GM 454 power/MPG issues

[Gary - K7GLD]

My last MH was quite some time back, a '76 or so 22 ft. Winnebago on a dodge chassis, with a 440 engine - gobs of power, but MPG sucked at 5. 5 MPG max - and now, the latest:



Just bought a clean 27 foot '88 Winnebago Super Chief with 58K miles on the clock. All in all in great shape both cosmetically and mechanically, but the power seems low for the size of the engine vs the MH, and the MPG really sucks at a bit over 5 MPG with careful driving at 55 MPH or so - lots of mountain grades here in eastern Oregon, John day area, and these grades require range 2 with the TH-400, and in high, not enough power on any but the lesser and shorter grades - we're talking 3000-5000 ft. elevation.



This engine has dual exhausts, a 4 barrel carb, and the smog pump setup - and I guess my basic question is, is this the best this rig will do in regards to power and MPG, or is there likely something practical that can be done to improve things?



Is this just the typical way these things are, and too impractical or expensive to improve, or what?

 

[AClayton]

Gary,



The 88' model year was the last year of the old carb set-up and consequently was saddled with all the latest emmisions crap. You should have more power available though and I'm suspecting the computer is retarding your timing when you climb the long grades due to the extreme heat generated. These carb'ed rigs are famous for that... . the old quick fix was to run an extra ground through a switch installed in the dash to control the electric fans. The fans are set at 220* to come on and also when dash air is used. We used to activate this switch manually when approaching grades to aid in the cooling and thus help alleviate the retarded timing syndrome.





Also..... invest in a quality aftermarket exhaust system and air intake. Banks-Power has a powerpack for MH's and includes a new exhaust and intake and a few other components to bump up power. I realize the diesel population on TDR resists the use of Banks products but for gas powered MH's,they do help and they're not loud.



I used to be able to get 10mpg with mine,but it was much lighter than yours. I had a 22' footer. Keeping speed at 55mph should render close to 10mpg... . but not 100% sure. Many of the guys in our RV club that had these rigs probably exhaggerated about mileage,Grandfather included,but 10 really doesn't seem that far off.



I have heard of people advancing the timing with good results in power but the economy was poor. I did this and noticed more power but also more heat and less mpg.



Heat is the biggest killer for these rigs... . hurts mileage and power suffers. Good exhaust and intake and set of headers will help. Could also have plugged convertors. Free up the exhaust and things should feel better.



Alan

 

[WestTN]

Some of those had problems with the distributor. The shaft in it is actually a shaft in a tube. Over time, and with extended oil changes, they tend to gum up and do not properly advance the timing. This will KILL fuel mileage as well as lower available power.

 

[Bill Stockard]

Some of those had problems with the distributor. The shaft in it is actually a shaft in a tube. Over time, and with extended oil changes, they tend to gum up and do not properly advance the timing. This will KILL fuel mileage as well as lower available power.

You are correct. I owned two different 454s and they both had distributor problem you describe. Also the mechanical advance weight pivots would bind up with rusty looking dust and wouldn't advance properly causing low power and poor fuel mileage. I drove one of the 454s over 350K miles and it was a 50-75K mile service routine to remove the distributor, clean the shaft of gum and oil residue and clean and re-lubridate the mechanical advance weight pivots.



Bill

 

[HBarlow]

After 1970 and prior to the '90s the EPA-imposed tree hugger religion took all the power out of those old gas engines. Your engine has very low compression, a short duration low lift cam, small port heads and small valves, retarded ignition timing, and probably an EGR.

You know the solution as well as I do but the question is do you want to spend the money and effort to locate, purchase, and install the heads, cam, ignition, intake manifold, and carburetor to only improve it to perhaps 8-9 mpg. You can make it run better, pull the hills better, but a fuel economy champ you cannot make it.

Gas engines make lousy towing motors, even the modern ones with computer managed port fuel injection.

 

[fox]

Harvey has it.

