XJR Eaton Supercharger 'Blanked off bypass valve'
#1
12-27-2015, 03:31 PM
XJR Eaton Supercharger 'Blanked off bypass valve'
Hi to all and hope all your christmas presents were jag related
last month i purchased a car i have not seen yet...a 96 5 speed manual XJR....and its got a 'modification'
the bypass valve has been blanked off.....quote unquote
I have done some research on similar sounding mods done on cobra mustangs and was wondering if in general this is the same thing or is this some specific mod done on the Eaton appliction fitted to the XJR6
help on understanding the tech reasoning would be appreciated
by the looks of the mustang mods it would seem to put the blower in constant boost air supply mode at what would normally be idle and sub boost speed....under idle or non boost speed circumstances the bypass valve allows air to intake after the blower meaning that effectively the blower is in free wheel until demand for boost
has anyone else done this to an XJR
https://www.rpmoutlet.com/boost-bypa...oost%20bypassc
How To: Eliminate Boost Drop Off (eliminate boost solenoid))
last month i purchased a car i have not seen yet...a 96 5 speed manual XJR....and its got a 'modification'
the bypass valve has been blanked off.....quote unquote
I have done some research on similar sounding mods done on cobra mustangs and was wondering if in general this is the same thing or is this some specific mod done on the Eaton appliction fitted to the XJR6
help on understanding the tech reasoning would be appreciated
by the looks of the mustang mods it would seem to put the blower in constant boost air supply mode at what would normally be idle and sub boost speed....under idle or non boost speed circumstances the bypass valve allows air to intake after the blower meaning that effectively the blower is in free wheel until demand for boost
has anyone else done this to an XJR
https://www.rpmoutlet.com/boost-bypa...oost%20bypassc
How To: Eliminate Boost Drop Off (eliminate boost solenoid))
#2
12-27-2015, 04:16 PM
#3
12-27-2015, 04:20 PM
#4
12-27-2015, 08:11 PM
Veteran Member
#5
12-28-2015, 03:52 AM
'blanked off bypass valve' is a bit of a crude statement but it's what was described in the sale ....but I will ask the previous keeper about it to get some detail and repost with any specifics
Im guessing that it must be related to the links I posted with opening question....
Inasmuch that the bypass system enables the car to intake air for combustion by bypassing the SC resulting that the SC is not the route for intake air at idle or speeds in the normal vacuum range......but put your foot down and the bypass is closed causing intake air to be directed through the SC.....whoooooooot!
from reading the threads the purpose of a bypass system is two fold (1) better on fuel economy when not needing boost (2) reduced noise from blower when not on load (on our cars I don't think the bypass serves to vent over boosted situations and as such is not acting like a BOV)
So the Mods primary purpose of 'bypassing the bypass valve' results in all intake air coming through the SC at all times with the supposed positive advantage that there is less delay with boost. (and if it in fact does act as a BOV it means that it does not vent in overboosted situations meaning more boost at higher RPM's)
However there are apparently a few down sides
1) because all air always comes through the SC then IAT's will be higher than they would if the intake air were allowed to bypass the SC at idle or normal running vacuum speeds
2) it worsens economy as a result of all intake air coming through the boost route
3) constant whine from SC (that's good or bad depending on your liking for it) but could result in higher wear on the SC mechanism
The Mustang guys seem to be with 'who cares about the economy' ' I love the noise' and 'so what if it breaks'....which are all values I can go with having a B&M 174 SC on a 5.0 foxbody....Jaguar owner opinions my be less liberal
Anyway when i get a look we will all know unless someone pipes in with a 'yea i have done that'
Im looking forward to finding out what the car is like to drive when i go to pick her up next month....Andy Stodard's CPS bracket, 12.5% bigger crank/SC pulley, 5 speed manual, CAI, mods to exhaust...and the blanked off bypass valve!
Should be an interesting drive home
Last edited by xxxscimitarxxx; 12-28-2015 at 04:04 AM.
