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John Beech
Frequent User
Username: jbeech

Post Number: 98
Registered: 10-2016
Posted on Saturday, 03 December, 2016 - 08:37:   Edit PostDelete PostView Post/Check IP

Sorry folks, this was supposed to be a brand new thread, not information added within this thread - oops! I'll ask David Gore to move it . . .

Done and moved to the appropriate Topic......John, would you please check the photos and captions below, some of them do not appear to match. If this is the case, I can fix this if you can send me the correct photos and captions. I have sent you a PM with an email address for you to send me the images.

- Convoluted and involved post . . . the Backspace-key is your friend.

Based on a thread in which Vladimir mentioned his US-sourced Camargue is equipped with a Holley 4-barrel carburetor, a private conversation ensued. I learned the manifold was stock and the Holley had been fitted by a previous owner. Moreover, he insisted the carburetor's base flange was merely slotted about 1/4" for two of the mounting bolts and otherwise, there was nothing especially involved in fitting it to the manifold. Thus informed of a possibly easy way to modify the car's performance characteristics, and fervently believing a picture is worth a thousand words, I asked for and kindly received a photo of said manifold.

Camarge 4-barrel intake manifold

- Vladimir's naked manifold was available for a photo because the engine is presently disassembled for rehabilitation.

My interest was in part based on a coincidental conversation with Larry, our local RR chapter-president (and über-experienced retired-RR and all-things-automotive, mechanic). He expressed a keen personal interest in installing a 4-barrel carburetor on one of his Rollers (one that he drives a lot). This, because he believes he'd obtain significantly improved fuel economy (and I'm pretty sure he's right). Anyway, I sympathized with his interest because motivating 2-1/2 tons of steel isn't exactly cheap in terms of gasoline consumption when virtually nothing has been done by Rolls-Royce in terms of optimizing the engine's performance. In short, it's my opinion quite a bit of horsepower has been left at the table . . and where's the fun in that even if you're just the chauffeur? Thus piqued, I investigated further.

As background, it should be noted that while the twin SU carbs on Tootsie function perfectly, Larry has his ducks in a perfect row because cruising on smaller (1-3/16") primaries should deliver significantly greater fuel economy versus operating the engine on the larger (2") bores that are always at part throttle. This is the benefit Larry's principally after. However, while that's all well and good, what holds rather more interest for me is the fun factor of a 4-barrel. This, because when the need/desire arises, opening a pair of secondaries offers that kick in the pants for which V-8 powered American cars are well regarded (and I bet this is the case in performance-oriented Australia as well). Thus, in concept, the switch to a 4-barrel carburetor holds promise. Especially because in my admittedly limited experience, accelerating Tootsie is akin to driving a heavy old Ford pickup truck equipped with a 1-barrel carburetor because in effect, that's exactly what the Roller uses, a pair of one-barrel carbs (each feeding 4-cylinders). Anyway, the term gutless wonder comes to mind because basically, there's just no punch! Yet with 380ci of displacement, she should be able to manage war emergency power with greater alacrity 'and' save money by burning less fuel when driven in a sedate fashion because the comparatively tiny primaries would serve the engine's needs perfectly (and with better throttle response to boot).

That would just leave the exhaust part of the breathing to attend to but I recall mention by Robert Noel [Reddington aka Bob UK] of using, if I'm not mistaken, slightly larger exhaust diameter components, plus muffler and resonator chambers, which he's made himself!

Anyway, as long as finding, making, or modifying a suitable manifold - and - making it work isn't a huge pain in the hind end (as to make it motivationally-impossible), I continued because while 'anything' is possible, I don't want to be stupid. However, since I'm both stubborn (and presently) sufficiently motivated, I've proceeded further because I view this as an interesting expenditure of my time. Oh, and regarding the difference between motivationally-possible, improbable, and freaking-impossible, I once saw a very large mixed-breed canine attempting to mount my little Dachshund bitch (and with her active cooperation) and have no doubt absent my intervention they would have eventually succeeded. Or as we all know, where there's a will there's a way! But I digress . . .

It's also worth noting; this fits in with my philosophy regarding Tootsie, e.g. of being willing to do pretty much anything as long as it's easily reversible. Basically, with her I draw the line at cutting into the wheel wells and re-contouring the lips to fit larger rims/tires because I cannot unbolt said modification. Of course, if Tootsie were not such a nice low mileage example I might feel differently. Put another way, some girls have perfect hooters and a bit of lipstick suffices to tart them up, while with others, there's a significant benefit derived by augmenting the front bumpers. This image, which I tripped across on the internet, serves to make my point regarding doing a little massaging of the basic Rolls-Royce recipe.

