I believe old scangauges didn't read map values right. Just my bad memory though. Do you have a boost elbow installed on the compressor housing of the turbo?
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Scangauge Boost Accuracy? Is it the same as MAP?
I'm a bit confused between MAP and Boost, and what the numbers shown on my Scangauge mean (and how accurate they are).
My truck is (to the best of my knowledge) entirely stock, save for the Airdog fuel pump I added. I run a Scangauge on the truck and selected MAP as one of my parameters to display while driving. I was told that this would show my "boost" level, but I'm not positive that Boost exactly equals MAP anyway (I thought they were different, slightly). I've heard a lot of conflicting information on this subject, including one recommendation of subtracting normal atmospheric pressure from the MAP number to know my boost.
Today I was doing some reading about various modifications for my truck, and was hearing that stock boost should only be around 18-19psi. My Scangauge often shows the MAP at 29-31 psi when I'm climbing hard under load (ex: steel 2 horse trailer with tack room up a 7% grade at 7,000-10,000 ft at highway speeds).
To me that suggests one of three things:
1) My truck wasn't actually stock when I got it -- not a likely scenario
2) My Scangauge isn't capable of accurately measuring this parameter - that's possible
3) MAP numbers are not equal to Boost numbers -- also quite possible.
Can someone help clear up some confusion on this issue, so I know what's going on in my truck a bit better?
My truck is (to the best of my knowledge) entirely stock, save for the Airdog fuel pump I added. I run a Scangauge on the truck and selected MAP as one of my parameters to display while driving. I was told that this would show my "boost" level, but I'm not positive that Boost exactly equals MAP anyway (I thought they were different, slightly). I've heard a lot of conflicting information on this subject, including one recommendation of subtracting normal atmospheric pressure from the MAP number to know my boost.
Today I was doing some reading about various modifications for my truck, and was hearing that stock boost should only be around 18-19psi. My Scangauge often shows the MAP at 29-31 psi when I'm climbing hard under load (ex: steel 2 horse trailer with tack room up a 7% grade at 7,000-10,000 ft at highway speeds).
To me that suggests one of three things:
1) My truck wasn't actually stock when I got it -- not a likely scenario
2) My Scangauge isn't capable of accurately measuring this parameter - that's possible
3) MAP numbers are not equal to Boost numbers -- also quite possible.
Can someone help clear up some confusion on this issue, so I know what's going on in my truck a bit better?
1 - 13 of 13 Posts
Correct...I believe old scangauges didn't read map values right. Just my bad memory though. Do you have a boost elbow installed on the compressor housing of the turbo?
https://www.youtube.com/watch?v=7RhrgFWaIvY
Hmmm, interesting. Mine isn't anywhere near as high as yours though, at least not in those kind of cruising conditions. I think at idle I'm maybe around 9 MAP on the scangauge (memory could be off here), and normal highway cruising might read around 20ish. The truck really doesn't climb into the 31 MAP range until I'm hitting it hard on the big climbs, etc.
I wish I could provide some exact numbers right now, but my truck is on jack stands while I wait for some wheel hub assemblies to arrive (Fedex told me that the east coast storms delayed my shipment until Friday).
Anyway, when I get it back together I can post to let you know how my SG reads the MAP through the power range.
As for the other question: no, I don't have a boost elbow or anything like that installed yet (that I know of). I was considering mods of an Edge EZ and a 4 inch exhaust, which is what got me reading up on this subject in the first place. Otherwise, aside from the Airdog, a fuel pressure gauge, and 285 tires that came on the truck when I bought it, I'm pretty much bone stock.
Perhaps one of you can explain the point of the boost elbow, and how to spot a non-factory fitting of this type, because I think I might have one in my hand... or perhaps there is one in my truck, and I'm holding a stock one. When I bought the truck the old owner (who clearly knew less than I know about trucks) handed me a fitting that he said: "a guy gave this to me and told me to put it on the truck and that it would give you more power... I don't know what it is, but you can have it". Well, I'm obviously no expert myself, but Googling boost elbows for a Cummins produces a picture that is very much like the piece I'm currently holding (which until just now was residing in a bag of fuses that the old owner gave me for the truck).
Okay, after answering your question (perhaps prematurely) in my last reply, here's what I can tell you:I believe old scangauges didn't read map values right. Just my bad memory though. Do you have a boost elbow installed on the compressor housing of the turbo?
1) I think I have a boost elbow in my hand right now, and I think the part in the truck is *probably* stock. I don't know how to say for sure.
2) The piece I have in hand is a 90 degree fitting with a barb type fitting on one end, and a screw fitting on the other end. The truck seems to have a 90 degree fitting as well, but it appears more blocky (as an online example I saw indicated was the case for a stock piece).
3) My turbo is the HX35W if that helps, and the part I'm thinking you replace with the boost elbow is located right next to the tag on the turbo, on the bottom part of the turbo (just below the intake tube).
If I understand what I've read correctly, it goes something like this: a boost elbow simply reduces the amount of airflow to the wastegate of the turbo for the purpose of delaying the opening of the wastegate and thereby allowing the production of more boost. But, it sounds like doing this will throw an overboost code unless the truck is running a tuner with a boost fooler built in (Edge Ez, for example, I think?). However, our trucks throw overboost codes above 20-something PSI, and the turbo I'm running is rated to safely run up to 35psi, so I can run above stock safely if I use a boost fooler. Anyway, I think those were the conclusions I was supposed to get from what I've read...
If I'm wrong on this, please correct me! Either way, I'm at least 85% sure that I have the stock fitting in my truck at the moment.
You got it right. Good job searching.
MY question was leading to if you wastegate was opening at 20 psi or if a boost elbow was installed allowing for higher pressures.
I am guessing your scan gauge just isn't reading right.
Easy thing to do is snap a picture and we can tell you right away.
MY question was leading to if you wastegate was opening at 20 psi or if a boost elbow was installed allowing for higher pressures.
I am guessing your scan gauge just isn't reading right.
Easy thing to do is snap a picture and we can tell you right away.
On my scan gauge, it reads MAP and Boost. (BST) It reads boost fairly accurately, especially on the top end, it fallows my mechanical gauge.
My scan gauge is pretty new, if that makes any difference or not...
My scan gauge is pretty new, if that makes any difference or not...
My scangauge does read my boost accurately its only a year old but, I do not relay on it. I use the scangauge for monitoring other things that are not on my guage pod like lph intake temp and water temp
Interesting... I just checked my manual and it says that my scangauge can also monitor boost in addition to MAP. I don't have a boost gauge in my vehicle yet, and I didn't originally buy the scangauge for that purpose... but I'll use it for this purpose if it will work for itMy scangauge does read my boost accurately its only a year old but, I do not relay on it. I use the scangauge for monitoring other things that are not on my guage pod like lph intake temp and water temp
Mine is not accurate.
FWIW, I assume it has something to do with the Edge's boost fooling.
FWIW, I assume it has something to do with the Edge's boost fooling.
3) My turbo is the HX35W if that helps, and the part I'm thinking you replace with the boost elbow is located right next to the tag on the turbo, on the bottom part of the turbo (just below the intake tube).
I thought auto trans rigs had an HY35 stock, and HX35W was the 12 valve/ manual trans turbo?
I thought auto trans rigs had an HY35 stock, and HX35W was the 12 valve/ manual trans turbo?
be sure the scangauge is set for boost it comes preset for MAP but in our trucks you need to custom set it for boost it is in the manual my manual gauge is right on with the scangauge
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