General [M]ayhem

Go Back   General [M]ayhem > General [M]ayhem > Automotive [M]ayhem
Register Members List Mark Forums Read [M]erchandise Calendar

Reply
 
Thread Tools
Jehannum
 
Jehannum's Avatar
 
Quote:
Originally Posted by Fiah View Post
So what you're saying is that with completely identical blocks/displacement/headers/throttlebodies/cams/everything, a big turbo delivering 20 PSI at 7000 engine RPM will provide more power than a smaller turbo also maintaining 20 PSI at 7000 engine RPM? So what, the same engine can now suddenly flow more air at the same pressure, displacement and RPM just because the turbo is bigger?
No, the compressor can flow more air, because it's more efficient.

And yes, my 300ZX went from 317HP at 13PSI on stock T22s to 348HP at 12PSI on GT28Rs. No displacement gain, no exhaust change, nothing different air (even AFRs were the same, though it did have to put more fuel down).
__________________
Your powers are useless! I'm wearing my tin foil underwear!

1992 300ZX: Not stock, 433 RWHP
1971 240Z: Toyota front brakes, 123 RWHP
1967 Pontiac GTO: not stock.
Old 10-12-2010, 05:37 AM Jehannum is offline  
Reply With Quote
#46  

Advertisement [Remove Advertisement]

opel
 
Quote:
Originally Posted by Fiah View Post
So what you're saying is that with completely identical blocks/displacement/headers/throttlebodies/cams/everything, a big turbo delivering 20 PSI at 7000 engine RPM will provide more power than a smaller turbo also maintaining 20 PSI at 7000 engine RPM? So what, the same engine can now suddenly flow more air at the same pressure, displacement and RPM just because the turbo is bigger?

At the same pressure, the big turbo is flowing more lb/min of air.
Old 10-13-2010, 12:01 AM opel is offline  
Reply With Quote
#47  

Fiah
Sinds ik als transseksuele prostituee bezig ben, heb ik mezelf eindelijk leren accepteren. PM me voo
 
Fiah's Avatar
 
Quote:
Originally Posted by opel View Post
At the same pressure, the big turbo is flowing more lb/min of air.
Only if a bigger turbo means that it operates more efficiently, with lower intake temperatures right? Otherwise I fail to see where that extra air would come from.
Old 10-13-2010, 12:31 AM Fiah is offline  
Reply With Quote
#48  

chronage
 
chronage's Avatar
 
CFMs are what matter
Old 10-13-2010, 02:41 AM chronage is offline  
Reply With Quote
#49  

Dongboy
I am Kruzens Brother
 
Dongboy's Avatar
 
Quote:
Originally Posted by opel View Post
At the same pressure, the big turbo is flowing more lb/min of air.

on an open test bed a bigger turbo will generally flow more lb/min than a smaller turbo at a given measured pressure. HOWEVER as stated - you are then going to either increase the dynamic compression of the engine by forcing more air into it or you will see a higher manifold pressure with the increased air pressure.

think about it this way - when the cams are top dead center you have a closed system - the turbo is pumping air through it and it has for those few thousandths of a second no where to go except into a closed box - the faster a turbo pumps the air in the faster the pressure will rise - you have peak manifold/intake runner pressure immediately before the next cylinder opens - you CANNOT make this event take any longer without putting in a different cam. the more pressure pumped into that temporarily closed system the more the pressure will rise. period. now looking at it as a dynamic system there can be gains found by increasing efficiency of the turbo - cooler charge is generally a benefit of a bigger turbo on the same engine - that's going to be more dense and thus more beneficial at the same pressure.

you guys are all saying "lol bigger turbo = more power at same pressure" - it also equals later spool time and if over sized will equal less average power band power. it's not just a simple "at one point on the chart it made more power so it's better" - engines are dynamic systems and have a lot more going for them than one data point.
__________________
bitch faced lobster OMGOMGOMGOMG - g0rg0n describing me
My '80 VW diesel buildup thread - http://genmay.com/showthread.php?t=645277
Old 10-13-2010, 10:44 AM Dongboy is offline  
Reply With Quote
#50  

Jehannum
 
Jehannum's Avatar
 
Quote:
Originally Posted by Tongboy View Post
you guys are all saying "lol bigger turbo = more power at same pressure" - it also equals later spool time and if over sized will equal less average power band power. it's not just a simple "at one point on the chart it made more power so it's better" - engines are dynamic systems and have a lot more going for them than one data point.

It may not come with a longer spool. If, for example, you go from journal bearings to ball bearings in the CHRA, the spool is dramatically different (BB turbos tend to spool quite a bit faster than journal bearing turbos). If you go from cast to CNC compressor/turbine wheels, spool is dramatically different (CNC stuff tends to be lighter, and thus spool faster).

Going from a T22 to a GT28R on my Z has shown pretty much the same spool characteristics.

It's not just a compressor map bukkake contest, but there's a lot on the map to consider, and if you're moving up from a WWII era turbo to a modern one, you may just get something for nothing (except dollars, lol).

Also, TDC on anything with more than 3 cylinders will have at least one more piston on intake stroke, so there's a little more to the characterization than "closed system, lol".
__________________
Your powers are useless! I'm wearing my tin foil underwear!

