The Top DSM Community on the Web

For 1990-1999 Mitsubishi Eclipse, Eagle Talon, Plymouth Laser, and Galant VR-4 Owners. Log in to remove most ads.

Please Support STM Tuned
Please Support Rix Racing

Compound Turbo Thread

This site may earn a commission from merchant
affiliate links, including eBay, Amazon, and others.

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

To simplyfy it down, a turbo chokes on inlet volume not mass. So the 16g can intake like 600cfm, it doesn't care if its at 14.7psia or 100psia, It can only move 600cfm. So if a 16g chokes at about 44lbs/min when the intake pressure is at atmosphere (14.7psia), its moving about 600cfm, now you increase the inlet pressure to 30psia (twice the pressue of atomsphere ~2 times the density) It should be capable of flowing 88lbs/min.




Why don't you just have a single garret housing machined for it?

Because I can't find a suitably large housing for high boost, especially on a 2.3, and the 2.5 outlet on the HX30 dictates a T3 flange. Even something like a Garrett .96 T4 housing would be too small in my opinion. The 21cm2 housing is LARGE, and the divider certainly isn't going to hurt flow. On John's WH1C and HX52 setup, the HX52 has a divided housing, and it still comes on quite quickly. That car is unreal fast.
 
Because I can't find a suitably large housing for high boost, especially on a 2.3, and the 2.5 outlet on the HX30 dictates a T3 flange. Even something like a Garrett .96 T4 housing would be too small in my opinion. The 21cm2 housing is LARGE, and the divider certainly isn't going to hurt flow. On John's WH1C and HX52 setup, the HX52 has a divided housing, and it still comes on quite quickly. That car is unreal fast.

I feel like the 21cm hx35 is gonna be small. I really think the 40 is gonna hold you back. Whats your end goal? If your gonna run the HX30 at a PR of 1, it'll be like having an N/A motor of at about 4l, or an old school v8 of 5l. Generally a 5.0 wouldn't even think about anything less than a 67mm, and that would only rev like 6k.

If kevin is over running a s475 with a 50trim, that almost indicates you might need something that big on top.

I've honestly not been impressed by any of the compounds built yet. They don't spool that great for the power they make, and seem to take a lot of boost to make the power they make.

FYI in the unlimited tractor pull world, compound guys are running 2 HX83's over a single HX82 or even a HX60 on smaller engines....Basically more than 2 times the volume flow on the astmosphereic side. Granted it's a different application, but they have been doing this longer than a dsm has existed.
 
I feel like the 21cm hx35 is gonna be small. I really think the 40 is gonna hold you back. Whats your end goal? If your gonna run the HX30 at a PR of 1, it'll be like having an N/A motor of at about 4l, or an old school v8 of 5l. Generally a 5.0 wouldn't even think about anything less than a 67mm, and that would only rev like 6k.

If kevin is over running a s475 with a 50trim, that almost indicates you might need something that big on top.

I've honestly not been impressed by any of the compounds built yet. They don't spool that great for the power they make, and seem to take a lot of boost to make the power they make.

FYI in the unlimited tractor pull world, compound guys are running 2 HX83's over a single HX82 or even a HX60 on smaller engines....Basically more than 2 times the volume flow on the astmosphereic side. Granted it's a different application, but they have been doing this longer than a dsm has existed.

I'm definitely going for response over outright power. The 21cm2 housing is quite large (I'll get a comparison pic up), and I'm only shooting for something over 600whp. This is a drift car, and needs all the low-end torque it can get. It also will have a rev limit of 7700 rpm. If I get it together and it needs changing, I'll definitely switch it up.

What do you mean they don't spool that well? I haven't seen many dyno's or logs.
 
HX35 12cm2 vs. WH1C 21cm2 vs. S200SX 1.00:

You must be logged in to view this image or video.
 
Any of you guys that are running holsets worried about boost on the top turbo? Most holsets don't even wake up until +30psi on a single application. So I would imagine the same would be applicable to an extent.

