Turbo combinations for my 1GZ

[Mr Ed]

Hen: The way its been explained to me is that turbos dont care about volume of air flowed, they work on pressure, where as its screw type superchargers that work on volume flowed, not pressure.

[Hen]

...turbos dont care about volume of air flowed, they work on pressure...

I think that's true. But in both cases above the turbo is (say..) doubling the inlet pressure at the outlet (compressor maps have the pressure ratio as one axis). Since the inlet pressure is higher in one case, the outlet pressure will also be higher.

Hen

[6BOOST]

You wouldn't pump the charger into the turbo's, it would be almost impossible to plump and divide airflow equally, you would however more than like plump both turbo's into theblower, so you would, effectively be feeding the turbochargers with atmosphere pressure, and hence, have to rely on their combined compressor flow to feed the total desired air into the engine. If you went the opposite direction, you would need a blwoer that is capable of 1700 odd HP, and would do little for anything but outright power, and I doubt the small .63 or .82 turbines on a small turbo would flow enough exhaust gasses to pass that 1700hp when the blower is pumping.

Remember, no matter what power you want to make, it has to go through those turbine wheels, power is made by airflow, back pressure with 2 GT30's and 1350rwhp would be astronomical, I'd expect in the vecinity of 3:1 of boost pressure. I've made the argument a thousand times, and I understand others may feel differently, but twin charging is just a huge waste of time and energy, IMO anyway.

6BOOST

[Bored?]

Well, the solution to the Hen vs 6Boost debate is to figure whether turbos care about volume airflow or mass airflow. Since all the garrett maps are specified in mass airflow and pressure ratio, I guess that they depend on mass airflow, however that's not as definitive an answer as I'd like.

Therefore, I believe 6Boost is right, if the supercharger flows more than the maximum flow of the turbo compressors, they'll be pushed off the right-hand side of their efficiency maps. It will probably still work, but the turbos will just be acting as inlet and exhaust restrictors.

I also agree with 6Boost that the best way to twin-charge is to have the turbos feed the supercharger, however I would only bother doing that with a roots or twin screw supercharger, since they do flow a fixed volume rather than a fixed mass.

Is that a useful thing to do? This is where I disagree with 6Boost. If you're shooting for massive power for your engine capacity, you have the choice of:
a) Using massive revs (no different to increasing capacity really)
b) Using massive boost

If you choose option b, you have a problem. If your boost requirements are higher than you can get with a single turbo at the required mass airflow, you have very few options. You could try to get custom compressor designed for higher pressures (larger exducer diameter and different compressor A/R), or you can go to two compressors in series, with the second being either another turbo or a supercharger.

Since you have a relatively small engine capacity compared to your desired peak flow rate, you're likely to get lots or lag. Using a supercharger for the second stage does help with this because the flow of the engine is now determined by the (increased) flow of the supercharger rather than the flow of the engine.

As an aside, you can in this scenario size the supercharger larger than necessary and use a supercharger bypass valve to control peak boost. That gets you better response when the turbos are off boost at the expense of a little bit less efficiency from your supercharger at high boost.

[oldcorollas]

nah.... twinscrew
that will sound unique enough

then again... turb 12 has a nice ring to it....

\/\/\/ good summary

[6BOOST]

Ok, the simple fact is, 1350rwhp(1000rwkw), if powered by a supercharger, will make no low down power, you will have to go centrifigal in terms of being able to mount it in a location to be able to intercool it. There are few blowers capable, and even if you used one, how many cars that make this power are s/charged?? Not many anymore. If you sed twin charge, the still deciding factor is exhaust flow through the turbine wheels. You will STILL have to size the turbochargers to pass enough air through the turbines to make 1350rwhp. Thses will still be laggy.

Next, if you twin charge, you'd use a screw supercharger. While the turbo's would be intercooled, the possibility of intercooling the screw blower mounted in teh valley would be minimal, giving high intake temps, prob in the region of 70-120deg C, not very conductive to power. The blower wouldn't be easily removable, so its a permanent item, as would be the turbo's, and its 12g just in parts for the 2x turbo's and 1 charger alone. Neither would be of much benefit to each other, anyway, it would still be laggy, and have teh same power potential of the 2 turbo's alone.

If you were talking twin charging, why not scrap the turbo's altogether and run a vortec or powerdyne/paxton centrifigal blower into a screw blower?? High pressure ratio's, high end efficency of a centrifigal blower and low end grnut and efficency of a screw blower. Easy to plump, no exhuast manifolds and dump pipes to fit in the engine bay, and no heat management issues....

6BOOST

[Bored?]

6Boost: Maybe it wasn't clear enough in my previous post, but I am in no way suggesting that twin charging is appropriate in this situation. It was an off-topic post. By "massive power for your engine capacity", I was more thinking of extracting 1500hp+ from a small capacity 4cyl. Like in the good-old-days of formula one. The hp/L in this case is nowhere that.

As for turbos feeding a screw supercharger having lag, at the very least it will have less lag than it would without the supercharger, since twin screw superchargers make boost from low rpm, so you will be producing more power at lower rpm, which means increased exhaust flow, which means reduced lag.

You are quite correct that the size (or at least flow) of the turbos would need to be the same with or without the supercharger in place. As per my previous post, the main reason to twin charge is when you need to achieve higher pressure ratios than otherwise possible. Twin-charging without using very high boost, could produce worse performance by causing the turbos to operate at pressure ratios which are too low. (Though this can be alleviated by wasting supercharger compression using a bypass valve.)

