blown 944

What kind of ratios are you seeing at what boost levels? I just measured mine and was surprised at how high it was.

Oddjob

About 1.7+ @ 15 psi w/ 26/8's

TurboTommy

At what RPMs should also be included.

I've measured several setups over the years (different displacements, turbos, etc.)
I can't remember exact numbers. It would have been great if had of kept notes, but it was of little interest at the time because all I cared about was that I didn't like the results.
Quite a few years ago I posted optimistic numbers, but I found out afterwards that they weren't accurate because the slightest leak in the test equipement will screw the results.
Therefore discounting that, most correct results were creeping up to, but not quite reaching, 2.5 at the higher RPMs at 17-18 psi boost. This included a so-called powerhaus k29/10 on a 2.8l and also a bone stock '87 which had the normal boost drop off to 9 psi.
In the mid range RPMs the ratios were always a bit better; about 1.7 to 1.8 IIRC.
After many years of learning ($$$), I've finally achieved a very noticable power producing 1.1 - 1.2

When you say your numbers are high; how high?

onspeed

what turbo you running to get 1.2?

And I thought over 2 is dangerous? you're saying stock 26/6 is doing 2.5?

blown 944

I measured 2.4 at 24 psi. Totally surprised me!! Rod was absolutely right about having more crossover pressure with the bigger pipes. The only thing I can think of is that the exhaust cooled in the crossover and became too hard to move through the turbine housing and became an exhaust brake of sorts. I was so pissed when I found out that I was not making any more power at 20 + psi vs 17psi. Measured the maf voltage.

Pitching the ts for now.

333pg333

Depending on the size of the X over pipes and the turbo inlet, I wouldn't be surprised if there isn't a bottleneck or stall occurring too Sid. At what point along the X over are you measuring?

thingo

Mine is around 1.25 at 17 psi@6500 as said it rises with rpm, mine is ok, I would think it would be possible to get it lower, but what actually works is not always obvious( or possible).

333pg333

Rod, is that with your current setup? What was it with the 2" pipes?

btw nice improvement yesterday!

thingo

It was a couple of psi higher if I recall, and noticeably laggier.

ehall

A quick question, somewhat related...I think. If you run a big valved head, (bigger than stock) should you expect higher Xover pressures as a result? If so, can that cause additional lag?
On a stock 26/6 or 26/8.

TurboTommy

If all else being equal, then a big valve head would cause slightly higher cross-over pressures, and less lag.
Remember, this is all else being equal.
There are some things that that cause higher cross-over pressures and also more lag; like a restrictive post turbo exhaust, for example.

ehall

Good. I thought that was the correct answer. Now I have to find my intake leak, before the turbo.