Is Blocking a Cast Iron Intake Heat Crossover worth any H.P.?

[travis]

I have never seen a measurable difference in fuel economy with or without the crossover blocked, but have definitely seen it be the difference between fuel boiling/difficult hot starting and not. On a street engine the only advantage I have ever seen leaving the crossover open was better cold weather driveability. Granted, I live in a part of the country where actual cold weather is usually only a few weeks or so during the year, but have 90+ temps for 7-8 months of the year.

[groberts101]

I block them. Just don't see the need for all that heat unless you live in Alaska.

Fuel economy. You need a lot less accelerator pump with a hot intake manifold.

I see fuel economy as important in a pleasure car. If I can get 25mpg instead of 20mpg, that means I can drive 25% more on the same amount of fuel. That means I get to enjoy the car 25% more. 25% more driving pleasure is a very good thing.

Your opinion, but does anyone else think a blocked exhaust crossover would cost 25% penalty in fuel economy? FWIW, I blocked the exhaust crossover on a build with which I'm quite familiar. There was very little difference in overall fuel consumption.

One major difference not yet touched on is sensitivity to pinging on the hottest days. As with the OPs build, this is iron head, iron intake. On 100+ days, it would ping. With the exhaust crossover blocked, pinging was reduced. Adding a cold air intake, the pinging was gone.

A secondary benefit is reduced fuel percolation in hot soak conditions. Some feel today's gasahol boils at a lower temp. Keeping the intake cooler reduces hot cranking times in some applications.

Right on. And what I believe is also being overlooked is the natural tendency for a cooler induction charge to allow more aggressive tunes to be used under part throttle/high load situations. Even allows much faster centrifugal advance ramping under WOT which fattens up the power curve. Doesn't always need to be about peak.. average gains make motors run harder too.

All the tricks to push compression and tunes are well proven and can easily add up in a cumulative manner. Sealed or ducted fresh air intakes, lower temp t-stats, header wraps, phenolic carb spacers, insulated fuel lines(preferably return style), cool cans,.. every little bit helps widen the margin or gives more latitude to live further out onto the ragged edge.

[rapidride2]

Decisions Decisions, i thought my mind was made up..lol.

[groberts101]

Decisions Decisions, i thought my mind was made up..lol.

Should depend on if you're one of those guys that cares about gaining tuning margin or not. If you run 12 degree base timing factory style mechanical advance tunes and also have a distributor vac pot hooked up to ported vacuum source?.. much bigger fish to fry before worrying about yanking intake manifolds, imho.

If you like to run more agressive tunes then yes.. without a doubt.. a cooler intake manifold will never hurt power potential. Never once heard anyone say they LOST power after closing them off on anything performance oriented.

[peejay]

I block them. Just don't see the need for all that heat unless you live in Alaska.

Fuel economy. You need a lot less accelerator pump with a hot intake manifold.

I see fuel economy as important in a pleasure car. If I can get 25mpg instead of 20mpg, that means I can drive 25% more on the same amount of fuel. That means I get to enjoy the car 25% more. 25% more driving pleasure is a very good thing.

Your opinion, but does anyone else think a blocked exhaust crossover would cost 25% penalty in fuel economy? FWIW, I blocked the exhaust crossover on a build with which I'm quite familiar. There was very little difference in overall fuel consumption.

One major difference not yet touched on is sensitivity to pinging on the hottest days. As with the OPs build, this is iron head, iron intake. On 100+ days, it would ping. With the exhaust crossover blocked, pinging was reduced. Adding a cold air intake, the pinging was gone.

A secondary benefit is reduced fuel percolation in hot soak conditions. Some feel today's gasahol boils at a lower temp. Keeping the intake cooler reduces hot cranking times in some applications.

I didn't literally mean "you will get 25% more economy", but I do like round numbers...

Personally I have noticed a not insignificant percent economy difference with a coolant-heated manifold vs. coolant ports blocked off. And the throttle response was a lot better, too.

[Ken_Parkman]

Read in a magazine about the aluminum foil trick so I tried it. Stuff blew out in short order, and the foil piled up in the mufflers and made the most horrible noise for a while. Not keen on foil.

[Circlotron]

Never once heard anyone say they LOST power after closing them off on anything performance oriented.

Read somewhere a while back about nitrous lowering intake temps so much that a significant portion of the fuel was still droplets of liquid at the moment the spark fired. Backing off on the intercooler actually helped power. Can't remember the details, sorry.

[BigBlockMopar]

I block all the crossover ports on the engines I put together for myself. Mostly all just streetdriven cars.
Once I didn't block one and had regrets the moment I ran the car because it pinged again when hot. Nothing more annoying then noticing your engine is struggling and being crippled at the exact moment you want to accelerate.

[groberts101]

Never once heard anyone say they LOST power after closing them off on anything performance oriented.

Read somewhere a while back about nitrous lowering intake temps so much that a significant portion of the fuel was still droplets of liquid at the moment the spark fired. Backing off on the intercooler actually helped power. Can't remember the details, sorry.

Sorry, should have excluded the nitrous ans alcohol guys since it's entirely possible to achieve too cold an induction package and change charge homogeneity reaching the combustion space. But since this OP is talking about a cast iron manifold I doubt it would ever happen in this particular scenario. Plus, if it did occur then the booster or emulsification package could be modified to further promote finer droplet sizes through the now lower temp induction.

[peejay]

Plus, if it did occur then the booster or emulsification package could be modified to further promote finer droplet sizes through the now lower temp induction.

It'd be nice if people actually did this.

Or you could go the old Barry Grant way and just run more fuel through the engine, so it fouls the plugs AND lean-stumbles at the same time since the fuel is coming into the chambers in droplets the size of golf balls.

[MadBill]

One of David Vizard's books (can't recall which at the moment) reported extensively on the interdependence of atomization and manifold/inlet air temperature. As one might expect, the better atomizing carb gained substantial power when matched with an unheated manifold, but lost vs. a standard one when running with a heated manifold.

In his old How to Build Horsepower Vol. 2. book he tested a ~ 300 HP SBC with a stock 650 Holley and with/without crossover heat in a Weiand dual plane manifold. Ambient air was 105°- 110° F. After ~ 30 sec. of WOT, charge temperature of the heated system stabilized at 105 to 110°. The unheated test produced 79-81°and a 2.5% across the board power and torque increase.

The engine had been built to the detonation limit with 91 octane fuel in the heated configuration at 10.2:1 CR, but the unheated manifold permitted an increase to 10.6:1 which picked it up another 4-5 HP.

[rapidride2]

2.5% would be worthwhile for me. It might be worth me making some to be able to pull out if driveability suffers too much.

[MadBill]

To quote DV: "The heat applied to most stock manifolds is appropriate for an Alaskan winter, so for anything less reduce the manifold heat as required."

[Truckedup]

I blocked the heat rider in SBC's that wern't driven in the winter.. You drive in cold winter weather and the poor vaporization until the engine oil heats the intake, maybe 20 minutes or longer if at low speeds.....And I believe that would be unvaporized fuel in the intake and on cylinder walls?