Quick Question,is the boost cut to 5psi max (uk 96)in 1st gear to save the transmission.

 

Shouldn't think so, in first gear the stesses are far less on the transmission than booting it at lowish revs in 5th. I might be wrong though so don't laugh if the above is plain rubbish!

 

There is no gear judge in the boost control code in the ECUs AFAIK.

The boost in lower gears is lower because the load is lower, and the engine revs too quickly for the turbo to make as much boost. In higher gears there is plenty of time under load for the turbo to spool up quicker hence the higher boost.

 

Usually the boost on most turbos is limited in 1st and 2nd gear due to the stress on the engine and drive train...

My old celica gt4 was limited to 5 psi in 1st and 2nd gear... think this is one of the functions of the turbo boost solonoid on our scoobs....Think its to do with all that power being transfered through the drive train from stationary when your in 3rd, 4th and 5th the car is already moving...

But 5psi seems low.

Dan

 

There was a mod with the celica where you by passed the turbo boost solonoid to give full boost in all gears proving that one of the functions of the turbo solonoid was to limit the boost in 1st and 2nd...


Dont know if this is the same on the scoob....

Dan

 

I am sure I dont get full boost in 1st or 2nd, (I have HKS EVC).

I was under the impession that, as J.Banks stated, the turbo cannot produce high boost as the revs rise far too quickly and you are then into the next gear...and so on.

I think I would reach iro 0.9 - 1.0 in 1st and 2nd gear, only in 3rd, 4th and 5th would I realise 'full' boost.

Cheers, MD complete with new MAF

 

In 2nd you can get plenty of boost if the boost controller adjusts the duty cycle. Stephen Done used rate of acceleration as a bias to the unused temperature boost compensation map to give increased boost in lower gear, but I think he just had clutch slip. However, I have had 20 PSI in 2nd gear without issue, so may be worth looking at again.

 

I will have a go tomorrow, I really dont like to 'push' the car hard in the lower gears as I am a bit mechanically sympathetic.

What does 20psi equate to in bar?

I remember when Mole and I fitted the HKS, we had not switched the little switch over properly....NO boost control at all, it spooled up so quickly the clutch was slipping like Billyo and I saw 1.8 on the display before the fuel cut kicked in!!!

Not really relevent I know.

Cheers MD.

 

1.38 bar

 

On a 94 legacy with fcd and bleed/restrictor (ecu can still pull back some boost) I now see 13psi in first, 15.5 in second no problem, and about 16.5 in 3rd, 4th and 5th. With the solenoid disconnected, I see about 8.5psi boost.

I think it's a result of throttle application too on my setup. Probably a function of the odd bleed/restrictor setup, but if I am in second a 4k, and floor it, I will just about see 14 psi before it starts to drop the boost at about 5.9k. Whereas if i floor it from 3k, I will get full 15.5 psi, probably due to spool up etc, and reducing duty cycles at higher rpm

Paul