Hey dudes, I'm looking to turbocharge a future project of mine but I'm running into a wall when it comes to properly sizing a turbo for the engine itself- I'm really hoping to find one used a make it work for the motor instead of a custom one. Does anyone have links or books they reccomend on the topic? It seems like I would already have to be building the engine itself before buying the turbo. For the record, it would be for a street car.
Find diesel engine with turbo that is double the liters of your car..
For example: 5.9 cummins turbo could work well on a 2.5-3.0 liter ish car...
The classic book is "Maximum Boost" by Corky Bell. The stuff in there on engine management is pretty dated at this point, but the basic turbocharger principles are still the same.
There's a bunch of calculations you can do regarding engine size, expected air use rate and pressure ratios, but the quick-and-dirty approach with used OEM turbos is to look for a car that's got a similar displacement engine to yours, making similar power to the level you want, and then get a turbo off that car. Want 300-350hp out of a 2L 4-cylinder? A turbo from an Evo or maybe an STi will probably work because that's what they used stock. Unfortunately, most OEM turbos are pretty small by aftermarket standards, they're usually set up to prioritize low end response with only moderate high end gains and if you try to turn them up they wind up running out of breath in the midrange.
I would be very careful using a diesel turbo, personally. They are often not designed for the EGTs that gas engines put out.
In reply to codrus :
"I would be very careful using a diesel turbo, personally. They are often not designed for the EGTs that gas engines put out."
- tell me more.
ohh in full disclosure.. I worked for Holset for a few years...
I have my students work through this:
http://www.gwellwood.com/subjects/mechanics/mechanics-level-3/selecting-a-turbocharger/
Might make it make a bit more sense for you?
There are LOTS of online calculators....
Fueled by Caffeine said:Find diesel engine with turbo that is double the liters of your car..
For example: 5.9 cummins turbo could work well on a 2.5-3.0 liter ish car...
The Nelsons taught us not to do that here: https://grassrootsmotorsports.com/forum/build-projects-and-project-cars/project-x-bomb/106566/page18/ excerpted here:
The ballance of diminishing returns. At the risk of getting long winded....
A 11.90 second car has a 9.71#/HP ratio. A 10.90 car is 7.30 #/HP. 9.90 is 5.32#/HP. 8.90 is 3.79#/HP. Long story short - you have to make crazy power or be crazy light to go fast. Aside from the budget restraint, we make all our decisions based on whether we can beat/meet 5#/HP. We scrape undercoating and weigh it in HP. We drill holes and count them in HP. We go to extremes to eliminate weight. Don't beat the horse....unload the wagon.
While installing too big a part on a slower car (11 seconds and slower) has less detrimental impact on performance, adding too big to a fast car is very "expensive" when it has to be accelerated. If you have a 30 pound IC and piping package in a 11.90 car, anything over 3.1 net HP gain is going to move the car quicker. On an 8.90 second car you use 7.91 HP to move the IC and anymore gain moves the car quicker. Not a big deal on IC choice - go as big as you can. Packaging is the greater restraint. The temperature drop and associated power gain far outweigh the weight penalty when you use a bigger IC.
OTOH turbos are heavy. We have two 70MM, one is 56# (truck) and the other 25# (aftermarket). The truck turbo takes 6HP more just to move it when compared to the aftermarket piece and it has higher discharge temps because it is not in the higher efficiency area on the map. Performance wise, it is expensive on a race car but the compromise is livable on a Challenge budget.
At the end of the day we look to find (80) places to remove 1 oz (a 1 HP equivalent), and we are always trying to right size the major parts.
If you're trying to find a used oem turbo then we need your specific requirements (displacement, power goal, and do you care when it spools) to give specific recommendations of cars that might have an appropriate turbo to rob. The more specific the requirements are, the more effort goes into picking the 'right' thing.
In reply to dculberson :
no... I don't see a discussion of EGT in that exerpt.. Just that the turbo is heavy vs. some chinese one.. Looks like he was close to off the map anyways..
