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Top Intake On Std Airbox

75coupe

By 75coupe,
in Engines & Forced Induction

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75coupe Grand Master

75coupe

Posted
Posted

I have a bonnet with a vent above the airbox...

I am currently using a pod filter with no box.

I want to use the airbox with a blitz style lid like in the photos below...

I have two small issues;

1. What can I use on the lid I have made to mate with the latches on the std airbox, admittedly I have made the lid a nice snug fit so it may not even need them but it would be alot better. I do have some hooks I could use but I don't have a drill to go that will go through them (even a drill for hardened steel) and don't have a propane torch or at least I can't find my torch fitting for the gas bottle.

2. I am going to use fire retardant foam to complete a tunnel from underneath the bonnet vent to the top of the airbox lid, so it will be completely sealed from engine bay air , any ideas on how I can get a profile of the foam to fill this gap, as the bonnet is shut I cannot see the gap between lid and bonnet?

And do I really need to use fire retardant foam or do you think I can get away with std foam?

I was considering as well making the hole about 15mm wider all round, do you think it is really needed, I would of thought the opening is more than enough considering the std snorkel is smaller?

comments or suggestions?

post-26316-1207884963_thumb.jpgpost-26316-1207884887_thumb.jpg

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**RB2530** Proficient

**RB2530**

Posted
Posted
2. I am going to use fire retardant foam to complete a tunnel from underneath the bonnet vent to the top of the airbox lid, so it will be completely sealed from engine bay air , any ideas on how I can get a profile of the foam to fill this gap, as the bonnet is shut I cannot see the gap between lid and bonnet?

comments or suggestions?

post-26316-1207884963_thumb.jpgpost-26316-1207884887_thumb.jpg

As far as getting a profile is concerned a trick which I use sometimes is this...

Get some aluminium foil and scrunch it up very loosely and place it around the edge of the airbox. Then close the bonnet... open up the bonnet and hey presto, in the foil you should a fairly accurate profile of where the the inside of the bonnet comes to imbedded in the foil...There are many things apart from foil that you can use but I find foil works best...It squashes with a minimum of force and will not recover after the force is removed..It may take a few goes to get it perfect but it has worked well for me every time..

As far as using the clips...wont the bonnet hold down the aluminium frame anyway??

As far as fire retardant foam is concerned I dont see a need for this...I would use some thermal insulating to prevent engine bay heat from transferring into the air stream...

If you really want to get efficient, line the base of the air box (probably the outside) with thermal insulation foam...You can even wrap the intake pipework with the foam..All this prevents heat soak from the engine bay ...

Good luck

GeeTR Grand Master

GeeTR

Posted
Posted

First what does the “vent” look like in the bonnet? As if its facing backwards, its not really going to promote airflow into the hole.

Could you rivet some shaped alloy tabs to the sides, so the latches can grab them?

What ever “hooks” you have that are impervious to decent metal drill bits... must be made of depleted uranium lol,

I doubt serious heat or flame could reach the foam your using; specific flame retardant stuff wont be needed.

As for profiling, I never though of al-foil, that’s pretty clever.

When mounting gear at the top of the engine bay, I dislike the idea of wasted space between it and the bonnet. (fuel reg, remote oil filter etc) I used normal corrugated cardboard, with run of the mill bamboo skewers pushed into the end. The height of the cardboard is a known measurement, as is the location I hot glued it. Close the bonnet, open again, and hey presto; the “resolution” of the shape is obviously dependant on how many skewers you use. From here it’s too easy transferring the shape onto more cardboard to use as a template.

chiksluvit Experienced

chiksluvit

Posted
Posted (edited)

that lid looks really well made..

it really depends on what the vent's like... normal foam will be fine, since most of the foam filters out there aren't fire retardant anyway, but fire retardant foam's preferred..

i'd also be worrying about the elements coming through the vent slowly destroying the foam too, you might want to consider using rubber for the job

or just use the stock airbox lid... that's what i ended up using after trying all those experiments with the intake... made no difference with power on dyno