Low compression makes them run HOTTER. Find some closed chamber heads, a carb that can be tuned correctly. Leaner isn't always best. Then let it breath.

And it it is available, use E-85 but build the motor with 12 to 1 compression for it. Gas is not an option if you do.

 

[AClayton]

Harvey has it.

Low compression makes them run HOTTER. Find some closed chamber heads, a carb that can be tuned correctly. Leaner isn't always best. Then let it breath.

And it it is available, use E-85 but build the motor with 12 to 1 compression for it. Gas is not an option if you do.

12 to 1 compression for a MH? I have never seen a high compression GAS engine built for towing and torque.



We all know how to get power out of theses engines the hard way... I seriously doubt Gary is in the market for a major overhaul on his purchase. The distributor service is a very good place to start and after that,make the necessary changes to the exhaust if power is still un-acceptable.





These motors were only good for 230hp and I think 350tq. Not much at all and I think the only reason they're even driveable is because of the 3spd transmission with no OD. Hp to the wheels is about 140 which is comparable to many modern,SMALL V-8's of todays gas-powered pickups.



Harvey is correct about all of the smog-management on these engines. When I owned my 88' back in the 90's,I lived in an area without emmision testing and removed much of that crap and bypassed the rest. Result:Very little if any change to the driveability of the RV. On top of that,as mentioned earlier,the heads don't flow well and the compression was only 7. 5 to 1



I stand by my original posturchase the Banks kit and I will add ... . servicing the dist.



Alan

 

[fox]

Re-read my post!!!!!!!!!!!!!!

I said if it is available , to use E-85 and build the motor for 12 to 1. Gas won't be an option then though.

I know of guys who built 454's for motorhomes with 9+ compression, built

right they really can do the job---for gas motors.

Get the heat out of the chamber as soon as possible AFTER power stroke.

That same motor in a pick-up , stock got 10-11 mpg.

Simply swapping out the heads to closed chamber, 350hp hydraulic cam, and a small holley 650 spread bore carb, made the mileage go to 15-16 and power felt like it doubled.

Try the same with a high octane fuel, E-85, it likes 12+ compression (some have been built with 15!!)

The ethanol carries the heat away, burn cooler too.

It if different the Methanol, so it can stay in the system all year.

 

[fox]

Heres a little more on it.

Get rid of those peanut port heads. Get rid of the little cam that is used. Open up the exhaust. Huge difference.

You are right as stock they were a joke.

Spend the time to get a good carb tuned and it will be a nice driver.

 

[RVTRKN]

Bosses Suburban had the 454 with the TBI system on it, and was always mad when we towed our boats to lake Mohave, when he couldn't keep up with me on Baker grade in my 94 2500HD Ram with the 360 gasser. His father in law was a GM mechanic and went through the engine and found the timing off a tooth. After it was repaired he traded it in for another Suburban (wifes choice) and it still could not keep up with my Dodge. :-laf

 

[Gary - K7GLD]

Basically, what I'm hearing is that the largest part of my "problem" is poor design and engine strangulation - none of which has an easy "fix", other than the distributor suggestion - this engine uses the HEI setup, used several in the past with decent results, but will check that out.



I sorta hoped that perhaps the use of the smog pump setup was causing significant problems - we don't have smog checks here, and it COULD be removed, but probably not worth it unless it was a proven issue, and significant MPG/power improvement was available with it's removal.



Things like better heads and other labor and $$$ intensive approaches are probably not practical in a relatively low usage rig like this, intended primarily for relatively local fishing trips only during summer months. It's just that the MH is so nice overall, that the potential option for longer and more frequent trips is attractive, and might be considered IF the MPG could be massaged up closer to the 9 MPG range or so - but for uses other than fishing when I need the MH to tow a boat, I still have the 5er and truck - and IT get *3 times* the MPG of the MH - and FAR more power to boot!