1992 300ZX: Not stock, 433 RWHP
1971 240Z: Toyota front brakes, 123 RWHP
1967 Pontiac GTO: not stock.
Old 10-13-2010, 12:01 PM Jehannum is offline  
Reply With Quote
#51  

mrselfdestruct
 
I think TongBoy might be referring to the boost threshold, not the actual time it takes to spool. Also, another thing to consider besides the air charge temperature is that in most setups the pressure before the turbine is greater than that in the intake manifold. For this reason a bigger turbocharger can result in a reduction in backpressure and therefore increase the flow without an increase in manifold pressure.

This is the same reason why most people running turbocharged street cars will use camshafts with little to no overlap whilst setups with very large turbochargers and exhaust combinations can get away with pretty wild profiles. In this situation the turbocharger will simply build boost against the valves as TongBoy stated previously.

I think it may also clear up some confusion to point out that our theoretical upgraded turbocharger and exhaust does not do anything magical to increase the power output, it simply reduces air charge temperature and backpressure. The engine's output is only improved by the increased density ratio of the air you feed it and at 15psi this cannot exceed 2.0 unless you bring your intake temperatures below atmospheric.

Someone please correct me if anything I've said isn't correct.
Old 10-13-2010, 04:13 PM mrselfdestruct is offline  
Reply With Quote
#52  

ScHpAnKy
The only place you can get milk in a bag.
 
I want that size tire, what are they?
__________________
Yup, still from Boston
SexiOne's pool boy
Old 10-13-2010, 04:40 PM ScHpAnKy is offline  
Reply With Quote
#53  

[H]ard|On
tell me i is retarded and i will just potato
 
[H]ard|On's Avatar
 
Quote:
Originally Posted by Tongboy View Post
are they both then crammed back through the same exit pipe for a few feet? if so they'll both provide exactly the same output

I see your point, but there are so many cases of this:

Quote:
Originally Posted by Jehannum View Post
No, the compressor can flow more air, because it's more efficient.

And yes, my 300ZX went from 317HP at 13PSI on stock T22s to 348HP at 12PSI on GT28Rs. No displacement gain, no exhaust change, nothing different air (even AFRs were the same, though it did have to put more fuel down).

The last time this came up we were talking about just a few extra PSI making what seemed a disproportionate amount of extra power on an s52. That's easy to understand - it's simply not a linear relationship.

It gets tougher for me when it IS the exact same motor, having the same measured PSI in the intake mani, or even less and making a good deal more power. What I gather so far is that it IS possible to use more CFM at the same pressure at the same RPM - due to valve overlap, for one and restrictions like the valves for another... Let's say you're boosting 10 psi over ambient in the manifold - your cylinders will fill to 8 before the valves close and combustion begins. A larger turbo can maintain this open system easier - same PSI *in the mani* - but filling the cylinders with even more air increasing volumetric efficiency.

Here's another Q: do larger turbines typically spin slower than smaller ones or do they all have to spin about the same to be in their efficiency range?
__________________
Make Genmay Great Again
Old 10-13-2010, 04:50 PM [H]ard|On is offline  
Reply With Quote
#54  

Dongboy
I am Kruzens Brother
 
Dongboy's Avatar
 
mrselfdestruct actually raises a really interesting point that is frequently forgotten and is a commonly overlooked part of a turbo application - exhaust manifold pressure and how it relates into the whole turbo world.
__________________
bitch faced lobster OMGOMGOMGOMG - g0rg0n describing me
My '80 VW diesel buildup thread - http://genmay.com/showthread.php?t=645277
Old 10-13-2010, 05:01 PM Dongboy is offline  
Reply With Quote
#55  

AtomicFire
 
AtomicFire's Avatar
 
a small turbo spinning it's guts out at 20psi will make less power on the same exact setup as a larger turbo running in it's efficiency island because the smaller turbo is spitting out hot, less dense air.

This has been proven a lot of times in the Subaru world. Get a VF43 at 21psi that's basically way above it's efficiency level, and it will make around 300 wheel hp. Get a GT3076R and run it at 18psi and make 380 wheel on the same exact setup.

This also makes sense because if you put meth/water injection on the VF43 setup, you can get up to 330hp or so due to chemical cooling of the intake charge.
Old 10-27-2010, 03:45 AM AtomicFire is offline  
Reply With Quote
#56  

tegandje
LOOK AT ME, IM A FUCKIN HIPSTER
 
tegandje's Avatar
 
But if you do meth, you can't drive properly because you'll be itchy!
__________________
b35b36db324a18b072d431f4fbb833d1 [y yuo throw haet :( :(] porn may <3's yuo.
Old 10-27-2010, 03:53 AM tegandje is offline  
Reply With Quote
#57  

[H]ard|On
tell me i is retarded and i will just potato
 
[H]ard|On's Avatar
 
Quote:
Originally Posted by AtomicFire View Post
a small turbo spinning it's guts out at 20psi will make less power on the same exact setup as a larger turbo running in it's efficiency island because the smaller turbo is spitting out hot, less dense air.

This has been proven a lot of times in the Subaru world. Get a VF43 at 21psi that's basically way above it's efficiency level, and it will make around 300 wheel hp. Get a GT3076R and run it at 18psi and make 380 wheel on the same exact setup.

This also makes sense because if you put meth/water injection on the VF43 setup, you can get up to 330hp or so due to chemical cooling of the intake charge.

__________________
Make Genmay Great Again
Old 10-27-2010, 02:02 PM [H]ard|On is offline  
Reply With Quote
#58  

Reply


Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump



All times are GMT -7. The time now is 03:50 PM.



Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.