Dellorto carbs...are they any good?

sidecar · Post by **sidecar** » Wed Jul 23, 2008 7:14 am

Hi Guys,

I've got the chance to buy 4 twin choke 45mm downdraft carbs along with a set of Rover craft manifolds.

I was wondering what you guys think of these carbs.

The lump is a 4.6 with stage III heads and a Piper 285 cam in it. At the moment its running a gas flowed Edelbrock performer manifold and a 500 carb.

I've been told by V8 Dev that they are good carbs but they are tricky to setup, they are critical of fuel pressure, and they ocasionally catch fire

I've also been told by JE Dev that they will be too small.

They don't come with any trumpets, filters or throttle linkage so all that will have to be sorted. Also I'm not sure what to do about the thermostat as that's fitted into the performer manifold at the moment. Obviously there will be some pipework required for the coolant but I don't know if you can buy some sort of remove stat housing.

The vac for the servo will need sorting to!

It sounds like quite a lot of work!

Regards,

Pete

Ian Anderson · Post by **Ian Anderson** » Wed Jul 23, 2008 7:52 am

I would think 45 mm would be marginal
The 48 or 50 mm would be better but then yiou are probably looking at webbers at about £3000 for a set and manifold (new) and a whole lot of extra bits to set up (emulsion tubes, jets etc)

A bloke in the GT40 club ran a 3.5 rover mild tune on delortos and reconed thay were great but would never give consumption other that £40 each time he took the car out for a spin! (Petrol was 80 p back then too)

By the way he had removed the water impeller and had an idler pulley fitted and ran purely on an electric water pump to get around the thermostat problem

If you are going for the bling look of quad carbs - why do you want filters etc - they mess up the look.

You also need to look at how you mount them - bopth sides the same way or "back to back" this will give different suction through the venturies at differnet rev ranges - likewise you have to be very good at linking the throttle cable / linkage to ensure both side open at the same rate.

But I love the blong factor and would buy a set in a flash for my set up and probably spend a load more time getting them to run

Ian

CastleMGBV8 · Post by **CastleMGBV8** » Wed Jul 23, 2008 8:36 am

Pete,

I know a guy with a 4.6 MGBV8 with modded heads and cam on Dellortos and it runs very smoothly.

I think you can probably swap the chokes/venturis to 48mm, they are available from the co. on the link below for £19 per carb.

Re. thermostat housings, these are available as a seperate item in the form of a bridge between the two cooling ports with a standard housing in the centre, i wouldn't have thought linkages would be too much of a problem either.

If the carbs are cheap and in good nick I would be tempted to go for it, they are no longer being produced but most spares seem to be available.

http://www.dellorto.co.uk/merchandise/p ... ctionID=53

Good luck,

Kevin.

sidecar · Post by **sidecar** » Wed Jul 23, 2008 9:06 am

Cheers for the advice guys!

I must admit the price is good BUT I've spoken to several tuning shops and they all do say that they're a bitch to setup.

V8 Tuner has really put some doubts in my mind, he reckons that I'd be lucky to see 9 BHP more over the setup that I've got now and I'd lose some low down torque. He reckons that I'll end up taking them off as they are such a PITA! He also reckons that an edelbrock 600 would give me another 20 BHP! Fitting that would be a piece of pee!

I don't want to buy the carbs then flog them on as the guy is selling them to me at a real good price because he knows me, he would expect to see them on my car.

I JUST DON'T KNOW WHAT TO DO! (My head hurts!)

