1995-2000 LS400 Air Box Modifications

[JBrady]

My old post pictures no longer work so I am making this post to show the procedure for modifying the stock air box.

I tested this mod back to back against the stock system at the dragstrip with multiple passes. Gained a solid half a mile per hour trap speed. That works out to apx 5rwhp. Minor, yes, improvement, yes.

The goal was to insure maximum cool air with minimum restriction.

BTW, the stock filter is superior to the K&N for these cars. The large round filter has tremendous surface area and excellent filtration. The K&N seems like a quickie design with a large solid plastic disk in the middle. No reason to run other than stock.

LS400 K&N filter

Excellent stock filter

Below is the finished product. I am not happy with the blue foam but that is what was available. Hood is rarely open. I will replace with black when I can find some.

IGNORE the wrap of the MAF tube as that is a very minor mod and not part of this particular discussion. You will see it in most of the pictures but ignore it and focus instead on the mods to the filter box.

Notice the STOCK appearance (not including the MAF tube)




Here is from the view from the engine looking forward. You can just BARELY see the blue foam between the factory air duct and the filter box. This is PART of the seal between the underhood air and the filter box.

You will see how this is made in following pictures.

 

[JBrady]

Here is the stock air duct removed. Notice the way the foam fits snugly around the filter box and creates a gasket to block off underhood heat when the stock duct is in place.



Here is another angle of the above. You can see the VERY dirty air filter and the modified stock filter box cover.

 

[JBrady]

With the filter box cover and filter removed you can see the back of the filter box and how the foam surrounds the bottom and really seals off any underhood heat from the filter element.

 

[JBrady]

Here is the stock molding and gasket that surrounds the headlight assembly. It is easily removed and creates a large flow area for air to reach the filter.

I have ran this way for thousands of miles including HEAVY rainstorms and water has never reached the filter itself.




Here you can actually see around the headlight and directly at the filter itself showing the direct airpath for cold air reaching the filter. This is just part of the path as their is an inch or more around the entire headlamp.

 

[JBrady]

Here is the way I modified the stock filter cover for airflow.

Stock filter cover




Plastic cut away leaving a strong functional cover that exposes the entire filter surface to cool air.



One more angle of the modified cover.

 

[jibbby]

What should we call this intake upgrade? Maybe the JBI ? Much like the BFI...

Looks good to me, good work......

 

[drifty325i]

Nice thread Lex. Looks like a good mod

 

[Death By Bass]

so, ah, how exactly is the air even getting into the intake? haha

as far as I can see, there's a headlight in the way, very efficient that is.

 

[LS400GUY]

My old post pictures no longer work so I am making this post to show the procedure for modifying the stock air box.

I tested this mod back to back against the stock system at the dragstrip with multiple passes. Gained a solid half a mile per hour trap speed. That works out to apx 5rwhp. Minor, yes, improvement, yes.

The goal was to insure maximum cool air with minimum restriction.

BTW, the stock filter is superior to the K&N for these cars. The large round filter has tremendous surface area and excellent filtration. The K&N seems like a quickie design with a large solid plastic disk in the middle. No reason to run other than stock.

LS400 K&N filter

Excellent stock filter

Below is the finished product. I am not happy with the blue foam but that is what was available. Hood is rarely open. I will replace with black when I can find some.

IGNORE the wrap of the MAF tube as that is a very minor mod and not part of this particular discussion. You will see it in most of the pictures but ignore it and focus instead on the mods to the filter box.

Notice the STOCK appearance (not including the MAF tube)




Here is from the view from the engine looking forward. You can just BARELY see the blue foam between the factory air duct and the filter box. This is PART of the seal between the underhood air and the filter box.

You will see how this is made in following pictures.

J Brady, I know it's off topic, but could you share your maf wrap mod rational? Also, with the airbox mod, how often do you replace the filter? Thanks in advance.

LS400GUY

 

[JBrady]

J Brady, I know it's off topic, but could you share your maf wrap mod rational? Also, with the airbox mod, how often do you replace the filter? Thanks in advance.

LS400GUY

The plastic tubing of the factory MAF to TB tubing will conduct heat. It is located right next to the radiator and in the hot air stream from the fan. It will therefore be continuously heated. By wrapping it I insulated the tube from this heat. By doing this the cold air flowing through the tube has less of this heat to absorb. Overall the effect is small but it was free and easy to do. Anything to reduce the heat going into the engine will increase the density of the charge per volume and hence power. This mod may be worth one tenth of one horsepower. Not much and is why I said ignor it UNTIL you have focused on how and why the cold air mod is worthwhile.

Here is SRQ400 (from CL) 99 SC400 with a SRT conversion and using gold foil insulation for the same reason. His way has much more bling than mine!

http://mysite.verizon.net/res6pb6m/id11.html

 

[JBrady]

so, ah, how exactly is the air even getting into the intake? haha

as far as I can see, there's a headlight in the way, very efficient that is.

Post #4 is for "How the air reaches the filter for Dummies"

I would explain how the air gets through the grill and up from the air dam as well as why there is a high pressure area in the entire area but I am sure you already understand that. The fact that the headlight blocks water from directly hitting the filter is a definite bonus. Water fails to make the turn while the air of course has no problem. Cheers.