1965 Hillman Imp with Honda Goldwing flat 6. Chasing sounds - new exhaust box time...

[yoeddynz]

Thanks fellas.

Yeah the bright blue really pops out on a grey day

[yoeddynz]

I have a confession to make. I feel dirty for what I have done and must come clean.

I have raised my car

Hear me out though. I know its a terrible thing but my hand was forced and it had to be done.

So after my birthday cakes had been all eaten, mainly by me (little fatty), I decided I needed to look at the suspension. My front springs are essentially Rootes 'Monte Carlo' spec which means 195lb" and 9.5 inches long, or about an inch shorter, with one less coil than standard imp springs...



But because I'd modified the spring perch on my stock dampers to make the car even lower it meant the Monte springs were not captive at full droop without the aid of retaining straps. These are fine in use in the UK and quite a common fitment on lowered Imps but they wont pass the muster here in NZ for certification when that time comes. I also had a total lack of any height adjustment without resorting to various spacers beneath the springs etc.

So I started looking at various coilover kits made specifically for the Imp. There's at least three brands out there that do kits, all made in the UK and all quite expensive once freight is added into the equation. Luckily I ended up chatting to a fella called Frank in Australia who I've bought stuff from before. He imports and sells Gaz coilovers as well as loads of other Hillman based items. He had a near new front pair he was removing from one of his Imps and offered me a good deal on them. They are the 'short' dampers to suit lowered imps and he was including the appropriate 'super low Monte Carlo' springs. These are 8.6 inchs long and needed if I wanted to keep my Imp sitting nice and low.

So while they were on the slow boat from Australia I started looking into the rear shocks. The stock Imp items were working ok but I knew that one was low on oil and not ideal in action. I was informed that Nissan Navara D21 front shocks were an almost straight swap so I got a shiny almost new pair from a ute at the local wreckers to try out. To my surprise they were actually considerably softer in damping than the Imp items, both in bump and rebound.

Still, I had them to try so I machined up some suitable spacers to suit and the smaller Imp bolts and the top bushes..



Bolted them in place and went for a drive.

Nup. I don't like. Too soft and a bit too wallowy. Passable for normal driving on smooth roads but start driving with a bit of enthusiasm and the back end starts getting a little bit flighty, especially in sharp compressions. I would have to sort something else out and started looking into ideas. Then the Gaz coilovers and super low springs turned up. Here are my standard Montes next to the super lows. The same coil count and rating but just set shorter.



I wanted to test them just to be sure so things got a bit scientific..





They were rated exactly as they said on the tin. The Gaz dampers and superlow springs showed the overall length from bottom eye to the top of the spring to be very similar to my modified dampers and standard Monte springs. Things were looking promising for me to keep my Imp at the same height.



So I fitted them..



I then removed my retaining straps and the arms dropped further, so releasing my springs from captivity I had to wind the collars up 15mm to hold the springs from rattling about. Oh well. I suspected I might end up in this situation. On the bright side it does mean the excessive negative camber has been removed and I also wont be smashing so many hedgehogs/other roadkill with my license plate.



I went to sleep and had nightmares about my new lofty height. This morning I revisited it and replaced the absurdly thick, what look to be just generic damper top mount rubbers with my old stock Imp items. This moved the shaft fixing up 5mm so allowing the collars to be lowered the same amount. So I now have a 10mm extra ride height with room for adjustment and completely captive springs. The camber is about bang on for what is recommended on a road imp. I took it for a good drive to try them out but I'll talk more about that soon.

Moving back to the rear dampers. I removed the soft Navara items and looked at my leaky unit. The shaft has a small amount of light corrosion just below the bumpstop. Although it was fine when I'd fitted the shocks, 13,000kms thereabouts of driving since has seen it lose fluid.

I had a plan. They are pretty common designed double walled units. There is a gap between the outer tube and the inner tube that the piston slides up and down. As the shaft enters the damper the oil height increases from displacement. This cavity was down on fluid. I drilled a tiny hole near the top, through the outer skin and whilst extending the shaft out I added oil with a small syringe. I then tapped the hole and fitted a small machine screw and O-ring. The shock works perfectly enough now, at least until I get some replacements.



Now it was time to look at the rear ride height. The new engine and gearbox is at a guess something like 20kg heavier than the Datsun setup. I'll have a better idea next time I weigh the car. Its enough that the car has sunk maybe 5 or 10mm. Not a lot but combined with the higher front it now had a distinctly nose up, bum down look that I'm not keen on. Plus I'd like the driveshafts to be a little straighter. They were heading slightly uphill to the hubs with the angle getting steeper as the rear squats under acceleration.

