[yoeddynz]

When you moved the shell into the shop I was seeing/feeling the lines quite similar to an early 60's Corvair, also rear engined flat 6 and air cooled.

Thanks for the kind words.

When Hillman were designing the Imp they apparently brought in a Corvair to look over and I agree - you can definitely see a vast amount of the lines and features are so similar!

I love the Corvairs. Very nice looking cars.

 

[RambozoClown]

You can do a lot with a Corvair.

 

[AZgl1800]

Matt's Off Road Recovery is in my top 5 YT videos to watch
and the others he mentions fill in the rest

 

[yoeddynz]

You can do a lot with a Corvair.

That Corvair = pretty damn cool!

 

[yoeddynz]

Update coming soon. Before then though - I have some questions with regards potentially increasing the size of the exhaust headers. I might start a thread elsewhere for this though. Guessing that this technical forum is the best place.

 

[DaveO430]

Update coming soon. Before then though - I have some questions with regards potentially increasing the size of the exhaust headers. I might start a thread elsewhere for this though. Guessing that this technical forum is the best place.

Looking forward to an update. I don't know if increasing the size of the headers would make any difference but I doubt it with everything else being stock.

 

[OnaWingAndaPrayer]

Mother honda has done an incredable job optimizing the performance on these bikes . Making changes to the exhaust or the air filter/inlet can possibly cause problems.
Looking forward to the next installments.

 

[Nitrowing]

Optimized? For gasoline with low octane? To cover 200'000 miles with little maintenance?
Mild cams, poor timing, twin carbs, tiny headers... there's a load of power waiting in there.

 

[tamathumper]

Enlarging the headers probably won't add anything, and may take something away.

 

[yoeddynz]

RE: exhausts and induction. I reckon I'll start a new thread on that one. Then it can get as messy/heated/involving as we like and keep this thread on track? But looking forward to it the discussion

Back to the Imp.

Time to mount up.

First thing was to remove the air from the nearside chassis rail. It was a bit frilly right where I want to bolt a crossmember..



I bought some bobbin style rubber mounts, 60 in hardness, from the local engineering shop. They are British made mounts so somehow they will probably leak.

I cut some plates that then bolted to the stock Subaru gearbox mount points. Then shuffled the engine/box into the position I wanted it to sit. I had measured the level at which Imp one sat on the ground, finding that the bottom of the rear side windows were pretty much level. I set Imp two up on the hoist at the same level and made sure it was level across the car. Marked things, measured things, checked clearances. Once happy with all that I got some cardboard and started making little shapes with folds out of it. Added a bobbin and the other end went through the original Imp gearbox chassis mount, hole enlarged a mm to take a 10mm stud.



Kept trying them until things looked good and transferred the shape to steel. Bent the shape in the... bender.





Tacked in place..





Removed to be reinforced and fully welded..







Finished and fitted...





Now for the front of the engine.

Or is that the back of the engine?

The other end. I plonked a bit of steel in place.



I didn't want to go much lower than the sump. I went for some low profile bobbins that were ideal. Cut some more plate to suit and drilled, tapped, bolted them in place on the engine end plate. Played with more cardboard and then steel, folded and tacked till I had things that held bobbins.



welded them up..





Next job was to make a crossmember.

Now there was going to be lots of moving this engine/box in and out of position. Not just now while building the crossmember but in the future of the build as I do exhausts/piping/induction etc. The huge steel bench we have in the workshop that I had been moving the engine in and out on was just that - huge, heavy and often in the way. Plus its set in height so when I wanted to move the engine position up and down it was via the car hoist which is not exactly finely controlled.

I needed a bespoke engine table that was easily height adjustable.

Enter stage left the 'Engine cart 2000'..



I whipped that lot above in one evening using an old height adjustable Bedford truck seat base, some spare steel offcuts from the steel rack and some budget castor wheels from Mitre 10. I added some plywood for the top and then I sat on it whilst twiddling the knob - which made things go up.

