DuPuis Family Cobra Build

I drove my other daughter to school in the Cobra this morning, and am picking up my son from school at the end of the day for the last day. I think driving the kids to school will be a good thing to do with this car. :)

I hooked up the MegaSquirt's autotune, which is pretty good overall it seems but at least enough to work on getting the tune closer in the ballpark. I've had some spots that are both significantly rich and significantly lean, and the throttle tip-in enrichment settings I played with some to get where I want them. I also messed around with the coasting fuel cut-off, something that I normally prefer not having, but the decel popping was annoying and I'm sure annoys other people more than it annoys me.

After getting home I sat outside for a bit and looked at the car, where I noticed that the front brake rotors are smaller diameter than the rear - something I'd missed before. On the rear I went with the 95 Mustang Cobra brakes, which are the same caliper as standard but a larger diameter. Functionally the brakes are fine, but it looks wrong. So that may be something I look into to update eventually, but I've got other fish to fry first.

There will be continued tuning for a while, but MegaSquirt does make this pretty simple to do.
 
All three kids have gotten their drive to/from school in the Cobra. The school year is over, I've (finally) achieved the milestone I set out. And they all agreed that it was a big deal to them, lots of fun, and they want me to do this more when the next school year starts.

upload_2023-5-23_12-13-31.png

upload_2023-5-23_12-13-6.png

This morning I did some tuning, and then I did some additional tuning both before driving to pick up my son and then while waiting for him to get let out. The computer interface makes this really easy:

upload_2023-5-23_12-16-24.png

The big thing that I was immediately noticing as problematic was the lack of throttle tip-in enrichment (accelerator pump in carb terms). The software makes this really easy. I was able to play around some with me moving my right foot and seeing where the delta throttle position would be, which helped to make me pick my x and y points on throttle enrichment. Huge and immediately noticeable response on the drive back. It still could use some more, but this is a big improvement.

The first issue I seem to be coming across is that at some combination of throttle and RPM it feels as though there's a cut-out occuring. I was observing it at full throttle at 4500 RPM and part throttle around 5500. It could just be that area needs more fuel tuning, which I'm going to work on first and wouldn't surprise me at all. I have the Microsquirt set in ITB mode (which is a combination of MAP/speed density and Alpha-N/TPS-based) and I definitely do not have that set properly yet.

It might also benefit from some better plugs, and it might have too much of a spark plug gap. Edelbrock (cylinder head manufacturer) had a recommendation and I went with those, but they could also have gotten worn some with how the engine's been treated the past couple of years (poorly, bad mixture, sitting, etc.). I'll keep working on fueling for a bit first, though.

What's most amazing to me is how all of the little imperfections that were bugging me looking at the car in the shop now just don't matter driving it. It drives really, really well. There are lots of details to work on, and I'll do those, but now I can focus on some minor things while I get the RX-7 improved for the next track night and get the RV ready for our summer travels, making notes and minor changes here or there.
 
Ted said:
One of the fun things I'm already seeing with this car is how many smiles it gets. The Harley riders with no helmets look at me like I have 2 heads driving a car with a helmet on, but with no windshield the wind and face protection makes wearing my motorcycle helmet natural.

We got there right as the school busses were letting out, and a bunch of the kids were looking, pointing, and smiling. I used to be that kid, so it makes me smile to see that there are still kids like that. :)



I used EBC Greens on my Jaguars back over 20 years ago and other than that I've only used them on motorcycles. I was originally going to go with Hawks as a lot of folks have recommended them with manual brakes on these cars (and I like them on the RX-7), but after looking through the various options, the yellows looked to me like they would fit the best. I don't want pads that have to warm up to get to a good bite, and want a high initial bite. Seemed like the yellows fit the bill better than the others. Dust is fine, for one it's a performance car, and also the rims are black. :)
Click to expand...

