V6 Twin Turbo - Turbo sizing.

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Postby Lith » Fri Jan 11, 2008 2:57 pm

RedMist wrote:There is possibly one more thing to consider. If I'm not compeditive, which I doubt, I'll decompress the engine, run a new transaxle, and upsize the turbos...
So far I'm considering
TD04H-15g
TD05-14g
T25


Is there any specific reason you aren't going with a single turbo setup? In some ways I could imagine (being you are running with a V6) its for simplicity but in other ways it could make it more complex (ie boost control etc). I figure you will need custom manifolds etc anyway.... with a single you only need one oil/water feed/return made up which could help quite a bit.

The other bonus is a single turbo is cheaper to buy and potentially easier to replace, and probably more support/understanding. For the power level you are going for a single GT30R or something of that sort would be insanely responsive, and if you got greedy you'd be able to turn the boost up and/or go a bigger turbo with minimal changes. Just throwing ideas out there...
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Postby RedMist » Fri Jan 11, 2008 3:21 pm

The fuel cell is directly infront of the engine. THe only way to intercool it is to run a cooler in each of the sidepods. In addition I dont know if I can run a pipe over the top of the transaxle yet, and until the car lands I wont.

I like the symmetry of the twin system and I had thought that a twin setup of small turbos was more responsive.
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Postby barryogen » Fri Jan 11, 2008 3:57 pm

RedMist wrote:I had thought that a twin setup of small turbos was more responsive.


As I understand it, you are right.

two smaller turbines should take less time to spool up than a single larger one of the same capacity... no doubt there will be downsides too it aswell, complexity would be one major one, cost would probably be another, but I'm not aware of any others, but those two are fairly big ones that would explain why OEMs don't do it..
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Postby IH8TEC » Fri Jan 11, 2008 4:44 pm

i wouldn't necessarily agree with that. you'd split the cc's to run a small turbo each would pretty much be the same as running one bigger one with full 3.5L

regards boost control, me or barry have NO spiking whatsoever, which is why i run it, running 25psi i dont want any spikes as it's critical it doesn't, barry runs 30 with no spikes. very good form of control 8) regards the difference, as long as the manifolds were pretty much same length etc, i can't see it being much of a problem.
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Postby barryogen » Fri Jan 11, 2008 4:52 pm

IH8TEC wrote:i wouldn't necessarily agree with that. you'd split the cc's to run a small turbo each would pretty much be the same as running one bigger one with full 3.5L


Think of the turbines as flywheels, two smaller ones take less energy to get up to speed than a single larger wheel... something about torque on an axis, or distance from centre of torque application... the physics eludes me at present.
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Postby IH8TEC » Fri Jan 11, 2008 4:58 pm

then think you have alot more torque (using your discription) spinning one bigger one. being such a high compression, high litreage motor (3.5L) it's not gonna have much effect, you could spool a t70 easy enough with that setup. but he doesn't need that much power. mate has a trust t78 on a 3L with alot lower compression and gets 20psi (500hp at the rear wheels) by like 3000ish rpm

your spinning a bigger turbine that is probably the same or slightly bigger than the two small ones together. i recon it would be better, but if you can't physically work the piping for a single turbo, then it doesn't matter
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Postby Adamal » Fri Jan 11, 2008 5:25 pm

Its more the lag with the gear changes.
Change gear, plant foot, no response until the turbo spools up past the boost threshold, where it starts providing enough air flow to counter-act its parasitic effect.

Smaller ones are going to reduce this as there is less mass to spool, therefore giving better response time after changes. Downside is that if you go too small, it'll be restrictive and won't supply power all the way through to the redline, it'll drop off early.

I remember when I had to drive my mates Familia GTX to work for him to take it to get scrutineered. Being from a long liniage of N/A engines, it was quite a weird feeling.
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Postby IH8TEC » Fri Jan 11, 2008 5:30 pm

but what i'm trying to say isn't it really a similar mass,

ie mass of two small turbos = same as one bigger one?
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Postby Lith » Fri Jan 11, 2008 6:56 pm

Gah I never answered that question as its a hotly debated thing. I sit on the fence about it at this stage, but I think its a bit random that people convince themselves that two smaller masses on an axis are better than one bigger one? It will need the same amount of force to accelerate anyway!! It would apply if you only had to accelerate one of the turbos, yes - but then you have half the equivalent flow.

THEN you have double the frictional force to contend with, two cores...

The MAIN advantage I can think of is the ability to better focus exhaust pulses to turbine wheel when using smaller pulses, ie - if you have a small motor with big turbo. That gets made completely redundant when you use an equivalent bigger single turbo with a twin scroll housing and properly designed manifold however.

The twins vs. single stereo type imho came from when most big singles were terrible plain bearing truck turbo things, these days people know more and there is better technology.
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Postby RedMist » Fri Jan 11, 2008 8:10 pm

Out of curiousity, how do the Toyota turbos compare?
The CT20b or the CT12a? I, like everyone else, am having problems finding compressor maps.
The only advantage I have for using the CT20b is I'm already running one in my ST205 rally car, have another spare. However considering its reasonably laggy in the ST205 road car I doubt two of them spool well on the VQ.
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Postby Adamal » Fri Jan 11, 2008 8:56 pm

They may be suitable for the VQ though. Are you keeping the standard cam setup? The CVVT system produces good flow throughout the whole rev range, whereas the 3S doesn't have any kind of VVT at all.
See if you can find a dyno of a 350Z, torque curve is flat as!

