10's in time my friend. i think the slower time was from the 60 foot as well. i also need to turn up the timing. still running 19deg
One of the key factors on turbo’s is back exhaust pressure.
This same backpressure also has a large affect on spool rpm, combined with the rest of the motor; Turbo, compression, cam, exhaust, heads, tune, converter, etc.
Typical street application turbo chargers have 200% backpressure.
That means; At 20PSI boost, you have 40PSI exhaust pressure before the turbo.
This makes your turbo only 50% efficient, and, decreases your effective cylinder filling.
So …………
I started working on a calculator program to determine camshaft timing, etc etc.
It will never be a “professional calculator”, but, it is amazing to see some of the cause and affect of cam timing and overlap. Which brings up the $1,000,000 question;
On a HA set-up, do you want the cam biased towards the intake or exhaust?
I started a thread on this a while back and never got any responses.
If anyone has any backpressure measurement data (boost vs exhaust pressure), I will run some more calcs and post them.
Anyway ………… since the restriction is in the turbine, a 4” DP (Example only) will not be of much benefit. Matter of fact, it could actually hurt the car as the gasses cool off with the expansion into the 4”, and velocity drops.
Anyway ………. Back to topic.
To truly determine how big of an A/R you need, you will need data.
IMHO, It is not just about HP, but a balance between HP and TQ.
Having said that, a bigger A/R on the same set-up will typically narrow the powerband, but give more HP (Peakier). The assumption here is that the car ran OK and was not choked out to start with.
My instinct tell me that a size change from 0.63 to 0.83 A/R on the turbine side, is about a +200-400 RPM stall change.