The Triumph Dolomite Club - Discussion Forum

The Number One Club for owners of Triumph's range of small saloons from the 1960s and 1970s.
It is currently Fri Mar 29, 2024 9:20 am

All times are UTC




Post new topic  Reply to topic  [ 11 posts ] 
Author Message
PostPosted: Fri Jul 26, 2019 12:05 am 
Offline
Future Club member hopefully!
Future Club member hopefully!

Joined: Tue Jan 10, 2012 12:39 am
Posts: 516
How do folks connect a vacuum advance on a Mangoletsi Sprint twin 45 manifold? Or do I run without one? Road car with a balanced bottom end and a Kent DMS1 cam.

_________________
Russ Cooper
Dursley
UK


Top
   
PostPosted: Fri Jul 26, 2019 12:46 am 
Offline
Future Club member hopefully!
Future Club member hopefully!
User avatar

Joined: Thu Oct 06, 2011 1:13 am
Posts: 3173
Location: The continent
I use a similar system as these guy's in the pic below but you can leave it disconnected also. Make sure it's 32 degrees max at high revs. Best is to use a programmable ignition to have a curve that suits your engine.

Jeroen


Attachments:
helm.jpg
helm.jpg [ 88.57 KiB | Viewed 731 times ]

_________________
Classic Kabelboom Company. For all your wiring needs. http://www.classickabelboomcompany.com
Top
   
PostPosted: Fri Jul 26, 2019 8:35 am 
Offline
TDC Member
User avatar

Joined: Tue Oct 03, 2006 5:48 pm
Posts: 8446
Location: Winscombe, North Somerset, England
I think when I first installed my 45s I didn't use one. Later on I fitted a Megajolt system.

_________________
Sprintless for the first time in 35+ years. :boggle2: ... Still Sprintless.

Engines, Gearboxes, Overdrives etc. rebuilt. PM me.


1997 TVR Chimaera 450


Image


Top
   
PostPosted: Fri Jul 26, 2019 7:51 pm 
Offline
Future Club member hopefully!
Future Club member hopefully!

Joined: Tue Jan 10, 2012 12:39 am
Posts: 516
Turns out I didn't need to worry, the Dellortos have got a vacuum port built in.


Image

_________________
Russ Cooper
Dursley
UK


Top
   
PostPosted: Sat Jul 27, 2019 1:38 pm 
Offline
TDC Member
User avatar

Joined: Sun Sep 08, 2013 3:35 pm
Posts: 1735
Location: St Annes on Sea, Lancs.
Quote:
Turns out I didn't need to worry, the Dellortos have got a vacuum port built in.


Image
Is that ported vacuum or manifold vacuum? The former's mostly for emissions not performance. My twin choke manifold had it's own vacuum spigot.

Graham

_________________
The 16v Slant 4 engine is more fun than the 3.5 V8, because you mostly drive it on the upslope of the torque curve.

Factory 1977 TR7 Sprint FHC VVC 697S (Now all of, but still needs putting together)
B&Y 73 Dolomite Sprint UVB 274M (kids!)
1970 Maroon 13/60 Herald Convertable (wife's fun car).


Top
   
PostPosted: Sat Jul 27, 2019 11:40 pm 
Offline
TDC Member
User avatar

Joined: Sat Apr 12, 2014 11:02 pm
Posts: 2279
Location: Nr Kenilworth
ideally you'll need to collect vacuum from each port and t piece it all together. One cylinder will give very jerky response.

_________________
Membership 2014047


Top
   
PostPosted: Sun Jul 28, 2019 5:33 pm 
Offline
Future Club member hopefully!
Future Club member hopefully!
User avatar

Joined: Thu Oct 06, 2011 1:13 am
Posts: 3173
Location: The continent
Quote:
Quote:
Turns out I didn't need to worry, the Dellortos have got a vacuum port built in.


Image
Is that ported vacuum or manifold vacuum? The former's mostly for emissions not performance. My twin choke manifold had it's own vacuum spigot.

Graham
You can't take off the vacuum needed for the advancing system from the manifold. When your carb take off is at the airfilterside of throttle valve when closed that's the one to use.

Jeroen

_________________
Classic Kabelboom Company. For all your wiring needs. http://www.classickabelboomcompany.com


Top
   
PostPosted: Thu Aug 01, 2019 4:33 pm 
Offline
TDC Member
User avatar

Joined: Sun Sep 08, 2013 3:35 pm
Posts: 1735
Location: St Annes on Sea, Lancs.
There's a widely reposted article that seems to cover the issue, though admittedly its originally for a different context.

