Best 3" downpipe w/external gate for 6768

[racerxrick]

After porting and chamfering the exhaust housing to the maximum I am still having overboost problems. At this point we are convinced that the 39mm wastegate combined with fairly small wastegate piping is the main issue. (We have another DP in the shop we can "borrow" with a 42mm gate and the gate tubing is considerably larger)...I don't know the brand of my current DP.

Link to my related and recent post w/pics: http://www.turbobuick.com/forums/th...precision-states-to-port-exhaust-hole.432828/

I plan to run 25-30psi though need to control boost for transbrake launches (we have wired/installed a Turbosmart Eboost2 electronic boost controller). Right now with exhaust housing fully ported and 39mm gate I still made 17psi 1st gear/23psi 2nd on a 10# spring.

I'm not seeing a lot available...how about this GN1 DP w/46mm wastegate? http://www.gn1performance.com/products.asp?cat=144

Maybe a custom built DP with atmosphere dump?

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[V6sleeper]

Have Brian Cotton fab one up with Turbosmart Hypergate.

 

[TT/Ameasap]

I control mine with stock setup through SD2 chip. I have been 25psi rock solid

 

[Boost231]

How low are you trying to go? That 39mm gate will flow alot.

 

[racerxrick]

Have Brian Cotton fab one up with Turbosmart Hypergate.

that's a good idea, I like that gate. Also I believe Arizona GN fabs pipes.

 

[racerxrick]

I control mine with stock setup through SD2 chip. I have been 25psi rock solid

The car has a FAST classic and was already converted to external gate

 

[racerxrick]

How low are you trying to go? That 39mm gate will flow alot.

Well I'd like to be able to control boost down for transbrake launches. Would love to be able to launch at 20psi but that may be optimistic. Plus for Mexico will need less than that. However I do plan to use the turbo in the 28-30psi range down track.

Agreed the 39mm gate should flow plenty. My concern is the piping to and from the gate is small (at least compared to the DP we have for another GN in the shop. I do plan to install that one for test purposes.

 

[ijames]

After you try the other pipe, can you just modify your dp with larger tubing for the wastegate? If you're happy with the rest of the fit and finish you have now, seems to me that that would be faster, easier, and cheaper than starting from scratch and having to worry about clearances down by the control arm, crossover pipe, and firewall all over again.

 

[racerxrick]

After you try the other pipe, can you just modify your dp with larger tubing for the wastegate? If you're happy with the rest of the fit and finish you have now, seems to me that that would be faster, easier, and cheaper than starting from scratch and having to worry about clearances down by the control arm, crossover pipe, and firewall all over again.

good points and a consideration for sure...however looks like the typical Precision gate alone will be close to $400 and more for a Tial. TR Custom parts and GN1 show 3" pipes w gate for just under $500. Ideally having a gate mount fabbed into the header side would be the best solution. In the end just looking to be cost effective and relatively simple.

 

[forcefed3.8's]

The gn1 downpipes fitment is hit or miss, and the gates are chinese junk that will seize up.

 

[racerxrick]

The gn1 downpipes fitment is hit or miss, and the gates are chinese junk that will seize up.

Thanks, this is the kind of honest staright forward response I'm looking for. I've been out of the TR world for nearly twenty years and need all the help I can get!.

 

[V6sleeper]

Thanks, this is the kind of honest staright forward response I'm looking for. I've been out of the TR world for nearly twenty years and need all the help I can get!.

That was a great answer from forcefed, your probably gonna have to spend a grand on a fab'ed pipe and a good wg these modern days.

 

[racerxrick]

That was a great answer from forcefed, your probably gonna have to spend a grand on a fab'ed pipe and a good wg these modern days.

these modern days LOL..yeah I guess I've been around a while now and it seems more complicated. I had a 87' Limited with TA49, Art carr conv., TransGo shift kit, custom Jay Carter Chip, fishtank valve boost control, boxed control arms, stock intercooler, DP and injectors on 8" slicks...ran 12.17@109mph on race gas and 25psi (then 11.77@112 on a small shot of nitrous). Then finally 11.17@120 with built stock internals on the juice.

As far as my current issue it seems the BEST option is boost control on the header side though maybe the easiest and less costly route is modifying my current DP for a bigger gate. Should have time tomorrow to install the "borrowed" DP as the o2 bung should be installed today.

 

[V6sleeper]

these modern days LOL..yeah I guess I've been around a while now and it seems more complicated. I had a 87' Limited with TA49, Art carr conv., TransGo shift kit, custom Jay Carter Chip, fishtank valve boost control, boxed control arms, stock intercooler, DP and injectors on 8" slicks...ran 12.17@109mph on race gas and 25psi (then 11.77@112 on a small shot of nitrous). Then finally 11.17@120 with built stock internals on the juice.

As far as my current issue it seems the BEST option is boost control on the header side though maybe the easiest and less costly route is modifying my current DP for a bigger gate. Should have time tomorrow to install the "borrowed" DP as the o2 bung should be installed today.

Nice setup, I had a similar one back in the days... Te44, Dynotech trans, 7th injector, red stripe converter, Atr pitbulls, quad air 108 chip, kb fpr, atr Superpump, unknown stretch ic mabe thunder fab,. on Cam2 car use to fly.

 

[slimtastic]

your external gate wont control boost because that stock wastegate hole drilled into the side of your stock style turbine housing is at a HARSH 90 degree angle which promotes no flow through it/ you may have a killer wasegate but under power it stalls any "would be" wastgated exhaust and then you start to overboost as a result.

build a nice smooth transiontion into your passenger side manifold for a wastegate and then plumb it up to the downpipes flange and youll never have overboost issues again

its like trying to take a turn at an intersection while driving 90 mph... while taking a on ramp on the hwy at 90 mph is easyyyy

 

[forcefed3.8's]

I worked on a car with a gn1 3" ext gate downpipe with a 6262. The original gate seized so I installed a tial 44. It was my spare with a 4lbs spring. I was able to make 5 lbs of boost before adjusting the controller. This is an unported turbine housing and untouched gn1 flange.

 

[slimtastic]

with a big turbine/turbine housing that makes (comparibly) alot less backpressure/ your wasegate approach angle becomes more and more important because your shifting your tubo's "control" away from backpressure and more towards flow.

fix the wasegate inlet angle, and youll fix your boost issue

 

[84BuickGNYorkPA]

I have a hye-tech 3" SST downpipe that I bought from them years ago. Well the external wastegate pipes to the Tial valve where carbon steel and eventually rusted/wore through. I had them removed and had new SST pipes installed by my fabricator friend at work, what we discovered was the return pipe to the exhaust flow went into a hole that was about half the diameter of the wastegate pipe, one heck of a restriction, just reporting what we found.

Chuck

 

[racerxrick]

all good replies everyone...thanks.

UPDATE: Just installed the borrowed DP (3" w/42mm gate and larger diameter gate piping)...boost control is good now. Went ahead and hooked up the Turbosmart eboost2 and was able to adjust on the money. Now we need to figure out how to program another boost group for the transbrake.

Looking at my DP I think it's best to go ahead and order another rather than modify mine...heading in the right direction.