On the front of the Edelbrock carb there are 3 vaccum ports, one (smallest) goes to vac the dissy, the other 2 are blanked off.
On the RPI website they state that the middle port (the largest) is used and connected to the breather on top of the rocker cover...... has anyone done this ??
Edelbrock Carb vaccum pipes
Moderator: phpBB2 - Administrators
-
mike-b
- Forum Contributor
- Posts: 209
- Joined: Thu Mar 25, 2010 8:49 pm
- Location: Markfield, Leicestershire.
Hi,
I too have a weber 500 on my Rover V8, though it may be a different model the principle is the same. At the front - rad end I have two vac connections and at the rear a larger vac.
The instructions that came with my carb stated the larger vac was either for the engine connection at the rear of the block or a rocker cover. I put mine to the rocker cover and the emission test never gives any problem, however there is no block connection on my V8.
So you could run it from a rocker cover or at the rear of the block.
Hope this helps ... mike
I too have a weber 500 on my Rover V8, though it may be a different model the principle is the same. At the front - rad end I have two vac connections and at the rear a larger vac.
The instructions that came with my carb stated the larger vac was either for the engine connection at the rear of the block or a rocker cover. I put mine to the rocker cover and the emission test never gives any problem, however there is no block connection on my V8.
So you could run it from a rocker cover or at the rear of the block.
Hope this helps ... mike
Mike B Drives a 1984 Mk2 Granada ghia V8.
Yes, thanks... I was reading about using the port to go to the breather, I have a pipe from the top of the RH rocker cover, the port at the rear of the carb is blocked with an threaded bung, the front has the 3 pipes small meduim and large in the middle.. I think i will try and connect the middle large outlet via a filter to the breather on rocker cover...
did you have to change your timing or did the car run ok ?
did you have to change your timing or did the car run ok ?
V8 powered tub of plastic
-
mike-b
- Forum Contributor
- Posts: 209
- Joined: Thu Mar 25, 2010 8:49 pm
- Location: Markfield, Leicestershire.
Hi,
The car ran ok using the larger vac on the rocker cover, however the mixture was wrong but that was a carb metering rod problem - NOT the breathing system as such.
In short the system allows the engine to eat its own muck from the crankcase thus relieving it of some crankcase pressure. The rocker with the hose to the carb vac also has the oil filler cap on it, the other rocker cover has a breather ( to under bonnet air ) so in short one rocker cover is letting foul air from the crankcase out and the other rocker cover is letting clean air in.
The emission test at MoT time is never a problem so the system must be Ok.
Cheers, Mike
The car ran ok using the larger vac on the rocker cover, however the mixture was wrong but that was a carb metering rod problem - NOT the breathing system as such.
In short the system allows the engine to eat its own muck from the crankcase thus relieving it of some crankcase pressure. The rocker with the hose to the carb vac also has the oil filler cap on it, the other rocker cover has a breather ( to under bonnet air ) so in short one rocker cover is letting foul air from the crankcase out and the other rocker cover is letting clean air in.
The emission test at MoT time is never a problem so the system must be Ok.
Cheers, Mike
Mike B Drives a 1984 Mk2 Granada ghia V8.
I only have one rocker cover with a breather fixed to it, the otherside is the oil filler cap, I am sure I have seen somewhere a Rover V8 with a pipe to the back of the engine near the lifting eye above the bell housing, I guess if I can put pipe from rocker to Carb vac with a T piece to a fresh air supply this will be good enough ?
V8 powered tub of plastic
-
mike-b
- Forum Contributor
- Posts: 209
- Joined: Thu Mar 25, 2010 8:49 pm
- Location: Markfield, Leicestershire.
Hi Redders,
In your first post you mention two of the three vacs are blanked off ... How?
You are correct that there is a connection at the rear of the crankcase, though that does not apply to all RV8 engines.
If you have only the one vac connection at the carb I would look at the possibility of a vac connection from the crankcase connection to the inlet manifold where the carb is joined to it.
Due to manifold suction that would always be sucking the crankcase muck as required.
If you "Tee" off the vac from carb to dizzy and join the "Tee" to the crankcase you won`t have a proper working vac at the dizzy, the air pressure in the inlet manifold is NOT the same as the air pressure in the crankcase.
