[Diy_efi] Detuning Motorhomes

Fri Jan 14 15:21:56 UTC 2011

OOPS, More on Intake Manifolds.

Many people have gone to a typical aluminum performance intake. They flow much better, but they don?t fit under the floor. So you need to build a box to fit the intake and be willing to crawl over it every time you get into the driver?s seat. There are also at least two companies making exact replacements for our manifolds in aluminum. They look very nice and should work well and weigh less, but I?ve never used one. 

I should also mention that a large welding / engine rebuilding company in our area crack checks, repairs, welds the exhaust crossovers shut and machines the intake manifold. Welding cast iron is not what I would consider a home process. The company also repairs the front hubs for these GMC?s for the shop by machining off the damaged or undersized bearing ID and underwater spray welding new material to the hub. Then they machine the bearing ID surface to a tighter tolerance and re-machine the half shaft splines that shrink in the welding process. It all makes for a nice tight front bearing assembly.

From: diy_efi-bounces at diy-efi.org [mailto:diy_efi-bounces at diy-efi.org] On Behalf Of Aaron
Sent: Friday, January 14, 2011 10:02 AM
To: diy_efi at diy-efi.org
Subject: Re: [Diy_efi] Detuning Motorhomes

Next, let?s talk about the intake manifold.

Frankly, the OEM 75 lbs cast iron monster sucks. It was designed to allow the Old big block to fit under the hood of the Toronado. The carb base sits a full 2+ inches below other Olds big block manifolds. That added to the severe angles the air fuel mix has to travel to get to the valves. And as we all know, in a wet manifold as soon as you turn the air fuel mix, the fuel wants to keep going straight, then pools in the corners. Also, the exhaust crossover under the manifold was pushed further into the cam shaft valley. Since it?s a big block making lots of heat stuffed into an engine compartment with marginal air flow for cooling. Things get hot. I?ve removed coffee can filling  carbon bricks from the bottom of the manifold and the OEM steel intake gasket / valley pan. Another thing about the intake manifold crossover is how close it is to the bottom of the carb. Think cold fuel slamming onto hot cast iron. Both the 455 and 403 crack in this area and let exhaust into the intake in high vacuum conditions.

6. Have the intake checked for cracks. Usually the intake crack at the exhaust crossover directly under the carb base. They can also crack around the EGR port that is used for the choke stove. I even had some cracked down the secondary throttle wall starting from the carb base.

7. Have the exhaust crossover ports welded shut. Losing the heat under the carb base does not affect the cold starting of these beast. True the choke setting of a carburetor stays on longer, but the loss of fuel savings at cold start up seems worth the gain in not having gaskets cooked or creating carbon gravel in the oil. Mondello sells a cast iron plug that can be wedged into the head. I?d tried those before having the intakes welded shut. They work, but everyone I ever install came loose and rattled with every exhaust pulse. Sounds like a rod knock.

8. Use the thick two piece intake gaskets that are not made from steel and do not have the valley pan. If you?ve closed off the exhaust crossover, these will help keep more heat out off the intake manifold.

9. Watch the adapter plates closely. The adapters that change the spread bore to a GM TBI and even the square flange bolt pattern don?t always fit correctly. Pay close attention to the spread bore gaskets. Some leave a gap on the secondary bores, which makes for a fun intermittent vacuum leak. Also the TBI IAC on some kits hangs over the plate leaving the gasket flapping in the wind. The TBI IAC may also run over one of the rear bolt heads for the adapter plate. This also doesn?t seal well.

10. The GM TBI adapter plates move the center of the air filter toward the distributor. With the large diameter HEI cap and the air filter housing bump into each other. You could use an aftermarket open air filter, but I find them loud at WOT and they suck a lot of hot engine compartment air. I use a calibrated tapometer (hammer) to increase size the existing relief in the lower part of the steel OEM air filter housing.

More tomorrow.

From: diy_efi-bounces at diy-efi.org [mailto:diy_efi-bounces at diy-efi.org] On Behalf Of Aaron
Sent: Thursday, January 13, 2011 3:49 PM
To: diy_efi at diy-efi.org
Subject: [Diy_efi] Detuning Motorhomes

I would love to.

Mostly I like to hear myself type and since I?m at work, it beats working.

First, I?ve always installed kits. I?m lazy that way and I don?t have to make wiring harnesses.

The kits include Howell Fuel Injection, Turbo City, Holley Projection and Holley Commander 950.

The Howell and Turbo City are 7747 GM ECU?s with GM or Holley OEM TBI units.

The Holley Projection was a flakey P.O.S. analog ECU with a two barrel TBI. The O2 sensor for closed loop is an extra cost. I hated them so much I REFUSE to discuss them further.

The last is the Holley Commander 950 with a digital ECU with software and a 4 barrel TBI.

And although I did not help with the install many GMC owners switch 7747 GM ECU with the internal board from Dynamic EFI. One of these gentlemen also went to multi port injection.