I really didn't expect a sports car or drag racer from this older big block gasser setup, and low power with decent MPG - OR lots of power with POOR MPG might be acceptable - but DANG, I sorta hate to see BOTH down so low!



I doesn't help that virtually ALL our usual RV travels here involve LOTS of long, steep grades - and they all seem to be UPHILL both directions! :-laf



I guess the truck/5er overall performance has me spoiled! :-laf:-laf

 

[fox]

The design issue is from the large bore. And long stroke with a short rod. (rod to stroke ratio).

To get a complete burn they held heat in it longer. The factory doesn't want to tighten manufacuting specs to get a good quench. Closed chamber heads will help it it is machined to 35-40 thousands (. 035-. 040) This will really help low end and mileage. I know you don't want to get into it this far.

This is partly why a 360 will out do it.

 

[SRath]

Good grief!
"Inherently bad design, rod to stroke ratio, 360 will outrun it, blah, blah, blah"

The 454 has been around and moving big loads for a long time. from work mules to race engines, it is a very tough motor to beat.

As a tired and/or poorly maintained smog motor, your's is exactly what the government wanted it to be. But the sky, and your wallet, is the limit on what it can do.

My '88 crew cab 4x4 has a TBI 454. At 160k, it still runs pretty good, but "pretty good" isn't enough, and it uses some oil.

Ready to drop in is a new 454 (0. 030 over) with all the goodies for great torque and fuel economy. Built specifically for a big 4x4 or RV. Edelbrock heads, flat top pistons, MUCH better cam, etc. It has @480hp and pushes 700lb/ft torque, will run on pump gas, and uses all required emissions equipment. Fuel economy will also be MUCH better than stock because this engine is efficient; not smothered.

You can do the same to that MH 454. Forget 12:1 if you plan to travel. E85, and 105 octane race gas, is simply too hard to find.

Aftermarket aluminum heads are getting pretty cheap these days and nothing the factory ever produced can compare. Or you could simply find some early 70's heads (forget closed chamber unless you want a high-octane race motor), flat tops, and good RV cam.

Don't put up with a questionable distributor. Don't even dink around with it. Again, the aftermarket has BRAND NEW units ready to drop in for under $75 that are much better built with performance/towing curves. Headers and Flowmasters (if you like nice sound) or at least free flowing mufflers will gain you both power and economy. You cannot beat either an Edelbrock Performer series carb or a well-tuned Q-jet on that motor.

If you have reservations about what to do, visit edelbrock's website and learn about pre-matched Performer packages. They take the guesswork out and match cam, intake, carb, heads, etc. for your specific needs.

For economy, I drive my Cummins, but for "Great truck" and HP, even with the tired old 454, I drive the Chevy.

There is NOTHING wrong with a good, carbureted 454. the question is going to be: What are you willing to do to it and what can you get away with vs. the smog nazis.

I also have a spare 454 on an engine stand that I built for a dually crewcab 4x4 I had. Straightforward, simple, carbed motor with a good cam and pistons and intake, heads, stainless roller rockers, etc. , etc. Some guy stopped one day and started counting out Ben Franklins until I let him leave with the truck, so the motor has no home now. My son keeps working on me to let him put it in his '73 Camaro... But we're doing a nice 355 for that. It's too bad you're so far away, Gary. I'm putting that one up for sale to free up some space and $2k is all it will take to own it.

Thing is, those old Chevy Big and Small blocks are still the best and easiest motors to do whatever you need to. Cheap, too, as far as motors go. Have some fun!

If my old '83 Chevy class C with a 97k on her little ol' 350 sbc can do the trip we just did so reliably, you can do even better with a 454. And no stinkin' mopar 360 will "outdo" a good 454. Sorry fox, but that isn't even realistic.

