SSpeeDEMONSS
New member
Based on area of the dimensions 2 stock chargers would be equivalent of an 82/116 compressor VGT.
Garrett
Garrett
Stock twin vgt
- Thread starter little luke
- Start date
little luke
New member
Damn. I think the biggest vgt I've seen for a 6.0 was a mtw stage 4. Its something like a 71/95 or 96mm. And I can't actually remember reading anyone using it.
While talking about it one might wonder why gasser vehicles often have "twins" and diesels often have "compounds"
From what I understand it is because of the fact that gasser vehicles have the luxury of high revving rpms (flow) but cannot withstand intense heat and boost (pressure).
Diesels on the other hand are exactly the opposite. We have a much more limited RPM band (flow) but we can build immense amounts of boost (pressure ratio) and heat with no problems.
That is important because of how diesels use compressor maps/turbos and how we build our turbo systems. What we need most in diesels is a high running pressure ratio. Without that we would not make much power. If you plot a lot of compressor maps you will see that we usually try to run the biggest turbo possible, without crossing over the left side of the surge line, and building the most boost possible. That makes us ride the left side of the compressor map. When someone in the diesel world looks at a compressor map and compares "maximum flow" they usually don't understand that with a diesel truck you will never reach the right side of the compressor map so that number is useless... what we need is a high pressure ratio to try to get as much flow as possible without surging
Often times a gasser vehicle it is just the opposite. With those high revving motors they have the ability to reach the right side of the map and possible choke out the turbo. They also have to limit their boost before they blow up their motor. They are usually more worried about choking out the turbo and less about building really high boost. They use the maps/turbos way differently than us diesel guys do... SO...
Compounds are utilized to achieve super high pressure ratios (boost)... which is what diesels need to make BIG power (but would blow up most gasser vehicles)
Twins have the ability to double the flow without having a super high pressure ratio (boost)... which can be used on high revving motor that can't handle the boost.
Hope that makes sense
From what I understand it is because of the fact that gasser vehicles have the luxury of high revving rpms (flow) but cannot withstand intense heat and boost (pressure).
Diesels on the other hand are exactly the opposite. We have a much more limited RPM band (flow) but we can build immense amounts of boost (pressure ratio) and heat with no problems.
That is important because of how diesels use compressor maps/turbos and how we build our turbo systems. What we need most in diesels is a high running pressure ratio. Without that we would not make much power. If you plot a lot of compressor maps you will see that we usually try to run the biggest turbo possible, without crossing over the left side of the surge line, and building the most boost possible. That makes us ride the left side of the compressor map. When someone in the diesel world looks at a compressor map and compares "maximum flow" they usually don't understand that with a diesel truck you will never reach the right side of the compressor map so that number is useless... what we need is a high pressure ratio to try to get as much flow as possible without surging
Often times a gasser vehicle it is just the opposite. With those high revving motors they have the ability to reach the right side of the map and possible choke out the turbo. They also have to limit their boost before they blow up their motor. They are usually more worried about choking out the turbo and less about building really high boost. They use the maps/turbos way differently than us diesel guys do... SO...
Compounds are utilized to achieve super high pressure ratios (boost)... which is what diesels need to make BIG power (but would blow up most gasser vehicles)
Twins have the ability to double the flow without having a super high pressure ratio (boost)... which can be used on high revving motor that can't handle the boost.
Hope that makes sense
powerstrokin15
New member
were running a barder 71mm VGT on a shop truck.. spools as fast as stock, and almost completely cleans up 225/100s. food for thought if you wanna go that route.
Be careful when leading people to believe these turbos "spool as fast as stock". The reason being is everyone goes out and buys one and then realizes that is not true. Then they think something is wrong with their truck or want to buy another brand turbo or return the one they bought
When it comes to big VGT turbos...
Yes they build boost fast
Yes with an auto tranny and lots of fuel they spool quick off the line.
Lock the truck in OD at 1400rpms and try to tell me they spool as fast as stock.
Hook up a big trailer and tow at 1700rpms up a grade and tell me it spools as fast as stock
I have many videos/dynos/compressor maps etc that show they do not "spool as fast as stock" in many different situations. Get above 2200 and they do spool faster than stock... but most people forget and leave that part out
The reason I make it a point is because lots of people jump on the band wagon and are sold a bill of goods... then when they start to notice turbo lag (especially with an manual tranny or tq converter locked in OD), high cruising egts, or have issues towing... they think something is wrong.
I get inquiries everyday from people who bought big VGT turbos from other vendors expecting low end spool up like stock turbos... they call hoping to send me their turbo so I can "fix" or "modify" those turbos.
I just do my best to properly inform people of the truth before jumping in and buying something they expect to spool as fast as stock.
powerstrokin15
New member
will it spool the same with stock fuel, no.. does it build the same boost at the same RPM as a stock charger on stock fuel, no. but let me rephrase. does the charger spool considerably fast for its size even when in OD pullin hills in WV? yes. its actually very surprising. its a great charger for someone wanting to stick to a VGT but yet still make bigger power because of the fuel it can support, and spool great, close to stock, drives like stock for what it is
did i say throw a 71mm on with stock fuel? no.. you'll run into the same issue your customers are having. but i was under the assumption this guy planned on adding fuel, which this setup i spoke of has worked great for use with better than stock fuel.theres no way hes ever gonna run twin's of that size with stock fuel.
regardless its not my place to argue on his thread, about setups that hes not even asking about. I just wanted to state there are large VGT chargers like the MTW charger he referenced that do in fact work well if that is a route he's considering.
edit: i guess im in the wrong for not specifying clearer above.
did i say throw a 71mm on with stock fuel? no.. you'll run into the same issue your customers are having. but i was under the assumption this guy planned on adding fuel, which this setup i spoke of has worked great for use with better than stock fuel.theres no way hes ever gonna run twin's of that size with stock fuel.
regardless its not my place to argue on his thread, about setups that hes not even asking about. I just wanted to state there are large VGT chargers like the MTW charger he referenced that do in fact work well if that is a route he's considering.
edit: i guess im in the wrong for not specifying clearer above.
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I hope you did not take offense to any of that... I just try to educate as much as possible so people are not disappointed and stuck afterwards.
They are not MY CUSTOMERS having problems. They are OTHER CUSTOMERS that were hoping for a fix when they called me and ended up realizing that they were sold on a bad bill of goods because they read something on the forums. Big VGT turbos do not spool as fast as stock down low... but they do spool much faster than expected, much faster than non-vgt turbos, and spool faster than stock in the upper rpms.
You can throw as much fuel as you want at it... it will not spool as fast as a stock turbo down low. If you don't believe me then dyno them back to back... or simply lock the tq converter in OD at 1200rpms roll into the throttle as hard as you can without letting it downshift... then do the same thing on a stock charger. No matter how much fuel you throw at it you wont get it to spool as fast or as soon as a stock charger down low in the rpms.
little luke
New member
I'm following you. I kinda felt like alot of this went along with that I learned in my fluid power classes, but the turbo and the physics behind it have thrown my thinking off. A pump that's driven by its own fluid path adds a whole new degree of difficulty when thinking about it as compared to an electric pump. Or maybe I'm way off base with my line of thinking. Either way, I'm still playing with the compressor maps and trying to understand it all. And honestly I'm still drawing out the twin set up and toying with the idea on paper out of boredom.
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