Rover v8 3.9 Twin Turbo Build - Turbo Selection

stirlsilver · Post by **stirlsilver** » Wed Dec 26, 2012 12:14 pm

Hello everyone, it has been some time since I have used this forum now. However, I'm in a position where I would like a reality check on my work of selecting a turbo.

Note: I have checked through all the posts in the Forced induction section, i've seen that subaru turbos are a good option.

For anyones curiosity, the build thread is here (now 28 pages long!!):
http://www.aulro.com/afvb/projects-tuto ... oject.html

For the purposes of this question what I am trying to build is:
Engine: Rover 3.9L
Target Power: 300hp
Number of Turbos: 2
Fuel: LPG
Transmission: Automatic
Car Use: 4wd - Need boost early to improve low down torque

The process I have taken in sizing the turbos is as follows:

On the garrett website, I used their boost adviser application:
http://www.turbobygarrett.com/turbobygarrett/webadviser

And used the following inputs:
Power target: 300hp
Engine Displacement: 241cu.in
Twin Turbo
Air/Fuel Ratio: 15.5:1
BSFC: 0.42 (is this reasonable for a RV8?)
Valves per cylinder: 2
Volumetric Efficiency: 0.80
Mid Range RPM: 3500
Peak Power RPM: 5000
Type of intercooler used: None (I will use an intercooler but don't know the specs at this stage, so this should be worst case scenario)
Pressure: 14.7
Air Temp: 21

For the above inputs I'm given the following results (Mid Range; Max Power):
Power: 208hp ; 298hp
Boost Pressure: 15psi; 15psi
Pressure Ratio: 2.02; 2.02
Intake Manifold Temperature: 231degF; 231 degF
Corrected Air Flow: 11.36lb/min; 16.24lb/min
Torque at Crank: 313lb/ft; 3131lb/ft

Recommended turbos:
GT1548 - Compressor efficiency is too low, so not considered
GT2052 - 52 Trim - This one looks the best to me.
GT2052 - 50 Trim
GT2052 - 48 Trim

In my hours of searching the internet for information, I came across this calculator:
http://www.squirrelpf.com/turbocalc/index.php

To avoid typing all the information in again, below is a screen capture of the calculator:

One entry not shown in the screen capture is where is shows that 2 turbos are selected.

With the information entered above, the following are entries i'm not 100% confident on:
BSFC - As I mentioned above, is 0.42 reasonable??
Volumetric efficiency - The values for peak power and redline were scaled according to the torque curve of a dyno result I found on the internet. Apparently VE is proportional to torque. Anything below peak power I just left as 80%
Intake Temp - These are the defaults. If I enter 231degF for max power and red line (from the garrett calculator) the required boost pressure jumps to 20.6psi!

Below are the curves produced by this calculator for turbos that I think I can possibly get hold of relatively easily (should the info I input be correct!):

Garrett GT2052

I think the Saab 9.3 Linear uses a GT2052ELS, however some places seem to say GT2082ELS?

TD04H-13T

As far as I know Subaru imprezas use the TD04L-13T. Hopefully the TD04H abd TD04L have the same curve!

It would be great to get any input on the turbo's i've narrowed down on!!

Thanks in advance!
Stirling

UPDATE
Shortly after posting this, I found out the following on the Mitsubishi turbos:
http://team-rs.ru/technical/images/TD04_turbos.pdf

Model code explanation:
TD04H-13T-6
TD04 - Turbo family
H - Shaft & wheel designation
13T - Compressor wheel designation
6 - Turbine housing A/R

Looking through the document:
TD04H - Inducer 52mm Exducer 44mm
TD04 - Inducer 47.2 Exducer 40
TD04HL - Inducer 52 Exducer 45.6
TD04L - Inducer 46.8 Exducer 41.2

So that means that chart I put up is not for the subaru!

