With all talk about heat soak, and the release of the BBK SSI Intake I have been thinking.....
Why is there all this talk about heat soak?

If the plastic intake doesnt soak up heat, then it must stay in the cylinder heads right? Although the intake is cooler, keeping the charge cooler for the length it flows thru the intake, it would get even warmed quicker once into the head where there is more heat stored (since it cant transfer through the intake).
So, in theory, the metal intake, which would help remove a lot of heat from the cylinder heads thus keeping the velocity of the intake charge up (warmer air, same principal as turbo mounting right?) and possibly dropping the temp at the combustion chamber (from the heat transfering to the intake more than in a plastic setup).

Just thinking about the whole heat soak topic.

I know higher temps mean more prone to pre-ignition.

 

Meaningless at street level performance.
Otherwise all the aftermarket intakes would be composite by now.

 

i agree.

 

Your theory would be true if there were only a "set" amount of heat present in the cylinder head at any given time. However, heat is being added and removed all the time. The heat is added by combustion, and removed by the cooling system, plus being radiated to the surrounding air, as well as being conducted to any surface that is bolted to it. The temperature of the cylinder head is regulated by the cooling system. This temperature will be the same, regardless of whether or not heat is transferred to the intake manifold.
(Just look at your engine on a cold morning. It takes a little longer to heat up, but it still reaches the same temperature is always does.) If the intake manifold was metal and could conduct heat well, it would soon reach the surface temperature of the cylinder head, as regulated by the cooling system, and heat would no longer be absorbed by the intake. The cylinder head would still reach the same temperature it did before, except now you have the intake manifold that's just as hot, causing the intake charge to heat up that much more. If the manifold didn't absorb any heat, the cylinder head (as well as the intake port) would be the same temperature, but it wouldn't have the whole manifold to heat the air up, just the intake port. I agree that while normal street driving under normal conditions this isn't much to be concerned with (you know, grandma driving to bingo), it is a factor that should be taken into consideration in any hi-performance application, especially if you live in hot climates (like I do). Heat soak of the intake charge causes the ignition timing to be backed down, either through the intake air temp sensor, or through the knock control; not to mention that hot air is less dense and makes less power. It is very noticeable here during the summer. A metal intake manifold would just make it worse. If a metal intake has no effect, then why do you gain horsepower with a throttle body coolant bypass? If the throttle body can have an effect on the intake charge being that it's flow path is only 2-3 inches, why wouldn't the intake have an effect, being that the runners are much longer than that? And why do so many racers ice the intake manifold between runs?

On the flip side, hot air is good in turbo applications ON THE EXHAUST SIDE of the turbo, not because hot air has a higher flow velocity, but because the exhaust gasses are hot and under pressure. A hotter gas in under more pressure in the combustion chamber, which causes more rapid expansion of the gasses in the exhaust port and header/downpipe, which produces more exhaust volume, which causes the turbo to spool faster. The quicker the turbo can spool, the sooner it will feed boost to the engine and make more power (less lag).

As a side note, most aftermarket intake manifolds are metal because it is cheaper to design and cast a metal manifold than it is to design and mold a plastic one (compare any metal manifold to the FAST LSX and see the price difference). General Motors did it because the benefits far outweighed any additional expense. They also "sold" hundreds of thousands of these manifolds, so in the end it didn't cost much.

Bottom line: if heat soak of the intake charge has no effect, or is beneficial, then there would be no cold air intakes, no plastic intake manifolds, no IAT sensor relocation kits, no throttle body bypasses, and no intercoolers of any sort. The cooler you can keep the induction charge before it gets to the combustion chamber (to a point), the more power you will make, with less chance of detonation.

 

I don't think more heat would be stored in the cylinder heads, they will still transfer heat to whatever they are connected to even if it be the air, the composite intake just doesn't heat up as fast because it is also better at releasing heat than metal is so it stays cooler longer.

 

Tooslow02, good points that I obviously overlooked. I agree to a point the cooler the better, depending on which aspect. I was thinking along those lines, but thinking that the Al intake could outweigh the Nylon in benefits overall for certain applications, not looking that way now though.
On a different board I posted this topic in, a friend replied in ref: warping the Nylon, making Al better, but that we all know is exact opposite, the Al holley may need milling, but I have yet to hear of a Nylon on needing it. And another points out the ability to tap a DP into the Nylon....I let him know we can do that too, and then the Al intake could handle a nitrous backfire....til it rips the intake off the heads destorying **** sure, but the nylon LSX has burst disc!