[1jzracing]

interesting thread and some interesting ideas/ theories to say the least!!!

heres a little side perspective

.... who has ever seen or heard of a successful twincharger set up wining races at a drag strip or otherwise???? ..... personally i have never heard of it so FORGET IT! if it workes then lots of people would be doing it

.... if your looking at 1000kw then your shooting too high the rpm and internal stresses on a V engine would most likely blow it to bits, how about cams and valvetrain to cope with 8-9000rpm!! and further more where are you going to find a trans and diff etc to cope with it, that isnt from a door slammer or something then all you have a megadollar undrivable monstrosoty

.... look at whats been done with a 2.5L where 300 - 350 kw is capable, drivable, and relitively easy to achieve.... and hey 700kw would be absolutly mind blowing!!

dont be afraid to go farly big with the turbo's still, my scenario would be 2x GT35's easy and cheap, sitting on short runner manifolds, prepped standard rods and crank, set of 8.5:1 wiseco's or similar, set of 265 cams with big springs and a tidy up in the ports.

you will have your 6-700 kw at 20 to 24psi and only about 7000 rpm, it would be drivable realistic and achievable

if your looking for any help on anything stainless like manifolds or piping etc in sydney let me know

good luck keep us informed,

[Bored?]

.... who has ever seen or heard of a successful twincharger set up wining races at a drag strip or otherwise???? ..... personally i have never heard of it so FORGET IT!

Argumentum ad populum and appeal to common practice are both well known logical fallacies.

How about the lancia Delta S4 group B rally car. It was twin charged and basically dominated WRC in 1985, at which point WRC moved away from group B rules.

There aren't many classes of racing where twin-charging is possible these days. Most classes have:
* Directly banned either superchargers or turbos or both (F1)
* Implemented intake restrictors (LMP/WRC)
* Implemented boost limits (Champ)
* Fuel type restrictions

All of which directly or indirectly limit the possibility of boost levels high enough to require twincharging or compound charging.
Just because it is banned doesn't mean it doesn't work. In fact, often it means the opposite of that.

(I don't know what the exact rules are for the top-fuel drag classes, but as I understand it roots-type blowers are the only thing allowed.)

if your looking at 1000kw then your shooting too high the rpm and internal stresses on a V engine would most likely blow it to bits, how about cams and valvetrain to cope with 8-9000rpm!!

Of course 1 Mw is going to be tough on an engine, but people have done it with much worse starting points than a v12. The fact that it's a v-engine doesn't have a lot to do with it. In fact, a v12 is probably in a better position to do it than any other engine, given that it has a simpler crank shaft than a cross-plane v8, and it is an inherently balanced design.

As for cams and valvetrain to cope with 9000rpm... many OEM engines will do that easily. With adequately lightweight valves and retainers combined with adequately heavy valve springs people have achieved ridiculous numbers. Check out www.exvitermini.com / gtr700 for high rev insanity, they're getting this kind of power out of an rb26, proving that with enough money and engineering skill, you can have lots of power. Of course nothing lasts long at those revs...

[oldcorollas]

bah, V12 or V8, it is still only a "baby" 5L.. it just naturally sounds better

[1jzracing]

they do sometimes use it on truck racing but they use 2 turbos and run up to 60psi boost but thats only because the engines are too big to rev, a 12 should rev quite nicely

if you can make 800hp from a single turbo 1.5L engine (old F1 cars) then twin charging is not needed,

not to mention space you will need huge intercooling and the engine bay is going to farly full with a V12 and two turbos with all the associated piping let alone all the extra plumbing to add a supercharger, not to mention the size of a big enough charger unit also

the LAST thing you want is shit sticking out of the bonnet!

it all comes down to cost, sure almost ANYTHING is possable but i doubt this project would warent the extra $30,000++ to gain that last 2-300 kw and then have something that makes all its power between 6 and 9000 rpm and becomes totally undrivable

as stated its still only 5L!

it has been done and the cost is like $60,000++ but i think a turbo supercar engine will breath considerably better than this v12

[Norbie]

they do sometimes use it on truck racing but they use 2 turbos and run up to 60psi boost but thats only because the engines are too big to rev, a 12 should rev quite nicely

That's compound turbocharging, not twincharging. It's done to acheive huge pressure ratios, which on an engine of that size would not be possible with a single turbo. This isn't relevant to the current discussion.

if you can make 800hp from a single turbo 1.5L engine (old F1 cars) then twin charging is not needed,

Again that is not relevant. No-one is saying you can't acheive 1000kW with turbocharging alone, of course you can - but the idea of twincharging is to have boost at lower RPM than would be possible with a large turbo alone. Do you think those turbo F1 engines had good boost response at low RPM? Somehow I doubt that was part of their design brief!

[1jzracing]

No-one is saying you can't acheive 1000kW with turbocharging alone, of course you can - but the idea of twincharging is to have boost at lower RPM than would be possible with a large turbo alone.

yes you can its called antilag

[6BOOST]

To make 1000rwkw, the engine will "only" need around 30psi of boost, 7500rpm redline and a VE of 80% or better. All highly achievable.

Twin GT35's won't make full boost till 4500rpm, with a redline of around 7000rpm, its not exactly street friendly, twin 3076's on the other hand full boost @3300rpm and 600rwkw... Nice

Anyway, good luck with the project, if anything its certainly stirred some imagination among the toyota camp

6BOOST

[Norbie]

yes you can its called antilag

Which is fine if you don't mind replacing your turbos every couple of weeks.