Disabled 4 cylinders on a TBI motor :) MPG Gain???

[Jims86]

Better take the spark plugs out, with no valves opening the suction and compression from those pistons has to go somewhere.

No, you want that compression to balance it out, otherwise it idles really choppy. Acts like a spring.

a guy did this to a carbed Cadillac in the 60s or 70s...got over 30 mpg. oil companies caught wind of it and he, or his project were never heard from again.
For carbed, just take the pushrods out of the cylinders you want to disable. I think 2,3,5, and 8 are what people usually run on when this is done.
dunno if it will work with 1,4,6, and 7.
The carb is no worry...there will be no vac on the disabled side to draw fuel.

 

[Shawn]

There is no reason it wouldn't work on a carbed motor but the disabled cylinders need to have their valves closed. If you have one cylinder with an intake valve that won't close/seal, it's gonna shake and do some weird stuff! Not to mention it will eventually backfire in the disabled intake tract. the disabled half of the intake, even in the carbureted ones, is still connected by small passages in the base of the carburetor and possibly the intake so your cylinder with a non sealing intake valve will allow flow in and out of that cylinder from the side in use and if your ignition system is still intact it will eventually light off. That in and out from one side to the other will also jack with the "signal" the venturis need to work right on the side in service.

By a bad intake I mean I had a bent rod and the valve was worn off where the rocker had slipped off to the left. If I just pull both intake and exhaust I could run on 7? What do I need to do with the spark?

 

[jpoole]

Better take the spark plugs out, with no valves opening the suction and compression from those pistons has to go somewhere.

What is compressed just pushes back down. It's how all the late model manufacturers are doing it. I just cant switch mine back without a lil effort. The plugs stay put. You know I'm driving it right? This is my fourth night to drive it to work

 

[HotRodPC]

Off-topic for shawn

By a bad intake I mean I had a bent rod and the valve was worn off where the rocker had slipped off to the left. If I just pull both intake and exhaust I could run on 7? What do I need to do with the spark?

I hate to make the suggestion for you, cuz it's purely nothing more than a patch job, and will be short lived. Remove the rocker. Get a angle grinder. Grind that valve tip flat as you visibly can, and replace the rocker with a different one. So long as you have enough meat to keep the valve keeper in place, you should be good to go.

If you can't get to the valve tip with the wheel, with the spring and retainer on, then bring the piston almost all the way up. Pull the spark plug. Shove some nylon rope in the cylinder and fill it up. Then bring the piston the rest of the way up. This will squeeze that rope up tight against the valves and hold the valves up in the head. Get one of those on the motor valve spring remover tools, I think they're about $10. Remove the keeper, retainer and spring. Now you should have plenty of room to grind that valve tip flat and smooth. Once smoothe and flat, reassemble, let your piston back down, pull the nylon rope out, replace rocker and rock on. I'd say you can expect 10-15,000 miles out of it before the valve tip starts getting nasty again.

 

[jpoole]

No, you want that compression to balance it out, otherwise it idles really choppy. Acts like a spring.

a guy did this to a carbed Cadillac in the 60s or 70s...got over 30 mpg. oil companies caught wind of it and he, or his project were never heard from again.
For carbed, just take the pushrods out of the cylinders you want to disable. I think 2,3,5, and 8 are what people usually run on when this is done.
dunno if it will work with 1,4,6, and 7.
The carb is no worry...there will be no vac on the disabled side to draw fuel.

I know for a fact there are passages that tie the left and right side together on the Tbi dual plane intake. Im pretty sure the carb intake is the same as far as where the egr dumps in which ties both sides together.My brake booster gets its vacuum off one of the disabled runners. 1,4,6,7 are the ones I have disabled. It doesn't matter as long as its every other one in the firing order

 

[Jims86]

I know for a fact there are passages that tie the left and right side together on the Tbi dual plane intake. Im pretty sure the carb intake is the same as far as where the egr dumps in which ties both sides together.My brake booster gets its vacuum off one of the disabled runners. 1,4,6,7 are the ones I have disabled. It doesn't matter as long as its every other one in the firing order

Yeah, your right....would be good to plug it...if he has EGR.