"This article was originally posted at Camaros.net by JohnZ, a former GM engineer. I had a request for a copy of it but it's too long for a PM on this board.

As many of you are aware, timing and vacuum advance is one of my favorite subjects, as I was involved in the development of some of those systems in my GM days and I understand it. Many people don't, as there has been very little written about it anywhere that makes sense, and as a result, a lot of folks are under the misunderstanding that vacuum advance somehow compromises performance. Nothing could be further from the truth. I finally sat down the other day and wrote up a primer on the subject, with the objective of helping more folks to understand vacuum advance and how it works together with initial timing and centrifugal advance to optimize all-around operation and performance. I have this as a Word document if anyone wants it sent to them - I've cut-and-pasted it here; it's long, but hopefully it's also informative.

TIMING AND VACUUM ADVANCE 101

The most important concept to understand is that lean mixtures, such as at idle and steady highway cruise, take longer to burn than rich mixtures; idle in particular, as idle mixture is affected by exhaust gas dilution. This requires that lean mixtures have "the fire lit" earlier in the compression cycle (spark timing advanced), allowing more burn time so that peak cylinder pressure is reached just after TDC for peak efficiency and reduced exhaust gas temperature (wasted combustion energy). Rich mixtures, on the other hand, burn faster than lean mixtures, so they need to have "the fire lit" later in the compression cycle (spark timing retarded slightly) so maximum cylinder pressure is still achieved at the same point after TDC as with the lean mixture, for maximum efficiency.

The centrifugal advance system in a distributor advances spark timing purely as a function of engine rpm (irrespective of engine load or operating conditions), with the amount of advance and the rate at which it comes in determined by the weights and springs on top of the autocam mechanism. The amount of advance added by the distributor, combined with initial static timing, is "total timing" (i.e., the 34-36 degrees at high rpm that most SBC's like). Vacuum advance has absolutely nothing to do with total timing or performance, as when the throttle is opened, manifold vacuum drops essentially to zero, and the vacuum advance drops out entirely; it has no part in the "total timing" equation.

At idle, the engine needs additional spark advance in order to fire that lean, diluted mixture earlier in order to develop maximum cylinder pressure at the proper point, so the vacuum advance can (connected to manifold vacuum, not "ported" vacuum - more on that aberration later) is activated by the high manifold vacuum, and adds about 15 degrees of spark advance, on top of the initial static timing setting (i.e., if your static timing is at 10 degrees, at idle it's actually around 25 degrees with the vacuum advance connected). The same thing occurs at steady-state highway cruise; the mixture is lean, takes longer to burn, the load on the engine is low, the manifold vacuum is high, so the vacuum advance is again deployed, and if you had a timing light set up so you could see the balancer as you were going down the highway, you'd see about 50 degrees advance (10 degrees initial, 20-25 degrees from the centrifugal advance, and 15 degrees from the vacuum advance) at steady-state cruise (it only takes about 40 horsepower to cruise at 50mph).

When you accelerate, the mixture is instantly enriched (by the accelerator pump, power valve, etc.), burns faster, doesn't need the additional spark advance, and when the throttle plates open, manifold vacuum drops, and the vacuum advance can returns to zero, retarding the spark timing back to what is provided by the initial static timing plus the centrifugal advance provided by the distributor at that engine rpm; the vacuum advance doesn't come back into play until you back off the gas and manifold vacuum increases again as you return to steady-state cruise, when the mixture again becomes lean.

The key difference is that centrifugal advance (in the distributor autocam via weights and springs) is purely rpm-sensitive; nothing changes it except changes in rpm. Vacuum advance, on the other hand, responds to engine load and rapidly-changing operating conditions, providing the correct degree of spark advance at any point in time based on engine load, to deal with both lean and rich mixture conditions. By today's terms, this was a relatively crude mechanical system, but it did a good job of optimizing engine efficiency, throttle response, fuel economy, and idle cooling, with absolutely ZERO effect on wide-open throttle performance, as vacuum advance is inoperative under wide-open throttle conditions. In modern cars with computerized engine controllers, all those sensors and the controller change both mixture and spark timing 50 to 100 times per second, and we don't even HAVE a distributor any more - it's all electronic.

