East Anglia Meet

The East Anglia meet last week was at the Ship Inn, just north Ely, beyond Littleport on the river. Not particularly far for us to go, only half an hour or so. Very good turnout of a good selection of Cobra kits, and our car finally got to meet some other cobras!

Rev Limiter

I decided that a rev limiter would probably be a good idea as when the wheels spin in 1st or 2nd (and sometimes 3rd) the revs can rise so quickly you can't get off the throttle fast enough. Thanks to the good old UK Cobra forum, I am the proud owner of a Pertronix rev limiter. Limit set to 5400 as per engine builders spec.

Installation is easy peasy, you tee off the +ve and tach from the distributor, add an earth and you're done. I had no idea how these work but its fairly straightforward. The box looks at the tacho feed and when it goes over the limit it dumps the power feed for the distributor to ground through a resistor and hey presto - no spark and engine revs drop. Revs drop below the limit and the distributor power feed comes back on again.

I found somewhere nice and discreet for it to go, on the bulkhead behind the header tank. (header tank temporarily removed in photos below)

The only minor annoyance was that the branch of the wiring loom that this fits into has the water temp/oil temp/ oil pressure wires on it so I had to disconnect all of these and re-do the sleeving but I now have a deep feeling of joy and satisfaction at a job properly done. We could easily have just bodged on an extra couple of wires but managed to resist the temptation.

Data!

Managed to get some data off the new AFR gauge and attempted to make some sense of it. For reference our engine baseline setup was as follows:

12 degrees initial advance

34 degrees all in at 3000rpm

Carb calibration point 10 

.116 primary jets

.073 x .047 primary rods

stock secondary setup (.017 rods)

The first bit of data I got had showed that at cruise it was giving roughly 12.3:1 AFR which seemed a bit rich. On WOT it was bobbling around 13 ish which seems ok and is normal. Based on no real knowledge at all I decided to go back to the stock calibration (position 1 above). Unfortunately in my carb calibration kit I didn't have the correct combination of rods and jets so I ended up going to position 9 instead which has the following setup:

.113 jets

.068 x .047 rods

This should lean things off a tad on partial throttle acceleration and may help the cruise mixture (hopefully)

We went on a good blast to the local club meet just north of Ely and gathered plenty of data at all sorts of engine conditions. Frustratingly we lost the revs logging after a few minutes so we don't have any RPM data.

The screenshot below shows very clearly what is going on for a good hard bit of acceleration. The manifold vacuum (red) goes to zero when you push your foot to the floor, then you can see when I changed gear as the vacuum rises momentarily. The blue trace is the air fuel ratio on a scale from rich (bottom) to lean (top). 

First off its pretty obvious when I floor the throttle there is a lean spike. This would suggest the accelerator pump shot isn't enough. On full throttle as the revs rise the AFR stays relatively constant at about 14:1. This is too lean for best power. It needs to be somewhere around 12.5:1. This would suggest I'm too lean in power mode. It seems to show that my guess as to the improving things by going to calibration point 9 was a perhaps a bit misguided so I returned to cal point 10 (are you still following?!). I also moved the accelerator pump shot to the hole closest to the carb to give a bigger pump shot.

I realise that the slightly lean WOT mixture may well be the secondary jets but I want to tinker with the primaries first to make sure I properly understand what is going on.

One useful thing from the data is that on very light throttle cruise the manifold vacuum is about 9.7in.hg. This will be useful when I come to look at the staging springs. Chatting to the chaps on the forum its entirely possible that the springs are too strong so the rods are in the "up" (rich) position at cruise because the vacuum isn't sufficient to keep the rod down in the lean (cruise) position.

Went out for another drive to collect some more data with the new setup.

First thing I noticed is that the lean spike hasn't gone away. When driving the car it seemed to bog a bit when going for mega throttle so I think I might put the accel pump shot back to the middle slot as the car felt better before. 

The good news is that on WOT after the initial spike, the mixture is closer to 13:1 - an improvement from 14:1 but still not in the optimum zone for best power. 

Air Fuel Gauge Installation

After much hammering the passenger side exhaust was dismantled completely so I could take the collector to have a boss welded in it.

There we go, that was easy. Friendly local engineering place just happened to be welding stainless so they had all the gas ready. Tenner and an afternoon is all it took.

I took my time to reassemble with care. High temp copper RTV on all the slip joints and a good bead on header/manifold. I scraped all the old stuff off the exhaust manifold and could see most of it was orange but some of it was black so presumably exhaust gases had been escaping from a poor seal. I took a little more time, left the gloop to partially set before reassembling. Couple of self tappers in the header/collector slip joints for security and jobs a good un. 

The drivers side is a lot more difficult to take apart because of the brake servo so for now I've just got one sensor in the passenger side. The gauge only has one lambda channel anyway but at some point in the future it will be interesting to compare the two sides.

The wiring was very straightforward, although if I'm honest it was about 10% bodge. The master loom fuse is in a box behind the dash in the centre of the car. The general fuse box for each separate circuit is on the passenger side but doesn't have any spare fuse slots and would require major surgery to add a new circuit so I just tapped off the main loom feed and fitted an inline 5A fuse. The AF gauge loom then requires a tee from the tacho feed, dash backlight feed an and earth. Pretty simple really. I cut a 3" square bit of ali and cut a 2" hole in the middle for the gauge and dangled it off one of the lower dash mounts.

It looks like an afterthought add-on (which it is) but when we make a new dashboard I will investigate making a mount where it can swing out the way when I'm not using it.

Post Painting Rebuild Part 1

Feels like we've gone back in time 2 years, dashboard off, seats out, parts all over the place, only this time trying not to scratch the paint.

The first job I decided to attack was those awful fog/reverse brackets. I've kept the same horrendous plastic lights until I see something better I like but now they are dropped below the body. All I did was take the old swan-neck bracket, chop the U-bend bit off and turn them upside down. Slightly less offensive now:

Feeling motivated, next job was the washer jet. I bought a fancy shiny one off Europa spares. The first pilot hole drilled was unfortunately off centre so I drilled another and had to cover up the original hole with a large washer. Could have gone terribly but I think I saved it:

Driver's side mirror and wind wings next:

The passenger side mirror suffered an accident when I tried to make it stop folding in at high speed. Luckily a full field of rear view is easily had with the driver's side and centre mirror which incidentally is a suction mount. It was originally intended to go on the top of the scuttle but the suction thingy only seems to work on glass.

Tunnel carpet and rear bulkhead carpet is also back in. I took the opportunity to rotate the seatbelt bolts slightly as the seat belts were being twisted and not sitting flat. Now the car is back at home I can take the time to show the changes to the door/dash edge area. The door now blends nicely into the shape of the cockpit surround and the edge of the dash is now closed off.

Job to add to the list - a nice stainless finishing ring for carpet hole around the gearstick.

Last job of the day, refit side vents.

The terrible IVA mirrors also went in the bin.

Finished Painting!

Painting now complete! Drove it home with the absolute minimum of parts on. Now have a mountain of small jobs to do!

Paint Progress

Painting is coming on nicely, not long now!