I put some EBC bluestuff pads on the GTI this weekend in preparation for next week's Track Night, along with a set of Centric high carbon rotors. I was a little concerned about how well they would operate when cold, and the pedal did need a little more pressure at first, but they've bedded in nicely and the difference from stock is no longer noticeable. I'll report back with a pirep next week. I'm hoping the GTI will be fairly gentle on the brakes, the front rotors are 340 mm, same as the Golf R, but with the GTI single piston caliper. That's a big rotor for a 3000 lb car with 220 hp.
 
  • Like
Reactions: Ted
Did you get #5 cylinder figured out, and if not, does that affect the fuel ratio read-out or the learning negatively at all?
 
455 Bravo Uniform said:
Did you get #5 cylinder figured out, and if not, does that affect the fuel ratio read-out or the learning negatively at all?
Click to expand...

That's a good question. No, I haven't figured out why the #5 cylinder won't pull vacuum from my hand while the other 7 will just yet. The O2 sensor is in the left bank exhaust (which is where the #5 cylinder is) so any richness or leanness on any cylinder there would impact the reading there.

One thing that I'd noted was that after my first drive, the readings were very rich. I reseated the MAP sensor and it got back to normal. I didn't have the computer hooked up in that time period, but my guess is that there was vacuum leak around the MAP sensor that was impacting the reading of the MAP sensor and thus impacting AFR. That may prove to be a problem point in which case I'll have to figure out another solution.

I need to check for vacuum leaks around that #5 cylinder as that seems the most likely. I also may need to richen up the mixture in the few areas where I have it running leaner, as I have 14.7 as my target in the low throttle/low RPM areas. I think I may have heard a bit of pinging there and I'll probably richen that up, just do something around a 12.5ish baseline. I'm running premium fuel and compression is only around 9.5:1 with aluminum heads, but 14.7 might prove a bit lean at the moment if there's a lean cylinder that is actually seeing something even a bit leaner than that. The ignition timing I'm running is basically a canned curve, starting with around 10-15 degrees at idle (that would be at a normal idle of say 700 RPM), around 25ish by 1500, and then maxes out at 35-38 degrees. There's very little vacuum advance in there, only a few degrees, which I think could be improved upon. I haven't driven it enough to mess with ignition timing yet.

I will need to do some more alignment work. The left front wheel needs to be raised a little bit (other 3 I seem to have about perfect), and then I'll need to do a bit of toe in. Too much toe out now, and the steering wheel isn't 100% straight. I'll get those things taken care of at some point, probably when the front Yellow Stuff pads. The rear yellows showed up, so depending on how things go this week and next week I'll find a time to put those in and make adjustments.

Yesterday after getting home from bringing my son back from school for the last day I'd crossed over 100 miles on the odometer. That's not fully accurate as the initial drive was registering something on the order of 2-3x the actual speed I was going since the speedometer wasn't calibrated yet, but let's call it just around 100 miles on the car thus far. The thing just keeps driving better with expected minor tweaks, and few issues. The car's exceeded all of my expectations.
 
Sounds like you are almost out of projects. RV is basically done, Cobra same same, and RX-7 on its way. Whats next? Cant have you getting too bored...
 
charheep said:
Sounds like you are almost out of projects. RV is basically done, Cobra same same, and RX-7 on its way. Whats next? Cant have you getting too bored...
Click to expand...

Not even close. I still have a good number of tickets on the RV to do, the Cobra will need paint and body work as will as continued tweaks along the way to get to where it's a car I just drive and enjoy. There's not a shortage of work there.

I ordered another carb rebuild kit for the RX-7 and I'm going to see if there's some more fueling/power to be had out of that engine. But at some point I do also expect that there will be an engine swap involved. That car is definitely far from done, and I expect to continue to be the primary track weapon.

Don't forget about the diesel swap in the Land Rover, that's been on the back burner for some time, and I've also got some projects on the R1150GS (which remains my primary dirt ride) that will need to be done.

Nope, not even close to out of projects...
 
SoonerAviator said:
He still has a tractor problem to sort out, lol
Click to expand...

Yeah, I’ve mostly accepted that with other plans nothing is happening with that this year. And I’m leaning towards just reducing the fleet.
 