Now, to the widely-misunderstood manifold-vs.-ported vacuum aberration. After 30-40 years of controlling vacuum advance with full manifold vacuum, along came emissions requirements, years before catalytic converter technology had been developed, and all manner of crude band-aid systems were developed to try and reduce hydrocarbons and oxides of nitrogen in the exhaust stream. One of these band-aids was "ported spark", which moved the vacuum pickup orifice in the carburetor venturi from below the throttle plate (where it was exposed to full manifold vacuum at idle) to above the throttle plate, where it saw no manifold vacuum at all at idle. This meant the vacuum advance was inoperative at idle (retarding spark timing from its optimum value), and these applications also had VERY low initial static timing (usually 4 degrees or less, and some actually were set at 2 degrees AFTER TDC). This was done in order to increase exhaust gas temperature (due to "lighting the fire late") to improve the effectiveness of the "afterburning" of hydrocarbons by the air injected into the exhaust manifolds by the A.I.R. system; as a result, these engines ran like crap, and an enormous amount of wasted heat energy was transferred through the exhaust port walls into the coolant, causing them to run hot at idle - cylinder pressure fell off, engine temperatures went up, combustion efficiency went down the drain, and fuel economy went down with it.

If you look at the centrifugal advance calibrations for these "ported spark, late-timed" engines, you'll see that instead of having 20 degrees of advance, they had up to 34 degrees of advance in the distributor, in order to get back to the 34-36 degrees "total timing" at high rpm wide-open throttle to get some of the performance back. The vacuum advance still worked at steady-state highway cruise (lean mixture = low emissions), but it was inoperative at idle, which caused all manner of problems - "ported vacuum" was strictly an early, pre-converter crude emissions strategy, and nothing more.

What about the Harry high-school non-vacuum advance polished billet "whizbang" distributors you see in the Summit and Jeg's catalogs? They're JUNK on a street-driven car, but some people keep buying them because they're "race car" parts, so they must be "good for my car" - they're NOT. "Race cars" run at wide-open throttle, rich mixture, full load, and high rpm all the time, so they don't need a system (vacuum advance) to deal with the full range of driving conditions encountered in street operation. Anyone driving a street-driven car without manifold-connected vacuum advance is sacrificing idle cooling, throttle response, engine efficiency, and fuel economy, probably because they don't understand what vacuum advance is, how it works, and what it's for - there are lots of long-time experienced "mechanics" who don't understand the principles and operation of vacuum advance either, so they're not alone.

Vacuum advance calibrations are different between stock engines and modified engines, especially if you have a lot of cam and have relatively low manifold vacuum at idle. Most stock vacuum advance cans aren’t fully-deployed until they see about 15” Hg. Manifold vacuum, so those cans don’t work very well on a modified engine; with less than 15” Hg. at a rough idle, the stock can will “dither” in and out in response to the rapidly-changing manifold vacuum, constantly varying the amount of vacuum advance, which creates an unstable idle. Modified engines with more cam that generate less than 15” Hg. of vacuum at idle need a vacuum advance can that’s fully-deployed at least 1”, preferably 2” of vacuum less than idle vacuum level so idle advance is solid and stable; the Echlin #VC-1810 advance can (about $10 at NAPA) provides the same amount of advance as the stock can (15 degrees), but is fully-deployed at only 8” of vacuum, so there is no variation in idle timing even with a stout cam.

For peak engine performance, driveability, idle cooling and efficiency in a street-driven car, you need vacuum advance, connected to full manifold vacuum. Absolutely. Positively. Don't ask Summit or Jeg's about it – they don’t understand it, they're on commission, and they want to sell "race car" parts."

So, it seems, if you want vacuum advance for emissions reasons it wants to be taken off before the butterfly, and for performance reasons, after it.

Graham

_________________
The 16v Slant 4 engine is more fun than the 3.5 V8, because you mostly drive it on the upslope of the torque curve.

Factory 1977 TR7 Sprint FHC VVC 697S (Now all of, but still needs putting together)
B&Y 73 Dolomite Sprint UVB 274M (kids!)
1970 Maroon 13/60 Herald Convertable (wife's fun car).


Top
   
PostPosted: Thu Aug 01, 2019 9:18 pm 
Offline
TDC Shropshire Area Organiser

Joined: Sun Aug 21, 2011 5:12 pm
Posts: 7014
Location: Highley, Shropshire
I find that fascinating Graham and, as they say, every day a school day!

I'm not going for the ins and outs of whether or not your particular car NEEDS vac or not and I don't have any Dellortos or Webers here to look at.

