Dellorto carbs

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agnoraan
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Dellorto carbs

Post by agnoraan »

Do any of you guys have any experience of using quad down draught Delloroto DRLA 40's on a Rover V8? I've got a Rover 3.5 that has the usual 390 Holley and Edelbrock intake. The car runs really well and is good on fuel.

At some point I might swap in a Rover 4.0 that I've got with a cam and some head work, but I want to retain driveability and a reasonable fuel economy as I'm looking to tour the continent next year with the car. I've been offered a set of four Dellorto DRLA 40's on Rovertec manifolds and was wondering if I was going to end up in a whole world of hurt in fitting these. If they're set up properly are they that worse on fuel economy than a set up 390 Holley or are they comparible due to better efficiency? Also I'm assuming that the performance should be more crisp and sharp? I had a pair of DRLA 36's on my old 1640 VW engine and that gave really good economy combined with power compared to the factory Solex carb.

Are the Dellortos hard to tune, or is it a case of balancing them in sync and then jetting accordingly ( the car has bungs in the exhausts for lambda sensors) Would it require setting up on a rolling road or is it something that can be achieved via the lamda? I'm not looking for all out balls to the wall performance, but a set up that drives nicely, gives reasonable economy and looks period correct

Thanks in advance
cheers...NIge
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Roger King
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Re: Dellorto carbs

Post by Roger King »

Personally, for decent road use, maintenance and driveability, especially if you're touring Europe (which I do a lot of), I'd stick with the 4-bbl. If you think about it, with the Dell'ortos you will have 8 accelerator pumps instead of 2 (or4), 8 primary jets instead of 2 etc. etc.
I have no real experience of downdraught Weber/Dell'ortos, but plenty of experience of sidedraughts. In my view, whilst they can certainly be setup for road use their real advantage is in racing, for which the throttle butterflies will be either shut or wide open. For road use your fuel consumption must go up - you have a much wider total aperture breathing into the engine, with more 'forced' (i.e. pumped) injection. For 8 barrels with 8 cylinders a rolling road session is pretty much essential to get the best out of them.
BUT - far more important than any of this are the engine design considerations: heads, C/R, porting, valve sizes, cam profile and overlap, exhaust manifolding, design and flow (it's no use getting more mixture in there if it can't get out) etc. etc. There ain't much point in deciding on one element of the motor without considering how they will all work together.
I have my cars set up on the rolling road, then when I get home I stick the wideband sensors in and take a set of readings, also hook up my timing light (they're all different) and note the readings at idle and with the timing all in, usually 2750 or so. I then know what to try to replicate when I check the tune each year. Repeat rolling road every 3-4 years. I wouldn't do a first setup with a wideband device.
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Re: Dellorto carbs

Post by Paul Blore »

Whilst I agree with the second point, I don't necessarily agree with the first.

Whether the carb is designed primarily for racing or not very much depends on the model. Weber IDA carbs are primarily for racing and any settings, other than for WOT, are pretty much a compromise. However, the IDF is a road carb, as is the DCNF, which can both be very well setup for road use.

There is an optimum air:fuel ratio for an internal combustion engine of between 13:1 and 15:1 depending on whether you want optimum performance or economy. Most engines tend to run around the 14:1 ratio. This doesn't change whether you have a Holley or Weber/Dellorto carbs.

A single Holley or similar is always a compromise because you're trying to get a single carb to feed eight cylinders equally, but all with different inlet manifold lengths. I can't be done. The advantage with Webers etc. is that you can fine tune each cylinder independently of the rest, so a better overall state of tune is possible. However, that does take some skill and patience. On the flip side, as Roger points out, you have eight accelerator pumps, so you can use more fuel if you're heavy footed, but in return, you get better performance.

However, to qualify all of the above, your Webers/Dellortos must be in good condition because if they're badly worn, they will leak air in through the spindles and you'll never get a good state of tune and any benefits will be lost.

There's no escaping the fact that they look fantastic and make the most amazing noise and that might be all the justification you need.

I'll certainly not be swapping the Webers on the Ferrari for a Holley. :)

Paul
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Roger King
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Re: Dellorto carbs

Post by Roger King »

I think my point was that their advantage really shows in racing - I know they can work on the road as I did 15,000 miles in my Healey 3000 with triple 45DCOEs on it - also my Jensen Healey came from the factory with DHLAs fitted. I can tell you they did not help the Healey's fuel consumption but increased it by one third. And from experience I know that unless you have decent downloadable capability for your Innovate (or whatever you are using), it is very difficult to maintain a Lambda of 1 by setting up on-road. I'd still strongly recommend using a rolling road (with all the extra information that will give you) for initial setup and choice of parts. How are you going to swing the dizzy in whilst you're driving for each jet change? It'd take days! That reminds me - you need to be sure you have the right jets etc. as Dell'Orto and Weber jets are not interchangeable. Or at least they weren't on the models I had.
In any case, overriding all this is that it is pointless to consider carbs out of context. They can only be considered as part of the whole, in particular the cam. Why would you change the characteristics of fuel delivery without changing the way the engine can use it?

You might have a job finding a 4-bbl for the 308, Paul! Sticking Webers on the 427, then?
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Re: Dellorto carbs

Post by Karl »

This can be discussed in length, but one thing for sure:
These carbs have only one accelerator pump each, feeding two outlets.
I am just overhauling two 40 IDF and two 44 IDF`s at the moment.
Karl
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Migge
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Re: Dellorto carbs

Post by Migge »

But Niges is talking about DRLAs, right?
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Roger King
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Re: Dellorto carbs

Post by Roger King »

Karl wrote:These carbs have only one accelerator pump each, feeding two outlets.
That's two jets, Karl. Two big fat squirts of fuel. One shot per barrel.
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agnoraan
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Re: Dellorto carbs

Post by agnoraan »

Yes Migge, I'm talking of quad Delloerto DRLA 40's with a 32 choke. Inerestingly I was talking with a guy yesterday that has these carbs fitted to his 3.9 engine and it returns 28mpg on a run and 17 mpg running around town.That car has slightly reworked heads with a Hurricane cam fitted. Once fitted and set up, he's never had to tune them or play about with them and it allegedly runs like a scalded cat all the way to 7000 rpm!!
. He says the secret was in fitting a "Megajolt" ignition system, thereby doing away with the dizzy and instead running four coil packs. He was able to map the fuel curves etc to get the car to give optimum performance and economy. I need to look into how that all works now before making a decision. Oh, I also need to have a chat with "my man" about fitting and tuning these as "bodymen" are notorious for being bad mechanics, so it's not something that I'd attempt myself :wink:

These would look nice though wouldn't they :lol:

Image

cheers...Nige
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Dale Bowman
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Re: Dellorto carbs

Post by Dale Bowman »

My old Daytona was running a 375 BHP 289 engine which had 4 x 44 IDFs fitted. If it was driven carefully and at a steady 65-70 on the motorway it returned 19-20mpg. Quite a different story though when they were used properly. But at least I could get to the track fairly cheaply :D
Same as your friend Nige ... I had them tuned when I first brought it into the UK and they weren't touched again
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Karl
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Re: Dellorto carbs

Post by Karl »

I mean: the wording is just wrong, there are not eight pumps, just four with two outlets. Also Dellorto only has one pump.
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