The rear springs are standard 1" lower, slightly stiffer Monte spec.

So I made some 15mm spacers. Probably only needed 10 but I can machine them down. It now sits as such. Bum slightly up. Half a tank of gas. Exactly no bags of cement thanks Barry.



Hannah measured both front and rear arch heights as I sat down into the car and shut the door. Interestingly, and I think quite a good thing, is that the car drops 10mm equally front and rear.

I'm going to try this new setup out before deciding if I skim my spacers down.

Another important issue I really wanted to sort out was the exhaust drone. Every time we would take the car for a drive the drone was overpowering. I wanted to believe that we'd get used to it or learn to drive around the drone zone of roughly 2300rpm but it was futile. It had to be addressed.

Mention of J pipes, resonator pipes or 1/4 wave resonator pipes or whatever name they might have was mooted by several people. Not just on for this car but also on other peoples threads and on the oldschool exhaust discussion thread. I read up about them and they sounded like an ideal potential solution but I really just didn't have any room to fit them between the exhaust box and the headers.

But how about inside the box? Extend the inlet within, tee off from that to the outside and use an elbow to send pipes forwards. I looked through my collection of random stainless tube fittings..



Something like this?..



Hmmmm... it could work and was worth an investigation.

Car on the hoist and within 5 minutes the entire exhaust box was removed. V clamps are fantastic. I removed the gazillion 6mm bolts, broke the silicone seal and removed the lid. Some measurements were made and a holes were cut as neatly as I could with the plasma cutter.



I hole sawed some stainless tube that matched the inlet diameter..



Welded a slightly smaller 32mm pipe and fitted the tees into each end of the box.



Pulled out the heavy length of 50mm 304 stainless bar and cut off some discs



Those I machined up into stepped flanges. 4 holes drilled and tapped in them to suit and then welded onto the outlets on the box.



The J pipes had the other flanges welded on via the inside..



Above the new Tee pipes within the box end expansion chambers I added a shelf of stainless perforated sheet that bolts in place and then filled the void above with more packing. This was just another way I could absorb some sound..



Lid was siliconed back in place and bolted down. Now the J pipes. I fabricated those up with the bends and made them as long as I could. There are multiple websites with ample information on how to calculate the required length depending on engine rpm, frequency, cylinder count etc etc. But they are usually dealing with exhausts that have just one main exhaust pipe to J pipe off from.

My setup is like two 3 cylinder engines really with their own separate exhausts. I wasn't sure which calcs to use. But pretend I have just one exhaust feeding off both banks I was looking at a J pipe length of circa 800mm. I figured I would halve that and my finished J pipes came out at just on 405mm with the ends almost meeting the rear arch inners. I figured I can always chop them down in length so better to start as long as I can.

I found some ideal stainless penny washers for the end caps..



J pipes installed...



They are a bit ugly though. Although I can't see them from within the engine bay they are easily visible outside and I don't like seeing them. I have also never really liked the way the box ends don't tie in with the back corners so I had an idea to try. I carefully made these stainless guards..





There were already some useful holes I had added to the valance lip for the Datsun exhaust..



Guards/ugly pipe hiders in place...



Time to try it out. I was pretty confident that there was going to be some amount of noise suppression but how much ? Upon start up we could both tell it was quieter. Took it for a drive to go pick up yet another customers rusty Hiace for work and yes - it was quieter!!! The drone was knocked right down. Its still there at certain loads but no where near as horrid.

Now as per the earlier mention of a drive to try out the new front shocks. Well it was also a good chance to try out the exhaust. This time I was sans Hannah. It meant I could thrash the car to my hearts content without Hannah having to cling on for dear life. There are no grab handles in the car and the Recaros only hold you so much. I took the laptop though and used it as a chance to let the autotune see some of the more extreme areas of the fuel map.

30kms of twisty hillclimbs local to us and a good solid use of the throttle travel. Damn its fun. The exhaust is much better drone wise but I almost want a little more sound. From inside the car its still more straight six than flat six. I'd like more of the guttural, raspy Porsche flat six sound. My exhaust/engine sounds smoother. A bit of this could be because its water cooled and the Porsche 911s I like most are aircooled (and usually twice the capacity...) They are almost clattery at idle, slightly hollow. I do some have other ideas floating in my head about future exhaust designs. I know these engines can sound more 'Porschey' but I don't have as much room to play with as the bikes I have been viewing.

But wow- this engine is a little gem. I'm tending to keep it in gear for much longer between corners because its so smooth at high revs whether I'm on or off the throttle. It'll be much better when I build my new dash and have a rev counter right in front, that's for sure.

