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Username Post: PCV???        (Topic#347265)
farm rat 
Contributor
Posts: 106

Reg: 09-13-16
09-21-17 08:37 AM - Post#2708373    

Is it better to run the PCV off the carb or the intake?



 




IgnitionMan 
Valued Contributor
Posts: 3219

Reg: 04-15-05
09-21-17 09:02 AM - Post#2708376    
    In response to farm rat

Primary end of carb.



 
farm rat 
Contributor
Posts: 106

Reg: 09-13-16
09-21-17 10:34 AM - Post#2708388    
    In response to IgnitionMan

Thanks buddy.

Now, how about the brake booster? Carb or intake?



 
Shepherd 
Frequent Contributor
Posts: 1035

Loc: Lake George, NY
Reg: 11-11-15
09-21-17 11:13 AM - Post#2708396    
    In response to farm rat

Intake, you need larger volume for the booster.



 
farm rat 
Contributor
Posts: 106

Reg: 09-13-16
09-21-17 01:58 PM - Post#2708416    
    In response to Shepherd

Thanks



 
Bel Air kiwi 
"3rd Year" Silver Supporting Member
Posts: 3808
Bel Air kiwi
Loc: New Zealand
Reg: 04-24-14
10-01-17 09:05 PM - Post#2709450    
    In response to farm rat

Hi Farm Rat, if your carb has a spigot for PCV then that implies it was designed, (jetted) to run the extra air. So definitely use that carb point.
Also see if you can find out what value or part number PCV valve matches that carb/car.

Brake boost should be off the manifold, or a pump system. When you dive to the brake pedal you will have closed the throttle and the manifold signal begins to rise imediately to assist the booster.

If that is not enough boost then you need auxiliary supplies and/or tanks. Small turbo diesel pick ups with car style brakes use a booster pump on the alternator.

They tend to max out at 30"Hg at best but routinely produce in the 20-25"Hg range which is usually more than enough. The down side is they need a constant oil feed and sump return like a turbo.
My experience is these unit really last and the local auto electrician gives me new units when he replaces complete alternators.

Plan B is to use an electric Vacuum pump and tank system. There are kits in the aftermarket but in my view they are over priced. You could look for an OE unit you can use, but it will need to be big enough.

Be aware it will make noise and vibrate, it will need a relay.
Do Not make the mistake of getting an OE unit that is not for brakes, as some VW ,AUDI,etc use these pumps for the climate control system.

Cheers Kiwi


48 3100 RHD, 51 Deluxe 4DR RHD, 51 Bel Air parts car, 52 Bel Air P-Glide LHD. Others 23T, 32 Tudor, 58 Edsel pacer 4DR HDT, 79 F250 351C RHD. 69,70,82 Capri. No mobile, no TV, and no Jap cars.

And when it was laid to waste, they called it peace.


Edited by Bel Air kiwi on 10-01-17 09:11 PM. Reason for edit: No reason given.

 
farm rat 
Contributor
Posts: 106

Reg: 09-13-16
10-02-17 11:19 AM - Post#2709504    
    In response to Bel Air kiwi

How would you match a PCV to your carb?



 
IgnitionMan 
Valued Contributor
Posts: 3219

Reg: 04-15-05
10-02-17 12:35 PM - Post#2709512    
    In response to farm rat

It would be matched to the vacuum level the engine produces, not the carb.

A valve for a 390 horsepower 427 big block is completely different on spring tension, to match the higher vacuum, than one for a 425 horsepower 427 big block that has significantly less operating vacuum because the intake valve closes later on the higher horsepower engine, lowering both Dynamic Compression Ratio, and idle/lower RPM vacuum, from increased mixture reversion up the intake ports.

What idle vacuum level does the engine produce now?



 
MikeB 
Ultra Senior Member
Posts: 10058
MikeB
Loc: Plano, TX
Reg: 08-28-03
10-09-17 07:19 AM - Post#2710276    
    In response to IgnitionMan

To elaborate on Dave's comments, I once bought several PCV valves from Rock Auto (at very low prices), all for different Chevy engines from the 60s-70s. Thought I could test them with a Mityvac, but couldn't generate enough air volume.

So then I installed each one on a warmed-up engine to see which one let the engine make the most vacuum. The difference among the valves at idle was no more than 1" hg, but I chose the one that consistently made made the most vacuum. As I recall, the engine had been making around 16" vacuum at idle, and it jumped to 17" with the new valve. Could be the old one was designed for an engine making high vacuum, and started opening a little too soon for my engine. I suspect that a 425hp/427 valve wouldn't start opening until something lower than 12"-14".



1982 C10 SWB pickup: Unmolested base truck, original paint. Originally had 250 six and 3-on-the-tree
Now has 355 with Vortec heads, RamJet roller cam, LS6 beehive springs, TH350
Retired, but working part-time on 50s-70s cars & trucks.


 




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