free hit
counters
Distributor S3 NA - Engine/Ancilliaries - The Lotus Forums Jump to content
ekwan

Distributor S3 NA

Recommended Posts

Any idea which other cars would use a distributor (Lucas 43D) similar to this, ignoring the advance characteristics as this could be separately mapped?

The S3 NA is a Lucas 43D distributor with mechanical advance only. 

Share this post


Link to post
Share on other sites
Upgrade today to remove Google ads and support TLF.

Thats interesting. The description suggests that a non-vac distributor is best suited to race rather than road cars.

Why then does the S3 NA have one? 

Share this post


Link to post
Share on other sites

The Bosch FI engines ('86 - '88 in North America and Australia) only used mechanical advance.  The vacuum capsule was only used to increase engine speed during warm up.

Share this post


Link to post
Share on other sites
2 hours ago, slewthy said:

Thats interesting. The description suggests that a non-vac distributor is best suited to race rather than road cars.

Why then does the S3 NA have one? 

The distributor on an S3 NA is non-vacuumed, hence a 43D model. The ones with vacuum are 45D's.

Share this post


Link to post
Share on other sites

Sorry - I meant why does the NA have a non-vacuum Distributor given its main use is that of a road car?

Share this post


Link to post
Share on other sites

My Elite's both have no vacuum either, 76 and 80 models, but I have seen some pics of them with vac.

A quick google, on Pistonheads the consensus seems to be that vacuum advance is beneficial, and makes sense to me:

https://www.pistonheads.com/gassing/topic.asp?h=0&f=81&t=680424

For road cars the vacuum advance gives improved idle cooling and quality, fuel economy, throttle response and driveability, and it enables both spark knock control under full throttle accelerations, and leaner fuelling for light loads.

This is because the vacuum advance allows the distributor to supply optimum spark timing, proportional to both the load and the speed output. Without it, the distributor can only vary spark timing in proportion to engine speed and ignores the need for around 20 degrees of timing advance at light loads. The change in optimum timing at light loads is that when operating at light loads, the mixture is leaner and less dense, which cause the combustion charge to burn slower, which means that to reach peak pressure at the optimum point in the cycle, the spark must be initiated earlier. Failure to do so results in "retarded" spark timing with all the associated issues of higher fuel consumptionand emissions but also, importantly, less power.

All engines are different, and have different spark timing requirements, but they are all the same in that as load is decreased, additional spark timing is required for optimum combustion.
There are only a few applications where vacuum advance is not a benefit - Racing engines, Heavy duty large trucks, and other engines where there is a relatively constant speed and load.

MG Mark

Share this post


Link to post
Share on other sites
5 hours ago, slewthy said:

Sorry - I meant why does the NA have a non-vacuum Distributor given its main use is that of a road car?

Vacuum is mainly for fuel economy and emissions during light acceleration. As the Esprit is considered a "sports car" (in quotes), fuel economy or emissions (way back when) isn't a prime consideration, hence the vacuum delete. Similarly, for Alfa Romeos too of that era.

Edited by ekwan

Share this post


Link to post
Share on other sites

Lotus would have fitted one if gave either a an economy or performance benefit.   Why wouldn't they?  (maybe cost - unlikely)  My assumption would be that the characteristics of the engine & tune was such that there was no benefit or perhaps drawbacks in some conditions.  That;s just a guess of course.  Many (50%?) of british cars of the 70's/80's used a 43/45 dizzy.  Th only difference is the blanking plate and the baseplate of the distributor is locked.    There is a very good chance of finding a genuine NOS unit on Ebay.   Of course the overall advance and advance curve are certain to need modification

Share this post


Link to post
Share on other sites

On early Esprits the vac advance was added for emissions only, and the vacuum fed to it was sent via a valve which cut it off after warm-up. So its not needed at all.

But I dont believe any other car used the same distributor with the internal oil seal. I did read somewhere a Jag might have also had this but cant find any confirmation of this. It would depend if any other used a horizontally-mounted distributor with no oil seal in the drive in the engine as per the 9xx.

The oil seal could be fitted by machining the housing.  SJ sell the oil seal but the one they sell is 5mm thick which I found is too thick, it needs 4mm. The size is 12 x 22 x 4.

Without this large amounts of oil leak into the inside of the unit.

Share this post


Link to post
Share on other sites
1 hour ago, Andyww said:

On early Esprits the vac advance was added for emissions only, and the vacuum fed to it was sent via a valve which cut it off after warm-up. So its not needed at all.

I would also add to this that the richer mixture at the warm-up phase significantly cools the in-cylinder temperatures. As such, it would be possible to run at more advance ignition timing without the danger of detonation.

Share this post


Link to post
Share on other sites
3 hours ago, Andyww said:

But I dont believe any other car used the same distributor with the internal oil seal

I always forget about that! 

