Updating a GA16DE powered B13 hillclimb car

[RallyBob]

This is a small (re)build thread for my friend's 1991 Sentra. He has raced the car since it was new, and has done autocross, hillclimbs, track days, ice racing, and SCCA rally with it over the years. His favorite event, bar none, has been the Mt. Washington Hillclimb in New Hampshire. He ran it every year it was run from 1990-2001, again when it returned in 2011, and in 2014. He's probably got the most runs under his belt of any modern day competitor there.

Since this car was always a street car (and his daily driver), his old engine I put together back in 1999 was pretty tame. It had to run pump gas and it had to pass emissions. It made all of 113 whp.

Still, in 2014 he went faster than he had ever gone up that hillclimb, even though the engine was VERY tired. Some suspension mods and a weight loss regiment for the car (2170 lbs caged, down from 2470 lbs in rally trim) allowed him to run up the 7.4 mile mixed-surface hill in 7 minutes and 26 seconds. It's literally like a 7 minute dyno pull, as he almost never lifts on his drive to the top. So while he went as fast as ever, he also drove it as hard as ever and nearly had an 'oops' moment which had him reflecting on his efforts.

It was decided that I would give him my stillborn engine project from my own street Sentra that got wrecked in an accident. It's basically a stock (1500 mile old) GA16DE with ceramic coated pistons, polished and shotpeened rods with ARP bolts, a ported head, JWT turbo cams, and a modified OEM exhaust manifold for a TD04 Subaru turbo. We're not looking for ultimate power here, but rather a fat torque curve and good response.

Turbo mocked up on modified exhaust manifold on my old car.


The one area that was lacking IMO was the intake manifold. I had the chance years ago to adapt some GSXR-600 motorcycle ITB's to the stock Nissan intake, and recently began working on the rest of the induction system. I'm emulating the Audi Group B style dual plenum intake manifold design here. It gets a little bit complex on the intake as I'm retaining the OEM IAC controls (we're using a PnP Megasquirt ECU), but so far everything fits within the allotted space. The hardest part was the vacuum rail I fabricated, which ties into the GSXR primary injector holes, after the throttle plates. A lot of stuff going on there in a limited space...

Budget is a huge concern, and I only had $1200 into all the engine components and turbocharger. Basically I only bought stuff when I could get a deal or swap labor. I'm hoping that, including the ECU, we finish at around $2500 for the total package. My own labor not included.

It all started with building a wooden hammerform, and creating the main plenum of the intake. I used .098" thick 5052 aluminum for most of the intake parts. The plenum volume ended up being a little bit over 1.8 liters.

[RalliartRsX]

Very damn nice! I am subbing to this!

[2_Liter_Turbo]

Nice, interesting to see this level of effort into a GA16!

[RallyBob]

Nice, interesting to see this level of effort into a GA16!

Ha, well...the car is a known entity and I had 95% of the parts already. I will build at least a new rear suspension and maybe front crossmember and a-arms. Thinking about the Bilstein 46 mm struts as well. We keep softening the car up and it keeps going faster. No sway bars right now, running 450 fr/300 rr springs. But the Koni's aren't ideal for the hillclimbs the car runs. I'd like to go down to maybe 350/250 springs and better dampening.

Not to mention, the GA16 is actually pretty well suited to boost from other cars I've seen. I'd be very happy with 225-250 whp. I've seen Suby guys get 280 whp from that turbo before.

Our other car is a '91 SER money pit (SR20VE, supercharged, PAR dogbox). That thing has snowballed and neither of us have the money right now to finish it. We still need a PAR 5th gear, dry sump parts, another ECU, bigger injectors, 50 mm ITB's, bigger wheels, struts, bigger brakes, and time to finish the 'body kit' and aero.

[RallyBob]

You've gotta admit, the GA might be slow but it takes a beating!


Bumper cam from 2014 Mt Washington.
http://youtu.be/rr26uIHYct8

[Def]

That hill climb was awesome. So much WOT...