#6
01-17-2016, 03:51 AM
Senior Member
Blocking off the bypass valve is a really bad idea. That is the view of an applications engineer who works for Eaton who design and make these superchargers, so I'm not inclined to disagree with him. Blocking the bypass will cause cavitation inside the supercharger when it is working against a closed throttle due to the high differential pressure created across the supercharger. This will generate a lot of heat inside the supercharger, making it less efficient.
There is no advantage in blocking the supercharger bypass, so there is no point in doing it. It does not act a s a "blow off valve - BOV". It might leak a bit of boost pressure, but i don't think that is a strong enough reason to block it off, for the reason explained above. The increased power consumed driving the supercharger with the bypass blocked reduces fuel economy by about 2mpg (Imperial).
BTW, don't think of the bypass as allowing air to enter the engine without passing through the supercharger. Instead think of it as allowing all the surplus air that has exited out of the supercharger to be routed straight back into the inlet, because the engine can't consume it. If you were to measure the direction of flow through the bypass valve when it is open you would find that it is flowing from the outlet back to the inlet, so the air is flowing "away from the engine", not in parallel with the flow through the supercharger. Remember that the whole principle of the supercharger is that it is trying to pump air at a greater rate than the engine can use it. At 100% volumetric efficiency the engine is only trying to consume 4.0 litres of air every two revs because it's a 4 stroke engine. A 90 cubic inch supercharger running at 2.5 times engine speed is trying to displace 7.4 litres in 2 engine revs.
There is no advantage in blocking the supercharger bypass, so there is no point in doing it. It does not act a s a "blow off valve - BOV". It might leak a bit of boost pressure, but i don't think that is a strong enough reason to block it off, for the reason explained above. The increased power consumed driving the supercharger with the bypass blocked reduces fuel economy by about 2mpg (Imperial).
BTW, don't think of the bypass as allowing air to enter the engine without passing through the supercharger. Instead think of it as allowing all the surplus air that has exited out of the supercharger to be routed straight back into the inlet, because the engine can't consume it. If you were to measure the direction of flow through the bypass valve when it is open you would find that it is flowing from the outlet back to the inlet, so the air is flowing "away from the engine", not in parallel with the flow through the supercharger. Remember that the whole principle of the supercharger is that it is trying to pump air at a greater rate than the engine can use it. At 100% volumetric efficiency the engine is only trying to consume 4.0 litres of air every two revs because it's a 4 stroke engine. A 90 cubic inch supercharger running at 2.5 times engine speed is trying to displace 7.4 litres in 2 engine revs.
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#7
01-17-2016, 04:44 AM
Blocking off the bypass valve is a really bad idea. That is the view of an applications engineer who works for Eaton who design and make these superchargers, so I'm not inclined to disagree with him. Blocking the bypass will cause cavitation inside the supercharger when it is working against a closed throttle due to the high differential pressure created across the supercharger. This will generate a lot of heat inside the supercharger, making it less efficient.
There is no advantage in blocking the supercharger bypass, so there is no point in doing it. It does not act a s a "blow off valve - BOV". It might leak a bit of boost pressure, but i don't think that is a strong enough reason to block it off, for the reason explained above. The increased power consumed driving the supercharger with the bypass blocked reduces fuel economy by about 2mpg (Imperial).
BTW, don't think of the bypass as allowing air to enter the engine without passing through the supercharger. Instead think of it as allowing all the surplus air that has exited out of the supercharger to be routed straight back into the inlet, because the engine can't consume it. If you were to measure the direction of flow through the bypass valve when it is open you would find that it is flowing from the outlet back to the inlet, so the air is flowing "away from the engine", not in parallel with the flow through the supercharger. Remember that the whole principle of the supercharger is that it is trying to pump air at a greater rate than the engine can use it. At 100% volumetric efficiency the engine is only trying to consume 4.0 litres of air every two revs because it's a 4 stroke engine. A 90 cubic inch supercharger running at 2.5 times engine speed is trying to displace 7.4 litres in 2 engine revs.
There is no advantage in blocking the supercharger bypass, so there is no point in doing it. It does not act a s a "blow off valve - BOV". It might leak a bit of boost pressure, but i don't think that is a strong enough reason to block it off, for the reason explained above. The increased power consumed driving the supercharger with the bypass blocked reduces fuel economy by about 2mpg (Imperial).