Ted said:
Actually it’s very intentional to have only a single passenger. It forces one on one time rather than kids fighting in the car time.
Click to expand...

As good a reason as any to have a (2-seat) sports car.
 
  • Like
Reactions: Ted
I posted a video on a bunch of little details I took care of before first drive/go kart:

 
That 351w sounds healthy! Have a decent set of THX computer speakers + subwoofer on my home computer when I played the first drive video and the sub was definitely thumping. Regarding the oil vapors and such, what is your breather/PCV setup? May want to put a standard oil cap on the driver's-side oil fill and then go with a PCV into a catch-can/breather system off of the passenger valve cover.
 
  • Like
Reactions: Ted
SoonerAviator said:
That 351w sounds healthy! Have a decent set of THX computer speakers + subwoofer on my home computer when I played the first drive video and the sub was definitely thumping. Regarding the oil vapors and such, what is your breather/PCV setup? May want to put a standard oil cap on the driver's-side oil fill and then go with a PCV into a catch-can/breather system off of the passenger valve cover.
Click to expand...

I just have a breather on the passenger side. However that valve cover has no baffle to prevent oil from splashing into the breather, and I suspect that’s my issue. I’m going to pull that cover and look at it first, probably add a baffle and then see what that does for me. I think I already would benefit from doing a valve adjustment so I may as well do both at once.

I also need to play some more with the tune… but that will take time.
 
Last edited:
Very nice Ted! It sounds fantastic.
 
  • Like
Reactions: Ted
kayoh190 said:
Very nice Ted! It sounds fantastic.
Click to expand...

Thank you. Sound was a huge part of the design goal; and I feel like I’ve nailed what I was going for pretty well.
 
Managed to get a bit of time in the shop this afternoon and got a few things done on the Cobra. I got the EBC Yellow Stuff pads installed front and rear, raised the left front tire height a hair (it was a bit low).

The toe was set too far out. As is common on these cars, some trimming of the outer tie rod was required to get enough adjustment. So, I got that trimmed and back together.

I’m not sure when I’ll drive it next, but I want to address the oil coming out of the breather before I drive it much more. So if I get some time to work on it again I’ll probably pull the valve cover, do a valve adjustment, and see about putting a baffle in to stop the oil from coming out.
 
Mod the valve covers and run 2 breathers on each side. You got 351 CFM ratcheting back & forth through them…

edit- also, I think you had a funky cylinder - maybe ring blow on that cyl and it’s related to the breather issue. Haven’t thought this thru, but may be connected in some way.
 
Last edited:
FormerHangie said:
Since there's still no sign of an allocation for my Porsche, I bought a 2017 GTI to use as a track rat and grocery getter. My first Track Night of the year is May 31, at Road Atlanta.

Here's a picture:

View attachment 116830

That's the important part.
Click to expand...

My daughter has been learning to drive the GTI over the last few weeks. This morning, she went to Target in it, without me, so her first solo as a manual transmission driver. She's been out two or three more times since then, I think she's hooked. She's working both days this weekend and she's planning on taking the GTI both days.
 
Today was the first day of school for the kids, which also makes it the first time I've driven the Cobra since the end of school for them at the end of last summer. Between me being home solo with the kids quite a bit (Cobra is not a 2-seater), focusing on motorcycling, and then our big RV trip, there wasn't any opportunity to drive the thing.

But after the first set of drives, I had put on some new brake pads (EBC Yellow Stuff) and made some changes to the alignment to try to get it more dialed in. While there were some engine/running issues noted, the poor braking of the very hard pads was a bigger concern. The EBC Yellow Stuff pads are a much more aggressive compound, and were supposed to have much more bite. These seem to work very well, and the car stops well with reasonable pedal effort.

The alignment was way off, having even positive camber, and I got it to have about 0.5-1 degree negative camber, caster seemed ok. And then as it turned out, the toe was way, way off. This morning it was very darty and I got it adjusted what should be better now and I'm going to see how that works out the next time I drive it.

