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What are your opinions on adding a cold air intake to a 91? The only time I've ever added a cold air intake to a vehicle is when I owned my 2007 Subaru WRX.
The factory intake does a pretty good job of drawing in cold air, so the only advantage to look for would be increased air flow. You still may be able to get some benefit from that, but there's a far cheaper and probably easier way to do it than buying an aftermarket intake. If your filter housing still has the louvered panel on it, you can just cut those louvers out, if that hasn't already been done (it's one of the most common mods Corvette owners do). Look up some Vette mod videos, you'll see what I'm talking about.
Problem too is on the TPI’s, with the MAT sensor in the upper plenum, the ECM makes a final air temperature calculation that includes the coolant temperature, due to the heat soaking of the sensor in the plenum. At lower to mid engine speeds, the calculation is nearly overwhelmed by the coolant temp anyway.
Notwithstanding what Tyler Scott said about the Corvettes already having a “cold air intake” from the factory…which is true...
You really only get a benefit of playing around with the MAT if you get an actual air temp sensor (instead of the coolant sensor that GM used) and then relocate the sensor to the air duct (preferably outside the engine compartment) and then start re-tuning the MAT tables in the calibration.
The factory intake does a pretty good job of drawing in cold air, so the only advantage to look for would be increased air flow. You still may be able to get some benefit from that, but there's a far cheaper and probably easier way to do it than buying an aftermarket intake. If your filter housing still has the louvered panel on it, you can just cut those louvers out, if that hasn't already been done (it's one of the most common mods Corvette owners do). Look up some Vette mod videos, you'll see what I'm talking about.
Problem too is on the TPI’s, with the MAT sensor in the upper plenum, the ECM makes a final air temperature calculation that includes the coolant temperature, due to the heat soaking of the sensor in the plenum. At lower to mid engine speeds, the calculation is nearly overwhelmed by the coolant temp anyway.
Notwithstanding what Tyler Scott said about the Corvettes already having a “cold air intake” from the factory…which is true...
You really only get a benefit of playing around with the MAT if you get an actual air temp sensor (instead of the coolant sensor that GM used) and then relocate the sensor to the air duct (preferably outside the engine compartment) and then start re-tuning the MAT tables in the calibration.
At part throttle idle/cruise warm air is desirable for economy and efficiency, smoothness of operation. Warm air offers improved distribution, as expansion of the air leads to velocity increase, reducing the impact of variables which promote disorganization due to the ports and tubes being quite oversized. Cold air would have a negative impact on engine cleanliness, carbon cycling, fuel efficiency, emissions, etc... everything would suffer if it was allowed to be ingested cold. Therefore all OEM manufacturers of all engines in the world take steps to ensure the incoming air is appreciably warmed and smoothed before being fed to the intake manifold. It is unwise to disturb these methods ; one may re-engineer them, or take your own steps to procure them, but never delete them for engine operation, efficiency and cleanliness will suffer.
At wide open throttle Cold air is desirable, but there is a caveat I will get to later. These type of Engine's ports are originally designed to accommodate wide open throttle to some extent which is why they are so oversized for idle and cruise in the first place. At wide open throttle now the situation is sort of reversed- you no longer need the warm air energy content to expand the air for its velocity. Instead, you want to fit as much air molecules into as small a space as possible so whatever volumetric flow rate an air pump is capable of could be maximized for its displacement, whether we are talking about engines, blower or turbocharger inlet conditions these are all volumetric fluid pumps that follow the law of continuity: what goes in must come out. So it seems like common sense or logical to get the air as cold as possible to max this rate of mass moving into the volumetric pump.
At wide open throttle, you may wonder why efficiency, economy, cleanliness, are not negatively impacted by the cold air. We have to address each of these by itself I think.
