Twincharging advice 1

[jbond]

Hi,

I am currently rebuilding my 3litre turbocharged engine and am looking into the possibility of twincharging it. I'd appreciate some guidance, because I'm an electrical engineer and not an automotive engineer but I have read the thread titled "twincharging estimated results" from back in Jan '07 and learnt what I could from it.

My final goal is for a nice flat torque curve with boost building up early and holding up till near red-line which is about 7500rpm. Let's say intended boost is 30psig, which is 3PR (pressure ratio) and the turbo will boost 2PR and the supercharger following the turbo is boosting 1.5PR.
If I only have room for 1 intercooler, should I place it after the TC or after the SC? I am guessing after the SC but I am wondering what will happen to the SC if the incoming air is really hot? Do I have to worry about the SC overheating? The type of SC I would be looking at is an Eaton M62 or M90.
And what about the compression ratio? Will it be ok (at 8.5:1) for the extra boosting or do I have to reduce it further?

Displacement - 3L - 183CID
Valves - 4 per cylinder - 2I and 2O (mentioned here for VE% estimates)
Configuration - V6
Engine Displacement per Revolution - 1.5L - 92CID
Required SC Displacement per Revolution - 1.5*1.5L = 2.25L - 1.5*92CID = 138CID
Bore-stroke is an over-square type at 87mm x 83mm with the compression ratio adjusted at 8.5:1.
More information on the engine data is available at the following link:

http://www.amztech.net/pages.php?vid=13

M62 Blurb:
In the middle of Eaton's supercharger family, the M62 displaces 1.035 liters and is suitable for the majority of engines between 2.2 and 3.5 liters. As such, the M62 is the ideal choice for passenger cars, SUVs and light trucks around the world.
Displacement: 1.035 Liters
Max. Outlet Pressure: 2.0 Bar
Max Speed Cont (inst.): 14,000 (16,000)
Flow at Max. Speed @ 1.8 Bar: 810 cubic meters / hour

M90 Blurb:
A workhorse of the Eaton supercharger group, the high-performance M90 is an ideal complement to engines ranging from 3.5 to 4.0 litres. It's smooth operation and silky power delivery make it ideal both for performance vehicles and luxury sedans.
Displacement: 1.484 Liter
Max Outlet Pressure: 2.0 Bar
Max. Speed Cont (inst.): 12,000 (14,000)
Flow at Max. Speed @ 1.8 Bar: 1135 cubic meters / hour

This means that running the M62 will require it to be 2.18 (2.25L/1.03L)ratio overdriven.
If this SC is overdriven at 2.18 ratio, then at 7500 engine rpm the SC will be spinning at 16.35 krpm, which is greater than the recommended 14krpm continuous and the 16krpm instantaneous speed limits.

Running the M90 will require it to be 1.52 (2.25L/1.484L) ratio overdriven.
If this SC is overdriven at 1.52 ratio, then at 7500 engine rpm the SC will be spinning at 11.4 krpm, which is less than the 12krpm continuous speed limit rating, so it should be ok by my understanding. Have I done my sums right? And am I understanding this correctly? (I don't know much about SC)

At the below link, is a graph that illustrates air flow in a similar sized engine (the 3L mitsubishi GTO) as a function of boost pressure and rpm.

http://www.stealth316.com/images/gt42-56trim-jlspec.gif

Unfortunately, the bottom axis is in CFM, but if you look at the original Garrett compressor map then you can get a good idea of the lb/min that corresponds appropriately:

http://www.turbobygarrett.com/turbo.../Turbochargers/gt42_images/451888_9comp_e.gif

The importance of this graph, is that it shows the amount of airflow that I can expect in my engine at a given boost level and a given rpm. Sizing for max rpm (let's say 8krpm) and at 3PR equates to about 70lb/min. Does this mean that I need to find a compressor map that will flow 70lb/min at 2PR (the engine will be flowing 70lb/min at 3PR but the turbo will see that same flow and be boosting it to 2PR only)? Or at such high rpm will the SC be out of it's efficiency region, and I'm better off bypassing it with a wastegate and utilising the TC to boost it up to 3PR (the turbo is at a higher efficiency typically at the higher PR for the given flowrate on the compressor map if the turbo isn't too big).

To double check this figure, at 8krpm and at 3PR there should be 8000*3*92 = 2'208'000 cubic inches of air per minute and air density in pounds per cubic inch is 0.0761/1728 which gives an air flow of 97.2 lb/min which is neglecting the expected declining volumetric efficiency at that high rpm. The graph of the GTO engine assumed 85% VE and when that is multiplied by the 97.2 figure then the result is 82.5 lb/min. So which is correct? I will presume 82 lb/min at 8k rpm is correct, please advise me if I am making a mistake.

