My Twin-Turbo SBC 240Z Build by PaulR

By diyauto
( 2 )

My Twin-Turbo SBC 240Z Build

Compliments of PaulR @


Sometime back in 2004, after seeing Siliconeboy’s turbo project in process http://forums.hybrid...ead.php?t=89810 , I got inspired to do a Twin Turbo set-up in my 350 Chevy powered 240Z. It didn’t take to long to find the Corvette manifolds and a pair of T3/T4 (.60/.63) from Ford Turbocoupes (inspired by Mike Sitar’s “toohighpsi” Capri http://www.toohighps...TT/BudgetTT.htm 

These items sat in my garage collecting dust for the next 4 years 

So, last spring I decided it was finally time to get this project in gear. I started by installing an intercooler and relocating the surge tank I was using to supply the Holley Commander EFI system. 

I built an air hat using the tank from a “pancake” style air compressor that I had burned up the motor on. 

Since I wanted to keep the car on the road for the summer, I ran the air hat and intercooler on the NA engine… that got some interesting comments from people peeking under the hood. I jokingly told them that it was a high-tech cold air intake system.

Around September of this year I parked the car in my shop and got busy building. Lots of stuff had to be relocated to make room and to avoid heat issues. Fuel lines, brake lines, and wiring was re-routed. I moved the battery to the back of the car and used the spaced to mount a bunch of other stuff where it would be out of the way (fuel filter, relays, 2-BAR MAP sensor, coolant overflow tank, Wide-Band O2 sensor module)

I fabbed up the manifolds (thanks again to Siliconeboy for the idea)

Did some fit checks.

Built the down-pipes, cold side, etc

It’s now all together, (as of today) but I haven’t fired it up yet. Hopefully this weekend.

And, it all fits under the hood J

Thanks for the compliments. I plan to keep it fairly tame (at least at first). The engine really isn't built for boost. It's a 2-bolt block w/ cast crank and hyper-eutectic (sp?) pistons (9.5 CR). I would like to hit 400 rwhp, which I figure I can get with around 6 psi boost. Next winter I plan to build a motor that can take 10 or 12 PSI (forged internals, 4-bolt, etc)

BTW, this is stictly a street machine.


Wow, you guys are too kind  and not one person asking "Why do you need more power??" 

This site is great!

Yeah, I wasn't too sure about the fit before I started, so I did a fit check using 3D CAD first. I knew it had been done before, but to be sure... (images from ProE)

The outside color is close to stock (the engine bay is the original paint) I remember going thru color samples at the paint store looking for a close match. It is actually a mix for an AMC blue. Delstar DAR14025 is the color code. It was painted over 15 years ago (d*mn, I must be getting old )


She runs!! I just fired it up and checked for any obvious issues... no leaks, no smoke, etc. Compressor spins  Just let it idle a bit then shut it down. Need to set the wastegates for lower boost before I take it for a spin. I want to try things out at 6psi just to make sure all is good. The wastegates are now set for 10psi (checked with my air compressor and boost gauge) so I need to modify. They're the stock inernal wastegates, but I found a write-up on how to decrease the boost with an external spring. Also need to make some changes to the Fuel Management system (Holley Commander 950)


I set the wastegates to start opening at 6psi (added the external spring), down from the stock setting of about 10 psi.

got them re-mounted and just started tuning. I've got the fuel map set so that it's running pretty rich right now. Hope I can find the time to do some serious tuning soon.

Don't know  I haven't taken it out of the garage yet. I just got the tune set tonite so it will idle good now. When I rev it up, it bucks a little before smoothing out, but the A/F meter shows about 11.5:1, so I know I have a little tuning to do before I get it on the road. Turbos spinning up sounds cool!!! I tried video w/ my digital camera, but the audio is horrible. Unfortunately I've got another commitment this coming weekend, so probably a couple more weeks. Hey, like I said at the beginning this has been a project I started 4 years ago... what's a couple more weeks 


The 3D model is to scale. I found a CAD model on the web and checked it against dimensions that were in a GM book I have. Should be the same as the ones in the sticky at the top of this forum. You're welcome to a copy (ProE or a nuetral format like IGES or STEP). PM me and I'll send it to you. If a moderator wants to add it to the sticky, let me know.

I haven't run it hard enough to get real hot. but I do have stainless heat shields over the tubines. ( made from a sauce pan I bought at Value Village for 69 cents  ). So far, I can put my hand onthe hood and it is comfortably warm. I'll probably glue some insulation on the hood above the turbos before I get on it.


Sorry for the lack of updates... I was out of town for 16 days, then I was helping my son work on his Datsun 510. Anyway enough of the excuses  

I got it on the road for the 1st time last week. A few nagging annoying problems, but nothing major so far. I have an oil leak that appears to be coming out of the back of the intake manifold. I'm guessing the seal between the manifold and the lifter valley (I did use a generous bead of RTV, not the stock gasket). Not sure if its boost related or not, but it wasn't leaking before the turbos went on. I tried disconnecting the PCV, thinking I was boosting into the crankcase thru it, but it only got worse! I also have an intermittent electric problem that I need to track down that kills the engine. I might be the supply for the MSD module, but it doesn't happen long enough to trouble shoot. Just a PITA when it decides to quit... especially in traffic 

OK, so impressions? I have to say WOW! The boost comes on pretty quick and you can definitely feel it. The 1st day I took it out, the roads were wet (this is near Seattle!) and no matter what speed I was going, the rear end would break loose when boost started kicking in, not a very friendly car to drive in the rain. We just had a couple of dry days, so I got to "feel" the acceleration pretty cool! Remember, I've got the wastegates set to only 5psi, so I not adding a ton of power, but its definitely working for me. 

I want to add some insulation to the hood above the turbos (gets pretty hot to the touch, but no paint discoloration) and fix some of the other minor issues, but so far I'm happy with the results.


I think the seal was bad all along and the added blow-by is now pushing oil out the seal. It may be hard to inspect because it's so tight to the firewall (set back even further than JTR by 3/4 inch). Maybe if I pull the distributor I can get a better look. At worst, I'll pull the intake and re-seal. I didn't expect much blow-by since I did a leak-down check before I added the turbos and the worst cylinder was 97% The thing I don't understand is why it got worse when I disconnected the PCV. I unhooked the line that goes to the base of the Throttle Body and plugged it and just left the PCV in the valve cover open and I got lots of oil running down the bell housing. I hooked it back up and its leaking just a little.

Thanks for the reply... I'm now hooked on boost