Unplugging the Temp 1 sensor results in about a 10% enrichment across the rpm range.
Stock 914 float their valves at about 5500rpms so even if the ECU was providing enough gas there isn't much hp there.
Dual springs help and give you about 500rpms of usable hp around there.
Geoff
What camshaft
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raygreenwood
- Posts: 11895
- Joined: Wed Jan 22, 2003 12:01 am
Dave...excellent explaination! What I do to my MPS's...does nothing to affect "what" the MPS sends tothe ECU. Without a lot more knowledge on my part of the internals of the ECU (Brad Anders has more of that than I do)...I would not know what changes what have to be made internally in the ECU to utilize changes to the signal in the ECU.
I'm not changing the signal output from the MPS, I am changing the timing of it and delaying the return to a de-tuned position during the enrichment phase. You can fine tune with this a lot, but gross increases in enrichment are best done with changes in fuel pressure and CHT reading.Mostly what I am doing is changing the sensitivity of the MPS to various ranges of vacume...that are more befitting an engine of higher tune
You can also use a vacume impulse switch or a TB mounted switch on a sub-miniature relay to quickly ramp up or down the CHT value, in-line. I have not made one clean-enough to not be noticable yet. Probably have to go to a solid state switcher.
By the way, the injection generally drops off between 5200 and 5500. Thats because the cyclic rate of the injection system has been reached....from what I have read and been told. There is also no reason that at a given calculated point, you could not set up a reverse pressure bleed like I have previously described, to ramp up the injection pressure a pre-determined amount...at say 4900 rpm....to begin adding more fuel even as the injection approaches its own internal ability to enrich. Ray
I'm not changing the signal output from the MPS, I am changing the timing of it and delaying the return to a de-tuned position during the enrichment phase. You can fine tune with this a lot, but gross increases in enrichment are best done with changes in fuel pressure and CHT reading.Mostly what I am doing is changing the sensitivity of the MPS to various ranges of vacume...that are more befitting an engine of higher tune
You can also use a vacume impulse switch or a TB mounted switch on a sub-miniature relay to quickly ramp up or down the CHT value, in-line. I have not made one clean-enough to not be noticable yet. Probably have to go to a solid state switcher.
By the way, the injection generally drops off between 5200 and 5500. Thats because the cyclic rate of the injection system has been reached....from what I have read and been told. There is also no reason that at a given calculated point, you could not set up a reverse pressure bleed like I have previously described, to ramp up the injection pressure a pre-determined amount...at say 4900 rpm....to begin adding more fuel even as the injection approaches its own internal ability to enrich. Ray
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Racer Chris
- Posts: 665
- Joined: Sun Jan 13, 2002 12:01 am
This is what I was referring to. It isn't necessary to design a custom cam or redesign the d-jet to make significant gains. A properly built 4-2-1 exhaust will actually improve the operation of the MPS by changing the vacuum signature from the intake manifold. Valve size increase and port work are unnecessary for it to work. Fuel usage will be improved, A/F ratio will even out across the rpm range, and midrange power will increase by close to 10 percent. If all the stock components are working properly you will gain more with less effort by bolting on a good exhaust system.raygreenwood wrote:It really is about the exhaust.
If you are convinced that the stock HE exhaust is the only choice for you then you will spend a lot of time and $$ working around it to come up with half the improvements of a guaranteed bolt on improvement. What's more, if you do all that work to the engine and FI system, the exhaust system will improve on that by a similar amount too. Not only that, you can use it on any other engine you build in the future (carb or FI) because it is a bolt on.
Billyisgr8 fabbed his own 4-2-1 header and it worked. It was crude by professional standards, but highly effective. He probably doesn't have any direct comparisons to a stock exhaust, but I am sure one of the reasons his combo worked so well is the exhaust. I wouldn't be surprised if a more agressive cam would work with the d-jet along with a good 4-2-1 exhaust. You would still have to find a way to get more fuel in at higher rpms though to realize the full benefit.
Instead of dual springs as Geoff suggested, HD single springs or ceramic lifters will get you the additional 500 rpm, but you won't get any more power.