And down. It was designed to match up with the main workbench in height so I could slide the engine and box straight on. Engine and box are quite light as they are and I can shift them about easily but that wont last when the flywheel/clutch/pistons/heads/gearbox internals are all back in their rightful homes.

I painted it grey because I don't like blue steel and Mitre 10 had loads of plasticoat spray paint on clearance.



I couldn't help but mask the old sticker on the seat base..



Hannah varnished the plywood so it looked pretty. But then I realised that sliding the engine off and on was going to ruin the ply, nor was plywood a very slidey surface. So a bit of old stainless kitchen bench got cut up for the top layer.



Now in action..



Aint that just so cute.

 

[yoeddynz]

So now it was much easier to move the whole assembly about the workshop and into position under the car- which now handily sits a bit higher in the air which was nice for the next stage.



Crossmember time.

I wanted this to be more organic/factory looking then the simple box section one holding the Datsun up. It had to be strong and allow plenty of space for exhaust pipes heading backwards to a silencer assembly that will be slung under the rear valence. It also had remove easily from the car, ideally still attached to the engine if need be.

I started by making some mount points that would bolt in and out easily onto the chassis rails. Captive nuts welded on some angle iron that sits on the inside of the rails. 4 bolts per side. These bolted in place with 3mm alloy spacers on each side to allow for differences between this car and Imp one, which I know has rails a few mm closer.

Plasma cut a strip 50mm wide from 3mm mild steel plate. Welded some mounts on it to suit the bobbins hanging from the engine. Bent a curve in the plate till it sat where I wanted and had the shape I desired. Then started cutting cardboard again...



and transferring it to steel...



Tacked it altogether..



Added tubes to it for easy access to the engine mount nuts which made for a cleaner look. I could close off the angles on top and make it all pretty like.





I welded what I could on the inside of the crossmember. I really didn't want exposed welds on the outside or any lumps. Then welded the outside. I had to be strategic because even though it was all 3mm steel it would still move a heap as the welds cooled- shrink on the welded edge and shorten or lengthen the whole length either way. My final welds had to pull it back out in length as they cooled and shrunk so it matched the rails. To much relief I got it pretty much bang on and it all still lined up sweet.







The whole time I was building this bugger I was thinking 'ooh this is going to be hefty..' and stressing. Trying to find a happy medium between strength and weight but strength really was the most important thing. I didn't want my engine to fall on the road. As it was it turned out ok. Not a bad weight at all. I hung it on some scales..





Not bad at all. Just a smidge heavier than the alternator for example. Certainly brute enough. I was happy.

I bolted the whole lot in place, lowered the wheely cart 2000 out of the way and there it sat, engine and box finally suspended on their own mounts.

Beautiful I thought.

So beautiful that I had to take the car off the hoist and snap some pics...







Would ya look at that. Damn that looks cool. I was ******* stoked. This was a big occasion. I patted myself on the back and then took some more pics and measured some things..

Clearance under the car was great. The crossmember was only about 10mm lower than the exhaust on IMP one however this was also far further forward. It'll be gravy.



The room between the inlet faces on the heads and what would be the underside of the parcel shelf was almost bang on what I had very originally measure it to be when I first mocked the untouched engine up under Imp one. About 170mm..





Neat. I'd better start ordering some induction goodies eh.

So that's that. Engine is now a bolt in thing. When the time comes I'll be transferring this crossmember along with the suspension crossmember over to Impy one. But I'm a long way from that point.

I put Imp two back on the hoist, gracefully rolled the engine cart 2000 back in place, 'UNBOLTED'

the engine and box and rolled it away. Engine was slid back onto the bench and I am now going to look at making a custom alternator drive pulley and mounting the alternator (probably the old prelude/civic item I scored from the wreckers)

 

[DaveO430]

I thought the cross member looked awfully low at first but the on the ground picture shows it not too bad.

