My Intake Mod

Spurshot · June 15, 2015

I thought I'd approach this a little differently than others have.

I have a 5.3L and my first thought was to do a little mod to the intake to increase the flow. I know the popular thing to do is to buy a $200-400 "CAI" or the Airaid MIT tube. I gave it some thought and didn't like the idea of extra noise. I don't like the filters supplied with the "CAI"s.

So, I thought I'd put a bigger throttle body on it. First, I bought the 6.2L throttle body. $100 It is a 87mm throttle body. Same one on the truck and the LT1 Vette. A 5.3L has a 80mm throttle body. It won't fit on the 5.3 intake manifold. Different bolt pattern and smaller hole for the throttle body. I thought about making an adapter plate. I was a machinist in a past life. Still have some access to machines.

Then I saw that a 6.2L manifold was $110. I bought it. I figured I could return it, sell it or whatever if it didn't fit.

Then I found out the intake duct from the air filter box to the throttle body had a larger diameter connection on the 6.2L throttle body. The difference in the duct (big squarish box looking silencer) is just a rubber hose connector, which is bonded on the plastic. So, I just bought a new 6.2L intake duct. $85

So, I'm at about $295 + shipping. I'm probably $360 or more into it.

Here's the mod work from today.

Before

Duct removed.

6.2 duct vs. 5.3 duct

Intake manifold removed.

Oil in the ports. Gotta get the oil separator can installed.

Finished.

One part I didn't get was the PCV line for the 6.2L. I forgot it was different. The 5.3L line goes from the front of the block (valley) to the driver side about midway down on the side of the intake manifold. The 6.2L PCV line goes from the same point on the block to just along side the throttle body on the driver side. I used some 3/8" ID fuel line. I'm going to ditch that connection anyway, when installing the oil separator can.

It started right away, but it had a delayed throttle closing when revving it in the driveway. I ran it and revved it for a while, going all the way to full throttle quickly several time. The delayed throttle closing seemed to go away. I drove it for about a 1/2 hr. The first time I put significant throttle in it, it fell flat. Then it started working better and better with subsequent accelerations. It didn't take long 2-3 and it was working fine. It felt strong on the accelerations I did do, up to about 70 max. I just don't have a good place I feel comfortable doing a full 1/4 mile.

I know what you're thinking...."How much difference did it make?"

Well to tell you the truth, I don't know. I had the best laid plans. I bought a Bluetooth OBD2 connector and some performance measuring software. I just never really got around to using it. It didn't seem like a put a different engine in it. But it seems like it's making more power. I'll know more when I get it tuned. I'll probably get it on a dyno.

Edited June 15, 2015 by spurshot

SouthernSilveradoGuy85 · June 15, 2015

I'm glad you posted this. I was thinking of putting the 6.2 TB on mine just today actually. I actually have the Airaid MIT so I thought all I would need other than the TB would be the different coupler for the tube. I don't really want to get into replacing the intake manifold just for a little bigger TB so I may not do it.

As for the oil, I used the CRC GDI cleaner. It seemed to have taken a few days to feel the difference or it's just my mind telling me it felt better. Hell the other day I was backing up when I got to a deadend looking for a place and I not only scratched off a little, it left 2 black marks. I didn't think it could do that since I didn't WOT it and I only have the 3.08 gears. The road was somewhat dirty so maybe that played a roll. It says on the CRC can to do it every 10,000 miles. I do plan on a catch can in the future and I'll just use a couple cans to try to clean the valves and runners before installing it.

Edited June 15, 2015 by SouthernSilveradoGuy85

Spurshot · June 15, 2015

I'm glad you posted this. I was thinking of putting the 6.2 TB on mine just today actually. I actually have the Airaid MIT so I thought all I would need other than the TB would be the different coupler for the tube. I don't really want to get into replacing the intake manifold just for a little bigger TB so I may not do it.

As for the oil, I used the CRC GDI cleaner. It seemed to have taken a few days to feel the difference or it's just my mind telling me it felt better. Hell the other day I was backing up when I got to a deadend looking for a place and I not only scratched off a little, it left 2 black marks. I didn't think it could do that since I didn't WOT it and I only have the 3.08 gears. The road was somewhat dirty so maybe that played a roll. It says on the CRC can to do it every 10,000 miles. I do plan on a catch can in the future and I'll just use a couple cans to try to clean the valves and runners before installing it.