Here's my rationale.. Turbo is an airpump. If you have a diesel of say 6 liters that produces boost in the 3krpm range that is acceptable for you.. then it should work on 3 liter producing good boost around 6krpm... give or take..
EGT issues would manifest in cracking of tubine housings... turbine blade failures (unlikely due to large scale use of inco in the industry) and potentially shaft seal failures(more likely)...
Vigo said:If you're trying to find a used oem turbo then we need your specific requirements (displacement, power goal, and do you care when it spools) to give specific recommendations of cars that might have an appropriate turbo to rob. The more specific the requirements are, the more effort goes into picking the 'right' thing.
Fueled by Caffeine said:In reply to dculberson :
no... I don't see a discussion of EGT in that exerpt.. Just that the turbo is heavy vs. some chinese one.. Looks like he was close to off the map anyways..
Here's my rationale.. Turbo is an airpump. If you have a diesel of say 6 liters that produces boost in the 3krpm range that is acceptable for you.. then it should work on 3 liter producing good boost around 6krpm... give or take..
EGT issues would manifest in cracking of tubine housings... turbine blade failures (unlikely due to large scale use of inco in the industry) and potentially shaft seal failures(more likely)...
The final paragraph says that it has higher discharge temps due to being on a less efficient area of the map. I'm not gonna be frustrated at a lack of data from a family solving practical problems in their garage.
Besides, I'm gonna be turbo-ing an engine that will be 1.8 - 2.0 Liters at most. Outside of some 4-cylinder diesels I can't think of a diesel turbo that WOULD fit properly, and even then there are undoubtedly better choices for less money, like a used Subaru TD04. But I don't have the specifics yet on this motor, so while I appriciate the ideas I really just need knowledge and material at this point.
So stock turbos off of ~2.5 liter stuff should be good options, or if you want more power maybe stock turbos off of slightly larger engines like 7mgtes?
Fueled by Caffeine said:In reply to codrus :
"I would be very careful using a diesel turbo, personally. They are often not designed for the EGTs that gas engines put out."
- tell me more.
ohh in full disclosure.. I worked for Holset for a few years...
So I know that for LONG durability, temps are kept to just under 1700F/925C for a gas turbo, What is it for diesels? I've really wondered that, as you do see diesel turbos for sale, since they all want bigger and better.
(And I know anyone with a good T-couple can measure that virtually all turbos will limit out near there, Depending on the cat layout, though, it would not be the limiter, though)
I have "Maximum Boost" and thought it provides good background info. From there it's a matter of math and looking at the maps to find the best compromise between cost, availability and performance.
I thought I remember reading a comment on the forum years ago from someone who claimed Corky Bell got some things wrong, but I can't recall what or who said it.
I'd suggest reading the book then play around with online calculators or just create a spreadsheet.
T.J. said:I have "Maximum Boost" and thought it provides good background info. From there it's a matter of math and looking at the maps to find the best compromise between cost, availability and performance.
I thought I remember reading a comment on the forum years ago from someone who claimed Corky Bell got some things wrong, but I can't recall what or who said it.
I'd suggest reading the book then play around with online calculators or just create a spreadsheet.
The one thing- the book was written in 1997. We've had 20 years of turbos since then, so the available maps are not exactly up to date. Even if you can get the update (2003), there have been a TON of turbos- both for diesel and gas- that have come to the market.
In reply to alfadriver :
Agree it's an old book. Find maps via the internet. Use book to learn the theory.
Diesel turbos may be heavy but they are dirt cheap and any gorilla capable of operating a propane torch and snap ring pliers can rebuild them good as new for very little money.
Holset HX35 with a BEP housing for quick spool time is the easy button as the DSM guys have been doing this for almost 2 decades.
Is it the most efficient turbo? No, but it's cheap, proven, reliable and Holset turbos make 4 bangers run like freight trains on amphetamines.
