gt2871r will run okay? - Page 2 - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

mct3351 · 10-20-2010, 07:04 PM

Quote:

Originally Posted by jspaeth;

How much horsepower does a SR20 with a T25 make at 15 psi?

The same stock SR20 with a 3071R at 15psi?

Assuming you're asking sarcasticly (if ur not being sarcastic I could plot you hypothetical dynos in excel comparing the expected output of those two scenaros)...Not any where near the same amonut of peak power which is exactly what I said in the two previous explinations, for reasons which I have also already explained. Did u read it? FYI they'd produce similiar peak torque numbers though. Because for a shot period the t25 could provide adequate mass flow rate to achieve 15 psig manifold pressure. Then, as the revs increase, it would no longer be able to sustain the mass flow rate required the keep the manifold pressurized to 15psig. The torque curve will dive and the hp will flat line.

Are you still disagreeing with my original statement that the stock fuel system on an sr20, as installed on an sr20, can handle any turbo known to man at 7 psig manifold pressure?

jspaeth · 10-20-2010, 09:32 PM

Quote:

Originally Posted by mct3351

Assuming you're asking sarcasticly (if ur not being sarcastic I could plot you hypothetical dynos in excel comparing the expected output of those two scenaros)...Not any where near the same amonut of peak power which is exactly what I said in the two previous explinations, for reasons which I have also already explained. Did u read it? FYI they'd produce similiar peak torque numbers though. Because for a shot period the t25 could provide adequate mass flow rate to achieve 15 psig manifold pressure. Then, as the revs increase, it would no longer be able to sustain the mass flow rate required the keep the manifold pressurized to 15psig. The torque curve will dive and the hp will flat line.

Are you still disagreeing with my original statement that the stock fuel system on an sr20, as installed on an sr20, can handle any turbo known to man at 7 psig manifold pressure?

After doing some further reading and rethinking things, I want to offer an apology and say that I agree with you about your explanation.

If I understand you correctly, you are suggesting that a T25 vs a 2871R (for example) are SUFFICIENTLY efficient enough at 7 psi that the difference in output air temperature shouldn't be much......thus, the mass air flow from the two WOULD be the same.

However, at 14 psi and higher RPMs, I believe you suggest that the T25 is basically INEFFICIENT enough relative to the 2871R that it will not flow as much mass (air density goes up).

I believe your explanation was a good one, but I was not thinking clearly (LONG FUCKING DAY, trust me).....

So, hypothetically, the T25 at 15 psi and GT2871R at 15 psi....comparison:

Assume that they both spool by 3500 RPM and fix them at 15 psi (JUST SUPPOSE....).....so then (as an example), they may produce the same mass air flow (and thus torque) up to say 5000 RPM (JUST AN EXAMPLE again), but beyond this point, the T25 starts becoming so inefficient that even though they are still both at 15 psi outlet pressure, the T25 just can't keep pumping air at that pressure and at the same DENSITY as the GT2871R....thus, the T25 torque curve begins dropping off earlier, even though the boost pressure is the same in the 2 cases....

Sound correct now?

So okay, I give in, you are correct :-)

Sorry, again.

codyace · 10-20-2010, 10:03 PM

I can undertand your example, in fact I said it very simply in the fact that I agreed that at 7 psi both will probably be safe for the stock system.

BUT what I had disagreed with was your '7psi is 7psi' statement...which was probably (after your explanaiation) misunderstood by me at first, and then (attempted at least) cleared up after.

And after all of that said, I would love to see a true 2871r on a stock everything setup, versus a t25 making the similar 240/250 whp, to see what truely would be 'more powerful' over time.

Ultimatley though, there is ZERO point (to me) on running that turbo on stock everything...but to each his own.

mct3351 · 10-21-2010, 08:03 AM

Couldn't have said it better myself. Good call on bringing up density.

The ABSOLUTE temperature of air greatly affects its density (when volume isnt fixed) and thus the mass flow required to pressuize a given volume at a particular engine speed. Hotter air from the compressor will mean less mass flow rate is required to pressurize the intake manifold (loss of torque). The boost gauge will be reading constant which is what you guys were talking about in saying 14psi is NOT 14 psi, when comparing the t28 to the 2871.

All you can infer from a boost gauge is volumetric flow rate. Volumetric flow doesnt say much for the imperical quantity (moles) of air going through the engine (thats why MAP efi requires a temperature sensor). Mass flow rate does equate to air molecules. More mass means more air molecules which means more fuel which will equate to more power. Word of warning though: If that mass is too hot when it gets injested by a cylinder and compressed again (gets even hotter) the propensity to knock will increase (engine damage).

Quote:

Originally Posted by jspaeth

After doing some further reading and rethinking things, I want to offer an apology and say that I agree with you about your explanation.

If I understand you correctly, you are suggesting that a T25 vs a 2871R (for example) are SUFFICIENTLY efficient enough at 7 psi that the difference in output air temperature shouldn't be much......thus, the mass air flow from the two WOULD be the same.