The GT4202R - 774595-8 Garrett Turbo flows 75 lb/min at 2PR - this is close enough and would be perfect for 7.5krpm. Info on this turbo can be found here:

http://www.turbobygarrett.com/turbobygarrett/catelog/Turbochargers/GT42/GT4202R_774595_8.html

If bypassing the SC, so the TC is producing the 3PR of boost, then the GT4094R > 751470-19 Garrett Turbo flows 75 lb/min at 3PR nicely, and since this is a smaller turbo it would be easier to fit in my engine bay that is already short on space. Turbo info can be found here:

http://www.turbobygarrett.com/turbobygarrett/catelog/Turbochargers/GT40/GT4094R_751470-19.htm

The GT4094R comes with turbine housing option of 1.19 A/R. Any thoughts on whether or not this will be sufficient? It seems to flow up to 37lb/min before the backpressure starts rising (looking at the turbine map - but I never really know how to read these). I'm guessing that after 37lb/min then backpressure starts rising and could end up being larger than the 3PR charge air pressure? This means that the TC wastegate would be relieving 38lb/min (75-37) of air?

I've probably already exceeded my quota of allowable number of questions in a single post, but please be patient I'm learning!
I appreciate all of your guidance, and if my above understanding is correct, then my next step is looking for space in an already cramped engine bay for a big GT4094R turbo and a SC.

Cheers,
Matt.

 

[Lou Scannon]

I don't have any answers for you but I will point out that a compression ratio of 1.5 will result in a pressure ratio greater than 1.5, due to temperature increase.

 

[JOHNDOE333]

I currently have the M62 Eaton on my factory supercharged Nissan Frontier. I am disappointed that the unit was not intercooled like the M110 on the Lightning. I am unsure if a sandwich style air to water intercooler is included with the M90 or not (in production models that is). I believe I was making 9 pounds of boost stock with a mechanical compression ratio of 8.9 to 1. I replaced the 2.700 diameter supercharger pulley for a 2.400 and gained 2 pounds of boost for a total of 11. The blower rpm prior to the swap I believe was around 14K at 5,900 engine RPM. Afterwards I believe that number climbed to around 16K. I monitored the knock sensor and saw no issues with premium fuel. However, the power did drop off a little after driving around for a while. Which I blame on the loss of density from the rather warm blower and myself for being so ignorant that I thought I could get away with that amount of boost on a non-intercooled vehicle with almost 9 to 1 compression and a standard flow cooling system in Texas weather. Just food for thought on blower selection. I personally would go with the M90 and turn it slower. Not to mention the M62 has a press on pulley and the M90 is bolt on I think.

Good Day

 

[wgknestrick]

I cannot even begin to imagine how you are going to fit all of your "plans" into any engine bay that would fit your V6. Just fitting the turbo plumbing including EWG(s) is going to difficult. V6s aren't easy to turbo with a big single to begin with because of the difficulty in merging the 2 manifold banks.

The GT42 would be way too big to use in a twin charging system on that engine. You can make 800whp with that turbo alone. The GT40R is a much better choice, but you are still in the 650-700whp range with that depending on exhaust housing (go for the 1.06 A/R). This is without SC too.

Problem in the end is going to be that you can't really beat a turbo only system in either peak HP or power band. The turbo system will come on a little later, but will still have 3-4K of RPM to play with. It will be easier to tune, and probably run better when it is all said and done.

You are going to sacrifice too much efficiency trying to fit that SC in. It is always best to pick one power-adder and do that very well.

 

[j2bprometheus]

jbond-

I don't know what the peak cylinder pressure capability of your engine is but I would guess this:

If boost reached 30 psig, the peak cylinder pressure would be too high and engine damage / failure would happen very quickly.

This might not be a big problem if you plan on racing this engine and re-building it frequently.

Gasoline engines typically have low peak cylinder pressure capability compared to diesels. Example: GM bragged that its inline six cylinder gasoline engine could handle peak cylinder pressures up to 1000 psia. Diesel engines that I have worked with typically have peak cylinder pressure capability between 2000 psia & 3000 psia.

 

[JOHNDOE333]

I would imagine based on the work JBond is putting into his project that he plans on running a properly built long block to handle such boost pressures...I hope. For instance a good high expansion/low silicon content 2618 aluminum alloy forged piston, ductile iron top compression ring with plenty of end gap, heads studs, copper head gaskets, o-ringed block or heads, etc. etc. Not to mention decent lower end parts. Sounds like he is going to build a full out race set-up.

