Patrick's Twin Turbo 350 Build Thread

Sean had exhaust port flanges for the 350 available, so you could build your own manifoilds, also sometimes the Burton kits are still available as resale. If you search the forum for older info about this there is quite a bit.

 

You may also be able to cut up some SBC headers and flip them if you can get flanges as Max Damage mentioned above. The position of the Burton manifolds isn't ideal (see my struggles with brake mc clearance a few pages back). I'd like if they were farther forward.

If going single I'd put the turbo on the passenger side to avoid this problem with the brakes, if you remove your AC box there's a decent amount of room over there!

 

Another option is twins off the stock manifolds with a oil pump....it works perfectly the LS guys myself included have put MANY miles on these setups....THEY WORK...and there's PLENTY OF ROOM....two dirt cheap TE44 or TE60 turbos from the v6 guys would absolutely kick ass on a 350cid.....will it look as cool as custom built turbo headers or a 78/75 single mounted front and center ..no....but will it run a 3800lb GS into the low 10s....absolutely

 

Good info. My reasoning for putting it on the DS side is I want to keep the a/c ..I'm in Houston; non-negotiable. Pat I will look at your TT post this... Is this wishful thinking on my part or do you think it is possible to maintain the power steering pump....and my sanity?
As this is a mystery motor all I know is the cam and that it may be a 10:25 motor which may poo poo the idea...Im sure there is a way to have some idea of the compression ratio if I take a compression test and know the cam specs.... Larry would probably know....

 

Unless it's built with aftermarket pistons its not 10 to 1 and certainly not over....the 350 sp /GS engine was rated at such but was really around 9.6

That said...I would put a thicker Felpeo gasket on it ...service the heads...even ad larger valves when you upgrade the springs..a must when running boost

To make life simple ...run twins under the floor as I suggested..you can then keep all accessories in the factory configuration...

Or you can run a single on the pass side...build a "box" under the pass seat there's a good 2in to be had to pus the turbo up...a t70 to 78/75 will fit fine and hang no lower than a muffler would.
Heat barrier on both sides of the floor and a coated exhaust housing will manage the heat just fine

 

I don’t know if anyone has tried this and whether or not they had any success.
I would TRY and emulate the 86/87 Turbo Buicks set up. Get the brackets (may take some time and searching) shelve the A6 compressor and use an R4 low on the drivers side. Shelve the power steering pump and use the “Turbo style” pump and remote reservoir.
I can’t see how it can’t be done as the V6 and 350 are the same at the front
Use the factory left iron manifold to crossover to a fabricated right side header and mount the turbo to the fabricated header GN style.
Doing it this way you’d only have to fab up one manifold/header, AND less complexity under hood.

 

The LC2 approach is the probably the best and one I suggested years ago...it just makes the most sense....and you gain alot of positives....

 

I didn't see any problem keeping the power steering when I was mocking up the Burton twins. If anything would get in the way it would be intercooler piping, but the pump seems low enough that it won't be a problem. The turbo is way farther back than the pump!

 

What would you guess it would cost for a twin/single set up ?
BTW, swapped the 2:54 rear end for a 3:23. Still need to do the brakes but it should make a huge difference.

 

Running twins under the floor- who has done this? I like that idea.

 

Expect 5k .....I had twin 62mm in my 2013 1le camaro...mounted off the stock manifolds...made 1019rwhp ......

 

Cost depends on a bunch of factors. I haven't even finished my turbo build yet and this thread started in 2019! Granted I also had to redo the entire car more or less. Can you weld and fabricate? How comfortable are you with electrical (EFI)? These will help immensely otherwise paying someone will be very costly.

Here's some questions to ponder:

-Single or twin? As you can see there are advantages to both

-Intercooled? An intercooler will add power but will add more complexity. For example, I moved my radiator back about 5" in order to have room for one, which required lots of fabrication. I will be aluminum welding the tanks on my core and all of the intercooler piping myself.

-Carb or EFI? A good blow thru carb can't be had for ~$1000 so I'm told. EFI will be more precise tuning wise and has some nice features like controlling timing per boost, but again is way more expensive if you factor in fuel system upgrades. Setups can run from mild (self learning TBI) to wild (standalone, sequential, individual cylinder afr) For example, I had to learn to bend fuel hardline, do an EFI tank swap, and will be knee deep in wiring my EFI.

-Stock or built motor? Are you planning on doing this to a stock motor or building the motor for boost? Obviously boosting a stock motor is more of a gamble, but if you keep boost moderate it'll probably work okay. This is what I'm doing but I am half expecting the motor to blow up at any time haha. I'm planning on getting a pro to build a forged internals motor for me in the meantime.

I know this is a lot of info, and I'm not an expert either so take it with a grain of salt! It can definitely be done but it helps to have a solid plan. Here's the rough outline of my plan for reference, these are just the big items but there are also a million little things that will add up:

-Used Mark Burton manifolds ($500)
-Turbonetics C15 TNX turbos pair ($1400)
-Garret Intercooler core, custom end tanks, piping etc ($600)
-Holley Terminator X EFI ($1800)
-Holley Sniper EFI fuel tank and pump ($700)
-CSU carb hat ($300ish)
-Dyno tune $$$?

Hope this helps a bit! You could also save yourself the trouble and just buy Sebastien's twin turbo car, he's sadly selling it:

https://v8buick.com/index.php?threads/68-gs-california-350-twin-turbo.391696/

He'd also be a great person to get in touch with an ask questions as I did!

 

Thanks guys, great overview; it always good to know what one is getting themselves into. Agreed on Sebastien's car- shame that he is selling it....
Given what you are saying , it would be more of a project than I want to get into....buying his 68 would be best option though I don't have the funds. I hope whoever buys it will keep us up to date on its progress. Looks like he has done a excellent job and has not cut any corners. What I may end up doing is putting a 75hp kit on it in the late summer and call it a day.....

 

Where's that hood

 

Thanks for pushing me to update the thread! I have been so busy that I've been neglecting it (and the car), but I did manage to get Craig's work of art mounted and have been driving with it for the past few months. Fit and finish are amazing and Craig went through leaps and bounds to not only make me a custom airbox design that will feed the turbos, but also package it with excellent care and was communicative the whole time. I highly recommend his hood, Craig's been amazing to work with.

Here are some shots of it in the car. I still need to have it painted and once the turbos are on get it plumbed. But I actually think the primer color looks pretty good on my car as is!




Hood pins installed:







View from inside:

 

Where you get the hood? I like the dash can you show more? How does it work

 

Craig (mltdwn12) was doing them out of 'glass a few years back. Super cool.

See https://www.v8buick.com/index.php?threads/70-72-fiberglass-gs-cowl-induction-hood.358228/

Devon

 

Idk if a 350 is worthy of a nice hood like that...

 

Sure it is

 

I can take some pictures of the underside/airbox. On a normal carbureted car the air box would seal to the air cleaner similar to a stock GS. On mine I was planning on routing the inlets of the turbos back to the air box!