Quad Downdrafts

[Ian Anderson]

I run a Rover based engine in my GT40.

It currently runs the Rover Hotwire Efi system that is a bit problematic due to the radical cam I have that does not like to live in the 1500 to 2000 rpm rev range at low throttle - this just corresponds to speed limits in the gears so I end up either kangarooing or running at higher evs in a ower gear! (More noise!)

It ends up that the chips this system used cyle at about every 2 seconds and this causes the kangarooing.

Anyway I have been toying with going to a carb for a couple of reasons
1) No damn electronics!
2) More period correct
3) Potentially more stable through the above rev range tansition / low throttle area

Now I had been looking at a 4 Barrel Weber / Edelbrock 500 unit which appears to be the right spec for the 3.9l Rover engine

Then I have managed to turn up a Quad Downdraft manifold for the Rover
This would run either Weber or Delortos
There is also a "reasonably priced" set of 4 Dellortos that I can acquire - they are sized 40.

Now can anyone say if the Dellorto 40 is a good bet or a pig to set up and keep right / worse than Quad Webers? And lastly is the Size 40 sufficient or would they be restrictive?

Then lastly have also turned up a cross ram set that will run sidedraft webers. Is this better or worse than downdrafts? Certainly different!

So many questions so I apologise in advance.

Thanks
ian

 

[Jim Rosenthal]

OK, I can't comment on all of these but I will try to be helpful:

The Dellorto DRLA is very similar to the Weber IDF. The 40 size ought to be fine for a 3.9 liter V8. It has more to do wtih jet and emulsion tube etc sizes than the main venturi size. A good source of info on Weber IDFs and Dellortos is www.cbperformance.com they are a California tuning outfit that has a lot of experience with those carbs. They sell parts and tuning manuals.

You will probably have no trouble with the Edelbrock carb. They are easy to tune, and reliable. Is the manifold a dual-plane? This is what you want, not s single plane, I think.

There's nothing wrong with a cross-ram setup, but the tuning length of the intake pipes may or may not be what you want. AND it may not fit in a GT40 due to the dimensions under the rear window. The Edelbrock and the downdraft Weber/Dellorto rigs will fit, more than likely. And look like they are supposed to.

 

[Cliff Beer]

Ian, given the difficulties you've had so far with the efi, it might be wise to move to the four barrel/Edelbrock for a first step as this will undoubtedly be easier to set up than either the webers or dellortos. You'll be able to get your engine running nicely, remove any complicating variables and then take the step to weber/dellorto downdrafts as a second phase.

Incidentally, the downdraft dellortos (prob DRLAs as Jimbo suggests) are excellent carbs. Personally, I think they are as good or better than either weber IDAs/IDFs, everthing else being equal. Parts availability and set up information isn't quite as readily available but it's not bad. As Jimbo suggests, there are lots of variables to configure to make the dellortos work - jets, emulsion tubes, venturis, etc. I believe the dellortos also have progression holes drilled in the throat just off the butterfly and these can differ across different versions of the DRLAs, so, make sure you have a matched set to start with.

I think you'll like the sound of downdrafts right behind your ears!

 

[kiwi ka]

Ian
For my little bit of input, I am running a 3.5 ltr Rover in my Mclaren replica and whilst I will not be racing it, it is a track car only so will get a fair bit of stick. The 4 twin choke 40mm Del Orto`s came straight off 2 Alfa 33`s and sat in the box waiting 5 years to breath. All I did was clean them up, check them out for jet size which as standard Alfa, turned out correct for a starting point and ran the things. They were a little rich ? (black plugs) and I had balanced them before running some 30 laps. Tomorrow the car gets dyno`d so we will see how far out they are. The car was very driveable even though I had one choke slide in upside down so that was probaly the rich part. The motor has got the highest cam that you can run with hydrolic lifters plus all the good bolts etc.
Cheers

 

[Russ Noble]

Ian,

I have run the 500 Edelbrock on a 5 litre Rover motor with an XE268H cam and home ported big valve head and it was very tractable. Tried both a single plane and dual plane manifold and both were very drivable. Carb works well straight out of the box although some minor changes may be required to optimize

 

[Ian Anderson]

Guys

Thanks for the input

My car is predominately for the road so it has to comply with the following Hydrocarbon and HC levels - possibly more difficult to meet with the quads so again more lean towards the 4 barrel Edelbrock.

3.5% Co
1200 ppm HC

Weber Edelbrock 500 carb Land Range Rover V8 Kitcar MG on eBay, also, Range Rover, Car Parts, Cars, Parts Vehicles (end time 13-Feb-09 20:10:15 GMT)
Gives the carb and manifolds available Dual plane and Dual Port with the second being a lower manifold - worth it for the GT40?

So would the emissions likely meet the above limits with a carb?

Chaars
Ian

 

[Jim Rosenthal]

Why don't you look at the Edelbrock web site and see if they sell this manifold for the same engine? Wasn't that engine made by Buick/Olds/GM originally? 500 quid seems rather a lot. Is that in line with prices you've seen before?

 

[Jim Rosenthal]

Well, Edelbrock makes the manifold; it's a Performer model. Look on Jeg's and Summit and see what they sell it for over here.

 

[Ian Anderson]

Hi Jimbo

Yes I'd probably get it from USA as even with the GBP falling it is still notmally cheaper to buy and ship it over!

Ues the Rover is the same as the old Buick block and is commonly found in Range Rovers, Morgans, Old Rover cars, Some Vans, boats etc so fairly common but have a poor head that restricts breathing somewhat.
The engine was not my choice but came with the part built kit and was probaly about £8000 worth with the original purchase and then the work done to get it up to 250hp ish. (That is enough to get the Gt40 along nicely on the roads)

I just posted to the RPI E bay site as they are well respected over here and seem to be fair - even if a bit pricy!

I'm just in a qandry - I love the 8 throttle stacks of Weber / Dellorto but realise the more parts the more work keeping it all going!

The 4 barrel for that reason to me makes sense and has the reputation of being easy to set and forget.

Ian

 

[Jac Mac]

Dont leave town until you have seen your own country- you have the best guy for this stuff right in the UK, much better than re-engineered decades old USA stuff - 4bbl manifold is at bottom of the page- get your chequebook out & he can get you up around 6 liters-- Welcome to Wildcat Engineering