From: TMo5018257@aol.com
Date: Mon, 14 Dec 1998 16:49:33 EST
Subject: [imps] Re: Legendary engines...
Regarding the 5 bearing engines......
Yes, there are meant to be six cast. One is definately in the London area, fitted to the back of the ex-Adrian Evans Davrian prototype and used in London traffic every morning.....much respect!
I saw one such engine in George Bevan's workshop about 6 years ago, a beautiful piece of engineering. He also had a one-off twin cam Imp engine propped up against the wall. When asked about it, he dismissed it as being a waste of time claiming that a good well engineered Sport head would produce the same power.....shame it wasn't developed.
There is a chap in Newcastle (I think) that has managed to fit a twin cam 16 valve motorbike head to an Imp bottom end (don't ask me which one, bikes all look the same to me) and this has proved pretty entertaining and reliable....so far.
Cheers,
Tim
From: Ewins, Paul
Date: Tue, 15 Dec 1998 09:40:18 +1100
Subject: [imps] Re: Legendary engines...
>He also had a one-off twin cam Imp engine.
> When asked about it, he dismissed it claiming
> that a good well engineered Sport head would produce the same power
Sometimes 4 valves really doesn't achieve enough of a gain to make it worth while.
In the end it is all about how much fuel and air you can jam in at once, not how many valves you use to do it. As always the initial good design of the engine makes for relatively small gains in most areas of tuning.
To take an example from the other end of the spectrum, the McGee quad cam big block engines built for top fuel drag racing looked good for another 500hp on top of what the hemi blocks they evolved from already produced, but in the end the smaller valves couldn't take the load (about 5500 hp) and the engines were too fragile to make the gains that were there on paper. Despite a number of different approaches in a sport where engineering is everything the two valve engine still reigns supreme.
> There is a chap in Newcastle that has managed to fit a twin cam 16
> valve motorbike head to an Imp bottom end
I've seen a picture of this done to a mini and often wondered if it was posible on an imp.
The likelihood of finding something with the right distance between the cylinder centres and a close enough bore size and chamber volume seemed too small to bother looking.
Paul Ewins
Date: Tue, 15 Dec 1998 00:35:51 +0000 (GMT)
From: Paul Waites
Subject: [imps] Re: Legendary engines...
> Regarding the 5 bearing engines...... > > Yes, there are meant to be six cast. One is definately in the London area,
> fitted to the back of the ex-Adrian Evans Davrian prototype
Hasn't Peter Arnold got one of these 5-bearing engines in his Clan? It would have been one of the last engines that Ian Carter was working on.
Colin (Valentine); Is his engine one of these six?
Paul
Date: Tue, 15 Dec 1998 10:26:26 +0000
From: am018 Andy MacFadyen
Subject: [imps] Re: Legendary engines...
I think I remember the twincam head being used in the early days rally cross (by Peter Harper ?)
Certainly if you compare the best Greetham 998 with pre DFV Formula One engines eg the 1.5 Litre Coventry Climax V8s the power re litre is in the same league as 2 valve per cylinder version and not far short of the 4 valve version used by Jim Clark in 1965.
Andy
From: Smith, Neil
Date: Tue, 15 Dec 1998 10:39:54 -0000
Subject: [imps] Re: Legendary engines...
The guy in my local garage (Mend-A-Car in Bromsgrove) was telling me yesterday that he did his apprenticeship at Rootes, and that he had seen a V8 engine made from two Imp engines stuck together. He had no idea what it was ever used for, but it sounded interesting.
From: Graham Miller
Date: Tue, 15 Dec 1998 10:47:11 -0000
Subject: [imps] Re: Legendary engines...
This has always been my preferred win-the-lottery silly car idea. Even more bizarrely a few years ago I saw in a bike magazine a photo of a two imp engine, V8 powered motorbike. Stranger still, it wasn't even given a feature so I know nothing much about it... I hope someone will post soon to tell us about 1.5 litre Coventry Climax F1 engines and why you couldn't go up to about 2.2 or 2.3 litres using a couple of 1140's...
