External Wastegate

[tridentt150v]

I've got a '98 GTS.25t with a Hks cast low mount [extrude honed to clean it up] and a Garrett GT3076 WG.

I will probably be running this setup with 14-18psi and shooting for around 270-280 rwkw. External wastegate will be a Hks 40mm standard. Boost is controlled by a Hks evc IV. I have pretty much all the normal mods, fmic, cams, pod, zorst, z32, etc etc Motor is stock, no forgies, conrods or thicker gasket.

What spring rate should I get, 10 or 14 psi? It all comes down to when I want it to start bleeding boost off, but I'd appreciate some experienced comment.

[Craved]

keep the spring setup as close to the target as possible to reduce the work the EBC needs to do.

but you need to know what your minimum would be, as you might know 14psi spring means that will be the minimum boost you can run

[R31Nismoid]

14psi

As above, the spring closest to the target PSI is what you want to avoid gate creep because of a weak spring

[r33_racer]

however depending on wastegate size and if its close enough to whats needed for your choice of boost pressure, it may spike or play up and infact need to be swapped for a weaker one and use the ebc to bring the boost upto the desired level.

But generally closest to desired pressure so less work for the ebc. Just outlining our experience in the past where we have had to do that with the weaker spring.

[Guilt-Toy]

i got a 9psi spring in my car and the $22 boost controller (see thread) holds 20psi all the way through the rev range. Its really weird but it works. I know it shouldnt but it does lol

[R31Nismoid]

Do you get any creep when its loaded up in 4th/5th?

I did with my 7psi spring & 17psi

Only in 4th sometimes and 5th all the time, as you loaded up i could hear the gate open prematurely.

Sounded like an exhaust leak as it was only just opening.

But it was enough to delay boost a good few hundred RPM than normal

[Guilt-Toy]

none at all. seriously i should scan the dyno sheet i printed with the boost curve on it as well. im looking at it now. in 4th gear it goes up to 21psi at 110ks an hour and drops to 20psi at 130ks an hour and holds 20psi all the way to rev limiter. the line is straight as - no curves nothing.

Con at C&V wreckons he has never seen a bleeder type valve hold boost like that before and he would expect that kind of boost line from a eboost or something similar.

I dont know why it works so well on my car but it does for some reason.

[tridentt150v]

Thanks, I'll go with a 14.