Exhaust: over under sideways down

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59Elva
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Joined: Fri May 15, 2026 2:59 pm
Location: USA, upstate ny
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Exhaust: over under sideways down

Post by 59Elva »

The 1275 in my pickup was still breathing thru the 948 HS2 and 1-1/8 exhaust pipe. I bought a damaged Spridget exhaust manifold on eBay and cut off the flange. Also from eBay a box of thirty 1-5/8” assorted pipe bend rejects from a header builder.
The challenge is the manifold exits close to the engine bay floor and is angled forward. To clear the floor and stay clear of the brake pipes I directed the flow forward and used the U bend to spiral back and up passing thru the “window” with plenty of room. A two foot length of flex pipe connects to the muffler mounted just behind the rear torsion bar anchor. Ad libbed on the fly without a design or measurements using five of the thirty pieces that looked like they could fit. Tacked together with a flux wire welder which is very messy. I will complete with TIG or oxy gas.
Intake will be thru an old HS6 connected to a “minispares” manifold. I will need to fabricate some kind of bracketry for the throttle and enrichment cables.
Also this carb has no tap for the vacuum advance. I will have to figure that out too.
Looks a little like a sixties formula one pipe. Maybe I’ll gain hundreds of horsepower .😉
Wish me luck, hope it works.
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Bill B. ‘59 Pickup USA
philthehill
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Re: Exhaust: over under sideways down

Post by philthehill »

I approve of your ingenuity but I think that the H6 (not HS6) carb may be a bit too big for a standard 1275cc engine.

59Elva
Minor Fan
Posts: 158
Joined: Fri May 15, 2026 2:59 pm
Location: USA, upstate ny
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Re: Exhaust: over under sideways down

Post by 59Elva »

H6, thank you Steve for the correction. If my math is correct the throttle plate area of twin HS2’s as fitted to the 1275 Spridget is 2.45 square inches. The 1.75” H6 is 2.41””. About 98%, pretty close. That assumes the bridge and piston opening is proportional and I don’t know if that is true. Don’t remember if I took fluid dynamics in college but if I did I don’t remember the content.
What was fitted to the Mini Cooper? I thought I had a copy of David Visard’s book Tuning The A Series Engine but don’t know where it got off to. If I recall the theory behind a larger single carb is the intake pulses were closer and more even. I only know the truck wasn’t running optimally with the 948 setup.
Bill B. ‘59 Pickup USA
59Elva
Minor Fan
Posts: 158
Joined: Fri May 15, 2026 2:59 pm
Location: USA, upstate ny
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Re: Exhaust: over under sideways down

Post by 59Elva »

Oops. Thank you Phil. If the H6 doesn’t work I still have a twin HS2 setup that I can try to rebuild. Rebuild kits are becoming scarce and expensive over here. I don’t even know where to look for needles.
Bill B. ‘59 Pickup USA
philthehill
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Location: Hampshire
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Re: Exhaust: over under sideways down

Post by philthehill »

The classic 1275cc Mini Cooper was fitted with twin HS2 carbs. The special tuning version was twin H4 carbs.
The H6 will work well with a big valve head, high lift camshaft and LCB etc.

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