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raygreenwood
- Posts: 11895
- Joined: Wed Jan 22, 2003 12:01 am
Oh I agree totally Chris! Part of the point I was trying to make, is that even just with a minor 10-15% upgrade on a 1.7 with a better flowing factory type exhaust...the performance upgrade is quite noticable. But...bear in mind, that this upgrade...as you noted...took a few tweeks to the MPS. There are a couple problems with the stock exhaust. Design restrictions to start with. Its just not a super high velocity design. The other is volume. Even with the Ernst....a 1.7 is about all the volume is can handle.
The next rpoblem you will run into by just goiing to a very free-flowing exhaust, is that the change even with a stock cam will make enough cylinder scavenging with the built in valve overlap to force other changes. The mps may run out of the ability to react to the new vacum signature...or may even become over-sensitive, depending upon the spec. There will be an accuracy issue. All of this can be adjusted around.
If you do have a better exhaust, the addition of larger valves and a better than stock cam will have very noticable results. Much less so if you stay with a restrictive exhaust.
Yes, exhaust is one of the most important. I believe the correct operation of the other ramped up components keys off of that. But...If you go too much more efficent than stock and stay with an all stock system....there will be lean spots. A lot of that, even without screwing with the MPS...can be taken care of simply with stabilizing the fuel pressure so it does not fluctuate. That is already a sore spot that most people do not realize....in basic D and L jet. Ray
The next rpoblem you will run into by just goiing to a very free-flowing exhaust, is that the change even with a stock cam will make enough cylinder scavenging with the built in valve overlap to force other changes. The mps may run out of the ability to react to the new vacum signature...or may even become over-sensitive, depending upon the spec. There will be an accuracy issue. All of this can be adjusted around.
If you do have a better exhaust, the addition of larger valves and a better than stock cam will have very noticable results. Much less so if you stay with a restrictive exhaust.
Yes, exhaust is one of the most important. I believe the correct operation of the other ramped up components keys off of that. But...If you go too much more efficent than stock and stay with an all stock system....there will be lean spots. A lot of that, even without screwing with the MPS...can be taken care of simply with stabilizing the fuel pressure so it does not fluctuate. That is already a sore spot that most people do not realize....in basic D and L jet. Ray
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Racer Chris
- Posts: 665
- Joined: Sun Jan 13, 2002 12:01 am
During the Grassroots Motorsports comprehensive dyno session I was quite amazed at first at how the A/f ratio and BSFC numbers were stabilized with the 4-2-1 header versus all the other systems tested. Dick (I can't believe the filter won't print D!ck)Shine made only minor tweaks to the MPS to bring the engine to a good A/F mixture across the rpm range. I had been told in the past that a free flowing exhaust would likely burn a piston due to excessive lean condition and was apprehensive about going that route. Instead it turned out that the exhaust with the most scavenging also helped the most.raygreenwood wrote:... The mps may run out of the ability to react to the new vacum signature...or may even become over-sensitive, depending upon the spec.
Yes, exhaust is one of the most important. I believe the correct operation of the other ramped up components keys off of that. But...If you go too much more efficent than stock and stay with an all stock system....there will be lean spots. A lot of that, even without screwing with the MPS...can be taken care of simply with stabilizing the fuel pressure so it does not fluctuate. That is already a sore spot that most people do not realize....in basic D and L jet. Ray
I have been quite impressed with the work you have done on the d-jet system, particularly with the upgrades & repairs to the MPS. Therefore I completely accept what you say about the fuel pressure. I certainly wouldn't have thought of that right away.
I just thought of this - with oxyfuel welding equipment two stage gas pressure regulators are used instead of single stage regulators to keep the pressure stable as tank pressures drop. Perhaps a better pressure regulator is available to help with the d-jet system in a similar fashion.
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lmcchesney
- Posts: 135
- Joined: Thu Nov 20, 2003 8:11 am
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raygreenwood
- Posts: 11895
- Joined: Wed Jan 22, 2003 12:01 am
Yes! You are on the right track. The pressure stability problem is 3 fold. Most probably, those who in the past increased to really good exhaust systems and then burned a piston...most likely had fuel supply problems they were not also addressing.