BTW, don't think of the bypass as allowing air to enter the engine without passing through the supercharger. Instead think of it as allowing all the surplus air that has exited out of the supercharger to be routed straight back into the inlet, because the engine can't consume it. If you were to measure the direction of flow through the bypass valve when it is open you would find that it is flowing from the outlet back to the inlet, so the air is flowing "away from the engine", not in parallel with the flow through the supercharger. Remember that the whole principle of the supercharger is that it is trying to pump air at a greater rate than the engine can use it. At 100% volumetric efficiency the engine is only trying to consume 4.0 litres of air every two revs because it's a 4 stroke engine. A 90 cubic inch supercharger running at 2.5 times engine speed is trying to displace 7.4 litres in 2 engine revs.
As you know I have yet to collect the car in question for a couple more weeks...at which time I will be asking to see this modification and if possible undo it before I drive away.
The answers you provide are clear enough ...summarily that higher intake air temperatures are a bad thing and it begs one to think why anyone would do this modification
Having said that I also have a Carburetor fed 5.0 ford ohv V8 fitted with a B&M 174 displacement supercharger (same as weiand)
the plumbing for this set up looks as simple as it gets.....
carb > SC > intake > engine > exhaust
I see no bypass system but given that this is more a drag race engine than a a modern car set up might explain the simplicity
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#8
01-17-2016, 12:33 PM
Veteran Member
be a bad idea. But the idea of ensuring the bypass remains closed under
full boost seems to be attractive. What say you?
And if I may ... some thread drift ...
Presuming 100 percent volumetric efficiency for discussion, since I
don't know what it should be, what about fuel flow?
While looking at fuel filters some hours ago, I ran into 2 gallons per minute
as a flow rate. At no specific pressure.
That translates to 7.57 liters per minute if US gallons are presumed.
At six thousand rpm, a 4.0L engine, again assuming 100% VE, flows
3000 x 4 = 12,000L per minute.
With a A/F of 12/1, the implication is 1000 liters of fuel.
Yet the fuel filter is rated by one manufacturer at 7.5'ish liters
per minute.
There is huge slippage in the arithmetic, but are the fuel filters
fitted adequate under full demand?
The E46 BMW fuel filter fitted to the 2.5L to 3.0L models
is huge in comparison. Easily four times the surface area.
#9
01-17-2016, 06:39 PM
Veteran Member
#10
01-17-2016, 07:06 PM
Veteran Member
#11
01-17-2016, 09:07 PM
Veteran Member
Having read the linked articles and a few more, blocking off the bypass would
be a bad idea. But the idea of ensuring the bypass remains closed under
full boost seems to be attractive. What say you?
And if I may ... some thread drift ...
Presuming 100 percent volumetric efficiency for discussion, since I
don't know what it should be, what about fuel flow?
While looking at fuel filters some hours ago, I ran into 2 gallons per minute
as a flow rate. At no specific pressure.
That translates to 7.57 liters per minute if US gallons are presumed.
At six thousand rpm, a 4.0L engine, again assuming 100% VE, flows
3000 x 4 = 12,000L per minute.
With a A/F of 12/1, the implication is 1000 liters of fuel.
Yet the fuel filter is rated by one manufacturer at 7.5'ish liters
per minute.
There is huge slippage in the arithmetic, but are the fuel filters
fitted adequate under full demand?
The E46 BMW fuel filter fitted to the 2.5L to 3.0L models
is huge in comparison. Easily four times the surface area.
be a bad idea. But the idea of ensuring the bypass remains closed under
full boost seems to be attractive. What say you?
And if I may ... some thread drift ...
Presuming 100 percent volumetric efficiency for discussion, since I
don't know what it should be, what about fuel flow?
While looking at fuel filters some hours ago, I ran into 2 gallons per minute
as a flow rate. At no specific pressure.
That translates to 7.57 liters per minute if US gallons are presumed.
At six thousand rpm, a 4.0L engine, again assuming 100% VE, flows
3000 x 4 = 12,000L per minute.
With a A/F of 12/1, the implication is 1000 liters of fuel.
