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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

Why not fit one,LS1 that is
WASP

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.

Thanks for the explanation but you now have me thinking...

Can somebody with a SP have a look at the part number on the actual actuator?

It might just be possible that when all the work was done a few years ago that an actuator with a lower PSI rating was installed or the spring tension
might also be failing.
Or even worse they used an actuator off an SE? ( JUST JOKING )

Can actuators be tested for accuracy ?

I know it looks like i am nit picking but i want things just right..


t

It might just be possible that when all the work was done a few years ago

What was all the work? What was wrong with it?

Tezzax5 wrote:So i am contemplating getting the actuator rod replaced.
Basically i have had the car spun up on a dyno ...
... will be the next thing to sort out...(possible piggyback solution)

I am just wanting to help punch up the mid range ...

it..... BEGINS!!!

Tezzax5 wrote:Thanks for the explanation but you now have me thinking...

Can somebody with a SP have a look at the part number on the actual actuator?

It might just be possible that when all the work was done a few years ago that an actuator with a lower PSI rating was installed or the spring tension
might also be failing.
Or even worse they used an actuator off an SE? ( JUST JOKING )

Can actuators be tested for accuracy ?

I know it looks like i am nit picking but i want things just right..


t

I'll have a look for a part number on the weekend. The actuators are certainly available to suit different applications (boost pressures).

They would be able to be tested, but faulty ones will show up as fluctuating boost levels being achieved, which doesn't seem to be the problem with yours.

Thanks for that MR G

I really just want to confirm that a lower pressure actuator was/wasn't used.

Minx the car had a conrod bolt failure at around the 103k mark and everything in the engine bay was replaced with brand new bits.

The previous owner spent over 10k replacing the lot with brand new oem parts.
(the receipts make for interesting reading )

My gut feeling tells me there should more sting in the tail.

If the replacement turbo came from Mazda then it will probably be running less boost than it originally had. When my turbo was replaced under warranty it only made 6 PSI compared to the 7.5PSI of the original.

You're probably not interested but rather than playing with the actuator I installed an electronic boost controller. I tried the t-piece mod and found the boost to be to aggressive. On my car it made the throttle lift off issue even worse. Wet weather driving was just a whole lot of wheelspin. With the boost controller the boost comes on a lot more progressively, even more progressive than stock, and it's much easier to drive in the wet. There is the added bonus of having multiple boost settings for various conditions ie wet/commute/race. It cost a bit more than $2.50 though.

Yes a good, well set up EBC would be a good solution. Garry what type do you use, and did you set it up yourself? I'd like to get one too but just haven't gotten around to it.

It's only a used povo Blitz Dual SBC I got from Ebay but it does the job I want it to do. I originally set it up myself but the last time I got the ECU reprogramed I got the guys to set it up on the dyno to run the maximum safe boost for the tune.