In D-jet...and even worse in L-jet, there are fuel pressure problems. In D-jet, its realy instructive to put a very good fel guage on, with a schrader valve to remove all air, and an insulated vibration free mount. In the average D-jet car...and by that I mean one with a few miles on it but in good shape and tune.....here is wha you see:
The fuel guage flickers at idle....in very exacting movements, about 2 points negative, swing up to about 1 point positive (3 pt. range). The + point is simply a shock reaction to fuel on the increase and is part of the nature of the bourdon tube in the guage, so ignore it. Its 2 psi swing.
A fast rate of flicker almsot mimicking idle seed, is indictaive of good vacume balance per cylinder, injector output balance and overallgood condition. However, that 2 psi drop at idle with a 28 psi baseline is about 7.5% fuel pressure and volume loss. For the most part, this is due to the long fuel lines...and lots of fuel mass to move.
A loping swing of the needle may indicate one injector flowing more han others, or higher or lower signature created by one cylinder or the other...and/or too much valve lash...or even a worn cam lobe. It can aslo be high resistance in various connections.
What you get when timing is slightly increased, or when accelerating is an extra 2 psi drop for a split second when opening the throttle (for a total of 4 psi...which is almost 15% loss for a split second). Timing changes change the vaume radically on cams with overlap. This causes a very very fast 5 psi swing. You can hardly see the needle. Its a blur....but its moving. Thats not good.
A weak regulator can cause all of this. I generally backstop weak D-jet regulators with a second D-jet regulator that is set to about 18 psi. Its arestriction for a restriction an fixesthe leakdown problem at shut off and helps stabilize the main regulator. Backstopping the main regulator got rid of all the idle chatter. The guage was rock solid. Except...on acceleration. The fuel pump could not refill the lines fast enough to keep up. You get a lean spot. Ading a second pump and splitting the rails off to two pairs solved this 100%. The change was so drastic that I actuall had to readjust the MPS. Both the main stack and the outer stop, as the were set richer than needbe to make sure that I encountered no lean spots through the mid and upper ranges...but insured that I idled rich and had flat sspots off the line. Imagine what that can do for the fuel curve!
L-jet rising rate regulators are generally accurate in their range, but have an all or nothing characteristic because of where their vacume signature comes from. They have no middle range of adjustment. They are not sensitive enough.
One other thing to remember, lots of people disagreed with this...but it is fact. Once you start tuning all the things we are speaking of, valve, fuel ,cam, exhasust...ou are at a much higher rate of tune than factory stock. The MPS gets sensitive even more to vacume leaks. The factory PCV valve, though quite necessary...is an impediment. It dumps manifold pressure when it vents into the plenum. It dunps less than 1/2" from the MPS junction. It causes the fuel guage to swing..and enrichment to happen. It has no rhythem of rhyme as to when it kicks open...and is not controlled by the ECU. It opens by both vacume pressure and backpressure combined. Even adding more spring pressure does not correct it, as the main issue is that it opens up in unplanned fashion. The best fix for this, is to make it constant flow and restrict it by 3/4 diameter. That meas that it is a very slight constant vacume leak...that never changes. It too causes enrichment...but across the board and all the time...which can be adjusted out and compensatedfor with the MPS or with a fuel pressure tweek. Ray
In D-jet...and even worse in L-jet, there are fuel pressure problems. In D-jet, its realy instructive to put a very good fel guage on, with a schrader valve to remove all air, and an insulated vibration free mount. In the average D-jet car...and by that I mean one with a few miles on it but in good shape and tune.....here is wha you see:
The fuel guage flickers at idle....in very exacting movements, about 2 points negative, swing up to about 1 point positive (3 pt. range). The + point is simply a shock reaction to fuel on the increase and is part of the nature of the bourdon tube in the guage, so ignore it. Its 2 psi swing.