Loaded for bear,  <BR>or what a supercharged Roller looks like when money is no object

- The quest for performance, a supercharged Roller as art when money's no object - note the roll cage!

Anyway, Vladimir thought obtaining a similar intake wouldn't be easy because only just over 500 Camargues were ever made. While that's very true, I was rather more sanguine because as a manufacturer myself (granted, on a tremendously smaller scale), I know how very loath I am at making a part with just one possible application. Or put another way, how diligently I seek to reuse existing parts whenever possible. Considering the investment required in casting an intake manifold is not exactly insignificant for any manufacturer, even Rolls-Royce, I suspected the manifold was perhaps more easily sourced than Omar imagined. After all, even the mighty are not immune to the exigencies of economics.

Armed with Omar's photo, I considerd myself quite fortunate when Chris at Flying Spares soon confirmed he had one, which I promptly purchased. Thus ended a very brief quest to locate and purchase a 4-barrel manifold suitable for Tootsie's 6.3L engine. Whether I was lucky will only be determined by the next guy's effort (and success) in finding same.

Mulsanne Turbo intake manifold - top view

- Viewed from above, the Mulsanne-turbo intake manifold reveals a spreadbore mounting pattern - hmmmm

However, this isn't the end, but only the beginning of this story. First, the easy stuff. For example, the OEM carburetor is outfitted for pressure (basically contained in a sealed box) because it's for a turbocharged application. I neither have a turbo (nor any desires) but I was rather curious about the appearance of the Solex 4A1 carburetor because the mounting pattern on the manifold looked suspiciously like that of the ubiquitous Rochester Quadrajet. If you're not in the know, the Rochester Quadrajet carburetor is both loved and hated and was fitted to quite a lot of General Motors automobiles. Wikipedia has a decent enough entry:

https://en.wikipedia.org/wiki/Quadrajet

. . . and since GM and RR made deals for power steering, air conditioning, and the transmission, it wouldn't be any great surprise for other incestuous tendencies to reveal themselves if you look. Anyway, at it's most basic, the Quadrajet is quite capable of delivering both very good performance 'and' excellent fuel economy because of the disparity in size of the two sets of bores. What's this got to do with the the price of eggs in China? In parts it's my astonishment at learning how very dear the Solex is for prospective purchasers (thousands of pounds at Flying Spares, from whom I lifted this image).

The Solex 4A1 pressure carburetor

- Solex 4A1 pressure carburetor as used in turbo applications like Mulsanne


Meanwhile, with some judicious poking around on the internet, I satisfied my opinion the two are related because not only does the Quadrajet look like a kissing-cousin but a quick visit to my local NAPA revealed (via a manifold gasket) that a Quadrajet is a perfect fit needing but to slot the two aft mounting holes about the same 1/4" mentioned by Vladimir.

The uniquitous Rochester Quatrajet, a very popular spreadbore carb

- The uniquitous Rochester Quatrajet, a very popular spreadbore carburetor


New Quadrajets are relatively inexpensive, too at <USD$400 and with many units sized specifically for ~400ci engines. After all, the 6.3L is about 380cu and the 6.75 is 411ci so we're in the ballpark of the displacement of American iron (and vacuum secondaries cover a host of sizing sins). For specific example, this is new carburetor for a light pickup truck probably weighing (in real world use) about the same as a Roller, or 5000 pounds:

http://tinyurl.com/j7ou8a5


In the alternative, Holley plays in the spreadbore league with the popular 0-80555c carburetors, also priced under USD$400.

Holley 4160 sopreadbore mounting pattern 650cfm carburetor is easy to tune

- Holley spreadbore 650cfm carburetor is easy to tune


However all is not bliss in Mudville. Note the area of the manifold where the thermostat resides. It's MIA because in the Mulsanne Turbo manifold, as compared to the SU-manifold pictured below, it's just not there. Of course there may be RR parts to complete the picture (we'll see) but it wouldn't surprise me in the least.

SU-carb manifold - top view

- SU-carb manifold - top view


Thus, some homework remains . . . but things don't look any worse than maybe welding an inline thermostat housing to the manifold:

Billet aluminum inline thermostat housings are readily available for <USD$100

- Billet aluminum inline thermostat housings are readily available for <USD$100

Or use one of these types, also under a hundred bucks!

