How to you size a wastegate?

[Scott Y]

I have plans for a 20G on my GVR-4. I need an external wg, and I see 38mm Tials selling for $215 and 40mm selling for over $340.

Aside from the diameter difference, are there other considerations that make a 40mm a better choice than a 38mm? Does the extra 2mm flow that much more to enable better boost/creep control at our altitude?

I found a stainless recirc O2 housing here that's built for 38mm Tials that I thought looked pretty cool: http://store.straightlinespecialties.com/product_info.php?products_id=240


Thanks for any input.

[dsm_gsx97]

It really depends on the boost you want to run. Here was an interesting read when Googling this subject to help http://site.mawebcenters.com/evanstuning/tech11.html

Not particular to our cars, but interesting to read. I think the 38mm personally would be fine on a 20G. I had a 20G internally gated that only had a 34mm wastegate. I was able to run 23psi before the wastegate would blow open. I think it would have done better if I could just get the door to stay shut for full boost. A 38mm external on a 20G would be a dream on a street car running 18psi to 27psi, IMO of course. :cool:

When getting an external setup that dumped back into the exhaust I went with Victory Performances O2's. 3 Years on it now with no issues. Fitment was great (on a 2G).

http://www.victoryperformance.com/product/Detail.cfm?ProductID=504

Adding it up its $392 shipped for it for what you want. A hair more because of wastegate flanges (see below), but exceptional quality.

$295 2.5" O2 housing
$50 Tial 38mm flanges (optional if you have them already or buy the wastegate from him)
$35 Reroute back into exhaust
$12 shipping
-------------
$392

[dsm_gsx97]

This one is good reading too for sizing wastegates

http://forums.performancecar.co.nz/phpBB/viewtopic.php?p=455903&sid=6fb262a8e34b5c51fc93dcadb2bf238c

[Scott Y]

Regarding the housing from my 1st post:. I talked with him and he seems like a nice guy, they're making a batch of the housings right now. The bonuses are lifetime warranty, fits stock downpipe location, and I don't have to order flanges separately.
Get a Tial 38mm from FP for $215, and the total (minus gaskets, shipping,etc) is 355+215=570.
Experience counts, and if you've had your victory performance housing for 3 years with no issues, that's hard to argue and its definitely worth investigating their product

Decisions, decisions.