A fast rate of flicker almsot mimicking idle seed, is indictaive of good vacume balance per cylinder, injector output balance and overallgood condition. However, that 2 psi drop at idle with a 28 psi baseline is about 7.5% fuel pressure and volume loss. For the most part, this is due to the long fuel lines...and lots of fuel mass to move.
A loping swing of the needle may indicate one injector flowing more han others, or higher or lower signature created by one cylinder or the other...and/or too much valve lash...or even a worn cam lobe. It can aslo be high resistance in various connections.
What you get when timing is slightly increased, or when accelerating is an extra 2 psi drop for a split second when opening the throttle (for a total of 4 psi...which is almost 15% loss for a split second). Timing changes change the vaume radically on cams with overlap. This causes a very very fast 5 psi swing. You can hardly see the needle. Its a blur....but its moving. Thats not good.
A weak regulator can cause all of this. I generally backstop weak D-jet regulators with a second D-jet regulator that is set to about 18 psi. Its arestriction for a restriction an fixesthe leakdown problem at shut off and helps stabilize the main regulator. Backstopping the main regulator got rid of all the idle chatter. The guage was rock solid. Except...on acceleration. The fuel pump could not refill the lines fast enough to keep up. You get a lean spot. Ading a second pump and splitting the rails off to two pairs solved this 100%. The change was so drastic that I actuall had to readjust the MPS. Both the main stack and the outer stop, as the were set richer than needbe to make sure that I encountered no lean spots through the mid and upper ranges...but insured that I idled rich and had flat sspots off the line. Imagine what that can do for the fuel curve!
L-jet rising rate regulators are generally accurate in their range, but have an all or nothing characteristic because of where their vacume signature comes from. They have no middle range of adjustment. They are not sensitive enough.
One other thing to remember, lots of people disagreed with this...but it is fact. Once you start tuning all the things we are speaking of, valve, fuel ,cam, exhasust...ou are at a much higher rate of tune than factory stock. The MPS gets sensitive even more to vacume leaks. The factory PCV valve, though quite necessary...is an impediment. It dumps manifold pressure when it vents into the plenum. It dunps less than 1/2" from the MPS junction. It causes the fuel guage to swing..and enrichment to happen. It has no rhythem of rhyme as to when it kicks open...and is not controlled by the ECU. It opens by both vacume pressure and backpressure combined. Even adding more spring pressure does not correct it, as the main issue is that it opens up in unplanned fashion. The best fix for this, is to make it constant flow and restrict it by 3/4 diameter. That meas that it is a very slight constant vacume leak...that never changes. It too causes enrichment...but across the board and all the time...which can be adjusted out and compensatedfor with the MPS or with a fuel pressure tweek. Ray
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camgrinder
- Posts: 1
- Joined: Sun Jan 11, 2004 11:01 pm
cams
My name is John, I am the manager at Elgin Cams.
We make 2 cams that will work with your style fuel injection.
The "330" cam is one step up from stock and our 256 (6408)
is the next step up. I have sold our 268 degree cam (6708) but I
usually hear back about idle problems.
These cams were designed back in the 1970's. Im thinking
we can come up with something better if there is a big enough
demand. Maybe a 262 to 266 degree cam with .430" or .450" valve lift.
You can also widen the lobe centers to 110 and reduce overlap.
IF anyone has flow test data with the intake system and exhaust
system installed, you might find a dual pattern might work. Maybe
even a larger intake cam lobe and smaller exhaust cam lobe.
http://www.elgincams.com/c-por3.html
We make 2 cams that will work with your style fuel injection.
The "330" cam is one step up from stock and our 256 (6408)
is the next step up. I have sold our 268 degree cam (6708) but I
usually hear back about idle problems.
These cams were designed back in the 1970's. Im thinking
we can come up with something better if there is a big enough
demand. Maybe a 262 to 266 degree cam with .430" or .450" valve lift.
You can also widen the lobe centers to 110 and reduce overlap.
