GM 454 power/MPG issues

[Gary - K7GLD]

First step will be tweaking the OEM distributor for more advance - seems pretty retarded as it currently is - the older TH400 had no O/D or converter lockup, so unfortunately, no help there. Rig already has a "cold air intake" - the mice and pack rats love it, judging by the nests I found inside the air cleaner cover. :-laf



Got a timing light coming - tossed the older ones I had when we moved here - the diesel and newer computerized vehicles don't need them - didn't think I'd be puttering around with another Dinosaur... :-laf

 

[MMeier]

Well, the Carb guy SRath pointed me to didn't figure much advantage in going into the Quadrajet, since it was just newly rebuilt - I bought one of the fancy and VERY reasonably priced distributors pointed to further above - will wait a bit before deciding what or where to dig in next, engine wise. MH goes to shop Wednesday for transmission service, and I went ahead and ordered new Bilsteins for the rear of the MH, since my impression on the short drive I took was that the front ones helped.



I'm pretty convinced that gains are available if the timing could be advanced - but as far as I can see. it's virtually IMPOSSIBLE to check timing in a conventional manner - the front of the engine is totally covered by the dashboard overhang, and the fan shroud finishes off THAT avenue - must be some other way to do it - will check over on IRV2, and get ideas, unless some here have been down that road, and can pass me a clue...

Didn't some of those gasser motorhomes have a special bellhousing that had an access hole to time the engine back there when you yank the doghouse off?

 

[Gary - K7GLD]

Didn't some of those gasser motorhomes have a special bellhousing that had an access hole to time the engine back there when you yank the doghouse off?

Turns out, this engine has a timing tab on the UNDERSIDE of the engine, pretty easily viewed from behind the front crossmember - just hadn't been that far back under the front of the MH to see it there. One apparently knowledgeable guy over in the IRV2 forum, said that one difference when using that lower position, was that it required use of cylinder #5 for the timing light, rather than #1 as is used for the "normal" topside timing tab - still would like some confirmation on that one...

 

[RVTRKN]

Gary, hand crank your engine to TDC for the #5 cylinder and the lower tab you are talking about should be on or very near the tab.

 

[Gary - K7GLD]

Gary, hand crank your engine to TDC for the #5 cylinder and the lower tab you are talking about should be on or very near the tab.

Well JEEZE!



ANYONE could do it THAT way - *I* wuz looking for the EASY way out - someone ELSE'S experience! :-laf:-laf



And, of course, all I need do is hook up the light to #5, see if any dampener marks are anywhere close, if not, go to #1...

 

[AClayton]

Gary,



I did some up-to-date testing on my MH this past week for a general rule of thumb for you. My rig is 35' long and has 2 slides and I tow a 3800lb. Honda CRV... . MH is 17. 8K un-loaded and will assume 20K loaded the way my wife packs:-{}Last week I left for Huntsville,Alabama from my home in DC metro area and drove at a very consistent 65mph. Grades on I-81 can be bad but certainly not as bad as the NW... . but on the way south I achieved 8. 2mpg. Oddly enough... . the way back only rendered 7. 9mpg. Tach in MH at 65mph says 2200rpm. An occasional downshift to 4th on my Allison sends the R's to a comfortable 3300. I have the Banks kit with 3" 70 series flowmasters with 3" pipes all the way back. The headers are stainless steel and have an H-pipe aft of the collectors to even out the exhaust pulses.



Those numbers are hand-calculated and the dash claimed I was getting almost 9mpg..... a little off I'd say!!My RV seldom lacks power and can easily climb even the nastiest grades with confidence.



I did some checking on the Banks Website and called my salesman and he said the kit for your rig is $2200. 00 bucks. A lot of money I know,but the kit is dyno tuned and it will help your engine breathe much better..... AND Banks is a proven name among the MH crowd. Go to any Campground and ask an RV owner about Banks or who is Banks..... I bet they all know. I firmly believe you should be able to at least hit the 9 mark..... maybe close to 10 with all the upgrades and distributor work.



