Tezzax5 wrote:Here's one for the experts?
On a SP the boost pressure is measured from?
A...waste gate
B...actuator
C...Inlet manifold
I do realise that you get a slightly higher reading straight from the wastegate hence the T-piece mod on some cars (I don't want to go down that path)
So i am contemplating getting the actuator rod replaced.
The car was slightly detuned before i bought it.
Basically i have had the car spun up on a dyno to help locate a BOV low boost issue..(problem solved thanks to the lads at MX5 Plus)
I am not that interested in overall kws just boost pressure at this stage as there as far too many variances in getting maximum hp
According to the mapping my fuel is still very rich which will be the next thing to sort out...(possible piggyback solution)
I am just wanting to help punch up the mid range and i believe that on my car the boost pressure is still a little low.
It's just under 6 for those interested....(measured from the manifold)
...LS1's are just soo much easier to figure out
Hi tezza,
Boost pressure can vary between turbo outlet to throttle body due to pressure losses through the intercooler piping. So it can be measured at any point along that path.
The pressure that the engine see's, i.e what is in the combustion chambers, is most accurately measured from within the intake manifold.
The standard SP arrangement is for the wastegate actuator line to come straight from the turbo outlet, where it has not suffered any pressure loss. The wastegate actuator controls how much boost the turbo produces, and is a set amount. On the SP the wastegate actuator is set to a default of ~8psi, so it pumps 8psi to the wastegate actuator, which opens the wastegate, thereby preventing further boost increases. Now, because there is a pressure loss between turbo outlet and intake manifold, that 8psi can easily become ~5 or 6psi by the time that air enters the engine. The t-piece mod relocates the pressure source for the wastegate actuator, making it post intercooler. So, the boost is taken from the throttle body AFTER it has lost a few psi through the i'cooler system. This then means that the turbo would be pumping out ~10 or 11 psi to overcome the pressure loss through the i'cooler, but by the time that ~10psi has reached the intake manifold and pistons, the pressure seen there will be ~8psi, which the SP ecu was designed to fuel for. The changes aren't so linear, but you get the idea...
Your dyno run would have measured the pressure from the intake manifold, which is the only sensible place to measure from as that is as close to what the pistons will cop in boost pressure.
In my opinion the threaded wastegate actuator rod is a poor solution.
Come and have a look at my setup and I'll explain how it operates. Can compare with the pulsar too as that controls boost differently again... The t-piece mod is not dangerous, it simply gets the expected (ecu program) boost pressure to the engine. The ECU does not measure boost pressure, so it just dumps a pile of fuel in based on air flow and revs. A bit more to explain perhaps, hope that helps.
)
