Project Nissan Sentra Spec-V Part 7: Installing a Turbo System

Project Nissan Sentra Spec-V Part 7: Installing a Turbo System

By Mike Kojima

Some good news for our project is that Redline Track Events has revamped their rules set so our Spec-V is now eligible to run in the less exotic Modified class.  Now we have a chance since we no longer have to compete with mega buck efforts like Chris Rado's Scion TC monster.  The car was designed to run DOT radials so now we can run in a class where they are required.  This will also cut our tire budget.  Now that our car has a chance of being competitive we will turn our attention to our turbo system.

Follow our project here!

 Project Nissan Sentra Spec-V Part 7: Installing a Turbo System
We had started our Project with the intent of using a fast spooling Garrett GT28RS Disco Potato turbo.  It became quickly apparent that we would need much more than the DP's 350 hp capability to be competitive in Time Attack so we changed courses in mid stream and decided to run a bigger turbo, a GT30R. The compressor on our GT30R dwarfs the GT28RS.
 Project Nissan Sentra Spec-V Part 7: Installing a Turbo System
The Turbine discharge is a lot larger for a lot more flow as well.  Note the divorced flow path for the internal wastegate.

Since the long stroke QR25DE does not like high rpm, we have chosen to limit its maximum revs to 7000 rpm and make power by adding turbo boost.  Jim Wolf Technology designed our turbo system to produce power over the widest possible range of RPM rather than peak power.  The JWT system was also designed for simplicity, lightness and reliability over maximum power.

Project Nissan Sentra Spec-V Part 7: Installing a Turbo System
It was apparent that our newly built JWT experimental turbo system was going to be massively outgunned on the track even though it would have been wonderful on the street!
Project Nissan Sentra Spec-V Part 7: Installing a Turbo System
Goodbye small GT28RS, hello GT30R!

We had started with a smaller turbo, an uber fast spooling Garrett GT28RS otherwise known as the Disco Potato.  This turbo can produce a maximum of 350 hp or so.  We quickly realized that this was probably too little horsepower for us to have any hope of being competitive.  This lead us to scrap much of our original system and upsize to a Garrett GT30R.

 Project Nissan Sentra Spec-V Part 7: Installing a Turbo System
Burns Stainless supplied us with thin wall 90 degree and straight 321 stainless tubing.  With a 3” radius the burns 90 is extremely tight.  With exotic 321’s superior properties, you can get away with real thin tubing for less weight.  321 is expensive, more difficult to fabricate and harder to weld but it is a superior material.
 Project Nissan Sentra Spec-V Part 7: Installing a Turbo System
We also used these stainless steel doughnuts from The Chassis Shop.  Doughnuts are made by welding two stampings together to create a tighter longer radius bend than can be made by a mandrel bend.  These things can help you package many sorts of things in tight places.

We could have gone more exotic and designed an equal length tuned header with external wastegates but we jointly decided with JWT that we could easily make more than 500 whp with a very simple system using a log manifold and internal wastegate.  In racecars simple is better.  A log manifold packages much better, is less likely to crack, can spool faster and is lighter.  An internal wastegate makes the exhaust plumbing simpler and more reliable.  We also felt that it would be hard to get more than 500 whp to the ground in a FWD car with the technology we could afford.  It would also be difficult to get the drivetrain to be reliable with more power than this as well without exotic and expensive technology.

 Project Nissan Sentra Spec-V Part 7: Installing a Turbo System
Mike Smith, Jim Wolf Technologies master fabricator starts by test fitting our new turbo to our old manifold.
 Project Nissan Sentra Spec-V Part 7: Installing a Turbo System
Once he has an idea of where the new turbo can fit, he gets a rough idea of where the larger T3 size flange has to fit.


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Wednesday, February 02, 2011 8:40 PM
Great article. I love that you guys featured Mike Smith in this article as he has done so much for the Nissan community. Also love the tip on using a cordless drill to sharpen the tungsten, I'll be stealing that one!
Wednesday, February 02, 2011 9:46 PM
Fun article. However, I'd be slacking if I failed to point out that the machine in the pictures is a horizontal belt sander and not a surface grinder. A surface grinder is a rather different type of animal. ;)

That's a pretty tight downpipe fit..
Thursday, February 03, 2011 2:49 AM
AWESOME work on the downpipe! They're really masters in the field :D

Just curious, does the bead blasting and satin finishing improve strength / reliability? Coz i'd rather have the shiny, superbly welded bit in the engine bay instead, LOL!
Thursday, February 03, 2011 4:51 AM
The finish would protect against corrosion right? Stainless will corrode, especially if other bits of metal get onto it.

