19 replies to this topic

[IronmanG]

I'm running a 7 port and in an effort to try and boost the torque, and in discussion with AC I'm going to make up an airbox. I looked at the P600 but there isn't enough room.
I currently have the JC40 itg dome filter. 40mm internal size.
So the new airbox still clips onto the existing backplate I was thinking to strip the foam off and use the cage as a template to make a fibreglass box with a 75mm outlet drop it down in the front corner near the solenoid to fit an air filter.
So in theory I should get cooler air in, maybe take away a bit of resonance between 3k and 4k, and improve the torque for better driveability.
I haven't used fibreglass before so any tips welcome.
Has anyone tried fitting a cold air duct and seen any improvements

[sonscar]

On a non Mini(mgb V8)I had an underbonnet cone filter and replaced it with the original v8airbox feeding from the front grille.The improvement at idle and in traffic was noticeable.This was with the original injection plenum and throttle body,Steve..

[IronmanG]

On a non Mini(mgb V8)I had an underbonnet cone filter and replaced it with the original v8airbox feeding from the front grille.The improvement at idle and in traffic was noticeable.This was with the original injection plenum and throttle body,Steve..

Cheers Steve.
I'm sure there is a calculation for it all to figure out how big it should be. From what I read 75mm covers up to 150hp so happy to go a bit more smaller if I have to. And the longer the duct to the airbox the better? Like having long runners?
I might be able to run it the opposite side with a U bend past the alternator and across behind the grille
All ideas are welcome.
I know turbo Phil made up a cracking plenum for his and its detailed on here

https://www.theminif...ne-build/page-4

Edited by IronmanG, 31 May 2023 - 03:26 PM.

[PoolGuy]

You might get some ideas here>>>> https://store.jenvey...nents/air-boxes

[growlerbearnz]

Here's the airbox I made for my '63: https://63miniresto..../18/airbox-mk2/

I have since removed the cold air duct, as it was restricting flow above 5500rpm. 

Edited by growlerbearnz, 01 June 2023 - 10:16 PM.

[IronmanG]

Here's the airbox I made for my '63: https://63miniresto..../18/airbox-mk2/

I have since removed the cold air duct, as it was restricting flow above 5500rpm.

Ok ye looks good. What size hose were you using. Whats the hp of the engine

[Java_Green]

I have learnt that you should not exceed an airflow velocity of 90 m/s. Out of this, it is pretty straight forward to calculate what duct size you need. 

[sonscar]

My 3500cc V8 revs easily to 6500 rpm and sucks through a 34 mm inlet tube to the filter box,am I leaving some power on the table?Just curious,Steve.

[IronmanG]

Reverie who make carbon airboxes suggest 75mm tube is good for up to 150hp. I think it was 100mm for 230 or so. That would suggest you are
I wasn't sure how it worked so I just worked out the area of 75mm tube vs the size of my current inlets, or rather what my current inlets should be!
Although SC run a 50mm inlet on their large throttle bodies for a 5 port
50mm would be much easier to run

Edited by IronmanG, 02 June 2023 - 09:28 AM.

[IronmanG]

I have learnt that you should not exceed an airflow velocity of 90 m/s. Out of this, it is pretty straight forward to calculate what duct size you need.

I have no idea? How do you do that

[Java_Green]

I have learnt that you should not exceed an airflow velocity of 90 m/s. Out of this, it is pretty straight forward to calculate what duct size you need.

I have no idea? How do you do that

I did it when I was about to choose size of single throttle body (aimed for one not to big as that would make end up in worse throttle response)
As an example:
Engine volume (Veng) = 1293cc = 1.293E-3 m^3
Max engine speed (n) = 8000 rpm = 8000/60 rps (revs per second)
Max air velocity (v_air) = 90 m/s
Duct or throttle area (A) = ?

