can we get a duscussion going about this please?

Also- I know porsche has a dual stage turbo that spools 4# then spools 8 at higher RPMS....

has anyone done twin turbo with 2 different size turbos? small for of the line then HUGE for top end?

 

Single turbo...works great in drag racing because turbo lag isn't a worry really since they come off the line where the turbo is deep into making boost. It also works great on large engines becasue of sheer exhaust gas volume, so again lag is not noticiable. Efficieny will be higher in a single turbo set up.

Twin turbo....great for packaging concerns in V type engines. Helps lag a little, but this should not be the change over point from a single turbo system. OEM's use this alot cause its more practical to have to T25's than a T45 which is rare, expensive to fix and is loud.

Sequential Twin turbo....where a turbo feeds into another.......I have seen this maybe twice and I see no point to use it yet, since most will turbos flow enough air to make insane power levels without the use of a turbo feeding another turbo. But maybe soon...

The reason I went with two turbos on my engine is three fold,

1. I have a rather large engine compartment so the twin setup will fit better and be more simple. This isnt always true though, if you have a smaller engine bay like the 4th gens, a single turbo is somtimes easier to build.
2. The turbos I chose will flow around 90 lbs/min in total, and getting a single turbo for that flow need, would be harder to get and repair than the two more popular turbos I am going to use.
3. Looking through the compressor maps of turbos, no single large turbo gave me the boost curve I want. Two smaller ones did allow the proper boost curve though, so this is what I chose.

Hunter

 

Turbo spool doesn't depend on how many turbos- its all about the size.


Sequential is not one feeding another- that has a name (i forget), and is what's used w/ race engines to come up w/ like 4-5 bar.

Sequential is all exhaust gasses flowing into one turbo to make full boost at low rpm, then having a second turbo come on later.


This is what the supras use. They have the same size, although #2 has a slightly larger exhaust housing.

I've driven a 996, i don't know what kind of setup they use, but i can tell you boost comes in very low in the rpm and pulls hard all the way to redline.


A small first turbo then a larger second is plausible, i don't know if its been done.

And for the person who's wanting to step in and say "no, because the second one will out flow the first and push boost back across it " save your breath (or fingers), pressure equalizes, not volume.

 

Mikael,

Thanks for correcting me, your totally right bout the sequential thing.

About the Porsche turbos, I dont know much bout them but I wil ask a friend of mine that works at a repair shop and see if I can get on the inside scoop.

Hunter

 

I'm afraid its not that simple hunter. As i see it, the only way to resolve this is for me to drive your car. No two ways about it.

 

sorry, wrong. Lag is definately an issue in drag racing....you would not believe the tricks the big thumper racers have to do in order to get their turbos to start spooling at the line. Did you know that to help make ANY boost with that big of a turbo at the lights those cars run DUAL REAR CALIPERS? You are correct that efficiency CAN be higher in a single setup because the larger single turbos have larger wheels and the larger wheels are more efficient while producing air thus creating denser air and in the end more hp BUT they are bigger and you have to make them spool. Also, one of the main reasons why no one allows twin turbos in the big classes is because they are afraid of the power they make.


it may fit better but it is not more simple...it may fit more simple but a twin setup is never more simple. You have two turbos, two wastegates, 2 downpipes, 2 etc

That isn't true, a T76 (standard with a Q-trim wheel and not the newer more efficient GT-Q wheel) can produce 90lb/min. with a single T76 and a built motor you can make 1000hp

dont put TOO much thought into compressor maps....what kind of boost curve do you want?

Hunter [/B][/QUOTE]

 

My thinking single vs twin... What do you personally like. I have twins and am kind of looking at the other side of the fence with a single but since i already have all the pieces for using the pair of turbos might as well leave well enough alone. Do I see a liking for either one NO. I have run a single and a twin Personally the single (although only a t-72 q) was a blast and spool up was very quick. The thing i see though with all this is this. IF you are going to run a thumper you don't care about down low in revs you are focusing on a set power band (rpms where you are in power) You focus your drivetrain to take effect of this so it helps out your turbo choices if it is too big (wanting that last ounce of power) With the use of a v8 powered car for what we are talking about in all effect your not going to go below prob 3k and in 90% of the cases not going to go over 7k. You will have enough exhaust volume to really blast the turbo into boost.

