Twin Turbo thoughts and ideas..

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Mats
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Re: Twin Turbo thoughts and ideas..

Post by Mats » Wed May 12, 2010 2:15 am

la_strega_nera wrote:
GarthW wrote: Ben-yeah they go single because there straight six engines...a V6 is simply better suited to a twin i think.

Nice pis mate, very nice fabrication. 8)

Ok, thanks for the help y'all. I'm gonna keep single configuration, and if that dont do it, i'm going japanese, nuff said...i want big power lol.

Think i may be well wasting my time with old alfas...
They go a single because a good modern single is very responsive, and a darn sight cheaper than buying two decent smaller turbos...
Not to mention the packaging nightmare with two turbos on the same side of the engine.
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Re: Twin Turbo thoughts and ideas..

Post by Zamani » Wed May 12, 2010 12:57 pm

What can I get away with in a 3.0 with big overlap cams and 10.5:1 static compression? I'd be happy with 275 bhp for, low boost 7000 rpm engine. Will 0.5 bar boost with water injection and intercooling be possible? Single turbo of course. Don't mind if the boost comes in a little later. Not looking for big fat torque curve. I want to mimic a 3.5L NA engine without opening up the engine :) . If not possible, I'll just wait for my 24V to be ready.
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Re: Twin Turbo thoughts and ideas..

Post by xrad » Wed May 12, 2010 3:03 pm

Zamani...not sure I understand your post completely above..but for turbo boost, I think you want to avoid any major cam overlap...
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Re: Twin Turbo thoughts and ideas..

Post by la_strega_nera » Thu May 13, 2010 5:37 pm

GarthW wrote: Think i'll do it up abit more, and simply enjoy it. 8)
Correct answer :)
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Re: Twin Turbo thoughts and ideas..

Post by GarthW » Thu May 13, 2010 10:51 pm

Hey Zamani, i dont see why it should be a problem...i remember years ago they were saying you could never turbocharge a bridgeported rotary engine, where nowadays it is being done..and huge overlap there. :o

By all means do abit more homework, but should be ok i believe?

Cheers Ben. :wink:
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Re: Twin Turbo thoughts and ideas..

Post by kevin » Fri Nov 23, 2012 12:33 pm

Some Pics of two GTV that have been tested at the garage at the track . Very neat work . Owner of the one is ex member of this board . Maybe he might surface . Their has been big effort here in strenghtenning the transaxle box. The TT with normal exhausts is a road car.
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Re: Twin Turbo thoughts and ideas..

Post by Duk » Sat Nov 24, 2012 12:38 am

Seeing as how Kevin gave this thread a bit of a jump start, I'll add some recent learnings and observations to sticking turbo's onto engine 8) .

Most of a turbo charger's response will come from achieving 2 simple things: Keeping every single aspect of turbo plumbing volume down while maintaining high outright flows!
To a degree, a case in point is the Nissan Skyline GTR RB26DETT engines. From the original RB26 in the R32 GTRs to the last of them in the R34 GTR, the engine stayed basically the same. Same bore, stroke, conrod length, compression ratio etc!
And while the power always stayed at the Japanese agreed 208KW, the torque curve of the R34 is substantially broader (much more low RPM torque) than the torque curve of the R32 and R33's.
What is obvious is the changes in exhaust manifold and turbine housing design. The RB26 engines all used Garrett T/GT25 based turbo's and exhaust manifolds to suit. But when you look at the R34 turbine housings and and exhaust manifolds, while they used T25 flange patterns, the R34 turbine housings actually use smaller turbine housing inlets (about 12% smaller looking at the R34 GTR turbo on my desk) with the outlet of the exhaust manifolds made to suit!
If you give this some critical thought, you can see the true benefit of this.
According to Hugh McInnes's book on turbo charging (yeah it's old, but still has plenty of relevant information), exhaust gas exhaust gas speed out of an average exhaust port will need to be increased in velocity by between 3 and 4 times! But if you look at the average merge collector in a turbo exhaust manifold, you will see that there is a sudden increase in cross sectional area where the exhaust ports all join together.
That increase in cross sectional area will cause the exhaust gasses to slow and loose energy. That energy loss could have been applied too the turbine wheel and then too the compressor wheel!

