IPSC

Ok here is the sit rep. The car is an 89 with a K27/6, Autothority MAF and chips along with the typical jetted banjo bolt. This was all part of the PO upgrades. It has low power i.e. 225 RWHP. I have been replacing vacum lines and looking for leaks. I plumbed in a boost gauge last week and it is (or was) making 12 PSI that would drop off right away to a solid and steady 10 PSI. So after getting a straight hard pipe in it, I plumbed in a MBC and dialed in what gives me 15 PSI that dropps off to a steady 13 PSI.

SO...

What is causing the boost to drop off like that? Waste gate? Should I leave it at this setting or turn it up to 17 PSI that drops off to 15 PSI ?

IPSC

turbo8

set the boost to what your chips are ment for

schnellfahrer

If you still have the stock wastegate, that's probably the reason for the boost drop up top.

IPSC

Yep it's a stock wastegate. I have a guru rebuilt wastegate going in, hopefully in the morning.

IPSC

aeronautica86

before turning up your boost, you really need to get a Wideband O2 gauge or go to a dyno that has one and check your air/fuel ratio

IPSC

Dyno day is coming, the last time it was on the dyno it was running way rich. by 3000 RPMs it was 10 to 1 and falling. Going to trouble shoot that problem one the Dyno hopefully

IPSC

aeronautica86

the problem with turning the boost up with the autothority chips is that even though they are quite rich in the mid range, they usually lean out up top, so if you turn the boost up the mixture will be even leaner in the higher rpms which will lead to a blown headgasket or worse

jgporsche

also the stock exhaust can cause boost to drop off.

IPSC

Is the current 15 PSI falling to 13 PSI dangerous?

IPSC

aeronautica86

probably not, I think most autothority stuff is made to run around 15 psi

it would be best if you had a way of tuning the air/fuel ratio, such as a piggyback controller like the SMT6 or S-AFC II, with one of these you can tune fuel curve for max power and reliablity - you could then run anywhere between 15 - 18psi reliably (with good tuning) and make good power.

badass951

Unless the chips were made for a K27/6 then you probably will not be able to run more than 12psi or so without going lean in the top end. Autothority chips tend to run VERY rich in the midrange and begin to lean out as the revs climb.

IPSC

I would tend to think that the chips would be made for the K 27/6 as the came as part of a Powerhaus 100 hp "kit" that they sell. However I am just guessing at this point really.

IPSC