Yet the fuel filter is rated by one manufacturer at 7.5'ish liters
per minute.
There is huge slippage in the arithmetic, but are the fuel filters
fitted adequate under full demand?
The E46 BMW fuel filter fitted to the 2.5L to 3.0L models
is huge in comparison. Easily four times the surface area.
Another way of looking at it is that a Jaguar XJR fuel pump is rated for 108 liters per hour. So, (108 /60) is 1.8 liters per minute, and 1.8/.264 is .45 gal/min. For an XJR, two fuel pumps could supply nearly a gallon per minute, still well within your 2 gal. filter spec.
Last edited by sparkenzap; 01-17-2016 at 09:21 PM.
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#12
01-17-2016, 09:14 PM
Veteran Member
#13
01-18-2016, 02:55 PM
Senior Member
As stated by sparkenzap, air:fuel ratio is a mass-based ratio, so cannot be used to calculate a volume of fuel based on a volume of air, as they have very different densities.
The XJR 6 has twin Denso fuel pumps that deliver 90lires/hr fuel flow each, giving a total of 180litres/hr = 0.66 imperial gallons/hr.
Plums is right that a 4litre engine running at 6,000rpm at 100% manifold volumetric efficiency would flow 12,000litres of air per minute. However on any pressure charged engine, this would not be the same volumetric flow rate of air flowing into the air intake of the engine because the air in the manifold is already under pressure, whereas the air entering the intake is at atmospheric pressure. For instance if an engine was running at 1 atmosphere gauge of boost pressure, then it would be at twice the absolute pressure of the air entering the engine at atmospheric pressure. So if a 4L engine at 6,000rpm was consuming 12,000litres of air out of the manifold, then 24,000litres of air would be entering the intake system, so the atmospheric volumetric efficiency would be 200%. Most people tend quote the "atmospheric" volumetric efficiency, but drop the word "atmospheric". However, manifold volumetric efficiency can be a useful term if trying to understand how well a pressure charged engine is breather, once the effect of the boost pressure has been excluded.
For a naturally aspirated engine, atmospheric boost pressure and manifold boost pressure are the same.
A highly tuned engine can consume 100%-105% of its own swept volume every 2 revs, but only over a narrow speed range at which this volumetric efficiency is optimised. If this volume of air is at a pressure higher than atmospheric pressure, then the volume of air , corrected back to atmospheric conditions will be greater.
The XJR 6 has twin Denso fuel pumps that deliver 90lires/hr fuel flow each, giving a total of 180litres/hr = 0.66 imperial gallons/hr.
Plums is right that a 4litre engine running at 6,000rpm at 100% manifold volumetric efficiency would flow 12,000litres of air per minute. However on any pressure charged engine, this would not be the same volumetric flow rate of air flowing into the air intake of the engine because the air in the manifold is already under pressure, whereas the air entering the intake is at atmospheric pressure. For instance if an engine was running at 1 atmosphere gauge of boost pressure, then it would be at twice the absolute pressure of the air entering the engine at atmospheric pressure. So if a 4L engine at 6,000rpm was consuming 12,000litres of air out of the manifold, then 24,000litres of air would be entering the intake system, so the atmospheric volumetric efficiency would be 200%. Most people tend quote the "atmospheric" volumetric efficiency, but drop the word "atmospheric". However, manifold volumetric efficiency can be a useful term if trying to understand how well a pressure charged engine is breather, once the effect of the boost pressure has been excluded.
For a naturally aspirated engine, atmospheric boost pressure and manifold boost pressure are the same.
A highly tuned engine can consume 100%-105% of its own swept volume every 2 revs, but only over a narrow speed range at which this volumetric efficiency is optimised. If this volume of air is at a pressure higher than atmospheric pressure, then the volume of air , corrected back to atmospheric conditions will be greater.
#14
01-18-2016, 09:16 PM
Veteran Member
I'm thinking that
"180litres/hr = 0.66 imperial gallons/hr"
has a slipped decimal point in there or something.
In any case, looking at the various conversion methods shown
on various sites that the maximum consumption at WOT is in
the range of 35-45 gph. This is presuming the factory HP numbers
and ecu enrichment at WOT.