I have had both the 35 and now a 40 and for each turbo that was true, I was un-impressed until after 30psi.
 
I feel like the 21cm hx35 is gonna be small. I really think the 40 is gonna hold you back. Whats your end goal? If your gonna run the HX30 at a PR of 1, it'll be like having an N/A motor of at about 4l, or an old school v8 of 5l. Generally a 5.0 wouldn't even think about anything less than a 67mm, and that would only rev like 6k.

If kevin is over running a s475 with a 50trim, that almost indicates you might need something that big on top.

I've honestly not been impressed by any of the compounds built yet. They don't spool that great for the power they make, and seem to take a lot of boost to make the power they make.

FYI in the unlimited tractor pull world, compound guys are running 2 HX83's over a single HX82 or even a HX60 on smaller engines....Basically more than 2 times the volume flow on the astmosphereic side. Granted it's a different application, but they have been doing this longer than a dsm has existed.

Your first paragraph is pretty much along the same line of thinking I had when looking at his plan. I am impressed by how some of these are being packaged though. I am also enjoying how far we've come in terms of what proper stage sizing, intercoolers and plain jane E85 is letting a gas 4-cyl get away with in terms of low rpm airflow and boost.

As far as the split in size between stages being too small, I think that greatly depends on the overall power goal and the vehicles intended purpose.

John Wheeler's WH1C/HX52 for instance would seem a bit tight on the stage sizing, and so did Paul's but I think that was to accomplish the flat torque that is otherwise hard to come by on a small gas motor.

From what I understood, this is because they were intended for street duty as well.

Kevin's though, would seem to be fully drag oriented. Which is where a split like you see on the pull trucks would come in.

I recall seeing on YB that he had been contemplating moving up from the S475 because he is running off the right side of the map since his Primary PR is so low.

Maybe he'll chime in when he sees this..

My understanding of compounds for a drag car not worried about response after initial spool-up.. would have me looking at a T6 S400-88 to put over that 50-trim.

Then using Link or AEM to run a boost control solenoid for the 50-trim that would spike to say 30psi and make enough exhaust flow (~ 6L displacement worth) to get the 88mm lit and then drop them back to more appropriate work distribution.

On my 5MT FWD I would be looking to rev to the moon to hit the traps at the top of third on a 26" or 28" tire, Kevin's car being a RWD Auto on a much bigger tire of course may not need the rpm though

This is from looking at the relatively low rpm V8 guys in the 331-347-366CID range and they are getting some great results with those turbos.

Say 2.0PR on the 50-trim and 2.25 on the 88mm to get them on their sweet spots.

My 1.5L Honda Compound project is looking to be going towards the bigger split between stages as well as a lot of RPM. I have two mockups in progress at the moment one is a 14B in an 8cm housing feeding a Open T4 61mm Garrett.

This will more than likely be the first one I get up and running. The other is a geared a bit more towards experimenting with stage sizing.

I have an assortment of DSM flanged turbos, and I intend to run two small primaries feeding an even smaller secondary.. that same 8cm 14B fed by two Small 16Gs in either 8cm DSM flange housings or 10cm T3 housings and this is looking to be my attempt with that approach.

Predicated on the idea that the two small primaries will be less likely to surge, that the polar moment of two smaller turbine wheels would lend to better response, two turbine housings/wastegates would help keep backpressure low and that those turbine footprints allow for a lot of interchange-ability.

The secondary turbo's turbine stage will have a 60mm or 66mm gate on it allowing me to run a very small turbo for response and still run a big set of primaries I'm hoping.

Initially I was thinking three T25's (also two into one) would make for a blast in a street car.. but they run out of steam fast and would probably make for some nasty back pressure
 
Any of you guys that are running holsets worried about boost on the top turbo? Most holsets don't even wake up until +30psi on a single application. So I would imagine the same would be applicable to an extent.

