Cold Air Intake! 88 Chevy P30 Chassis

[BrandonMc]

This RV has had a fuel vapor locking issue ever since I bought it. An altitude vapor locking issue due to fuel delivery hoses not sealing properly because of age, and a heat lock as well. I've gone over much of the fuel system, cooling sysyem,and electrical system, and heat shielded, replaced hoses and parts, and a lot of things.


I'll be testing this setup over the course of the next summer to really find out how this improves the ride so what I'm saying is so it hasn't been test driven. Also, I am curious for suggestions about having the regular air filter AND this other black cold intake air filter as you can see in the pictures. thoughts?


This is what I'm thinking will be the ultimate remedy (or so I hope) for the vapor lock, because it's pulling super heated air from behind the doghouse and right in front of the doghouse from the old air intake mounted right above the radiator.The cold air temperature should be reduced down to at least 50 degrees Fahrenheit on the intake!! It is seriously hot underneath the hood. heat lock usually occurs shortly after the thermostat opens at 195deg.

One degree f should equate to 1HP of extra power.

The two major purchases made for this project were a 4" flexible air intake hose, and a 4"cold air intake kit. I fabricated another shroud out of some sheet metal and riveted and cobbled this all together as you can see in the second post. One consideration was to remove the old coolant reservoir tank for the radiator for the extra room.

[BrandonMc]

I am going to buy a new coolant reservoir because the old one is cracked and old and repaired once already as you can see it propped up in there just not connected, as well as one electrical ground still hanging loose for when I get to it. Still need to wrap some automotive heat reflective tape on the connections to the aluminum pipe, and make a support hangar.

Nothing spectacular about the installation. If you do this yourself you will need to spend some time and try to orient the parts to use in the most intuitive manner. I didn't order this kit thinking it would work without some fabrication and modification, and I didn't use every part either.

Cool air will now reach my carb rather than something out of a dragons breath! It's seriously not good for an engine to breathe air that hot! Will update you on the effect of the modification this summer. Likely in the dead heat of July. 

[Froggy1936]

I believe your problem is not the air entering the Carb But The fuel lines being heated from their position near the exhaust system  If they are in the heat stream they need move outboard of the frame into cooler air . The cooler air will help with MPG though .Also an electric fuel pump plumbed into the system will also help  Frank

[Rickf1985]

I agree with Frank. Vapor lock is from fuel boiling in the fuel lines and has nothing to do with the temperature of the intake air. Intake air temperature just affects air density and really does not make any difference as far as the heat itself. What you are doing is fine but unless you are running some form of supplemental intake heat such as a heat riser from the exhaust manifold then you are going to experience carburetor icing once the temps get down around 40 degrees and high humidity. That can be real bad for both the engine and mileage. In the summer you are now picking up the superheated air right off of the hot road surface as opposed to the cooler air above it and that original intake position was in front of the radiator so it was getting the coolest air coming in the grill. The tubing you used is also going to cause some restriction and turbulence due to the ribbed design. I think if you put a temp probe in the intake in the summer you are going to be disappointed. I also agree with the electric fuel pump which you should already have in the tank. Have you checked both the pump and the regulator? I do not agree with the placement of the regulator where they put it, I believe it should be placed close to the front right before the factory mechanical pump to keep the higher pressure on that long line. I have never had a vapor lock issue with mine which is basically the same as yours even with a bad load of fuel this past summer that had close to 20% alcohol in it. No power at all but still no vapor lock.

[BrandonMc]

Both great considerations, thanks. Did not consider summer road temperatures, but probably still would run cooler than where the air had been drawing from!

The RV loves to drive at interstate speeds mainly, and that would have likely been due to airflow under the hood is my best guess.

[Rickf1985]

Look at the original air intake position and tell me where there is hot air in front of it? The radiator is below and behind it. Take that deflector off of the original and then there is nothing between the intake hose and fresh air. And a lot less corrugated hose. Your call, but definitely watch for icing.

[Sasquatch]

I fought this issue for years on my Exec.  I did everything from multiple pumps, re-routing lines, cold air intakes, jetting, insulated carb spacers, and even installing a metered return line from the carb back to the tank.  I have no idea why some coaches have no problem with vapor lock (VL) and others do.  But in my experience, once you have it, unless you find a smoking gun as to why, there will be little you can do to fully eliminate it.  The problem comes down to the ethanol in our fuels.  The alcohol vaporizes at a much lower temp than straight gasoline.  My problems surfaced when ethanol, E10, became widespread.

The only way I was able to eliminate the problem was a fuel injection kit.  And quite frankly, despite the $$ spent, it was well worth it and would NEVER, EVER, go back to a carb.  You can get kits now for about half the price I paid 8 years ago.  But since I installed the kit, the coach has never run better, never missed a beat, better power and a slight bump in economy.  Turn key and go. 

I tell everyone with an older coach.  If you even think you are going to keep the coach for any number of years and plan on using it, just get a kit and do it.  I probably spent the cost of the kit over 10 years of trying to resolve the issues in parts and my labor (time).  The modern kits are fantastic.  They have wide band O2 sensors and are self learning.  Bolt on and go.  Heck, they even have systems that are returnless now so you do not need to run additional fuel lines back to your tank.  My coach runs perfect now no matter the altitude, temperature, or what fuel I buy.  It just alters the fuel maps to compensate.  I can be at 10k elevation in a snow storm (not wise, but I have never been accused of making great decisions all the time) or 100 degrees below sea level in Death Valley, the coach does not care and runs perfect.