The gear change is getting better and better with use as the shaft bushs loosen up a bit. I have ideas for improvements too but no rush. Its a delight to drop from 3rd to 2nd, a gear change that can make or break the fun to be had in a car driven hard on hills I feel.

The program managed a good amount of changes to the fuel table and its pretty good now. Start up hot or cold is great. Just a few bits to smooth out.

I'm going to tweak the throttle plate stop screw and idle bleed appropriately. I think the throttle disc is a bit sticky when closed which doesn't help for light throttle action when trying to move off slowly.

The rear navara shocks, as noted previously were not helping. Looking forward to the next drive now I have originals back in, complete with all their oil.

The front shocks are actually about the same as what I had originally. I have set the damping to what I feel is about the same as the originals. It really doesn't require much damping in the front (unless some internet Barry has finally managed to persuade me that 3 sacks of concrete in the front really is the way to set up rear engined cars)

I am going to dig out the go pro, hope the batteries are not dead and try to get some better camera angles along with better exhaust sound representation. I really want to hear what its like from outside with the new exhaust and better tune.

[911hillclimber]

Phew!
Tha'ts a big update.

iirc the stock Imp front end gets a lot of negative camber when lowered?

Lots here use 'helper-springs' to keep the main spring in contact with suspension on full droop. The slat steel spring squashes with very little force to fully coil bound at normal working movement.

Just a thought.

You can get the from the UK from Demon Tweeks I think.
Used them on my hot Impreza years ago in ATS adjustable coil-overs.

[yoeddynz]

Cheers. I have looked indy helper springs but the ones I've found so far are too thick when compressed. I can only fit them at the bottom and the collar lip does not extend up very high. I'm pretty happy with the front height as it is now, 10mm higher, because the camber is about right.

Yes - quite a bit of camber change due to the simple swing axle fronts.

I think I will probably drop the back down 5mm to level things out but I'll drive it first just out of curiosity. Good to know that occupant weight lowers the front and rear equally though!

[911hillclimber]

You might have to eat more cake! lol.

Google shot:

[yoeddynz]

Yeah man. That's how to do low!!! Stunning. But also very unusable on our local roads. Unless its airbagged like a couple of Imps out there are.

This little beauty is one of my favourite Imps. Created quite a few years ago. Its well known among the crowd for being properly low without any cheating like using airbags. Its suitably shabby too.

[yoeddynz]

​After my last long wall of text I'll try to keep my updates more frequent and smaller.

The throttle was a bit sticky and made gentle opening awkward. Parked the imp outside in the sunshine..



Removed the access cover..



Adjusted the throttle stop screw about a half turn in. Just enough to stop the throttle plate from sticking. You can see it here with a mirror...



Then wound the idle bleed screw in and touched up the tune around the idle area on laptop from the comfort of the rear seat..



It's now much better in action and way easier to drive off.

Although I'm happily getting the last bit of wear out of the old tyres and they always feel super stable and grippy when getting low, like a semi slick, they most likely wont pass another wof test. They have always worn on the outside which I found odd considering the amount of negative camber. I have always swapped them back to front regularly but they still wore as such. I thought I best check the toe angle. I'd previously done it with string. Not the best way and quite a faff. So I made these measuring jigs up..



They bolt in place like so...



Making it much easier to check the toe angle very accurately..



Turns out I had set it pretty close. It was a little bit too much toe in so I adjusted it out to suit the specs and I'm happy enough now to get some new tyres soon.

Another small job I should have done years ago was to make some form of face level ventilation. My imp gets quite fumy if I open a window. I had asked on the facebook Imp owners group and it looks like its an imp thing that most folks cars suffer with. You have to hermetically seal the back end up of every little hole and gap to try avoid it but its tricky and my imp is possibly worse now with the centre exit exhaust outlets.

I just had to do something about it. I got this lot..



Cut a hole here in the plastic ventilation pipe the comes from the fan/pickup and heads to the heaterbox..



Pushed some alloy tube wrapped in gator tape into hole...





and popped the flexi alloy ducting in place...



I'll look into teeing the ducting off and run some to the passenger side as well. I need some neat little eyeball vents which I'll then fit into my new dash layout I have planned. But even this alone is a game changer. Even just driving up our driveway I could feel the flow of fresh air. Sooooooooooooooo much better. Wish I did this years ago!

Final bit for this blurb. From the very first time I started the engine on the bench there has been a little random whistle. It didn't bother me at the time because I was just so happy the engine ran tbh. But now its annoying me. Its not there at idle. Only when you open the throttle a bit from idle will you get a little squeak or if driving and it goes under a moderate load it can be quite loud.

