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Contemplating buying an already modified 993 turbo
What is the highest tech, most modern bolt on turbo option currently available for each required peak max flow rate? Talking about ‘97 993 Turbo with a manual transmission. I’ve heard stories of people swapping in a larger compressor wheel in the modified stock k16 housing, which makes a lot of sense to me for a hot toddies street car. Found stuff with search, just wondering what’s the latest and greatest.
Todd at protomotive is your answer. I have the k16’s with 16g billet wheels. They are enough to snap stock rods.
have you seen the rods in a stock 993 turbo? They are weak to say the least. Todd knows how to tune the car and pull the torque out of it as to not snap the rods.
I’m super close to getting my car running. I had protomotive build the motor with pauter rods, reliefs cut in the pistons and Todd’s new special web cams to keep the hydraulic lifter setup and get gt2evo grind. Check out the red car he has on instagram. That was motor #1 with the cams. I’m motor #2 with the same goodies. Gt2 oil pump, flame ringed, nitro ringed, heads welded, all the stuff to make over 1000hp. The xona turbos are on the red car. I know it made 700whp with stock intercooler.
What is a 16gxt compressor wheel? Would like to know more.
Turbo engines are usually easy on the rods, it's the naturally aspirated engines with high compression, high rpms, and heavy domed pistons that break rods. XT billet compressor wheel
Also, a clarification about the goals. I'd like to have everything to appear as stock as possible, but nevertheless hit about 550 Nm (about 400 ft-lbf) at as low rpm as possible and extent the torque curve flat at that level as high rpm as possible. I think stock 993 turbo hits 450 Nm at 2400 rpm, peaks at about 540 Nm at 4500 rpm, and falls again below 450 Nm at 6100 rpm. So let's say a theoretical goal could be perfectly flat torque curve at 550 Nm in the 2500-6800 rpm range and then holding the power constant for the 6800-7500 rpm band. Not saying I can do that, just saying that'd be nice.
Here are some questions that I'd like to hear people's answers and opinions on. I'm just thinking out loud and looking to start a conversation. Just killing time, there's no urgency here, but please chime in if you also would like to kill some time!
As a reminder, the background of these questions is trying to create an engine that is as close to stock as possible while hitting 550 Nm of torque as early as possible (2500 rpm?), extending it at a flat level all the way to 6800 rpm, and then holding the (about) 520hp crankshaft power level constant for the 6800-7500 rpm range. (520hp at the crank would require the compressor to flow about 24-30 lbs/min at high efficiency.)
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Has anyone measured the peak power pressure drop thru the stock air filter? I know that most tuners sell "performance" filters, but that's an easy high margin item to sell so they'd probably sell it even if there were no benefit. Or another way to ask the same question, what's the CFM rating of the stock air filter and the performance filter alternatives at say 1.5 inches of water (i.e., 0.37 kPa) pressure drop?
Next, the mass air flow sensor. I absolutely don't want to try to tune a turbo car with the MAF going out of range. Been there, done that, got the t-shirt. Does anyone have the factory specification document for the 993 stock MAF? There are really two separate issues I am interested in. The second first is the mass air flow (kg/h) at 5.0V MAF voltage that the ECU still considers a valid observation, how much mass air flow in kg/h at 5.0V, either empirically or based on factory spec documents? Alternatively, if someone has a data log from the dyno, about how much rwhp does the car make when the MAF voltage gits 5.0V? The second issue is the inherent maximum measurement range of the sensor at voltages above 5.0V, at which point does the voltage flatline (this usually happens way above 5.0V) in the most adverse temperature and humidity conditions?
At stock peak power (say 408hp of the base turbo model), how much vacuum does the low-pressure intake side pull at the compressor inlet? With the previous turbo project that I was involved with, we spent a huge amount of time diagnosing and solving this issue. In my personal opinion, if one can keep that pressure drop to the minimum, everything else downstream is easier. The problem, of course, is that it's physically challenging to do so in cramped engine bays.
What is the mass flow limit of the stock k16 turbo's compressor in the 993 turbo? From Pelican Parts, I read: K16/24 flow rate = approx. 27 lbs/min
k16/16g flow rate= approx. 35 lbs/min
k24/18g flow rate= approx. 40 lbs/min
If I understand correctly, the 16g is a Mitsubishi compressor wheel in expanded stock KKK K16 compressor housing. Does anyone have a compressor map for this wheel, either in custom k16/16g turbo or in it's native habitat? Is 16g the same as 16g-xt or is 16g-xt a more modern version? I can't seem to find a compressor map for 16g-xt to save my life, I worry that the compressor wheel is too large for my meager purposes. Then again, it might be exactly right if 28 lbs/min and 1.9x pressure ratio are highly efficient on that compressor map.
What's the injector duty cycle at the peak power for stock 933 turbo? How much room do the stock injectors have at the stock fuel pressure? What's the nominal flow rating of the stock injectors? I see some kits selling a 5.0bar fuel pressure regulator, how for does this take one in terms of fuel flow at say 85% duty cycle?
Camshafts:
- Where is the stock 993 turbo in terms of the camshaft specifications? What are the duration, lift, and the centerlines for intake and exhaust cams?
- Can the camshaft be easily advance and retarded while installed in the car? I understand that the LSA can't be adjusted.
- If one has to pass Euro-2 (1996) emission standards (with catalytic converters installed), how many degrees of camshaft overlap (at say 1mm or 0.05") and what kind of TDC lifts can one still accommodate in a 993 turbo and still pass the tailpipe test? (I am not talking about purely bureaucratic requirements here, nobody's going to cam doctor the cam at the inspection site.)
- If one were to run the 993 turbo camshafts in an otherwise normally aspirated engine, what would the torque curve look like?
