Pcv and brake servo piping.

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JinxJay
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Pcv and brake servo piping.

Post by JinxJay »

Hi folks, I have a 66 coronet with power front discs. This seems to be a rare option. On the back of my engine I only have one vacuum take off. I have a single pipe coming off that goes to a T piece. Then runs to both the servo and PCV valve, the brakes don't feel quite right and this set up doesn't seem right to me. Although I've not had an early car before it might be correct, it just doesn't seem right to me.

Anyone have any ideas?
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Derek
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Re: Pcv and brake servo piping.

Post by Derek »

My servo vacuum comes from the back of the carb in a tri piece. Headlights, servo and pc valve.
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Dave999
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Re: Pcv and brake servo piping.

Post by Dave999 »

on a six clylinder 1 goes to the fat pipe into the base of the carb and one goes to a connector on the inlet to no.6 cylinder
not sure which way round is correct but suspect the carb one is for the booster its gets the benefit of vacuum pulses from 6 or 8 cylinders

dunno what you V8 boys do but i'd suggest the PCV connection into the t piece is having a BAD impact on the vacuum for the booster as the PCV is just a hollow pipe with a weight and light weight spring in it. all of the suck for the booster is going to be used sucking up oil fumes


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JinxJay
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Re: Pcv and brake servo piping.

Post by JinxJay »

Derek wrote: Wed Jun 30, 21 3:12 pm My servo vacuum comes from the back of the carb in a tri piece. Headlights, servo and pc valve.
hi Derek, thats what ive seen on later 68,69,70 cars and makes more sense as its pulling total vacuum from the manifold via 3 fittings,
mine seems wrong as its one small fitting splitting into two.

i'm wondering if its worth fitting the later tri outlet,
JinxJay
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Re: Pcv and brake servo piping.

Post by JinxJay »

Dave999 wrote: Wed Jun 30, 21 3:19 pm on a six clylinder 1 goes to the fat pipe into the base of the carb and one goes to a connector on the inlet to no.6 cylinder
not sure which way round is correct but suspect the carb one is for the booster its gets the benefit of vacuum pulses from 6 or 8 cylinders

dunno what you V8 boys do but i'd suggest the PCV connection into the t piece is having a BAD impact on the vacuum for the booster as the PCV is just a hollow pipe with a weight and light weight spring in it. all of the suck for the booster is going to be used sucking up oil fumes


Dave
thats just what i was thinking Dave, i'm stuck as i dont have outlets on the carbs though, just the single fitting in the manifold.
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Pete
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Re: Pcv and brake servo piping.

Post by Pete »

Great car.

I would think that I would ditch the PCV connection and just plumb the Booster pipe direct to the inlet to see if it makes a difference and prove that the Booster was actually working correctly first. You can address the PCV accordingly.

I thought that Carters had a take off point at the front in the same way that the Edelbrock copies have today - I could be wrong.

I had hell-and-all trouble trying to get the Carters working on my 426 Hemi.
Despite numerous rebuilds, they flooded the Venturi's all the time. Caused really rough and inconsistent running.

I hope you have better luck.

All the best.

Pete
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Dave999
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Re: Pcv and brake servo piping.

Post by Dave999 »

as pete says dump the PCV and run the pipe down the back of the engine for rust proofing effect :) if air blows across the end you get a Chimney draw effect in the pipe:) or into a catch can which is potentially better environmentally and doesn't spatter the underside of your car with oil.

Instead you could fit a restriction in its pipe bulkhead hose-barb fitting with the middle soldered up and a small hole drilled through would do. or even just a really restrictive fitting. stick it in the PCV pipe. you then bias more of each vacuum pulse to the booster. balancing act, adjust till brakes feel better.

the smaller the hole the slower the suck that gets through to the PCV you basically flatten the spike into a curve for the PCV, and more of it will hit the 1 way valve in the booster instead.

really is analogous to a bucket with 2 holes in it if 1 is tiny-small in comparison to the other. you can guarantee less water comes out the small one
but the pressure behind both holes is the same, same water same depth in bucket same bit of bucket sized atmosphere above it, you just don't run out of water as quick with 1 hole smaller than the other.

vacuum is just a negative pressure, in theory its the same all across the manifold but it comes in waves from each induction stroke, and the place where they all converge is at the carb. thats one reason why its in the middle. :)

Dave
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JinxJay
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Re: Pcv and brake servo piping.

Post by JinxJay »

Dave999 wrote: Thu Jul 01, 21 9:50 am as pete says dump the PCV and run the pipe down the back of the engine for rust proofing effect :) if air blows across the end you get a Chimney draw effect in the pipe:) or into a catch can which is potentially better environmentally and doesn't spatter the underside of your car with oil.

Instead you could fit a restriction in its pipe bulkhead hose-barb fitting with the middle soldered up and a small hole drilled through would do. or even just a really restrictive fitting. stick it in the PCV pipe. you then bias more of each vacuum pulse to the booster. balancing act, adjust till brakes feel better.

the smaller the hole the slower the suck that gets through to the PCV you basically flatten the spike into a curve for the PCV, and more of it will hit the 1 way valve in the booster instead.

really is analogous to a bucket with 2 holes in it if 1 is tiny-small in comparison to the other. you can guarantee less water comes out the small one
but the pressure behind both holes is the same, same water same depth in bucket same bit of bucket sized atmosphere above it, you just don't run out of water as quick with 1 hole smaller than the other.

vacuum is just a negative pressure, in theory its the same all across the manifold but it comes in waves from each induction stroke, and the place where they all converge is at the carb. thats one reason why its in the middle. :)

Dave
That's a great idea Dave. I'm going to try the pcv disconnected and with a restriction see if there is a difference on how it is now. I've also ordered the multiple outlet fitting of the later cars from the states. See if that improves it as well.
JinxJay
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Re: Pcv and brake servo piping.

Post by JinxJay »

Pete wrote: Wed Jun 30, 21 8:17 pm Great car.

I would think that I would ditch the PCV connection and just plumb the Booster pipe direct to the inlet to see if it makes a difference and prove that the Booster was actually working correctly first. You can address the PCV accordingly.

I thought that Carters had a take off point at the front in the same way that the Edelbrock copies have today - I could be wrong.

I had hell-and-all trouble trying to get the Carters working on my 426 Hemi.
Despite numerous rebuilds, they flooded the Venturi's all the time. Caused really rough and inconsistent running.

I hope you have better luck.

All the best.

Pete
Thanks Pete. I think it's a great car too. I'm going to try just the servo and see if it improves.

Only my front Carter has an outlet and it goes to the vac on the dizzy.

So far my carter's have been spot on. Starts and idles very well. Not had chance to drive it in anger yet. So I'll have to see how it goes.
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morgan
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Re: Pcv and brake servo piping.

Post by morgan »

Hmm. I'm not sure I have a PCV.
I run breathers straight down, but from memory I can remember the headlight and brake vacuum but nothing else. :-k
Going to go have a look now...
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