2871r/enthalpy what PSI for 300whp?

[spools420a]

Hey zilvia what psi would be recommended to make 300whp with this common setup of

redtop sr20
2871r - 64
z32 maf
550cc inj
freddy fmic
enthalpy ecu
91 oct and base timing program
basic bolt ons like
megan 3 inch test pipe
megan turbo elbow
mbc
though oem exhaust piping and muffler test pipe back.

[dorkidori_s13]

most of the posts ive seen about the GT2871R seem to point to 12-18psi to hit 300whp depending on modifications and tune. it seems like most folks were also running stage 1 or stage 2 cams with turbo to help the head breathe a bit better as well. i will be going with a GT2817R later this year to replace my aging (and leaking) S15 Spec-R turbo. im currently putting 260whp out in 91 octane at 14psi on the ol S15 spinny thang.

i think what may limit you is running the enthalpy ROM tune instead of a full stand alone which can be dyno tuned in real time... and possibly your injectors depending on how much duty cycle you have to push them toward in order to make the desired 300whp. usually when you start getting up in the 85-90% range, youll need to go with bigger injectors. i think my Tomei 740s are only in the 45-50% duty cycle range currently. im guessing yours at 300hp are going to be near the 80-90% range as they are quite a bit smaller.

[spooled240]

Originally Posted by spools420a

though oem exhaust piping and muffler test pipe back.

This is going to be a problem. On my KA turbo I was only able to get 8 psi of boost with the OEM cat-back even though the wastegate was set at 12psi. If you're set on a stock-looking muffler look at the 3" HKS sport.

With some mild cams and ~14 psi you should be at least close to your goal.

[xpinoyxmk]

I was on an enthalpy tune before the ecu burnt out. Never dyno'd to see what it was putting down but my setup didn't really change (z32 mafs to iat) after getting my Haltech and getting it tuned by Martin (owner/tuner of enthalpy). It put down 310whp.

gtx2867r @ 18psi
hks 740cc
93 oct

Hope this helps you out.

[inopsey]

it really depends on what brand of dyno you want to see 300whp on, and who tunes it/how agressive the tune is. on a dynojet, around 15psi, with a dyno dynamics closer to 20psi

[Kingtal0n]

Always use a dynojet, so you can compare with other cars.
Dynojet can't be fooled or tricked like other dynometers.

I've tuned maybe 20 or 30 of these, they always do like this:


make sure its below 11.8 and above 10.8 a/f ratio,
You really need some aftermarket low lift cams, like poncam 256, to take advantage of the sr20 head and keep boost low enough to be practical. always match sr cam to sr spring, i.e. tomei cam + tomei recommended spring.

Stock exhaust is fine up to 320rwhp in my experience, no issues using internal gate. You just need a quality boost controller like the profec B spec-II.
You can use the stock exhaust to 350 or 380rwhp if you know what you are doing, it requires an external gate and knowledge of exhaust gas pressure vs valve diameter

[Kingtal0n]

Oh your question... what psi? Lets look at the map


Looks like compressor outlet pressure of at least 1.8 pressure ratio will be desirable... so a minimum of 11.6psi off the compressor is a starting point.
Then we factor in pressure drop. Compressor wheel is a PUMP just like any pump it will produce what engineers call 'pump head' and everything after the compressor will take a chunk of that head, so for example, the bends in the pipe, the roughness of the pipe, the volume and length of the pipe, the intercooler, the throttle valve, the intake port/shape/design, the head/valve, all of that is considered an obstacle to the pump head and will reduce the effective flow and pressure of the turbocharger outlet.

To put it another way, everything after the compressor will cost power. That includes the bends, pipes, even the intercooler, all of those items will reduce pump head and therefore impose limitations to compressor flow rate downstream of the wheel.

Luckily the math is easy and quick to estimate... you don't need to think that hard. Just over estimate (use a conservative outlook)

If the compressor jams out 12psi and we lose 2 or 3psi from the pipes and intercooler etc... that leaves our intake manifold pressure at 9 or 10psi of boost pressure.

Looking back at the map, 12psi at the compressor wheel is good for maybe 37lb/min max flow rate. Minus mileage, friction, wear and tear, time, (being conservative) lets call it 35lb/min down the road and for the sake of reality is a max flow rate of that compressor near 12psi of outlet pressure (9 or 10psi intake manifold pressure).

35lb/min at reasonable temperature with typical gasoline fuels will net roughly 350bhp or around 300rwhp, maybe 290rwhp or 310rwhp, you know its not exact.