Think about this, a twin turbo 60* V6 or a twin turbo inline 6 will have 240 crankshaft degrees between exhaust events within each exhaust manifold! So with such a large gap between firing events, why would you want an exhaust manifold and turbine housing design that allows the exhaust gasses to slow down via a large increase in cross section area around the collector and turbine housing inlet, only to then try and get them to speed back up through as they are pushed into the turbine housing's nozzle???
If you look at turbo'd Audi's of the last 15 years or so, you wouldn't!

A/R (Area/Radius; Garrett) Ratios/Nozzle Cross Sectional Area (cm2; Mitsubishi):
As mentioned, the job of the turbine housing is to increase the exhaust gas speed so the it is fast enough to spin the turbine fast enough to make the (comparatively) small compressor wheel spin fast enough so that it can pump more air than what the engine would otherwise use.
IE: Generate boost pressure!
The smaller the turbine housing's A/R ratio or cross sectional area number, the more the nozzle narrows around the inside of the turbine housing, the greater the increase in exhaust gas speed.
The trouble is, with small nozzle area, while they will increase the gas speeds of relatively low flow levels of exhaust gasses, as outright exhaust gas flow increases, the turbine housing will start to choke and the engine will start too push against ever increasing amounts of back pressure. This will result in a huge increase in exhaust gas temperature (and all of its associated problems) and pumping losses!
The waste gate, however, provides a path of least resistance for the exhaust gasses! :D And so long as the wastegate's flow isn't exceeded, can provide MUCH need relief for the pre turbine exhaust gasses while still maintaining high average exhaust gas speeds.
In a nut shell and very simplistic, use a small A/R ratio/small cross sectional area turbine housing and a decently large wastegate. Audi have done the exact same for 15+ years and their low RPM torque numbers are legendary!

Exhaust Runner Diameter:
Until recently, I would have suggested making sure your exhaust runners were the same diameter as your exhaust ports. Most people will swear black and blue that making sure you exhaust ports flow really well is an absolute must, when adding a turbo or 2 too your engine! And to a degree, they are right. But maintaining as high an average exhaust gas speed is critical to achieving excellent turbine wheel (and so boost pressure) response!
Again, why allow the exhaust gasses to speed up and slow down only to then speed them up again as they are pushed into the turbine housing?
Blatantly pilfered from the http://www.toymods.org.au/forums/tech-conversions/ of which I am a member, http://www.toymods.org.au/forums/tech-c ... ifold.html has an excellent example of the effectiveness of providing well flowing, small diameter exhaust runners and how they effect the torque and power characteristics of an engine!
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Re: Twin Turbo thoughts and ideas..

Post by Giuliettaevo2 » Sat Nov 24, 2012 2:49 am

but the small A/R will give better spool up and better trque low in the rev range. but it will also give back pressure and higher intake temps at higher revs and limit max power... :? it all depends on what you want from the engine...

R34 also used the ceramic turbine wheels which shatter if you up the boost over 1.0-1.2 bar...

The thing we learned over the years is that the mapping makes all the difference between a succesfull build and a lousy build.

Personally i like the turbo's to come in with a kick so you really know you're driving a turbocar. :mrgreen:
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Re: Twin Turbo thoughts and ideas..

Post by Duk » Sat Nov 24, 2012 2:54 am

Giuliettaevo2 wrote:but the small A/R will give better spool up and better trque low in the rev range. but it will also give back pressure and higher intake temps at higher revs and limit max power... :? it all depends on what you want from the engine...

R34 also used the ceramic turbine wheels which shatter if you up the boost over 1.0-1.2 bar...

The thing we learned over the years is that the mapping makes all the difference between a succesfull build and a lousy build.

Personally i like the turbo's to come in with a kick so you really know you're driving a turbocar. :mrgreen:
Small A/R ratios will give fast response, then you use a bigger than normal wastegate to bleed off pre turbine housing back pressure.

No ceramic turbine wheels in the R34 GTR turbos.
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Re: Twin Turbo thoughts and ideas..

Post by Giuliettaevo2 » Sat Nov 24, 2012 7:33 am

Duk wrote:Small A/R ratios will give fast response, then you use a bigger than normal wastegate to bleed off pre turbine housing back pressure.

No ceramic turbine wheels in the R34 GTR turbos.
The R34 also has the ceramic wheel.. here you can see a nice little movie about them. :wink:

A friend of mine owned an R34 GT-R and he replaced the original turbo's for a big single. Original turbo's had the ceramic wheels fitted.

