Air filter box modification

[lusciousthelock]

Hi peeps, just after some advice on air filters and air boxes.  My Sceptre runs two stromberg's inside its air box which then sucks nasty hot air in from the engine bay. Due to the design of the engine bay, it get's really hot in there and with the exhaust manifold underneath boiling the petrol in the rear carb I've been having some rough running problems in heavy traffic.

I've ordered a pair of heat shields to help with the heat and then thought about the air filter's themselves. Pancake filters would look nice or even ram-pipes for the noise but in this engine bay at the rear with all the heat, I just don't think they would work. But as a performance aid, would removing the two internal filters from the air box, then running a 3" cold induction feed from the old entry point of the air box to the lower front of the car with a cone filter at the end help it breath or would keeping the filtration closer to the carb's themselves be better?

[dodgerover]

Can you duct cold air from the front of the car or under inner wing to the existing air filter inlet? If you do this beware of the ram air effect causing it to run lean at motorway speeds.

Heat shields and wrapping hot things with asbestos tape would all help as well.

[composimmonite]

There were tens of thousands of cars fitted with the 1725 and twin carbs, that included a high number of Sceptres, which run perfectly OK with standard airbox so if you have trouble with the rear carb then it's your car and not a design fault. I suspect the heatshield will probably solve the problem. Nothing wrong, however, with your idea of running a pipe to the front of the car so it sucks cooler air.

Have fun.

Paul.

[colnerov]

Hi, there is a theory that the filter should be as close to the carb as possible, because anything over half the max revs has a column of air rushing in at a fair old speed (ISTR 40 mph but don't quote me) and when you shut the throttle off that air has got nowhere to go and can push the fuel back down the jet. the filter acts as a kind of cushion.

Colin

[logicaluk]

What about building a custom air box with some bell mouthes enclosed in the box, modern easy to find cheap filter and a cold air intake sure ive seen this done on a spitfire once or twice.
Dan

[lusciousthelock]

Not sure why it's so hot in there now, but I had to take my manifold off to repair a crack. I had the crack welded up and then while the manifold was off it was treated and painted, ever since Ive had lots of heat. Does red VHT paint cause this effect??? Maybe there was a heat shield originally fitted? The carb's and exhaust have been on and off so many times in the past year that I may have misplaced something. All I can tell is the heat at the back of the engine is causing a misfire while sat in traffic after say a five minute wait. As soon as the air start's flowing, all is good with the world.

How good is the heat wrap tape? I wouldn't be able to touch the manifold due to access but the twin downpipes look perfect for wrapping? Are there any associated problems with this wrap?

[logicaluk]

It sounds like a shields been left off, or a fuel pipe routed incorrectly, or the carb has been knocked out of tune or dizzy advanced increasing heat. I've been told wrapping promotes rot on mild steel systems, but never done it myself.
Dan