Good luck - Alan

 

[Gary - K7GLD]

I sure appreciate the up to date info Alan - and your setup is obviously doing lots better than what mine has done so far in both power and MPG! My new hi-performance distributor showed up today ( a BEAUTY!), and the timing light I ordered should show up later this week, then some basic engine tuning can begin. I assume the later 454 engines with the fuel injection and O/D trannies will do better than the older stuff - but doubt that is all that's holding mine back - so will have a project to work on for a while! :-laf

 

[SRath]

Gary, The FI, especially TBI, is not that much better than a well-tuned carb, ime. Edelbrock and Holley both offer stand-alone TPI if you have your heart set on computerizing. At least with their systems, you aren't shackled by factory low-performance computer parameters.



I hope you didn't get their last distributor at that price! I still need to order one for the kid's '73 Camaro. You will have all the spark and accuracy you need with that distributor.



Banks systems are good, but very pricey and certainly NOT unique. You can accomplish the same thing through careful matching of components or other manufacturer's "kits" for less money. Just like with these Cummins motors.



A good RV cam, flatop pistons, (I like stainless roller rockers, too), a nice Eddy Performer dual plane intake, and a Q-jet or Edelbrock carb (stay away from Holleys if you want mpg), headers, dual exhaust with crossover and free-flow mufflers, and that distributor will all combine to wake that Rat motor right up! Heads are a big ticket item, but heads also give you the most improvement. Especially aftermarket aluminum heads. But older, pre-smog, stock heads reworked well will also do an admirable job. You can't go wrong with an Edelbrock Performer Package on a properly built shortblock or longblock. Even those packages can be more or less duplicated with less expensive, hand-picked parts. I have done it both ways.



Grandpa's MH is going to raise some eyebrows with a motor and sound like that! Especailly when you kick 'er down into passing gear and the Big Rat roars!



I sure wish you lived closer! I have the longblock and intake you need sitting homeless on an engine stand right now... I even have some new headers, but they are for a Chevy pickup and I couldn't guarantee they'd fit a MH.

 

[AClayton]

Scott... . I totally agree with you. Based on reading many of Gary's post's,I suggested the Banks kit due to cost reasons and for simplifying performance upgrades without the hassle of trying and removing different hi-po parts. It is MH specific and takes the guessing out of it.



IMO,any exhaust upgrade combined with the dist. he bought will render outstanding results.



Alan

 

[Gary - K7GLD]

My reluctance on the exhaust setup, is because the MH already has some pretty good 2 1/4 dual pipes, and headers that look sorta aftermarket - definitely NOT cast iron, but a welded tube header style - but they ARE marred by the EGR tubes restriction.



While what's currently on there isn't as good as full, purpose-built duals, they should be close enough to place them a bit lower in priority than the distributor and possibly the carb for now. The timing light showed up today - but a sore back sorta prevents me from dashing out and throwing myself under the MH to check and adjust timing - maybe tomorrow.



Scott - should be more of those distributors, they sure LOOK nice, and what a bargain!



BUT, if they ARE all gone - might swap you mine for that GM 454 you have there on the stand! :-laf

 

[Soot4Life]

After spending mucho $$$ on attempts to get my 94 454 Itasca to get off the porch & run with the big dogs I found what others here have found... . I needed a:
intake that breaths (K&N or similar)
quality headers (Edelbrock on mine) with free flow exhaust
top quality distributor... no discount heartbreakers
vacuum lines changed almost every year... it gets hot under the dog house
efficient torque converter & deep pan

I decided I didn't want to invest any additional $$ on a rig that doesn't log that many miles per year. I still only get 8 mph pulling my horse trailer but pull it does. I'm now planning on selling the MH and putting a simple shell on my Dodge. A bed roll, Coleman, and an ice chest works fine for me. The wife wanted the MH.

 

[Gary - K7GLD]

After spending mucho $$$ on attempts to get my 94 454 Itasca to get off the porch & run with the big dogs I found what others here have found... . I needed a:

intake that breaths (K&N or similar)

quality headers (Edelbrock on mine) with free flow exhaust

top quality distributor... no discount heartbreakers

vacuum lines changed almost every year... it gets hot under the dog house

efficient torque converter & deep pan



I decided I didn't want to invest any additional $$ on a rig that doesn't log that many miles per year. I still only get 8 mph pulling my horse trailer but pull it does. I'm now planning on selling the MH and putting a simple shell on my Dodge. A bed roll, Coleman, and an ice chest works fine for me. The wife wanted the MH.

