Boost Build Vs Gears

[PhilGTR]

Does boost build up quicker in say 1st gear and with a slightly larger spike than compared with in 4th gear?

My boost controller is set up at 12psi and on the dyno in 4th gear it shows somethin like 12.5psi at like 3krpm and the tapers off to like 12psi at around 7-8krpm. But then when i run it on the street and take off in 1st gear, i check the peak boost on my profec B spec 2, it reads usually between 13.5-13.8psi.

Is this just an inaccuracy in the boost controller or does it actually spike higher in lower gears?

[Hijacker...]

Different load on the street compaired to Dyno!!

[GTAAAH]

My experience is the opposite, all the cars i've been in that do spike or that have some amount of variance in boost, boost higher in 3rd/4th as opposed to 1st and normally by a few psi

[Robo's]

Weird too, my boost in 1st gear is far lower than 4th gear.

[R338OY]

Me too. It gets higher in 3rd for me, by up to 2psi!

[MBS206]

Higher gears I find generally bring boost on earlier (If say accelerating from 2000RPM) As the turbo has more time to accelerate.

But I generally find that it spikes around a bit more in the lower gears as the boost controller has less time to react to boost spikes.

It also depends on how the boost controller is setup.

[mad082]

yeah it would be a mix of things that determine what it does. in higher gears it can generally build more boost as there is more load, but in low gears the boost can spike so much quicker that it goes higher before the controller knows what's going on.

[benl1981]

I have a GCG highflow on the rb25. 15psi is up by about 3500-4000rpm in 2nd then less than 3500rpm in 3rd and 4th.

In 1st though I think I only have 6psi at ~3900rpm and 11psi ~5000rpm.

Is this normal? Anyone with HKS2535 or GCG turbos noticed what there boost is like in 1st. The car is very quick but I reckon the stock turbo is better at <4500rpm in 1st. I think I had 7-8psi by 3500rpm in 1st with the stocker. I guess the load isn't there in 1st so I shouldn't be too tough on it.

Edited January 23, 2008 by benl1981

[paulr33]

engine load makes boost

bring the engine under load, it will make boost quicker

under first gear the ratio is that high the engine isnt under much load and just has lots of acceleration

[benl1981]

Yeah I understand about the load. Just looking for comparisons with people who have similar sized turbos

[benl1981]

Anybody with 2535 or gcg monitored the boost build in 1st?

Please let me know if you have

Cheers

[GeeTR]

My understanding is that boost is pressure the engine isn't ingesting, load is time based as the higher the gear the slower the motor RPM is accelerating (therefore there's an increased resistance to air flow going into the motor)

This combined with the fact your often using more throttle to maintain adequate acceleration in higher gears results in a greater "backlog" of air in front of the motor, meaning more boost and finally more power. Its s viscous cycle 

As others have said Phil, your generally more likely to experience a boost spike in higher gears, not lower, as its these higher airflow / faster boost transient conditions that tax a wastegate and EBC's chances of responding accordingly.

In your post though, your not comparing apples to apples. How does your 4th gear max boost and spiking issue compare to 4th gear on the street?

EDIT: Noticed im talking to a dood who asked a Q 4 months ago - whoops.

Boost in lower gears can be affected by dump, zhaust size, WG flap sealing ability... and most importantly EBC.. are you running one? It's not completely easy to compare your setup to others.

Edited January 29, 2008 by GeeTR

[SiR_RB]

diggin up and old thread here....

ive got my profec b spec running 13.5psi in my r32 gtr, usual mods aftermarket front pipes, high flow cat, 3.5" cat back, pods..

if i come to a stop, reset Peak Boost, then take off hard in first, go in second gear and take it easy, if i go into Peak boost again it shows it peaked at 14.5ish psi, but the thing is i never see this displayed on the screen ? the screens shows 13.4 -13.6psi

then i did another test, reset peak boost while driving in 4th, drop it down to second and accelerate, then go into 3rd etc then cruise it, peak boost shows 13.5psi...which is good !

so my questions is why does it peak to much in 1st gear ? why isnt it displayed on the screen ? but is saved as "peak boost"??

any info would be great !

[JonnoHR31]

probably from boost building much quicker when it first comes on. the profec doesnt react quick enough to stop it spiking 1psi. you could help it by lowering the start boost and gain a little bit but thats gonna make boost build slower in other gears. personally i wouldnt worry, 1psi extra in first isnt gonna make the slightest difference

[SiR_RB]

start boost is 88 (8.8psi, they say should be around 4psi ish lower then ur boost level)

gain is at 8% and holds boost perfectly !

[JonnoHR31]

dont worry about it then. sounds like a very conservative start boost and gain already

[SiR_RB]

cheers !

just had me abit worried, but figured it must peak in such a quick time that the screen doesnt even get time to register it on the screen...so everything should be sweet

thanks again

[mad082]

if you aren't seeing it show up, that shows just how short of a period of time it is at that amount of boost for.