I have had both the 35 and now a 40 and for each turbo that was true, I was un-impressed until after 30psi.

We'll see how this goes. I'm planning on running the HX30 on 20psi or so, and the HX40 at 35. If it needs more to make the power I want, I'll turn it up.

As far as the split in size between stages being too small, I think that greatly depends on the overall power goal and the vehicles intended purpose.

John Wheeler's WH1C/HX52 for instance would seem a bit tight on the stage sizing, and so did Paul's but I think that was to accomplish the flat torque that is otherwise hard to come by on a small gas motor.

From what I understood, this is because they were intended for street duty as well.

Kevin's though, would seem to be fully drag oriented. Which is where a split like you see on the pull trucks would come in.

Maybe he'll chime in when he sees this..

My understanding of compounds for a drag car not worried about response after initial spool-up.. would have me looking at a T6 S400-88 to put over that 50-trim.

Then using Link or AEM to run a boost control solenoid for the 50-trim that would spike to say 30psi and make enough exhaust flow (~ 6L displacement worth) to get the 88mm lit and then drop them back to more appropriate work distribution.

On my 5MT FWD I would be looking to rev to the moon to hit the traps at the top of third on a 26" or 28" tire, Kevin's car being a RWD Auto on a much bigger tire of course may not need the rpm though

This is from looking at the relatively low rpm V8 guys in the 331-347-366CID range and they are getting some great results with those turbos.

Say 2.0PR on the 50-trim and 2.25 on the 88mm to get them on their sweet spots.


Initially I was thinking three T25's (also two into one) would make for a blast in a street car.. but they run out of steam fast and would probably make for some nasty back pressure

It's John Whalen btw, they got his name wrong at Shootout, haha.

Yeah my setup is definitely for a large, broad torque curve and transient response, both of which are important for drifting, especially when you're up against LSx powered cars that make 300wtq at 1500rpm haha. Keep in mind that the HX30 only flows a bit more than a Big 16g. And caged's setup seems to be working well.

Speaking of which, how much boost are you running on each turbo caged?

When you're getting into three turbos, you're definitely adding a LOT of weight to the front of the car, which is probably fine for a street/drag car, but not so much for something that needs to handle well.

Compounds definitely open up the turbo choices depending on what you're designing the car to do.
 
We'll see how this goes. I'm planning on running the HX30 on 20psi or so, and the HX40 at 35. If it needs more to make the power I want, I'll turn it up.



It's John Whalen btw, they got his name wrong at Shootout, haha.

Yeah my setup is definitely for a large, broad torque curve and transient response, both of which are important for drifting, especially when you're up against LSx powered cars that make 300wtq at 1500rpm haha. Keep in mind that the HX30 only flows a bit more than a Big 16g. And caged's setup seems to be working well.

Speaking of which, how much boost are you running on each turbo caged?

When you're getting into three turbos, you're definitely adding a LOT of weight to the front of the car, which is probably fine for a street/drag car, but not so much for something that needs to handle well.

Compounds definitely open up the turbo choices depending on what you're designing the car to do.

Ooops haha :coy:

The added weight helps in my applications, all of which are built for the big end, but I'll ballast and balance where necessary in the Honda as that does occasionally go around corners. And the turbos in this case are starting quite small.

A lot of that added weight is going to be over the back half of the transmission and behind the front axle near the firewall which should actually move the mass center in the car away from the engine block and then leaving only a couple lengths of tubing, an intercooler and the meth tank up in the fender well to go ahead of the front axle.

Battery, fuse box, windshield fluid bottle, etc is all being relocated.

The weight in general adds much appreciated stability at speed, especially in a car that is only 2500lbs to begin with.

The big single on my current DSM had a 62lb shipping weight, compared to a couple of TD05H units thats not bad. LOL

I'm hoping to use the Honda as a test bed that will shed light on theories I have.
 
I dunno, I don't really have much for experience with compounds other than max power type stuff.