 

[Rednaxs60]

Great thread as always. This would be a great design engineer tutorial. If you're going to design something, the design engineer should have to work on it first before letting it loose on the unsuspecting public.

 

[AZgl1800]

I am totally in awe of your skills, I kept thinking this looks like it was done up in CAD, ready for the Factory.

 

[yoeddynz]

Thanks for the nice comments fellas. Glad its entertaining for you. Another post soon!

I thought the cross member looked awfully low at first but the on the ground picture shows it not too bad.

Yeah I know what you mean! the photos look deceiving. While I was building the crossmember I kept having to stand back and double check I'd got it right because it looked so low. One reason is that on one side of the car shell its so rotten that much of the bottom of the rear 1/4 is missing.

I forgot to add this photo to the last post. It shows well that there is ample room below the crossmember. Remember that early on I had made solid bars that bolt in where the rear shocks sit. These mean that the car is resting at the same height as my main Imp and it should be the ride height the car will be with the goldwing engine in place (I'm still expecting the whole setup will be within 20 kgs of the existing datsun engine setup, maybe even closer)

 

[yoeddynz]

Righto. I'll pop this up here rather than start a new thread because it really has most relevance to what I'm doing. For good reason most Goldwing owners would not even bother to touch any of this because the bikes work so well at what they are designed to so.

Please excuse me for some of the talk about goldwing stuff that you already know. This thread is posted up on two other forums, car forums, where most know nothing of Goldwing innards.

Look at this lot I have to play with.

Here's a head. Lovely little things. Nicely made. Very clean and simple. Brilliant hemi design. Not sure on the valve angles but I could picture it flowing nicely (based on the knowledge of my mildly edumacated mind about such technical enginy things, stuff gained from reading old cars and car conversion books etc)



I measured the valves. The inlet is a fairly decent 33mm thereabouts.



Exhaust 28mm



Not bad. Not bad at all really. I dunno if they have anything mildly flash like a 3 angle seat. I suspect not. Goldwings are a pay grade above such frilvolous race engine nonsense. But I think I do happen to have a valve grinding setup and some seat cutters amongst the engine reconditioning stuff I was given a year or so ago.

Anyway.. I won't get too excited because as far as maximum flow at stratospheric revs go it heads downhill from the valve sizes. Just look at the size of this inlet port...



25mm

Extravagance ! Not really much room to open it out either, nor risk mucking about with the port innards. Too risky.

Now the other end of the equation.



Exhaust port is 28mm one way and 23 the other. I think its cast like that on purpose to aid the low engine speed air flow (these engines are all about torque... and I'll probably mention that several times as I go on, just as I take a sip of my finest scotch. Lets not mention those dirty words like bhp and redlines)

The exhaust headers are comical. But I shouldn't really laugh because I know full well that the technical boffins at Honda know a heck of a lot more than me about cylinder head flow and tuning engines to suit bikes that are made to cruise all day long for a lifespan in the vicinity of 1,000,000 miles.

But still. They are funny..



At first glance one might be fooled into thinking they are maybe 26- 28mm like the ports. But they step down to an internal diameter of 23mm. Outside measures ap at around 26mm.



The valkyrie items are not bigger from what I can gather. They just have a poncy bit of shiny chrome tube over them so they look bigger..and shiny.

So there we have it.

Plans thus far.

My intention is to start the induction side with some bmw k75 itbs, injectors mounted into custom flanges to suit. They are about 34mm thereabouts so hugely more than big enough. They are not perfect though and will involve a bit of tinkering because the K series of engines have port spacing at 75mm and the Goldwing ports are spaced at 90mm. But they are separate and things could be adapted I'm sure.

These ..





I'm probably going down this route mainly for the induction sound, the response and the looks. Topped with K&N filters (breathing in that super hot engine bay air....) with machined alloy covers. Hmmmmmmmm yummy.

