Has anyone with an STi 7 managed to get full boost in 1st and 2nd gears?

I know I can't.

Mods: decatted downpipe, induction box, Blitz SBC-DC.

If full boost in 3rd gears and up is 1.40 bar, 1st gear can only get 1.1+ bar, 2nd gear 1.2+ bar.

Higher boost profiles show similar pattern (unless of course I set full boost at 1.1 bar for 3rd gear).

Any quick solutions to this other than anti-lag system?

Thanks!

EDIT: Forgot to mention this theory: I read or heard somewhere that STi 7 is difficult to get full boost in lower gears because the 6-speeder has such a close ratio that the engine never imposes enough load on the turbo for it to spool up to high boost numbers (like 1.3bar or above). That is, say in 1st gear, by the time the turbo gets enough load to boost up to 1.1bar, the rev has already reached the redline. Is that true?

[Edited by GDB - 28/05/2002 07:52:41]

 

Your latter theory is indeed true. All open loop boost control systems do this. For me, its more of a concern "seeing 1.4bar on my gauge" as opposed to "only hitting 1.1bar in 1st gear".

 

Hehehe...

RT it's me 6877 just in case you haven't noticed. Our friend 399R needs to boost 1.6bar in gears 1 and 2. I think he's quite pissed that a few days ago all those mean machines with anti-lag were blowing him away.

 

Har! I didn't know that it was you...

 

You won't, unless you are pulling a 2 tonne trailer, which makes it a bit pointless....

Boost is linked to load, and the gearing in first and second means it isnt getting much load.

That's why you will see max boost going uphill in 4th to 6th gears.

 

I used to have a Toyota GT-4 carlos sainz and in first and second gear the car would only give you 70% boost were as in third boosts was 100%.

The reason being is to reduce power on lower gears and avoid them
being chewed up beyond any recognition!

I guess this is why most rolling roads tset the car in third...?

Plums.

P.S. It was possible to overide this by fooling the ecu.

 

You mean 4th????

Matt

 

Yeah your probably right Matt!

Although I heard 3rd would be easier......

due to lower speed on the rollers?

Plums.

 

a dawes device set to stock boost would sort this out.

 

A DD wouldn't sort this out!

F

 

What does 1 bar of boost equal in PSI.
I thought 1 bar was 15psi....if thats the case then 1.4 is 21 psi from a STi??? Does that not sound high to anyone???

 

A Dawes Device will be able to sort the boost levels out, you can set it as low or as high as you want within reason of course.

We sell loads of them to stop boost spiking issues and they work very well.

My Sti is peaking at 1.4 bar + 20.58 PSI. I keep my eye on it though.

1 bar = 14.7 psi.

Jamie

www.j-w-racing.com

 

I repeat...doesnt over 20psi sound too high for factory cars with a factory ECU????

 

Bruiser,
My std JDM STI7 can touch 1.4bar WOT in 4th gear. Std engine, std exhaust. Downpipe still in place, with blanking plate in front of wastegate and all...

Decat'ted, we've seen 1.7bar peaks. Scary? Yes!
Which is why there's been so much talk of controlling these spikes.

 

What were these boost pressure measured with. A gauge fitted aftermarket??? Or using a tuning shop's equipment??
What is the factory claimed maximum boost??? And what does it drop to after the peaks of 20pounds+. Have all STi's had this peaking in the past???

 

Nope, its measured with the STI Genome Boost gauge. But not only on my car, I know of at least 5 other cars with the same findings. Perhaps you should have a look at the thread on "decat boost spike fix idea" in this forum.

 

RT- Is that a factory fitted boost gauge?? Or an optional extra??
Have you got a pic of this gauge...I have been wanting an STi boost gauge for as long as I can remember!!!!

 

RT,

Is that the re-badged Defi (they are nice ) or the Lamco (not so nice )?

Matt

 

The gauges are "official" STi Genome unit. It houses three 60mm gauges, replacing the section where your clock is now on the dashboard. The "official" gauges are actually Defi units with STi logo stamped on them. It costs more of course than the 'replica'.

