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IPM 08-12-2003 07:14 AM

'81 454 prevenative maint. & upgrades

I bought my motorhome in October 2002 and joined the walley club. Member Number 7006.

Here's what I've done to the big block. Some is prevenative maint. and the rest upgrades. I'll start with potential improvement comments and then note the completed work.

Went to the Galax ralley. During the drive I noted a large increase in pulling torque, especially when the stock cam comes on strong at 3000 rpm. Coolant temperatures at steady cruising with ac on and 85F dropped from 220F to 180F and below.

I think there's much more potential improvement for the spark timing and fuel delivery. For the spark I'm considering upgrade to '90 vintage or later stock GM engine management. Get the harness and ECU from a pick and pull. This would provide knock sensor referenced, spark mapped to RPM, load, temp, etc. instead of just mechanical/rpm and mechanical vacuum/load. There's cheap shareware and freeware out there to tune better than stock for these GM systems with a laptop and eprom burner. (WEB LINK Reference Reading -

It would also then be easy to swap to TBI for fuel. The quadrajet seems to be inefficient at lower RPM's. I like quadrajets but TBI is so much easier to tune/measure/monitor/change/adjust.

ac compressor - 134a swap also
water pump
fuel pump
power steering and brakes pump
fan clutch
oil cooler - used turbo volvo 740 unit and moved in front of passenger side wheel
oil cooler lines - Napa cloth brades hoses, approx. $4/ft.
spark plugs - bosch copper
spark plug wires - generic
rocker cover gaskets
oil cooler adapter gaskets
exhaust manifolds - headman headers from Summitracingonline
one pair flowmaster mufflers
DIY dual exhaust via 2.25" pipe and a torch
all coolant hoses
temp regulator - 180 installed
radiator cleaned and flow checked
fuel tank fittings resealed and rubber fuel lines replaced
coil, cap, rotor for dizzy
timing set to stock

Transmission cooler - same location as engine oil cooler
separate DC fan for transmission and engine cooler.

I'm considering installing a set of variable duration Rhoads lifters to improve torque responce below 300rpm.

Could I please have your comments, suggestions, question, concerns, advice, shared experiences regarding the 454 big block in a classic motor home?


Mike Rosendale

59toaster 08-12-2003 08:11 AM

Honestly the Quad CAN be tuned to work very well. There are several folks posting here that say they are getting 11-12 mpg with their MH. My pull truck for our Airstream is a 88 454 Subruban with a TH400. I barely get 10 mpg. I have put it on a exhaust analyizer thing I had misxture problems and I don't. The Quad just seems to do a little better once it gets up to cruise. I think it leans out a hair more then the FI does.

As for converting. I'm about to under go this conversion on one of my trucks. It's possible to do but there are some vairables you need to be aware of. The cam in your engine is a different grind then what a 454 that was set up for FI is. Knock sensors are not all the same. They are tuned to the block.

Vehicles I would recomend as a doaner would be 87-91 GM Suburbans and Crew cabs with the 454. The 454 throttle body with the preheat riser is a bolt on in place of a carb. The 350cid version is not. The FI in these trucks was almost like a aftermarket FI set up. THe main harness is completely seperat from the rest of the vehicles harness. 87-85 454 van would also be a simular set up.

If you want to save yourself a lot of hassle then contact This guy has a small buisness where if pulls used FI, Flow tests the injectors, makes a NEW harness and sells it as a kit. He can custom tailor a chip to work with that cam. He also has a link to WinADSL shareware. This is a program you can install on a lap top and plug into the test port and get real time ECM readings. You can also data log it and he can fine tune the chip to the engine from that information.
Tell him the guy From ColoradK5 sent you. :D

I'm about to get him to put me together a system for my 4x4.

59toaster 08-12-2003 08:13 AM

heck I should have clicked you link. You got half the information I posted right there. :D

IPM 08-12-2003 08:17 AM

Hey 59 toaster, thanx for the doaner

59toaster 08-12-2003 09:00 AM

Re: Hey 59 toaster, thanx for the doaner

Originally posted by IPM
No problem.

Ohh one other thing I ment to tell you. 90 or 91 is when they started running the 4l80. The ECU on those models drove both the FI and the transmission. Before that it was the the TH400 or TH475. The ECM is going to have to be reprogramed for sure if the truck had a 4L80. It will throw codes and might even kick into limp mode Thinking it had a transmission failure. If the doaner had the TH400 you might actully get away with out programming. Hard call till you get it on there and see how it reacts to the cam.

TH400 has electric kick down. On your MH there will be a trigger switch on the throttle. Most likely right at the peddle. On a FI set up that switch is not there. It's triggered by the ECM. You could leave it as is or you could tie it into the ECM. The gain to tieing into the ECM would be if the ECM sees the engine coming under load at a lower throttle input it will down shift the transmission earlier on it's own.

On my burb at lower speeds like around 40 it will down shift out of 3rd at half throttle with not much more delay then if I had gone full throttle for passing gear.

