Prop to Diff bolts

The wisdom of the cobra forum suggests that all is not as it should be, either the holes are slightly in the wrong place (but correct relative to each other) or another suggestion that the prop itself is larger than standard so the knuckles on the joints are bigger. Anyway the solution was to ditch the bolts and use some 10.9 studding with a plain shank section in the middle. I was directed to some Ford to BMW wheel nut-stud adaptors on Ebay by Dave Brookes and these did the job.

Dash for IVA

Just a couple of pics to show the solution for the radius requirement for the IVA. If the bottom of the dash is a hard edge it needs minimum 20mm radius so I cut a slot in a bit of 20mm O.D. aluminium tube and wedged it on the bottom of the dash. The tube will get covered in black vinyl when we get round to it.

Also, interestingly. it seems the gear lever is a lot further forward with a tremec box so if you are using the Dax dashboard rather than making your own you may need to check clearance to the dash of the gear stick when in 1/3/5th gear. This isn't a problem with the getrag box as the gear lever is miles away

Update 14/10/13 to add picture of lower IVA rail with a bit of vinyl around it. Doesn't look half bad, the vinyl is held on with some double sided trim tape and just needs tweaking a little where its rucked up.

Prop shaft - first attempt

With a project as complicated as this you can guarantee there will be highs and lows along the way. Rolling the car outside on its wheels for the first time was a high. As was fitting the body, fitting the engine and starting the engine.

I think yesterday morning was definitely the lowest point. So close to the finish, most of the things on the car work but it still doesn't move under its own steam. I ordered the prop shaft back in March and this morning it finally arrived.

Here it is. We have remarked several times how short the prop shaft will be. Observe the shortness:

Now observe the not-so-short distance from the gearbox to the diff:

After almost 6 months of waiting and the prop shaft is nearly 5 inches too short. One of the most annoying parts is that I've seen this happen before from Dax in someone's blog and I thought maybe I should check so the same thing doesn't happen to me, but I didn't.

We consoled ourselves by making progress on a number of other things but I have been making preparations to book the IVA for mid-October and this is a serious blow to that target. After almost 3 years it's becoming a struggle to force ourselves into the garage and get the remaining jobs done, and that was before this set back.

 Anyway, stuff crossed off the list today:

Speedo bracket has been made, fixing holes drilled and just waiting for paint to dry.

Air filter studding cut to sensible length and nasty wing nut swapped for a shiny dome nut.

Wind screen estutcheon plates where the windscreen pillars go through the body have been sealed with silicone to stop the rain getting in.

Passenger side heater vent glued back on after I snapped it off accidentally a few weeks ago

Passenger footwell front/side/other side carpet glued in.

Diode added from fog light feed to headlight feed so when the rotary light switch is on "fog", the headlights stay on.

Diodes added to indicator dash light. Left + right go into a single lamp on the dash and this connection meant when you indicate left or right you get 4-ways. I bought a bunch of Zener diodes (3W, 24V breakdown (zener) voltate) which I put on the feeds from L+R to stop the voltage "leaking" undesirably into the wrong indicator circuit.

Took the dash off to make carpeting easier and did some minor loom tidying on the back of the dash. Good job I did too as I noticed some of the fixings for the gauges had come loose, presumably from running the engine. I had a lucky dip bag of shake proof washers which I liberally applied on every fixing I could see.

Edited 13/10/14 to update with picture of speedo sensor bracket:

Exhaust Baffles extra silencing.

Forget Magnaflow, Powerflow, Jetex and other well known custom exhaust manufactures.

May I introduce you to the latest in vehicle exhaust noise management - the Spontex Exhaust System

Both sides now sporting a stainless steel washing-up scouring pad for extra noise reduction. Not tested yet.

Updated 14/10/13 - Tested last weekend and not much of a reduction in noise. The meter reading was 110dB average so its down a tiny bit, but not much. I took the end of the pipes off to have a look at the pads inside and it soon became clear why they haven't reduced the noise much:

The exhaust pressure had pushed it all to the end so it was only doing half a job! It would seem that one per side isn't enough to really do much use.

Exhaust Baffles

Much interesting work took place at the weekend, I got some baffles off ebay (dB Killer) I think the ones I got were for a bike. My exhausts are 5" with a 3" ID baffle the full length of the side pipe. The plan is to stuff an extra baffle, intended for a puny 3" exhaust down the centre of the existing baffle. Others have then stuffed some stainless steel scouring pads from Tesco to further bring down the noise. We are taking a vaguely scientific approach and taking measurements of 1) original 2) extra baffles and 3) extra baffles + scouring pads.

These are the baffles:

and these are the sidepipes and existing baffles:

This is the new baffle wrapped in stainless scouring pads ready to be fitted. Looks a bit amateur (matches the rest of the car then!) but I'm well informed that it does actually work.

The weld at the end of the existing baffle is just visible and was removed with a dremel where it had penetrated through. This allowed the new extra baffle to slip in with a bit of help from Mr Wood and Mr Hammer. Then, out came the cobalt drill bits to drill through both baffles and fit a retaining screw.

End cap back on and job done.

Now as for the measured noise reduction, this post is a bit of a cheat as I did the passenger side exhaust on Monday night. On Sunday due to rain and the water pump deciding it was bored of keeping the water on the inside, we only added the extra baffle to the drivers side. The results were interesting though. With a calibrated sound meter (not a smart phone app!) with the original baffle we measured an average of 100dB (left and right) at tickover. The test in the IVA manual says the sound meter has to be 500mm away from the exhaust, level with the outlet at an angle of 45 degrees. The engine has to be at whatever rpm equates to 3/4 max engine power and the noise limit is 99dB. Until a couple of years ago it used to be 101dB. We had a guess that 3750 was probably about right for this, although its probably a little higher, more like 4250.