However, at 14 psi and higher RPMs, I believe you suggest that the T25 is basically INEFFICIENT enough relative to the 2871R that it will not flow as much mass (air density goes up).

I believe your explanation was a good one, but I was not thinking clearly (LONG FUCKING DAY, trust me).....

So, hypothetically, the T25 at 15 psi and GT2871R at 15 psi....comparison:

Assume that they both spool by 3500 RPM and fix them at 15 psi (JUST SUPPOSE....).....so then (as an example), they may produce the same mass air flow (and thus torque) up to say 5000 RPM (JUST AN EXAMPLE again), but beyond this point, the T25 starts becoming so inefficient that even though they are still both at 15 psi outlet pressure, the T25 just can't keep pumping air at that pressure and at the same DENSITY as the GT2871R....thus, the T25 torque curve begins dropping off earlier, even though the boost pressure is the same in the 2 cases....

Sound correct now?

So okay, I give in, you are correct :-)

Sorry, again.

codyace · 10-21-2010, 03:47 PM

Quote:

Originally Posted by mct3351

Couldn't have said it better myself. Good call on bringing up density.

Agreed...I think Justin and I sort of mistook your generic comment at first. We all are saying the same thing, but form different perspectives. That's why we were bringin up the total mass flow (lbs of air) that each compressor makes at specific PSI...all to often people on here just say 'well 8 psi is 8psi' and we took it that way.

nevertheless · 10-22-2010, 07:34 PM

I have a question what psi should I run at..
freshly built cp pistons/ eagle rods
apexi metal headgasket
arp headstuds
255 walbro
stock injectors tho.
s14 t28

S13 curtis · 10-22-2010, 08:36 PM

Quote:

Originally Posted by nevertheless

I have a question what psi should I run at..
freshly built cp pistons/ eagle rods
apexi metal headgasket
arp headstuds
255 walbro
stock injectors tho.
s14 t28

The same as if it was stock because of those injectors!

Anything over 9-11psi on a S14 T28 with 370's its going to get lean at stock fuel pressure.

Corbic · 10-22-2010, 09:02 PM

Quote:

Originally Posted by sr20boi

so i should just drive it easy? i have no other car so im going to have to be driving it.. and ya i do have all that stock. thanks for the info.

Better off bypassing the turbo.

codyace · 10-23-2010, 09:09 AM

nevertheless - you could have easily searched that

Quote:

Originally Posted by Corbic

Better off bypassing the turbo.

LOL

slim_240 · 11-03-2010, 10:41 PM

don't wanna thread jack but since we're kinda on the subject, is there a limit difference on a N62 and a Z32 maf?

Sileighty_85 · 11-03-2010, 11:57 PM

Quote:

Originally Posted by slim_240

don't wanna thread jack but since we're kinda on the subject, is there a limit difference on a N62 and a Z32 maf?

the N62 is the 300ZX MAFS, Same MAFS

slim_240 · 11-04-2010, 06:28 AM

ahh i see. thanks

10-20-2010, 10:03 PM	#33
codyace Post Whore! Join Date: Dec 2004 Location: Poconos, PA Age: 36 Posts: 8,030 Trader Rating: (58) Feedback Score: 58 reviews	I can undertand your example, in fact I said it very simply in the fact that I agreed that at 7 psi both will probably be safe for the stock system. BUT what I had disagreed with was your '7psi is 7psi' statement...which was probably (after your explanaiation) misunderstood by me at first, and then (attempted at least) cleared up after. And after all of that said, I would love to see a true 2871r on a stock everything setup, versus a t25 making the similar 240/250 whp, to see what truely would be 'more powerful' over time. Ultimatley though, there is ZERO point (to me) on running that turbo on stock everything...but to each his own. __________________ *Want Air Conditioning in your SR20 Swapped car? Check out www.sr20acbrackets.com for more information! Quest Alternator Conversions for SR20!* Check my Group Buy! Tired of lousy internal gates? Go external wastegate with one of my manifolds, Check out my group buy

11-03-2010, 10:41 PM	#40
slim_240 Zilvia Member Join Date: Jun 2009 Location: dallas, tx Posts: 246 Trader Rating: (3) Feedback Score: 3 reviews	don't wanna thread jack but since we're kinda on the subject, is there a limit difference on a N62 and a Z32 maf? __________________

11-04-2010, 06:28 AM	#42
slim_240 Zilvia Member Join Date: Jun 2009 Location: dallas, tx Posts: 246 Trader Rating: (3) Feedback Score: 3 reviews	ahh i see. thanks __________________

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10-22-2010, 07:34 PM	#36
nevertheless Zilvia Junkie Join Date: Jan 2009 Location: omaha, ne Age: 30 Posts: 502 Trader Rating: (5) Feedback Score: 5 reviews	I have a question what psi should I run at.. freshly built cp pistons/ eagle rods apexi metal headgasket arp headstuds 255 walbro stock injectors tho. s14 t28