Using a bigger wastegate to let out the extra pressure is not so good an idea in my book. :? That would be a waste of energy that could also be used to drive a bigger compressor wheel... :)
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Re: Twin Turbo thoughts and ideas..

Post by kevin » Sat Nov 24, 2012 10:09 am

The owner of the mid mount 155 tt learnt the hard way on this subject with manifold design and pressure . With the 24v motor in the back they had to make the manifolds longer in order for the turbos to fit in front of the the roll cage brace . BUT not only were they longer they made them with 45 mm pipe not 41mm . The result was diabolical , it simply took forever to spool up . Lesson learned quickly . Good article DUK
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Re: Twin Turbo thoughts and ideas..

Post by Duk » Sat Nov 24, 2012 11:06 am

Giuliettaevo2 wrote: The R34 also has the ceramic wheel.. here you can see a nice little movie about them. :wink:


D'Oh! But I'll wait and see............

Giuliettaevo2 wrote:Using a bigger wastegate to let out the extra pressure is not so good an idea in my book. :? That would be a waste of energy that could also be used to drive a bigger compressor wheel... :)
If you have a good balance between wastegate size and A/R ratio, then a larger than standard wastegate can be used to keep pre turbine pressure under control. As I mentioned before, this is how Audi have done it for years and their engines have awesome low RPM torque numbers. The R34's have more low RPM torque than the R32 and R33 because Nissan finally started to get their heads around the required sizes of exhaust runners, collectors and turbine housings. Exhaust ports were still too big, though.

Kevin, your friend with the 155 should have been using 35mm pipe and no bigger. 32mm would work better again.
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Re: Twin Turbo thoughts and ideas..

Post by Mats » Sun Nov 25, 2012 5:57 am

Giuliettaevo2 wrote: Personally i like the turbo's to come in with a kick so you really know you're driving a turbocar. :mrgreen:
Yes, a knee at 3500 rpm thatlets you know that the gates of hell has opened... :twisted:
Also, you don't get that strangled feeling over 6000 rpm (or even 5000rpm in some cars), I really dislike when you kind of drive into this invisible wall.
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Post by SydneyJules » Wed Nov 28, 2012 4:44 am

Yeah but that torque hit in a transaxle will only last for a limited time frame, as we all know!

That kind of torque hit is fine if you haven't got enough traction, so keep the tyres skinny!

Garth, I reckon keep the single, get one made up, get your pipes coated after you've welded a new flange on, and try and be as efficient with what you've got.

The beauty of a 2.5 (or a 2.0) under boost is, you can probably creep up on the torque limit that will break the transaxle (because this is what's going to twist your donuts into oblivion- the reason why I haven't ever run into issues revving mine to 8- there's no massive torque hit).

I reckon with a boosted 3.0, you're going to hit that wall heaps sooner. The oversquare 2.5 will be a bit gentler, and just as quick. That's my plan, anyway-

Just enough power NOT to break the whole thing!
Fixing it bit by bit....
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Re: Twin Turbo thoughts and ideas..

Post by Mats » Wed Nov 28, 2012 5:48 am

In the world of physics, that torque "hit" is just a slow ramp up in torque, it won't add any hammer effect or anything like that. The gears will spin several complete revolutions during the ramp so nothing like a clutch dump or similar.

I think we need to define what we mean by response as well, for me it's the time between steady state driving along and until the boost starts rising when you floor it INSIDE the working rev range of the turbo. Personally I don't care much for turbo installations that are designed for trailer towing, i.e. Comes in at 1500rpm and starts hauling untill 5000rpm.
People who do care for such installations however, always seem to think that response is a rpm number where the turbo actually start to produce boost. I have never understood this. Might be interesting for a daily driver for people who do a lot of overtaking without down shifts but for us who actually use the gearbox it's quite useless as far as response go... 8)

Now, as far as for slowing down exhaus gas and losing energy, the big marine diesels in ships are designed with large exhaust chambers between the exhaust port and turbo to slow down the gasses as much as possible and remove pressure pulses as this is better for the turbo efficiency. Sure it's a completely different installation but my point is that if it was bad for the efficiency to slow down tje gasses and then speed them back up again they wold never have done it on ships where every fraction of a percent efficiency means a lot of money in fuel cost.
The exhaust gasses may slow down, but the pressure goes up!
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GTV 2000 -77 - Died in the fire.
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