Finally back on the road (after 10 years)

[69427]

Took the '84 for a test drive today. The last time I drove it was at a track day in Michigan in 2004. After three moves from Indiana to Orlando to Kansas City and some no-start issues after sitting during this time I final got it runnable. Been wanting to upgrade to a bigger/newer/more efficient turbo for quite a while so I thought I'd try to get some data to see where I'm at right now. Modified my present test gauge setup so that the gauges are no longer on an angle.



The Magnehelic is plumbed to the turbine outlet downtube, the higher range gauge hooks to the turbine inlet, and the small gauge is the manifold/boost gauge. I still need to add one more gauge to measure the compressor inlet pressure to see how much drop I'm getting across the throttle blades. The wires hanging in the picture are from a buffer circuit that ties into the ESC module and flashes a retina burning bright LED I have attached to the rearview mirror to let me know when I'm getting detonation (and telling me to get my foot out of the throttle).

I put my track day exhaust on the car as it has less backpressure and will simplify the gauge readings and make some of the future decision making calculations easier.





The 3 1/2 inch track exhaust is 30# lighter than the stock mufflers and Y-pipe (20# vs 50#). Plans are to replace that over the winter with a 4" aluminum piece that should take another 10 pounds off the car.

Took the car out for a drive on some of the back roads, and got into the throttle after the engine warmed up. Didn't have my accelerometer hooked up but I swear this 355 pulls every bit as hard as the 427 in the '69. I only tried one WOT run as I heard the engine detonate pretty quickly, reminding me that there's still a half tank of 2-4 year old fuel of questionable octane.

I've missed all the track days this year with this car but I'm going to make sure that all the updates are done in time for spring track days.

 

[BBShark]

Both cars running at the same time, congrats! I wish I was as productive as you. It's all I can do to keep up with oil changes on the vehicles I have.

 

[denpo]

10 years is a heck of a long time, it must feel good, congrats.

 

[69427]

Thanks for the encouraging words, guys. I appreciate it.
Despite how much a lot of Corvette people seem to look down their noses at C4s these days (and 84s in particular :amused I do enjoy driving this car (once I shitcanned the L83 and the DN 4+3). If I hadn't been so focused on trying to get some better handling and weight out of my antique 69 I probably would have had time earlier to get this car back on the road. I am really looking forward to some fun track days next year.

I always knew that a turbo added a bit of backpressure to the cylinders (and my old modest size turbo is probably worse) but I had no idea until I was reading one of my turbocharging books and the author commented that he regards a good street turbo setup to have a turbine inlet pressure (TIP) to manifold boost pressure ratio of about 2 (the race guys get that number substantially lower). Two to one is easy enough to do the math there. I set the wastegate at 7 psi several years ago when I first started to recalibrate the fuel and spark tables in the ECM. On my lone (short) WOT trial the other day I noticed the TIP gauge hit 15 psi right before I got out of the throttle. I didn't have time to look at the boost pressure and I am only guessing that it was probably at 5-6 psi. So, it looks like the system is operating in the general direction it should, but there are definite efficiencies here that beg for improvement (I'm speculating that the author was referring to gauge pressure, rather than absolute pressure which would have made my readings seem more efficient than I believe they actually are).
The 3 1/2" exhaust system downstream of the turbo seems good for now. I saw 8" H2O (about .3 psi) backpressure, and the 4" aluminum replacement I mentioned earlier is primarily for weight reduction.

 

[SuperBuickGuy]

C4 isn't my first choice, but they're still amazing cars... how does the rear diff hold up to the turbo?

 

[69427]

C4 isn't my first choice, but they're still amazing cars... how does the rear diff hold up to the turbo?

The rear is just a D36, but I haven't had any issues over the years. I don't drag race (so no big shock loads) and most track days are run using third and fourth gears so there's not a lot of engine torque multiplication going on. Probably the biggest problem I'll run into is if I do something stupid while leaving the starting line at a low speed autocross. :amused:

 

[69427]

Got the last gauge mounted (the one at the nine o'clock position). I've got this plumbed to the compressor inlet to see how much of a pressure drop I'm getting across the throttle butterflies and the turbo ductwork.



Also picked up a piece of 7" OD aluminum tubing to make a short muffler (8-10") on the 4" aluminum tubing that will replace the 3 1/2" (steel) track exhaust system on the car. This ought to be about ten pounds lighter than the present system (and 40# lighter than the street exhaust system).



I got all the two year old fuel pumped out of the tank and replaced with fresh 93 octane stuff. Just looking for a nice day now to take the car out again to do a couple of test miles and read the gauges. Next step after that is to do some serious shopping around for a larger, more efficient turbo (okay, actually the next step is to see what unneeded parts and stuff I have laying around in the garage that I can sell to pay for a future turbo purchase :wink.

