Carb at high elevation

[burleyman]

Thanks for the link to the carb cheater. I thoroughly enjoyed the video, and learned a lot. I have carbs, but no dramatic altitude changes.

The non-metallic air bleed plate used could help keep heat away from the carb, also. I've had good luck with a short piece of fuel line with a screw inserted for vacuum caps.

I did try using exhaust gas temperature and a finger operated valve in the line years ago, but not for altitude changes. Automatic finger cheater, great idea. I don't think he said anything about better gas mileage.

I sometimes wish my early EEC-IV simple EFI 5.8L Ford was carb equipped. For emergencies, I have a spare ECU, distributor, ignition module, throttle position sensor, MAP sensor, and special code reader. Dropping the tank to replace the in tank fuel pump is a chore. If a truck instead of a van, there would be a hole cut in the bed.

I know which system suits me best broken down somewhere if you don't mind dirty hands and fingernails. That goes back to what you said about the wall of parts.

The Ford variable vacuum carbs, especially the ones with the metal venturi blocks, do a good job with altitude changes. They are a sideways version somewhat like your Edelbrock, except movements and positions are controlled by vacuum instead of directly by your foot. They depend upon a rubber diaphragm to move the venturis. Sort of a MAP sensor.

 

[85_Ranger4x4]

I have a fairly thick phenolic spacer, a edelbeock will not tolerate being too close to the intake. Fuel boils out of the bowls when you shut it off and floods it very quick without a spacer.

I have heard stories about the vv carbs (mainly horror stories), I really ought to check into them if for no other reason just to see how they work.

The PO of my truck was a believer of the bolt in a hose for plugs. He must have thought it sucked pretty bad, I still laugh that most were grade 8

 

[craig333]

Very easy to change the jets on my Solex. It's just the gas that leaks out onto the manifold thats a bit disconcerting!

 

[ntsqd]

No matter what, an NA engine is going to feel the altitude. If you let a turbo engine spool down it too will feel the altitude until you manage to get it to spool back up. BT, DT.

That said I've had my old '91 Suburban from -281' (Badwater) to 12,400' (Barcroft Station) and it's TBI system was able to compensate. I would give some serious thought to a GM TBI system, particularly one based on all GM parts, so long as you're under ~300HP output. Above that you you start to really push the system beyond it's design envelope. Pared down these systems are pretty simple and don't need a lot of sensors etc. As EFI computers go, they're not very smart, but they're smart enough. Howell used to and may still sell complete kits with proprietary tuning, but you can put one together in a JY. If you find a 305cid donor then it should be pretty close right out of the donor.

I REALLY don't like any of the aftermarket EFI systems. At least not until you get into Motec and similar territory. I'm not seeing that kind of cash floating around. Much below that and they don't even know what "MTBF" means, much less have any idea of how their parts would rate. OEM EFI has to be durable and reliable in ways that the common aftermarket EFI's can't match.

 

[ExpoMike]

No matter what, an NA engine is going to feel the altitude. If you let a turbo engine spool down it too will feel the altitude until you manage to get it to spool back up. BT, DT.

That said I've had my old '91 Suburban from -281' (Badwater) to 12,400' (Barcroft Station) and it's TBI system was able to compensate. I would give some serious thought to a GM TBI system, particularly one based on all GM parts, so long as you're under ~300HP output. Above that you you start to really push the system beyond it's design envelope. Pared down these systems are pretty simple and don't need a lot of sensors etc. As EFI computers go, they're not very smart, but they're smart enough. Howell used to and may still sell complete kits with proprietary tuning, but you can put one together in a JY. If you find a 305cid donor then it should be pretty close right out of the donor.

I REALLY don't like any of the aftermarket EFI systems. At least not until you get into Motec and similar territory. I'm not seeing that kind of cash floating around. Much below that and they don't even know what "MTBF" means, much less have any idea of how their parts would rate. OEM EFI has to be durable and reliable in ways that the common aftermarket EFI's can't match.

Yep, I can totally agree with this. My plan with my M1010 project is to swap out the 6.2L diesel and put in a 7.4L gas (454 BBC). I am going to use a TBI setup, which is fairly simple and basic but will give me better mileage and altitude compensation. Carbs are fine for some applications (all of my classic/hot rod cars have them) but bouncing around offroad with all of the difference in altitude, they just don't compare.

 

[85_Ranger4x4]

No matter what, an NA engine is going to feel the altitude. If you let a turbo engine spool down it too will feel the altitude until you manage to get it to spool back up. BT, DT.

That said I've had my old '91 Suburban from -281' (Badwater) to 12,400' (Barcroft Station) and it's TBI system was able to compensate. I would give some serious thought to a GM TBI system, particularly one based on all GM parts, so long as you're under ~300HP output. Above that you you start to really push the system beyond it's design envelope. Pared down these systems are pretty simple and don't need a lot of sensors etc. As EFI computers go, they're not very smart, but they're smart enough. Howell used to and may still sell complete kits with proprietary tuning, but you can put one together in a JY. If you find a 305cid donor then it should be pretty close right out of the donor.

I REALLY don't like any of the aftermarket EFI systems. At least not until you get into Motec and similar territory. I'm not seeing that kind of cash floating around. Much below that and they don't even know what "MTBF" means, much less have any idea of how their parts would rate. OEM EFI has to be durable and reliable in ways that the common aftermarket EFI's can't match.

Most aftermarket EFI systems use parts for OE injection systems. I was looking at ACE throttle body setups the other day on the 'tube. They straight up say use this part number for an injector and this number for a TPS and this one for a O2 etc. Seemed GM based.

Of course if the ECM goes belly up you still have a brick.

EFI is kinda sorta not really on the table right now. I know it is better, it is a goal to inject this thing at some point. There are so many ways to crack that nut I am still sorting it out too.

Right now it is basically make do with what I have or stay home.

 

[1stDeuce]

It's pretty easy to change the metering rods on an Edelbrock. Pull yours and figure out what size they are. Order a set several sizes larger. That effectively plugs up the metering passage and leans it out. Should be fine to 5000' or so as is, then swap the rods to lean it up when you get to Colorado. Run it that way while you're here, put the orig rods back in when you leave. It'll be fat at 12,000' and if you do it right, a little lean at 5000.

Another thing that you can use to fine tune a bit is an adjustable fuel pressure regulator. Edelbrock carbs generally don't like more than about 5psi so most setups end up with one. If you turn the pressure down a few psi, it effectively lowers the fuel level in the bowl and leans it out a bit. Not perfect but an option...

You'll have to do some googling or hit up Edelbrock's help line for suggestions as to how big to go with the rods...

 

[sargeek]

Old enough to spend a lot of time driving an NA engine at altitude in the Colorado Rockies. Builds a lot of character trying to drive and start the manual transmission uphill when the engine won't idle. Three pedals with two feet - and I was lucky as the truck had a granny first. Once you get the truck running you have the complete loss of power.

The other problem everyone is forgetting about an NA engine is the fun of vapor lock - trying to get the trails in the first place. Hot days, high altitude, hot engines a very bad combination. Nothing like sitting on the side of I70 waiting for your gas line to cool down.

The modern injected engine makes it way easier to navigate the Rockies - An elevation change of more than 5,000+ in less than an hour of driving is a lot to compensate with a carburetor. Your experience may vary. I would look for an aftermarket injection system so you can enjoy the trails and not struggle with your engine.

My tool of the time was a full-size Bronco with a 302, and 4-speed manual. It successfully took on Imogen Pass and a number of other fun Colorado Adventures.