Cost is all over the board. Everyone has a web page. I recommend checking them all out.

As for the conversion, let?s start with the fuel system.

1.       You need to block off the mechanical fuel pump hole. The cam mounted eccentric can and should stay.

2.       I strongly recommend dropping the tanks and adding a return port to the top of the front tank. First it gives you a good chance to check / replace your fuel lines. There are four sizes and all told something like 75 feet of rubber. Second, it puts all the returning fuel into the front tank. The front tank is the reserve tank. We you flip the switch on the dash to reserve, this is the sending unit / pickup it switches to. I have followed instructions that put the return into the fuel fill pipe under the driver?s seat. It?s an easier way of installing, but I don?t like driving them that way. If you dump the return from the TBI into the fill, some of the fuel goes to the front tank, some to the back. I typically drive until I need to use the reserve tank then start looking for gas. With no control over the tank that is filling extra fuel is returned to the rear tank quickly. I end up having to flip the switch several times to get to the gas station. If the fuel is dumped into the front tank, I don?t have to flip around to find all the fuel in my tanks.

3.       High quality rubber fuel line is fine for the install. I?ve tried new steel brake tubing along the frame in the past, but I?m concerned that they may pick up too much heat from the road. I do however use steel tubing to run the fuel up the back of the engine compartment to the TBI, then use a short rubber spacer for the last connection. S.S. Braided line with hydraulic fittings are the best, but very expensive.

4.       I typically run one High volume / low pressure fuel pump, like the Carter 4600 rotary style, to feed the high pressure EFI pump. Since EFI pumps don?t like to suck fuel and the pick up from the rear tank is 10? away, I give it help. Trying to diagnose a fuel pump sucking itself into vapor lock is NOT fun. Some people run four pump total. One for each tank. I?ve never had any issues with my setup connected after the fuel switcher on the frame rail.

5.       I typically run two fuel filters. A lower pressure filter after the low pressure pump and a high filter after the high pressure pump. The Carter pumps were original equipment on the Willy?s military jeeps. The amount of trash these pumps can handle is remarkable, so I?ve never worried about filtering them beyond the screen / sock on the pickup.

If you pull the tanks on a 73 or 74, they do NOT have installation on the underside of the floor boards. The 75 to 78 have an aluminum sheet with a foam backing that will expand with age and heat. If you replace your rubber fuel lines, look closely for any place the insulation has flattened the old rubber. It?s usually the vent line, which does NOT help our fuel filling experience. 

OK I?ve got to go back to work.

I?ll write more tomorrow.

From: TomC [mailto:tcsibor at valrox.com] 
Sent: Wednesday, January 12, 2011 8:48 PM
To: Aaron
Subject: Re: [Diy_efi] sorry + list on holiday ?

Aaron,

I have 2 of those motor homes and my neighbor has one also. Ours are 1973 and 1977 models so have the 455 rather than the 403. Would you mind telling me a bit about the conversion? Any problems? Costs? Gotchas?

Thank you
TomC

On 1/12/2011 5:18 AM, Aaron wrote: 

It?s quiet, very quiet, almost too quiet.

So I feel the need to share a recent story.

This past year I help tune a Holley Commander 950 put on a 78 GMC motorhome with a 403 Olds  engine.

I was impressed with the way it ran. 

But the customer was not.

He has come back to the shop owner I was helping and complained about the power level at take off.

Seems he keeps spinning the tires leaving the stop light.

He ask if we could de-tune his motorhome.

????

De-tune a MOTORHOME !

Now that?s now a phrase I thought I?d be saying.

From: diy_efi-bounces at diy-efi.org [mailto:diy_efi-bounces at diy-efi.org] On Behalf Of Dan
Sent: Wednesday, January 12, 2011 2:14 AM
To: diy_efi at diy-efi.org
Subject: Re: [Diy_efi] sorry + list on holiday ?

Wohoo, I win. Found it in the spam box
On a different note, has this list gone very quiet, or am I just not getting the emails ?

Dan

  _____  

From: Bill Shaw  <mailto:b.shaw at comcast.net> <b.shaw at comcast.net>
To: diy_efi at diy-efi.org
Sent: Wed, January 12, 2011 12:32:26 AM
Subject: Re: [Diy_efi] sorry

Why do I always get left out?  I didn't get one either!

Bill

On 1/11/2011 10:31 AM, Aaron wrote: 

I did not get an email, but I?d be willing to give you grief about it if you?d like.

From: diy_efi-bounces at diy-efi.org [mailto:diy_efi-bounces at diy-efi.org] On Behalf Of Jay Rabe
Sent: Tuesday, January 11, 2011 9:36 AM
To: Do It Yourself fuel injection
Subject: [Diy_efi] sorry

My gmail just got hacked and im pretty sure you guys got a message starting "hows the weather today?"  Please disregard and delete it.  I changed my password already.

Sorry for the inconvenience.

Jay

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-- 
Tom Csibor 559-474-4590

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