"I decided I didn't want to invest any additional $$ on a rig that doesn't log that many miles per year. "



YUP - my situation exactly! This is pretty much a local use vehicle - and it would take a long time to recover even the cost of a good exhaust system in MPG savings - that's why so far, I'm focusing upon the cheaper/easier "fixes" to see what can be accomplished.



Another reason I'm hesitant on a full-bore performance exhaust is, there's no place within nearly 300 miles round trip from here equipped for the job on a MH - and added to that, is the smog pump setup and the related plumbing into the exhaust system. I doubt an aftermarket "performance" setup woul provide for that - and if I then needed to remove ALL the emissions stuff, that's quite a job, and leaves me pretty vulnerable if this county ever decided to require smog checks for stuff like this MH...



Our '88 already has the K&N, along with a "cool air" intake duct to feed it. The timing light I ordered arrived, timing had been set to 4 degrees BTDC static, and I moved it to a nudge over 10 BTDC - no signs of pinging, little more vacuum, and pulled the hills better on the fishing trip we returned from this afternoon, CAREFULLY checked the MPG - FULLY topped off the tank before and after the trip - 110 miles round trip, about 40 of those are steep 45 MPH winding road, so lots of 2nd range used - but did pull longer steep straights in 3rd range (no O/D in this transmission), as long as I could keep speed up to 55 MPH or so to keep engine in it's power band.



Bottom line - exactly 7 MPG. Not great by any means - but better than the previous 5 MPG I thought I was getting - but much of that was failure to properly fill the tank to the fill neck - this thing's worse to completely fill than our trucks, and will take another 10 Gallons AFTER you THINK it's full...



I'd sure love to try this thing out in the flatlands - but that may take a while, and this fishing trip is pretty typical of most of the type terrain we will usually travel. Then too - the old '76 Winnebago 22 footer we had with the Dodge 440, didn't seem to make ANY difference whether the road was flat OR steep - it got 5 MPG, and that was IT!



Not sure exactly where to go next with this - might be a little more timing advance left - but better be careful - and it seems the kick-down is not operating, if I mash the throttle at lower speeds - 30-40 MPH or so - the transmission stays in direct range, unless I manually shift down. No mechanical linkage I can see, so the kick down function must be totally controlled by the engine vacuum/modulator?



(EDIT) I find that the TH400 kick down function is electrically operated, probably off the throttle linkage near the accelerator pedal - will check tomorrow...

 

[MMeier]

Gary, might be wrong, but IIRC, the kickdown switch is by the carb linkage.

 

[Gary - K7GLD]

Gary, might be wrong, but IIRC, the kickdown switch is by the carb linkage.

It varies by year and vehicle model - the one in our '88 MH is mounted on the accelerator pedal linkage right at the firewall. It isn't even close to making any contact with the linkage - probably never has, but the switch checks out OK, and I'll get around to properly positioning it so it activates only close to WOT.

 

[SRath]

Gary, You still need to definitely check the vacuum modulator for the kickdown as I mentioned before. That is a common source of vacuum leaks, not to mention it won't kick down when you need it to. Either the vacuum line or the modulator itself can be bad. Generally, it is metal line most all the way with just a short length of rubber hose at each end to connect.

The electrical kickdown switch could be either by the carb linkage or down on the accelerator pedal. Soot4Life gets pretty good mileage considering how heavy a horse trailer is.

There are headers available for your application, Gary. Complete with smog tube fittings if needed. Simply going to a basic do-it-yourself dual exhaust from the stock manifolds back will also help if you do not want to deal with headers. One nice thing about a MH is all the wide open space underneath to route exhaust without a need for bends.

8 mpg is not terrible in steep terrain, but I'll bet you could get a little more. It is tough to evaluate fuel economy in the mountains. So many variables. With a MH, just a little wind from the front or sides makes a huge difference.