals for my race cars and I can go with my cam guy also with something to match the torque converter. With the added HP what mods are good for the tranny? I don't want to rebuild the engine and then the transmission come apart. However, I have a great big 482 Olds with a th400 that may find its way in the truck being that it is 2wd. This engine is a rebuilt stroker Olds with aftermarket everything, may consider dropping it in there til the 454 is done.

4L80E upgrades to take more then 550 HP, and the 4L80E is the same as the TH400 except the added 4th gear. I would install the transgo stg 2 shift kit and a ford style superduty cooler made by tru-cool (if you have enough room in front as it is 8.5" by 22.75 by 1 1/4 thick). It has a 40,000 lb gvw rating and cools so well it comes with a thermostatic bypass valve. The transgo kit is the best in my opinion because it has a relief valve in case your vehicle ever goes to limp mode or suffers any kind of electrical failure that causes full line pressure which can litearly crack the third/direct piston or drum (I have seen this personally), and turning up the epc is a bandaid approach which will cause bangy/harsh shifts even when driving real easy.

One of the weakest points in a 4l80e is the cushion plates in the direct and fwd clutch drums,they often crack and cause clutch pack to jam when transmission tries to shift. I have also seen the input shaft (which appears to be very beefy) shear off at lube oil holes. One suppliers offers a billet input shaft for guys with big power. I have helped built 4l80e's for hot rods running 800 hp that are holding up with a few basic mods like the transgo stg2 and blue plate racing clutches/heat treated kolene steels,6pack 3rd drum vs 5 pack stock and a computer that adds line presure under high tps settings.

As for the Torque converter, can't go wrong with the dual or triple disc converter. The 4L80E is a good tranny up to its limits. I believe it is limited at 750 foot pounds of torque - may be off there a little. As mentioned a Transgo valve body kit in your 4L80e tranny and should not have a lick of problems with it again.

It included drillling some holes in the seperator plate and VB along with changing out a valve (power valve) and a few misc parts. For all intensive purposes if one adds a good tranny cooler, temp guage, and keeps up on maintinence then the 4L80E will be able to hold it's own with the limited power of the 454. Heavy towing and unlocked convertor operation are the main killers of the 4L80E or any other automatic transmission.