1. Efficiency
Combustion efficiency we can call as simply brake specific fuel consumption, which is fuel mass rate to work ratio. (lb/hr of fuel to horsepower, or grams of fuel per minute to Watts)
The fuel mass to work ratio is supposed to be best when cylinder pressure is highest, e.g. the highest compression of a piston engine has the best efficiency conversion of fuel to work. That is why auto manufacturers keep trying to find ways to make higher compression reliable in modern engines, they are going up not down.
If we have to ask ourselves, what is the limiting factor for our compression and efficiency? Why not use ultra-high compression all the time?
It turns out that the real issue is the fuel quality to technology ratio available. If everybody was forced to only use E99 for example, the compression could be much higher in all combustion engines around the world. Likewise with advanced technology such as Direct Injection, lower quality fuels could be utilized at higher compression ratios. Thus there is a blend of technology and fuel quality which is leveraged against the maximum cylinder pressure developed by any given engine at wide open throttle operation (gasoline engines with pistons) which sets the hard limit on efficiency conversion of fuel to work ratio.
When taken this way, it becomes evident that the mass of air with the highest temperature will produce the largest compression pressure.
That is, an engine will produce the most power and efficiency conversion of fuel to energy with the highest mass of hottest possible air it can consume.
The only reason this is not actually done is because of the fuel quality to technology ratio as we discussed which codes a hard limit on the pressure.
For example vehicles running E85 frequently do not use intercooling and observe temperatures of 250*F+ of intake air temp without any issues because the fuel quality can handle the temperature and so can the engine components. Temperature and its influence on fuel behavior are the actual reasons why we are forced to use colder air with gasoline low quality fuels: gasoline is a poor fuel choice for performance. It is an economical fuel with a pressure spiking capability due to temperature input, a behavior which is far tamer in racing fuels which allow much higher temperatures and pressures without spiking 'detonating' their pressure signals.
And so this is the caveat I spoke of at the beginning. We can gain efficiency with temperature, AND power, if the fuel quality to technology ratio can cover the spread and there is no loss from the volumetric pumping action. For example if my turbocharger inlet temp is 80*F and the wheel speed is 62,000rpm with a pressure ratio of 1.8:1 the flow rate of the engine is set by whatever mass of air is entering the turbocharger inlet because of the law of conservation of mass (law of continuity), so no matter how hot the temperature of the air is when it reaches the engine has no affect or influence on the mass flow rate of the engine, and in fact the higher the temperature is when it reaches the engine the more energy will be in the air and the higher the pressure will be everywhere at that mass rate and the more power could be made if the fuel to tech ratio is agreeable.
When we look back at part throttle this familiar theme emerges again- the warmer air contains more energy and will result with higher pressure given the same mass flow to move a vehicle. In other words when the power requirement to move a vehicle is lets say X, a constant, and we are trying to make BSFC better by pre-warming the air which will reduce the fuel usage because combustion pressure integral will be higher area thus more power emerges from the same amount of fuel which means less fuel can now be used to produce the same energy as before.
3. Cleanliness
What is carbon cycling?
During combustion of gasoline style fuels, there are unreacted fragments of hydrocarbons. These often contain radicals and cations capable of forming conglomerates. That is sticky, tar-like substances that accumulate on pistons/rings and the hard, diamond-like coating that sometimes forms on pistons, valves, rings, etc... And these carbon compounds also make their way into engine oil via blow-by and circulate through the engine creating deposits, which leads to eventual wear and failure.