Jono FD3 · Post by **Jono FD3** » Wed Dec 26, 2012 1:43 pm

I would have said that cramming in 15psi of boost through a 3.9 would give you alot more than 300hp..... I have seen somwhere on here that, that sort of presure would put it close to 400hp!!!
VI would be higher than that with a turbo I'd of thought (not sure what the engine is in stock form) and slapping a monster IC on there would be a massive bonus to performance..... I'm seeing inlet temps of 3c above ambient air temp in my RX so reading a figure of 230f is a little alarming as that is over 110C.... that would need to come down to 70c MAX I would say, but the lower the better!

I'm thinking about doing this aswell, but need to dyno my 3.5 to set it up properly before I head down this path as it's a bit of cash to get this set up properly... but I was looking at using twin Impreza TD04L's and aiming for just over 300 pushing about 8psi.

Eliot · Post by **Eliot** » Thu Dec 27, 2012 9:42 am

Regarding the calculator - i'm not understanding the inlet temperature field. I would of thought you specifiy the ambient inlet temp and it would calculate the resulting outlet temp. I do like how it plots the compressor maps automaticly for you, I remember spending hours doing it manually.

I see it has an entry for i/c loss, but no further details on i/c or even a request for the ambient.
If i put in a requested BHP of 300, i get a boost pressure of around 7psi - which is about what i would expect a low boost setup should give on a 3.9 v8.
As suggested, 14 psi of boost would be 350-400 bhp, but you will need forged pistons, lower compression ratio (8.5-9), good head bolts, gaskets and ideally supporting breathing mods (heads,cam, inlet, trumpets, plenum etc)

Always use an intercooler - even on low boost setups. Use air to air if you can physically fit it in.

Given that a scooby is a 2L engine, I'm not suprised that two of those turbo's will suit your 4L engine.

Here's my storry of a TT setup - albeit on a chevy rather than a weedy rova..

http://www.mez.co.uk/turbo1.html

stirlsilver · Post by **stirlsilver** » Thu Dec 27, 2012 1:33 pm

Jono
Thanks for the feedback, I went back and revisited the garrett boost advisor (shown below), but this time I enabled an intercooler of 70% efficiency (which I am not sure yet what a 70% efficient intercooler means). When I was playing around earlier, it obviously made a big difference.

Also, the BSFC numbers I seem to have used look like they are very optimistic. So I should dial that up as well (using info from http://www.land-and-sea.com/dyno-tech-t ... g_bsfc.htm as a reference). The updated inputs and outputs are below.

Eliot
It's interesting you have come across this post. I've actually read through your information already as it is very relevant for what I am doing, and you documented it very very well. If you look on the earlier Aulro link you will see that I was even using your excel sheet

Regarding the squirrel calculator, I'd say the only place it accounts for the intercooler is in the pressure drop of it, and it leaves it up to the user to input the expected post intercooler temperatures.

I plan to use two top mounted intercoolers which I will weld onto either side of the standard rover plenum and have each turbo feeding each side. I'll then add thermal insulators to the plenum connections and also remove the coolant circuit from making contact with the plenum to make it as cool as possible.

Anyway, back to calculations:

Below are the Inputs:
Power target: 300hp
Engine Displacement: 241cu.in
Twin Turbo
Air/Fuel Ratio: 15.5:1
BSFC: 0.45
Valves per cylinder: 2
Volumetric Efficiency: 0.80
Mid Range RPM: 3500
Peak Power RPM: 5000
Type of intercooler used: Air/Air
Pressure Drop: 1psi
intercooler effectiveness: 70%
Pressure: 14.7
Air Temp: 21

For the above inputs I'm given the following results (Mid Range; Max Power):
Power: 209hp ; 299hp
Boost Pressure: 11.75psi; 11.75psi
Pressure Ratio: 1.87; 1.87
Intake Manifold Temperature: 112degF; 112 degF
Corrected Air Flow: 12.23lb/min; 17.48lb/min
Torque at Crank: 314lb/ft; 314lb/ft

