explain the process of blocking the centerports of a 455 with freeze plugs., Doews this make the heads the same as Stage II heads? What size freeze plugs? Do you just pound them in? Any help and I would be very Thankful. Thanks Guys
Short version - some people block the heat riser ports between the cylinfer head and intake. The benefit is it keeps the intake cooler, and subsequently cooler fuel/air mixtures are denser, and produce more power. Stage 2 heads had a significantly different exhaust port configuration than production 455 heads, so no - it does not accomplish that. I believe there are two sizes of ports, for my 71 heads the Dorman 555-008 plugs were the correct size - 9/16ths? As I recall, my 73 heads had bigger plugs...
...and in the process of killing the exhaust crossover function, you disable the EGR system, and the divorced or hot-air choke (if applicable). The cold manifold will probably cause driveability problems until it eventually gets some heat in it. The colder the manifold, the worse the driveability problems.
coolant 2000ish degrees. heat source : mostly in the front and only touching the intake in rear not flowing across it exhaust 600ish degrees at idle. 1100-1300ish on cruise, heat source: both sides of intake in middle under carb. this will warm everthing up significantly
FIFY. The intake is warmed by heated oil splash from below, coolant at the front and (less so) at the back, and via conduction to the cylinder heads. Some engines have deliberately-heated intake air coming from the exhaust manifold heat stove via the Thermac air cleaner. It's cooled by the latent heat of evaporation of the fuel/air mix. This can be fairly powerful--Smokey Yunick talked about his 209 cid "Chevrolet" Indianapolis 500 engine, running alcohol and turbocharged, collecting frost on the air intake tubes between turbo outlet and intake manifold due to the evaporation of that much alcohol. Exhaust heat makes a BIG difference.
The metal bathtub intake gasket would prevent that, would it not? You need some sort of splash shield even with composite gaskets to prevent the PCV from sucking oil as well, but it does shield the bottom of the intake from hot oil.
I've got two 455 cars with Aluminum manifolds and surface mounted coils, no thermac or manifold pipe - both cars have the passages blocked at the heads. I regularly drive both cars in 30-40 degree weather, have never had an issue with drivablity (although the 71 does take a long time for the choke to heat - maybe 5-10 minutes, I dialed in a LOT of pulloff). The only car I ever had a problem doing this with was my 65 Nailhead with an "airgap" style manifold. Didnt have a drivability problem so much as a big flat spot on acceleration when the fuel wouldnt "flash" off the ports. Put the heat back in at the heads and blocked it off at the carb pad, ran like a champ again.
I would think it should be pretty clear if you block the heat source off a thermostatic choke wont work correctly.......but an electric one will. I have very little street drive time on any of my buick motors, race only, never had any issues getting the gas to change state from liquid to vapor, even on a cold motor. I also if course dont run a choke but never had any issue even on a cold winter morning getting the motor to start right up. sometimes I need to move the car out to make room in the garage. might have to cover the pedal a little till the motor gets a little temp to get a flat idle
I will definitely say there might be some cold drivability issues when completely blocked off but all you need is a single 1/4" hole drilled in one of the holes near the choke pulloff to provide all the heat it needs and the intake needs for quicker warm up. The typical paint burning off the intake manifold near the exhaust passages shows how hot that exhaust is. Do you really need that much heat in a performance application? If a cold air intake system or a hood scoop are meant to deliver cooler outside air to an engine how can reheating it in the intake be an advantage? Again I'm talking about from a pure performance angle. If you want to talk pure drivability GM had the hot air hose off the exhaust manifold plumbed to the air cleaner housing for cold weather drivability. Even they knew there could be too much of a good thing because they included a flapper and thermostat that would shut off the exhaust heat passage if it got too hot. In no small co-incidence it would also close when you went to full throttle. From what I've heard drag racers who run Methanol sometimes don't run a radiator because the engine runs too cool. I'll go by paraphrasing the old racer adage, "Oil pan in the furnace, intake in the icebox."