Paul's initial setup didn't impress me because from the dyno sheets, it didn't seem to make much power for the amount of boost it was, and it seemed lazy on spool for a 16g. I seem to recall a bolt-on HX40 would do what that's doing.

I kinda think that the added restriction of the bigger charger slows down how the little charger comes on. I wonder how pauls would have been with a 14b in it.

RWD, seeing what your doing I think your gonna want a smaller little turbo run at like 10psi with your setup to get it to come on quick enough. I think you might even be better off with a twin charged setup, as that will give you the off idle response you want, and not hinder the top end.

It's neat to see you guys playing with stuff. I really wish the awd drive train would handle the torque, without going to a gaymatic, and I'd be building a remote mount setup. Probably a hx40 on top of a 14b, or even a 13g to get it to come on real quick.
 
I think Paul's setup was impressive for the amount of mass flow he got through that relatively small primary and had he not run into clutch issues it probably would've been a whole different ball game.

And as far as his boost numbers not correlating with the power, I look less at that and more at the airflow vs. the power he was making.

I agree though that it seemed slow spool for a 16G and knowing what we all have learned from him and kevin, as well as the diesel world (what little the guys in the know give out at least haha) that a bigger interstage pipe between the turbines would have likely helped and a bigger turbine on the primary charger was also called for. And as you mention definitely attributed to the other turbo getting in the way.

Curious to see Paul's next stab at it!

You're definitely onto something with that 13G/HX40 combo

250awhp spool with ~700awhp top end would be a ball on the street.

For me it would just blow the tires off every-time I so much as looked at the gas pedal
 
I did indeed run off the map on the S475. You can see it in the back pressure log. Where it deviates from 1:1 is where it ran out of compressor.

As fas as the compounds not spooling well, you could look at it this way. The S475 with the 96mm turbine wheel and 1.32 AR T6 housing would never spool on a 2 liter. The previous owner of the car actually tried it and didn't make boost until AFTER 1000 feet and over 9000 rpm. I'm able to spool it around 5k rpm without nitrous. At 6500 it makes nearly set boost on the 2 step. It would come up better with a bigger small turbo though, I have a pretty wide spread in my setup between the little 50 trim and the monster T6 turbine. Needs more exhaust energy to get going. I had some trouble with it at the Shootout last year, a coupler had split. Normally I can leave at full boost on a pro tree with it.

With what I've learned since then (had a hell of a season this year) I know the next rev will kick a lot more ass. The nitrous worked better than ever for me this year after some more changes, but I would still like to get away from it again.
 
I think Paul's setup was impressive for the amount of mass flow he got through that relatively small primary and had he not run into clutch issues it probably would've been a whole different ball game.

And as far as his boost numbers not correlating with the power, I look less at that and more at the airflow vs. the power he was making.


I think that the airflow vs boost is more an indicator that the setup is efficient.

Power vs. airflow just indicates that the tune is good.


This whole thing is kinda depressing to me. The 4g in a dsm seems to be the turbocharger workhorse, its just crippled by it's little clutch, and trans's that attatch to it. So you say fu(k it, lets turn this bi*** 90* and put a proper trans behind it. Well now you need to run dr's on the street to have any hope of utilizing the power.

My other play toy is a 63 ford, with a 302 in it, no need for compounds there. A single HX52 would spool like a 14b and still make enough power to split the block in half.
I want to play, but no playgrounds in the neighborhood. It's just a goddamn bummer.

I think Paul's setup was impressive for the amount of mass flow he got through that relatively small primary and had he not run into clutch issues it probably would've been a whole different ball game.

And as far as his boost numbers not correlating with the power, I look less at that and more at the airflow vs. the power he was making.


I think that the airflow vs boost is more an indicator that the setup is efficient.

Power vs. airflow just indicates that the tune is good.