BTW Gary, I'd be checking for a serious vacuum leak if I were you. Maybe even the distributor's vacuum advance can. That old smog motor you have looks like a spaghetti nightmare with emissions crap; most of it vacuum operated. Those old rubber hoses like to crack and leak, too. Get yourself a good timing light with built-in advance and decent vacuum gauge. Eliminate the easy and obvious first. If the carb has not been previously messed with, LEAVE IT ALONE unless you are an expert! Most "carb problems" are really ignition problems, and ignition includes vacuum for advance. More good carbs and motors have been ruined by neophites with screwdrivers "adjusting" things they do not understand and then pronouncing them "junk" than you can believe.

A vacuum leak will yield POOR power and economy faster than anything else. Every symptom you describe can very well be caused by something that simple. Engine too lean, high temps, no advance, no power, no mpg...

 

[Gary - K7GLD]

SRath - thanks for the interesting info, sorta gets the brain cell (yup, all one of it!) working...



The MH is still too new and untried to us to make any major commitments to, but as time and usage increases, might get motivated to do some upgrading. So far, I've installed new Bilstein shocks and steering stabilizer, TOTALLY rewired the headlights with individual hi/lo relays and 10 ga. wire direct from the batteries - and a replacement freezing unit is on it's way to replace to weak one the MH now has.



Not a whole lot of $$$ involved yet, but sure lots of perspiration on these HOT eastern Oregon days! :-laf:-laf

 

[SRath]

Gary, I was editing and adding on while you posted, so be sure to read the last part now about the vacuum leak. Good luck and don't give up on that motor! If you gotta have a gasser, that's the one you want!

 

[Gary - K7GLD]

Gary, I was editing and adding on while you posted, so be sure to read the last part now about the vacuum leak. Good luck and don't give up on that motor! If you gotta have a gasser, that's the one you want!

Not sure of the pick-off point for the gauge, but this rig has an OEM vacuum gauge installed, and the readings look quite good - about 17 inches at idle, slightly below 15 at light cruise around town - but mostly down in the red below 10 when we hit the grades...



It's undoubtedly a good idea to check all elements around the distributor - I've rebuilt several of these, as well as the Carter and old Rochester 4-barrels - and this engine had a full tuneup just before we got it, including a rebuilt carb - not that that means a whole lot, pretty easy to forget a hose connection during a tuneup... .

 

[Mark31]

Bosses Suburban had the 454 with the TBI system on it, and was always mad when we towed our boats to lake Mohave, when he couldn't keep up with me on Baker grade in my 94 2500HD Ram with the 360 gasser. His father in law was a GM mechanic and went through the engine and found the timing off a tooth. After it was repaired he traded it in for another Suburban (wifes choice) and it still could not keep up with my Dodge. :-laf

I can't imagine my (departed) 98 1500 5. 9 (360) magnum out performing any 454 that could still crank up and run. If it truly was a magnum, my third grade cap pistol was a howitzer. Mark

 

[RVTRKN]

SRath, the 454 was an engine of the old era that is trying to survive the new era of fuel injected motors with computers. They were good engines in the early years and yes you can build one for high HP, but in the stock form they are crap.



If you take the money it takes to do what you are suggesting, you could beef up your CTD and generate twice the HP and torque. Chevy's were the engines to beat after the production Mopar big block Hemi was discontinued in the early 70's. (Big mistake by Chrysler) I am a fan of the old muscle cars Chevy produced and would buy any of them today, but any GM engine, car, truck or Chasse built in the 80's and newer, are junk. All you have to do is lift the hood and see the smog crap were the engine should be, even with the new gassers or Duracraps, you can not see any engine.



In 92 I bought the first fuel injected Dodge Dakota Magnum 318 engine, it was the very first for Dodge and was only in the Dakota. In 94, when I bought my 2500HD Magnum 360 gasser, it was not my first choice but I could not the afford the CTD, those were the best stock gas production engines I have ever driven. (And BTW, you can see the engine) That 454 I out pulled with my 360, every time we went to the lake was the reason my boss tore his 454 down, now I can't explain why GM would of had the timing off a tooth, but it was. Maybe it was for smog, or maybe it was a mistake but it just proves my point about newer GM's.



