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I picked up a 5.7L intake setup off of ebay and threw it on this weekend just so see what would happen. Oh my GOD!! I should have done this years ago. What a difference an afternoon and a trip to Home Depot make. I would strongly suggest anyone with a stock pre-'98 3.8 give this option a serious thought. No, it's not as sexy as an FIPK or SLP system, but it's practically free! (I spent about $40 including shipping and my Home Depot run.)
I've been thinking about adding a cold air kit to my car for a while now, but really didn't like the idea of hacksawing bits out of my engine compartment or having an open cone in my fender well pretty much exposed to the elements. I know, many of you guys run them just fine with no problems, but I'm a little paranoid about such things. I have a very high mileage car (over 222K miles now) that functions as my daily driver and I refuse to do anything that may have an impact on long-term reliability such as allowing the car to ingest water during a torrential downpour at highway speeds.
As an engineer, I took a look at what we really had under the hood, thought back to my fluid dynamics lectures, and did some quick back-of-the-envelope calculations. My findings surprised me a little.
The first thing that occurred to me was that the 5.7L engines use the same stock airbox as the 3.8s. As most of you know, the pre-'98 3.8s have three part intakes consisting of the airbox, the silencer assembly, and the goofy little plastic intermediate tube. The fact that the 5.7L uses our airbox says that this part (that we all got free with our cars) is designed to have sufficiently low restriction to flow ~50% more air than the 3.8s can take at full throttle. Also, the stock airbox actually pulls its input air from behind the driver's headlamp and the fenderwell, effectively giving us a poor-man's cold air kit from the factory. Throw in a stock-replacement style K&N air filter and I seriously doubt that the stock airbox represents a significant choke point in our intakes, especially when you consider that we are only using just about 2/3 of their designed flow capacity. Quite to the contrary, I think it works pretty well.
So, where was the restriction, you ask? Easy. All that ridiculous plastic plumbing GM tried to pass off as a silencer assembly and I-tube. Before I slam GM too much, we have to remember that we all bought what is flippantly called the "secretary's car" in the line-up, so many of the V6's design choices were made for quietness, smoothness, or comfort instead of performance. Still, a quick set of measurements and a few punches on my trusty calculator show that the silly little stock I-tube is only ~1 5/8 x 4.5 inches in size (~7.3 sq. inches cross section) at its tightest point (where it squeezes behind the radiator). This says that the air moving at this point inside the I-tube must flow at nearly 90 mph to supply the engine at redline. Then the flowing air falls into the silencer cavity, which is designed to trap and damp unwanted intake acoustics while it abruptly turns the flow 90 degrees. I'm sure putting this in our cars made sense to someone, just not me. (I guess I'm not a secretary.)
The 5.7L intake's nominal x-section of ~11 sq inches is 50% larger, dropping redline tube flow speeds to ~60 mph. It's I-tube has a funky T-shaped x-section at the radiator choke-point that looks very similar to the K&N's, but the K&N's deletion of the airbox let's them do more to optimize the airflow over the entire run. The stock 5.7L's intake still uses a silencer, but its a resonance tube-type stuck to the inlet elbow which is easily removed and capped with a 2" rubber pipe cap w/ supplied hose clamp, and some rubber cement. You can also use the 1LE inlet elbow if you wanna spend some more money. My goal however was to spend as little as possible on this, so my MacGyver patch was good enough.
The only mods I needed to do were using a pipe cap to block off a port in the I-tube as well as a 3/8" plug pipe plug and old screw to seal off holes in the inlet elbow. I then drilled a 5/8" hole in the I-tube to accept the old inlet air temp sensor from my old intake. No wires were cut since the stock sensor had plenty of slack to allow me to move it without worry.
So, what are the results?? In a word, Awsome.
Now, I'm sure you "real Cold Air" guys are all turning up your noses right now, but I noticed a clear and immediate seat-of-the-pants improvement for about $40. That's pretty hard to beat. The engine seems to spool faster and feels like it provides more torque over the entire RPM range. The infamous 30 mph downshift nearly snapped my neck beck on the way home from work today. The exhaust note also seems to sounds a bit better through the stock Y87 dual exhaust. (Sorry, no audio clips yet.)
I want to run the car a bit to let the engine computer adjust before doing a few G-Tech runs, but I'm pretty optimistic on the results. I'll also reoprt on any mpg changes since I've got my entire fuel usage history in an excel spreadsheet (I did mention that I'm an engineer). Even if I do not get any measurable improvements, getting rid of that stock silencer and I-Pipe really woke up my engine.
