gt2871r will run okay?

[jspaeth]

Originally Posted by mct3351

You will be perfectly fine running 7 psig (stock wastegate setting) on a 2871 up to 7,500 rpm with a stock fuel system. You wouldnt make any more power at 7 psig on a 2871 than you would with a t28 at 7 psig, beacuse the t28 is still in a decent effiency range on a 2.0 liter motor at 7 psig and 7k rpm. This is all true as long as all the other "bugs" are worked out (base timing, maf wiring, boost leaks, water temp, injector condition, fuel pressure...etc).

Yeah, that makes SENSE!



Please do not give out information that is wrong, unless you want to send this guy $3000 for a motor rebuild when his engine blows.

Two different turbos do NOT (necessarily) put out the same mass air flow at the same psi.

The S14 SR T28 turbo does not flow the same air at 7 psi as a GT2871R at 7 psi, so please do not tell people that.

[mct3351]

If you could read a compressor map you'd see that at 7 psig manifold pressure a stock t28 can efficiently and adequatly provide mass/volumetric flow to keep up with a 2.0 liter engine to 7,000 + rpm. Your assumption only holds true when the volumetric/mass flow rate demand (calculated as a function of engine speed, displacement, manifold pressure and intake air temp.) exceeds the cabaility of the t28 compressor. This happens around 12-14 psi when comparing a t28 to a 2871. So, yes 14 psig with a t28 is not the same as 14 psig with a 2871. But, a t28 and a 2871 will provide approximatly equal mass/volumetric flow rates until redline when the flow rate demanded of the compressor is only enough to maitain 7psig of manifold pressure on a 2 liter engine.

Additionally, I personally ran a 2871 on stock injectors and maf for about 6 months. From memory, at the stock wastegate setting the injector duty cycle barely ever got over 80% and the stock maf never read over 4 volts (as measured with a powerfc).

So, as you can clearly see, the stock fuel system is completely adaquate to handle ANY sized turbo/supercharger capable of maintaining 7 psig manifold pressure up to 7,000 rpm with reasonable intake air temperatures (ie. not -40 F or anything of the likes). It however could not keep up at say 10,000rpm (if the engine could spin that fast) or if the engine was larger than 2.0 liters.

Originally Posted by jspaeth

Yeah, that makes SENSE!



Please do not give out information that is wrong, unless you want to send this guy $3000 for a motor rebuild when his engine blows.

Two different turbos do NOT (necessarily) put out the same mass air flow at the same psi.

The S14 SR T28 turbo does not flow the same air at 7 psi as a GT2871R at 7 psi, so please do not tell people that.

[jspaeth]

Originally Posted by mct3351

So, as you can clearly see, the stock fuel system is completely adaquate to handle ANY sized turbo/supercharger capable of maintaining 7 psig manifold pressure up to 7,000 rpm with reasonable intake air temperatures (ie. not -40 F or anything of the likes). It however could not keep up at say 10,000rpm (if the engine could spin that fast) or if the engine was larger than 2.0 liters.

OMG.......please answer this question for me.....


Would you say that you agree with the following statement:

"7 psi is 7 psi is 7 psi.......it doesn't matter what turbo it is, all that matters is that it's 7 psi in the intake manifold".

I would like a YES or a NO answer to that question.

[mct3351]

"it doesn't matter what turbo it is, all that matters is that it's 7 psi in the intake manifold">No, there are many other important considerations.

To expand on what I said:

"So, as you can clearly see, the stock fuel system is completely adaquate to handle ANY sized turbo/supercharger capable of maintaining 7 psig manifold pressure up to 7,000 rpm with reasonable intake air temperatures"