Now lets consider the engine displacement and see if these compressor goals match our engine flow rate,
2L Is 122 cubic inches so,
122*7000rpm/3456 = 247CFM
Now add boost and assume 95% Volumetric efficiency at 7000rpm,
Take out 5% VE: 247 * .95 = 234CFM
Add 12psi of boost to the intake manifold: (12/14.5) * 234CFM + 234CFM = 427CFM
Converter CFM to MASS by using typical air temperature conversion: 427CFM * .078 = 33.3lb/min
converter lb/min to bhp: 330bhp
converter bhp to rwhp (assume 12% drivetrain loss): 333 * .88 = 290rwhp

*note the constant I chose as .078 could be typical-anywhere from .068 or .085 depending on the air temperature which is reflected in the density of air. This is where it is critical to defer volume rate to mass flow rate.
Also Note that VE I chose at 95% could easily be 90% or 105% depending on the head and cam selection.
A stock camshaft at 6000 or 7000rpm would also be more near 70% or 80% perhaps.


So to answer your question with a 95% to 98% confidence interval of approaching 300rwhp using the posted compressor map, even in the face of reality, time, friction, usage, plumbing/piping/intercooling head loss, inefficient this and thats, you should see 11 to 13psi compressor outlet PRESSURE and approx 9 to 11 intake manifold PRESSURE to achieve your desired flow rate of 35lb/min (300rwhp) from a dynojet as a maximum output from that compressor wheel according to the map, using typical gasoline fuel and typical temperature (70-90*F Ambient & post intercooled w/ gasoline) If the engine has a cam upgrade which can achieve at least 95% VE at those posted RPM.

Couple caveats.
1. the compressor maps often more conservative than reality so some of those turbos might support more power than the map claims
2. Temperature has a massive effect, lower IAT can dramatically change the compressor wheel mass flow rate. This is because the compressor does not flow MASS it flows VOLUME rate, the reason the map is presented to us in MASS rate is because they have taken the liberty of assuming some specific temperature in their volume flow rate calculation which was then used to convert the map into a MASS rate for people to quickly tell at a glance what sort of power to expect. So you MUST consider that original temperature they used as a constant (and it is NEVER constant Temp in reality) when you are examining those compressor maps in terms of MASS flow rate.
For reference, The typical mass rate conversion is done using approx 90*F iirc air temperature, or something near that.
So for example if the ambient temp drops into the 50*F or something low like that, it will dramatically affect compressor mass-rate.

3. The compressor can only flow some volume rate as discussed in #2, but the caveat on top of that caveat is the fact that any air molecules LOST downstream of the compressor will cause imbalance of compressor/exhaust flow rate, the demand of the exhaust wheel is increasing based on however many air molecules are lost from the compressor. In other words, #3 says that if you are leaking boost, the exhaust gas pressure AND temperature will rapidly rise and destroy the engine. Thus you MUST ENSURE there are no boost leaks. You MUST PRESSURE TEST the entire system from the compressor wheel to the engine before running boost pressure or you WILL probably Destroy the engine.

4. Stock exhaust... and stock cam will both limit engine VE severely. SO many more intake manifold pressure (PSI) will be required to achieve these numbers. I would say 20% to 35% extra PSI to achieve the same rwhp using those stock components. Figure 18psi or 22psi might be required.
Luckily, pressure in PSI at the intake manifold is not so important... for a few reasons.
A. the intake and head on these engines is made of metal, so high Pressure cannot explode those parts (like an LS1 intake manifold would)
B. 15psi or 18psi or 22psi is negligible compared to the 800psi or 1000psi of combustion pressure... so it does NOT reflect in the reliability of the engine's internals, the fuel quality cares only about the TEMPERATURE and ultimate COMPRESSION (800psi~), not the 'beginning pressure' of 20 or 30psi or whatever.
C. The compressor map dictates efficiency and we can see that after 12+ PSI of outlet pressure, the efficiency only gets better and better. SO in reality we are better off using MORE pressure in PSI, as required or as by engine flow rate allows.
D. The intercooler ability to cool air is more dependent on the total mass of air rather than the volume. In other words, if the engine VE suffers and more PSI of boost is required, the outlet temp of the compressor is increasing rapidly, however an intercooler can effectively cool the same mass-rate of air similarly, reduced density due to high air temp means a larger volume of airflow per unit time, as each molecule of air is more spread apart from it's partners the (heat) energy may be more effectively extracted per unit volume as well (it is faster and easier to cool a high temp low density air volume than it is to cool a very dense high temp air volume, i.e. pressure does NOT directly control density by itself). Thus we may rate intercoolers in terms of 'potential power' and their pressure drops as 'potential volume flow rate' separately. So while pressure drop is increasing with additional volume flow rate of expanded air due to high temperature input, our compressor potential flow rate always has the final say in whether that pressure drop influence can limit engine power... up until, of course, some physical law limitation such as the velocity of air approaching the speed of sound for example, or at the influence of turbulence.