However if I don't do itbs for some reason then my next choice will be to fabricate some neat looking runners that are fed from a single centre mounted plenum, in a sort of slight race car like finish. A single throttle body and a nice machined top to the plenum chamber. This would be the easiest and quickest route, with the stock inlet runners lending themselves to being modified to suit.

ECU I already have (Megasquirt 3 since you ask) can do fully sequential on six. This will give me the ability to tune for a really sweet idle, better off the mark acceleration at low revs and hopefully better economy.

The exhaust. Here's a pic of the stock headers attached in place. They need a tiny bit of chopping and moving about to clear the back of the engine mount area, plus they sit too low, below the sump.





I'm undecided about mucking about with the headers themselves for what would probably be small gains. I wouldn't want to go any larger than 28mm od on the tubes and from my googling so far it's not a common size for stainless or mildsteel bends. I would love to have a person who is super well qualified and really experienced (which is more important really) about such things as exhaust airspeed and the effects the primaries have. Someone who does this for a living. But otherwise I'll keeping trawling through all the various opinions that google offers from men in pubs and their dogs, stack all the offers and snippets of info up an a big pile and select the mean average.

With a hint of gut instinct weighed heavily on by how much I can be arsed.

So far it seems that great exhaust sounds can and are to be had from these engines by mucking about with everything past the primaries. I suspect the gas leaves these little pipes with sod all resistance and Honda was happy with the airspeeds they got because if not it would have been very easy for them to have increased the size of them with no real other issues.

But they didn't. So I'm probably going to concentrate more on the length of them, keeping the pipes as equal as I can an look more deeply into what happens afterwards.

I'm super keen to hear lots of sage exhaust advice from other men in pubs though - if only to give more my mean average pile more height.

 

[DaveO430]

I never was big into performance, I was a dealership tech, just needed to know how things were supposed to work as designed and keep them that way so I don't have anything to add to that.

 

[tamathumper]

You're on the right track with air velocity down the exhaust pipes, which aids in scrubbing exhaust gases. A lot of guys in the Porsche forums make their exhaust bigger to "let it breathe", and end up with dubious gains, a little more at the top end, and a little harm at the bottom end, or vice versa. According to some of the guys at the pub, you might want to make sure you maintain the ratio of each pipe length to the others to avoid pulse wave interference, which would back up into the flux capacitor. Or, something like that. Great thread and posts, as always.

 

[yoeddynz]

Yeah my gut feeling is to leave well alone with regards to port sizing etc and most likely the sizes of the primary exhaust pipes (headers). I'll have enough to do just with the itbs and fuel injection install plus the rest of the exhaust to think about!

I have had an amazing amount of information offered by one knowledgeable fella on another forum. Most of the theory I already knew but I have learned a few more bits from this following wall of text that I will share with you all.

Put the kettle on/crack open a beer....

"
I've found Don Terril's Speed Talk to be a good forum for getting a higher quality of pub talk when it comes to engine tuning. There's an advanced engine tech subforum which you need to be signed up to access, but signing up is free. They tend to point people towards Pipemax for header dimensions, but there's still a lot of quality information on there.

It's a little tricky to calculate the cross-sectional area of ellipses as it involves regressive estimation, but having transcribed a rather long formula into excel I've got your exhaust ports coming out at 505 sq mm (although yours will be slightly bigger as it's a more rounded end ellipse than this formula expects). The 23mm headers are 415 sq mm. You're right that it's tricky to find a direct match, but I've seen 28mm and 30mm mandrel bends available in 1.5mm wall, which give 491 and 572 sq mm respectively.

Options I suppose would be keep the original headers, use 28mm round for a little step up, use 30mm for a bigger step up, or use 30mm and squash the end in a vice to better match the profile of the port.

