andydavies

What boost pressure should I expect on a 97 UK turbo? Fitted a boost guage today, at WOT pressure went to 14psi, then dropped virtually instantly to 12psi and held. Car is standard apart from decatted zorst. I was thinking of fitting a Dawes but I thought they recommended no more than 14-15 psi, if thats correct what would be gained??

The_Judge

The boost pressures you've mentioned are there or thereabouts.

In theory, you should be able to up that another 2 or so psi (if you want to), assuming your AFR and timing are OK of course. Do you have a Knocklink...?

If you didn't want to take the boost any higher, a manual boost controller such as the Dawes or GBE, will allow the same level of boost to come on alot stronger. The stock boost control allows "wastegate creep", which quite simply put is the wastegate starting to open from about 7psi, gradually opening more and more until max boost is achieved. This makes for smooth acceleration. The MBC keeps the wastegate completely shut until the presure on the MBC reaches the level you specify, and only then allowing the air to flow to the wastegate actuator. This makes for more of a punch in acceleration. Same max boost, just comes on quicker and for longer.

Incidentally, the "recommended boost" differs from car to car, and is based on many variables. If you have a Knocklink, boost gauge, and preferably an AFR gauge fitted, you'll be able to specify your own recommended boost, tailor made for your car...

andydavies

Cheers for reply.
At the moment I do not have knocklink, I was only intending to fit AFR with the MBC. Are both required, or do you just need both if running higher boost levels? If recommended boost differs from car to car, how do you determine was best for your car?

The_Judge

To be honest, if you're not increasing the boost pressure, you could probably get away with not having either. But unless you have lots and lots of willpower, the chances are you'll be far too tempted to increase the boost above factory level so you might as well get the monitoring stuff sorted first. You can then learn how to use it all, understand what you're seeing, and then increase the boost safely. If you have to choose one over the other though, go for the Knocklink.

Trial and error, lots of patience, and common sense. For instance, it's taken me months of tatting with different boost pressures, starting at 16psi, then fitting a FCD and increasing to 17psi, then using Millers and increasing to 18psi, to finally settle on 16psi with Optimax and no octane booster. MY00 TD04 didn't consistantly like 17 or 18psi, which you could "feel" whilst accelerating through different gears. Sometimes it would be lightning quick, other times very stifled. I also didn't like the knocklink activity at 3500 revs in 4th or 5th gear...

andydavies

Cheers, I will start at normal boost levels and see how it goes.
Andy.