If I had unlimited money to throw around, it would be to build my 04. 5 CTD.





Gary - K7GLD, there are some inexpensive things you can do to help your 454, I would recommend a larger exhaust and a modified air intake system so it can breath better. (K&N kit for example)

 

[Gary - K7GLD]

Here's a reply I got from over in the IRV2 group - pretty well matches advice here - and is from someone apparently quite close to my own situation:

Nope... . When I picked up the 83 Itasca (33) it was sick and delivered 4. 5 MPG and both ends leaving the Coachell valley (Palm Springs) were 2nd gear only..... Ran hot. . "Ignition timing retarded" so in go the proper ignition center and weights (375 center and 41 weights) which now handed out a 22º mechanical advance and bumped up the base advance from 4º to 10º. You will hafta cut the vacuum advance back to 10º or so... Next step was the "Thorley headers" with 2 1/2 pipes along with some flow masters 70 series mufflers... . Dang near 8 MPG but that was not e'nuf so into the carb for the jet change (73) and the power rods spring which from the factory is setup at 11 inches of manifold vacuum and they pull up and dump a ton of fuel down the primary barrells... Swapped out the 11 spring for a 6 inch spring and now I'm a dab over 9 MPG while towing a Saturn SC2... Once I quit being lazy I'll install a (LM1) fuel sniffer and go from that point. . Enjoy. Jim

 

[SRath]

"SRath, the 454 was an engine of the old era that is trying to survive the new era of fuel injected motors with computers. They were good engines in the early years and yes you can build one for high HP, but in the stock form they are crap. "

All I can say is you never strapped your arse in behind the wheel of an LS6 Chevelle SS then... :-laf

And even the REAL Hemi's (426) were toast when they ran into a chevy with a COPO 427. I respect those motors. The junk they now fool people into buying is living a lie based on the 426 legend when they say "hemi". Pure advertising gimmickry.

There are plenty of good "factory" 454s still on the job. Bring your mighty mopar 360 around sometime. I'll put my tired old TBI 454 up against it for pulling any day. My brother has a "Magnum 360 dodge 4x4". It's a joke! My old '75 chevy 4x4 with a 355 will KICK it's butt all day long. And because it is a computerized piece of crap, there is very little you can do to it.

I get so tired of hearing this new generation sing the praises of high tech junk and speak condescendingly of yesterday's cars, trucks, and motors (like they know anything about them). R. I. P. , "Looky there! How quaint! What is that thing? (The carb or the motor?). Gee, i wonder if they could actually do the speed limit back then... You actually DROVE those cars?!! Where's the ipod and GPS? How could you ever find your way across town without satellite navigation? Are you serious? Not even a heated steering wheel?!!! blah, blah, blah... "

Detroit did NOT go broke when they built REAL cars and trucks with REAL motors that people could both afford ('cause they weren't FORCED to pay for a whole lotta compuerized crap they didn't need) AND work on AND modify.

Detroit sure is broke now, isn't it?

They have not dreamed up, much less manufactured, a vehicle that will ever be considered a "collectible", much less a "muscle car" in decades. They all look alike and they might as well come with the hood welded shut. Pure crap.

If you gotta have FI, then put TPI or TBI on a proven motor like the SBC 350 or BBC 454. Unlike today's motors, they can handle anything...

I own my dodge ONLY because that's how Cummins' come wrapped. As much as I admire the cummins, and I know what they are capable of, the fact remains that there is a true DOG from the mopar factory! 210 HP?
LMAO!!

So why do I, and so many other love them? Because, just like the venerable SBC and BBC of the seventies, there is almost NO LIMIT what you can do to them! And because they are TOUGH!!

Simple is better. Period. Just look how many guys here went back to a 12 valve after trading "up" to a 24 valve with it's computerized crap. I wouldn't own one. Guess I'm just an analog guy in a digital world, but I'll take simple, tried and true over gee-wizmo gizmos any day.