Edited by chiksluvit
**RB2530** Proficient

**RB2530**

Posted
Posted
or just use the stock airbox lid... that's what i ended up using after trying all those experiments with the intake... made no difference with power on dyno

Dyno testing will rarely show improvements gained from CAI and air box mods. This is true and the reason being is you dont have decent air flow at the front of the car apart from the cooling fan that is commonly aimed at the radiator..Obviously when you are out driving there is a fully developed laminar flow hitting the front of your at a speed approximately the same as your road speed...This is a very different scenario to the Dyno set up...So I agree that the dyno may not show any improvement, but thats not to say they dont exist..

The way to test for intake mod benefits is:

1. Place thermocouple in your airbox or in filter element and another thermocouple where the air comes into the carfront bar to pick up ambient temp at the front of the car..Your design is well designed if you get no or just a very small increase in temp between these two point...You can also do this between the airfilter and the throttle body to check for IC and IC pipwork efficiency

chiksluvit Experienced

chiksluvit

Posted
Posted

temp wise, stock airbox is totally sealed from heat sources

and i agree, your test does work

but that's temp, how about ram air effect?

stock box has the snorkel directly aimed at the front, where some pod setups or lidless airbox doesn't, unless like he said, use the duct from the bonnet, again that depends on how its designed too

even in real driving conditions stock box has the advantage with the front facing snorkel

Dyno testing will rarely show improvements gained from CAI and air box mods. This is true and the reason being is you dont have decent air flow at the front of the car apart from the cooling fan that is commonly aimed at the radiator..Obviously when you are out driving there is a fully developed laminar flow hitting the front of your at a speed approximately the same as your road speed...This is a very different scenario to the Dyno set up...So I agree that the dyno may not show any improvement, but thats not to say they dont exist..

The way to test for intake mod benefits is:

1. Place thermocouple in your airbox or in filter element and another thermocouple where the air comes into the carfront bar to pick up ambient temp at the front of the car..Your design is well designed if you get no or just a very small increase in temp between these two point...You can also do this between the airfilter and the throttle body to check for IC and IC pipwork efficiency

75coupe Grand Master

75coupe

Posted
  • Author
Posted
ummm

what happens when it rains?

Its not a daily driver, and I don't know about you guys but driving my skyline in the wet doesn't really turn me on... But I guess I'll just have to see how it goes if I get caught in the rain...

Although I'm keen to see or hear about howw the ARC airbox works since they have a top mounted foam filter with no cover or snorkel so how does it get its cold air and if it is through a bonnet intake then what does it do in the rain?

**RB2530** Proficient

**RB2530**

Posted
Posted

The stock airbox is not sealed from heat...You have heat transfer from the engine bay into it...It is made of plastic and heats up...The heat transfers throught the plastic towards the inside...The inside wall heats up and there you have it...Heat into the inlet air...

As far as the RAM effect is concerned, the factory snorkel is pretty piss poor...The end of it does not see the road speed stream anyway because the bonnet is in the way. It is design just 'pull' cold air from just above the headlight...

Btw I worked it out once that any ram effect at 100km/hr will give you about 0.25 psi pressure increase and thats all...It is not much...And as soon as you try and draw more through it than what is flowing into it naturally due to road speed itself, you end up with vacuum inside anyway...

A good airbox design is:

1. Insulated from the engine bay as much as possible.

2. Has an inlet or inlets that are large enough to introduce more cool road speed air into the airbox than the engine is likely to need.

3. Is not completely sealed so that excess road speed air can flow out of the airbox...(if this doesn't occur flow into the airbox will also be limited and it will start to heat up...

GeeTR Grand Master

GeeTR

Posted
Posted
....3. Is not completely sealed so that excess road speed air can flow out of the airbox...(if this doesn't occur flow into the airbox will also be limited and it will start to heat up...

This also helps prevent the "shuffleing" some people get, when the slightly pressurised air dicks around with the AFM hot wire.

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