[LoSt180]

My new goal in life is it actually understand the math & theory in that post.

[Kingtal0n]

Originally Posted by LoSt180

My new goal in life is it actually understand the math & theory in that post.

It might seem like 'alot' because I wrote alot to give a full picture,

but in truth the math is not even college level, its intermediate algebra only...

so the math isn't the issue, I am sure anybody can do it.

The theory is a little more involved but still pretty simple,

text wall
The engine is a air pump, and so is the turbo. both displace some exact amount of air per revolution in a perfect world. We simply find those numbers using classical formula and compare them, and because the manufacturer of the turbo provides a compressor map which correlates air volume flow rate to air temperature (the islands on the map are efficiency which is basically air temp, center is coolest) we can make safe assumptions about the total mass flow potential of the running engine at some compressor flow rate by making sure it appears on the map somewhere and hasn't run off the edge on either side.

*more info*
There is some minor fluid mechanics, but it is basic. You must understand the volume flow rate from a device, and how this is different from fluid mass flow rate. Air is a fluid. Air mass is derived from knowing volume flow rate AND air temperature. All intercooler abilities and ambient air temperatures and turbo efficiency will always vary, there will always be some unrealistic approaches to these sort of problems, which means we have to look at several distinct "worst and best case" scenarios when attempting this sort of calculations.

*VE*
The other necessary aspect is engine volumetric efficiency and how it compares to engine flow rate in volume flow and mass flow. A cylinder filled 100% with fresh incoming air is considered 100% VE, but this can happen at 0rpm, 2rpm, 2000rpm, 5000rpm, etc... which means an engine flow rate is independent from VE, which means power output has nothing to do with VE by itself, you MUST combine VE to some engine RPM or somehow derive a mass flow rate to get power output figures from an engine.

Another variable is the amount of airflow pulled into the exhaust system during overlap, which adds to mass flow rate overall (it will tax turbo flow rate a little bit) and may help achieve a high 100% VE by doing so. This additional flow rate must be accounted for because the compressor flow rate is sensitive to all losses, whether they are boost leaks or exhaust overlap leaks it will tax the compressor and raise the exhaust gas pressure and temperature. A large boost leak can destroy an engine by raising the EGT and EGP because of this simple fact and it happens all the time.

And yet another issue is debatable... can a cylinder fill more than 100% full? Can you achieve 101%+ VE? It is common to use VE values over 100% (when say, tuning an engine) When dealing with forced induction since we are technically filling cylinders beyond 100% full... and yet that doesn't quite make logical approach since nothing can be more than 100% of anything. This brings a slew of questions to the table... how much of the 100% of cylinder fill is exhaust gas, and does exhaust gas count as VE? There is always some exhaust gas present even if its just 0.01% so technically VE can never truly be 100% for any engine, as it is impossible to remove every single exhaust gas molecule between events. Next, Naturally aspirated engines can fill a cylinder beyond 100% VE by utilizing the kinetic energy of incoming air, timed to the overlap period perfectly with the right valve events, causing 102% or 105% VE and bumping torque slightly beyond what should be possible. But a cylinder can only be 100% full, right? So how do we account for this additional VE without using nonsense numbers beyond 100%. The answer is in the air density, and in order to compare VE numbers beyond or near 100% we must set that density in our equations to some standard or relative to a known value. It is commonly accepted that atmospheric pressure and temperature is the derived air density from which 100% VE can be derived. In other words, if the cylinder is full of ambient air temperature and density air to 100% full, then VE is 100%. But common sense should kick in and tell you there is no way a cylinder with a 1400*F piston surface and 650*F valves contains air that is merely 80*F at any time. What this boils down to is we must work with a 'theoretical VE' value, a value for VE which correlates to engine torque & cylinder fill but has nothing to do with actual VE of a real engine. This will keep calculations simple and allow us to account for increasing air density and high temperature air without knowing the exact temp or density of the air. This is possible because mass airflow rate correlates to power, NOT torque, so the number we see on the chassis dyno will generally match up with the compressor wheel speed shown by our compressor wheel speed monitor (or paper-based calculations) and we can skip all calculations involving the engine and not have to worry about what is realistic VE.

