Compound Boost

compond boost

There is an article in MM&FF about this.

The conclusion, not good. Very small amount of improvement for a great deal of $$ and very complex. The issue has to do with pumping efficiency. The compond set up has a lot of pumping loss which translates into HP loss.

was just reading a few blogs in another forum today about compound boost. person that has it seems to be very happy with performance . though i have no idea about cost involved. if nothing else it would have to look bad ass

It all comes down to efficiency. If you look at the compressor maps for turbos and superchargers, you'll notice that in general, turbos are more efficient. Efficiency is simple, the less efficient the compressor, the more heat that is added during compression. This extra heat hurts performance by increasing the likely hood of detonation and decreasing the mass of air your engine consumes each cycle. So your goal is to choose a compressor that puts you at peak efficiency for the desired boost level.

Turbos can supply efficient boost at levels up to and beyond 25psi. The only time when compound compressors would be benifitial, is running insane boost levels, where a single compressor would be inefficient. It is common on aircraft engines to run compound compressors, but due to the reduced atmosphere, they are running very high pressure ratios, where a single compressor can't operate efficiently.

Another consideration is how the compressor is driven. Superchargers take power from the crank, and the power drawn can be quite substatial, at 100hp or more. In fact, the supercharger on a top fuel dragster takes more power to drive than the power that a 350 chevy makes. Turbos on the other hand are driven by exhaust energy. There are some losses, but the cost is much LESS.

So, in summary, unless you are planning to run more than 25-30 psi of boost, the most efficient way is with a single turbo, carefully chosen for your operating range.

Hellion makes a single and twin turbo kit for the 03-04 Cobras. My dream car is a 2003 Sonic Blue Cobra with a ported, pullied Eaton compounded by the Hellion Hellraiser Twin Turbo system.

Inefficient? Maybe; I don't know a great deal about it like you guys do. But, what I just described will make 1000 hp or close to it, and still have all the low end torque of the Eaton. I'm sure the upgraded turbo's will make well over 1000 hp. Hellion's kit is made to be used with or without the Eaton on, so hey, why not leave it on?

Can that power be made with a single or twin turbo system without the Eaton? Sure. Can it be done with a huge twinscrew? Possibly, but it would be about maxed out. So IMO, the compound boost setup is the best of both worlds, and I say go for it.

sneaky98gt said:

Hellion makes a single and twin turbo kit for the 03-04 Cobras. My dream car is a 2003 Sonic Blue Cobra with a ported, pullied Eaton compounded by the Hellion Hellraiser Twin Turbo system.

Inefficient? Maybe; I don't know a great deal about it like you guys do. But, what I just described will make 1000 hp or close to it, and still have all the low end torque of the Eaton. I'm sure the upgraded turbo's will make well over 1000 hp. Hellion's kit is made to be used with or without the Eaton on, so hey, why not leave it on?

Can that power be made with a single or twin turbo system without the Eaton? Sure. Can it be done with a huge twinscrew? Possibly, but it would be about maxed out. So IMO, the compound boost setup is the best of both worlds, and I say go for it.

Click to expand...

You read my mind, man.

Excessive mechanical complexity is unreliable, lame, ill advise, and stupid.

There are plenty of ways to make a Mustang fast without turbocharging. Turbocharging is the most challenging thing that you can attempt. Trying to make a turbo car even more mechanically complex with compound boost is just plain stupid unless you are uber rich and have lots of time on your hands.

That is MY opinion on this subject.

lets see...if i can remember all the stuff i posted on this awhile ago.

car made like 1049hp or something like that at 41lbs of boost on the compound set up...
give me a big single with something like a 76mm turbo at 30lbs and see what numbers it makes my educated guess is near 1000rwhp.

1- less cylinder pressure
2- lower IAT2
3- less complexed

your taking air... compressing it. which makes heat. forcing it into an intercooler (or atleast should) then forcing higher then ambiant IAT's into a blower compressing it... again... what does hot air plus compression=... anybody??? HOTTER AIR then your forcing it though an intercooler thats not that great! you will soon find the limit of that stock intercooler system. and even then to make more HP then a 76mm turbo at full boost on race gas your IAT's and cyl pressure will be crazy...

wanna make 1100hp... single 88mm on c16 with an air to water set up on 30lbs

Shiroelex said:

You read my mind, man.

Click to expand...

Anytime.

1991notchbackLX said:

I can't find the Hellraiser kit listed on the Hellion website. I suppose you'd have to call to have one fabbed up. Any other opinions out there?

Click to expand...

96-04 Mustang Twin Turbo System - All V8 Models - 400 to 1,200+ hp

Here's one. Yea, when I searched their website, I didn't see one either, but when I googled it, one came up. Strange. I know they make them, though.