But I would like to point out that the SU has it's Vac advance takeoff mounted in the (one) carb body, but still on the engine side of the throttle butterfly which is the "correct way" for it to be according to Graham's article above. If the takeoff on the Dellortos are in a similar position then it should be fine!

But if not, And since Webers often DON'T have a vac takeoff, I have a work around to propose!

On both My Vauxhall Omega 2,2 petrol engine and my Peugeot Expert's 1.9 turbo diesel engine, there is, within the vac takeoff pipe for the servo, a combined non return valve and smallbore takeoff pipe. Not sure what it feeds on the Pug, On the Vaux it provides vacuum for a vac operated heater valve control. But one of these valves could surely be incorporated into a Sprint's servo hose to provide uniform vacuum for a distributor as it gathers vac from the manifold balance pipe. I don't suppose such a valve would be particularly expensive, even as a main dealer part and I can confirm that having 2 non return valves in the servo pipe does not compromise either engine OR brake performance in the slightest as the Carledo has been running like this for years!

Steve

PS JohnZ? As in John Z DeLorean? Who was once a design engineer at GM and was virtually responsible for the first proper "muscle car" the 64 Pontiac Tempest GTO! Before he went over to the dark side!

_________________
'73 2 door Toledo with Vauxhall Carlton 2.0 8v engine (The Carledo)
'78 Sprint Auto with Vauxhall Omega 2.2 16v engine (The Dolomega)
'72 Triumph 1500FWD in Slate Grey, Now with RWD and Carledo powertrain!

Maverick Triumph, Servicing, Repairs, Electrical, Recomissioning, MOT prep, Trackerjack brake fitting service.
Apprentice served Triumph Specialist for 50 years. PM for more info or quotes.


Top
   
PostPosted: Fri Aug 02, 2019 8:01 pm 
Offline
Future Club member hopefully!
Future Club member hopefully!
User avatar

Joined: Thu Oct 06, 2011 1:13 am
Posts: 3173
Location: The continent
Always good to read a story that explains the vacuum advance.
Only manifold vacuum is not suitable. Never is and never was. I'm on a holiday now and not going to type a whole story on my phone but never wondered why car manufacturers actually don't take off the ignition vacuum from a brake servo hose or the actual manifold but always from a hole just behind the throttle valve, carb or injection? Making pipes and tubes around the engine to reach the dizzy when there's an easy way just a T from any manifold tube?

Everyone who has connected some vacuum economy gauge knows that ignition vacuum is not behaving as ordinary manifold vacuum. Therefore the econometer is connected to the manifold and not T'd inbetween the ignition vacuum line. The tr6 us for example retards the ignition at idle using an extra oposite vacuum servo using plain manifold vacuum. Just to retard at idle for emission reasons and the conventional advance vacuum servo connected to conventional way to the carb using the ported hole at the throttle valve. Many German cars have the same dual vacuum layout for the same reasons.

It's a nice story from that gm man explaining the why and how about the vacuum advancing and he's totally correct but you can't just use manifold vacuum on your advancing system and when your carb doesn't have the connection you can't just drill a hole or T it from your brake booster hose.

Jeroen

_________________
Classic Kabelboom Company. For all your wiring needs. http://www.classickabelboomcompany.com


Top
   
PostPosted: Fri Aug 02, 2019 9:52 pm 
Offline
Future Club member hopefully!
Future Club member hopefully!

Joined: Tue Jan 10, 2012 12:39 am
Posts: 516
Quote:

On both My Vauxhall Omega 2,2 petrol engine and my Peugeot Expert's 1.9 turbo diesel engine, there is, within the vac takeoff pipe for the servo, a combined non return valve and smallbore takeoff pipe. Not sure what it feeds on the Pug, On the Vaux it provides vacuum for a vac operated heater valve control. But one of these valves could surely be incorporated into a Sprint's servo hose to provide uniform vacuum for a distributor as it gathers vac from the manifold balance pipe. I don't suppose such a valve would be particularly expensive, even as a main dealer part and I can confirm that having 2 non return valves in the servo pipe does not compromise either engine OR brake performance in the slightest as the Carledo has been running like this for years!

Steve
Steve, any more information on the Omega or Peugeot valve/takeoff? I checked on my Dellortos and the pipe seems to be a red herring so may need to find something.

_________________
Russ Cooper
Dursley
UK


Top
   
Display posts from previous:  Sort by  
Post new topic  Reply to topic  [ 11 posts ] 

All times are UTC


Who is online

Users browsing this forum: AhrefsBot [Bot], Google, Trendiction and 29 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Limited