The pressures are still coming out to be very high...Part of what is killing me here (and I didn't realise before) is that LPG is working against me here. The reasons it works against me is:

LPG uses more volume than petrol - Reduces Volumetric Efficiency, i read somewhere that it is around 4%! which I haven't shown in this calculation.
Air to Fuel Ratio - LPG is about 15.5:1 (Petrol is about 14.7:1). Since the calculation of actual flow rate is HP x A/F x BSFC/60 it is easy to see that for LPG you need more air. However, 15.5/14.7 = 1.05 which is pretty negligible.

So perhaps I'm using the wrong BSFC, but I don't think the Rover v8 engines are particularly efficient. Looking at that BSFC link I gave earlier it says:
4-stroke (high compression, closed loop) - 0.35 @ Peak Torque
4-stroke (turbocharged, closed loop) - 0.45 @ Peak Torque (this is the value I used)

Running the calculator again with a BSFC of 0.35 the Boost adviser gives 5.25psi. Maybe a turbo charged Rover v8 runs somewhere around 0.40 BSFC (which gives 8.5psi)?? It's all guess work now

Anyway, the reality of the matter is that it doesn't change the turbo selection.

One thing that is a concern for me however, is that I want to keep the engine at 10.5:1 CR. If I boost it to 8psi, that means the effective CR is 10.5 x 1.65 = 17.3:1 CR. As far as I know, LPG can only really go as far as 15:1. Is this assessment correct or have I missed something when calculating the effective CR?

Thanks in advance guys

Jono FD3 · Post by **Jono FD3** » Thu Dec 27, 2012 4:01 pm

Any turbo charged engine has a CR of less than 9.5 (ish) and that is engines that are designed to take boost, but NA engines you need to drop it slightly further, especialy an old design engine! 9.2:1 normaly allows you to run up to 10psi boost pressure, any more than that you are going to suffer with detenation and smashed pistons (unless you fit forged) then you can run 15psi or there abouts!

Basicaly if you want it to last, you need the CR droped to about 9:1 or you will be needing a bucket to clear the road of rover bits!

JP. · Post by **JP.** » Thu Dec 27, 2012 4:18 pm

Forget Garrett calculator.
Squirrel get you there http://www.squirrelpf.com/turbocalc/

If you do the math right you don't need an intercooler. Just finished a turbo project which is intercoolerless. Have a nice intake charge temp at 42' celcius with an outside temperature at 18' celcius.
( Ford 2.6 V6 with custom build Garrett T3 55 @7psi)

Measure is to know, get yourself an Intake Air Temperature gauge which can be found for just a few quit on eBay and then you'll know if you need an intercooler.

As the Rover engines are all alloy you can forget the basic rules of how much boost you can run on e certain compression ratio. These basic rules are all about cast iron boat ancors.
In basic 9.5cr + 10psi wont do you harm, just get your stuff right ( ignition boost retard, fuel pressure & fuel mixture ).

Jono FD3 · Post by **Jono FD3** » Thu Dec 27, 2012 7:07 pm

Although 42c isn't over the top, if you compair the difference between 42c and 21c with a cooler it's a no brainer..... you get a better charge of air in to the chambers which means more fuel can be added, resulting in more bang for the same pressure, and lets face it 7psi is very low pressure and as the pressure increases so does the charge temps

so if you were to run yours at 1 bar (twice what you have at the moment) you will see temps sky rocket and end up destroying your engine as a result!
Trust me on this one, I've been there, done that and seen the results 1st hand, as a result I will always run an IC on a turbo setup, and the biggest unit I can physicaly fit in the space!

Also could I ask, why do you think alloy is more forgiving with boost compaired to cast? it's well documented that you can turbo a cast block more easily due to the strength..... but the main thing is the combusion chambers, which are all steel apart from those stupid nikasil coated alloy bored engine which tend to eat themselves after a period of time!!