When you are comparing realistic forced intuction options you would usually pick something at least as capable as what you have, so to simplify the explination lets rule out anything smaller than a t28 (ie. t25 and smaller turbos). If you were to assess the air flow rate demand created by a 2 liter engine between 3k rpm and 7k rpm with 7 psig manifold pressure and realistic intake air temperatures, the fueling ability of the stock injectors and the metering ability of the stock maf are within their limitations regardless of the type of forced induction. When comparing a specific pair of turbos like the 2871 to the t28 you will see that the maximum flow rate possible is greater in the 2871. But, at 7 psi manifold pressure the t28 is well within its range of flow rates at that pressure when installed on an sr20. So, then why would you expect the 2871 to produce more power when compared to a t28 at 7 psi on an sr20? It cannot increase the pressure of the air and keep it any cooler than ambient air. So, all things being identical, a t28 on an sr20 running 8 psi will make MORE power with a stock fuel system than a car with a 2871 at 7psi and 600cc injectors and a z32 maf. Additionally, when comparing the t28 to the 2871 as installed on an sr20 that redlines at 7k rpm, the 2871 wont provide a preformance advantage until the two are push past ~ 11-14 psi manfold pressure. That is where, the torque curve will begin to decline and the power curve will flat line prior to redline on a t28 powered car. The 2871 torque curve will remain flat and power will continue to climb up to redline (disregarding other non relevant to this discussion things like cams and intake manifold geometry). This is because you have reached the limitation of the t28 compressor wheel.

If it's a pretty common fact that the stock fuel system is capable of 250 whp would you expect a 2871 to make 250 whp at 3-4 psi manfold pressure as stated above by you? Would expect a 2871 to make 250whp at 7 psi...I dont think so.

Just because the 2871 has a performance range that is superior to the t28 doesnt mean it will provide an advantage within the performance range of the t28.


Simply put
7 psi is 7 psi (comparing t28 and 2871)
14 psi is NOT 14 psi (comparing t28 and 2871)

Originally Posted by jspaeth

OMG.......please answer this question for me.....


Would you say that you agree with the following statement:

"7 psi is 7 psi is 7 psi.......it doesn't matter what turbo it is, all that matters is that it's 7 psi in the intake manifold".

I would like a YES or a NO answer to that question.

[jspaeth]

Originally Posted by mct3351

Simply put
7 psi is 7 psi (comparing t28 and 2871)
14 psi is NOT 14 psi (comparing t28 and 2871)

As far as whether or not your OEM fuel system can HANDLE the airflow, this statement may be true.


But the fact is that the MASS AIR FLOW out of those two turbos at the SAME boost level is NOT THE SAME.

[mct3351]

So you dont get it? I'm done trying because IMO those explanations are sticky worthy.

"But the fact is that the MASS AIR FLOW out of those two turbos at the SAME boost level is NOT THE SAME." = This broad all encompassing statement is absolutly WRONG! The only slight variance, at 7psi, would be in which efficiency island your on.

To the OP, believe what you want. I will NOT be sending you $3000 if you blow up your stock long block (valued at ~$1000), so you probably shouldnt run more than 3 psi

[codyace]

Originally Posted by lok

you are fucking stupid.

i have had my sr for 7 years....

I have tracked and drifted all these setups and still have a perfectly good motor.

'Runs well' and 'Runs right' are certainly two different things. Kids run 15/16 psi on a t25 without issues, others explode them at 10.

It's not worth the risk, or the minimal gain to push my luck. You're not getting a trophy for running it, and nissan ain't helping you rebuild it if explodes, so why bother pushing it.

Originally Posted by mct3351

This broad all encompassing statement is absolutly WRONG! The only slight variance, at 7psi, would be in which efficiency island your on.

What does efficiency islands have to do with total air flow like Justin is trying to explain to you? 70% efficiency on a turbo that doubles the flow of a another turbo in the 80% efficiency is MUCH more air flow and MUCH more power.

7 psi is not 7 psi on anything. t25 to gt35, YSI to F2.

I think what you are trying to say, is that at 7 psi neither the t28 or the gt28xx will blow up the engine...and that's probably true. BUT that's not to say that 7 psi is the same amount of total flow from both. You can NEVER relate BOOST per safe....A t25 car with S3 cams will push everything past the limits, it just flows air like crazy.


So while you may be right about 7 psi not making a difference, your explanation is totally wrong.

Offtopic What I'd like to see is a comparison (albiet it will never happen) of a t25 at 14 psi vs a 28xx at 7 psi to see what has a better average power band....and then measure it across time.