The few name brands offering a flow rate on this type of fuel
filter state 1-2 gpm, or 60-120 gph.
Remembering that these numbers are for a fresh, clean fuel
filter out of the box under lab conditions, I am thinking that
the word "marginal" applies in our application.
A flow rate of 60 gph does not leave much headroom in real
life use for a 45 gph requirement.
I'll be changing my fuel filter RSN. (real soon now)
"180litres/hr = 0.66 imperial gallons/hr"
has a slipped decimal point in there or something.
In any case, looking at the various conversion methods shown
on various sites that the maximum consumption at WOT is in
the range of 35-45 gph. This is presuming the factory HP numbers
and ecu enrichment at WOT.
The few name brands offering a flow rate on this type of fuel
filter state 1-2 gpm, or 60-120 gph.
Remembering that these numbers are for a fresh, clean fuel
filter out of the box under lab conditions, I am thinking that
the word "marginal" applies in our application.
A flow rate of 60 gph does not leave much headroom in real
life use for a 45 gph requirement.
I'll be changing my fuel filter RSN. (real soon now)
#15
01-18-2016, 10:21 PM
Veteran Member
#16
01-18-2016, 11:15 PM
Veteran Member
Well it could have been anything along the way, but the
external fuel filter is a far sight easier to replace than the
pump sock.
I'm just thinking aloud that replacing the fuel filter regularly
is better than not replacing it
And the lack of headroom implies that it needs more frequent
changes than what might be possible otherwise.
I was the victim of not only double failed pumps, but also a truly
incompetent indie. In the end, even though they had over 30
days to do the job, and were instructed to change the filter, it
was not changed. When I pulled it out, it was far from pretty.
I suspect that it had something to do with the pumps demise.
The Supra had a "no need to replace" fuel filter as confirmed
by a factory engineer. But, the thing was huge. Maybe 20
times the volume of the filter selected by Jaguar.
external fuel filter is a far sight easier to replace than the
pump sock.
I'm just thinking aloud that replacing the fuel filter regularly
is better than not replacing it
And the lack of headroom implies that it needs more frequent
changes than what might be possible otherwise.
I was the victim of not only double failed pumps, but also a truly
incompetent indie. In the end, even though they had over 30
days to do the job, and were instructed to change the filter, it
was not changed. When I pulled it out, it was far from pretty.
I suspect that it had something to do with the pumps demise.
The Supra had a "no need to replace" fuel filter as confirmed
by a factory engineer. But, the thing was huge. Maybe 20
times the volume of the filter selected by Jaguar.
#17
01-19-2016, 01:59 PM
Senior Member
#18
01-25-2016, 08:55 AM
Hi,
I have the blanking plate on my x300 XJR.
It came from a member of the old XJR forum/website, who produced and sold them. I think the theory was is reduced boost delay, although I can't quite remember, it was a long time ago.
I've had it on my car for a while, not sure exactly how long, maybe 6 or 7 years, in which time the car has done about 20k miles.
I didn't do a before and after dyno or any sort of test, but the car certainly 'felt' slightly more responsive, I know that's very subjective.
I didn't notice an increase in fuel consumption. The Supercharger whine does seem to be louder and there is a faint drone at cruising speeds that wasn't there before. Overall I'm happy with it.
Hope this helps your decision on whether or not to remove it.
I have the blanking plate on my x300 XJR.
It came from a member of the old XJR forum/website, who produced and sold them. I think the theory was is reduced boost delay, although I can't quite remember, it was a long time ago.
I've had it on my car for a while, not sure exactly how long, maybe 6 or 7 years, in which time the car has done about 20k miles.
I didn't do a before and after dyno or any sort of test, but the car certainly 'felt' slightly more responsive, I know that's very subjective.
I didn't notice an increase in fuel consumption. The Supercharger whine does seem to be louder and there is a faint drone at cruising speeds that wasn't there before. Overall I'm happy with it.
Hope this helps your decision on whether or not to remove it.
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xxxscimitarxxx (01-25-2016)
#19
01-26-2016, 05:43 AM
Senior Member