Hillman imp + Honda flat 6. Musical engine swap game..

I fitted Stainless heater pipes to my TR7 V8 (RV8 all alloy engine) 25 years ago, no leaks yet!

Very hard to keep an eye on what's going on within the cooling galleries though.

For now I shall relax and make sure the coolant is correct as per above. I have read to check it for a positive charge.

In time I will change out the water pipes to alloy where needed. Luckily I can isolate the ones on the engine (certainly the lower one at least) from not touching/earthing to the engine block which from what I have read on the subject will make them a no risk thing.

But there's heaps of other thing more pressing before I look at those mods.

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.

So the J pipes are closed at the end? They're just for resonance?

Also, I think I speak for us all when I say that nobody wants to hear about your 'leaky unit'.

Yeah. It does read a bit risque. Especially when I follow it up by mentioning my shaft has a bit of corrosion just below its bump stop

Painting a picture that.

Also teaboy - please hurry up, finish that bimmer, sell it off for max profit and get your 911 on the road so we can compare exhausts.

I know my engine can sound even better when I find videos like this..

yeah I'd like to get some better vids for sure !

I've set the limiter at 6000. It'll do more, up to the point the hydraulic followers can't keep up I guess. But peak power is at 5400 or 5800 so not much point going further.

The Valkyrie engine has a higher limit. Same block but the head is missing the hydraulic lash adjustment and instead valve clearance is by adjustment on the fingers like many Honda bike engines. I think possibly a slightly peakier camshaft profile and a accordingly higher revs.

I'd love some of those heads and they are cheap but freight is the killer.

Imp 911 gt3 RS

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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...



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.


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