Quad 40 downdraughts

ppyvabw · Post by **ppyvabw** » Sat Feb 07, 2009 6:48 am

Are 40's gonna be too small for a 5 litre conversion? They take 36mm chokes i think.

Any thoughts?

kiwicar · Post by **kiwicar** » Sat Feb 07, 2009 7:33 am

If this is a a low rev torque monster then they might be OK, however I would think you really want 45s or better still 48s, it all depends on how highly tuned your engine is. 48s are a bit large for a 3.9 apart from a race engine but the extra litre should put them about right, but it really, what are your heads, what cam and what revs is it meant to operate over?
Mike

Darkspeed · Post by **Darkspeed** » Sat Feb 07, 2009 8:02 am

I think you will struggle with 36mm chokes in a 40 - the suggested maximum choke size for good signals to the jets is the Carb size (40) minus 7 so 33mm chokes 34's at a push

Choke selection from the Weber charts for 625cc at 6000 max power, maybe a bit high, is 42mm so a 48 carb would be minimum.

If the Max power is down at 5000 then 36mm chokes appear in the range but would need a 45mm carb to have a decent operating range

Andrew

ppyvabw · Post by **ppyvabw** » Sat Feb 07, 2009 3:19 pm

Bummer

There's some on fleabay but they are 40s. Might be worth bidding just for the manifold maybe? And hunt out some 48s? Can't afford new ones tho so I might be searching for a while for a decent matched set?

Kiwicar, I think you've advised me about my 5 litre before and said I'd be better speding mney on decent heads rather than going to 5 litres.

I'm gonna build the engine to 5 litres and modify some standard rover heads myself. Then save up for some nice Merlin heads I think.

It's not for a low rev torque monster, it's for my MG. Cam wise, I'm thinking one of the more radical hyrdraulic crower cams or real steel typhoon or tornado cam so up to 6500rpm and good midrange/upper range torque.

ppyvabw · Post by **ppyvabw** » Sat Feb 07, 2009 3:21 pm

ppyvabw wrote:Bummer

There's some on fleabay but they are 40s. Might be worth bidding just for the manifold maybe? And hunt out some 48s?

Although on that note, are the fixings for the 40s and the 48s the same?

Wotland · Post by **Wotland** » Sat Feb 07, 2009 5:48 pm

ppyvabw wrote:Bummer

There's some on fleabay but they are 40s. Might be worth bidding just for the manifold maybe? And hunt out some 48s? Can't afford new ones tho so I might be searching for a while for a decent matched set?

The one on Flebay at this time is one 5 degre inclined M4471. For MGB you preferaly need an M4470 no inclined.

If you are looking for an pair of downdraught manifolds I will have one sooner.

Ian Anderson · Post by **Ian Anderson** » Sat Feb 07, 2009 7:16 pm

I must be blind
I have searched E bay for Webber, weber ida odf weber 40 etc and nothing comes up with a quad set.

Just the sort of thing that would bling up the engine bay on the GT40

Give us a link if you're not bidding and if you are please say so we don't fight the price up!

Ian

ppyvabw · Post by **ppyvabw** » Sat Feb 07, 2009 8:35 pm

I'm in two minds about bidding. I'll let you know.

Wotland · Post by **Wotland** » Sat Feb 07, 2009 8:48 pm

I follow myself the auction for an friend. He is also just interested by the manifold.