I think it could help in spooling, despite the capacity towards each turbo (1750cc per bank) being smaller than the 3S's 2 litres. My guess is you'd get a similar throttle response.
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Postby RedMist » Fri Jan 11, 2008 9:16 pm

I've seen many a dyno of the VQ and some of the twin turbo VQ conversions. And indeed they are very flat. The VQ definately one of the strongest 3.5 V6's I studied, hence the purchase.
Yes the stock variable intake system will be retained. NZEFI have experimented with a Toyota VVTi and gotten huge mid end gains with it. (although with minimal mods my 20v vvt torque curves didnt intersect at all)

Its a pity there isnt any compressor maps released for the TOyota turbos. I really cant compare these turbos against anything like the GT25.
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Postby Lith » Fri Jan 11, 2008 11:02 pm

RedMist wrote:Out of curiousity, how do the Toyota turbos compare?
The CT20b or the CT12a? I, like everyone else, am having problems finding compressor maps.
The only advantage I have for using the CT20b is I'm already running one in my ST205 rally car, have another spare. However considering its reasonably laggy in the ST205 road car I doubt two of them spool well on the VQ.


In my opinion you'd be on the right track assuming they'd not spool well on the VQ35. I don't think too much of the Toyota turbos myself, especially if you are going to be going for ~450hp - if I understand correctly people swap the stock 2JZ twins for a single GT3582R and find no loss in response.

If you are going antilag then I'd maybe consider the cheapest strongest turbos you can find... you'll potentially need to consider them as a regular rebuild item doing that.
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Postby strx7 » Sat Jan 12, 2008 8:54 am

Lith wrote:If you are going antilag then I'd maybe consider the cheapest strongest turbos you can find... you'll potentially need to consider them as a regular rebuild item doing that.


Thats one of the advantages of the TD04/TD05 mitsi turbos, a) pysically size wise, they'll flow more power than most if not all other turbo types (why steve murch loves them) b) dime a dozen to get hold of the turbo's themselves and rebuild kits etc. c) we all know they can take anti-lag.
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Postby Lith » Sat Jan 12, 2008 10:25 am

strx7 wrote:Thats one of the advantages of the TD04/TD05 mitsi turbos, a) pysically size wise, they'll flow more power than most if not all other turbo types (why steve murch loves them) b) dime a dozen to get hold of the turbo's themselves and rebuild kits etc. c) we all know they can take anti-lag.


Don't agree with the last one, though I can't say I've compared turbos on antilag haha. The only people I do know who have run it have destroyed TD04s and 5s though. +1 on the cheap to rebuild TD series turbo, though. They also can spool exceptionally well for what they flow.

Main reason I wasn't focussing on them earlier is RedMist said he wanted a ball bearing turbo, but then the focus on cost started coming up and everything on his shortlist was plain bearing so I figure thats been overruled haha.
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Postby Paulio » Sat Jan 12, 2008 10:43 am

dualcharge with a GT30 :twisted:
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Postby RedMist » Sat Jan 12, 2008 11:00 am

Lith wrote:
strx7 wrote:Main reason I wasn't focussing on them earlier is RedMist said he wanted a ball bearing turbo, but then the focus on cost started coming up and everything on his shortlist was plain bearing so I figure thats been overruled haha.


True, but there are advantages to having a plain bearing turbo... first on the list is they are cheaper! and the TD05 is so stupidly cheap. Its just a matter of getting a pair of 14g's, which dont appear to be that popular, or possibly a TD05H-16g (small wheel) . And... if I decompress, a nice pair of 20g's would strap on well.
The greddy twin turbo kit uses a pair of 18g's but from what I can tell they appear to be a bit big for the stock compression engine. The dyno curve is no where near as flat as that of the APS kit with a pair of GT25's. And the Jim Wolf kit, a pair of Garrett Sport-530's.
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Postby RedMist » Sat Jan 12, 2008 1:31 pm

I've come full circle.

On spending many many hours reading reviews on twin turbo kits for the VQ35 and studying compressor maps for many more hours, I think I'm probably better off keeping the status quo and going Garrett GT2554R.
Beautiful turbo, just need to ensure I get the right amount of oil to it and drain it properly. Which may be an issue if the offroader is cantered at a 45 degree angle for an extended peroid of time.

Now all I need is to find a place that can do me two turbos, flanges, gaskets for a good price.
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Postby barryogen » Mon Jan 14, 2008 9:21 am

RedMist wrote:Now all I need is to find a place that can do me two turbos, flanges, gaskets for a good price.


I believe that we have a sponsors section for that very reason :)
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Postby JustinSpiderholden » Mon Jan 14, 2008 9:46 am

Hey

Try horsepowerinabox.com, have had a lot of friends buy turbo's from them seem to be very reasonabke, and shipping is very quick
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