Weber 40 IDA upgrades
 

Hi all!
I am building a 911 engine, originally from a 1967 911L (130 hp), standard cams, with a 2.4 cylinder and piston kit fitted.
It will have a sport air filter and a sport exhaust system.
Taking in consideration that I don't want to modify the engine any further,I would like to know if there are any upgrades I can do in the carburettors to improve the engine's power without affecting the road use.

Many thanks to any suggestions.

You can change the size of the venturi and jets to optimize for your new configuration. You did not say if you used T, E or S pistons/cylinders and what is the compression ratio you achieved. The difference with stroke of the 2.0 motor (66) vs the 2.4 motor's (70.4) will result in a motor with a much different comp ratio than the published comp ratio of the 2.4 piston/cylinder set.

If you're carbs need rebuilding, then Performance Oriented can do a performance mod for more breathing by flattening the throttle shafts. This increases wide open throttle area without sacrificing drivability at part throttle. I'm not sure it would help you if you didn't increase the port sizes on your heads too.

911L engine is only made for a 1968 Porsche

Thanks for your feedback.

Tomkirkcis, Thanks for your advice.
The Set I have are the same mesures as the original 2.0 L pistons only changing in diameter (86 mm). That is a very old Set I have, bought some years Ago, and I beleive I odered them as an overbore for a 2.0 liter Engine.
I have been checking them today and Regarding pistons it seems to be ok. The only problem is the top of the cylinders. They are the same size as the Standard 2.0 L cylinders but they don't fit the the heads... They are the grooved type as the 2.7 engines, so I will have to modify its seats to use the old gasket type.

Dug,
Thanks for your suggestion. That was one of the mods I was considering... I would rather prefer to find someone in Europe to do the rebuild or, I will try to do it myself if I find the kits and the parts to modify (jets? Venturis?)... and also if I find some guidance from this board.

Targa68
Why? I am using this engine (from 1967), on a lookalike 914-6 Gt replica and as far as I'm concerned, if you use a 914 gearbox, the right engine/gearbox mountings, correct engine tin, everything works fine! Or Am I wrong...?

AlexJ I thiln Targa 68's comment is about the fact you are calling the engine a "L". The 911L was a 1968 US only model. There was no 911S in the US in 1968 and the 911L was basically an S chassis with a 130hp motor. Targa68 comment is if the motor is from an L, it must be 68. In any case a 130 hp from 67 or 68 would be nearly identical except for possibly the case material.

The venturis and jets are availble from many sources. The issue is knowing which ones will work with your engine build. Trial and error can be expensive.

There are more qualified people on this board than me, who could suggest sizing, and sell you the parts, but no one will offer advice unless they know all the details of the engine build.

Your original post said the piston and cylinders you are using are 2.4. Those would measure 84 mm. Your last post says they are 86mm. I still do not know what you are using for pistons and cylinders. or what compresion ratio you have.

Tomkirkcis, Thanks for your message.
I have to admit that I didn't make myself clear enough.
This cylinder/piston kit is not from a 2.4 Engine. It is a kit to increase the capacity of a 2.0 liter Engine to 2.4 cc. through the larger diameter 86 mm. compression ratio is the same - 9.0:1

Yes, you and Targa68 are right regarding the wrong designation of the Engine - it is in fact a MY67 Engine from a standard 911.

I also would like to add that I am using a MSD ignition kit.
Regarding the carburetors, I have to say that I am not looking for something too radical. Just a slight "tune up", to gain a few more hp...

"They are the same size as the Standard 2.0 L cylinders but they don't fit the the heads... They are the grooved type as the 2.7 engines"

Are you using 2.7 heads? What size are the ports?
Are you using the stock cams?

I had stock 40IDAs on a 2.5 short stroke engine with Solex cams and it was a fantastic engine. No mods to the carbs necessary. Unless they need a rebuild and you will have the throttle shafts out anyway, I wouldn't bother.

cheers,
dug

My motor is a 2,5l. 66 stroke, 90mm bore, 8,4 to 1 CR. E cams. Heads ported to 35mm I and E.

I am running 32mm venturis. A good size for my motor.