Good Day,

 

[jbond]

Just some extra background to what I included (engine-wise) in my first post, here is a wiki blurb on the block:

The VG engine family consists of V6 piston engines designed and produced by Nissan for several vehicles in the Nissan lineup. The VG series started in 1983 becoming Japan's first mass produced V6 engine. VG engines displace between 2.0 L and 3.3 L and feature an iron block and aluminum head. The early VG30 featured SOHC, 12 valve heads. A later revision featured a slightly different block, and DOHC, 24 valve heads with Nissan's own version of variable valve timing for increased high RPM efficiency. The block is a particularly strong design with a single piece main bearing cap, and is capable of reliably supporting more than 1000hp. The production blocks and production head castings were used successfully in the Nissan GTP ZX-Turbo and NPT-90 race cars which won the IMSA GT Championship three years in a row.


It comes stock with a crank girdle, which I believe is rare on a production car? More common on race engines...

My rebuild material list:
ARP head and main bolts
JWT R5 Cams (R5 VG30DE(TT) CAM SET 90-95 RACE 272/.385" 229@.050"+4 DEG ADV ON EX LC.)
JWT heavy duty valve springs to suit R5 Cams
Bronze valve guides
Stock valves and lifters - no head flow portwork, just port matching the intake plenums etc
Greddy heavy duty timing belt
Commetic MLS head gasket
ACL race series head and main bearings
ACL race series hyperlight forged pistons (low silicon content, 347grams piston and 90grams pin, top ring is steel nitrided)
SCAT rods (4340 chrome moly rated 180hp each)




but like I said, i'm electrical (engineer) not automotive - so any suggestions for improvement are greatly welcomed!

 

[hyperformancevw]

it would be pointless to twincharge that engine. we have built a 350z with a greddy twin turbo set up. it uses two mitsubishi 18g turbos with a very simple internal wastegate. the kit was a bolt on procedure and we modified the tune slightly with the supplied e-manage software. the car could produce 5psi at around 2800rpm and made 482whp on only 12psi. the engine was built with quality rods and pistons and the fueling was the only thing holding the car back. boost came on silky smooth and fast. i would think a similar style set up would be ideal for your engine. an alternative would be a garrett gt25 turbo. two gt25 turbos can support 500whp and should spool in the 2500rpm range. not to mention ease of installation on a "v" configured engine. what power level are you shooting for? a useable 500whp car is a rocket on the street.

 

[hyperformancevw]

is this installed in a 300zx?

 

[dgallup]

350Z uses the VQ engine series as do most current model Nissans & Infinities.

 

[hyperformancevw]

yes i know i was just using it for reference because it has the same general layout and dynamics as the VG engine series and it is the same brand.

 

[hyperformancevw]

with two ball bearing turbos like the gt25 on the VG engine you should see boost not much over 2000 rpms and it will be plenty capable of 500whp. twincharging the engine would see boost maybe a few hundred rpm sooner. on a performance vehicle, how often does it really see below 2000 rpm? seems like it would be an engineering nightmare on a compact "V" configured engine and the end result would be dissaponting. i agree with wgknestrick that you should just pick one power adder and do that well and on a V6 the obvious choice for a usable engine would be twin turbo.

 

[patprimmer]

With a Roots blower you see FULL boost at idle speed WOT depending on manifold volume, normally within one or two turns of the engine.

This gives much more rapid throttle response to even the quickest turbo reaction time.

Whether or not this is necessary is down to the application and the preference of the driver.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[hyperformancevw]

i dont see when you would need 20psi below 2000 rpm. i have driven many roots blower vehicles including a kenne bell svt cobra and to make FULL boost, it takes a few hundred rpm. it would make 10psi just after throttle tip in, but wouldnt make the full 18psi untill 1800rpm.

 

[XXXLR8R]

How much expansion pressure energy would be sacrificed by mounting a pair of quick-spooling Holsets onto the collectors of an 8L V-10's long-tube SS headers, as opposed to the common (and more efficient) practice of mounting the turbine housing within inches - instead of feet - of the exhaust ports?

We shouldn't need to make more than 10psi with this scheme.

TIA

 

[Lou Scannon]

The Wright R-3350 Turbocompound aircraft engine featured blowdown turbines for exhaust energy recovery that had the advantage of minimizing any increase in exhaust backpressure.
Any scheme to capture exhaust blowdown energy without imposing significant backpressure generally requires a dedicated design, e.g. pulse converter.