I'm planning on building up a fast road/race 3.9 Rover V8 with ported big valve heads etc.

I want to run quad downdrafts on it, and all the suppliers I've contacted reccomend Weber 40 or 44 IDFs, which are pricey new.

I've been offered a set of rebuilt 36 DRLA Dellortos at a good price. Will they be a bit small, or maybe just right to give a nice midrange pickup?

Cheers

Fred W B

[Edited on 3/3/07 by Fred W B]

Sounds a bit small to me. At about 500 cc/throttle I'd expect 40 mm or bigger.
I think you should be able to get some used 40-44 IDFs from VW aircooled swap meets, obviously you'd need two matching sets...
Alfa Sprint TI from breakers would yield 40DRLAs...

Where are you looking to have your powerband and max rpm?

[Edited on 3/3/07 by Lippoman]

It depends on how much power you are expecting to get. That will determine the choke size you need which in turn will decide the ideal barrel size of the carb and also the max/min size that you will get away with. 30mm chokes are the biggest you want to go to in 36mm carbs. Any bigger than that and the venturi effect of the choke is reduced too much and the carb won't meter the fuel properly over its whole operating range. An out and out race engine could take a bigger choke as it only has to meter fuel for max throttle but for a road engine thats no good.
If you have a look at the puma racing site on the links page you will see his choke size/ hp guide so basically if you're looking for more than 250hp then 36s are too small.

check fleabay, I bought a set of 40 dells for cheap, the guy was shipping them right from Italy, and was selling webers as well

Thanks for responses guys.

The engine spec will be:

Block - 3.5 Liter block bored to 94mm, thin wall liners
Pistons - standard 3.9
Rods - Standard 3.5
Compression Ratio - 9.8:1
Cylinder heads - ported to approx stage 2 spec.
Valves - Inlet 1.64" (41.7 mm) Exhaust 1.4" (35.6 mm) Stainless Steel Tuftrided, hi-flow bulleted guides.
Valve Springs - Heavy Duty
Lifters - Rhoads Bleed Down
Rod and main bolts - ARP
Head gaskets - composite
Camshaft - Crower Comp-U Pro 50232 (power from 1800 - 5500 rpm, Redline 6500 rpm, 276 & 281 Advertised Duration)
Ignition - MSD M6L
Distributor - MSD billet mechanical advance unit
Exhaust - Fabricated Manifolds, 38 mm bore, each pipe is 850 mm long


I hope it will make maybe 260 - 270 HP?

Cheers

Fred W B

exhaust2

[Edited on 5/3/07 by Fred W B]

[Edited on 5/3/07 by Fred W B]

Hey fred, '

Buy a toyota 1uzfe engine and get all that including a forged cranck 6bolt mains and 4 valves per cylinder, for a fraction of the price that all that work costs.

also 4 liter btw
stock engine on itb's puts out a tad over 300hp cams are restriction

grtz Thomas

Hi fred,
I put quad 44 IDFs on my 4.6 using a home-made manifold. The carbs were popular on pintos I believe. I now regret the choice & wish I'd built up a megasquirt or emerald system. Whatever - you can also put bike carbs on - I dare say you'll get better metering with CV carbs at part throttle & while they still don't look like downdrafts, such a setup would look pretty damn good!
Rescued attachment carbs.jpg

One thing worth keeping in mind is future tuning. If you intend to do some in the near(ish) future, then it may be worth buying carbs that are a little oversize to allow for the required increases in power? Oh, are you after the old quad IDA look, or just quad carbs? I'd be tempted with 8 CV/bike carbs as they'll give better fuel and quite possibly a touch more power.

36s are probably too small. 40s on 32mm chokes would be better. These were standard fitment on many 1.7 Alfa boxers so there are plenty s/h ones in circulation, the only problem is getting 2 matched pairs. 44 webers or 45 dellortos were never fitted as standard to any "normal" cars so are consequently rarer s/h. the 44 idf webers were used on gp1 escort rs2000s and as with any period escort stuff the s/h price is ridiculous.(A pair on a pinto manifold made over 600 quid on ebay here last week!) If you want I could ask around the Alfa racers here and see if anyone has 4 identical 40s?

I want to stay with the Rover and trad carbs, as I want the car to look as if it was built in the late 60's. Also, having period dated and appearing parts makes my chances of being accepted to race this car in the local classic's class much higher - until I get too fast for them of course

Searching the net, and other suggested sources I find that for 260hp, 3900 cc, power peak at say 5200 reccomded venturis are 31 or 32mm as stated by posters above. Weber recommends carbs between 10 and 25 percent bigger so, working with 32 mm that would be between 35 and 40 mm. Other sources say add minimum 6 or 7 mm to the veturi, so that would be 38, or 39 mm minium.

I agree that the 44 IDF's are the way to go, if money was no object, but I am tempted to give the 36's a try anyway.

I have been offered the 36's by an old codger locally who is the local "guru" of carbs. He has a whole house (not just his garage) full of secondhand carbs, and supplies most of the local racers. A perfectionist, he refuses to sell a carb unless he has rebuilt it completely, down to refurbishing the bodies and replacing every gasket.

My considerations include:

It has been suggested that downdrafts are more tolerant of air speed across the venturi than sidedrafts, and as the above "rules" are mainly based on sidedraft setups hopefully downdrafts could be the lower end of the suggested scale.

In my application, at the moment, possibly better to undercarburate than overcarburate.

Second hand 40's are not available locally. Hughjinjin - if you could find 4 identical 40s, I would be very interested.

44 IDF's
Cost new in UK (UKP 900, South African Rand 13 000 for 4) or USA ($1460, SAR 10 950 for 4 ), excluding transport to South Africa, duty etc.
Jetting is "as supplied" and any alternate chokes, jets etc required to set them up would have to be sourced and paid for.

36 DRLA's
Cost SAR 5400 for 4 in my hand, refurbished second hand, with linkages.
Old codger has stock.
Old codger offers help with set-up.
Old codger offers to swap venturies, jets etc at no cost.
Intake bore actually measures 42 mm

What would you do?

Suppose the best of both worlds would be if we could find 4 off 40 cores for old codger to rebuild locally?

Cheers

Fred W B

[Edited on 6/3/07 by Fred W B]

I see your point Fred!
on the alfas the 1.5s ran on 36mm carbs with 30mm chokes. when the 1.7 was introduced with 32mm chokes they switched to 40mm carbs. these were normal civilised(ish) road cars. You may well get away with 31mm chokes in your 36s. What does your old codger say?

The fella who bought my car was talking about injecting it, I'll drop him a line & see if he wants to offload the carbs & manifolds if you want.
Bob

Old codger reckons 32 chokes in the 36's will be fine.

Bob - I would be very interested to know if those IDF's might be available.

Cheers

Fred W B

I'll drop the guy aline tonight - he might have sold or crashed it by now....
Bob

I've found a set of 40's, u2u sent

and replied to, cheers

Fred W B

Fred, I got a reply from the guy; he's out of the country but intends to convert to megasquirt during the summer so if you can hold on 'til then would probably do a deal (he's apparently bought the necessary bits...) Meanwhile he wants to keep the car mobile.
If you can't wait (and these things usually take longer than people think) then I'll let it drop
cheers
Bob

Thanks for the effort Bob, as you say lets leave this one there for the moment.

cheers

Fred W B

Thanks to hughjinjin, I managed to buy a set of used 40's Dellortos' in the UK.

They have now arrived here and will go to the old codger to be rebuilt .

Cheers

Fred W B