This whole thing is kinda depressing to me. The 4g in a dsm seems to be the turbocharger workhorse, its just crippled by it's little clutch, and trans's that attatch to it. So you say fu(k it, lets turn this bi*** 90* and put a proper trans behind it. Well now you need to run dr's on the street to have any hope of utilizing the power.

My other play toy is a 63 ford, with a 302 in it, no need for compounds there. A single HX52 would spool like a 14b and still make enough power to split the block in half.
I want to play, but no playgrounds in the neighborhood. It's just a goddamn bummer.
 
I did indeed run off the map on the S475. You can see it in the back pressure log. Where it deviates from 1:1 is where it ran out of compressor.

As fas as the compounds not spooling well, you could look at it this way. The S475 with the 96mm turbine wheel and 1.32 AR T6 housing would never spool on a 2 liter. The previous owner of the car actually tried it and didn't make boost until AFTER 1000 feet and over 9000 rpm. I'm able to spool it around 5k rpm without nitrous. At 6500 it makes nearly set boost on the 2 step. It would come up better with a bigger small turbo though, I have a pretty wide spread in my setup between the little 50 trim and the monster T6 turbine. Needs more exhaust energy to get going. I had some trouble with it at the Shootout last year, a coupler had split. Normally I can leave at full boost on a pro tree with it.

With what I've learned since then (had a hell of a season this year) I know the next rev will kick a lot more ass. The nitrous worked better than ever for me this year after some more changes, but I would still like to get away from it again.

How big of a compressor can you mate to the 96mm BW turbine? Were you thinking along the lines of the S480.. or closer to the 88 so you have room to grow?

With regards to a larger secondary bringing it up faster.. is that based solely on added flow? the expansion ratio?

My line of thought, flawed as it can be would suggest that with the smaller secondary, less heat/energy would be taken out of the stream by the smaller wheel as well as more would be bypassed.

That the greater heat from the larger proportion of unmolested bypassed exhaust flow as well as the extra heat left over from gasses passing through a smaller turbine that cannot take full advantage would have a higher post turbine EGT and subsequently a greater turbine inlet temperature for the primary charger.. does that stand to reason?

I seem to recall you saying you wanted to get away from the nitrous if possible, do you think a S200sx-58 in one of the divided T3 or Airwerks T4 housings would let you get up on the converter?

Or are you keeping your cards close to your chest on this one? :sneaky:

I think that the airflow vs boost is more an indicator that the setup is efficient.

Power vs. airflow just indicates that the tune is good.


This whole thing is kinda depressing to me. The 4g in a dsm seems to be the turbocharger workhorse, its just crippled by it's little clutch, and trans's that attatch to it. So you say fu(k it, lets turn this bi*** 90* and put a proper trans behind it. Well now you need to run dr's on the street to have any hope of utilizing the power.

My other play toy is a 63 ford, with a 302 in it, no need for compounds there. A single HX52 would spool like a 14b and still make enough power to split the block in half.
I want to play, but no playgrounds in the neighborhood. It's just a goddamn bummer.

From what I'm learning it doesn't take a whole lot to split a 302 block down the valley though! a 351W on the other hand.. can you tell I'm looking at getting into a fox body?

The clutch option quickly become expensive with the torque these 4Gs are putting down now, especially as early as some of these compounds are coming on-line. Twin and triple plate sintered discs with a 300M input shaft is probably the only way to at that stage.

As far as boost v. flow wouldn't that relationship be altered a bit by the multiple stages of compression? Genuine question..

I would think that realistically the given massflow that the primary would provide at say 2.0PR is going to be more or less the same, but because it has to pass through another compressor stage it will end up greater in the manifold. So not necessarily a commentary on engine VE/demand flow but more a inherent by product of running two turbos where they are putting out "cool" air and moving enough of it to make the power you want.

And because you can only drop the secondary stage PR so low while maintaining efficiency and moving that requisite volume at a given rpm (regardless of secondary inlet density at that point) without running up your IAT by shifting off an efficient portion of the map and possibly winding up in the choke region.. it would to my mind atleast seem to be a step backward to drop secondary PR too low after the primary lights off just for the sake of dropping manifold pressure. :aha:

Does that make sense to anyone besides me? :confused:

I'm trying to think of a way to word that more succinctly..
 
