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  Custom Build Crate Motorhome Motors (455 & 403)

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What should you look for in a motor for your GMC?


We here at the Co-op are asked this question often and it's good to be able to say we can answer that question.  The 403 & 455 Olds motors were a perfect choice to produce the considerable torque on a reliable basis that the GMC needs.  In fact, over the years, I have sought to answer this issue.  I was first challenged by a good friend and GMC owner Arch as he likes to be called.    He was attending a rally here in Florida which from Carbondale Ill. is a pretty big deal.  You guessed it, Arch dropped his motor leaving the Rock Crusher Rally so he had Mr. Hook bring his "ole girl" over to our place.  This is a bittersweet part of this business, I got word from Arch last week that his ole girl went under the floor recently.  "Burial at Sea" for this historic vehicle to me somehow feels fitting but anyway on with the information-- Arch wanted a better motor than was available.  he pointed out that there are different requirement pulling a 4500 Toronado and a 12,000 pound GMC.  He wanted something special and this is where our motor program got it's marching orders and from there we sought the best motor for this unique application.  Born from a legitimate pilgrimage to power the GMC best.  Best means more than just the "best motor" but also encompasses economy, reliability, serviceability and of course longevity.  


Motor selection:
First,  first talk about what power plant to consider, to rebuild the motor that the coach has--- change the motor, what would be best.  best in our application needs to include serviceability as a main ingredient.  Unless YOU want to be the diagnostic and repair tech for your coach,  you need to have a drive train that is easily serviced.  "Easily serviced" means more than the ability to get to the component parts.  it must be easily recognized by any tech you may run into on the road.  A service writers job at a repair center is to first determine if the vehicle coming in for service is something they can work on.   Do they have the expertise, tools and equipment, parts and can see that the vehicle has not been modified beyond a reasonable point where they can fix it.  If you an explain that your GMC is nothing more mechanically speaking than a 1976 Toronado, chances are good you will be able to find help.  Will they  feel the same way with a highly modified motor up to even a different motor in the coach?  I would not want to flip that coin!  No, we feel that powering the GMC with the original 403 and 455 Olds motors is the right thing to do.  The right thing for maintenance and repair, the right thing because we feel the folks putting together the GMC had it right.  A 455 Olds motor is an awesome "torque monster".  it hase huge water jackets, a massive crankshaft, a solid valve train and the block, well just try to move one around.  I cut my teeth in motors with the Mopar Hemi and let me tell you that you had better eat your Wheaties is you want to pick up a 455 or a Hemi crankshaft! With the fact that these motors were originally in the coach, thousands were produced for everything from the family 4 door sedan, racing application to our coach-- there are plenty of cores still available and many aftermarket manufacturers are still making parts for the 403 and 455 motors. 

There was a time when we investigated engine swaps to the 454 larger Chevy motors.  After an install we found the modifications were too great and the final outcome was a morphodite that no one on the road would work on!  No, sorry but for my money a moor swap is simply not cost effective and reliable in my book. 

What about Diesel?  There have been some diesel motor swaps and my hat goes off to those who have undertaken this job.  Diesel motors product torque and economy-- 2 things that really do fit our application and they work but again when you think about serviceability on the road and maintenance-- oh and the expense swapping to a diesel, while it may be pretty cool and all, really is not a viable option if you consider the whole picture.  Folks many times do thigs "just because" hey, I do that!  But if you are seeking the best all round solution to the issues, even guys who have done all those exotic motor swaps, even they will usually agree that aqll around, building up the 403 & 455 motors makes the best sense.  No offense to those who have but once again, for my money, diesel is not the answer.

OK, so beating up that question, I hope you understand why I feel the 403 and 455 power plants built up for our unique application is the right decision.

These are our "colors", gun metal grey-- a big hunk of meat to go into your pressure cooker-- I like it!

What does the motor need to do:
Next, to answer the question at the top of the page, you need to first talk about what a power plant in a GMC needs to do.  First and foremost, it needs to be reasonably priced.  Why would I say that first?  The reason for having a GMC is to use it and in using it you need to choose things to do to it considering it's economy.  It takes a long time to justify spending big bucks for a power plant.  You can invest $12,000 into a  455 long block motor, would take a long time to make that cost effective-- no, we need to build a special motor but there also needs to be a budget involved.. Anything can be done with cubic dollars, what happens when you try and build something nice at a reasonable price--- ah, now that's the trick!

