Help me choose a turbo for my 200 I6 please

6

66Comet

New member
Please help me figure out what turbo is the best to suite my current application and future needs, I am on the learning curve so please be considerate of my ignorance. I want to learn and experiment with a turbo on my stock setup but spend money once in the proper direction for a built motor if possible.

stock 200ci out of a 1978 fairmont with the flat log head (roughly 60K miles)
or I could swap the head from the above motor to my
stock 200ci out of a 1966 mercury comet (125K miles), I think it might be better to just swap the fairmont motor in completely.

Below I followed the example on Garret Turbos website (http://www.turbobygarrett.com/turbobyga ... ch103.html) on how to calculate Air Flow Actual and Pressure Ratio to find the proper turbo using the turbo map. Do the following calculations look right? Is my volumetric efficiency even 85%? This all seems like a huge guess. To be honest since I am boosting my stock motor for now I only expect 180-200HP flywheel at best but I want to buy a turbo that I could use down the road in a few years when I do a full motor build. Am I wrong in doing this, how will this affect my performance only using 1/3 of the potential of the turbo (probably 6-8psi)?

Volumetric Efficiency 0.85 %
Horsepower Target (flywheel) 460 HP
Engine Displacement 200 CI
Maximum RPM 5000 RPM
Temperature
Barometric Pressure
Intake Manifold Temperature 130 F (100-130 average)
Brake Specific Fuel Consumption (BSFC) 0.55 (0.50-0.60 or higher)
Air/Fuel Ratio 11

Wa = HP * A/F * BSFC/60
Wa = 46.383

Wa = Airflow actual (lb/min)
HP = Horsepower Target (flywheel)
A/F = Air/Fuel Ratio
BSFC/60 = conversion to minutes

MAPreq = (Wa * R * (HP + Tm))/(VE * N/2 * Vd)
MAPreq = 41.184 psia

Boost = MAPreq - 14.7 psia (at sea level)
Boost = 26.484 psig


MAPreq = Manifold Absolute Pressure (psia) required to meet the horsepower target
R = Gas Constant = 639.6
Tm = Intake Manifold Temperature (degrees F)
VE = Volumetric Efficiency
N = Engine Speed (RPM)
Vd = engine displacement (cubic inches, convert from liters to CI by multiplying by 61.02, ex. 2.0 liters * 61.02 = 122 CI)


P2c = MAP + delta P loss
P2c = 43.184 psia

P2c = Compressor Discharge Pressure (psia)
MAP = Manifold Absolute Pressure (psia)
delta P loss = Pressure loss between the compressor and the manifold (psi) (avg 2psi)


P1c = Pamb - Delta P loss
P1c = 13.7 psia (at sea level)


P1c = Compressor inlet pressure (psia)
Pamb = Ambient air pressure (psia)
delta P loss = Pressure loss due to air filter/piping (psi) (avg 2psi)


Pressure Ratio = P2c / P1c
Pressure Ratio = 3.152




Also I notice that if I had a 250ci motor like the others it tremendously drops my boost down to 18psi which sounds right according to the results we have seen by others. But if I punch in 200HP in the formula with my 200ci motor I get negative boost and the only way I see to correct this is to drop by efficiency down to 40% (0.40)? Maybe the 200 motor is just not feasably going to work with 460hp and I should be aiming at building a 250ci block for the future motor swap which then makes buying the proper turbo now not possible with the CI change. Possibly a cheap $180 ebay turbo for now if this is the case, let me know what you guys think.
 
I should probably also mention that I am going for low to mid range response for drive-ability, this will be a spirited driven street machine and will not see the track very often.
 
low to mid-range response and a 400+hp 3.2 liter may not fit in the same sentence.

A friend has a 2.5L which makes an easy 350whp with an HX35/40, goes great above 5krpm, below that it is as slow as its N/A equivalent.

I like holset turbos. For 200hp and FAST spooling try finding an HX25 or HX30 (the turbine flanges are different). The HX25 is what I run on my 1.9L MGB, makes 180whp at 11psi, starts to spool around 2300rpm and is all in about 2700rpm.

For something to go into boost in the mid to low 2krpm range try an HY35 or HE351CW(the VE will work if you can rig a VNT controller up).

I briefly ran an HY35w with an 8cm turbine on a 300, would start to spool about 12-1300rpm and by 1500rpm would make 10psi. This is too small for me.

For 450 to 500 hp try the HX35 (7blade compressor). This is what I run on the EFI 300. Starts to spool at 1800rpm and is at 6ish psi by 2200rpm. The HX35 has a divided turbine scroll, I am not using a pulse paired manifold. If you use a pulse paired manifold the spool time will come down a good deal.
 
