Weber manifolds 34mm to 39mm intakes

[JohnJL]

I have a set of weber 40IDA3Cs which came with a motor I just rebuilt. Upon reassembly I've found something I didn't expect...this motor and these carbs came to me together...

The heads are date stamped 3-73 and have injector ports welded up. Their intake port diameter is ~39mm.

The bottom of the manifolds on the carbs have an inside diameter of ~34mm.

I would have expected to see the manifolds and the heads have matching size and a smooth transition. It seems strange to me the 40mm venture carbs would have such smaller manifolds, and it seems strange to have a >2mm lip between the manifold and the intake port.

I could grind away at the manifolds or on some spare phenolic spacers to match the ports together but that seems strange. Are there other weber manifolds made to fit 39mm ports?
Anyone advise?

Thanks

[larrym]

you could grind away - but you will screw up the flow

go to PMO and order a set of their manifolds - made for this match-up purpose $400

you can probably get $50-75 for your old stock manifolds

[1QuickS]

I can taper bore the OEM manifolds to match your heads and carbs. Otherwise PMO manifolds are the way to go. If you get the tall PMO manifolds then it may be difficult to use OEM air cleaner assembly due to the limited amount of headroom in the engine bay.

[Trackrash]

Kinda interesting that someone would port the heads, but not the manifolds.

Post a pic of the manifolds, they don't look like stock Porsche. If they are the taller aftermarket manifolds I personally would match them to the heads. If you make a smooth transition from the manifold to the intake port you should be fine. You could call PMO and talk to them to get their opinion. Their tall manifolds are an attractive option.

Back when Porsche used Webers (all 40 mm) the intake ports ranged from 32 (T and E) to 36 mm (S). What are the details on your motor? 39mm ports seem fairly large.

[JohnJL]

Originally Posted by larrym

you could grind away - but you will screw up the flow

go to PMO and order a set of their manifolds - made for this match-up purpose $400

you can probably get $50-75 for your old stock manifolds

Yeah, I don't want to grind them. I am sure I wouldn't end up with balanced flow.

I have this and another motor to finish up. The other one will be EFI and I need manifolds for that one too. I'll have to check the heads on that motor and see if I can use these manifolds for that motor.

[JohnJL]

Originally Posted by 1QuickS

I can taper bore the OEM manifolds to match your heads and carbs. Otherwise PMO manifolds are the way to go. If you get the tall PMO manifolds then it may be difficult to use OEM air cleaner assembly due to the limited amount of headroom in the engine bay.

Here are some pics. The manifolds appear to be approx. 8.5 cm tall. I am running ITG filters on top of them under a stock 1971 trunk lid. I recall it being pretty roomy still.

on closer inspection these are 40IDTP3C1, not 40IDA as advertised...

[JohnJL]

Originally Posted by Trackrash

Kinda interesting that someone would port the heads, but not the manifolds.

Post a pic of the manifolds, they don't look like stock Porsche. If they are the taller aftermarket manifolds I personally would match them to the heads. If you make a smooth transition from the manifold to the intake port you should be fine. You could call PMO and talk to them to get their opinion. Their tall manifolds are an attractive option.

Back when Porsche used Webers (all 40 mm) the intake ports ranged from 32 (T and E) to 36 mm (S). What are the details on your motor? 39mm ports seem fairly large.

I thought it was strange too.

The motor is a 7R case with 90mm 9.5:1 90mm mahle pistons for 2.7l. The heads have the eibach high-lift springs, single plug. Cam is webcam's solex grind. The motor has all the proper prep...oil bypass, hydraulic tensioners, restrictors, SC pump, etc. Its going in a 'canyon carver' not a race car so I'm hoping for a broad torque band with the ability to safely spin it a bit over 7000 if needed.

I am really surprised to see this mismatch as these bits used to run OK when the motor came to me ~6 years ago...

[1QuickS]

Those are PMO intake manifolds, "REP" are the initials of Richard E. Parr. The IDTP carbs are not as friendly to a performance motor as IDAs although there are some things that can be done to them. The 40mm throttle bores with 34mm main venturis should work well with a 2.7 using Solex cams.

Better to mismatch small port to large so the 35mm intake ports into the 39mm ports isn't such a bad deal...perhaps the turbulence at that interface helps mix the fuel...

[JohnJL]

Thanks Paul.


Does Richard Parr not list a phone number? his site only says "fax or write us." no email or phone numbers? I want to see if I can exchange these for a set of manifolds that match, I think.

[1QuickS]

He prefers his distributors to do the talking.

Best bet is to sell those and buy new since you didn't buy them yourself.