Extenal Wastegates Options

[elvasoshexai]

ok.. so the wastegate actuator on my ct20b is fubared.. i get boost creep like crazi...

i was going to get an external wastegate to replace it and weld the internal one shut.

i just hv a question about size.

i was planning on getting a tial 38mm w/ either .5(7.252psi) or .6(8.702psi) bar... i hv an mbc and plan to run probably 10psi neway tho...

however, the shop my car is at, a customer has a 48mm wastegate but wants a 38mm and he said that customer is asking if i want the 48mm turbosmart wastegate in exchange for a tial 38mm...

i'm assuming 38mm is a good size for a 5sfte...

would i b better off w/ the tial 38mm or the turbosmart 48mm?
the 48mm seems kinda big... i'd possibly get a lot of lag?
not sure what other pros/cons there would be between the 2?

any help? thnx

This post has been edited by elvasoshexai: Nov 28, 2007 - 12:59 PM

[easternpiro1]

i was just asking myself what different size wastegates were for and after this discussion, its clear.
LIKE diluted mud . Can someone re-word? i follow, but want to be sure

[Tony_the_Tiger]

i was just asking myself what different size wastegates were for and after this discussion, its clear.
LIKE diluted mud . Can someone re-word? i follow, but want to be sure

Here's how wastegate really works... All it does is vent and redirect exhaust away from the turbo and bypasses it to maintain boost. The few main factors to consider are manifold/wastegate design, exhaust back pressure and the amount of boost you plan to run. Don't even look at WHP at all because I had cars in here at 300 WHP needing a 50mm wastegate.

If your manifold has a wastegate location that is in clear path of all manifold runners, then you can mostly get away with a smaller wastegate. If you have a manifold that has a wastegate location that only vents out one or two runners only and has a nasty bend, etc, then you may want a larger one.

If you are running a turbo biased with a much larger turbine housing and wheel, such as most Garrett GT series turbos (smallest compressor trim within its family), then it has more "turbine" then "compressor". Turbos will larger turbines will dramatically lower exhaust back pressures, and therefore, it requires more wastegate. The natural least restriction path for exhaust to flow out is through the turbo instead (because of big turbine and lower back pressures between turbo and exhaust ports), and it would mostly likely keep going through the turbo instead of going out of the wastegate if the wastegate is too small. AKA boost creep

Another thing to look at is the amount of boost you plan to run. If you have a really large turbo say a GT35R, and you somehow want to run only 6 PSI, this would require a much larger wastegate too. Assume that 100% of flow going through the turbo equals max boost of 20 PSI for example.. Now you want to run 6 psi kinda puts it at 30% through the turbo and 70% out of the wastegate. The lower the boost, the bigger the wastegate.

So all this boils down to really... Run the largest wastegate vs price that you can afford and physically fit in your engine bay. That is why the Tial 44mm became so popular because it was compact and it is the largest wastegate in its size without breaking the bank =)