Kilgore Trout said:

Excessive mechanical complexity is unreliable, lame, ill advise, and stupid.

There are plenty of ways to make a Mustang fast without turbocharging. Turbocharging is the most challenging thing that you can attempt. Trying to make a turbo car even more mechanically complex with compound boost is just plain stupid unless you are uber rich and have lots of time on your hands.

That is MY opinion on this subject.

Click to expand...

Perfectly good point about a turbo car being more complex. But, I don't see how compounding the boost with an Eaton is any more complex than without the Eaton. The Hellraiser kit is made for the car with or without the Eaton, and the Eaton is already on the car, so I don't see how it is any more complex compounding.

srtthis said:

lets see...if i can remember all the stuff i posted on this awhile ago.

car made like 1049hp or something like that at 41lbs of boost on the compound set up...
give me a big single with something like a 76mm turbo at 30lbs and see what numbers it makes my educated guess is near 1000rwhp.

1- less cylinder pressure
2- lower IAT2
3- less complexed

your taking air... compressing it. which makes heat. forcing it into an intercooler (or atleast should) then forcing higher then ambiant IAT's into a blower compressing it... again... what does hot air plus compression=... anybody??? HOTTER AIR then your forcing it though an intercooler thats not that great! you will soon find the limit of that stock intercooler system. and even then to make more HP then a 76mm turbo at full boost on race gas your IAT's and cyl pressure will be crazy...

wanna make 1100hp... single 88mm on c16 with an air to water set up on 30lbs

Click to expand...

Once again, how exactly is it more complex? The kit is made for use with or without the Eaton, so I don't see how it makes it more or less complex by leaving the stock Eaton on there. Now if you were originally naturally aspirated, and wanted to put a supercharger and a turbo on, then yes, I'd agree with you about it being more complex. Especially if it were centrifugal instead of a roots. I'm not real sure how that would work.

Efficiency? Once again, I don't know anything about that like you guys do. But I do know that many people have made 1000 hp or close to with this system and the Eaton. This guy did it on 38 pounds and pump gas. Pullied Eaton (14 lbs) and about 12 pounds on each turbo and voila. Could that be done with a big single turbo like you said? Sure, but it wont make power before 4000 rpm. Talk about turbo lag.... And, you're talking about using race fuel. These guys are making that much power on pump gas. Big difference. High IATs? Spend $500 (which is pocket change when you're talking about twin turboing) on a meth kit and problem solved.

My point: Can this much power be made "more efficiently"? Sure. Absolutely. But can you make that much power and keep the low end torque of the Eaton with a just a single or twin system? I doubt it. It really would depend on how the car is driven. Strictly a track car: sure, go all turbo. A street car: I personally like the torque of a roots SC, and if you wanted to make big numbers, compound is the way to go.

And one last point. OP, you said something about using a twinscrew and compound boost. I don't remember who posted about it a while back, but they said it couldn't be done. Something about the twinscrew makes boost between the rotors, and if you pressurize them with extra (compound) boost, it will cause them to flex and go boom. So I wouldn't plan on that.

sneaky98gt said:

Efficiency? Once again, I don't know anything about that like you guys do. But I do know that many people have made 1000 hp or close to with this system and the Eaton. This guy did it on 38 pounds and pump gas. Pullied Eaton (14 lbs) and about 12 pounds on each turbo and voila. Could that be done with a big single turbo like you said? Sure, but it wont make power before 4000 rpm. Talk about turbo lag.... And, you're talking about using race fuel. These guys are making that much power on pump gas. Big difference. High IATs? Spend $500 (which is pocket change when you're talking about twin turboing) on a meth kit and problem solved.

.

Click to expand...

you said it right there... 38lbs of boost... stupid high cylinder pressures. no need to go that high to make insaine power.

btw turbo lag is kinda a thing of the past. its still laggy to a point but its not like the turbos of the early 90's

srtthis said:

you said it right there... 38lbs of boost... stupid high cylinder pressures. no need to go that high to make insaine power.

Click to expand...

Good point. But it is necessary when you're talking about pump gas vs. race gas. I'd be will to bet that he'd make real close to the same amount of power on 30 pounds and race gas that you spoke of.

And keep in mind that MM&FF made almost 1200 hp on the STOCK Eaton. I'd also be willing to bet that you could make that much power (on pump gas) by porting the Eaton (thus increasing efficiency), pulleying the Eaton, throwing some meth at it, and lowering the boost on the turbos.

btw turbo lag is kinda a thing of the past. its still laggy to a point but its not like the turbos of the early 90's

Click to expand...

I don't disagree. But there isn't a turbo out there that makes 15 pounds of boost at 2000 rpm like a positive displacement SC does.