Anyways, 100dB at tickover. At 3750rpm the average was 115dB, which is very very loud. With the extra baffle in (drivers side only) it was 96dB at tickover and 106dB at 3750rpm, which is an impressive reduction considering the passenger exhaust is still on full loudness. I then baffled the passenger side and re-tested. Tickover was still 96dB and 3750rpm was 105dB. I think this was because when you do the noise test with sidepipes you are only "listening" to one side at a time so the combined effect of silencing both sides was a little disappointing.

The water pump is hopefully not much of a problem, it was spurting a bit of water and steam from the gasket on the cover plate on the back of the pump. I didn't have the correct imperial spanner (shame!) to nip up the fixings so an imperial spanner set is winging its way from ebay.

On a more general note, this could be a good solution for track days as apart from cleaning off the weld on the inside of the large baffle and drilling the hole for the fixing screw it only took about 15 mins, which included locating the correct tools which were scattered to the four corners of the garage. 

Most UK tracks have a drive-by noise limit measured trackside on a main straight. At Donnington this is 98dB and at Snetterton this is as low as 92dB! Snetterton specifies the measurement is taken 20m from the track. They also have static noise tests which for road cars will be 105dB at the very most on a "noisy" day and can sometimes be as low as 98dB.

To meet the IVA noise regulations in the end more severe baffling had to be added. These beauties were constructed by the chap I got my exhausts off. They started off life very similar to my motorcycle DB Killer baffles and were then bent to match the shape of the end of the exhaust itself. A blanking plate was then cut to match the exhaust outlet shape and welded on the end. A good dollop of fibreglass wadding was then wrapped round and the hole thing held on with a big jubilee clip to avoid having to drill extra holes in the exhaust.

This is it fitted to the car, a 5mm radius stainless wire was bent to match the shape of the exhaust exit and welded on which then meets the IVA requirement for sharp edges as the exhaust in its standard form with no rolled edge would have failed that.

This worked extremely well and got my static noise below 90dB and my 3/4 max revs was tested at 97dB on one side, 98dB on the other side so passed the IVA noise test with room to spare. Driving with these fitted caused noticeable reduction in power and rather disappointingly made the engine so quiet that the tyre noise was the loudest thing when cruising along and rather spoiled the experience.

Completely Baffled

I've spent my evenings this week making some plates to shim the gearbox mount up to match the increase in engine height, so little progress has been made elsewhere. Once that is done the plan for the weekend is to fit the prop shaft, assuming it comes in the post and fit the baffles I got off Ebay (below). 3" OD so they will slip inside my existing baffles and hopefully bring the noise down a bit. The only noise measurement we have performed was on someones phone that maxed out at 106dB (the limit on the phone app). I don't expect for one minute this is accurate but it wasn't difficult to tell just by our own ears that it was VERY loud and needs some extra silencing to meet the 99dB IVA requirement.

The wisdom on the cobra forum is to stuff stainless steel scouring pads down the inside of the baffles and we should be around or just below the 100dB mark. Fingers crossed!

Engine Height Adjustment

Today's job was to shim the engine mounts to raise the engine by a minimum of 5mm. When we ran the engine we discovered the passenger side exhaust hits the chassis when you rev the engine and it kicks around on its mounts. Additionally over the last couple of months the mounts have settled and the engine sits lower than when installed. I couldn't even get a finger in between the exhaust and the chassis on the passenger side. The drivers side was ok, about 15mm.

Not having an engine crane, we had to improvise with two jacks, one under the sump on a large bit of wood to spread the load, and another jack and a bit of wood on the front edge of the block where there was just enough of the block showing to use as a jacking point. We did one side at a time, removed the long bolt through the engine mount and replaced with an even longer one as there wasn't any thread showing beyond the nut on the original Dax supplied bolts.

Pic above shows new nice long bolts with lots of thread. The threaded part of the bolt wasn't very long so had to pack out with a few thick washers. Put a bit of copper grease on the shank of the bolt and all was good.

For the height adjustment, the Internet is full of shim plates at $50 a pair but they are just a bit of steel of various thickness. The engine mount fixes in three positions to raised bosses in the block so we just packed a few washers in. 

You can just see the stack of washers between the mount and the bosses on the block. When all was finished, the engine had been raised by almost 8mm. This has also improved the clearance of the clutch slave cylinder which has been an issue for a while. I have started making some shims from 6mm plate for the gearbox mount as the whole engine is sloping backwards by quite a bit,  I think the gearbox needs to come up by 10-15mm or so.

Edited 20/9/2013

What we neglected to consider was that in raising the engine on the mounts, the engine/gearbox are now sloping downwards to the rear. For reasons that I'm not quite sure about the engine has to be level for the carb to work, and also to minimise wear on the prop shaft joints the output shaft of the gearbox needs to be reasonably in line with the differential (within 1 or 2 degrees).

I already knew before jacking the engine up that the output spline is 2deg off the diff input shaft, so now it would be even worse. Out of the garage, and into the workshop to rummage through my ever-more useful bin of scrap bits of metal. I found some likely looking bits of 6mm plate and set to work making some gearbox mount shims. The gearbox mount sits on a plate that goes across the centre of the chassis, with two M12 fixings on each side. This plate will be shimmed up a bit.

Diff end:

Gearbox end pre-shimmage:

Here's 12mm worth of shimmage (2 each side) having a bit of paint applied:

With these fitted the difference in angles of the gearbox and the diff was reduced to 0.7deg which seems entirely reasonable. The angle of the engine (measured on the machined face of the inlet manifold that the carb fits to) is 0.3deg sloping backwards (compared to the chassis to eliminate error from sloping garage floor). Apparently this is a good thing and will reduce the chances of stalling under heavy braking. Not entirely sure why though.