OEM manufacturers at various paces have developed ways to deal with these byproducts and the solution is strongly integrated with the PCV system and the pressures surrounding the piston rings which is exerted influence on behalf of the crankcase pressure. The crankcase pressure of all OEM engines is tied directly to the post air filter tract, whether turbo OEM or natural aspirated OEM makes no difference this is always the case. At wide open throttle the pressure behind the air filter is calculated to become 1"Hg to 3"Hg for modern OEM engines which applies this vacuum force suction to the crankcase in order to remove these harmful byproducts and reduce the pressure below the piston rings and in the ring pack which allows engine oil to drain properly from the rings and keeps the oil moving through the rings rather than losing light hydrocarbon chains over time and becoming a sticky glue in the rings instead. The reason light chains can leave is they have a very low molecular weight, closer to gasoline, these are the partially or completely unreacted short chains of hydrocarbons derived from gasoline fuels that easily turn to a gas and leave the ring pack, leaving behind the heavier and reacted conglomerates forming over time which cannot effectively evaporate or drain against high crankcase pressure, pressure directly influences the partial pressure of dissolved gasses and the boiling points/evaporation rates of liquids, this would become as a rate equation of adding mass and then draining mass over time where pressure cycling balances the adding with draining to keep a piston clear and rings free. The OEM does the math and designs the engine accordingly and then we come along and put a K&N Air filter or something and ruin the crankcase pressure, ruin the piston rings over time and the engine fills with deposits because of lack of effective PCV scavenging of the crankcase at WOT. But I digress. We need to focus on what is carbon cycling but first you needed to understand what happens to carbon that leaves the ring pack (it should go into the PCV system not the engine oil) and you need to understand that the piston ring seal behavior is directly related to the crankcase pressure, e.g. Blowby increases as crankcase pressure rises. As the piston is coming down on the power stroke the combustion pressure is decreasing and the force on the rings is balanced by the inertia of the ring against the friction of the cyl wall and the gas pressure applied to the rings, the gas pressure and friction is going to eventually unseat the ring, and the lower the pressure is inside the crankcase the longer the ring can hold on to it's seal. This is why vacuum pumps are traditionally associated with power increases as a function of ring tension, e.g. if running alot of vacuum in the crankcase you can use a very low tension piston ring and still get a great seal and free up power by having less friction. The friction is generated by the ring tension which is set depending on how the ring is intended to be used, generally wet-sump engines running little or no PCV have to use a higher tension ring or deal with the early unseating behaviors that high crankcase pressure produces which leads to smoking and oil consumption and ruined rings over time along with circulating deposits that ruin the engine.
On the piston surface and ring apical the problem of disruptive carbon coatings is solved by carbon cycling.
Carbon cycling is part of the combustion chamber design, carbon leftover from combustion is sequestered and held loosely enough that it can participate in the following reaction, thereby cycling back into use. A soft fluffy coating of carbon 'dust' is kept on the piston as a reservoir and carbon fragments are constantly cycling into and out of combustion as products over time, never remaining long enough to form conglomerates of tar or hard coatings. An engine with correct PCV setting and modern chamber design will have carbon on the pistons that easily wipes away with a paper towel leaving behind a very clean piston surface no solvents needed.
What does all of this have to do with cleanliness?
Combustion process has been intensely studied, modeled, computed, controlled, etc... As technology goes on it will become more and more precisely controlled.
When we discuss cleanliness we have to refer once again to the technology state and the hardware we are discussing specifically, sbc is far inferior to LS combustion chamber for example and the SBC is permitted far more 'dirty' reaction than an LS and a typical overvalve injected LS from 20 years ago is far from clean as something being produced now a days.
The cleanliness of combustion reaction strongly depends on the combustion model which was used to create the design of the chamber/piston/ports/valves/etc... for it needs to fall within some variable conditionals in order to produce a clean, methodical combustion reaction with as few unwanted products as possible.
For example, very cold air will not contain enough energy to produce the required combustion reaction as modelled for part throttle; there will be spaces in the chamber where more partially reacted products form and energy will be lost as disorganization emerges due to the model not participating fully as intended and designed. An engine isn't just an air pump after all - it is also an energy conversion device which relies on a chemical reaction rate that is set by some expected variables such as fuel quality and air temperature and even unexpected as oil temperature and valve temperature or even sound related.