1991notchbackLX said:

I'm looking for a spirited technical debate on the subject of compund boost. I'm hoping some educated members will chime in and release some knowledge on the subject. I'm contemplating putting a turbo on my '99 GT with an '03 cobra motor (mods in sig) while RETAINING the blower. Is it feasible? It would be nice to have the low RPM grunt of the blower and the terrifying highway pulling power of a turbo. Is there any kit on the market currently that retains the blower? Would the airflow of a turbo severely overdrive the stock roots style Eaton unit, or even a twin screw? What kind of fuel system upgrades/tuning would be required to accomodate a compound boost system? Please, post freely on the subject. Any and all perspective is welcome! Thanks!
Chris

Click to expand...

No reason to run a blower and a turbo. A turbo that will create power on a 4v engine will already out flow a blower. Either get a KB or a Whipple or slap a twin turbo setup on the engine.

Like everyone else said, its inefficient and a waste of money.

This whole low RPM thing is a completed joke. You arent launching your car at 1500 at a drag strip and these engines are trying to push around an 8k pound truck.

Now me personally for my 03 cobra...were I to want more power (which I do not, ever) I would build and add a turbo to the current eaton well before I dropped a few grand on a KB or whipple.
I would make more power and torque and actually spend less.
I would never ever remove the positive displacement type of supercharging from it. It's just soo much fun feeling like you have a big block under the hood...
I'd say most of you would not opt for a turbo over a pullied or a kb setup if you got to drive it with both for a while. You cannot hook the power well at anything over 500 and it quickly becomes clear that power over that becomes more and more useless. If your going for a dyno number then turbo can make HUGE numbers if setup correctly....if you want a really fun street car with a ton of guts, stick with the blowers.
Power is much more linear, predictable, and controlable.
If you already have a blower car...then go crazy and do a turbo one for the highway topend power...best of both worlds

Turbos can make BIG torque numbers too, but you have to carefully choose a turbo that can fully spool by a reasonable rpm. I guarantee that my 2.3 will put 98% of the v8s here to shame with the torque it produces at 3000-3500. I normally shift it at 5500 which is similar to where some people here make peak torque. Boost at low rpms. It starts spooling from 2000 and makes full boost well before 3k. Again, choose a turbo that matches your operating range.

I remember reading a hotrod article once where they seperately installed a positive displacement supercharger, centri. supercharger and a turbo on the exact same engine, with the exact same boost levels, and the turbo made more mid range and top end power than any of them. Turbos really can be very fun and responsive to drive, just like a positive displacement supercharger, but don't choose a turbo that doesn't reach full boost until 5000rpm. Get there before 3000 and you'll be amazed.

sneaky98gt said:

Good point. But it is necessary when you're talking about pump gas vs. race gas. I'd be will to bet that he'd make real close to the same amount of power on 30 pounds and race gas that you spoke of.

And keep in mind that MM&FF made almost 1200 hp on the STOCK Eaton. I'd also be willing to bet that you could make that much power (on pump gas) by porting the Eaton (thus increasing efficiency), pulleying the Eaton, throwing some meth at it, and lowering the boost on the turbos.



I don't disagree. But there isn't a turbo out there that makes 15 pounds of boost at 2000 rpm like a positive displacement SC does.

Click to expand...

lemme know next time some one launches a 4v mod motor car at the track under 3000rpm... odds are they cant drive.

srtthis said:

lets see...if i can remember all the stuff i posted on this awhile ago.

car made like 1049hp or something like that at 41lbs of boost on the compound set up...
give me a big single with something like a 76mm turbo at 30lbs and see what numbers it makes my educated guess is near 1000rwhp.

1- less cylinder pressure
2- lower IAT2
3- less complexed

your taking air... compressing it. which makes heat. forcing it into an intercooler (or atleast should) then forcing higher then ambiant IAT's into a blower compressing it... again... what does hot air plus compression=... anybody??? HOTTER AIR then your forcing it though an intercooler thats not that great! you will soon find the limit of that stock intercooler system. and even then to make more HP then a 76mm turbo at full boost on race gas your IAT's and cyl pressure will be crazy...

wanna make 1100hp... single 88mm on c16 with an air to water set up on 30lbs

Click to expand...

you took words out my mouth.. I was just about to say either go full turbo, or full supercharger (3.4 whipple)..

41psi on a supra would make 1200rwhp, you got 2 more cylinders too.. i bet that system wouldnt last more than a year running like that, and the boost pipe from the turbo probably has back pressure from the eaton..

srtthis said:

lemme know next time some one launches a 4v mod motor car at the track under 3000rpm... odds are they cant drive.

Click to expand...

That's why I said this:

sneaky98gt said:

It really would depend on how the car is driven. Strictly a track car: sure, go all turbo. A street car: I personally like the torque of a roots SC, and if you wanted to make big numbers, compound is the way to go.

Click to expand...