 

[MrMarty51]

I hate to make the suggestion for you, cuz it's purely nothing more than a patch job, and will be short lived. Remove the rocker. Get a angle grinder. Grind that valve tip flat as you visibly can, and replace the rocker with a different one. So long as you have enough meat to keep the valve keeper in place, you should be good to go.

If you can't get to the valve tip with the wheel, with the spring and retainer on, then bring the piston almost all the way up. Pull the spark plug. Shove some nylon rope in the cylinder and fill it up. Then bring the piston the rest of the way up. This will squeeze that rope up tight against the valves and hold the valves up in the head. Get one of those on the motor valve spring remover tools, I think they're about $10. Remove the keeper, retainer and spring. Now you should have plenty of room to grind that valve tip flat and smooth. Once smoothe and flat, reassemble, let your piston back down, pull the nylon rope out, replace rocker and rock on. I'd say you can expect 10-15,000 miles out of it before the valve tip starts getting nasty again.

Disconnect the battery before performing this operation.
A guy here, was roping the cylinders to replace the valve stem seals. Thought He`d speed up the operation, instead of cranking over with a ratchet/socket, He hits the starter, WEEEEELLLLllll, lets just say, it aint real purdy seeing preston running across the shop floor, and, a whats left of a piston and the small end of a rod hanging out the side of the block.
OH WELL, it was a customers truck and, it was in a ford dealerships shop. That happened over lunch time, when the mechanics/shop super comes back after lunch, needless to say, the mechanic AND his tool boxes was gone, never come back for His paycheck either.

 

[bigcountryguy19]

What is compressed just pushes back down. It's how all the late model manufacturers are doing it. I just cant switch mine back without a lil effort. The plugs stay put. You know I'm driving it right? This is my fourth night to drive it to work

I wasn't aware if that, thanks for the info. Does it run fairly smooth?

 

[jpoole]

I wasn't aware if that, thanks for the info. Does it run fairly smooth?

It's not bad at all. Right off idle it kinda feels like you are lugging the motor a little(it is swinging some dead weight around)but it goes away fast as rpms build. There is no noticeable difference in a steady cruise state.

 

[89Suburban]

 

[HotRodPC]

Whut? Never heard of running a 175 cu in. V4 wannabe 350 cu in V8?

 

[HotRodPC]

So now we just wait for some mpg results.

 

[Christian Nelson]

Hmm, makes a guy wonder just how well a 3400 V6 would do in one of these trucks, might get pretty good MPG, and not take as much of a performance hit as cutting out 4 cylinders..

Add a Turbo, and as long as you keep your foot out of it, you'd maybe have MORe power, and better MPG!

 

[HotRodPC]

Hmm, makes a guy wonder just how well a 3400 V6 would do in one of these trucks, might get pretty good MPG, and not take as much of a performance hit as cutting out 4 cylinders..

Add a Turbo, and as long as you keep your foot out of it, you'd maybe have MORe power, and better MPG!

I've always wanted to run a Buick 231 Even Fire 3.8 in one of these trucks with a manual trans and see how it would do on mpg. Kinda got the wind taken out of my sails, and I shouldn't have let that happen when I was told it would work to hard and get crappy mpg. But, I had to many projects anyway so I sold the 231.

 

[jpoole]

Hmm, makes a guy wonder just how well a 3400 V6 would do in one of these trucks, might get pretty good MPG, and not take as much of a performance hit as cutting out 4 cylinders..

Add a Turbo, and as long as you keep your foot out of it, you'd maybe have MORe power, and better MPG!

I think Hotrod was spot on when he suggested some 4.10 gears for the 4 cylinder. I would do it but I'm cheap. I actually thought about swapping a tbi 4.3 in cause it would be an easy bolt in swap but I never found one on the cheap. I don't believe the 3.4 60deg has the traditional sbc bellhousing bolt pattern so a trans swap would prob be needed also.