Anyway...it seems that we will never really know if there are any benefits since there arent any AL and Nylon Intakes of the same volume, runner size shape etc..

 

Good point. I don't think there's a way to say one is the absolute best manifold for all motors. Then again, I think we overlooked the main benefit of either manifold: the ability to port the **** out of it for monster cube motors, which is pretty much why the aftermarket decided to bother making them in the first place. Personally, I don't think you can go wrong with either one.

 

Air heat soak. Since air is not a good conducter of heat the only way to absorb the heat is to set still. Now driving around stop and go traffic, I can see the problem, Just off idle or at idle. But at wide open throttle there is not enough time for the air to absorb the heat. Think of it like running your finger through a candle. Go slow it will burn you, go fast and you did not feel a thing. You skin is like the air, in the intake. It needs to time to soak., We have done lost of testing with our intake, and have found nothing about hp loss. We even drove the car left around stapped to the dyno open the hood to make the connection and make a pull. The car repeated an earliy cold intake test. Now that intake was hot to the point to could not touch it. The reason car mfg build there intake out of anything but metal any more is money. It is cheap (and more accuate) to build part out of plastic. The intake use to be all one piece and now they are gong to a multi piece that is glue together. Just my opion.

Ricky

 

I agree - GM would give up 20hp if they could save $1 per vehicle(Why do you think we have to spend all this $$ on modding our cars!?!). They could care less about heat soak. IMO the heat soak "problem" with the aluminum intakes is negligible in all but the most extreme applications/environments.

In the end, only you can decide if the extra 2-3hp and warm, fuzzy feeling you get from a composite intake is worth the extra $300+.

It would be interesting to see a direct comparison of two intakes identical in every way except material - anyone have a couple hundred grand to blow on some prototype tooling?

 

LOL.. don't believe in heat soak with an aluminum intake, make two back to back passes at the drag strip and lay your hand on one for 1/2 a second

Do the same with the stock intake on your car. Bet you can hold it there for awhile

IMO, why are all the aftermarket intakes still aluminum? Because it's what they know and the $$$$ of setup.

GM produces them in such volume they can afford the R&D and production cost of composite stuff. I'm sure once the R&D/setup costs are out of the way, a composite intake is cheaper.. but the ramp up cost is more than most companies are will to burden themselves with.

 

That would be the Holley and the LS6 Notice how popular the Holley's are? (not)

 

It is also difficult to produce a metallic intake that has the glassy smoothness of a composite intake's runners.

 

If heat soak wasn't an issue, then no one would bother bypassing the throttle body coolant lines. For that matter, no one would bother icing their intake manifolds between passes. Why do they bother? Because it works. Because throttle bodies that are close to engine coolant temperature and metal intake manifolds that approach the temperature of the cylinder heads will heat up the air. Have you ever stuck your hand behind the electric cooling fans when they're running full blast? You would see that the air is moving pretty fast. You'll also notice that the air is very hot. If air going through mabye 1.5-2 inches of radiator can heat up that fast, I think it stands to reason that air moving past 2-3 inches of throttle body and winding it's way through the manifold's 15 inch runners will heat up.

While I agree that GM does anything to save money, in the case of the composite manifold, it wasn't because it's cheaper. If it was, all intake manifolds would be made of plastic, and the FAST LSX manifold wouldn't be 300-400 more than aluminum manifolds. The material is Dupont Zytel 6/6, which is a 33% glass reinforced Nylon 6 and is very costly, according to GM powertrain chief John Juriga. They used this material primarily because it weighs less, and it's much easier to mold a shape as complex as this one out of plastic than it is to cast it out of metal then machine it. Side benefits are increased flow velocity due to the smooth runners, which causes less turbulence; and the topic of our discussion, less heat transfer to the airflow. To make the overall engine height lower to fit underneath sharply rakes hoods, the manifold's plenum is on the bottom, nestled in the valley of the heads. This would contribute even more to heat soak if the manifold were aluminum. The added benefit of a plastic manifold is the prevention of heat transfer to the induction charge.