The throttle body is 7mm larger in diameter. Doesn't sound like much. But, that means the area of the bore goes from 5026mm² to 5944mm², or 18% larger area. Also, the 6.2L (LT1) throttle body has a much nicer inlet contour, where the 5.3L throttle body has a sharp step. Basically, the 6.2L throttle body comes machined similar to the "ported" modifications they do to the various throttle bodies

Edited June 15, 2015 by spurshot

robvas · June 15, 2015

Anyone used the JET thottle body on the 5.3?

http://www.jegs.com/i/JET-Performance/561/76108/10002/-1?parentProductId=2944748#moreDetails

Spurshot · June 15, 2015

From the picture of it, I'd be skeptical that it was a bit of a ruse. My aerodynamics training and flow work I did on a flow bench many moons ago, lead me to believe those fluted cuts in the throat are exactly the opposite shape of what is needed to enhance flow. That sharp step created from that shape causes flow separation and reduces flow. My 2cents

SouthernSilveradoGuy85 · June 15, 2015

How much of a difference do you feel with the 6.2 TB and intake manifold? I wouldn't mind paying $200 for the 6.2 TB and manifold if it's a noticeable difference, but I guess I wouldn't feel comfortable taking the intake manifold off of a truck and engine so new. I do have a TQ wrench so I know I could torque the bolts right, I just haven't done anything that far myself.

Higgs Boson · June 15, 2015

the intakes on the LTx motors are a piece of cake. No coolant or fuel.

07Softail · June 15, 2015

Camshaft next?

RT

Chris · June 15, 2015

Camshaft next?

RT

Oh he had the 6.2 bumpstick at the meet.

ryandemo84 · June 16, 2015

Spurshot or anyone else, have you thought about porting the throttle body and/or intake manifold? Would doing this make any significant gains?

Spurshot · June 16, 2015

Spurshot or anyone else, have you thought about porting the throttle body and/or intake manifold? Would doing this make any significant gains?

After looking at the 5.3L throttle body, you can see a sharp corner step. That can be rounded for some gains in flow. The butterfly shaft can be thinned a little. Will they result in noticeable horsepower gain? I dunno. "Significant gains" ? I doubt very much. I didn't spend much time lookin at the inside of the manifold. There's a few small anomalies from the mold lines that could be smoothed. But they put a lot of thought into the manifold design.

The cam is where I think the low hanging fruit is. A little more lift and duration while holding the overlap modest. That's the L86/LT1 cam. Keeping the full stock cam advance range capability should help keep fuel economy good. The aftermarket cams with more lift and duration require limiting the variable cam advance, which will limit fuel efficiency advantages of variable cam advance. But they can make more hp. I'm trying not to screw up the fuel economy badly.

A custom BB tune should make all this work together. If it makes 30 hp more with the throttle body, manifold, cam and tune, I'd be thrilled. More would be nice.

Edited June 16, 2015 by spurshot

ryandemo84 · June 16, 2015

Just a thought. Thanks for the response.

Spurshot · June 16, 2015

Just a thought. Thanks for the response.

It's conceivable to me that you might pickup gains similar to CAI mods, if someone knew what they were doing.

Higgs Boson · June 16, 2015

I picked up good gains with a ported intake on my C7, I would think good gains would be available on the truck as well.

Porting the throttle body will not do anything. I have a ported TB on my C7 and had one on a few other vehicles and it never did a thing, it's just cheap so I did it anyways. Not going to do it this time.

I also kill the cam retard under 3000 RPMs that is programmed in the stock tune and it feels more torquey and I have yet to lose any mileage. In fact, I kill AFM/DoD and low end cam retard and still get 20 mpg on the highway.

fondupot · June 16, 2015

Seems like a lot of work, for not much noticeable gain. I just installed the Airaid MIT on my 5.3L. Cost $135 shipped from Amazon. I have Corsa Exhaust on my truck and I didn't notice much difference in noise from the engine after installing the Airaid. But I did notice better throttle response. Maybe even a small boost in MPG. The jury is still out on the MPG.