Twin Plug Engine parts.

[davidppp]

Hello chums.

I would like to guage the viability of offering the bits to make twin plug motors...

As you all know, one of the biggest failings of the 911 engine is the shape of the combustion chamber, which can be helped by fitting a second plug...

I have sorted out the head machining reliably, and want to offer the distributor ...as you'll know, this uses the marelli cap from the Jag V12 and a special rotor arm on an adapted 911 dizzy...

I reckon it should be possible to sell the dizzy with rotor arm and cap for around 7-800 pounds provided I can get a minimum of ten takers...

Any interest?

Or are you all going to crankfired EFI?

Kind regards
David

[Mike]

Hi David, we met at husbourne talking with Andy.

I don't know why but I find this subject fascinating, I had considered as my next project a twin plug in an RSR rep, put everyone advises against it, which of course makes me want to do it even more!

The dizzy situation is changing now as more people are doing them, both in the states and in sweden, the machining of the heads I am told is straight forward enough, and people do have high butterflies, Andy! but the real problem seems to be the mfi pump.

I am told that to provide the fuel flow to make the lump rev to 8000 as the real thing, the 019 pump has to be modified not just by a different cam but by an engineering modification that is extremely difficult and expensive, thereby making this the most costly item in the build.

Does anybody know anything about this, or am I completly wrong here?

[davidppp]

Hello, Mike.

Yes, really enjoyed that chat with you and Andy..learned lots..

Great to meet real enthusuiasts..

The places to ask in UK are limited and you no doubt already know them...

Stateside you could try Pacific Fuel Injection...

Have you emailed mitso here ( Eric Lantz), who has done the exact 2.8 RSR engine in great and authentic ( read expensive) detail..

As you say, I'll be buying the one-off rotor arms in the US...from Aaron Burn..

The rest we can do here..

Kind regards
David

[Mike]

pssst, don't tell the wife but this is the picture I keep under the pillow and look at before going to sleep at night!



sad me never........

now, are those slide throttles or high butterflies, or is that one and the same thing? If they are not the same, what's the difference?

[Lightweight_911]

That's slide-valve injection...

[Lightweight_911]

This is another (my favourite) 3.5 litre slide-valve injection engine:



& here's a high butterfly injection set-up :



The descriptions are self-explanatory really - look at the position of the cross-shaft operating the throttle butterflies on the 'high-butterfly' injection as compared to the mfi road-spec engines & in your original picture you can see the levers operating the 'slides' at the base of the inlet 'stacks'...

[Mike]

thanks Andy, what the benefits, disadvantages of one system over the other, and how do build costs compare?

[Nick Moss]

I would be interested in one for my 2.8 motor. Is the dizzy kit the one that has been devoloped by Aaron in the USA?

[fetuhoe]

David,

I have a strong interest in Twin Plug engines but specifically for Historic Rallying and I am currently attempting to convert two engines.

The first is a 2 litre which will be used for the BHRC in the Pre-1968 Category 1 Class and would have to work with points as electronic ingnition is not allowed.

I am sure that I could use a 911R type semi-transistorised ignition but have no idea about circuit details.

I do have a Twin Plug Marelli distributor but this appears to be out of a Maserati 3500GT and I think it will be very difficult to adapt.

The second engine is a 3.0 litre which we plan to run on PMOs.

This car will run in Pre-1975 Category 2 Class and as such I believe that it would still have to run points but could use a 3.0 litre RSR type ingnition.

I have seen a photograph of the dizzy with the Jag cap and have e-mailed the manufacturer in the USA but without success.

Interestingly I can buy new Marelli Caps and 150 degree rotors to suit the Maser dizzy and this appears to be identical to the 911R cap shown on Ernie Willberg's website.

Tuthill Porsche have been running a Twin Plug 2 litre using a standard Bosch dizzy and a second dizzy driven from the end of one of the cams.

This car has been used in the Pre-68 Category and has been accepted at eligibility scruitneering but I am not 100% confident that this is a period mod. and have been unwilling to invest the amount of money involved, hence the Marelli dizzy.

Tuthill Porsche are also using Twin Plug 3.0 litre cars and there is talk of an Alfa Romeo dizzy being used but I have no real information.

I would be really keen on developing a suitable unit but need to bear eligibility issues in mind.

[Luke]

I know it's not original but a crankfired set up would be cheaper! Take a look at the XDI crankfire for USD1400 http://www.clewett.com/

[davidppp]

Hello guys.

Yes, the rotor arm is from Aaron Burn in the USA, the cap is the readily available and cheap (!) Jag one, and the adaptation of the dizzy done here...

I am aware of the system running a second dizzy off the fromt of the cam, and I know for a fact this was used in the 1970's..maybe earlier...

It is a MUCH cheaper mod than the "factory" type set up I'm doing..

In fact, only two machined parts are required...an ali plug/bearing/seal for the end of the cam carrier, and a steel shaft engaging the end ofthe cam to carry the rotor arm.

Given some 'thinking time" to design and set up, these parts would cost not a lot at all... much less in quantity of course.

And crank-fire is miles better all round of course..I'm doing a twin-EDIS6 set for myself..

But the fact remains most folk would use the Period Factory set-up if they could afford it..and the Jag cap on an adapted Marelli 911 dizzy body with points and two 3-pin CD boxes and coils does look the part and would be eligible for historic Motorsport purposes....

The main thing is the set-up costs of course..for this to be cheaper than gettting them from the States direct we'd need to do several
at a time..

Any more takers?

And, anyone have cheap machine/CAD time to put to use?

Kind regards
David

[fetuhoe]

David,

I have a 3-D CAD capability and routinely manufacture high speed rotating machines and have precision machining grinding, high speed balancing as well as a stock of high quality material and could easily provide small batch manufacture, I just don't have time to do the development.

[Herr Kuult]

And, anyone have cheap machine/CAD time to put to use?

Kind regards
David

David,

I've got CAD at work and home (it's my job, you see...), and I'm always happy to scheme up modifications like this. I've done a few "home" projects on old cars, and have been considering modelling up an injection installation using bike throttle bodies on my 911 - I expect this has been done already, but there's no fun in just forking out for someone elses work... .

Unfortunately we have no in-house machining at my work, but we do have a local machinist that are happy to help out with jobs like this. Alternatively, you can always out-source to China .

Anyway, let me know if this is of interest.

Cheers,
Paul.

[steve wright]

i'd be another taker. i've just rebuilt the 2.2 engine in my S as a 2.3ST and the heads have been drilled for the twin plug conversion. it was £400 which seemed reasonable (the heads were obviously already off the engine). as yet i've not been brave enough to look for an original dizzy. Autofarm are also looking at doing conversions with Bob Watson - i can talk to them if you like?

I've had no problems with fueling and the MFI with the higher spec engine. The car has been on the rolling road at Bob Watson's for tuning and runs well - the pump was brought round a few notches to richen the mixture but the standard space cam has been fine, although there is a flatspot at 3,200rpm when it is running megaphones. With a twin outlet exhaust and silencer, RSR cams, 40mm throttle bodies and 10.5:1 J&E 2.3 litre pistons it runs fine

[steve wright]

mate of mine with an RSR and TR would be keen also, potentially for two.