Turbo_B":20g6bl5x said:
low to mid-range response and a 400+hp 3.2 liter may not fit in the same sentence.

A friend has a 2.5L which makes an easy 350whp with an HX35/40, goes great above 5krpm, below that it is as slow as its N/A equivalent.

I like holset turbos. For 200hp and FAST spooling try finding an HX25 or HX30 (the turbine flanges are different). The HX25 is what I run on my 1.9L MGB, makes 180whp at 11psi, starts to spool around 2300rpm and is all in about 2700rpm.

For something to go into boost in the mid to low 2krpm range try an HY35 or HE351CW(the VE will work if you can rig a VNT controller up).

I briefly ran an HY35w with an 8cm turbine on a 300, would start to spool about 12-1300rpm and by 1500rpm would make 10psi. This is too small for me.

For 450 to 500 hp try the HX35 (7blade compressor). This is what I run on the EFI 300. Starts to spool at 1800rpm and is at 6ish psi by 2200rpm. The HX35 has a divided turbine scroll, I am not using a pulse paired manifold. If you use a pulse paired manifold the spool time will come down a good deal.
Click to expand...
Also I see you said HX35 on your friends that was only good above 5K, I assume that is the non 7 blade compressor?

Are you saying that I could run the HX35 at low boost 6-8lbs on my stock motor for now and when I build the motor could use the same turbo to boost up to 18lbs and make the higher end hp numbers?

Is the HY35w too small because you want more than 10psi? or is there some down side to hitting max boost early and riding the max boost all the way to rev limit? I assume that would be what people call over working the turbo?
 
Holset turbos come from diesel engines, the HX35 in its stock environment runs around 20psi and will go over 30.

The 7blade compressor is the latest rev and flows the most. The 8 blade is still good but only expect a high 400 to low 500 number from it.

Understand that for a turbo to spin it must impose some form of an exhaust restriction, the sooner you need the turbo to spin the greater the restriction on the exhaust.

Without VNT it is very hard to get low end power and big top end numbers.
 
Turbo_B":36rc3php said:
Holset turbos come from diesel engines, the HX35 in its stock environment runs around 20psi and will go over 30.

The 7blade compressor is the latest rev and flows the most. The 8 blade is still good but only expect a high 400 to low 500 number from it.

Understand that for a turbo to spin it must impose some form of an exhaust restriction, the sooner you need the turbo to spin the greater the restriction on the exhaust.

Without VNT it is very hard to get low end power and big top end numbers.
Click to expand...

I did do some looking last night and saw it was popular on the dodge truck diesel engines. Although I had problems trying to find a good place to purchase these, I was mostly looking at what kind of availability and pricing there was, any suggestions?

I had not heard of VNT yet, pretty cool idea to adjust the inlet of the turbine wheel.

I am not sure that you answered my question "Are you saying that I could run the HX35 at low boost 6-8lbs on my stock motor for now and when I build the motor could use the same turbo to boost up to 18lbs and make the higher end hp numbers?"

What I am taking away from what you are saying is that the HX35 7 blade will work well on my stock motor as it spools early and will make my initial boost goals mid range rpm for now? and can make the kind of high boost I might want on a built motor later? Or maybe you are saying that at 5K I might not hit 18lbs+ of boost?

Just trying to clarify on if this is best suited for my stock motor now but will not be a good match later or if this might work well for me now and down the road.
 
66Comet":s18w2fra said:
I am not sure that you answered my question.
Click to expand...


I provided you with personal experiences and a range of applications, you must figure out what works for your application. [/post]
 
Turbo_B":3rbij5na said:
I provided you with personal experiences and a range of applications, you must figure out what works for your application. [/post]
Click to expand...


Thanks, I guess all you can do is look at the map, get some close comparisons from people and just choose one and see how it works for your application. Thanks for your help.
 
The HX35 appears to be the same as the HX35W except the W has the wastegate? I'm not sure that its 7 blade or not. Still trying to track down a HX35 7 blade, maybe junkyards are a better bet than online?

Still looking for other opinions from others turbo experiences, want to get some other ideas before I make my decision final.
 
HX35 is a good sized turbo. Maybe a HY35 for a little quicker spool at the expense of top end. You should be able to find used ones for cheap. Your 200 horsepower goal is easily reachable, you'll probably have 300 ft/lbs of torque at that horsepower level too.

If cost is no object, Garrett GT-series (some variant of GT35 would be best) are the way to go. Ball-bearing, fast spooling, lots of trick parts. They're much more modern than the Holsets, more efficient, more expensive.
 
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