PMO conversion?

[chaos]

Hia Guys

Having probs with the injection on my 3ltr

So

I have neen thinking of converting my 1981 3ltr Sc lump ( Which is in my 1971 911r tribute) to 40 PMO's.

Looking on different forums it would seem I would need to update cams to 964's or have mine reprofilled, also need to get my dizzy curve changed (dont know to what though).

Has anyone over here gone down this route and can point me in the rite direction regarding pitfalls and can anyone in this country do the dizzy?

Tis quite a few pennies to spend so want to do it rite first time.

Thanks Dave

[Nick Moss]

Forget the carbs, fit PMO throttle bodies. More power, better economy, no smell.

Whichever way you go there is no need to change anything else, but I would fit a set of JE pistons, RS/S cams, maybe even twin plug it so it will rev better and combust better, reducing the chance of detonation.

[fetuhoe]

If you are not looking for a significant performance increase and you are not trying to improve throttle response it is quite feasible to convert the existing K Jetronic to an EFI system using the CIS throttle body.

This could use a programmable engine management system with a crank fire ignition and an EDIS coil pack.

If you use a system such as an OMEX you could have a very useable engine with improved horsepower and better economy/drivability.

964 cams are only popular as an upgrade for a K Jetronic as they will give a little more power without increasing the overlap beyond the capability of fuel system.

If you fit carbs or ITBs you can change cams for much more overlap but you don't have to as it will work with the existing cams and pistons.


If you want to carry on with the existing dizzy then re-curving is easy and the curve needed is quite well established.

We have converted 3 x 3 litre SC's to carbs and have used modified Zenith 40TINs, toe have standard pistons and cams and one has 10.5:1 pistons and S cams. They all run well but an EFI conversion would make a more civilised package.

If you want power and throttle response as a priority then carbs or ITBs would be better.

[40 scout]

Forget the carbs, fit PMO throttle bodies. More power, better economy, no smell.

No smell, forget the throttle bodies then !

That's all part of the experience

I went PMO carbs, fantastic, complete kit, Richard Parr very helpful re initial jetting.
Initial set up pretty well covered in the accompanying literature.

I know others prefer throttle bodies etc but I like low tech

Steve

[911hillclimber]

I have PMO's carbs on my 3.2 stock engine. They are too big for the engine at 55mm but are great.
Stock cams and an RS 2.7 distributor on points, so the lowest basic technology around, works well!

If I had my time again on this engine I would fit the PMO injection and crank fire/ecu/964 cams

Carbs will give electric response, smell, and be awkward when cold, and the fuel consumption is truly wicked.

The simplest approach is to go on PMO carbs.
Richard Parr there is utterly superb and very helpful.

A nice compromise I expect (do not know) is PMO carbs and crank fire ignition. PMO have a partner there who can (expensively) sell you the ignition parts.

[gridgway]

surely this is a time for a megasquirt? Triumph bodies etc....

[impmad2000]

I am happy to demonstrate my conversion. It works really well and hasn't cost a fortune.
viewtopic.php?f=27&t=10271
Tim

[chaos]

Big thanks guys for all the imput.

My engine has had a refresh a few years ago due to head studs breaking, praps I should have thought about upgrading then..grrrrr

I do hill climb the 911 so wanted more bottom end grunt which is why I was thinking carbs, also due to the SC cams being on the soft side (so I have read) I understand the 964 cams would help the power side...

If I was to fit the 964 cams, apart from having the power steering drive machined off what else would I need to do engine wise?

I am from the dark ages and so have little understanding regarding throttle bodies and the ecu set up I would then need, this is why I am asking/gaining information before I go and break the bank.

Would throttle bodies give me any power upgrade and where could I take the car to have it set up as like I hae said this would be beyond my limited capability?

On a side note : This is the problem of being off work due to having an operation...too much time to think about things and having a need do sumit...spend money...lol

Cheers

[911hillclimber]

I've hill climbed for 23 years, 12 of those in a 73T with 3 different engines.
You need good low down torque and extreme flexibility, not peaky cams etc.

Carbs will do the trick but more so a well mapped (tuned) injected engine will deliver in spades what is needed.

I gathered but did not use the Triumph bodies etc for little money, about £350 all off Ebay.

The money gets richer when you go for the ECU and mapping time.

Megasquirt is really good and will work well.

This DIY system is not bolt-on like the PMO parts are, so need to be reasonably 'techie' to do it or you will have to pay someone.

The carbs/dist/points is the very simplest way forward, but the injected route (PMO or DIY) will yield the better engine imho.

[PMNorris]

Forget the carbs, fit PMO throttle bodies. More power, better economy, no smell.

Whichever way you go there is no need to change anything else, but I would fit a set of JE pistons, RS/S cams, maybe even twin plug it so it will rev better and combust better, reducing the chance of detonation.

Hi Nick,
Would you increase the capacity and make it a 3.2 short block with the JE pistons (obviously with the equivalent cylinders) and RS/S cams, or stay with the current capacity? Do the JE piston increase compression sufficiently to give increased performance? If you do that, then would the 40 PMO's still be adequate, or would you then need 46's?

.... My 3.0SC engine with 40PMO's needs a top end rebuild, so I'll be tweaking it whilst I'm in there.

Many thanks
Paul

[Nick Moss]

If you are fitting new B&Ps then an upgrade to 3.2 would be the same price. With 10.3:1 CR, S cams and 46 PMOs you should get 260ish BHP.

[wadsworthi]

Hi Dave,

Hope you are okay?

I have just upgraded my car to 46 PMO's with JE pistons and new cams, it makes 250 BHP. It takes some time to get it exactly right, but goes well.

If you want more information then I think you have my email somewhere.

All the best

Ian

[911hillclimber]

iirc:

40's for up to 3 litre
46's for up to 3.2
bigger for bigger capacity.

I have the latter on my 3.2, 247bhp on Bob's rollers a few years ago, bog standard 3.2 with custom exhaust and silencers.

[wadsworthi]

I am sure you remember correctly Graham, but speak to Richard Parr.
I was sceptical, but it also will allow further development in the future without compromising the existing set up.

Regards

Ian

[chaos]

hia Ian

Good to here from you, email sent.

Cheers Dave