IMO it's a popular misconception that peak/max boost over RPM = greatest slope on the torque curve. A reason for this is boost pressure does not necessarily equate to air-mass - often times a 61/lbs wheel will move a whole lot more air-mass at less boost pressure then a 50/lbs wheel will move at a higher boost pressure. Therefore when boost-curves are discussed, I think what most people are after is really the torque curve.

A real world example is many of the race cars we tune. For example the Grand-Am cup (as with most race series) has a limitation on maximum boost pressure allowed. Therefore we spend a lot of time making MORE power and a better torque curve with less boost pressure. Many cars we tune make a lot more power with a better power curve than cars running substantially more boost pressure. So IMO to say one turbo makes more boost at a certain RPM does not necessarily imply that the vehicle actually has a better power curve.

Just my $.02

Cheers,

Gary
Gruppe-S

 

Ok. Unfortunately I can't help you with gt30r numbers, but I currently run a 50 trim AMS kit with a ported head, HKS 280 cams, and AMS VSR intake manifold and I get full boost (21-22psi) at ~4000 rpm in 3rd gear and ~3900 rpm in 4th. You could probably shave 200-300 rpm off those numbers with a different build.

l8r)

 

Thanx for the info

 

I kinda understand what your saying. Say i wanna push 23 psi and one turbo will hit that at 3800 but another one wont hit that until 4500. Are you saying the one that is hitting at 4500 is prolly making more power but they are the same turbo just different brands?? EXAMPLE both are 76.2mm compressor wheel and a 54mm exhaust turbine with an .82ar.

 

For auto x purposes the best turbo IMHO is the stock one. Or get a stock evo 9 turbo. I get boost very quickly and hold it all the time. Besides when you auto x yo really dont see low rpms anyway so you should never be in a position where you arent in boost. A good auot x driver will never be in a position where he/she has to build boost.

 

Okay i really want this to stay on topic, anybody with a gt30r kit of any brand, on a 2.0, with the basic mods like what i have ( which i posted on the first page), at what rpm's are you seeing full boost and what gt30r kit do you have????

 

rnr ram horn manifold... everything else is custom made.

 

Hi Gary,

could you please explain better this concept ?

Sorry but I'm not able to understand why...

I always thought that pressure is given by an air-mass compressed into a fixed volume ( ic pipes + ic + plenum ), so at an higher boost pressure always corresponds a bigger air-mass moved...

TIA.

 

got a dyno chart? curious about your HP and TQ numbers... PM if u want. a dyno chart or just the numbers would be nice. my buddy just got the 50 trim, waiting install wondering what numbers u put down, he has bout same mods, just no vsr and his cams are 264/272.

 

Hi, sorry for being confusing. Basically given the same turbo just because on one car the tune hits say 23psi at 4500 RPM and the other car hits 23psi at 3800 both cars can nevertheless have the same torque curve. Therefore from a driver's perspective just because one car hits "full boost" later doesn't mean the drive feels any noticeable difference in performance.

Hope that explains it better.

Thanks,

Gary

 

Hi. Although not entirely accurate the principle of inert gases (PV=NRT) can be applied. The variable here is temperature, where a smaller wheel will tend to heat up the air more thus creating greater pressure but perhaps no more air-mass. A larger wheel on the other hand will not heat the charged air as much and move more air-mass at lower pressures.

This is why it's important not to over-drive the turbocharger and to get a larger intercooler when needed.

Cheers,

Gary
Gruppe-S

 

Ah ok,

then you meant for the temperature/density issue...

thank you !

 

I don't have access copy of the latest chart right now, but the car made 400 whp and something like 330 wtq running 21psi on 93 Octane (AWD DynoJet).

l8r)