Last edited:
I dunno, I don't really have much for experience with compounds other than max power type stuff.

Paul's initial setup didn't impress me because from the dyno sheets, it didn't seem to make much power for the amount of boost it was, and it seemed lazy on spool for a 16g. I seem to recall a bolt-on HX40 would do what that's doing.

I kinda think that the added restriction of the bigger charger slows down how the little charger comes on. I wonder how pauls would have been with a 14b in it.

RWD, seeing what your doing I think your gonna want a smaller little turbo run at like 10psi with your setup to get it to come on quick enough. I think you might even be better off with a twin charged setup, as that will give you the off idle response you want, and not hinder the top end.

It's neat to see you guys playing with stuff. I really wish the awd drive train would handle the torque, without going to a gaymatic, and I'd be building a remote mount setup. Probably a hx40 on top of a 14b, or even a 13g to get it to come on real quick.

Don't forget, mine is a stroker. I'm sure the little HX30 will come on plenty fast enough. I don't need a V8 powerband to compete, just something close haha.

There is a line between spool up v.s total flow that I think has to be drawn. I picked the hx30 because the turbine and housing flow a lot more than the little bity turbos that could spool up "faster", and more compressor flow means more exhaust flow anyway. I really think this twin-scroll housing is going to have ridiculous spool.
 
From what I'm learning it doesn't take a whole lot to split a 302 block down the valley though! a 351W on the other hand.. can you tell I'm looking at getting into a fox body?

Lol nope, seems like 600whp and your on borrowed time.

The clutch option quickly become expensive with the torque these 4Gs are putting down now, especially as early as some of these compounds are coming on-line. Twin and triple plate sintered discs with a 300M input shaft is probably the only way to at that stage.
Yeah, I have a quartermaster now, and I fin hate the thing. Then you still have a trans that was only designed for 250ft lbs. The ppg gears are an option, but not a very good one at 10k

As far as boost v. flow wouldn't that relationship be altered a bit by the multiple stages of compression? Genuine question..
I don't think so, that relationship is a function of VE. If its taking you 40psi to move the air that another setup is doing at 30, I think it's leaving lots of power on the table. The extra psi is creating heat. Also if it's exhaust restriction holding back the flow (which it usually is on a turbo app) your getting beat up by not evacuating the chamber good on the exhaust stroke resulting in lots of charge dilution. I feel like you'll get beat up on pumping losses too because of the higher cylinder pressure due to the extra boost needed to force the air thru. Essentially you wasting energy compressing gasses that are already burnt.

I would think that realistically the given massflow that the primary would provide at say 2.0PR is going to be more or less the same, but because it has to pass through another compressor stage it will end up greater in the manifold. So not necessarily a commentary on engine VE/demand flow but more a inherent by product of running two turbos where they are putting out "cool" air and moving enough of it to make the power you want.
I'm not sure I follow this. The massflow will stay the same all the way thru the system, but the volume flow will be smaller after each compressor.

And because you can only drop the secondary stage PR so low while maintaining efficiency and moving that requisite volume at a given rpm (regardless of secondary inlet density at that point) without running up your IAT by shifting off an efficient portion of the map and possibly winding up in the choke region.. it would to my mind atleast seem to be a step backward to drop secondary PR too low after the primary lights off just for the sake of dropping manifold pressure. :aha:
I don't think so, the higher the primary PR, the farther from choke the secondary will run. Also keep in mind the the outlet temp isn't just a function of efficiancy, its a function of inlet temp, mass, and pressure ratio, and I think the change in efficiency has a very very small effect on outlet charge temp.