Regards,

Pete

ian.stewart · Post by **ian.stewart** » Wed Jul 23, 2008 10:06 am

45s will be fine, 4x45s will easily support 375hp, Dells are much better than Webbers for staying in tune, but you do need someone who knows how to set them up. But if they are way out of range to what you need take a deep breath, it wont be cheap, there is 8 of everything to buy,
45s will give you much better throttle response over bigger carbs, and better fuel consumption as you wont be at WOT to overcome low gas speed flat spots, but the smaller carb will be much better to drive,
They will SOUND AWSOME, dunno if the sound on this clip is any good, but play it LOUD!! it was running a bit rough/slow there, thats why the bonnet is off, 3 runs later I blew up the engine
http://uk.youtube.com/watch?v=6ta5Ke6Xrho
water neck/thermostat I got around the problem by using a Moroso remote thermostat housing and welding 2x25mm pipes in at the same angle as the pipes coming out of the manifold, you can just about see the housing in the pic below joined with silicon pipe.

The fire thing is only seen on sidedrafts, normally set up badly so fuel drips out of the bellmouths onto somewhere in the engine bay and a wee burp from the carbs sends it up in flames, Im not saying they WONT go up in flames, any car that has peterol/spark in or near has the ability to burst into flames
Fuel pressure problems, I dont see why this should be any more of a problem than any other carb.
As such I dont run a normal style filter, I use a large airbox fed from the front panel with mesh filters in front of this, If I have the Airbox off, I have a set of 8 balls strung together I pop over the trumpets just to keep small birds falling into the engine

sidecar · Post by **sidecar** » Wed Jul 23, 2008 4:32 pm

Hi Ian,

Thanks for the pic and the video!

I'll need to do some thinking!

Its a real pain that I get different info from different tuning shops!

On the Cobra forum one guy told me to check how much vacuum is being pulled at WOT, if its more than 1 - 2 inches then the 500 is too small.

I'm off out to try that test, I'll let you know how I get on!

Pete

ian.stewart · Post by **ian.stewart** » Wed Jul 23, 2008 4:52 pm

if vacuum is a problem you can use a Diesel alternator off something like a astra, they have a pump built on the back, I think some transits had them as well.
Ill make a call tonight to a mate who is a performance/modified car journalist [sp] he will have a good idea who is good and who is not.

sidecar · Post by **sidecar** » Wed Jul 23, 2008 6:54 pm

ian.stewart wrote:if vacuum is a problem you can use a Diesel alternator off something like a astra, they have a pump built on the back, I think some transits had them as well.
Ill make a call tonight to a mate who is a performance/modified car journalist [sp] he will have a good idea who is good and who is not.

Cheers Ian, I would be very grateful if you could make a call.

Basically all the 'proffessionals' said that they're a lot of work to setup.

V8Dev reckons that they will give more BHP than my current setup.

RPI...I can't remeber what Holley said! (apart from tricky)

V8 Tuner reckons that they will only be slightly better than my current setup and that I should go for an Edel 600 (500 fitted at the mo) The 600 could be worth 20 BHP

He also reckons that the piper 285 is a bit mild for these carbs, they are really only worth fitting if the max RPM was over 6.5k RPM. I only rev mine to 6 as it has standard rods, pistons, and valve spring retainers.

JE reckons that they will make more power but will cost a lot to fit, he wants 200 quid for the throttle linkage alone!

I've just checked the vac with the 500 at WOT and 5- 5.5kRPM, it was 1.5" wg, I was told on the cobra forum that more than 1-2 "wg means that the carb is too small.... so the 500 MIGHT be a bit marginal?

Regards,

Pete

ian.stewart · Post by **ian.stewart** » Wed Jul 23, 2008 7:13 pm

£200 for a throttle linkage

I built mine from bits of leftover in the garage and old scrap from work, took about a day and £3.00 for a pushbike brake cable

Nick Moore · Post by **Nick Moore** » Wed Jul 23, 2008 11:13 pm

A good guy to consult about Dellortos - what models are best and how to set them up - is Dave Powell, aka Davesideways. He has his own forum here: http://www.sideways-technologies.co.uk

mgbloke · Post by **mgbloke** » Thu Jul 24, 2008 3:41 pm

I have been down this route with my 4.6.
see http://www.v8forum.co.uk/forum/viewtopi ... lbrock+600

I have now changed the cam to a mechanical 238 from real steel.