Graham
From: Russell Maddock
Date: Tue, 15 Dec 1998 21:15:19 +1000
Subject: [imps] Re: Legendary engines...
>I think I remember the twincam head being used in the early days rally cross (by
> Peter Harper ?)
That rings a bell with me too.
Russ Maddock
Date: Tue, 15 Dec 1998 11:24:18 +0000
From: am018 Andy MacFadyen
Subject: [imps] Re: Legendary engines...
It was only after the DFV and FVA engines appeared that using four valves became worth while -- the key lies in the angle of the valves, most early engines used steep angles similar to those used in 2 valve hemi engines such as the old Jag XK or Lotus Twincam. At the end of the 1.5 litre F1 in 1965 the best four valve engine built this way might typically produce about 135 bhp/litre only about 5 bhp/litre up on the equivalent 2 valve hemi head. By flattening out the angle the swirl energy of the inlet charge dosen't disipate so quickly enabling much faster combustion. In 1967 once the initial camshaft vibration problems were cure on the DFV it was producing 420 bhp 140 bhp/litre which with development very quickly passed 160 bhp/litre and ouput per litre has soared ever since.
The real advantage of a four valve engines is that it can use faster valve accelerations which in theory should give top end power while maintaining semi-decent bottom end torque.
Andy
Date: Tue, 15 Dec 1998 11:38:49 +0000
From: am018 Andy MacFadyen
Subject: [imps] Re: Legendary engines...
First of all 1140s are pretty fragile anyway even if the revs are kept down -- ask the legendery Clan man Stan Share who has been Carter's best customer for the last 20 years.
Secondly producing a V8 from a four isn't that simple; for a start the crankshaft diametre required is much larger. About twenty years back somebody was taking to Adrian Evans about producing a Davrian using this approach it came to nothing.
Andy
From: Nickcleak@aol.com
Date: Tue, 15 Dec 1998 09:47:26 EST
Subject: [imps] Re: Legendary engines.....
> the two valve engine still reigns supreme.
I agree !
Remember it takes a meausurable amount of extra power to run all those valves up and down ...especially at very high Rpm...
Nick ....
Date: Tue, 15 Dec 1998 15:29:31 +0000
From: am018 Andy MacFadyen
Subject: [imps] Re: Legendary engines.....
No the power loss should either be about the same or even reduced as the valve springs are much lighter due the lower mass of the valves they have to control, also the valve lift is lower because the valve diametre is smaller -- a rare win-win situation.
Andy
Date: Tue, 15 Dec 1998 08:42:43 -0700
From: Dave Edge
Subject: [imps] Re: Legendary engines...
Yes I would agree, there should also be a more even application of force needed to spin both cams because 16 valves are opened per revolution instead of eight.
From: Nickcleak@aol.com
Date: Tue, 15 Dec 1998 13:10:38 EST
Subject: [imps] Re: Legendary engines...
> he did his apprenticeship at Rootes, and that he had seen
> a V8 engine made from two Imp engines stuck together.
i've seen one .. It's two MK I blocks and heads with an incredibly short stroke !
nick ....
From: TMo5018257@aol.com
Date: Tue, 15 Dec 1998 13:40:39 EST
Subject: [imps] Re: Legendary engines...
Hi all,
Regarding this short sroke Imp V8.....
I spoke to a chap in Newcastle who remembers it in action being raced in the back of a single seater in around 1975. He said that the damn thing screamed... didn't sound at all like a V8.
The V8 Motobike was at the Imp Club National Weekend in 1995. It really is two Imp blocks, chain driven together and is a work of art. It was built by a Rolls Royce engineer for fun..... Also there was a Morris Minor fitted with an Imp engine with 4 Amal carbs.... sounded lovely.
Cheers,
Tim
From: TMo5018257@aol.com
Date: Tue, 15 Dec 1998 13:47:49 EST
Subject: [imps] Re: Legendary engines...