If I were to do a compound, I would run a 14b or 13g as a secondary. I'd start be seeing as what boost level I can run one at and still have low drive pressure at 9k. I'd bet that's at about 9psi on a 14b. So then I'd set the gates up so that the 14b gives 20 or so until primary starts to come up, and take pressure off the secondary as the primary builds so that at full boost the secondary ends up back at about 9. Not sure how I'd do it or if it would even work. but thats where I'd start.


Don't forget, mine is a stroker. I'm sure the little HX30 will come on plenty fast enough. I don't need a V8 powerband to compete, just something close haha.

There is a line between spool up v.s total flow that I think has to be drawn. I picked the hx30 because the turbine and housing flow a lot more than the little bity turbos that could spool up "faster", and more compressor flow means more exhaust flow anyway. I really think this twin-scroll housing is going to have ridiculous spool.

Ahh the stroker should help. I'm interested to see how the HX30 does on it's own. Keep us posted.
 
Ahh the stroker should help. I'm interested to see how the HX30 does on it's own. Keep us posted.

I plan on breaking in the engine with the HX30 alone, so I should get some good logs. I'll definitely post them up.
 
How big of a compressor can you mate to the 96mm BW turbine? Were you thinking along the lines of the S480.. or closer to the 88 so you have room to grow?

The 80 would just barely get there, so I'd do the 88. It can be put on the 96mm/1.32 turbo for reasonable money too.

With regards to a larger secondary bringing it up faster.. is that based solely on added flow? the expansion ratio?

Airflow into the motor is airflow out of the motor (plus fuel mass), so putting more through creates more exhaust flow. I'm leaving on the 50 trim at max capacity, not enough to get the big turbo going easily enough.

My line of thought, flawed as it can be would suggest that with the smaller secondary, less heat/energy would be taken out of the stream by the smaller wheel as well as more would be bypassed.

That the greater heat from the larger proportion of unmolested bypassed exhaust flow as well as the extra heat left over from gasses passing through a smaller turbine that cannot take full advantage would have a higher post turbine EGT and subsequently a greater turbine inlet temperature for the primary charger.. does that stand to reason?

I think it would be the other way around, a bigger turbine would take less from the exhaust energy (less work done, shown in the lack of spool). The general line of thinking is correct though, the more left over for the big turbo the better it will spool. The problem is you have little control over that. Just put more mass flow through the motor, it will get the job done either way.


As far as mass flow vs boost, that doesn't really change much from a single turbo setup. It will go to shit however if back pressure is higher than a single turbo will be. In my case where back pressure is essentially 1:1, 40 psi on the single 4294 and 40 psi on the compounds resulted in the same power and track times. ~580 whp and 8.9 second ETs. The compound setup left softer and did more on the top end (mph) though since the 50 trim limits 60 foots to 1.35s.
 
I am confused by what you're saying about your setup. The S475 is a 98lb/min turbo. What boost are you running it at? You should be able to make 1000whp with that thing on a compound setup, how are you possibly off the compressor map at the pressure you are operating it at? It's working at atmospheric pressure, and it should be able to push the same amount of flow as if you were running it as a single.
 
I am confused by what you're saying about your setup. The S475 is a 98lb/min turbo. What boost are you running it at? You should be able to make 1000whp with that thing on a compound setup, how are you possibly off the compressor map at the pressure you are operating it at? It's working at atmospheric pressure, and it should be able to push the same amount of flow as if you were running it as a single.

He is running it into the lower right part of the compressor map where efficiency drops right down. The pressure ratio isn't high enough to Max out the compressor on the efficient part of the map.
 
I don't see how he could be flowing that much air at that low of shaft speed and pressure ratio. It doesn't make sense. You're saying somehow the car is capable of flowing more and making more power with a smaller single 67mm compressor?
 
He is running it into the lower right part of the compressor map where efficiency drops right down. The pressure ratio isn't high enough to Max out the compressor on the efficient part of the map.