Inlet and exhaust lengths I might be able to help a little with, although I'm still missing some key calculations and measurements which are quite difficult to get my head around! Would be interesting to use you as a guinea pig though

Inlet and exhaust dimension tuning
The goal of inlet and exhaust dimension (length and diameter) tuning is to try as best as you can to ensure that air pressure in the inlet is as high as it can be compared to the cylinder as possible and across the broadest rev range, and vice versa for the exhaust (with another point that you want it to be higher in the inlet than the exhaust during valve overlap).

You do this by tuning pressure waves that occur in the inlet and exhaust to rpm ranges that complement each other. Usually you'll end up with two (or sometimes 3) inlet tuning peaks, with troughs in the middle. The general idea is to tune one of those peaks for around or a little before peak power, and then use your exhaust tuning to fill the gap inbetween them.

Inlet tuning
For a long time, I bought into the idea that inlet pressure waves were caused by air piling up against the back of the inlet valve as it closes and bouncing backwards and forwards along the inlet at the speed of sound until it reaches an open valve again. Apparently that's not how it works at all! (or, rather, that does happen but it's nowhere near being the dominant effect).

What actually happens is the piston creates a strong negative pressure wave as it reaches its point of fastest acceleration (usually somewhere around 74-78 degrees of crankshaft rotation). This propagates up the inlet until it reflects off the atmospheric pressure at the end of the inlet and returns as a positive pressure wave back towards the inlet.

What you want to do is size the inlet tract so that positive pressure wave arrives back at the tail end of the same stroke that created it, when the piston has slowed right down at BDC, or has even started coming back up the bore.

So far, so easy to calculate. The issue is that the atmospheric pressure the wave bounces off at the open end migrates down the runner a distance that's dependent on the strength of the negative pressure generated by the downward movement of the piston and the diameter of the runner. As this is the complicated stuff that Pipemax does and I haven't worked out yet, the best I can offer is to get into the rough ballpark for trial and error, withe the possible suggestion that if it's not possible to fabricate a short enough runner, you can step up the runner diameter to make it appear shorter to the pressure wave.

How to work out inlet lengths
I've made a little calculator so people can plug in their engine's specs and get a rough idea of what inlet lengths to aim for, and which ones to avoid. You'll need to know your target rpm, your stroke, your rod length, and your cam timings (actual measured cam timings, not advertised as they're often quoted in deliberately obfuscated or incorrect ways). Ideally your inlet temp would be useful too, but that's not too tricky to estimate.

It's a little crude at the moment as I've no idea how far the atmospheric pressure travels down the inlet, but it should give you a rough range to aim your inlet tract length to.

Exhaust tuning
Exhaust tuning I know less about unfortunately. I know that there's two main effects you're tuning for, which is a similar wave tuning process as I've described in the inlet, and another process that works like blowing over the top of a beer bottle as one runner passes another in a collector.

What I do know is that it's not easy to get a runner setup that takes advantage of this on flat 6s (requires pairing cylinders across the banks), so the aim of the game for you is probably to limit the effects of the uneven pulse tuning. The oval exhaust port is probably an attempt at this as steps between the port and the exhaust runner help prevent waves propagating up the port (although this works by having the port smaller than the runner). I expect you'll want to have a bigger exhaust runner and have the step in the port intrude into its diameter, if that makes sense.

Saying that, in your setup you might have an opportunity to avoid the effects of merging unpaired cylinders and just go for the regular pulse tuning effect. 6 individual runners all the way to the rear of the car!

If the lengths work out, you could have 6 exhausts, 3 on each side, tuned to a length that hits the torque dip in inlet tuning. You can probably use the same approach as I've used in the inlet tuning calculator, but adjusted for exhaust valve opening and the speed of sound being much faster. Will see what I can come up with!

Can you measure your cam for me? I think I can probably work out the rest. Lift vs camshaft degrees with a dial gauge, a degree wheel and a set of v-blocks/lathe to hold it.

Edit: service manual doesn't have conrod length either so that too! "

 

[OnaWingAndaPrayer]

What did that header/collector come from ? Perhaps that is some mock up work you have done earlier .