thanks the entire setup will be for sale once i get any bugs worked out of it , need money to fund the twin turbo 427sb build for the itoc

 

You sir, are a provider of top quality entertainment. I love it!

 

Umm. What ??

Boost is a measurement of restriction. On the same complete engine, 20 psi of boost would represent the same airflow regardless of compressor.

Now if you said, 20 psi on my briggs n stratton riding mower, and 20 psi on a 540 cubic inch big block are not the same thing, you would be correct.

-- Joe

 

i hate to tell a mod hes wrong but in this case gta is right

a t3 turbo at 20 psi is only going ot move about 25 lbs of air on a 2.8 that will make about 250 hp @ 20 psi
strap a gt3582 on a 2.8 and its going to make about 300 hp at 12 psi

 

I can attest to the above.

PSI is just restriction, not cfm or lbs/min flow.

 

gee that'd be great if what little money i had wasn't going toward my planned 4.3 turbo swap done alot of reading, but i'm a total newb to tuning and turbos, and so far all i've got is my blown up (nearly) z28, everything else i'll need remains to be bought.

idk if it was ever covered, but what was you main goal of this build besides having a badass looking 3.4? was there a power goal?

 

there wa sno goal other then putting a 4-71 blower on the v6

 

i support hot rodders doing things just to do them, unless its a 350 swap (too common) or an ls swap (becoming way too common) they're just so boring to read through

 

Turbos don't make boost, they move CFM.

Turbos are not rated in boost.

A Turbo with 20psi of manifold pressure on any given motor tells absolutely nothing other than the fact that it's forcing air into the motor.

-- Joe

 

Bingo. Resistance is resistance, what matters is the amount of cfm being applied after that resistance reading. If we use two boost gauges at the same time to understand this, one measuring resistance in the plenum the more common way, and another measuring resistance just before the individual intake valve, they will give two different resistance readings. This is why 20-psi in the plenum from two different turbo's is essentially the same measure, it is meaningless, and the reason why it is meaningless is because it only tells half of the story. The better turbo moving more cfm will "follow through" after that first 20-psi resistance reading and will force just as much resistance on the second gauge nearest the intake valve, while the slower turbo will slow down after that first 20-psi resistance reading, and isn't really applying as much. This is why ebay turbo's are a lot cheaper than Turbonetic turbo's...

 

That is a good point, but I would be more concerned with the adiabatic efficiency of the compressor.

Besides, the phenomena you're speaking of isn't as common with short runner, single plane intakes with a large cross sectional area in the runner.

On something like a tuned port intake, say you saw 20psi in the plenum, you might see a little pressure drop in the actual intake runner of the head.

And even still, I don't see how the larger compressor could result in a higher resistance measurement at the valve without increasing the measured pressure in the plenum. I'd love to see a flow modeled in software to show it.

Besides, I doubt that is what they were talking about.. A good percentage of people on this forum, and even the industry seem to rate head units (and pulleys when talking blowers) in 'PSI' as if it was a meaningful comparison.


-- Joe

 

Bingo again, we want the highest efficiency possible. The boost gauge simply measures resistance, but it has no way of measuring usable cfm. We measure this by dividing the amount of power that goes into building pressure by the total power put into the compressor. An ebay turbo, and an Turbonetics turbo, at the same turbine and compressor size, can both be measured at 15-psi of boost pressure in the plenum, but what determines usable cfm is the efficiency of the pressurized air, as some turbo's, like ebay turbo's, although can achieve high boost resistance readings, are only more efficient at heating up the air charge, reducing power, and leaving a lot on the table...

 

We're in total agreement of that. If your outlet temperature is 300 degrees on one, and 120 on the other obviously the later will make more power (and not blow up).

But I still don't see how a higher flowing (more CFM) compressor will have a proportionate gain in pressure at the valve, without increasing pressure in the plenum.

Keep in mind 99.9% of the efficiency of a compressor is the impeller, and folks on ebay having been making replacement impellers that are much better than OE for quite some time now. I don't know if it's getting cheaper to machine helical impellers or what.

-- Joe

 

Don't forget in this compressor-centric view of the world that swapping from a T3 to a GT35 could very well also change the properties of the turbine as well. If you can't get your gas out of the engine how is it going to get pumped in? If you choke it at 4500 RPM on the turbine side, or you are trying to go off the map with the compressor at that RPM, you're not going to make power at the 6-7000 RPM the engine is capable of. By eliminating either the inefficient compressor at that flow and boost point, you allow the engine to run the "whole curve." It'd be much like sticking a set of stock exhaust manifolds on an engine with a set of AFR 195s and a big cam then being surprised when you go to 1 3/4 long tubes that it's not choked any more. Considering people have gained 40 or 50 rwhp due to cutting a flow master off, why is it hard to believe that you could gain 100hp by enlarging what is ultimately the biggest restriction in the system?

Besides that, the pulleys being rated in "PSI" is probably a lot like converters IMO. By that I mean they say "this is a typical stock engine, you put this setup on it and then run this pulley you'll get around this boost level. No, it's not accurate if you're not running the same configuration as they were but it's designed to be a rough baseline. Much like advertised duration or converter stall it's likely more useful within a single line of products to reference one to another (e.g. I need an 8 PSI pulley this 6 PSI one doesn't produce the desired amount of boost due to my heads being ported.)

 

Adding a blower doesn't change the compression ratio.. It changes the volumeteric flow. That is why you have to go to a 2 - 5 Bar Map instead of 14:7.1 Stoich 1 Bar

 

What does it do to the "dynamic" comperssion ratio. Meaning one of the valves, in this case the intake, may be open for a msec with the ext closed. Could it increase the DCR?