That is very cool work, fabbed race cars are always fun to look at. Far better than the bolt on weekend wonders most mags feature.
Mike Kojima
Mike Kojimalink
Thursday, February 03, 2011 5:46 AM
I don't think I called it a surface grinder, I think I said something about grinding the surface but I will check and edit if needed.

Bead blasting might improve mechanical properties slightly but on something that gets as hot as an exhaust it probably doesn't make any difference. We just did it because 321 has an ugly milky look to it from the mill.

Bead blasting doesn't affect corrosion resistance but 321 is highly corrosion resistant, especially at high temps. I think you are thinking of passivating as the process to eliminate corrosion on stainless causesd by metallic contamination..
Thursday, February 03, 2011 6:02 AM
Is the Flange fully welded in the last pic?

How is it able to seal if it doesn't have a 360ยบ weld bead?
Not nit-picking just curious.

I agree wit Fuergrissa that is a good 'tip' with the drill.
Mike Kojima
Mike Kojimalink
Thursday, February 03, 2011 7:37 AM
It's fully welded on the inside and skip welded on the outside.
Thursday, February 03, 2011 9:09 AM
Im excited to see what this car is going to do.
Thursday, February 03, 2011 9:51 AM
It looks great bead-blasted but I have to say I've always preferred the polished look of wire-brushed stainless TIG welds personally. Actually, from a purely cosmetics perspective, neatly done thermal wrap looks the best.

What are the calculations required for finding the turbo-lag RPM? I could sit around doing integrals all day to figure it out, but there's got to be a some shortcut. I'm really just trying to justify an anti-lag system. (muahaha!)
Thursday, February 03, 2011 3:50 PM
Thanks for e reply mike! I asked coz here at my place the cost of ceramic coating a turbo header is half the cost of the header itself! o.O
Thursday, February 03, 2011 5:35 PM
Mike Smith is the man! I'm looking forward to checking out your Sentra in a future event. Agreed, steeling the drill with the tungsten rob tip.
Andrew Saw
Andrew Sawlink
Thursday, February 03, 2011 6:59 PM
Hi Mike,

Have you considered alkie injection to be able to run more boost?
Friday, February 04, 2011 12:10 AM
Some really sweet work on that DP, and working with pretty difficult material on top of it - hat's off to Mike Smith for some super quality work!
Der Bruce
Der Brucelink
Friday, February 04, 2011 9:00 AM
I can't remember if you'd addressed this in earlier parts, but was the RPM range determined by the long stroke or the flow rate of the head?

If the stroke, I keep wondering (and this is probably counter-intuitive) why nobody destrokes the QR, turns up the boost and increases the RPM range? I know you'd lose torque but sometimes it's just so much fun in those high rpms!

I may have driven one too many F20c and F22c S2000s with a perma-grin!
Friday, February 04, 2011 10:59 AM
Those doughnuts are great for making that important first bend on FWD cars with accessories in the way. I'll have to remember that for the future downpipes.
Mike Kojima
Mike Kojimalink
Friday, February 04, 2011 12:17 PM
The 100mm stroke, the shitty 1.5 something to 1 rod ratio and the general crappyness of the engine. The head actually flows well. Justin Prado who frequents here has a lot of experience developing this engine so maybe he will chip in. He has built Destroked QR's before I think.
Friday, February 04, 2011 4:23 PM
That guy mike is crazy awesome at welding. Good article keep them coming! So what are the cars you will be up against?
Friday, February 11, 2011 2:37 AM
Mike, great stuff. These welds are pure art.
Congrats to Mr. Smith on a job well done.

Personally I feel it's a shame to do bead blast on such a nice weld, since it's no longer on display. I'd skip this part and keep to the original, rugged looks, if there were no technical excuse to do it.
Wednesday, January 25, 2012 6:46 AM
Mike, I kno that it's unrelated & it's been quite some time since that part of the build, but what was the cost of those KW coilovers? I'm sure it was pretty high being custom racing pieces & all
Saturday, May 12, 2012 5:57 AM
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