Lesson learnt.... the hard way!
 

I am prepared for the beating...... new engine, clutch, ignition installed everything wired and plumbed ready to go. Except one thing, the airbox popoff valve sitting on the bench. I had heard and read numerous times how these airboxes explode.... but..... just one start.... just for a minute..... then I will fit the popoff valve. Famous last words, cranked the engine for what must have been only a second and ....... BANG and I mean Bang....:eek:.. in the confines of the workshop it was defening. I had also read about Porsche engine fires so had the fire extinguisher at hand, lucky as a fire started under the airbox which was quickly extinguished. No major damage just a white mess!


Considering the ignition had been set up by the engine builder ready for starting and fine tunning this is most annoying..... to say the least.

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just a small crack..........

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So now I am up for about $600 (AUS) and two days work....... or maybe fit a set of webers!

I have a 2.7 airbox lying around does anybody know if they are the same size?

I've heard that the fire extinguisher powder is very corrosive, and not to wash it with water.....

Thanks, I will blow it out.

It's way easier to install the popoff valve with the airbox on the workbench anyways, good luck with it.

Don't have a pop-off? Here's another way to protect from this: just leave one of the clamps on this boot very loose or take the clamp off. Not better than the pop-off but this was often done in the days before pop-off valves. It works and since under operation this boot has negative pressure it is very unlikely it will come off.

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Brian

You don't mention the motor size but it looks like a large port 3.0 (large runners). If that's the case then a 2.7 airbox will not work (the runners are smaller on the 2.7.

The extinguisher stabilizing agent (really fine powder) is the problem that leads to corrosion. You'll need to make sure everything is really clean especially the electrical connections. Corrosion can start developing that won't show up as a problem until months from now.

Thanks Cliff, yes it is a large port 3.0lt so the search starts for a new airbox.... or maybe weld one up hmmmm.

Anyone have any suggestions on cleaning up the extinguisher powder?

CO2 or halon are better extinguishers and there is no nasty cleanup.

There has been a lot of debate both here and elsewhere regarding the most effective extinguishers so we wont go into that, our race rules state dry chem must be used so thats what was on hand.

Injection system removed from the car today, just a pic to show the extent of the damage..... like I said ..... big bang!

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Seriously considering changing to carbs, anyone got a good second hand set of 46mm's complete with all fittings for sale?

Go 40s......unless you are a track junkie......

The CIS system has been replaced with Webers. Being unable to find a suitable pressure regulator I installed a low pressure high volume pump and a low pressure reg and gauge. Almost ready to start.... almost..... can anybody tell me if these webers have a vacume port for the advance on the distributor?

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Oh so much room...........

Curious.. how do you plan to handle emissions testing??

JP, down here in Oz we only have to meet the emission standard of the year the car was manufactured, the trade off is we pay twice as much for parts as you do... lol.

Ok I didnt know what year your chassis was.. would be the same here really.. if it came with carbs we could fit them. I bet those webers sound sweet.. I fired up my 69 a few weeks ago and those webers make my 76 with cis sound like a toy.

Do you run any vacume advance on the distributor? 78 by the way

Oh well, if its a 78 we'd be busted in many states... as soon as the engine lid was opened.

Vacume on my 76? yes.. Its set up completely stock. when I bought the car it wasnt but I put it back the way fritz wanted it.. however, its been a biotch trying to fix all the vacum leaks to make it idle well that way.
Actually, as of this year I may be exempt from any checking.. we dont do emmissions in this state but an annual "inspection" is required.. So while "wrong" I think I could do it.. but here is my question.. how do you know you wont have a lean spot somewhere fitting webers to an engine that never had them??

Oh, and what about your cams?? I thought youd have to change them out to run webers???

You really shouldnt need a vacum line to your distributor.. set your advance at like 5800 rpm so its maxed... but cams... how you gonna make those webers work with no overlap on your cams??

I am new to this porsche thing..... but.... from reliable sources I have been told that putting webers on a standard 3.0lt large port motor will produce at worse the same power although a little more should be expected. To get the most out the engine different cams and pistons should be utilised. Although considering these are only 40mm carbs engine mods would be a waste. As far as lean spots if the tunning is correct then all should be ok. Should start tomorrow so we will see. Where is the vacume pickup on your carbies?