Why not just do a boost controller setup like many have and prob what porsche did to wastegate the turbos. I have set this up on my system using my boost controller.


I usually agree with you but on this one I do not. Most of the guys run manuals (one has a pg that i know of in a stang but most of the big thumpers run manuals) They use a two step of some sort to cut the ignition and wammo instant boost. I did it with my system a long time ago and it was wonderful with a manaul and turbo. Leave the line with whatever wastegated boost you have. The reasons they have dual calipers is they are trying to stop a car from 200+mph that weights over 3k, some are using carbon disks as well which don't work that great till they are heated up as well.
If you are having a turbo built (whichever size you are going to be able to get parts fairly easy. I would honestly rather a custom turbo from a reputable shop (Limit Engineering or Innovative Turbo) They will be able to service your needs down the road if you have a problem.

Steven

 

what about the twin turbo idea with 2 different sized turbos for a longer powerband?

 

I don't know of any kits that are in production- even for the supra, which stock comes w/ a sequential setup. Its very complicated, http://www.mkiv.com/manual/manualtt/...ion/index.html go throught that and you'll see what i mean.

Also what's a shame is how many supra guys run in TTC (true twin) to avoid the power drop around 5k RPM when #2 comes online.

-Mike

 

quote:
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I usually agree with you but on this one I do not. Most of the guys run manuals (one has a pg that i know of in a stang but most of the big thumpers run manuals) They use a two step of some sort to cut the ignition and wammo instant boost. I did it with my system a long time ago and it was wonderful with a manaul and turbo. Leave the line with whatever wastegated boost you have. The reasons they have dual calipers is they are trying to stop a car from 200+mph that weights over 3k, some are using carbon disks as well which don't work that great till they are heated up as well.



I have to agree with him and disagree with you, unfortunately. I'm one of those big thumper mustang racers now. At least in the Street Outlaw classes where manual tranny's are not legal, we use dual rear calipers not for the braking ability, but so we can spool up. We'll use a 3 step slaved to the brake pedal set at 2500-3000rpm. We'll get up on the brakes hard(even going so far as to pump the brakes up 7 or 8 times after the burnout) before pulling into the prestage beam and slowly roll into the throttle until we're foot to the floor with the motor bouncing off the 3 step. Then we'll ease up pressure on the brakes to slowly creap forward into the beams. As soon as we see both stage lites lit, we'll hit the transbrake button and we're already at 13-15psi. We go to crazy lengths to build boost, since we don't see any til 5000rpm with the big 91's and 101s.

 

I appologize then for my comments then im wrong thanks for clearing it up guys

 

im glad noslix started posting here.......looks like he will have some interesting input for us

 

Im not much of a drag racer myself, so I stand corrected on the drag racing knowledge.

I still think that using two more common turbos will be easier to repair and replace than a larger one, mainly beacuse I can buy a GT25 or GT30 on ebay for 500 bucks as opposed to a GT47 for 1500. But I can see in some cases where its more practical to use a single turbo.

As for packaging, yes you need to of everything, but in a way it makes it more simple to create and fit, if you keep everyting symetrical. Right now im creating my intake plumbing, and thats probably the only part for me thats been harder than a single turbo setup. The headers were very easy to create, downpipes and all other exhaust pieces worked like magic.

Ya compressor maps arent all they cracked up to be, but my boost curve will have bout 20 psi at 2700-3000 rpms, which is what I want.

Another reason for the two turbos is later I plan on looking at a closed loop system where 4 cylinders feed into a turbo and this turbo feeds those 4 clyinders with a seperate intake manifold from the other 4. I really dont know if this will give any benefits, but I wanna try it and see what happens.

Hunter

 

Talked to a few people about this once (hogans racing and some others) keeping the sides split does not show gains actually losses in some cases. I was going to do this on my motor but for a turbo setup they said to make a single plennum.

Steven

 

Thanks for the insight on that, I never really heard anyting about that kinda setup until I saw it used on a twin turbo v6 talon, but the guy hadn't tested to see what was better, he just built it that way because it fit better or something...

but thanks for the insight, saved me some money..lol

Hunter