Billet aluminum 90 thermostat housing

- Billet aluminum 90 thermostat housing


Or something like this can be ginned up, which has the added benefit of offering a higher fill point and is also easily within the capabilities of a skilled fabricator with a MIG welder (I have a large Miller water-cooled unit in the shop but the welder is a hired gun because my skills are abysmal).

This type housing comes with the added benefit of a higher fill point for the engine

- This type housing delivers a higher fill point to ease bleeding.

. . . or if it comes to it, hacking off a piece of one manifold and MIG welding it onto the other (along with some light grinding to ensure form as well as function). But hopefully (and more likely), the Mulsanne manifold I have is just missing some of the parts that RR made to move the water around. But I'm perfectly willing to weld and grind if it comes to is. Or maybe even weld an flat carb adapter-plate to the stock SU-manifold and hog out the holes to match! That might work - and with less expense, but only if there's enough metal available. Anyway, more as it develops.

Finally, I am actively considering this as well.

Holley Sniper EFI ~USD$1250

- Holley Sniper EFI ~USD$1250


. . . yes, it's about 3X the price of the carburettor but welding a bung into the exhaust to install an oxygen sensor brings a veritable host of modern functions to an old car. I welcome all thoughts and in any case, I am having fun with this because my back of the envelop calculations lead me to suspect this pays for itself in fuel saving despite my principal interest being the convenience of fuel injection, which I covet. Added to which, I can mount the control unit discretely and it will display water temp and turn on auxiliary cooling fans (or sound an alarm), which sounds interesting to me. This will also control NOX injectors (and the added fuel required) if an extra 100hp would come in handy occasionally, say for easier merges at freeway speed. Considering Rolls-Royce engineers specified forged rods and crankshaft, the occasional use of chemical horsepower isn't contraindicated in my view . . . as long as reason is used. Of course, and quite frankly, I'm just idly speculating out loud with this last regarding laughing gas - force of habit - like how a long time (and happily married) man will covertly eyeball a gorgeous gal perambulating slowly in a short skirt and high heels). Can't be helped.
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Alan Ford
Frequent User
Username: herne13

Post Number: 90
Registered: 8-2016
Posted on Saturday, 03 December, 2016 - 12:45:   Edit PostDelete PostView Post/Check IP

Nice choice the Holley Sniper EFI setup. If my carby plays up on 'Benny' 1986 Turbo RL which I believe is common for them then I too will be looking at the Holley as an affordable upgrade replacement. A rough comparison price to the USD shown is around 2k Au.
At least it was when I checked them out.
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John Beech
Frequent User
Username: jbeech

Post Number: 100
Registered: 10-2016
Posted on Sunday, 04 December, 2016 - 06:02:   Edit PostDelete PostView Post/Check IP

David moved this thread into the General-section when I wanted it in the SY-section. I understand why but the SY seems to have more traffic meaning by now I hoped I have had at least one response to my implied query regarding the flow of water at the front of an SY1 manifold versus that of the Mulsanne. Heavy sigh.
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Robert Noel Reddington
Grand Master
Username: bob_uk

Post Number: 1210
Registered: 5-2015
Posted on Monday, 05 December, 2016 - 01:24:   Edit PostDelete PostView Post/Check IP

SU carbs are as good as a Holley 4 barrel and twin SUs are considered a performance set up.

Where a Solex is fitted then a Holley 4 barrel works well.

I think changing from SU to Holley is a waste of time and will devalue the car.

Crewe tested their cars in Death Valley so providing the cooling system is serviced and not altered then every thing should be fine.

However the Shadow 3 or first of the spirits suffered from bad placement of the low water sensor however this can be modified so the low water works as Crewe intended.

My advice is to stay with SUs and a standard cooling system. Because we know it works fine.

I have noticed that some regions simply do not understand how constant vacuum carbs work. To fully understand go to SU web site or Burlen services.

I personally think SUs carbs are better than fixed choke carbs.

Turbo Charged cars.
Turbos and carbs have never worked well and the only set up that works properly without continual fettling is multipoint fuel injection.

One of the carbs shown is actually a throttle body injection system. This is may not be suitable for a turbo because the carb lives in manifold pressure. So check with maker first.

An oxygen sensor can be used as a guide to tune carbs and there is available a kit complete with a little round gauge calibrated in mixture with 14.7 to 1 being about right.

However best economy and performance is had when mixture slightly rich
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Omar M. Shams
Grand Master
Username: omar

Post Number: 933
Registered: 4-2009
Posted on Monday, 05 December, 2016 - 04:25:   Edit PostDelete PostView Post/Check IP

Dear John,

can we please focus on this statement:

Anyway, the term gutless wonder comes to mind because basically, there's just no punch! Yet with 380ci of displacement, she should be able to manage war emergency power with greater alacrity

I think you may wish to see if the two dampers on your carburetors go up and down freely.