I can imagine with a surface like that it'd be better to have quite a bit more travel and softer rates than a track car. The car was losing traction on power very regularly. Maybe a dual spring setup to get even more travel with long stroke struts at a slightly higher ride height so that you can have a firmer rate when cornering, but you've got a ton of droop with a lighter spring rate once the tender becomes unblocked.

[Def]

BTW - how did you plate the vacuum rail. At a plater or a DIY home job?

[RallyBob]

BTW - how did you plate the vacuum rail. At a plater or a DIY home job?

Paid a shop to plate them with yellow zinc. I looked at the DIY kits but I'd have needed a fairly large kit due to the rail lengths. It was ultimately cheaper.

As far as the suspension goes, I added tender springs last year for more droop without dropping the main springs off their perches. Seems to have worked better. I also added monoballs to the lower links on the rear uprights. That made a huge compliancy difference so when I go full custom I will have zero rubber or poly out back.

[RallyBob]

So here are a few of the mods I did last spring, prior to the 2014 hillclimb season. Previously the car ran 205/50-15 tires on 15 x 7 wheels. We had a set of 15 x 9 949 Racing wheels from the other (SE-R) project car, and decided to try to fit them to the Sentra SE. The front wasn't much of an issue as the car owner Tim had spaced the bottom of the front fenders out which gave adequate outer clearance. A little bit of wheel spacer shuffling and all was well.

Out in back, there was trouble in both directions. The outer fenders rubbed with the old wheels and tires, and when we removed the wheels spacers to test fit the 9" wheels they rubbed something fierce on the strut bodies. So I did two things: I made new rear strut housings from scratch (from aluminum), and made longer mounting flanges to push the strut housings more inward. That helped with inner clearance. But outward clearance was nil, even with hammered inner fenders. So I decided to make some fender flares from sheetmetal, and cut and rewelded the inner fenders to match. This gave the clearance required for the new 15 x 9 wheels and the 225/45-15 Hoosier A6's we planned to run.

Laying out the 22 gauge steel fender flares from my cardboard template.


I stretched and shaped the flares using a plastic teardrop shaped hammer and a shotbag, followed by a few passes through an english wheel to smooth the hammer marks out.


I roughed out the flare's outer edge on a t-dolly.


I made this special job-specific radiused t-dolly in order to make a more refined outer edge.


Tightening up the radiused edge.


For even more edge strength and no sharp edges, I hammered the outer lip over further.


Here the flares are fully trimmed and metal finished, ready to go onto the car.


Cutting out the stock outer fenders.


Hammering the inner fender out for more clearance.


Tack welding the new flare into place. I used all TIG welding. It's slower, but it's far more controlled and has a smaller HAZ (heat affected zone) than MIG welding. Plus the weld itself is much softer and smaller, which means it's less prone to crack and far easier to sand down. I used .030" ER-70S6 filler rod to weld it.


Here you can see I jump around the flare edge welding little 1/2" to 3/4" long beads to avoid warpage.


Fully welded.


Fully sanded down to 220 grit.


As you can see, that's a lot of tire on a Sentra!




Here's the custom grooving I gave the Hoosiers for Mt. Washington. The road goes from pavement to dirt and back to pavement so tire choice is always tricky. I selected this pattern after years of prepping tires for that particular hill. I leave the outer shoulder slick since I figure on asphalt there will be more grip therefore the car will roll over the tires onto the outer edges. But on dirt, there is very little lateral grip so the tires stay on the inner edges due to the negative camber we run. As it turns out, the car is very fast, very forgiving, and the tires wear dead evenly across the tread. So it seems to work well.


One of the things I did for last year's event was make an all aluminum header-back exhaust. We managed to save 30 lbs over the old steel exhaust with two mufflers. We won't be using this sytem for the turbo engine, that will get an all stainless side-dump exhaust system. Aluminum would melt on a turbo engine!


Here's Tim near the summit of the hill, right at 6000 ft. I figure at this point the car is making somewhere near 75-80 hp thanks to the altitude. Ouch.


Here's the car at 'cragway'. Tight righthand uphill corner on dirt. You don't want to go off on your left....




Another random pic on the mountain:

[2_Liter_Turbo]

Nice work!

[Def]

Nice fab work!