Off with the access hatch again and with Hannah driving the car I tried to pin point where it was coming from...

https://www.youtube.com/watch?v=r_vemXk ... ztB4AaABAg

Once home I continued the search, checked all the bolts, used bluetack to seal any suspicious gaps but no luck. I've not nailed the spot but I think its around the plenum chamber or possibly something funny in the throttle body. I got annoyed, gave up and we just went for another hoon to the beach for walk.


​

[911hillclimber]

De-snagging a modified classic is never ending.
I’m still doing bits n bobs on my 73 911 despite 35 years tinkering…
That includes an irritating throttle stick just above tick over, so you are not alone at present.

NZ looks great!

[Bootsy]

Looks great out in the wild!

[yoeddynz]

Thanks fellas

[yoeddynz]

Bloody hell time flies. I'd better do an update.

That noise. I took the throttle body off again and taped up the various superfluous holes..



Went for a drive and the sound was almost completely gone. Just a hint at certain load points under very light throttle openings. So it was indeed created by air passing over the holes - much like blowing across the top of a beer bottle.

Took it off again and filled the holes with JB weld epoxy..



I was now left with one remaining outlet that feeds air from the IACV into the throttle body. This one is the cause of the occasional 'hoot' sound at low throttle openings, higher load. Possibly the sharp edges could be transitioned out to curves which might help.



Its not enough to bother me though, especially as I now know what's making the sound. Just happy I don't have a vacuum leak.

Onto more fun jobs. The custom dash instrument cluster I want to make. Ages ago I'd got these instruments from a V6 engined Mitsi Pajero. Electronic speedo head, with analogue odometer. Very similar to the Toyota items of the mid to late 90s that I had used in my Viva V6.



I took them out...



Carefully popped the needles off using the two teaspoon method...



Knocked the internals down in size including removal of trip meter part..





Machined up some barrels from alloy to suit ...



..as well as some rings for spacing the gauge faces away from the acrylic fronts I'd cut out.



The needles were cut shoorter and the gauge faces cut down in diameter. Once tested and calibrated I'll make now faces with a more suitable looking classic font and style. I assembled them and stuck them onto a makeshift shelf on the dash for testing...





I then machined up an adaptor with the required m20 thread to suit the Subaru transmission...



Screws in here...



So a Toyota electronic (hall) speedo sensor can screw on top..



Went for a drive. The Rev counter works fine straight off and matches the rev counter readout on the tuning program.

The speedo reading is much closer than I was expecting considering I don't know what the gearing is on the transmission speedo output. The speedo reads about 10 percent out but does progressively go further awry as it gets closer to 100kph. When we next have a chance on a long smooth road my intentions will be to mark the speedo face using a GPS speedo as a guide for accurate speed (the Imps original strip speedo is terrible, wobbly and not accurate at all)

But none of this will happen for a little while because the clutch slave cylinder I thought I'd repaired decided to give up and make a puddle at the local fruit stall yard. We had been in town shopping and I could feel the bite point getting lower until the gears started getting very hard to select. Luckily where it finally gave up was only a few kms from home. I started the car in gear and managed to get home. This then happened that evening...



So it was time to swap back in the Datsun engine for a short while. I have clocked up 680kms on the flat six so its probably a good time to pop the sump off, check the oil pump chains have settled in nicely etc. There's a couple of spots between seams that weep oil so I'll clean them up and re-seal. It actually barely leaves a drip though and the transmission is completely leak free.

So the Honda is now out and sitting on the engine wheely stand 2000 TM. I made notes of all the various stages of removal, accounting for time spent and detailing anything that could be improved or tidied up. I'll re-write the notes in order so avoiding needless hoist ups and downs just to undo one bolt etc etc.

As it was it took just 2 hours to remove the whole Honda engine/transmission/exhaust/gearstick/cooling bits.

I then had to adapt a few bits for easier swaps such as wiring up the Datsun loom (all 5 wires..) to suit the plug that also serves the Hondas temp/oilsensor and alternator etc. The wiring is now plug and play. The axles also have to be swapped which is easy.

Before I plonked the Datsun back in place I really wanted to weigh it. I popped over to the farm across the road and nabbed our engine hoist back from their shed.



Removed the Imp transmission and then carefully lowered the engine onto the scales...





105kg. You chunky little monkey. Granted that is with everything in place inc clutch and exhaust headers. Google reckons a bare A12 engine is circa 80kgs but I was never sure. Now I know exactly what it weighs. I weighed the Datsun cross member, starter motor, exhaust box and even the stock gear shifter arrangement. Anything that was different to the Honda setup. I also weighed the stock Imp transmission.