*more VE*
The concept of VE directly correlates with cylinder pressure, from which torque is derived, for example all OEM naturally aspirated 2L engines no matter who designed will generally produce about 130 to 150lb-ft of torque maximum to the tires, as seen by thousands of dyno graphs, at near 100% VE. This can happen at any rpm, 1000rpm or 8000rpm, depending on the engine combination. Doesn't matter how much you port the head, big camshaft, super exhaust, etc... the cap to VE is near 100% for natural aspiration.
The correlation between engines (some more torque than others) is not linear due to myriad variables such as temperature, compression ratio, rodxstroke length, chamber design, ignition timing, etc... In other words if I set out to make a bit more torque than that I could definitely do it under the right circumstances, but it might not be reliable or cheap to accomplish. So again nothing is going to be exact in our equations, therefore once again as proper engineering students we should account for best and worst case scenarios. That said, there are limits, practical limitations to the amount of cylinder pressure and torque one may achieve which helps us rule out impossible results. For example it would be extremely unlikely to ever see 200lb-ft of torque or more from an N/A 2.0L engine, no matter what you do to it, when using typical gasoline fuel. We already know that N/A engines max out near 100% VE (102 or 105% is possible but not 115%+ that is unrealistic) and a torque figure of 200lb-ft would indicate over 115% VE already, so it can never happen unless the engine had insane compression and was running superior fuel than gasoline. Or perhaps being run with sub zero air temperature or something like that. It would not be practical or typical, or inexpensive to achieve such results.

Another aspect of VE that might be difficult at first is the fact that almost every engine in the world ever produced can achieve near 100% VE at some rpm. In other words, every engine will display some peak torque at some point, and it is almost always near 100% VE or 100% cylinder fill. That is because all combustion engines basically will have at least 1 specific RPM point where they are ideally effective/efficient at filling their cylinders, and that is where we find peak torque. This should help explain why VE by itself has no direct correlation to power. IF every engine in the world can achieve 90% to 100% VE at some rpm, then why don't they all produce max power? It is because VE doesn't correlate to power and is only one small piece of the power puzzle, you must have good VE AND at a high RPM as possible. 100% VE at 10,000rpm would yield good power even if the engine was only making 200lb-ft of torque. (200*10,000/5252 = 380hp) so in theory any N/A 2L engine could approach 350 horsepower if it could spin near 10,000rpm.

*How VE is really useful*
The theory of VE is important, but not super useful by itself. How can we use VE to gain useful information?
When we run an engine on the dyno from idle to redline at some intake manifold pressure (can be 0, 2psi, 5psi, 40psi, -5psi, -10psi, pick a number and hold it there) we generate a VE curve for the engine. This can also be called a torque curve. Basically the torque curve is a VE curve, it shows you how the engine cylinder is filling at each individual RPM breakpoint from idle to redline. If you point to the peak torque you could say this is peak VE or peak cylinder fill.

It tells us ALOT of information about the engine. Does torque fall off rapidly at some point? Does it spike wildly, jagged curve? Does it look 'good' (nice and smooth and kind of flat shape, like an arch or hill)? Any perturbations of the torque curve are warning signs about the engine, which could be some distress. And any sudden changes or drops in the torque curve indicate an issue with cylinder pressure, which could be cylinder fill (VE) or combustion related (e.g. spark blow out).
I always dyno my engines at 0psi of boost before using boost because it will lay the ground work expectations (VE curve) for higher boost pressure and take some guess work out of the tuning. In other words if the engine VE curve maintains it's shape and form and smoothness all the way from 0psi to 3psi to 5psi to 15psi to 30psi, this is a great sign of a healthy engine and good combustion quality. Probably Nice and safe if the curve looks the same shape and smoothness at 30psi as it did at 15 and 0psi, just higher up on the graph. Also the amount of torque gained per psi of boost is very important, as any diminishing returns tell you that the turbo or engine is having some difficulty in flowing air mass, could be an exhaust restriction or turbo is out of air for example. It is very easy to damage an engine at high boost pressures if you miss any of these warning signs, and you won't even realize there is a problem unless you established a VE curve from the get go.


*Cliffs* Summary
-We compare engine volume flow rate to compressor volume flow rate, then combine with temperature to get air density and mass flow rate which correlates to total power potential, and make sure to line up the compressor map with the engine flow rate ability at best and worse case scenarios.

-We establish a VE curve for diagnostic purposes and understand what VE is (torque curve relationship)