Fuel source
A reliable, economic motor for your GMC needs to run well on regular grade gas.  We're going the distance and doing it well as cheaply as possible has to include the cost of the fuel.  We want out motor design to run correctly with the lower grade fuels.  We use special low compression pistons to allow you to get the maximum performance from low octane fuels-- this is a critical issue and one not easy to address. 

Oil supply
The oil formulations available today are changing.  The API (American Petroleum Institute) has compelled because of pressure from our EPA to reduce the zinc/phosphorous (ZDDP) levels in oils so today's oil is actually harmful to our old flat tappet big block motors.  Right now, go do a search for "ZDDP" on the Internet-- if that doesn't scare you-- just like aircraft, we now must specify the fluids that go into our drive system.  A quality motor for today's GMC owner must take into consideration a lower internal friction spec. so you will not be naturally selected out of existence-- I think maybe darwin had a hand at what is happening to our vintage vehicles today.  Our Co-op Koba motors use a roller cam valve train to effectively modify our old war horse motor to use today's oils.  This is an extreme solution to a serious problem which usually puts the cost of a replacement motor out of reach for most of our budgets.  hey, but it has to happen!    We build only roller cam motors for the GMC because we all know we must all adapt ourselves to the future-- anything less and you are kidding yourself!

Best parts for the job and the build

As we have all been drilled in seminars on our parts supply pipeline, parts today are not what they used to be.  We are getting bombarded with cheap prices goods and it's as bad as in any category as it is with rebuilding parts for motors.  Offshore manufacturers and foreign processes and materials are being built.  You cannot assume the part you purchase will fit.  Quality is dubious, I mean how can you tell good products from some of this junk we're getting?  I'm sorry but industrial progress and the chase of the almighty dollar has backfired on us.  Products make you think you can have it all and it be cheaper than you ever thought.  Does this mindset sound familiar? I'm not saying we need titanium pistons and all that, but we can choose wisely on the performance parts that do something while leaving all that icing on the plate.  Our new process now has as a process checking every part for accuracy and quality.  This is so important but time consuming-- but-- and this is the key, this stage of a motor build now MUST happen and thats a big plank in our motor program.  Drew Koba, a contributing editor of Mondello's reference book, will be working with us as our parts source purchaser, QC and builder.  That's right, the architect of our original motor design is now back with us building motors.  Co-op/ Koba motors will be the outcome product of this corroboration.  Drew is a respected performance Olds motor builder and has been doing his thing for years.    Before we met, Drew Koba was building performance motors for specialty Oldsmobile application-- race motors, performance show stuff, just one of those guys you would go to if you wanted a really nice running Oldsmobile motor.  When I asked Drew to help us design what ended up being our custom motor program, he was keenly interested in what might come out of a motor with these design parameters.  He got with another Olds motor guru who together came up with our "Kryptonite cam" which was needed to drive the motor.  Ldet me make this analogy:  A cam is to a motor what the installed program is to your computer.  The cam tells the motor how to act in short, it does not matter how strong you build a motor, it needs the right cam to do it's job.  It may sound silly but the first time I was shown the torque spec of what our motor produced, the word "Kryptonite" came to mind.  You can see at a glance that our torque curve puts power where we need it, just off idle with a top off in the 3000 RPM range.

  Koba motor headers.jpg (148401 bytes)  Koba motor manifolds.jpg (112774 bytes)

Dyno fuel con graph.jpg (64548 bytes)  Fuel consumption graph

Dyno power torque graph.jpg (77279 bytes)   Power/ Torque graph

Just completed is our engine dyno spec. on our 403 "Co-op crate Motor", take a read



And now a comparison chart of horse power & torque on our 455 and our 403


Our motor has at it's brain our Kryptonite cam.  The sum of the parts is much more than it's list, this motor has soul!  Not only is it build rock solid, the thing will be ready to roll.  Taking out from a traffic light in a GMC is like doing a burnout in a car.  We whip our power plants from the word go, any corner cut in the production of a motor in this situation will simply not last.  We have over 70 motors on the road since our motor program began and now we are poised to really ramp up our program. 