- What's the rpm limit for the hydraulic lifters/adjusters with stock cams?
- If the idea is to [1] retain an acceptable idle, [2] sneak by emissions, [3] retain hydraulic lifters, [4] get the turbine to spool as early as possible (so early EVO and a lot of camshaft overlap), [5] extend the torque curve flat from 4800 to, say, 6800 (so more duration for both intake and exhaust), and [6] set the fuel cut at 7500 rpm, then what performance cams would one recommend?
I am looking at the piston shape and guessing that adding a second spark plug would be of only limited utility. This is in contrast to domed high compression pistons in normally aspirated engines. Agree/disagree?
What is the safe rpm limit for the completely stock 993 bottom end? It might be a lot higher than the factory stock redline, given the stock torque curve.
What oiling changes would one have to make for increased rpms and for increased thermal load form more power? What are the weak spots of the oiling system?
Are all the 993 turbo cylinder heads the same? Is there any variation in the exhaust port sizes? If so, which heads have the smallest exhaust ports? Nothing that I've read indicates that there would be any variation, but it doesn't hurt to ask. Does anyone have the stock exhaust port diameter at the flange?
The stock exhaust header between the cylinder head and the turbine inlet looks well conceived and durable. Are all the aftermarket header alternatives larger than the stock in inside diameter and do they all crack within the first year? (In the previous turbo project, we ended up prototype casting exhaust manifolds with tiny primaries for extreme durability and great spool.)
What fraction of the exhaust mass flow does the stock 993 K16 turbo pass thru the wastegate at peak power? Does the wastegate circuit have enough capacity to control the boost or will there be creep (especially with a free-flowing turboback exhaust)? Do people hand port the wastegate circuit (we've had to do that in other projects with free flowing turboback exhausts)? Are there any ways that the turbine side of the stock turbos can be improved easily, with the objective being spool at low rpms and low back pressure at high rpms?
How much turbine outlet back pressure does a completely stock 993 turbo have at peak power? What is considered the best aftermarket (or factory for that matter) turboback catted exhaust? Best being here the one that produces the lowest measured turbine outlet pressure at peak power while still maintaining an acceptable sound level and passing Euro-2 (1996) emissions (in a tail pipe test, I don't care about certifications)? In my personal experience with other cars, reducing the pressure and flow losses of the turboback exhaust is the easiest way to improve a factory turbo car -- is this also the case with 993 turbo? Here's a weird, model specific question: Does the distance of the cat from the turbine exit impact the rpm at which the turbine spools? I've seen something like this happen with other cars and I don't quite get it why -- it must have something to do with resonance tuning of the engine when the turbine is about to spool?
And the '97 and '98 Motronic computers are easier to program right? How granularly can they control the maximum boost allowed at each rpm?
Thanks for your attention and looking to learn more about 993 turbos!
There appears to be a lot of threads in the 993 turbo sites about “zero clearancing” compressors, which I take as meaning that the compressor wheel and compressor housing are set to clearance that is approximately equal to the worst-case turbo shaft bearing clearance. Has anyone measured the benefits from this process?
There’s a research paper on the benefits of reduced compressor clearances here:
The tip width is 4.28mm per this document (haven’t measured it myself). Quick math says that each 0.1mm of clearance reduction improves the compressor efficiency by 0.8 percentage points.
Yikes, too many questions.
Used to know some of the answers, my memory is fading.
Not sure if helpful but some tuners do use resistors on the stock maf to alter the 5v max.
5 bar fpr when using stock injectors seem to help or mask fueling problems for many tunes.
’Modified hybrid zero clearance turbos used to be the thing, k16/24 k24/26… various builders were a bit hush hush about exactly what they were using.
Many used off the shelf NA or RS cams.
hydraulic lifters are supposed to be very good and not limiting factor but many have gone/backdated to mechanical lifters
A quarter century is a long time, I'm late, I'm late, I'm so very late! Just bought a high-miles well maintained 993 Turbo, '97 by VIN and '96 by the first registration. It's not perfectly original so I might try to "improve" it a little bit...
In the 928 world, it's common to rescale the MAF sensor voltage signal to bring it back to the ECU 0-5V (or a bit higher in fact) readable range. This however is very risky for the Bosch MAF used in the 928 because the sensor voltage can suddenly flatline as a function of mass air flow at a mass air flow level that depends on temperature and humidity. It's a little dangerous to go far outside the manufacturer's spec with MAF scaling on a turbo car, in my opinion. For NA it's less of an issue, because throttle (and thus load) is pretty much on/off at high rpms.
You are certainly making a lot of power! What are you using for turboback exhaust? Do you happen to know how much turbine outlet back pressure stock 993 Turbo generates and whether the main restriction in the stock turboback exhaust is the cats, the piping, or the mufflers?
Originally Posted by Basal Skull
Yikes, too many questions.
Used to know some of the answers, my memory is fading.
Not sure if helpful but some tuners do use resistors on the stock maf to alter the 5v max.
5 bar fpr when using stock injectors seem to help or mask fueling problems for many tunes.
’Modified hybrid zero clearance turbos used to be the thing, k16/24 k24/26… various builders were a bit hush hush about exactly what they were using.
Many used off the shelf NA or RS cams.
hydraulic lifters are supposed to be very good and not limiting factor but many have gone/backdated to mechanical lifters
When the dyno was done I believe I had stock diy ‘improved’ heat exchangers (see pic in your other thread) was cat less (gutted stock cats) with ‘Roock’ mufflers.
When the dyno was done I believe I had stock diy ‘improved’ heat exchangers (see pic in your other thread) was cat less (gutted stock cats) with ‘Roock’ mufflers.
How much of a difference does/did gutting the cats make?
07-29-2022, 05:46 AM
Contemplating buying an already modified 993 turbo