I had inadvertently knocked the wire off the tranny and it would not do the same thing without that input on the modulator alone. In fact once it was in 3rd it would stay there untill I stopped. With the ecm it will actully down shift on deceleraton out of 3 down to second at about 20-25 mph. So it's a pretty nice feature that I personnally would hook up if possible. Should be able to tie into the stock relay but the TH400 doaner you will find a pair of relays allready on the harness. One is the TH400 kick down and the second is the fuel pump relay. They mount on the fire wall to the left of the distributor (as facing engine in truck).

IPM 08-12-2003 09:54 AM

Wow, you really have this worked
out - thought out! Thanx for the tips. I did not consider the tranny.

I plan on using tunercat for reprograming. Picked up an s4 dataman on ebay for $100, a couple of old laptops on ebay, several eproms on ebay, moates adapters, aldl to laptop connector, uv eraser from dataman.

customefis' diy book is great! That's what got me started.


dinoburb 08-12-2003 06:32 PM

I read with interest your items replaced or repaired on your 454. I would rethink the headmann headers and look at Doug Thorley 'Tri-Y' Headers. These are designed to add torque in the mid and low rpm rangs. The pipe diameter is smaller than most performance headers and the tri-y design flows beautifully.

TBI with the proper manifold ( Edelbrock Performer) and the Thorley headers is a 60% solution, and not a bad one either. However, adding a cam designed for torque will make the engine come alive. Crane's 266 or 260 cam (dual pattern) for the BB chevy will fit the bill nicely.

Dual 2.25's are excellent, but make sure there is a properly designed and added crossover pipe to smooth the engine and add some power.

One item that should be replaced to truely complete the job would be a new distributor. This item is most overlooked and can cause many of the runnability problems found in engines with some miles on them. Adding MSD or Jacobsen ignition systems, designed for off-road or tow vehicles will work wonders with the low and mid range driveability. Multiple sparks between idle to 3000 really makes a difference.

I have done much of the above and I've added a pair of early 454 large oval port heads with stock size valves and I have been able to power my way through much of what would have stopped the original 454 230HP engine. I have no idea of the HP the engine is producing but it is much more than stock and the torque is significantly better at all RPM's. I'm using a Holley 950 FI system but I had a JET built Q-Jet on the engine first and it ran very well. The Holley FI allows more adjustability and the engine runs somewhat smoother. It's a toss up as the Q-jet solution is 4X less expensive than the FI and runs nearly as well. If you go the carb route purchase a properly rebuilt model or a new one from Edelbrock.. Old carbs have numerous problems the most troublesome being vacuum leaks past the throttle shafts. A real PITA to diagnose and correct!

I hope the above is of some help.

Take care,


IPM 08-12-2003 07:59 PM

thanx for the info Sean
All the advice is good and should be added in the future.

The spark is definately weak. And TBI is a must, but I'll likely pull a stock gm engine mangement system to keep it cheap. There's a pick and pull outfit that has two yards here and one near you in virginia beach near the airbase. One can walk out with all the pieces cheap. About $25 for the tbi, $25 for the ecu, and they usually don't charge for the harness, small sensors, relays, etc. The stock dizzy can be reused since it already has the magnetic pickup. $25 if I take the donar dizzy with it's connectors, etc. Then later add the multiple spark. Unfortuately, the 350 tbi's are much more common in those yards than the 454's. Might have to mix and match as necessary. And exercise alot of patience living with the old stuff while gathering the parts.

I'll have to add a crossover pipe, but will keep the headmans since they are already installed.

I'm still pondering rhoads lifters instead of the better option of a new cam. This stock engine only has 40k on it. So the heads and cam would have to wait. Would not want to drop the radiator again either so soon. A better intake would be logical for immediate install if I were to add the rhoads lifters soon.

But the fuel and spark improvements will come first. Part of my fun is doing this stuff cheaply as possible.



59toaster 08-12-2003 08:21 PM

Those prices are awsome! I paid $200 for they system I have. That was complete except for the fuel pump.
It included
EGR control solonoid
VSS ( that is not going to work on my truck)
Throttle body
It all came off a 89 454 burb.

Parts I will need to get is a VSS that will still allow my cable drive speedo to function. The VSS needs to produce roughly 2000 pulses per mile
Knock sensor for a 350 (this is going on my toy truck).
I want to go with a frame mounted fuel pump for servicablility reasons.
Need to drop the tank and install a 1/2 inch return line.

I actually have two ECM's and harnesses. The 454 ecm I will be keeping as a back up for my Burb. It should plug and play. I have a 350 ECM that will go on the truck. Hope to get started on it in the next couple weeks.

I plan to do a write up. It will be posted on I'll let you know when I get it up on hte site.

IPM 08-13-2003 10:39 AM

59toaster, You will finish before I do!
So I'd love to continue to hear more about your project.

For fuel pump I was planning to pull from a ford the unit identified by custumefis for aprrox. $15.

I was going to try "switching" off the vss code and see if it works out.

Thanx for the tank return line reminder. I have to drop the tank to unstick the fuel level float and will add a fitting and line at that time.



IPM 09-02-2003 11:29 AM

Well, I've done more camping and
driving. I may delay the efi enginemenagement conversion to the next airstream. I think I want a rear bedroom; this unit is rear bath. Let's just see how long it takes to find another desireable motorhome. And how long I can stand the quadrajet and mechanical spark.

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