Our goal as engine would be tuning experts then is to recapitulate the original combustion models ideal performance metric scenario for our engine to remain efficient and clean during service. In order to do that we need to match the temperatures, pressures, fuel quality, etc.. expectations for part throttle or extended operation (200,000 miles) if needed. On the other hand if the engine is only used for racing purposes then the combustion pressure and temperatures will generally be much higher and the threat of disorganization and lost fluids energy transfer will be neglected due to the egregious amount of energy being produced and handled by the engine during racing. In other words, the question of cleanliness is a question of reaction energy and fuel behavior with respect to technology state and combustion chamber modelling design strategy. A well designed chamber can still effectively react all of it's hydrocarbon chains (or a great deal many/most) with precise control over fuel injection placement (right to the piston) and by injected the needed energy with the fuel (very high fuel injection pressure = massive kinetic energy input) to allow even cold and slow moving initial combustion states to proceed effectively and yield low emissiosns and high conversion of fuel mass rate to work, cleanliness thus contributes to efficiency but when people discuss BSFC they often focus solely on wide open throttle and not the Cruise conditions of the combustion chamber which matters if you actually drive the vehicle and need the economy and the engine to stay clean during that time.
2. I didnt forget economy but this should be rhetorical after reading the 3.
If we react more hydrocarbons per combustion event we also increase the energy extraction of fuel in theory (combustion is more complex than this blanket statement and Im sure this isnt always true) and this should improve economy and reduce emissions and harmful products of blow-by.
Again that requires the correct energy input, too little and it may disorganize and form unwanted products. Too much and the fuel could react suddenly exploding (detonate). The balance is striken between forms of energy input and energy reservoirs. For example sound is an energy reservoir in the intake plenum that can either assist with economy or work against it in the form of pumping losses. Exhaust gas velocity is an energy reservoir component of flow work which can be used as a form of available 'free' energy to drive intake flow into the cylinder during overlap. Fuel pressure at injection site nozzle design is an energy reservoir of injectable kinetic energy which can assist the intake airflow of an engine when timed correctly (injection phase tuning). Fuel, oil, and air intake temperature is a reservoir of enthalpy which plays a role in the sizes of engine parts and heat transfer among them which directly impacts combustion modelling - too cold of a spark plug or fuel for example have dramatic influence on combustion efficiency (conversion of hydrocarbon fuels to fully reacted products is what I mean when i say combustion efficiency in this context, if there are many unwanted side products then efficiency is poor. We can also say efficiency is bad when the conversion of fuel to energy is bad, but you can have a good conversion of hydrocarbons to products with a bad conversion of fuel to work at low compression ratios with great technology so I make this distinction evident now)
And so on. The idea as an engineer is take advantage of these reservoirs: Time the intake valve to open when the sound arrives. Time the injector to open when the piston is at peak piston velocity around 280 to 240* btdcc. Design the exhaust system to promote good velocity for most common operating conditions. Take advantage of the intake air warming to raise intake velocity and expand the air warmly so it can distribute systemically and produce smooth operation and input enough energy to combustion to have a good conversion fully to products with few byproducts as possible. These are both cruise and wide open throttle issues, the only difference is, at wide open throttle there is generally an energy excess in the form of heat of combustion which must be taken out of the chamber at some rate (spark plug transfer for example) in order to protect the engine from the fuel behaviors or high temperature of parts inside such as pistons which factory pistons are made from brittle fracture failure materials which do not like to expand in the heat, it is best to keep them cool. Forged pistons do not mind expanding more and will handle the heat, so if the fuel and piston are up to the challenge the temperature can be many hundreds of degrees higher in the chamber during racing. It allows flexibility with fuel energy content, you can use more gasoline style racing fuels, get more mileage, there is advantages to knowing where the energy is going rather than simply dumping it out of ignorance. But many types of racing do not care about mileage of the fuel, they have unlimited filling up with fuel time. Like drag racing I guess, you can fill up after each pass and only use a small fraction of what the tank can hold. So the issue of economy at wide open throttle is rarely any concern. Still, the conversion of products, energy conservation and utilization, blow-by sequestration, PCV evacuation, potential and kinetic energy, it will all influence how long the engine lasts, its cleanliness, and its ultimate potential, so these issues while at first glance seem "crazy" (who would use hot air on purpose?) Are actually the secret winning edge that an engineer following the numbers has the potential to extract both in economy for cruising around and ultimate potential of a powerplant
