Weber 40 IDA upgrades

[KTL]

Speaking to the Webers themselves, as long as you're planning to do work on them anyway, make sure the accelerator pump covers and the pump body (the block of metal) are flat so they will seal properly. The accelerator pump area is notorious for weeping or dripping.

You can flatten them yourself very easily with some fine grit wet sanding paper on a flat piece of glass. Color the surfaces with a permanent marker and you can watch your progress as the color is sanded off the uneven surface.

[AlexJ]

Originally Posted by NICE 69 S

Alex,
That set of pistons/cylinders will not work with the 2.0 heads. Even if you cut the heads for the head gasket (been there, done that) you will end up with about 7 or 8 to 1 compression. Either find a set of 84mm pistons that are specifically made to fit the old 2.0 heads (high dome with a chamfer around the edge), or bite the bullet and buy a set of 2.2/2.4 heads. Pretty sure that any 2.2/2.4 head will work. Almost all of them have 46/40 valves and 32/32 ports, and that is probably what you want.
Even though the description of the Piston/Cylinder set you have states that it is for a 66mm crank, that is for a 2.2L motor that does indeed have a 66mm crank. The difference is that the 2.2L/2.4 engine had a totally different piston dome and combustion chamber than the 2.0L motor. 2.4L engines have a 70.4mm crank.

Edit: Here are two choices of P/C from the same company that built the set you have, but made specifically for the 2.0 engine. Look closely at the piston dome and compare to the set you have, then you will understand why the set you have won't work.

81mm Porsche 911 JE Forged Piston & Cylinder Kit | AA Performance Products 2041cc
82.5mm Porsche 911 JE Forged Piston & Cylinder kit for 2.0 | AA Performance Products 2117cc

If you use the pistons you already have and buy some 2.2/2.4 heads, you will have 2300cc.

Bob B

Many thanks Bob! Now I know what I did wrong . It was very clear. 👍👍

[AlexJ]

Originally Posted by KTL

Speaking to the Webers themselves, as long as you're planning to do work on them anyway, make sure the accelerator pump covers and the pump body (the block of metal) are flat so they will seal properly. The accelerator pump area is notorious for weeping or dripping.

You can flatten them yourself very easily with some fine grit wet sanding paper on a flat piece of glass. Color the surfaces with a permanent marker and you can watch your progress as the color is sanded off the uneven surface.

Kevin! Thanks for the advice. I will do as suggested.
Very helpful. 👍👍👍

[AlexJ]

Just one more question to have it all clear:

What is the maximum recommended overbore on a standard 2.0 L cylinder? How far can we go, considering the safe minimums...?

[NICE 69 S]

Alex,
First you have to find an overbore piston that will fit in that cylinder and work with the 2.0L heads. Every bit of metal you take away from a stock cylinder reduces the cooling capacity of that cylinder, which isn't a good thing. I don't have any experience with boring stock cylinders, so I will leave it to others to chime in.
For me, I think the 82.5 set form AA with JE pistons is your best bet. You can sell the set you have and be out about $900. If you decide to go with the 2.2 heads, you will probably be out over $2,500, depending on availability in your area . I paid about $2,200 three years ago for some 2.2S heads that were fully rebuilt with sodium cooled exhaust valves and the larger 36/35 S ports to put on my 2.0 MFI engine with 2.2L S pistons. I originally built this engine in the early 80's with 2.0 heads (modified for the head gasket) and 2.2S pistons. Nobody told me at the time that I would be way down on compression. I never started that engine. Tore it down at the beginning of the year to put the 2.2 heads on it. I did tell you that I had "been there, done that" didn't I.
Bob B

[AlexJ]

Many Thanks Bob!
Now all is clear and I have the right information to take the best decision.
👍👍👍👍
Thanks to all who posted usefull information!

[Trackrash]

Originally Posted by AlexJ

Just one more question to have it all clear:

What is the maximum recommended overbore on a standard 2.0 L cylinder? How far can we go, considering the safe minimums...?

Taken from this thread New 2.45 Engine Build

Originally Posted by Henry Schmidt

I absolutely love this engine concept.
Not everyone has the budget to build without regard to cost so I see this as the best bang for the buck.
The last two engines I built for my own cars followed this design. 86mm is the perfect size cylinder when performance and reliability are the end game. No case modifications so a "numbers matching" collectable can always be converted back if the owner so desires.
The Nikasil coated Biral barrels (Nascar developed) are proving to be remarkably durable and seem to offer the cooling necessary to run these engines at their limit.
My engine were both built using Mod "S" cams because I prefer a more aggressive power band (changing with age) but the "E" cams have been a favorite for their driveabilty forever.
As a Mod "S" engine these little guys make 180 RWHP with exceptional throttle response.
It will be a pleasure watching this project go together.

These are the cars I built for myself using this now proven design concept.