I really wish I would have done this mod 100,000 miles ago. ;-)
I've been thinking about adding a cold air kit to my car for a while now, but really didn't like the idea of hacksawing bits out of my engine compartment or having an open cone in my fender well pretty much exposed to the elements. I know, many of you guys run them just fine with no problems, but I'm a little paranoid about such things. I have a very high mileage car (over 222K miles now) that functions as my daily driver and I refuse to do anything that may have an impact on long-term reliability such as allowing the car to ingest water during a torrential downpour at highway speeds.
As an engineer, I took a look at what we really had under the hood, thought back to my fluid dynamics lectures, and did some quick back-of-the-envelope calculations. My findings surprised me a little.
The first thing that occurred to me was that the 5.7L engines use the same stock airbox as the 3.8s. As most of you know, the pre-'98 3.8s have three part intakes consisting of the airbox, the silencer assembly, and the goofy little plastic intermediate tube. The fact that the 5.7L uses our airbox says that this part (that we all got free with our cars) is designed to have sufficiently low restriction to flow ~50% more air than the 3.8s can take at full throttle. Also, the stock airbox actually pulls its input air from behind the driver's headlamp and the fenderwell, effectively giving us a poor-man's cold air kit from the factory. Throw in a stock-replacement style K&N air filter and I seriously doubt that the stock airbox represents a significant choke point in our intakes, especially when you consider that we are only using just about 2/3 of their designed flow capacity. Quite to the contrary, I think it works pretty well.
So, where was the restriction, you ask? Easy. All that ridiculous plastic plumbing GM tried to pass off as a silencer assembly and I-tube. Before I slam GM too much, we have to remember that we all bought what is flippantly called the "secretary's car" in the line-up, so many of the V6's design choices were made for quietness, smoothness, or comfort instead of performance. Still, a quick set of measurements and a few punches on my trusty calculator show that the silly little stock I-tube is only ~1 5/8 x 4.5 inches in size (~7.3 sq. inches cross section) at its tightest point (where it squeezes behind the radiator). This says that the air moving at this point inside the I-tube must flow at nearly 90 mph to supply the engine at redline. Then the flowing air falls into the silencer cavity, which is designed to trap and damp unwanted intake acoustics while it abruptly turns the flow 90 degrees. I'm sure putting this in our cars made sense to someone, just not me. (I guess I'm not a secretary.)
The 5.7L intake's nominal x-section of ~11 sq inches is 50% larger, dropping redline tube flow speeds to ~60 mph. It's I-tube has a funky T-shaped x-section at the radiator choke-point that looks very similar to the K&N's, but the K&N's deletion of the airbox let's them do more to optimize the airflow over the entire run. The stock 5.7L's intake still uses a silencer, but its a resonance tube-type stuck to the inlet elbow which is easily removed and capped with a 2" rubber pipe cap w/ supplied hose clamp, and some rubber cement. You can also use the 1LE inlet elbow if you wanna spend some more money. My goal however was to spend as little as possible on this, so my MacGyver patch was good enough.
The only mods I needed to do were using a pipe cap to block off a port in the I-tube as well as a 3/8" plug pipe plug and old screw to seal off holes in the inlet elbow. I then drilled a 5/8" hole in the I-tube to accept the old inlet air temp sensor from my old intake. No wires were cut since the stock sensor had plenty of slack to allow me to move it without worry.
So, what are the results?? In a word, Awsome.
Now, I'm sure you "real Cold Air" guys are all turning up your noses right now, but I noticed a clear and immediate seat-of-the-pants improvement for about $40. That's pretty hard to beat. The engine seems to spool faster and feels like it provides more torque over the entire RPM range. The infamous 30 mph downshift nearly snapped my neck beck on the way home from work today. The exhaust note also seems to sounds a bit better through the stock Y87 dual exhaust. (Sorry, no audio clips yet.)
I want to run the car a bit to let the engine computer adjust before doing a few G-Tech runs, but I'm pretty optimistic on the results. I'll also reoprt on any mpg changes since I've got my entire fuel usage history in an excel spreadsheet (I did mention that I'm an engineer). Even if I do not get any measurable improvements, getting rid of that stock silencer and I-Pipe really woke up my engine.
I really wish I would have done this mod 100,000 miles ago. ;-)
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