Eliot · Post by **Eliot** » Thu Dec 27, 2012 8:33 pm

I agree - and as i stated above, fit an intercooler if you possibly can.
On my build thread i initially ran without one for about a week! - I was seeing 60'c inlet temps on a low boost system. Low inlet temperatures gives you a nice safety cushion - which should allow you to run moderate boost levels (<10psi) on a bone stock engine.
Hot day will see inlet temps in the high 20's and manifold temps will be over 80'c
Best setup is an intercooler placed at the front of the car - anything else is less than ideal. Even subaru bin the top mounted i/c in favour of a fmic on their world rally cars.

stirlsilver · Post by **stirlsilver** » Fri Dec 28, 2012 9:18 am

Jono FD3 wrote: Any turbo charged engine has a CR of less than 9.5 (ish) and that is engines that are designed to take boost, but NA engines you need to drop it slightly further, especialy an old design engine! 9.2:1 normaly allows you to run up to 10psi boost pressure

Thanks for the info. Is this for a petrol engine or a LPG engine?

What i'm finding confusing is that say petrol has a N/A CR limit of 11 and LPG 15. On say a nissan skyline which has a CR of 8.2, the stock engine is boosted to 10psi (and people tweak them to go higher) which gives an effective CR of 13.8. How can this work?? And then if it does work, then engine boosted on LPG should be able to go beyond 15:1?

JP. wrote: Have a nice intake charge temp at 42' celcius with an outside temperature at 18' celcius.
( Ford 2.6 V6 with custom build Garrett T3 55 @7psi)

Just for my info, what is your engine's CR and what fuel are you running on this setup? As far as I know increasing air temperature lowers the CR before detonation so this might give me some insight into my issue.

JP. wrote: In basic 9.5cr + 10psi wont do you harm, just get your stuff right ( ignition boost retard, fuel pressure & fuel mixture ).

If this is for a petrol engine, then assuming the octane differences between fuels 10.5cr + 10psi boost should work?

Jono FD3 wrote: Trust me on this one, I've been there, done that and seen the results 1st hand, as a result I will always run an IC on a turbo setup, and the biggest unit I can physicaly fit in the space!

I will be running an intercooler, i'll have to with thermo fans since this is a 4wd and will not always be moving quickly.

Eliot wrote: Best setup is an intercooler placed at the front of the car - anything else is less than ideal. Even subaru bin the top mounted i/c in favour of a fmic on their world rally cars.

The reason I want to go top mounted is due limit the amount of muck that would go through it. On a 4wd there is dust & mud which will quickly block it up and make it useless. By having it on top at least it has less exposure. The drawback is the heat rising up off the engine.

chodjinn · Post by **chodjinn** » Sun Dec 30, 2012 7:37 pm

When I had my 3.9TT, it ran about 10psi and had approx 320-330bhp. It did have stage 3 heads and a cam in it as well tho. Turbos were big rotomasters, approx T4 sized, but the turbos available nowadays are much better. ARP bolts are a must!

thewedgeshop.com · Post by **thewedgeshop.com** » Thu Jan 17, 2013 9:30 pm

Here is what I am running on a 3.5lt Single Turbo RV8 setup. Seems to run nice, boost is full by like 3100. I plan on running it up to 15psi with water injection come the spring time. No dyno time yet, hopefully soon.

Turbo ( Running 11psi )
Garret to4e 60 trim .58 A/R O trim T4 exhaust housing w/ 3 in Vband outlet
1 PTE 46mm external wastegate (3psi spring)
1 Tial 50mm BOV (6 psi spring)
Intercooler Core Size 11"X12"X3" Overall Size 18"x12"x3" 2.5" Inlet & Outlet 3" Core
Extreme Velocity Polished 4150 Carb Hat

Full specs are here.

http://www.thewedgeshop.com/clints-coupe.html

Thanks
Clint
www.thewedgeshop.com