I noted all the weights down in my Imp notebook and consulted the weights I'd put down for the Honda engine and scooby box.

The Datsun engine and imp box setup inc its specific driveshafts, exhaust system and gearshift setup comes in at 156kg

The Honda and scooby box with its modified CV driveshafts, exhaust and modified gearshift tips the scales at 170kg

I was quite pleasantly surprised at this and it does tie in well with the weight I'd got when I recently had weighed the car at the local weigh station where it was about 40kg more than when I first got the imp on the road over 5 years ago. Allowing for errors/weighbridge accuracy and the heavier Recaro seats I have added it looks pretty legit.

Happy with that I plonked the Datsun back in place, a process that went smoothly. I ran the low pressure carb fuel pump up front into the efi return line to the carb. My original Datsun coolant hoses still worked perfectly with the stainless pipes exiting the rear bulkhead that I'd modified to suit the Hondas EWP setup.

Swap a couple of wires on the fuse box, remove the efi fuses and turned the key. The Datsun started first turn of the key and settled down to a smooth idle. It actually sounded really neat.

I checked for leaks, refitted the engine cover on the rear parcel shelf and took it for a hoon.

God it feels slow and its so quiet. But its bloody lovely though. The gearshift is so sweet. Lighter than the Scooby box (although I have some ideas on how to improve its action)

So that's that. Back into its little garage for now. I need to get some new tyres and then get a fresh warrant of fitness sticker. I'd forgotten to mention earlier that I had taken it out to show the local retired certifier who is leaving his day job and will be getting back in certifications. He loves it and thinks its a very neat transplant. I've run through a few bits that I know I have to add or change to pass the cert and hopefully some time next year it'll be first on his list. Fingers crossed.



Good little Dastun...





Back into its home..

[911hillclimber]

Good read as ever!
Nice and sunny down under.

With just the clutch slave and a few odds n bobs to do you will soon be back to the Honda experience.

Datsun engine certainly looks good imho.

[yoeddynz]

Yeah I'll order a new slave cylinder (common as muck Ford Mundano unit) and give the engine a once over. Once the Imp has a fresh wof (MOT) I can swap the flat six back in place. The already certified Datsun swap has to be in place because I can't get a wof pass until the car has been certified for the Honda - hopefully next year.

The UK is lucky having a points based system on modifications - this swap would probably just go through a MOT test as is because it doesn't accumulate enough points to need an SVA test. But correct me if I'm wrong. I know things have changed a bit over the last ten years.

[911hillclimber]

There is a lot under review by the UK Government to historic cars , the DVLA and what are the rules to be.
Lot of people waiting to read the outcome.
I hope it will be good news….

[yoeddynz]

I'm sure they'll find a way to make it even more of a ballache to play with old cars...

So I needed some new tyres. I did some research, rang around local places and found a good deal. I hoisted the Imp up, removed the wheels and spent some time removing the old stick on lead weights. I then gave them a quick polish..



Took the wheels into the big smoke later that day and left them at the tyre shop while we went off to do very important city things that city folk do, like sitting in posh cafes eating yummy steak and cheese pies, talk about the stock exchange and shopping for outdoor furniture.



Later on we picked up the wheels and left the big city behind returning back to the quiet life.



Considering this is practically a hypercar there was no expense spared when it came to selecting tyres...



Fitted the wheels and out into the sun for a photo..



I took it for a hoon and other than the usual expected bit of 'brand new tyre wandering' I've always experienced they seem fine. Nice and quiet. They'll get better once scuffed off.


My old wof test fella that I have used for years has retired. I needed to find another 'sympathetic to old cars garage' so I drove it out to a place up one of the local valleys to a mechanic I'd got some advice from about Subaru transmissions. He really likes Imps, loves Datsuns and thinks the Datsun swap is great.

Perfect!

Booked it in for a wof test

Today I drove out there again. Its a great place. Loads of old cars in the fields surrounding the place and he has his old Hillman Hunter parked up next to the workshop. Tractors being worked on and lots to look at..



The car sailed through the test with the only issue being that it really needs rear reflectors to be fitted. My tail lights don't have any reflectors built in but its never been flagged before. He had some small ones in stock to show me what would be suitable so I picked some up on the way home and fitted them.



Made some little brackets for below the bumper mounts..



Fitted in place. They don't look too bad but I am hoping there might be some alternative Lucas rear light that has reflectors built in.



Imp is now all legal again and ready for summer..



The tyres were already feeling way better too after having really scuffed off the silicone releasing agent or whatever it is?