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I had a drag engine along with trans built to ship to Ireland where I spend some time. It's heads up racing. The engine specs are
84mm crank counterweighted
82mm thick wall cylinders
Fk 89 cam
Cb heads with lots of porting 44mm intake 40mm exhaust valve sizes
12.2 to 1 compression ratio
New HPMX 44mm carbs on match ported intake manifold s to the heads.
The Bug is a chop top light (about 1200 pounds)
My question is everything being equal would it be worth my while to step up to some 48mm HPMX Carbs. I had some 45mm Delortos but ran out of time to make them run right. What Hp gain can I expect if I go to the 48mm carbs? This is a drag car only.
I tried the search function but came up with nothing usable.

Hi Roadcow,

Drag racing in Ireland? Good to know you're up and around.

You do need bigger carbs. EMPI has some 48 IDA clones (at Weber 48 IDA prices). http://www.Kustom1warehouse.net has them. They come with 37mm venturis, but I think you'll need 40mm.

44's are good but cannot match the flow you need. Keep this in mind. Long stroke, large displacement engines take time to fill cylinders, and as RPM's go up, intake time decreases. So, we make up for it in high-end breathing. High-flow heads, high-flow carbs.

If you stick to 1/8th mile tracks, the 44/s with 38mm vents will work ... but I cannot see a Bonneville record-breaker like yourself doing less than going all the way.

Good luck, and win!

FJC

Thanks FJC! It's 1/4 mile stuff. I know that the 48 mm stuff will be better and the link you gave is exactly what I'm looking at but I'm wondering what kind of Hp gains that I can expect if tuned properly 48mm vs 44mm.

Hi Britt,

This is hard to quantify, but with 48 IDA's I'd say a 10% increase beginning at about 6500 RPM up.

This is significant, and you'll feel it in the second half of the 1/4 mile.

This is based on my 48IDA experience back in my IMSA sports car days at Daytona (mid-to late 1970's) and my more recent 44 IDF experience at Daytona with similiar engines.

A 44 IDF (even with 38mm venturis) just does not deliver like a 48 IDA on 40mm's.

Some of the drag racers here might be able to add more info. I am basing what I know off top end.

FJC

The 44's will choke this engine. Go for 48IDA's.

X3 on the 48IDA's,will wake up that combo