In fact the 500 carb is actually a 600 carb with a restrictor.

Been there done that and found that the 500 is much better for power and smoothness.

Mark

sidecar · Post by **sidecar** » Thu Jul 24, 2008 5:12 pm

mgbloke wrote:I have been down this route with my 4.6.
see http://www.v8forum.co.uk/forum/viewtopi ... lbrock+600

I have now changed the cam to a mechanical 238 from real steel.

In fact the 500 carb is actually a 600 carb with a restrictor.

Been there done that and found that the 500 is much better for power and smoothness.

Mark

Hi Mark,

Thanks for the link, some very interesting reading there!

I believe that even the 750 carb uses the same gaskets so I bet it's also the same carb as the 500 just with different venturies. If this is true the suppliers won't tell you because they want you to cough up for a new carb!

I also run an innovate LC1, my carb is setup quite differently to yours which proves that no two motors are the same. The details of my setup escape me at the moment but I know that I've got 104 secondaries fitted which are not even part of the standard calibration kit.
I also ended up cutting two needles in half just after the 90 degree bend so that I could turn down the power step by 2 thou by spinning them in my pillar drill. I then used a brass sleeve and solder to join the bends back on. This was done to get the acceleration AFR down to 12.5:1. I also run this at WOT. I run 13.5:1 at tickover and on cruise. The pump is on the leanest setting and even then I get a very slight rich bog! I was going to extend the pump arm with a bolt on extension so that I can lean off the pump a bit more.

I've decided not to go for the dellortos because I was getting too much conflicting information, the risk that they would be no good for my setup was too high, especially as it would be a 5hit load of work to fit them!

My vac at WOT was 1.5"Wg which I believe indicates that the carb size maybe marginally too small but I've decided to sort out my crappy headers first, they are all to short and there's a big step up just after the collector where the exhaust elbows out into each sidepipe. I plan the make a set of headers of 1+3/4" bore that are at least 30 inches long.

My motor has stage III heads and a piper 285 cam. I've also port matched the edelbrock manifold to the heads just like you did!

I might still buy a 600 or at least look at upgrading the 500, if it doesn't work out then I won't have wasted too much money. The headers are already costing a bomb just for the bends and flanges!

Thanks to everyone for their input.

Cheers,

Pete

minorv8 · Post by **minorv8** » Fri Jul 25, 2008 6:46 am

A comment about 500 and 600 carbs. It is correct that 500 and 600 share the same throttle size and also venturi size on secondary side. Primary venturi is smaller on the 500 primary size. I checked the emulsion tubes fitted to the 500 and 600 secondary venturies and they differ from each other. So even if it would be tempting to use a 600 primary venturi on 500 carb to make it flow more it may create interesting mixture settings.

OTOH, it would be very interesting to try different combinations to see whether they have any influence. The problem is that in the end it is still engine specific, what works on one engine does not work in another.

450 racein · Post by **450 racein** » Fri Aug 29, 2008 8:04 pm

Hi 45' delortos AB FAB, but and its a big but, well its like geting Claudia Shiffer into bed, alot of effort, but well worth it when you get out after for a fag and victory strut. good luck if you do , bin ther / carbs that is DB

topcatcustom · Post by **topcatcustom** » Mon Sep 01, 2008 2:50 pm

ian.stewart wrote:if vacuum is a problem you can use a Diesel alternator off something like a astra, they have a pump built on the back, I think some transits had them as well.
Ill make a call tonight to a mate who is a performance/modified car journalist [sp] he will have a good idea who is good and who is not.

As in to create vacuum in the crank case?
1) how does that affect carbs and
2) why would astra's and transit's be worried about that? Lol I thought a crank case vacuum pump was a nascar type mod!!!!! (which I would also like to do so I may be looking for a tranny alternator if I understood you correctly!!!)