LQ4 into a 3rd Gen/1972 Nova by frojoe

7 minute(s) of a 891 minute read

Well today was another productive and fun day in the garage.. and it wasn't even that cold! There was some good news and some bad news, luckily bad news is inconsequential.

The good news is actually just new parts I picked up. A random assortment of 3.5" tube and couplers, 4.0" tube and elbow, a random 2.5" bend and an old but unused 4" filter from my truck for mockup..

So the carbon 3.5" tube is just an experiment for a couple reasons: 1) mainly because the bend radius is tighter than the current setup's 3.0" tube, it should easily be able to handle the pressure and help keep post-intercooler temps down, and 3) because it looks cool and why not? If I end up using it, I will bond (using this crazy carbon-friendly epoxy we use at work) the elbow and straight together using a thin inside sleeve, and bond in ribbed ends so that the couplers don't blow off under pressure..

 

Here's a comparison of the current 3.0" charge pipe to a new 3.5" aluminum pipe, for comparison. The bend radius (CLR) is about 0.5" bigger on the 3.5" bend..

Here's a comparison of the current 3.0" pipe to the test 3.5" carbon elbow.. the CLR on the carbon is about 1.5" tighter than the 3.0" alloy pipe!  The inside of the carbon is very nice and smooth, and is about 0.085" wall thickness.

And some bad-but-whatever news.. I thought I had heard an exhaust leak a while ago, but just assumed I'd find a pinhole somewhere and easily plug weld it up. A little more than a pinhole! When I swapped from the Turbonetics TC-76 (which the piping was designed around) there wasn't any cracking. I remember the Precision 7675 being a bit tighter of a fit, and I was surprised I was even able to bolt it on without any downpipe mods. Well I guess it was preloading the wastegate via the downpipe when I tightened the downpipe to the turbo housing, as the crack started from that load direction. And look how gross those welds were! Such inferior work from 6+ years ago.... good riddance!

And more parts carnage.. here's some el cheapo Summit brand heat shielding.. the aluminum foil is just disintegrating off the insulation! I'll have to look into quality name brand stuff for the TT setup.

Next fun thing from today, confirmed that the alternator can definitely fit in the lower passenger side location.. even without notching the subframe.  

However, with the alternator rotated so the output post on the backside rotated is decently far away from any surrounding metal, the 4-pin plug for the regulator is pointed right at the crossmember. So I may still notch the subframe for access room to that connected if I can't find a different orientation that works. Or maybe just find a 1-wire alternator and be done with it. But I'm happy that it physically fits with the truck accessory drive.

The final post from today is the most exciting, also picked up an assortment of stainless weld elbows, one of each, to see which ones fit best!

On the left side starting from the top are SS304 schedule 40 2.5" weld elbows, "long" and "short" bend radii at 2.5" and 3.75" CLR, respectively. These are 2.45" ID, 0.210" wall thickness, and about 2.89" OD.

On the right side starting from the top are: SS304 16ga 2.5" tube (2.369" ID, 0.065" wall), and long and short SS321 schedule 5 2.0" elbows, 3.0" and 2.0" bend radii, at 2.248" ID, 0.080" wall, 2.41" OD. After discovering the previous turbo pipe cracking, my hunch was confirmed that I simply won't be using any of this thin-wall stuff, but it was good to get just to inspect and decide in person.

Ideally everything would be thick wall SS321 to retain heat and material properties at high temp, but 321 is so hard to find in any stianless blend let alone schedule 40, and it would be crazy expensive for long radius 2.5" stuff... so SS304 it will be.

The cool thing about the schedule 40 2.5" stuff is the inside perimeter is almost identical to that of a T3 turbo flange. I think I will grind a taper into the T3 flanges (they're 1/2" thick) to transition from the round to rectangular a bit better, and fill in and smooth the corners where there are gaps. But overall I'm very surprised and happy to see how close the profile are as-is, because squishing the round 0.210"-thick elbow into a rectangular shape on the end would suck.

I think the winning combo will be a long radius elbow from the manifold, then a short section of straight pipe, into a short radius elbow going into the turbo. I looked the short radius elbow over long and hard and really don't think it'll be too sharp of a bend for entering the turbo.

The nice thing is that after I updated my exhaust flow calcs with actual measured flange and elbow dimensions, the exhaust velocity from the head exhaust ports all the way to the flange is almost dead-on consistent. The exhaust velocity would drop off quite a lot if I were to use a T4 inlet turbo(far right numbers).

And here's a mockup of the Precision 46mm wastegates I'll be using.. plenty of room to route things I think..