Originally Posted by Catfish11
84 c-10 swb
ac power brakes
I am looking to get a new alumn. intake, currently using the stock iron. I have had problems with the heat cross over all year long. My carb keeps showing signs of gas at the top front gasket area and the engine is hard to start when hot. When the engine is cold it starts fine.The carb is a new rebuild from SMI, quadrajet. I have drop the fuel level to the lowest level possible and its still does the same. My conclusion is that the heat cross over on the stock intake is causing the fuel in the bowl to heat up . I am going to get a new alum intake soon and wanted to block off the heat cross over. I am in the D-FW area of Tx and temps are never freezing for long , maybe 5 days of freezing temps this year. We are also have hot temps almost all year long. While I am at it do I need the egr valve? I read that a performance engine is not needed but a DD that rpms will stay low it would be a good idea. What say you?
What are the emission rules where you live? Do you have to pass an inspection to license the machine? If you do then changes need to be done in concert with the rules you face.
What you're seeing with the carb is fuel percolation from the heat of the manifold. Whether the exhaust cross over is to blame as opposed to just the heat of the warmed up engine I can't say. Often a heat shield needs to be between the carb and the intake. Some intakes also funnel exhaust heat into the bottom of the carb around the primary throttle bore to heat them up so the fuel vaporizes better and to reduce ice formation around the butterflies. If this is functional it can be shut off with high temp RTV injected into the exhaust supply holes in the manifold. You can also use a thermal spacer between the carb and manifold made of wood or plastic these are at the on-line or local hot rod shops.
Aluminum intakes, with the exception of air gap styles, run hotter sooner than cast iron so they heat up an vaporize fuel pretty well soon after start up thus not needing a the exhaust heat cross over to force the situation. If you lived where the weather is cool to cold I'd be leery of turning the cross over off but in the usually warm southwest I don't see this as much of a problem.
EGR of course is a potential legal issue so as I said early on, check the local licensing codes and even if you're currently exempt, check where things are going in the future. Its a pain to have to put the emission stuff back on in a year or two after you lost the parts. EGR is in my mind a non-issue concerning the making of power, when functioning correctly, the only time it works is in cruise. It's out of the circuit at idle and WOT, or at least was designed to be, failures of the EGR or its controls are what cause problems resulting in these things being on or off at the wrong times. If not used, EGR, the mixture needs to be richened a jet size or two as the carb will draw air to replace the missing exhaust gas so this usually leads to insufficient fuel delivery without a jet or metering rod adjustment.
The real issue with these early emission engines isn't the emissions equipment hung on the motor, but rather the compromises to cam and ignition timing, compression, and combustion chamber efficiency made inside. Actually keeping AIR, PCV, and EGR systems functional while adding new style high compression heads with efficient combustion chambers like the Vortecs or even the Swirl Ports with a cam up around 200-215 degrees at .050 inch with an LSA of 112-116 degrees will add 100 horses. Combine that with long tube headers, true duals and dual cats and it will pass an emissions test with no problems if the engine is tight inside, you know no oil around the rings nor down the guides.
These compromises to the engine design were made because the factory's had to guarantee to the government that these things would be low emission engines for 50,000 miles or more with no owner maintenance. So it's easy to jack up the performance and still pass emissions as long as you stay on top of tune and internal wear.