Anyway the vac at the dissy is only being used at tick-over and just before the weights & springs inside the dizzy take over the job .... when the engine goes a little beyond tick-over the dizzy vac is no longer in use.
Anyway how are those other two vac`s at the carb blanked off? I may be able to help better if I know. Cheers mike
In your first post you mention two of the three vacs are blanked off ... How?
You are correct that there is a connection at the rear of the crankcase, though that does not apply to all RV8 engines.
If you have only the one vac connection at the carb I would look at the possibility of a vac connection from the crankcase connection to the inlet manifold where the carb is joined to it.
Due to manifold suction that would always be sucking the crankcase muck as required.
If you "Tee" off the vac from carb to dizzy and join the "Tee" to the crankcase you won`t have a proper working vac at the dizzy, the air pressure in the inlet manifold is NOT the same as the air pressure in the crankcase.
Anyway the vac at the dissy is only being used at tick-over and just before the weights & springs inside the dizzy take over the job .... when the engine goes a little beyond tick-over the dizzy vac is no longer in use.
Anyway how are those other two vac`s at the carb blanked off? I may be able to help better if I know. Cheers mike
Mike B Drives a 1984 Mk2 Granada ghia V8.
The bob weights don't "take over" from the vac advance system, the two can both be working at the same time and the total advance will be the sum of the two systems added together.
The vac system will be still be working with 12 inches of mercury and you can pull that much vacuum whilst cruising at considerable speed. You could also be running the engine at 3000 RPM whilst cruising so most of the bob weight advance will also have been added to the vac advance. This is all fine whilst the throttle is just cracked open but in my experiance with Eddy carbs used in conjunction with a Lucas vac canister is that they don't work too well together. The carb provides too much vac 'signal' even when the throttle is open quite along way, the result is too much total advance and the engine kicks back. This happens when the revs are high the throttle is starting to be opened when coming out of a bend in the road.
I spent months messing about trying to get good mechanical advance figures whilst at the same time still running with a vac system, in the end I gave up! You either have to run a poor mechanical advance setup along with a low static advance and the vac system or ditch the vac system which allows you to run a decent static advance along with a good advance curve and a good total advance. (The second option gave much better performance on the engines that I've worked on).
With a 3.5 lump using an Eddy carb I'd run around 12-14 degrees static, 36 degrees all in at 2700-3000 RPM with the vac system not being used at all. These figures won't work in conjunction with the vac system.
Oh using the ported or non-ported vac take off won't get round the problem either!
All just my humble!
Pete
The vac system will be still be working with 12 inches of mercury and you can pull that much vacuum whilst cruising at considerable speed. You could also be running the engine at 3000 RPM whilst cruising so most of the bob weight advance will also have been added to the vac advance. This is all fine whilst the throttle is just cracked open but in my experiance with Eddy carbs used in conjunction with a Lucas vac canister is that they don't work too well together. The carb provides too much vac 'signal' even when the throttle is open quite along way, the result is too much total advance and the engine kicks back. This happens when the revs are high the throttle is starting to be opened when coming out of a bend in the road.
I spent months messing about trying to get good mechanical advance figures whilst at the same time still running with a vac system, in the end I gave up! You either have to run a poor mechanical advance setup along with a low static advance and the vac system or ditch the vac system which allows you to run a decent static advance along with a good advance curve and a good total advance. (The second option gave much better performance on the engines that I've worked on).
With a 3.5 lump using an Eddy carb I'd run around 12-14 degrees static, 36 degrees all in at 2700-3000 RPM with the vac system not being used at all. These figures won't work in conjunction with the vac system.
Oh using the ported or non-ported vac take off won't get round the problem either!
All just my humble!
Pete
Last edited by sidecar on Tue Apr 09, 2013 8:32 pm, edited 1 time in total.
Hi Mike,
OK let me try, if you are standing at front of the engine looking at the carb from LH to RH on front of carb I have 3 ports, LH small which is the pipe going to the distributor then a 10mm ish size oulet in middle, this was blanked with a rubber blank pipe, then about an 8mm size pipe on far RH side this also was blanked with rubber cap.
On rear of carb is a allen headed blanking plug in a port in center at rear.
On rh rocker cover I have a breather port on top, the opposite side rocker cover has filler neck.
I read on RPI website that they connect the middle pipe at the front to the breather...