The best custom parts for the job and the best builder we could find, now THAT'S what I'm talkn' bout!


OK, so there is a BIG difference when you go to purchase a rebuilt motor.  Your buddy says he's got a friend of his dad who built 455 race boat motors.  While I'm sure he's a great guy, thats not the motor you want and thats not the collection of performance ideas you need to be around.  Another guy says "Motors are motors", just pick up a production motor and roll the dice!  Oh man, putting a production built motor in a GMC is like putting a stock motor on the race track!  Something bad can't help from coming out of that idea!  Ok, so now you pay a deposit and go see a performance engine  builder, you check out all the pictures in the guys office.  He makes you feel maybe that you are in the wrong place-- after all, are you looking to take first place in the race next month?  Should you care that you have chrome plated valve stems?  Hey, I can't see them from the drivers seat but is that important?  You talk to enough motor builders and pretty soon you will throw up your hands and run away!  And the cost of a motor from those folks just does not fit into your budget.  Sometimes you feel like no matter what you do, replacing the motor in your GMC will end up with you on the business end of the stick.  Been there?  Have you felt this pain?  Well, I have and I've been in the middle trying to do the best thing so many times I can tell you there are many pitfalls any of which will ruin your day.

Our long block motors are NOT the cheapest motor you can buy-- there will always be someone saying they can build you a motor cheaper.  But wait-- is that what you want?  Your GMC is not a "cheap" motorhome, it was the high dollar "mac daddy" of it's day.  Motorhomes are not cheap to have and maintain, you do not want a cheap motor in your coach!  Our motors are not high priced when you look at what performance folks charge to have a chunk of their world.  Our longblock motor is still $6500 plus core & shipping.  Yes, it's not the cheapest but just take a look at what it might cost you and it will become apparent what our custom purpose built performance motor has going for it.  We need a good core to build up your motor.  Good core motors are getting scarce, still around but a good 455 or 403 motor is something to hold onto.  We can do great things with a good core.


Quality Control

I don't care what parts are in a motor, it all has to work together!  In high school, my buddy and I thought we were smart and started in on his 340 Duster.  We picked up a pop up this, a roller that and pretty soon that car would never run again!  You've got to know what you're doing when it comes to building up a quality motor.  Does not matter, this is probably THE most important thing needed to produce a quality product.  Drew Koba will be personally assembling our motors, checking every part as the motor goes together.        We will know the pedigree of everything that goes into our motors.  Drew will then assemble each motor one at a time, no production here-- Drew is a stickler for accuracy, each cam is "degreed" in and completed will be delivered to our shop   where we will run every motor breaking in the cam and checking for any problems before it's packed and shipped out.  100% QC is the only way and we will do that ourselves!


The "W" word is one many people do not understand.  Let me help, some companies will produce a product and sell it with something that has less to do with the actual quality of the motor and more to do with a marketing scheme.  There are very few true guarantees in life and the best you can find is someone who builds a quality product and stands behind it.  Forget all they hype, in the end it's the quality of the product and what went into a motor that makes it a great buy.  We warrant our custom built Co-op/ Koba motors for 12 months.  That said, there are just so many things that will efect the quality outcome of your motor more than the motor warranty, we will be with your completely through the installation and set up of your motor.  Just a phone call away and as near as your mailbox, along with out motors comes us-- there are so many factors that go into installing a motor and getting it to run well, I am with you every step of the way-- 24/7, any time you have a question call me direct.  There is a list of things we want you to do that goes along with a quality motor.  Without this complete combination, there is no way you can expect to rely upon your rebuilt motor.  In other words, our motor will work well-- we will help you make this happen.


  Want to know more about our motor program? 

                            Want one of our Co-op/ Koba motors in your coach?

Call me right now (as long as "right now" is not 2 in the morning) and lets talk about it.  Tell me what you have, whats happening and we can come up with a plan.  Our goal is to have motors ready to go, give me a cal land lets figure this out.  321-299-5707


The 26 foot, 12,000 pound Antique Hot Rod with Plumbing -- GMC Motorhome