 

[mrvette]

I have owned only two turbo cars over the years, an '84 Dodge Colt, last of the small Colts, and first of the Colt turbos.....Mutsobitchy made, I had to put a new water cooled turbo on it, the old one burnt up, yeh, no shit.....drove it around a good bit, tons of fun with it, sold it to a buddy....it got him through college....

Second one was an '87 Dodge 4 dr ~2.2? liter can't remember the model name....the ex got it in the divorce, and let the kids beat the even living hell out of it.....inside/outside just destroyed...:surrender:

 

[69427]

Oops, dumbass move.

Took the '84 out for another drive around the country block. Once it got warmed up I got into the throttle a couple times. The detonation problem was remarkably reduced with the new 93 octane fuel. Went full throttle and was rather impressed with how well the engine was running and how well it was pulling. It's been a while (10 years) since I went WOT with it so I just thought that my memory was just flawed at how well it pulled. I noticed a touch of detonation activity (the ESC LED flashed a couple times), and made a mental note to pull a couple degrees out of the spark table at WOT. I glanced at the gauges and noticed that the boost was at 12 pounds. I thought HOW THE HELL can it be 12 pounds when I have the wastegate set at 7 pounds, and then I suddenly remembered disconnecting the wastegate boost reference hose ten years ago when I was trying to diagnose a low boost problem at a track in Michigan (I apparently forgot to reconnect it). I immediately got out of the throttle and took it easy on the way home, and also came to the conclusion that it's too damn inconvenient trying to read the gauges while at WOT on the back country roads. I'll have to do the full measurement process at the track next spring.
One upside, I am a bit encouraged that I may be able to bump up the (regulated) boost level a bit once I get a more efficient turbo on it. The downside is the '84 feels faster than the '69.

 

[69427]

Got the new exhaust pipe welded up. Just need to buff it up a bit to get the high heat flat black paint to stick decently. Here's a test fit.



My original plans were to make this in 4" tubing, but the scrap yard where I got the last bunch of that size was out of it, so I did it in the same 3 1/2" size that the previous steel unit was made in. The steel piece is 21#, while this piece is currently 8 1/2 pounds.
I have a small inline muffler on the old system, and I don't know how much, if any, muffling it actually does, but if this system is much louder than the steel system I'll weld up an aluminum muffler for it. The steel system isn't actually too bad noise-wise as it seems the turbo cuts down a lot of the noise peaks.

 

[mrvette]

I only played with a couple of 4 cyl turbo cars, and that silly turbo is more effective than the cat or the muff in quieting down the noise....

I was shocked.....:surrender:

 

[69427]

Been spending some time on a muffler for the '84. It's going to be a glorified glasspack, but with a couple mods. I took an 18" length of the 7" aluminum tubing I pictured earlier, and ovaled it out to about 5" x 9". I also welded internally a length of 2" aluminum tubing for a surge volume, and also to increase the surface (hole) area that is exposed to the fiberglass dampening material. I've got the internals mostly welded, and also about 200 freaking eighth inch holes drilled into the tubes. I figure I got about a hundred more to go. Before I weld the end caps on I need to figure out how big these holes finally should be. Here's a test fit pic, and I'll post an internal pic later.



The '84 isn't actually all that loud right now, but I'm kind of using this as a practice piece to see if I can eventually put a couple homemade mufflers in the back of the '69 while pulling a couple of pounds off the car.

 

[69427]

Finished the muffler a while back. Sounds reasonably quiet at idle and pretty decent when running the RPMs up in the garage. Been too cold to take a test drive, so I'm waiting for some decent weather one of these weeks to see what it sounds like under a decent load.



This exhaust pipe and muffler (about 6 or 7 feet in length) ended up at 13#. The steel part was 21#, while the stock mufflers and Y pipe was 50#.
Forgot to take another internal picture, but the muffler is essentially part glasspack (lots of holes in the center tube, surrounded by fiberglass insulation), and part regular muffler with some surge/dampening volume in it to reduce the noise wave amplitudes.

I'm now kicking around some design ideas for the mufflers in the sixty nine. I suspect that the horsepower numbers are somewhat similar in both cars, but the exhaust in the sixty nine is going to have more pulsed flow than the eighty four exhaust. I'm going to have somewhat large surge volume chambers in the sixty nine mufflers to try to clip the noise from that pulsed flow.
The present sixty nine mufflers are about 16# each. They flow well, and sound good, but I'd like to see if I can pull about 5# off each side with some custom mufflers.