Another couple of changes I made were related to the coolant overflow and the breather setup. The breather was getting oil thrown up into the filter which was then dropping down onto the exhaust manifold. So, I added a breather catch can with the goal of eliminating that. That worked, but the driver's side valve cover (other side from where the breather is) had some sealing issues, and is leaking pretty significantly. Some of this may be due to poor alignment of the valve cover gaskets and spacer (since I'm running a spacer for my valve covers) but I think I'm going to set my breather up as a PCV which should be good for the engine overall, and then still keep it with the catch can.

I hadn't yet installed the coolant overflow tank that I'd bought, and so I installed that as well. That seems to be working just fine.

My goal is to drive the car as much as I can while the weather is nice and keep on working towards making little improvements. The car starts up and runs well, and I'm enjoying driving it. Well, I'll enjoy it more when the alignment is making it track straighter. :)
 
Sac Arrow said:
Glad to hear. The Cobra looks like a dream project.
Click to expand...

Getting to drive it is extremely satisfying. It’ll be even better when it has things like a windshield.
 
Half Fast said:
FIFY. ;)
Click to expand...

I'm definitely looking forward to that, but that car is also definitely NOT ready for a track night yet. Very much in the getting sorted phase.
 
FormerHangie said:
My daughter has been learning to drive the GTI over the last few weeks. This morning, she went to Target in it, without me, so her first solo as a manual transmission driver. She's been out two or three more times since then, I think she's hooked. She's working both days this weekend and she's planning on taking the GTI both days.
Click to expand...
Do modern GTI's still lift the inside rear wheel under aggressive cornering? That was a weird feature of the one I had ('85).
 
charheep said:
How is driving it with your broken wrist?
Click to expand...

It's been fine. I'm not trying to turn the wheel with my left hand (I can't really) but it holds the wheel straight just fine.
 
Ted said:
I wear my motorcycle helmet while driving it now, does a similar job.
Click to expand...

I have to wear a full face helmet, not because of the safety part, but because if I don't, my cheeks will start flapping in the wind...
 
I drove the Cobra yesterday to drive my other daughter to school. The alignment is much better now, and I managed to get the valve cover gaskets sealed better on the passenger side. It was leaking very badly, but that seems to be more or less resolved now.

The Microsquirt is self-tuning with the O2 sensor, and my standard part throttle driving is pretty good at this point. At full throttle/higher power it's much too rich (like in the range of 10-11:1) and I suspect that some of the running issues I was having at higher RPM just comes down to it having too much fuel.

The TKO transmission was originally pretty hard shifting. After a couple hundred miles of driving, the fluid has made its way into all the little crevices and it now shifts very smoothly, as I'd expect it to. The shifter could stand to be tilted a little further forward, which I'll probably do at some point. But I think the bigger things now are simply finishing up the wiring for the seat heaters (as in, drilling holes and running it to the seats) and then putting the transmission tunnel cover on and getting the seats bolted down. From there, continuing to work on little details.
 
kyleb said:
Do modern GTI's still lift the inside rear wheel under aggressive cornering? That was a weird feature of the one I had ('85).
Click to expand...
I don't think so, the track's a lot wider and the rear suspension is a lot better. IIRC the '85 had a beam axle
Half Fast said:
FIFY. ;)
Click to expand...
So, who was it who sold that old RX-7 to @Ted, which distracted him from finishing the Cobra?
 
  • Like
Reactions: Ted
SoonerAviator said:
You got any ideas for the paint/body yet?
Click to expand...

Our initial plan has always been black with charcoal racing stripes, red pinstripes separating the charcoal from the black.

I think that will look good, but I’m also considering perhaps a more outlandish color. After all, it’s a replica, I can have fun with it. But with the black wheels (which I really like and will be keeping), the black paint is probably the best choice.

Paint won’t be happening for a bit yet anyway.
 
Ted said:
Our initial plan has always been black with charcoal racing stripes, red pinstripes separating the charcoal from the black.
Click to expand...

Invert the scheme; wheels will stand out better.
 
You must log in or register to reply here.
Back
Top