The best way to bring in cold air while simultaneously improving engine efficiency and economy is to insulate the engine fully like a modern engine
plastic intake manifolds, plastic covers, thick exhaust tubes, exhaust wrap, shieldings, engine blankets, reflective tape, ceramic coatings, crushed lava rock insulating cloth fibers, etc... These will improve engine efficiency via conservation of energy and reduce underhood temperatures
Venting is a last resort because energy is lost, like a leak. If you open the lid on a grill now you burn more propane gas keeping the food warm. The engine must maintain its heat energy like a grill so each combustion event and vaporization energy input can be balanced. If there is imbalance due to a leak then additional energy input from fuel is required and the overall temperature peak and valley will influence carbon fragment production, for example very cold spark plugs, remove too much heat, economy is lost, carbon buildup ensues due to the fragmentation issues with partially reacted hydrocarbons due to low incidence velocity rates due to the lost energy of heating. Pulling heat out of the air or chamber is non-linear yet synonymous in concept.
What are your opinions on adding a cold air intake to a 91? The only time I've ever added a cold air intake to a vehicle is when I owned my 2007 Subaru WRX.
The best way to bring in cold air while simultaneously improving engine efficiency and economy is to insulate the engine fully like a modern engine
plastic intake manifolds, plastic covers, thick exhaust tubes, exhaust wrap, shieldings, engine blankets, reflective tape, ceramic coatings, crushed lava rock insulating cloth fibers, etc... These will improve engine efficiency via conservation of energy and reduce underhood temperatures
Venting is a last resort because energy is lost, like a leak. If you open the lid on a grill now you burn more propane gas keeping the food warm
This is ridiculous. Your first reply was too long for me to waste my time reading.
This is ridiculous. Your first reply was too long for me to waste my time reading.
Its called law of conservation of energy
Why do you think this is the case
Theoretically, the thermal efficiency of the engine will improve if there is no cooling system.
Why does thermal efficiency improve if we stop throwing away heat?
Why doesn't everyone use oil coolers and keep water/oil at 100*F?
Is heat actually helpful in some way?
Do people not use exhaust wrap and ceramic coatings to insulate their engine exhaust systems since forever?
Do OEM not use thick walled cast manifolds and plastic insulating underhood/manifolds wherever possible?
Somebody along the line over the past 30 years put some goofy cold air intake on my car. They cut a big hole in the upper radiator shroud, put little cylinder-like air filter down through it, drilled more holes and screwed a hat down of it to make a half assed seal and thought it was going to make the car faster. I'm in the process of putting a new upper radiator support and stock airbox on the car. If I ran into whoever did that to this car I'd kick them in the nuts. After all that hacking they were just drawing air from under the shroud instead of above it. Little to no difference in performance.
I have a 1990 ZR-1 which i drag race sometimes. I made a "cold air" intake system for my car. Using the old A/O engineneering cold air kit I cut a larger hole into the front bumper
( 4in x 3in ) and fed the ambient (outside air) into a closed air housing using the stock air filter.To help reduce heat into my system I placed Alu bubble sheet between the radiator shroud and the bottom of the stock air filter. Also warpped the stock air filter assembly with DEI cool warp to reduce engine compartment heat out of the stock air filter.
Not sure if this helps but my car has run 11.54 @120 in the 1/4 mile and 7.52 @101 in the 1/8 mile. The car makes only 418 rwhp.
1990 White/Black #2546
one of a few 4l8OE transmission eq ZR-1's
John
The front plate is one I made and sold about 2 years ago.the plate was cut out
so outside air goes into the air filter and screen helps keep out paper. trash and slow cars. with this setup I get 20 miles per gal at 70 mph on the interstate and about 16 mpg around town.
John
