Triple carbs

[stephendell]

Also read this thread: http://www.renaultalpine.co.uk/PHPBB/ph ... highlight=

Having a manifold made would be very expensive ,they are normally cast ,to machine from a solid billet would be a nightmare and you would have to do it in two halves and I haven't the knowledge to do it properly .Thats why I was looking at putting an adapter plate to suit a big carb .This I thought would work as you only have to get the inlets positioned ,but as DG points out the std carb set-up makes this tricky .
The small carb is there for idling and initial acceleration then the big boys take over could you lose the smaller carb and position a big carb with a sandwich plate that's machined on its underside to channel to the twin inlets .

Yeah, but no, but yeah....

The problem is, the orifices in the inlet manifold that the carbs breathe through are about the same size as the venturis, and in the inlet manifold there are long ports that run to the engine ports and these are small too, so fitting a bigger carb will only make a slight difference, but a new carb would operate better and be smoother in operation, such as a Holley etc..

If youve got a workshop manual (or download it) there is a section on the inlet manifold which shows you a cut a way drawing of it, and youll see what I mean.

The other option is a V6 Turbo inlet manifold which has the inlet (could be opened to 65mm) dead in the centre and all the ports are equal length and unrestricted. Then a big centrally mounted carb could be fitted.

Has anyone got a technical drawing of the PRV ? In particular the inlet ports/manifold ,pitch,offset/dia ect .Just as an exercise ,I would like to get some indication of cost to produce a machined manifold .Thinking a bit more about it ,might be feasible to produce in two halves if you don't mind to much how it looks ,ie a slab from the outside .
I have found in the history file for the atmo ,a fax from PRV to De Lorean dated June 81.Attached to this is a SAE booklet concerning the prv v6 Volvo ( must get that anaorak cleaned )Its goes into great detail regards the engine design but a lot of it goes, whooosh ! see below

Cheapest way to make the inlet manifold would be to make two flanges (for the cylinder head side for each 3 ports) and then a slab type box (say an inch high) for all 3 carbs to sit on. Link up the flanges to the box with silicone pipe, rather than cast as in the original one from Simon Auto.

Reason why, is it would be so hard to do an all metal welded type because of getting all the angles spot on to mount both heads perfectly.

Beleive it or not, Richard Walsh bought one of the Simon Manifolds and he said he had to mod it loads to get it to fit, and that one is cast!

As long as I can get the correct dims for it the manifold will fit
I would create a 3D model and get it machined from that ,so it will be spot on as long as the info is
Casting is not that accurate and will be post machined to achieve the correct fitment but is by far the most economical method .
I could measure the existing manifold fairly accurately ,so that might be the better option ,its the connection to the heads that's crucial as the rest will be custom to equal flow lengths and carb mounting points/port .

As long as I can get the correct dims for it the maifold will fit
.

Only difficult thing is finding the exact angle of the V at the heads.

You won't find any written documentation which will help you with this, as all the different PRV's had different head heights, port dia's, and head thickness (hence the diffence between a GTA and A610 inlet manifold, or yes , you could measure the old manifold!

Flexi sections would be easy though..

If I take the atmo manifold off I can measured it very accurately to determine the angle.Flexi piping would be OK but terminating them will be difficult and the lengths will be uneven .If you machine the tracks then its easier to balance them out
I think it's worth looking at ,the original design was based on V8 theory and is basic in its design ,but has been compromised by economics and overcomplicated .The Solex set-up seems very odd given the layout .

I am of course a fully qualified engine designer not just the plastic cup holders

Beleive it or not, Richard Walsh bought one of the Simon Manifolds and he said he had to mod it loads to get it to fit, and that one is cast!

that was a b1tch of a thing to get to fit, one side did not match up with the ports while the V angle was also totally wrong. a lot of work to get it to fit as the ports are all now matched and polished, also the manifold has positive location to the head so the ports stay matched!!

Long time no hear Richard...where you been hiding?

We know the Simon kit fits the A310 2.7's, but maybe not the 2849 atmo. On the PRV's, the 2.8i R25 engine has the same inlet manifold as the Safrane V6, which we know doesn't fit a GTA turbo inlet manifold, only the A610 type.

I reckon the 2.7 PRV is the same casting types as the V6 turbo, and the 2.8 GTA atmo, is the same as the 25 2.8i/Safrane, and thats why it was so far out...

On the proper IDA3/C carb manifolds as found on the A310 2849 GT, they are seperate from left to right, so there will be no problems fitting them as they don't meet eachother, no matter what variant of 12v PRV you have.

ah but Lee - those electric handles are like the tease, once you've had the botch you know exactly where to pull!!!

srry, had a few wines 2nite!

lurv MT, hic !

Any use for testing the theory ,if I get a manifold machined
http://cgi.ebay.co.uk/Edelbrock-750-Vac-Sec-Carb-Carburettor-not-Holley_W0QQitemZ8004525449QQcategoryZ43120QQrdZ1QQcmdZViewItem

Bit big...thats 750cfm...for the atmo you need more like 400.

Edlebrock are good as they are actually made by Weber, but I wouldnt buy an old used one....you could be chasing new problems..

Yes I thought it was ,there are some 500,s and 350 's around and newer but a fair bit more

Hoorray or Booooo
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=4579878233&rd=1&sspagename=STRK%3AMEWA%3AIT&rd=1

Sell em!

Quoteth from a porsche site...

'The Zenith 40 TIN carburetors are not a good choice for performance applications. These carbs were equipped with 27mm venturis that restrict power potential to well below 175 HP. Since there is a very limited range of jets and other tuning parts, engines equipped with these are best upgraded to Webers or PMO's, due to the great range of venturi sizes and jet combinations. '