I was going to say go big or go home, but more seriously it depends a lot on what you want to do and how the rest of the car is set up. Obviously a dyno queen with a high stall torque converter can stand to run a turbo that isn't fully spooled until a 1000 rpm before redline. Conversely, oems like to use punchy quick responding tiny turbos to make their cars feel quick, but they often run out of steam way before redline.
I think the best all around turbo setup would be a turbo sized just large enough that it falls off just before redline. I definitely wouldn't want one so small that shifting at redline already puts you 1000rpm past peak boost in the next gear!
alfadriver said:Fueled by Caffeine said:In reply to codrus :
"I would be very careful using a diesel turbo, personally. They are often not designed for the EGTs that gas engines put out."
- tell me more.
ohh in full disclosure.. I worked for Holset for a few years...
So I know that for LONG durability, temps are kept to just under 1700F/925C for a gas turbo, What is it for diesels? I've really wondered that, as you do see diesel turbos for sale, since they all want bigger and better.
(And I know anyone with a good T-couple can measure that virtually all turbos will limit out near there, Depending on the cat layout, though, it would not be the limiter, though)
1200-1300 are what they design around. Truck's are looking for a 500,000-Million mile warranty period.. The materials and construction are not that different, so I'm surprised at the EGT argument. Yes, Gas turbos experience higher egt's.... I know some people are casting turbine housings out of inco..
In reply to Fueled by Caffeine :
It's a pretty big difference. I would not expect the materials to be so different that one would be 500F different though. And gas is for 150k min, if they fail before that on a regular basis, then the OEM gets to cover it.
freetors said:I think the best all around turbo setup would be a turbo sized just large enough that it falls off just before redline. I definitely wouldn't want one so small that shifting at redline already puts you 1000rpm past peak boost in the next gear!
That's pretty much what I'm looking for. My power range is "around" 250+, but thats largely from 1. Where the AW11 MR2 begins to get too difficult to control under power and 2. Because I think (but I might be wrong!) that in properly sizing a turbo that works well with the powerband and spools well I'll be happy with what 'number' I get. Plus, if I want more, it won't be *too* hard to upgrade, since most of the heavy lifting is done.
In reply to alfadriver :
1200-1300 is standard running temps. 1300 on the high end of standard. 1600-1700 were the upper bounds of sanity for testing. I believe I wrote the info above in a confusing manner..
You might check this out from Garrett.
https://www.garrettmotion.com/turbocharger-technology/how-a-turbo-works/
Ram50Ron said:Diesel turbos may be heavy but they are dirt cheap and any gorilla capable of operating a propane torch and snap ring pliers can rebuild them good as new for very little money.
Holset HX35 with a BEP housing for quick spool time is the easy button as the DSM guys have been doing this for almost 2 decades.
Is it the most efficient turbo? No, but it's cheap, proven, reliable and Holset turbos make 4 bangers run like freight trains on amphetamines.
This^. people have been doing HX35's forever on pretty much everything and I've never heard of a failure that's due to it being ran on a gas engine vs. diesel. they are cheap and readily available.
But in the other hand chinese turbos are getting cheap and reliable as well. VS Racing is big in the budget LS community and people push them hard making big power with little issue.
T.J. said:I have "Maximum Boost" and thought it provides good background info. From there it's a matter of math and looking at the maps to find the best compromise between cost, availability and performance.
I thought I remember reading a comment on the forum years ago from someone who claimed Corky Bell got some things wrong, but I can't recall what or who said it.
I'd suggest reading the book then play around with online calculators or just create a spreadsheet.
Let's just say you might want to skip over the section on intercooler design. Even Corky's changed his tune, and that doesn't happen easily.
alfadriver said:The one thing- the book was written in 1997. We've had 20 years of turbos since then, so the available maps are not exactly up to date. Even if you can get the update (2003), there have been a TON of turbos- both for diesel and gas- that have come to the market.
It was never a good book to begin with. There are far better options.
You'll need to log in to post.
