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Best air filter set-up?  Rating:  Rating
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 Posted: 10-28-2005 06:44 pm
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edward_davis
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Joined: 07-06-2005
Location: Eugene, Oregon USA
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Hello, folks.  I've been recently thinking about the air-cleaner setup on my 907.  I've got Stromberg carbs and a set of aftermarket paper-element aircleaners on the carbs.  Here's a picture of the engine from the JHPPG:

http://jhppg.com/gallery/1974-No-18713/DCP_1623

I also inherited most of the parts for the original aircleaner setup when I bought the car, and I'm wondering about the tradeoff of easier breathing vs. cool air intake.  The original system grabs air from in front of the radiator, which has horsepower impacts, but I assume that it is more restricting than the round-element filters that I'm using now.  Also, I imagine that the stock system would be slightly quieter, but I don't mind the noise so much. 

Does anyone know the stats about the performance tradeoffs of the two systems?  Seems like most of the photos I see of Jensen-Healey engines have the aftermarket intakes unless the car has been purposefully restored.  Has anyone made an aftermarket cool-air intake for the JH? 

I started wondering because I noticed that oil smoke from my temporary cam-cover leak was coming out the exhaust.  I worried at first about the engine 'till I noticed the smoke being sucked into the intake.  Once I installed the orange gaskets from the club shop, the problem went away.  But it planted seeds of doubt about where my engine air should be coming from...

Thanks.  Edward Davis.

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 Posted: 10-28-2005 11:30 pm
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Mark Rosenbaum
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I don't know of any published studies for any car using a 907 engine, but there are a few reliable articles (and a lot of hype, speculation, and unverifiable self-serving claims) scattered about on the internet.  My comments below are based on articles and other postings I consider reliable in whole or part, on my own observations, and on informed speculation.

In the JH, the stock filter arrangement is a bit restrictive compared to the dual pancake style filters from K&N and elsewhere.  The pancake filters supposedly provide a noticeable power gain, but I don't know how much, nor if they're the most cost-effective approach except when modifying an already-built engine.  (Disclaimer: my car has K&N filters courtesy of a PO.)

The GT and some Lotus cars used a different intake plenum with a front-facing inlet port that in the GT's case was ducted to the radiator bulkhead.  The 'ram air' effect this arrangement provides is probably trivial at speeds below 60 mph.  The long corrugated inlet hose is quite restrictive but ducting with a smooth interior might be arranged.  The use of cooler exterior air might increase peak power a modest amount.  I'd guess that the arrangement might increase peak power by 3-5 hp, best case.  This might translate to a top speed that's 1 or 2 mph higher.  IMHO this is of very little use in a street car.

The use of air inlet horns can usually improve an engine's air flow.  It's my understanding that for cars with Strombergs, the longer horns are beneficial in the upper mid-range (say 4500-5500 rpm) without hurting peak power much, but that the shorter horns are of little benefit for a street engine.  I'd want to ensure adequate clearance between any air horn and the plenum or filter assembly in which it was to be used, before spending my money.

Possibly a useful and simple arrangement would be a conical paper air filter rigidly mounted to the hose port of a stock JH plenum, combined with a rather large-diameter hose running from the front of the car, that would apply cooler air to the vicinity of the filter when the car was in motion.  There wouldn't be any significant 'ram air' effect, but there would be at least some outside air available when the car was moving, and the original crankcase ventilation scheme could be retained.  This might even be a good compromise for really cold environments, as the engine would receive warmer underhood air when the car was at rest and carburetor icing was more likely to occur.

 

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 Posted: 11-20-2005 06:22 am
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pbahr
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Joined: 04-15-2005
Location: Moorestown, New Jersey USA
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Edward,

Don't know if this will help, but I put a great air cleaner on YELODOG a few years ago using Lotus airbox parts.  I have Weber carbs though.  See the link for a visual.  The system grabs cold air, low restriction and is quet - what else could you ask for????

http://jhppg.com/gallery/album62/engbay

Pete

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