1. Max "air consumption" of the engine (only half of the engine working every crankshaft revolution and assuming no restrictions filling the engine what so ever):
air_cons = (Veng/2)*n = (1.293E-3/2)*(8000/60) = 0.0862 m^3/s (86.2 litre per second)

2. Max air flow through duct or throttle is equal to "air_cons":
air_cons = v_air * A = {assume concentric hole => A=pi*r^2} = v_air * pi*r^2
=> r = sqrt(air_cons/(v_air*pi))

If you now take air consumption formula from "1" and put it into the last expression in "2":
=> r = sqrt(air_cons/(v_air*pi)) = sqrt((Veng/2)*n/(v_air*pi)) = sqrt((1.293E-3/2)*(8000/60)/(90*3.14)) ~ 0.017 m (= 17mm)

So with given input data the duct or throttle radius should be above 17mm.

I hope this helps someone....

Edited by Java_Green, 04 June 2023 - 08:43 AM.

[IronmanG]

I have learnt that you should not exceed an airflow velocity of 90 m/s. Out of this, it is pretty straight forward to calculate what duct size you need.

I have no idea? How do you do that

I did it when I was about to choose size of single throttle body (aimed for one not to big as that would make end up in worse throttle response)
As an example:
Engine volume (Veng) = 1293cc = 1.293E-3 m^3
Max engine speed (n) = 8000 rpm = 8000/60 rps (revs per second)
Max air velocity (v_air) = 90 m/s
Duct or throttle area (A) = ?

1. Max "air consumption" of the engine (only half of the engine working every crankshaft revolution and assuming no restrictions filling the engine what so ever):
air_cons = (Veng/2)*n = (1.293E-3/2)*(8000/60) = 0.0862 m^3/s (86.2 litre per second)

2. Max air flow through duct or throttle is equal to "air_cons":
air_cons = v_air * A = {assume concentric hole => A=pi*r^2} = v_air * pi*r^2
=> r = sqrt(air_cons/(v_air*pi))

If you now take air consumption formula from "1" and put it into the last expression in "2":
=> r = sqrt(air_cons/(v_air*pi)) = sqrt((Veng/2)*n/(v_air*pi)) = sqrt((1.293E-3/2)*(8000/60)/(90*3.14)) ~ 0.017 m (= 17mm)

So with given input data the duct or throttle radius should be above 17mm.

I this helps someone....

My brain hurts

[IronmanG]

I have learnt that you should not exceed an airflow velocity of 90 m/s. Out of this, it is pretty straight forward to calculate what duct size you need.

I have no idea? How do you do that

I did it when I was about to choose size of single throttle body (aimed for one not to big as that would make end up in worse throttle response)
As an example:
Engine volume (Veng) = 1293cc = 1.293E-3 m^3
Max engine speed (n) = 8000 rpm = 8000/60 rps (revs per second)
Max air velocity (v_air) = 90 m/s
Duct or throttle area (A) = ?

1. Max "air consumption" of the engine (only half of the engine working every crankshaft revolution and assuming no restrictions filling the engine what so ever):
air_cons = (Veng/2)*n = (1.293E-3/2)*(8000/60) = 0.0862 m^3/s (86.2 litre per second)

2. Max air flow through duct or throttle is equal to "air_cons":
air_cons = v_air * A = {assume concentric hole => A=pi*r^2} = v_air * pi*r^2
=> r = sqrt(air_cons/(v_air*pi))

If you now take air consumption formula from "1" and put it into the last expression in "2":
=> r = sqrt(air_cons/(v_air*pi)) = sqrt((Veng/2)*n/(v_air*pi)) = sqrt((1.293E-3/2)*(8000/60)/(90*3.14)) ~ 0.017 m (= 17mm)

So with given input data the duct or throttle radius should be above 17mm.

I this helps someone....

So 50mm diameter would be adequate with your engine specs above with no restriction whilst maintaining a decent airspeed.

[growlerbearnz]

 

Here's the airbox I made for my '63: https://63miniresto..../18/airbox-mk2/

I have since removed the cold air duct, as it was restricting flow above 5500rpm.

Ok ye looks good. What size hose were you using. Whats the hp of the engine

 

The hose was about 75mm, but a bit restrictive at higher revs. With the hose removed it made 65hp at the wheels. 

[Java_Green]

I assume that hose was far from smooth inside creating a lot of turbulence.