Downpipes and wastegates facts vs myths

[turboc87gn]

Im wondering and it seems lately a few others are too what is the real differences between 3" and 3.5" downpipes ? Performance,turbo spool, from what i can tell if you have a 3" then upgrading to a 3.5" the gain isnt worh the expense but if are buying one anyway then buy a 3.5"..Ive also heard that some people are changing back to 3" cause the larger pipe caused the turbo to spool slower.At what performance level does this become a factor?
Also how hard is it to change the wastegate puck to the larger one for billet turbos that RJC sells to use an internal gate billet wheel turbos? Any experience with these or is external the way to go to control the boost? Since RJC dosent sell a 3.5 they step right up to the 5" you pretty much have to figure it out youself im sure im not the only one punch drunk with choices lol:biggrin:

In my case im wanting to buy a 6765 billet journal bearing and a 3.5 pipe with the rjc puck as ive been told and read several times that the dbb option isnt really worth the added expense and a journal spools fine but if i combine that with a 3.5 pipe that may slow spooling down am i gonna end up with a turd??? (i know converter selection plays a big part too but for now just wanting to see peoples experiences with pipes and gates....)

 

[gn4u2c]

external gate is superior period. If your not planning to go deeper than low 10's there is no reason at all to go 3.5 unless you like the bling factor that sums it up

 

[bison]

I just made 686whp with an internal gated a 3.5"dp that is hammered down to less than the cross sectional area of a 3" pipe near the frame. A previous owner did it for clearance and i never concerned myself with it because it wasnt visible. I might fix it and do some dyno pulls to see if it did anything but i doubt it will. Id run a 3" into the 9's as long as the ex outlet wasnt being covered by the flange. If you plan on running a large turbo id go 4 bolt and external dp. I dont see the need for any external on a 3 bolt setup unless the racer is using an AMS or similar device to apply pressure to the top of the wastegate. An external readily accepts this type of configuration. The best spooling is achieved with the largest possible exit out of the turbo dumped to atmospheric as fast as possible. Spooling slower is total BS.

 

[turboc87gn]

Interesting info bison thx...

 

[Buickforlife]

Very good information, subscribed.

 

[Quik Six]

I just made 686whp with an internal gated a 3.5"dp

Why did I not realize that you would be the one that Otto said made 686 rwhp on 22#'s of boost?

Very impressive!!

Phil Engle

 

[bison]

I just made 686whp with an internal gated a 3.5"dp

Why did I not realize that you would be the one that Otto said made 686 rwhp on 22#'s of boost?

Very impressive!!

Phil Engle

That must have been someone else. I was at 24psi:tongue:

 

[Quik Six]

Forgive me. I'm an old man and the mind is the second thing to go.

22 or 24#'s, that is a lot of power.

Sure like to see what it does at the track. Let us know how that goes.

Phil Engle

 

[GNVYUS 1]

I don't consider the DP wastegate option for GN's to be very superior vs Imports that have them mounted off the header. You're not gaining much IMO vs the internal gate when you run that tiny feed and return pipe bent at 90 degrees to the wastegate.

If I were to run a Billet 67/65 (like a cast 72/76), I'd go 4 bolt header and have the wastegate right before the flange and I won't bother with recirculating it back into the exhaust for cost reasons mainly.

 

[slimtastic]

ive never had a bigger downpipe cause slower turbo spool... usually when people step up to a bigger dp, a larger a/r housing is needed to actually use the dp for all its worth....and that ar housing change will slow spool down