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PaulAA

HS6 breathing

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Gents

Now that it's getting warmer, I'm keen to solve the issue of air supply to the carbs (twin HS6s on a TR6).  Hot weather running has always been lumpier than in the cool and the plan is to feed the air filters with cold air from ahead of the radiator cowl.

The PO ditched the original filter box in favour of K&N pancakes on the Strombergs.  I changed the Strommies to HS6s some years ago, but I've just realised, whilst drooling over Richard Good's website, that maybe I should have increased the filter size from 1.5" to 2.5" thick...

Back to the challenge.  I've just got hold of an original US carb filter box and the plan is to blend in a 76mm dia inlet (on the bottom, midway between the carb inlets) and seal up the remaining holes on the cover (treating it as a plenum in the process), position the filter on the outside of the rad cowl and connect the two with a 76mm dia PE flexible duct.  The cross sectional area is greater than the combined area of the two carb inlets.  Can't fail, eh?

So, the question is how to calculate the correct filter size to suit - will bolting the two 1.5" K&Ns on the end of the flexible duct provide enough air through-put?

Also, would it be sensible to insert low-rise velocity stacks into the ex-filter box?

Thoughts and criticisms welcome.

Paul

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39 minutes ago, PaulAA said:

Also, would it be sensible to insert low-rise velocity stacks into the ex-filter box?

Yes.  Though it just might affect needle choice.

40 minutes ago, PaulAA said:

So, the question is how to calculate the correct filter size to suit - will bolting the two 1.5" K&Ns on the end of the flexible duct provide enough air through-put?

Probably.  But I'd just get a single conical one.  There are makes other than K & N and I reckon one oiled cotton filter is much like another.  I don't think size is likely to be a big issue.  The one I have on the Vitesse is really quite small (very limited space) but seems to be just about enough provided it's fairly clean and fitted so it isn't hard up against the bonnet/heat-shield.  Even when I've not been smart enough to fit it in the best position the car pulls hard to 5,500.

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I modified a 2500s airbox, increasing the box depth by an inch or so, limited by the inner arch on the Vitesse, the front cover is removable, and the intake pipe in the centre is the full depth. I added a couple of very short stub stacks, just to radius the carb intakes, and a large K&N filter.

Mark

20200427_175007.jpg

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K+N filters (or whatever, but I would by branded, and K+N via fleabay are often well priced) seem to be very efficient. Even something about 4" diameter and tall will be more than enough for 200bhp.

I did worry, until a friend (with a "thing" for v8's) mentioned a twin turbo monaro he built. 2 smallish K+N's, made a little over 900bhp. So did another dyno run, with filters off. Made exactly the same power. After that I stopped worrying.....

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Chaps

Immensely helpful stuff - thank you all.

Nick, I'd gladly relieve you of that adapted airbox, but on the TR it sits into a recess in the wheel arch and there is no room under it.  I am therefore modifying my plan to attach the air supply to the engine side of the airbox backplate, leaving me just about enough space between the wheel arch and the forward carb jet to swing a 3" dia. duct.

Paul

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Footnote:

As ever, Ed Hollin has blazed this trail already.  Glad to see that I'm heading, if less competently, in the same direction...

Paul

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