So my thinking was, the small LH pipe will go to Dissy, then middle pipe on carb to the rocker cover (with filter in line) but I am not sure if that will pull a vacuum on the crank case ? so I thought somewhere I need to introduce fresh air into the crank case ? hence looking at the breather above the bell housing.. so I would tee that into the 10mm middle pipe on carb and to top of engine breather... Does that make sense ???
OK let me try, if you are standing at front of the engine looking at the carb from LH to RH on front of carb I have 3 ports, LH small which is the pipe going to the distributor then a 10mm ish size oulet in middle, this was blanked with a rubber blank pipe, then about an 8mm size pipe on far RH side this also was blanked with rubber cap.
On rear of carb is a allen headed blanking plug in a port in center at rear.
On rh rocker cover I have a breather port on top, the opposite side rocker cover has filler neck.
I read on RPI website that they connect the middle pipe at the front to the breather...
So my thinking was, the small LH pipe will go to Dissy, then middle pipe on carb to the rocker cover (with filter in line) but I am not sure if that will pull a vacuum on the crank case ? so I thought somewhere I need to introduce fresh air into the crank case ? hence looking at the breather above the bell housing.. so I would tee that into the 10mm middle pipe on carb and to top of engine breather... Does that make sense ???
V8 powered tub of plastic
Not sure if this will work but pipe like this....
http://www.google.co.uk/imgres?imgurl=h ... AQ&dur=623
The front of carb blanked ports look like this
http://www.google.co.uk/imgres?imgurl=h ... AQ&dur=623
http://www.google.co.uk/imgres?imgurl=h ... AQ&dur=623
The front of carb blanked ports look like this
http://www.google.co.uk/imgres?imgurl=h ... AQ&dur=623
V8 powered tub of plastic
The blanked off rear port and the large front port are basically the same thing, either one of them should be used in order to create vacuum in the engine by connecting it to a rocker cover. But I think that you need to use a PCV valve otherwise you are inducting a huge air leak into the carb.
I have seen an engine running without a PCV and the air leak meant that even when the tick over screw was backed right out the engine was still ticking over too high, it could not be stalled by shutting the carb! The mixture could still be set correctly because the pilot screws will allow for this.
The standard rocker covers may have some sort of PCV valve, I don't know as my engine uses SBC covers even though it is an RV8.
The other rocker cover should have a vent with a filter on it or a tube that connects to the base of the main air filter. This setup will allow the carb to evacuate the engine of gases by pulling a 'measured' amount of filtered air though the engine.
The other two small ports on the carb are meant for vac advance, one is 'ported' the other is not. If you look at the two small ports one sits about 5mm lower down nearer the base of the carb, this is the non-ported take off. They may well work with other dizzies such as when the carb is fitted on a SBC or Ford lump but like I said they don't work well on a RV8 with a Lucas dizzy.
I have seen an engine running without a PCV and the air leak meant that even when the tick over screw was backed right out the engine was still ticking over too high, it could not be stalled by shutting the carb! The mixture could still be set correctly because the pilot screws will allow for this.
The standard rocker covers may have some sort of PCV valve, I don't know as my engine uses SBC covers even though it is an RV8.
The other rocker cover should have a vent with a filter on it or a tube that connects to the base of the main air filter. This setup will allow the carb to evacuate the engine of gases by pulling a 'measured' amount of filtered air though the engine.
The other two small ports on the carb are meant for vac advance, one is 'ported' the other is not. If you look at the two small ports one sits about 5mm lower down nearer the base of the carb, this is the non-ported take off. They may well work with other dizzies such as when the carb is fitted on a SBC or Ford lump but like I said they don't work well on a RV8 with a Lucas dizzy.
As Pete says!
The big port in the middle would normally be for the servo so you get max vacuum with the butterflies closed, like when decelerating.
If you use this for a crankcase vent without a PCV valve it will suck in air and be a bugger to get idling. When you go to part or full throttle the PCV will drop shut until pressure builds up and forces it open to chuck the fumes back into the inlet manifold.
The two little ports you will notice are above and below the throttle plates. One will give you max vac signal at idle while the other has no vac. When you open the throttle the lower one will lose its vac signal, but the other one will start to get vacuum. If you have a vac gauge you can see how the two ports work when the engine is running. The dissy should be connected to the one thats under the throttle plates so it can read vacuum at idle.
