Engine and Transmission Tech

One of the more important aspects of port/intake vacuum was engine starting, and of course the idle quality. At the advent of emissions cars a little something called run-on developed and for a few years there you couldn't escape that odd sound as drivers turned off their ignition, the engine chugged and huffed as it tried for several seconds to die, finally running backwards before coming to a stop. Eventually the problem was overcome. You might ask what timing had to do with that, a good question indeed, but changing the timing was part of what eventually made it go away. Low compression was also partly to blame, and other factors. It was a poorly understood "feature" of new cars at the time.

But as mentioned you can try different advances at idle and most of what you see is that usually idle timing does not give the engine what it wants, whichever method of advance you use, and if it does often starting the engine is problematical with backfiring not an uncommon issue. On the MG-Roadmaster this was a big deal, breaking numerous starter noses until we finally went electronic with an advance map and laid that problem to rest. Another issue is temperature control. Timing has a great deal to do with how much heat is retained in the engine and there is a definite sweet spot where the engine will run cooler. As to what is the actual best, it really depends on the overall configuration and acceptable results can be had with either system, but for the ultimate in timing control there is no substitute for an electronic system. It simply has more flexibility in every aspect. I will say though, if determined to use a distributor the best approach is to use off the shelf parts provided by the manufacturer. That way if it breaks you can simply replace it and be on your way.

Ivor, that '63 327 very likely was running a road tube out the back of the block connected to a big flame trap in the lifter valley. That's typically how they dealt with blowby in those days. As a result if you'll recall, we had a dark streak down the middle of each lane of our roads comprised of oil which had soaked into the road, deposited there by those road tubes. The early pcv systems on those engines sought to circulate fresh air in an attempt to lessen the contamination of the oil supply and deposit of combustion byproducts inside the engine. And they worked too, but the self-contained systems that came later cleaned up the highways.

Jim



Edited 1 time(s). Last edit at 08/24/2017 11:43AM by BlownMGB-V8.

Thankyou.
Interesting what you say about starting - in that thread from which I lifted the text, a poster observed that when he hooked up the PCV port on a car that previously just fed into the filter, he had trouble with starting and idle.

Oddly enough, there seems to be disagreement about the effect of feeding blowby through a PCV. Some say it weakens the idle mixture, some say it richens it.
Either way, I realise now the PCV setup is something I need to decide on before I go for a rolling road session, which eventually I will, because making changes afterwards would likely muck up the tune.

Running on, gosh had forgotten that. Dieselling, it was sometimes called. Cars that just kicked a bit, cars with vacuum-break valves, .and cars you had to put in gear and stand on the brakes and let up the clutch to stop a hot engine. Those were the days.

Ivor

Odd, how the internet throws up solutions to problems one didn't even know one had.
An adjustable PVC valve.
[www.powerperformancenews.com]

Only $130 + $20 for the inline adaptor.

Maybe overkill for a small street engine.

Ivor

Looks like pretty good product. I would still vent the opposite valve cover to the air cleaner as WOT bolwby will exceed it's capacity.

On my 340 I used a modified European approach. I used a small filter similar to the Rover's orifice equipped small breather, then on the opposite side fitted the Rover flame trap, plumbed to a vacuum controlled heater valve that opens when the signal goes towards atmospheric. Then to manifold vacuum. This way under part or full throttle manifold vacuum is applied via a large line to the crankcase and the valve closes at idle (I have a high idle vacuum signal, unlike some). I do not at present have a system for idle I think, but a simple vacuum hose with an orifice would remedy that. I do not presently recall if I used an orifice in the small breather or not.

Jim

Here's my [Aussie] way of doing it on my 4.6 SD1 with the 1404.

Small mushroom KN style filter on LH rocker cover. Generic [Repco] PCV valve on RH rocker cover with hose running to the large tube oon the front of the carb. The back tube feeds the brake booster.

Dissy is plumbed into the "always on" LH port on the front of the carb [idles smoother, cools better, and pulls stronger from idle].

That setup will work most of the time. Where it tends to fall short is at WOT, and on some engines it may do fine while on others it won't. The issue is with the larger volume of blowby gasses at WOT which can well exceed the capacity of the PCV valve and its hose. If that happens the crankcase will pressurize and usually oil will be pushed past the seals.

Jim

By modding the rocker covers that came with the engine, I can arrange a PCV takeoff from each rocker cover, and a 3/4" outlet feeding into the air filter. The only thing missing from these rocker covers is,. bizarrely, any means of adding oil;, but Moroso have a solution for that - #68485 [www.jegs.com]

More prosaically, was watching today the installation DVD for the Edelbrock 1404, where a chap was idly tightening the hold-down nuts with a small wrench. There is no torque given in the instructions.

I ask because the TSM for my Rambler gives a torque (for the Holley) of 10/12 lb/ft, which seems to me far higher that this chap was using.
I don't want to warp the base... what torque do you use?
If it makes any difference, I'm also using a 1" phenolic spacer.

Ivor

Another option that you may want to consider is to add a vent tube from the fuel pump block-off plate. It works well, though an air/oil separator of some sort is useful for keeping the oil in the engine (some sort of small chamber with a stainless scrubby pad inside for instance, doubles as a flame trap, best if it drains back by gravity).

I was just looking at mine and noticed I had added an orifice fitting from the valve cover to manifold vacuum. With a small open vent filter at the opposite corner for fresh air and a vacuum valve to vent blowby it satisfies every demand. I simply tapped the Rover valve cover for a 10-32 hose barb and used one with an orifice. The valve feeds into the blower inlet scoop behind the filter, so under boost it is seeing very light vacuum. At cruise it closes. Uses the standard Rover flame trap.

Jim

It's taken me all this time to get it running.
The spark vanished.
Then it still wouldn't start, it just wouldn't.
So becoming exasperated I bought a new Edelbrock to replace the used one I had.
And it still wouldn't start.
In retrospect, there seems to have been some problem getting fuel into the carb as the accelerator pump wasn't making those squish noises and there was no smell of fuel. The pump and the pump pressure were and are fine, and the filter. No idea really.
But then it started, couldn't get it to idle very cleanly and before I really got into that it ran up to temp and the fan didn't work and there were two water leaks.
Investigating the fan revealed that one of the garages I paid to do work had wired the fan thermostat output to the horn. and the manual override had been wired to the rev counter. In truth there are few garages now who know how to do the basics. They just know how to plug modern cars into computers.
Now, two years after it last ran properly, and after employing three garages to work on the car because I lacked the time and inclination, here I am doing the job myself.
So, the PCV.
I have a low-rise manifold, the top of the flame trap is level with the underside of the filter so I need an S shape hose which I shall make out of copper plumbing parts.
The (newer) engine has very little blowby. The old engine could have been used for the humane killing of poultry, but the new one is very clean.
Been reading about PCV valves and the need to choose one with the right spring rate. We don't have a lot of choice over here. As a starting point I'm going to take the easy way out and plumb the flame trap to the air filter. If it gets oily, I shall put in a catch tank. Then as a third stage I could put in a PCV. I looked at various engines in the paddock at the Goodwood Revival, they all breathed into a catch tank then back into the filter. No PCV.
When it gets on a rolling road I'll check the blowby at WOT, and take it from there.

Whilst investigating why it wouldn't start, I took the top off the Edelbrock and was struck by how simple it seems compared to a Holley. At any rate, less to go wrong.

Ivor

Not really less Ivor, just arranged differently.

Keep an eye on that copper loop, it could fill up with oil.

Two things to concern you: PCV airflow at idle (orifice), and at part/full throttle (big tube).

You have the rest of the info you need.

Jim