Toerag

Just a kind of curiosity question, I've noticed that people want to go up to max boost ASAP (which I can understand), but they then let the boost fall as the revs progress towards the redline. They then do mods to raise the max boost which then starts breaking gearboxes and clutches. Would it not be a sensible idea to go the route of keeping boost high at high revs to create good power without gearbox breaking torque? I know turbos get inefficient and heat the air at high revs, but people never seem to get much more power out of their bigger 'more efficient' turbos. Any thoughts? Do I make sense?

john banks

Most people do it for engine longevity or turbo efficiency. When you look at the compressor map it makes sense to have the boost highest where it is most efficient and to drop it off if you are losing efficiency. I presently run mine about 2 PSI below what it will do from 6000 to 7000 RPM. It runs much cooler that way, you can advance the ignition more in the midrange as well - the trips up to 7000 RPM do not cause as much heatsoak into the intercooler, leading to lower overall charge temperatures.

Toerag

OK, so assuming that you're not getting detonation, then you could in theory keep the boost up? Are people breaking their rods and cranks by doing that? I don't think the valves will go (not enough revs), but how strong is the crank? Surely if the torque is dropping then the crank should be OK? I'm just trying to think of getting good power without breaking the gearbox. Perhaps nitrous is the way to go, having read good things about it on i-club?

john banks

It is charge temps, turbo efficiency and risk of det as well as what the turbo will actually flow with a maximum duty cycle that limits a lot of people. Some of the bigger turbos will hold the boost right to the redline even if it is fairly high, but for primarily a road car they are bigger than my preference as the boost thresholds are higher. Others don't mind and like the reward for changing down and going to high revs. All depends on what you like.

dowser

Biggest stress to engine is at high revs as well - coming to TDC on the exhaust stroke at 7k is a massive amount of piston deceleration for the conrod to bear with no compression to cushion the blow......add the increased temp from running high boost and it's a recipe for disaster on stock internals...imho. I'd like to be proved wrong though....

Richard

Andy.F

Since I modified my TD05 turbo it will hold max boost of 24psi to 7000 rpm , however the std (non Sti) cam profiles dictate the volumetric efficiency and limit the airflow at the higher revs therefore my power still drops off after 6000rpm.

I can actually get more power by reducing the boost pressure to 20 psi after 6000rpm due to generating less heat during compression.

To a point, more boost is better but there is a 'sweet' spot

Andy

Jamie Whitfield

I took delivery of my STI UK 4 weeks ago and in the time have slowly started to put some of my mods on it. First off was a Blitz NUR Spec R Decat system, which raised the peak boost level to 1.41bar (21psi), this however dropped to just under 1 bar.

I fitted a Dawes Device Race Version and have found that I can set the level to 1.2 bar (conservative for now), but as it holds its boost the car is far more quick. A safe mod, and a worthwhile one.

Jamie

www.j-w-racing.com

Bruiser.STi

What is a dawes device race version???

Jamie Whitfield

Please take a look here:

http://www.performanceexhausts.net/DawesDevices.html

Jamie

www.j-w-racing.com