Originally Posted by chris_seven (Post 8951216)

The carbon Air Box is interesting and nicely made but is it betterin air flow terms than a Rain Hat and a slightly angled runner on a manifold?

Again it doesn't quite meet the 'Retro' appearance we are trying to obtain but could be good in a Black gel coat.

Originally Posted by chris_seven (Post 8952386)

I am interested in the Air Box concept and how to correlate ait flow changes to powerband shape as the modelling must be relatively complex.

Originally Posted by chris_seven (Post 8953979)

I can also understand that it is possible to tune pulses in an induction system to improve the charge capability into an engine but I find it hard to understand how this works inside a complex box installed in an engine bay.

Originally Posted by chris_seven (Post 8953979)

What I don't understand is why, if airflow is restricted at peak power, the mid band will improve unless the cold air is a benefit until the box restricts flow which seems to say that the box isn't a good design.

Originally Posted by chris_seven (Post 8953979)

I guess my question is how much more performance will I gain if I replace the 'Rain Hats' we are planning to use with a 'box' and will it be worth the development cost.

Originally Posted by robcf (Post 8954046)

I've kicked the idea around for some time to try casting a set of throttle bodies for a 911.

The concept below consists of a tapered throttle body which can package up to a 50mm diam throttle plate.

The inlet side features at least a DCOE 45 bolt pattern (or up to 70mm between fasteners for a larger throttle plate).

Independent base idle adjustment via a screw actuating the throttle plate.

A throttle linkage (not shown) similar to the triumph units.


http://forums.pelicanparts.com/uploa...1452600223.png

Originally Posted by MetalDoc (Post 8954484)

My Jenvey's are attached to a 12mm phenolic resin spacer. I was told it is to limit heat transfer from the head. The engine is not running yet so I don't know how these ITBs perform.

Originally Posted by chris_seven (Post 8953979)

I can understand how 'cold air' boxes work and I think that there is some foundation for this type of device although there is a body of published work that suggests that Otto Cycle engines are only indirectly influenced by changes in ambient temperature. This is in part due to the 'closed' nature of their operating cycle.

Gas Turbines which have an open cycle are much more significantly affected and do show the order of power gains suggested by ITG when ambient temperatures reduce by 15degC.

What I don't understand is why, if airflow is restricted at peak power, the mid band will improve unless the cold air is a benefit until the box restricts flow which seems to say that the box isn't a good design.


I can also understand that it is possible to tune pulses in an induction system to improve the charge capability into an engine but I find it hard to understand how this works inside a complex box installed in an engine bay. I can see that these boxes may act as a plenum but for them to have measurable effects implies that standard systems must be very restrictive.

The 9% power increase claimed by ITG must mean a huge increase in the torque developed by the engine and I struggle to understand this dramatic change.

I have never measured the temperature in the engine bay of a 911 but with a relatively high speed ducted fan drawing large volumes of air through the grille in may not be as bad as we think.

I guess my question is how much more performance will I gain if I replace the 'Rain Hats' we are planning to use with a 'box' and will it be worth the development cost.

I would also like to know the impact on efficiency as part of our objective is to gain the throttle response of carbs whilst trying maintain the fuel economy of a K-Jetronic which may be incompatible. :confused:

Originally Posted by robcf (Post 8955604)

BTW do you know what the nominal distance is between the intake ports (cross car)?

Originally Posted by chris_seven (Post 8956028)

485mm between port centres.

Originally Posted by chris_seven (Post 8955568)

I always believed that Air Filters smooth the flow of air around the intakes and that this can and often does help in a 'busy' under bonnet environment. The question is how much more improvement is there to be gained by using a 'box'.

What I am less certain of is the extent of any pulse effect in terms of cylinder filling.

Inside one of these boxes must also be quite busy as the pulses and pressure waves will potentially interact and cause problems but I imagine that these problems can be minimised with careful design.

There are many good SAE papers on this subject which seem to suggest that Air Box resonance occurs in a very narrow frequency window and has a small impact on pressure - around 10 millibars is a typical quoted value for the air boxes used on F1 cars which I would expect to be quite good.

The conclusions that seem to come out of the published work is that airboxes only provide horsepower benefits in narrow rpm bands depending on their specific design but that they are very useful in filling in 'holes' in a powerband that can arise due to poor general airflow.

With the ITB design we are planning to use the only practical measurements we will be able to make will be 'open' intakes with simple trumpets, rain hats with ITG foam elements to replace the K&N filter and a stock 'Weber' Airbox.

I hope it will be an interesting comparison.

Originally Posted by chris_seven (Post 8956028)

485mm between port centres.