Topic

This document was produced by Mike Cunningham a keen MGF owner, it describes cold airflow modifications using standard airbox and panel filter.

Thanks for that, an interesting read.

I'm still not convinced the side 'intake' is the best position for a cold air feed, the air flow at speed is not going 'in' the intake as the pattern of dirt after a long run shows around the intake on the MGF.

The temperature measurement is showing that the cold feed is working well. Air in the induction should be around ambient for efficient combustion.

Paul, agree with you to a certain extent. If you just stick a pipe to the side vent and lead it to the engine bay then through a venturi, you will probably suck hot air out of the engine bay and not push cold air in so some effect with K&N/Piper but only that the ambient engine bay temp is reduced. If the airbox is enclosed then the engines suction will draw in cold air from the outside into a closed system as mike has done.

My compromise was CAF to the K&N but have airscoops on the intakes on both sides, I found this made a dramatic difference on responsiveness and pick up to no scoops, since cold air was now forced up into the K&N mouth and the scoop on the drivers side was pushing colder air into the engine bay. Now the science! ( or lack of it) - its all subjective, because I didn't test air temps at any point in the various iterations and don't have a mechnism to check the airpressure and flow before and after scoops were fitted. It just feels better

I will be going on a RR next week to baseline the car before the engine mods, so will have some indication of the K&N improvements but the airscoops will make no impact on RR as the fans cannot generate the volume of air at 50MPH.

T

Your right about the lack of 'ram' effect from the air intake.

The big difference is that the air that is, effectivly, sucked into the engine is substantially cooler than the original intake within the engine bay.

When I installed my Pipercross Viper into my Mk1 F I used 76mm tubing, which just fits the air intake, the increase in pipe diameter results in more air for the engine (I also fitted a 52mm throttle body).

So this setup has to be an improvement on the original setup - colder and greater volume of air = more oxygen for the engine. that,coupled with the substantially less convoluted pipe work gives an easy to measure benefit.

I originally just fitted the larger throttle body and, before resetting, my idle rpm whent from 850 to 1400, due to better 'breathing'. Once this had been reset and setlled down to the 850 mark I fitted the Viper and my idle revs went up to 1500, so both upgrades made a measurable improvement.

Now, back to the position of the intake:

A lot of the K&N setups had pipes going under the car but there are 2 disadvantages to this setup. Firstly, the intake is much lower than fitting to the side vent and, therefore, more likely to suck water into the engine. Secondly, I found a few articles regarding air pressure which stated that, due to the aerodynamics of a car, the underside is an area of negative pressure (which makes sense if you think about it) so is a less efficient area tha he 'neutral' pressure side vents.

My setup is here for for anyone who would like to read the 'how to'

Pipercross Viper Install

It would be better to have a 'ram' effect but I don't see an easy option for placement on our cars

I read this and it left me puzzled as to why MG/Rover changed the air intake from the MK1 position at the front of box to the MK2's at the rear which surely must be a worse position.

Anyway I thought I would try and route a pipe from the N/S vent to the intake on my MK2 but this was such a pain in the arse and being a steptronic the pipe if successful would get in the way of the gearbox dipstick. Looked at a MK1 box but it looked like it mounted different couldn't really find any pics good enough to confirm this. Anyway I thought can't be that hard to change the MK2 box to a front inlet.

So removed intake pipe (1 screw) cut a bit of spare plastic to cover up hole from an oil can and bonded that in. Then cut hole at the same level as original one to fit intake pipe into front of box (made sure this was a tight fit) then it was much easier to run a pipe from side vent to the new intake position.

I'm not sure about all the advantages of having or not having air scoops on the side vents but this is my opinion for what its worth. I think without, air passing over the vents would draw out air rather than push any in which I don't think is best thing but it would prob not make a lot of difference. As for ram air effect unless the air flow with the scoops can exceed atmospheric pressure its not going to make any difference except when you close the throttle and then the box could pressurise slightly not so much as to produce more power but maybe a slightly quick response when the throttle opened again. The other thing as we already know temperature of the air is reduced with this setup but the faster that air flows the colder it is (wind chill factor). When I was a youngster I did a test to see what the difference in temperature was between riding a motorbike with a fairing and riding it without compared to ambient temperature. At 30mph it was consistently 10F lower than ambient with no fairing and 3F with .. So fitting a scoop should provide a cooler air supply than without.

One of the things I don't know is how the modern throttle body is effected by very low temperatures. Something very few mechanics will encounter and I never did until I did breakdowns on the motorway is carb icing in winter. I got called out many times to modified cars that had performance air filters with not enough warm air around them to prevent the speed of the airflows wind chill factor from freezing the moisture in the air as it goes through carb ( a bit of cardboard and gaffer tape to reduce flow was normal fix) So anyway I wonder if this may effect things like air flow sensor in a modern system and if it would be wise to disconnect pipe into vent from the box in winter.

Interesting point.
I've had a cold air feed (CAF) for a number of years, and regularly monitor intake air temperature. I think that the MGF or TF is very unlikely to suffer icing of the throttle body, even with a CAF. The inlet air temperature is soon above freezing point even on the coldest day due to the position of the throttle body in the engine bay.

A piper viper has been on my shopping list for a long time, however as my F is LHD the nearest side vent is the offside would this still work?

The engine bay fan is in the way.