IF anyone has flow test data with the intake system and exhaust
system installed, you might find a dual pattern might work. Maybe
even a larger intake cam lobe and smaller exhaust cam lobe.
http://www.elgincams.com/c-por3.html
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lmcchesney
- Posts: 135
- Joined: Thu Nov 20, 2003 8:11 am
John,
We all will appreciate your input. Seems we are trying to define the limits of the combination of cam and D-jet. As Ray has stated, the vacum flux signature as interpurted by the Manifold pressure sensos(MPS). Jake states the following:
"BTW my 225 cam is based from a stocker. The only thing thats stock about it is the lift. The duration is heavily split and lobe centers modified. The intake duration is even LOWER than stock. It works, and works well in stock - 2056 engine. Larger than that and I would not think about it."
It seems that a large overlap produces alteration of the vacum signature and lift above, what was it 0.043. does not provide for incrreased flow. The Type IV also has problems with heat elimination. Chris has done extensive work on the exhaust side of the equation and has shown significant imporvement. But, still as Goeff said, elemination of heat is the crux of a 914 engine. Would you provide us with more input/information?
Ray, if we are using a parrellel fuel rale system(two pumps and rales) why not use two regulators tuned to equal working pressures?
Thanks,
L. McChesney
We all will appreciate your input. Seems we are trying to define the limits of the combination of cam and D-jet. As Ray has stated, the vacum flux signature as interpurted by the Manifold pressure sensos(MPS). Jake states the following:
"BTW my 225 cam is based from a stocker. The only thing thats stock about it is the lift. The duration is heavily split and lobe centers modified. The intake duration is even LOWER than stock. It works, and works well in stock - 2056 engine. Larger than that and I would not think about it."
It seems that a large overlap produces alteration of the vacum signature and lift above, what was it 0.043. does not provide for incrreased flow. The Type IV also has problems with heat elimination. Chris has done extensive work on the exhaust side of the equation and has shown significant imporvement. But, still as Goeff said, elemination of heat is the crux of a 914 engine. Would you provide us with more input/information?
Ray, if we are using a parrellel fuel rale system(two pumps and rales) why not use two regulators tuned to equal working pressures?
Thanks,
L. McChesney
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raygreenwood
- Posts: 11895
- Joined: Wed Jan 22, 2003 12:01 am
Because you will never find two regulatorsthat are tuned to the same working pressure...exactly. Keeping them that way would also be imossible, as they rarely wear at the same rate. Then you would be back to the same boat, unbalanced side-to-side. Since the spring in the pressure sensor is essentially blind to volume ...so to speak, its easier to simply meter both fuel pipes with the same regulator. Just plumb them to a "Y" and then into the regulator. Yes...at first the excess volume may open the already set valve farther...but a slight twist to the adjusting screw will ensure that 28 psi of pressure is applied across the restriction. Ray
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raygreenwood
- Posts: 11895
- Joined: Wed Jan 22, 2003 12:01 am
With D-jet, duration is what you want more than lift. The longer duration helps to provide a smooth sugnature. "Some" valve overlap also helps this, as noted earlier, because it helps to vent the "pile" up of the column of air as its transitioning through the open intake valve ...possibly at a velocity higher than the cylinder is drawing it in...wherin it meets a sort of restriction. Slight overlap in the exhaust cycle can augment filling and a decently smooth signature.
Too much overlap, and you suck out too much fuel charge with it, causing higher exhaust temps, losing too much compression ...causing inefficency...and again...heat. Not to mention potentially causing lean spots by cross scavenging the intake charge during the overlap. So...yes some overlap is a good thing. A lot...probably not. Ray
Too much overlap, and you suck out too much fuel charge with it, causing higher exhaust temps, losing too much compression ...causing inefficency...and again...heat. Not to mention potentially causing lean spots by cross scavenging the intake charge during the overlap. So...yes some overlap is a good thing. A lot...probably not. Ray
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lmcchesney
- Posts: 135
- Joined: Thu Nov 20, 2003 8:11 am
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Racer Chris
- Posts: 665
- Joined: Sun Jan 13, 2002 12:01 am
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lmcchesney
- Posts: 135
- Joined: Thu Nov 20, 2003 8:11 am
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MASSIVE TYPE IV
- Posts: 20132
- Joined: Fri Jul 07, 2000 12:01 am