Just my .02

Regarding your CAI mod.  You probably eliminated any gains from that kit by all the additional plumbing your engine needs to suck the air through.  At highway speeds, with all the open space under and around your engine compartment, you would be surprised to find that the under hood temps are not much higher than ambient air.  Part of my injection kit is a way to display all the engine parameters on a display.  I have a short intake with a large K&N and it sits right on top of the manifold next to cylinder #1, behind the radiator, on my 440.  At highway cruise my intake air temperature is only a couple degrees warmer than ambient air outside the coach.  The only time it gets warmer is sitting in traffic, and who cares at that point?

Another point.  Yes, colder intake air = better power.  But the inverse is also true, warmer intake air = better fuel economy.  But in a coach, the improvements either way would probably never be actually noticeable.

[iamcaper]

I would suggest running your fuel line through a transmission cooler to bring the fuel temp down. 

[BrandonMc]

FIELD REPORT  1000+mile trip

The larger cone type filter and the stock air filter did not restrict air flow considerably. I'll sometime try without the cone filter to compare my results.

The engine never once opened the thermostat the entire trip in the deserts of east utah, or flooring the pedal for minutes up three separate mountain passes. The highest being 11,800ft . The setting for the thermostat is the stock 195 deg f.

I think this mod considerably helped bring cool air to my engine and will considerably reduce the temperatures of the fuel/air mixture. Looking forward to testing this out and comparing to the high summer temperatures. 

[Rickf1985]

Brandon, The thermostat HAD to open or you would have had some major overheating within the first few miles. It opens and closes and most of the times just stays at a partial point in between to maintain the water at the 195 point. If you are not reaching the 195 point then I would guess the thermostat is stuck open.

[BrandonMc]

I can definitely hear when the fans kick on and it opens up. Or do the fans also have their own set temperature?

[Rickf1985]

The fan clutch is different than the thermostat. If you are not hearing the fan come on then either the fan clutch has gone bad or the water going through the radiator is not getting hot enough to engage the fan clutch. You mention fans as plural, are you talking about the radiator fan or the electric fans in front of the radiator? The electric fans are controlled by a sensor in the radiator and also the relay that runs on the A/C. They will run when the A/C is on or they will come on when the radiator gets above 230 degrees I believe it is. I have mine bypassed and on a switch and relay so I can turn them on and off as needed but I cannot hear them when the engine is running. The clutch fan on the engine will roar quite loud when it engages.

[BrandonMc]

ahh, then what I was hearing is the clutch fan engage. I was under the assumption that was also the thermostat opening fully.

[c farmer]

I fought this issue for years on my Exec.  I did everything from multiple pumps, re-routing lines, cold air intakes, jetting, insulated carb spacers, and even installing a metered return line from the carb back to the tank.  I have no idea why some coaches have no problem with vapor lock (VL) and others do.  But in my experience, once you have it, unless you find a smoking gun as to why, there will be little you can do to fully eliminate it.  The problem comes down to the ethanol in our fuels.  The alcohol vaporizes at a much lower temp than straight gasoline.  My problems surfaced when ethanol, E10, became widespread.

The only way I was able to eliminate the problem was a fuel injection kit.  And quite frankly, despite the $$ spent, it was well worth it and would NEVER, EVER, go back to a carb.  You can get kits now for about half the price I paid 8 years ago.  But since I installed the kit, the coach has never run better, never missed a beat, better power and a slight bump in economy.  Turn key and go. 

I tell everyone with an older coach.  If you even think you are going to keep the coach for any number of years and plan on using it, just get a kit and do it.  I probably spent the cost of the kit over 10 years of trying to resolve the issues in parts and my labor (time).  The modern kits are fantastic.  They have wide band O2 sensors and are self learning.  Bolt on and go.  Heck, they even have systems that are returnless now so you do not need to run additional fuel lines back to your tank.  My coach runs perfect now no matter the altitude, temperature, or what fuel I buy.  It just alters the fuel maps to compensate.  I can be at 10k elevation in a snow storm (not wise, but I have never been accused of making great decisions all the time) or 100 degrees below sea level in Death Valley, the coach does not care and runs perfect.

Just my .02

Regarding your CAI mod.  You probably eliminated any gains from that kit by all the additional plumbing your engine needs to suck the air through.  At highway speeds, with all the open space under and around your engine compartment, you would be surprised to find that the under hood temps are not much higher than ambient air.  Part of my injection kit is a way to display all the engine parameters on a display.  I have a short intake with a large K&N and it sits right on top of the manifold next to cylinder #1, behind the radiator, on my 440.  At highway cruise my intake air temperature is only a couple degrees warmer than ambient air outside the coach.  The only time it gets warmer is sitting in traffic, and who cares at that point?

Another point.  Yes, colder intake air = better power.  But the inverse is also true, warmer intake air = better fuel economy.  But in a coach, the improvements either way would probably never be actually noticeable.

Did you do a throttle body injection or multiport injection?