I use the the higher one as the vac signal to the modulator on my auto gearbox as I need it to see vacuum at high rpm to enable the kickdown in sequence with the kickdown cable.
I have tried PCV's in the past when I had chevy rocker covers on the Rover V8. But I then went to fitting rocker cover vents into the air filter above the carb and then just fitted filtered breathers straight onto the rocker covers. The filters are not really to stop crud getting out, they are to stop dust being drawn in when the crankcase goes into negative pressure.
REDDERS!
The older V8's had a small breather pipe at the rear of the engine just above the bell housing. On my factory built MGB V8 this just had a small fuel filter fitted. It does not connect to anything and most folk remove the pipe and blank off the hole as it seems to do no more than leak oil. The filter was there to stop dust getting into the engine.
"I guess if I can put pipe from rocker to Carb vac with a T piece to a fresh air supply this will be good enough ?"
All that will do is mess with the engine as you will be sucking in huge gulps of air under the carb and leaning the mixture right out.
What is the initial query? Is it just how to pipe up the dissy vac and crankcase vent?
The big port in the middle would normally be for the servo so you get max vacuum with the butterflies closed, like when decelerating.
If you use this for a crankcase vent without a PCV valve it will suck in air and be a bugger to get idling. When you go to part or full throttle the PCV will drop shut until pressure builds up and forces it open to chuck the fumes back into the inlet manifold.
The two little ports you will notice are above and below the throttle plates. One will give you max vac signal at idle while the other has no vac. When you open the throttle the lower one will lose its vac signal, but the other one will start to get vacuum. If you have a vac gauge you can see how the two ports work when the engine is running. The dissy should be connected to the one thats under the throttle plates so it can read vacuum at idle.
I use the the higher one as the vac signal to the modulator on my auto gearbox as I need it to see vacuum at high rpm to enable the kickdown in sequence with the kickdown cable.
I have tried PCV's in the past when I had chevy rocker covers on the Rover V8. But I then went to fitting rocker cover vents into the air filter above the carb and then just fitted filtered breathers straight onto the rocker covers. The filters are not really to stop crud getting out, they are to stop dust being drawn in when the crankcase goes into negative pressure.
REDDERS!
The older V8's had a small breather pipe at the rear of the engine just above the bell housing. On my factory built MGB V8 this just had a small fuel filter fitted. It does not connect to anything and most folk remove the pipe and blank off the hole as it seems to do no more than leak oil. The filter was there to stop dust getting into the engine.
"I guess if I can put pipe from rocker to Carb vac with a T piece to a fresh air supply this will be good enough ?"
All that will do is mess with the engine as you will be sucking in huge gulps of air under the carb and leaning the mixture right out.
What is the initial query? Is it just how to pipe up the dissy vac and crankcase vent?
Perry Stephenson
MGB GT + Rover V8
9.62 @ 137.37mph
Now looking for 8 seconds with a SBC engine
http://www.youtube.com/watch?v=nVscbPHgue0&list=UUqIlXfSAoiZ--GyG4tfRrjw
https://www.youtube.com/watch?v=eg3avnsNKrc&index=2&list=FLqIlXfSAoiZ--GyG4tfRrjw
MGB GT + Rover V8
9.62 @ 137.37mph
Now looking for 8 seconds with a SBC engine
http://www.youtube.com/watch?v=nVscbPHgue0&list=UUqIlXfSAoiZ--GyG4tfRrjw
https://www.youtube.com/watch?v=eg3avnsNKrc&index=2&list=FLqIlXfSAoiZ--GyG4tfRrjw
I run a K&N small breather on one rocker cover and a pipe from the opposite side rocker cover into the big outlet port on the front on the Edelbrock. The pipe has a PCV incorporated into it. Both the other smaller ports are blocked off as the Scorcher distributor has no vac advance mechanism (purposefully).
As others have pointed out, the Edelbrock/Weber 500 and the Lucas dissy advance don't get on together too welll so you'd be well advised to leave it out. Mine idles at 650rpm and there are no flat spots or stumbles anywhere in the off idle, cruise or WOT progression.
As others have pointed out, the Edelbrock/Weber 500 and the Lucas dissy advance don't get on together too welll so you'd be well advised to leave it out. Mine idles at 650rpm and there are no flat spots or stumbles anywhere in the off idle, cruise or WOT progression.