Here's a picture of the 'replica':
http://www.defi-shop.com/trihood/mtrhdfrm.html

I hate to use the word 'replica' because it invokes an 'inferior quality' emotion, while in reality it's the same as the "official" unit, as long as it is nicely painted to match the interior.

You can put any gauges inside there; I heard even 52mm fits by putting rubber around the round housing.

20psi = roughly 1.4bar sounds high, but apparently the JDM engine can take it well in its stride. We do have 98RON fuel though, not sure what UK is using.

My boost is read from the Blitz SBC-DC EBC; the vacuum is tapped at the fuel pressure regulator if I'm not mistaken.

BTW, thanks for the replies so far. Keep them coming.

 

Jamie - your peak of 1.4bar, is that in higher (3rd onwards) gears?

If so, what have you experienced as the peak boost in gears 1 and 2?

Finally do you have decatted or standard exhaust?

A JDM owner in America reported 20psi boost in 1st gear in STANDARD exhaust. After he upgraded to other goodies (including decatted exhaust), max boost in 1st gear is 17.5psi, around less than 1.2bar, which is what I and other decatted STi's can realistically achieve. Can't get any higher than that.

EDIT: geez forgot to add this:

Based on the new info on decat vs. non-decat boost profiles, I'm proposing a new theory:

In a non-decat exhaust where the downpipe is very restrictive, the revs don't climb as fast, as the engine has to 'work more' to overcome the flow-restrictive cat. The engine hence is exerting more load on the turbo, which in turn allows it to build boost HIGHER in the lower gears. In comparison a decat engine's revs climb so fast that the turbo doesn't have enough time to build boost past 1.2bar (as I mentioned in the 1st post).

Just a food for thought.

Anyway, a chap in America suggests disconnecting the actuator altogether, hence the turbo is allowed to spool to whatever level it wants to spool. Then, have a go in 1st gear and 2nd gear.

I think THAT sounds like the ultimate test whether or not the turbo can build boost past 1.2bar in lower gears, BUT that just sounds super risky borderline crazy.

Has anyone done that, in previous cars, while troubleshooting a problem, when totally pissed drunk... ???

[Edited by GDB - 5/30/2002 6:00:08 AM]

 

It boosts to those levels only in higher gears, with the centre cat taken out and a Blitz NUR Spec R Exhaust System, ITG panel.

Im still waiting for the DP and other mods to go on.

Jamie

www.j-w-racing.com

[Edited by Jamie Whitfield - 5/30/2002 8:52:54 AM]

 

Why do you want full boost in your quickest gears?? the only thing that you will do is damage your car cos if you do some standing starts (1.3 secs to 30mph remember in 1st) and you put all that power through your wheels something is going to give way!
The car has been designed to give its boost in the lower gears for a reason, the rest (3rd gear up) is designed more for safety reasons rather than anything else (thats why the boost drops off!) but like it has been said, it will eat your gearbox/clutch etc very rapidly with that ammout of power going through it.

Tony

 

Tony,

Our buddie wants a tad more boost in gears 1 and 2 because Evo's running anti-lag are kinda blowing him away in the local rally scene.

 

I doubt he'll get it.

Most of the theories talked about so far are partly true but not wholly.

Boost IS load related as Dave TS mentioned, so unless the dawes device can induce load I can't see how it would help? (i.e. it's not a "boost" problem, it's a load problem).

JDM STi7 will see anything up to 1.5 bar if in OEM trim. I'll record the boost profile on my Defi on the way to work and see what it's hitting through the gears.

Free flowing exhaust will help, but may even reduce the amount of peak boost in lower gears, it will spin through first and second so fast (due to improved gas flow and pick up) that although faster, peak boosts may be lower.


Mike

 

Mike, in stk trim, you'll only see 1.4bar or so if you suddenly give it WOT after cruising at a steady rpm in 4th gear.

If its off from the stoplights thru the gears, you'll never see 1.4bar. 1.2bar in 2nd gear, tops!

 

Yep, I know (I have a JDM Sti 7).
Figures of 1.5 bar are recorded on my Peak boost on both my digital SPA gauge and the Defi.

Yep, I fully understand the lower boost in the lower gears issue which is what I was attempting to get across in the previous post.

Mike
Scooby Mania