As far as ditching the aluminum exhaust on a turbo engine - you should keep it. The post turbine exhaust temps will be LOWER than on pretty much any NA engine. The turbine takes out a ton of heat energy (200-400 deg F easy), so the turbine housing goes from glowing to well below 800 F right at the turbo outlet.

I'd use a short section of stainless out of the turbo, but once you're past the oil pan I'd keep the aluminum exhaust (unless the diameter is too small - you want a 3" exhaust really). A 2.5" exhaust that's free flowing might be enough, but for a race car ya might as well go 3" if you can fit it.

[jfryjfry]

Curious about your tire size.... I run 255's on 9" wide wheels and they look to fit about the same as yours - I expected to see some stretch to fit the 225's but they look pretty square.

I guess no real question... Just interesting. Very nice car!

[RallyBob]

Nice fab work!

As far as ditching the aluminum exhaust on a turbo engine - you should keep it. The post turbine exhaust temps will be LOWER than on pretty much any NA engine. The turbine takes out a ton of heat energy (200-400 deg F easy), so the turbine housing goes from glowing to well below 800 F right at the turbo outlet.

I'd use a short section of stainless out of the turbo, but once you're past the oil pan I'd keep the aluminum exhaust (unless the diameter is too small - you want a 3" exhaust really). A 2.5" exhaust that's free flowing might be enough, but for a race car ya might as well go 3" if you can fit it.

The aluminum is only 2.5". I was planning on 3" stainless tubing for the turbo engine.

[RallyBob]

Curious about your tire size.... I run 255's on 9" wide wheels and they look to fit about the same as yours - I expected to see some stretch to fit the 225's but they look pretty square.

I guess no real question... Just interesting. Very nice car!

Hoosiers do tend to run wider than other brands. They list an 8.6" tread and 9.3" sidewall for this size.

[RallyBob]

Updating this old thread rather than starting a new one. My friend Tim hasn't done any racing since 2014, but he is entered in the 2017 Mt. Washington Hillclimb again.

I haven't done any fabricating or car stuff since fall of 2015. I closed my shop down and put everything into storage, bought a new house in another state, and have yet to build a new workshop there.

Tim was hoping to improve his car a bit more for this year, so two things were done. One, he fitted a Megasquirt Plug'n'play ECU and eliminated the MAF sensor. This was not without its share of issues, and the Megasquirt was sent back and forth 3 times for problems, and we abandoned one dyno session too as a result. Anyway, his 17 year old engine made 6 less HP than when it was new, but it made 12 more ft lbs of torque than when it was new. RPM range was entended as well. Better, but not as good as a turbo. That new turbo engine will have to wait until I have a new shop....

The second big change will be changing from Nissan B15 Koni sport inserts, to 46 mm Bilstein universal motorsport struts. Keeping in mind this is not a slammed to the weeds road racer, and does mostly rough New England hillclimbs, I went with the longest travel struts I could fit. We chose 7.8" travel front, and 8.8" travel rear inserts.

The front of the car has raised strut towers (1.5" higher), and I found I could lower the strut body relative to the mounting flanges a bit, and retain lots of travel in both directions at a slightly lower ride height than stock.

In the rear, since there's no halfshaft in the way, I can just lower the strut body a bunch relative to the mounting flanges and retain good compression and droop travel. More travel on rough roads = more grip.

The top pins were machined down to .750" for use with common 3/4" monoballs, and they were tapped for shrader valves as well.

I made some 1/4" thick chromoly camber plates to replace the old aluminum ones Tim had on the car (now bent up after years of rally use). The monoballs were 5/8" previously.

For the rear strut top mounts, I used the upper portion of the stock rear mounts. I removed the rubber bushings, enlarged the hole at the top, welded in a monoball housings and welded in bolts for mounting studs. With the low profile Bilstein spring hats, I have more room vertically than the OEM setup.

Unfortunately I ran out of steel while mocking up the strut flanges, and have to wait for more material. That, plus the 110 mile drive to where my welder is being stored (at a friend's race shop) means it'll be a week or two before I get back to work on these. But the top mounts are ready for zinc plating at least.