Share this post


Link to post
Share on other sites

I believe that engines running one throttle per cylinder ( IR, for short ) show intake vacuum characteristics quite unlike those of the far more common single throttle type. At idle the IR will show substantial pulses of vacuum cylinder by cylinder, and the vacuum will rapidly decay to minimal upon throttle opening. So meaningful vacuum modified distributor curves are not as readily accomplished with IR carbureted engines. Prior to EFI the Federal spec Lotus were equipped with Stromberg CD carbs, offering a bit more usable vacuum and also were applying vacuum retard at idle/slow run for the sake of catalyst activation. Nasty.

Share this post


Link to post
Share on other sites
11 hours ago, drdoom said:

I believe that engines running one throttle per cylinder ( IR, for short ) show intake vacuum characteristics quite unlike those of the far more common single throttle type. At idle the IR will show substantial pulses of vacuum cylinder by cylinder, and the vacuum will rapidly decay to minimal upon throttle opening. So meaningful vacuum modified distributor curves are not as readily accomplished with IR carbureted engines. Prior to EFI the Federal spec Lotus were equipped with Stromberg CD carbs, offering a bit more usable vacuum and also were applying vacuum retard at idle/slow run for the sake of catalyst activation. Nasty.

If you design an engine to run 4 X DCOEs or DHLAs, you aren't exactly expecting to use vacuum advance, are you? 🤣

Edited by ekwan
  • Like 1

Share this post


Link to post
Share on other sites
16 hours ago, drdoom said:

At idle the IR will show substantial pulses of vacuum cylinder by cylinder, and the vacuum will rapidly decay to minimal upon throttle opening. 

But enough inlet manifold vacuum to allow the original Elan (and the first Elites & Eclats) to raise the headlights & power the brake servo. :thumbup:

Share this post


Link to post
Share on other sites
9 minutes ago, jonwat said:

But enough inlet manifold vacuum to allow the original Elan (and the first Elites & Eclats) to raise the headlights & power the brake servo. :thumbup:

Only just though! The Elan struggled to raise them when going over a certain speed without lifting off to increase the vacuum.

On the Esprit the heater will often not turn on at speed either owing to not enough to open the flaps. I dont think the servo is really working optimally on the LC Turbo Esprit either.

Share this post


Link to post
Share on other sites

Aren't the lights up without vacuum?

Share this post


Link to post
Share on other sites

On the Elan they changed it around at some point, cant remember when.

Share this post


Link to post
Share on other sites
3 minutes ago, Steve V8 said:

Aren't the lights up without vacuum?

Later ones are as a fail safe device, using vacuum to pull them back down against a spring to pull them up. :thumbup:

  • Like 1

Share this post


Link to post
Share on other sites
24 minutes ago, jonwat said:

Later ones are as a fail safe device, using vacuum to pull them back down against a spring to pull them up. :thumbup:

B*ggers should have them operated using a Bowden cable. What's wrong with Lotus engineers 🤔

Share this post


Link to post
Share on other sites
3 minutes ago, ekwan said:

B*ggers should have them operated using a Bowden cable. What's wrong with Lotus engineers 🤔

Like the Opel GT:shock:

  • Haha 1

Share this post


Link to post
Share on other sites
On 11/03/2019 at 16:06, Andyww said:

The oil seal could be fitted by machining the housing.  SJ sell the oil seal but the one they sell is 5mm thick which I found is too thick, it needs 4mm. The size is 12 x 22 x 4.

Where would this seal be located? At the bottom of the shaft next to the drive, or at the top of the shaft just under the advance weights?

Share this post


Link to post
Share on other sites
On 11/03/2019 at 14:35, 910Esprit said:

Lotus would have fitted one if gave either a an economy or performance benefit.   Why wouldn't they?  (maybe cost - unlikely)  My assumption would be that the characteristics of the engine & tune was such that there was no benefit or perhaps drawbacks in some conditions.  That;s just a guess of course.  Many (50%?) of british cars of the 70's/80's used a 43/45 dizzy.  Th only difference is the blanking plate and the baseplate of the distributor is locked.    There is a very good chance of finding a genuine NOS unit on Ebay.   Of course the overall advance and advance curve are certain to need 

Anyone here know values of crank advance vs RPM for an S3 NA. Otherwise I'd have to acquire or borrow one and make measurements. 

Share this post


Link to post
Share on other sites
4 hours ago, ekwan said:

Where would this seal be located? At the bottom of the shaft next to the drive, or at the top of the shaft just under the advance weights?

Here is a picture. This is from someone else on here, apologies for not crediting as I cant remember who it was.

 

distributor.JPG

Share this post


Link to post
Share on other sites

Looks like a strip down & machine job. But otherwise, no big drama.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...