A friend of mine is running a 2,2 E motor with S pistons. 9,8 to 1 CR. His webers have 30mm venturis, and it sounds like a sport bike.

Many Thanks for all your help.

Dug, Could you please indicate a source for the Solex cams?
Regarding the heads, I am trying to use the original 2.0 heads. The grooved type, are the top of the 86 mm new cylinders.
As an alternative, I am checking if the original cylinders can handle to be rebored to 86mm. In this case, I wouldn't have to invest on machining the top of the cylinders - I will keep the original fittment heads/cylinders.

I am not an engine expert but 86mm pistons on a 2.0 or 2.2L stroke will result in only
2.30L. I have this setup now, from a kit with JE pistons and AA biral cylinders. Of course
it is not using the 2.0 heads which would not fit.

Not sure why you would want to go with this cylinder size and try to work with the old
heads and T cams. Will cost good money if the head work is even possible. And it
probably won't have much more power or reliability.

Seems to me that your piston/cylinder set up was made for a 2.2L or 2.4L motor with a head gasket. If so, these pistons have a very different dome profile than a 2.0L motor. The 2.2 and 2.4 motors had a much slighter dome than the 2.0 motors. If so, no amount of machining on the head is going to produce very much compression, and boring a 2.0 cylinder 6mm is problematic.
Why not take one of your pistons and see if it even matches up with the profile of the head. Look around the perimeter of the piston where it matches with the head and see if there is interference at the edge of the combustion chamber.
If these pistons were made for a 2.2/2.4 motor, you may find that your only solution is either get a different set of pistons/cylinders, or find a set of 2.2/2.4 heads to make this motor work.
Bob B

mskala, thanks for sharing your experience.

When I decided to build this engine, I planed to produce a reliable and cost effective engine, a little more performant than the original 130 hp this 2.0 liter engine produces, without compromising the normal road use.

I believed only changing its capacity would be a good upgrade regarding the final result I have defined.
That is why I am struggling to use as much standard parts from this engine as possible.

You referred "T" cams. In fact these cams on this engine are "E" profile, 2.0 Liter 130 hp engine. Or am I wrong?

Regarding the heads/cylinder fit, yes, you are right, they don't fit. But after beeing measuring and checking, it looks that it is not such a hard work to modify the cylinder's top to replicate the standard 2.0 liter engine head/cylinder fitment.

If anyone has ever did this, please inform. 👍😄

Thanks Bob for your comment.
As I bought this kit a long time ago, I could not determine where did I bought it from...
I was a bit surprised why this kit didn't have a direct fitment, without modifications.
Now I already found where I bought it from.
Please, Bob, have a look at this:
86mm Porsche 911 Piston & Cylinder Kit 2.2 & 2.4 | AA Performance Products

At the description, they also consider using this kit on a 66 mm stroke engine, expecting a different compression ration, obviously.
This kit will be a nice direct replacement for a 2.2/2.4 engine because it has the same configuration of the head gasket from the refered engines.

You are right. Maybe a new set of heads (2.2/2.4) would solve the problem but I have found some scary prices around... With that, I would save the original parts of the engine (heads, cylinders and pistons), which are in pretty good condition...

Which heads are you using?

I was thinking something else with the cams. According to the Bruce Anderson
book, a 67 non-S could either have the 'solex' cams (Type 901/05) or the 'E' cams
(Type 901/06).

If you manage to get your heads fitted, the valves are a lot smaller than the
ones used on the 2.2 and 2.4 engines.

My motor is based on a '71 2,2 motor. Heads and cases were bored for the 90mm 2,7 RS pistons and cylinder set. The heads were champfered for the larger bore.

It might be worth selling your heads and sourcing some later heads. The 2,2 T heads used to be relatively inexpensive and 2,0 FI heads might be worth something.

I have to make a correction: engine type is 901/07.
It means, from the information I have, it is an aluminium case 911 L (68), early engine.

2.2/2.4 pistons
 

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.

http://aapistons.com/collections/porsche-piston-cylinder-kits/products/porsche-81mm-je-forged-piston-and-cylinder-kit 2041cc
http://aapistons.com/collections/porsche-piston-cylinder-kits/products/porsche-82mm-911-je-piston-and-cylinder-kit 2117cc

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

Bob B