Went to the dyno to do a first dial-in on the carbs and made 169.9 hp at the rear wheels with no air filters. Was pretty jazzed, and then the dyno operator said "Now watch when we put the air box back on...it'll be even nicer."

We lost 20 hp.

It was the end of the day, and I still need to finalize exhaust before we really dial the thing in, but we pulled the snorkel and air filter to do one more run. We gained 12 hp back, so 162 hp at the wheels. This from a 2.2 six with E pistons, a bit of compression, Solex cams, a bit of head work, headers, a single-tip Leistritz muffler (now a two-tip Dansk sport muffler), and Webers.

My question: How many variations of the factory air box were there between 1965 and 1973? Carbs, MFI, T, E, S, etc? I know there were metal ones and plastic ones (my air box is plastic), but I'm wondering if anyone knows a link that explains the variations, or can provide Cliff Notes from which to start my research? I'd love to keep a factory air box on the car, as I like the noise reduction, but would like to get some of that power back. Engine also feels hesitant past 6000 rpm.

I know, I know—rain hats. I'd prefer not to go that way. Thoughts?

That is disappointing I don't like rain hats.. Though I guess I will be using them.

Good news is ill have some in about a week I can show you.
Working on 4s now

I bought Britain Smith's old carbs and airbox. It has a custom large velocity stack bellmouth on it and he said it makes better tq with it than without. I don't have the dyno graphs and number handy. But I would think making something like it would make for a quieter intake w/o much, if any, power loss.

I honestly don't know the answer. Here's some that I've seen:

Solex
Tall Metal w/metal snorkel. Metal butterflies holding snorkel on.
Tall Metal w/plastic snorkel. Metal butterflies.
Shorter metal w/plastic snorkel and breather tube. Metal butterflies.
Low plastic with enrichment and left facing snorkel. Seen both steel and plastic butterflies holding snorkel on. (-6 means it faces right)
Low plastic with enrichment and right facing snorkel plastic butterflies holding on snorkel.
Low plastic w/o enrichment, right plastic snorkel. plastic butterflies MFI
Low plastic w/o enrichment, left short snorkel with warm air flapper, plastic butterflies. Late MFI

MFI housings do not have the openings for the secondaries between the velocity stacks. They can be drilled out if you want a low plastic housing to fit a 914 w/o the cold start enrichment circuit.

Henry Schmidt told me to bore out holes in the backside of the filter console to allow it to breath better. This was for my 3.0 MFI in the 911. They have to be in the center round portion so the air still flows through the filter. Might be worth a try to watch the dyno numbers.

Odd because Bruce Anderson always touted that the dyno numbers were the same with the factory boxes.

Doesn't sound right to me that you're losing power with the air box?
170hp out of a 2.2E sounds pretty good to me.
The 3.0 SCRS ran pretty much a stock airbox and made something like 255hp I believe.

All the different iterations of the early 911's ran pretty much the same airbox, some plastic, some metal, some carbs, some MFI, but basically the same basic configuration.
Hopefully there is something easy that you're missing that will get you back that power you're missing with the airbox.

Already super helpful. Thanks!!



I'm game. Any pics of how you did yours?



My belief, too. Why I was (and am) perplexed...

Me neither!



At the wheels, no less. I was hoping for 160-170 at the crankshaft. Who knows how accurate the dyno is, but it's a pretty good one...so it may be making an honest 190-200hp. It was a very pleasant surprise. Engine builder undersold it, other than the smile and a twinkle in his eye when I asked what it might make, and if he thought 160-170 was achievable. He likes building the small-bore engines.




Hopefully, but not seeing it just yet.

Posted a request for same info over on the Early 911S board, and one guy has weighed in. There have to be more people with more info on this. After all, induction is a pretty important part of the equation—and there are a lot of us with carbs on flat sixes.

http://www.early911sregistry.org/forums/sh...es-from-1965-73

Fwiw, the factory air box sounds GREAT when paired with a Dansk sport muffler (I chose the 57mm two-out version sold by Patrick Motorsports). One ex-962 (and current) 3.0 RSR racer looked over in shock and remarked at how good the car sounded, then emailed the next day to say it was the best sounding 914-6—and flat six, period—he'd heard in a very long time. It's also quiet enough that you can still have a conversation at speed. Wind noise is more bothersome than the engine...which sounds wonderful and appropriately loud.

For me, it's the ideal setup. Would just love to figure out how to ensure I'm not losing 20 hp due to the air box, which all research suggests I shouldn't be.

Anyone?

It's too bad you didn't get to try with snorkel and without air filter to see how it compared to the fully assembled box. My guess is that the snorkel is your limiting factor, not the filter and that something like Britain's bell mouth would make up the power difference. The snorkel is a pretty small diameter restriction one of the more important parts of the intake.

Agreed, though the gaping hole when we removed the snorkel and the filter probably wasn't all that restrictive—and we were still losing 8 hp. (Continues head scratching)

There has to be an answer to this. Hoping someone can shed some light on whether there were different snorkels and/or main air boxes for 911T, E, S, RS, SC/RS, etc—particularly the plastic air boxes. They seem far more interested in antenna tips and hood strut stickers over on that other board.

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