Engine and Transmission Tech

tips, technology, tools and techniques related to vehicle driveline components

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BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5284 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: A leap in the dark - roll out the 4-barrel
Posted by: BlownMGB-V8
Date: August 24, 2017 11:38AM

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.


88v8
Ivor Duarte
Gloucestershire UK
(487 posts)

Registered:
02/11/2010 04:29AM

Main British Car:
TR6 74 2.5 injection six

Re: A leap in the dark - roll out the 4-barrel - PCV.
Posted by: 88v8
Date: August 24, 2017 03:06PM

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


88v8
Ivor Duarte
Gloucestershire UK
(487 posts)

Registered:
02/11/2010 04:29AM

Main British Car:
TR6 74 2.5 injection six

Re: A leap in the dark - roll out the 4-barrel - PCV.
Posted by: 88v8
Date: August 27, 2017 09:16AM

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


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5284 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: A leap in the dark - roll out the 4-barrel - PCV.
Posted by: BlownMGB-V8
Date: August 27, 2017 12:06PM

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


Robrover
Rob Thornton
Adelaide, Australia
(18 posts)

Registered:
10/01/2009 11:52PM

Main British Car:
1978 Rover SD1 4.6

Re: A leap in the dark - roll out the 4-barrel - PCV.
Posted by: Robrover
Date: September 06, 2017 03:59AM

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].


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5284 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: A leap in the dark - roll out the 4-barrel - PCV.
Posted by: BlownMGB-V8
Date: September 06, 2017 10:45AM

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


88v8
Ivor Duarte
Gloucestershire UK
(487 posts)

Registered:
02/11/2010 04:29AM

Main British Car:
TR6 74 2.5 injection six

Re: A leap in the dark - roll out the 4-barrel - PCV.
Posted by: 88v8
Date: September 20, 2017 05:45PM

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



BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5284 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: A leap in the dark - roll out the 4-barrel - PCV.
Posted by: BlownMGB-V8
Date: September 21, 2017 01:17PM

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
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