Hi all,
Twin cam heads...... refer Linton Twin Cam heads. Two of which were discovered at National Weekend about 2 years ago. One is owned by Gordon Wellbelove, who has overcome a lot of the design flaws (such as valves actuating without guides and seat) and now has it in such a condition that it can be fitted to the back of his Clan.......should be rather wicked!!
Cheers,
Tim
From: Nickcleak@aol.com
Date: Tue, 15 Dec 1998 15:30:14 EST
Subject: [imps] Re: Legendary engines.....
> No the power loss should either be about the same or even reduced as the valve
> springs are much lighter due the lower mass of the valves they have to
> control, also the valve lift is lower because the valve diametre is smaller
It depends what you are comparing with what, Ian carter did tests and did work out the extra power required .. on one of his experimental engines ..
Again i'd like to see figures , all those extra bearings , cam lobe friction , bearing friction cam follower friction cam belt friction with extra sprockets and idlers ,,
not to mention the extra valve springs and valve inertia whatever size ...
also if it's a 'tuned' engine the valves will be as big as possible and the cam lobes will be opening the valves just as fast as a 2 valve engine ...
My Favourite engine in mass production at the moment is the Volvo 4 , 5 and 6 cylinder all alloy units ,
The Normally aspirated versions are producing 70 bhp / litre and the turbo versions about 110 bhp/litre
they have valve sizes exactly the same as the Imp Sport , with slightly longer 7 mm stems , the exhaust valves are all stellite coated that's why after incredible mileages the exhaust valves and seats still have a shine to them .. perhaps a source of valves for the Imp ...
This engine has serrated Conrod bearing caps just like the Imp !
On the other hand the pumping losses should be less so maybe you are right !
But i can't see it somehow .. twice the number of components and friction can't be offset by say 80% at best of the inertia ...
nick ..
From: andy elias
Date: Tue, 15 Dec 1998 18:19:12 -0000
Subject: [imps] Re: Legendary engines...
i posibly have seen the v8 imp powered motor bike you speak of,while strictly not a v8 more like two 4 cyls running together ,two cranks joined by chain, i think , through one gear box, it was very well engineered and a solo bike not a sidecar jobbie .
From: Gary and Carol Henderson
Date: Wed, 16 Dec 1998 22:47:36 +-1300
Subject: [imps] Re: Legendary engines...
Hi
Come to think of it, there were a couple of 4-cyl Imp-powered drag bikes around here. They used the planetary-train of a Chrysler Torqueflite as the transmission - just rev, pull up the band & go!
Another had a 289 Ford V8 east-west! It's at Southwards.
Cheers
GaryH
From: Nickcleak@aol.com
Date: Wed, 16 Dec 1998 13:31:18 EST
Subject: [imps] Re: Legendary engines...
The one i saw had a flat plane crank like the TVR AJP engine .. they sound a little different no throb .. like the Tuscan racers .. The Imp V8 i saw is eventually going into an old F1 car of the era ,
Nick ..
From: Colin Valentine
Date: Wed, 2 Dec 1998 07:39:38 -0000
Subject: [imps] Re: Legendary engines.....
Paul etc,
Peter Arnold has one in his Pseudo Clan (It's Luff Shell) it went back to Ian Carter for overhaul just before his death. I recall Peter telling me that Ian had a list of about 10 or 12 engines being made. They aren't really Imp engines, more a series of 'one-offs'. I understand that the block is actually longer to accommodate bigger bores/longer strokes and the 5 bearings. Ian had a book detailing the precise spec of each engine, bores and strokes varied slightly for each. I think the book recorded the last owner known to Ian.
Any one interested in a genuine Coventry Climax Fire Pump Engine ? Complete on carry frame, as exhibited at the Minster FM Show this year.
It looks a bit like an Imp engine too, but I suspect if stripped nothing is actually interchangeable.
----------
Regards
Colin Valentine