I am confused by what you're saying about your setup. The S475 is a 98lb/min turbo. What boost are you running it at? You should be able to make 1000whp with that thing on a compound setup, how are you possibly off the compressor map at the pressure you are operating it at? It's working at atmospheric pressure, and it should be able to push the same amount of flow as if you were running it as a single.



I don't see how he could be flowing that much air at that low of shaft speed and pressure ratio. It doesn't make sense. You're saying somehow the car is capable of flowing more and making more power with a smaller single 67mm compressor?

40psi and 8000rpm on a 2.0 is about 73lbs/min if it's a decent setup at all. The choke flow on the turbo is 98, but thats kinda where it's efficient, I'd wager that it chokes a lower flow with less PR. Also he was running into trouble because where he was operating at was waaaay down in efficiency, like maybe 50% or less. So while it probably only takes about 40hp worth of power to compress the air, the compressors efficiency bones you and you need 80, couple that with a turbine efficiency that I'm sure sucks at that shaft speed, and viola bad drive pressure business.

I got a feeling what the ideal setup if you wanted the high pressure turbo to do most of the work would be an atmospheric turbo with a large inducer and a smaller than normal exducer, since you you won't need it to run at high PR's. I'd also assume you'd want a turbine with a monster inducer, that way it should make lots of low speed torque. Then basically the opposite on the high pressure turbo. Large compressor exducer, small turbine inducer.

I dunno maybe it would be better the other way around. Let the atmospheric turbo do all the work, and have the high pressure turbo run like 2.0 pr and just take it easy. Lots of ways to skin a cat I guess.
 
The whole point of a compound setup to run a large amount of boost pressure. If you run a huge secondary that requires a high pressure ratio to even start to work then you should be ready to run high boost pressure. My setup made decent power at 37 psi but it was completely usable. I could reach full spool around 5k, I could make 40psi of boost pressure at 3500 rpm on the stall with no nitrous...

I guess you can get as technical as you want with it with pressure ratios and back pressures and properly sized compressors and turbine housings but if you seriously just dumb the whole concept down and look at it like " I want torque at 3500 rpm and I want to make 700 hp or what ever, then I need a primary that is known to make good power and spool by 3500 rpm and then I need a large turbo that will effiecently make enough airflow for 700hp."

With my setup I pretty much just said. I want cheap, effective, and no nitrous. So the smallest hx35 framed turbo I could find and the most realistic big turbo that will fit and still spool around 5500 rpm. You obviously want both turbos to work effiecently at the boost levels you plan to put them at.

p.s. for some reason I can't put my thoughts on compounding into words. So I hope you get my ideas
 
^Makes perfect sense to me and think more people need to stop making crazy over engineered on paper threads and go out there with what you said in mind when picking turbos.

Since this is a new realm people will either have to pony up the cash to change turbos or just wait until the setup they want is proven by someone else.
 
The big turbo is the primary, it sees air first. Turbine order is irrelevant when talking about multistage compression.

If you look at a map for the 475 wheel at 2:1 PR, it ends at 90 lbs/min. I'm moving more than that, and the back pressure curve shows it as well. I could turn it up but 45 psi seemed like a nice round number. More boost is going to move more air so it's not going to fix the problem. I could run a dual channel CO2 boost controller and drop the secondary PR down and raise the primary PR to compensate, but it's cheaper and less complicated to upgrade the compressor wheel. It's no different than V8s running into this same problem.

My car now runs high 8s at ~32 psi (35R), and low 8s at 42 psi (6766), so I know I can go quicker on the existing compound setup, but I won't bother putting it back on the car without upgrading it.
 
Support Vendors who Support the DSM Community
Boosted Fabrication ECM Tuning ExtremePSI Fuel Injector Clinic Innovation Products Jacks Transmissions JNZ Tuning Kiggly Racing Morrison Fabrications MyMitsubishiStore.com RixRacing RockAuto RTM Racing STM Tuned

Latest posts

Build Thread Updates

Vendor Updates

Latest Classifieds

Back
Top