My long wheelbase Wraith flies up in the air at the front when I boot it - and that is with the later type (not-so-good) carbs. Your car should feel very torquey upon acceleration.




i wonder if your car is perhaps not running as intended. Is there a way for you to compare with another Shadow?
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Geoff Wootton
Grand Master
Username: dounraey

Post Number: 1509
Registered: 5-2012
Posted on Monday, 05 December, 2016 - 05:11:   Edit PostDelete PostView Post/Check IP

I've found that my SY1 has very good acceleration from standing start. Lots of low end torque and favorable gear ratios. I have no problem in keeping up with modern traffic and from the lights often find I am way up the road ahead of other cars even when using normal, if brisk acceleration. At higher speeds the engine could do with a 4th gear or overdrive, but at the legal 65 - 70 mph the engine revs are not so high as to be uncomfortable. The thing is, this is not a performance car. I find the engine power is adequate.

I like the fact the engine is totally unstressed - no worries about pushing it and it adds to the longevity of these engines.

Geoff
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Brian Vogel
Grand Master
Username: guyslp

Post Number: 2140
Registered: 6-2009
Posted on Monday, 05 December, 2016 - 06:32:   Edit PostDelete PostView Post/Check IP

I'll add to the chorus that's stating, in other ways, what Crewe used to say about these engines when horsepower figures were requested, "Power is adequate."

It's not truly neck snapping, nor would I expect it to be, but I have no "failure to launch" what is a very, very heavy piece of machinery to whatever speed I need it to be going in order to keep up with, or pass, any other modern vehicle.

Brian, at least not on SRH33576, I've still got issues to address with LRK37110
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Robert Noel Reddington
Grand Master
Username: bob_uk

Post Number: 1214
Registered: 5-2015
Posted on Monday, 05 December, 2016 - 08:08:   Edit PostDelete PostView Post/Check IP

0 to 60 mph in 10 to 11 seconds is more than enough.

Who goes from rest to 60 !!.

The mid range say from 20 to 60 mph is much more relevant.
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Christian S. Hansen
Grand Master
Username: enquiring_mind

Post Number: 444
Registered: 4-2015
Posted on Monday, 05 December, 2016 - 08:12:   Edit PostDelete PostView Post/Check IP

Time could perhaps be better spent other than reinventing the evolutionary wheel that the Crewe engineers have dedicated decades perfecting.
But then, to each his own. It is perhaps in the same realm as spending $200,000 restoring a vehicle in order to create $100,000 of value. To each his own. I admire that some have more spare time and disposible income that I ever will. Heavy sigh.
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Bob Reynolds
Grand Master
Username: bobreynolds

Post Number: 434
Registered: 8-2012
Posted on Monday, 05 December, 2016 - 08:28:   Edit PostDelete PostView Post/Check IP

When I first got my Shadow I was a bit disappointed at the acceleration. I know it weighs over 2 tons, but it does have a 7 litre V8 engine and I expected a bit better performance.

However, after renewing the ignition components, synchronising the carbs and adjusting the mixture I went for a drive around the block, just to check that it still worked and I hadn't messed everything up. I pushed the throttle about half-way down for a gentle take-off and the car took off like a rocket. I couldn't believe it, I nearly had a heart attack! The Flying Lady shot up in the air and she didn't go down again until I took my foot off! It was a totally different car. Even now, I'm not sure exactly what I did that made such a dramatic difference. The original settings weren't all that far off.

But it just shows how important it is to get the tuning settings exactly right for maximum performance.
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Brian Vogel
Grand Master
Username: guyslp

Post Number: 2141
Registered: 6-2009
Posted on Monday, 05 December, 2016 - 08:43:   Edit PostDelete PostView Post/Check IP

I could still be very tempted by EFI for the Shadow series cars, particularly if it could be installed in a way that is entirely reversible by a future custodian if they so desired.

My attitude of, "it's just a car, but a very nice car," is widely denigrated within Rolls-Royce and Bentley circles. They're not objects of worship for me nor do I value originality as the highest virtue in any vehicle, except perhaps for museum pieces.

Modifications are not anathema to me, up to and including the dreaded GM engine replacement in cars that would otherwise end up being completely parted out rather than just having an engine that's beyond economical repair parted out.

When I was trying to find the post where Richard Treacy talked about the "two stage braking" issue and air in the system, as SRH33576 was having that issue and he was advising me at the time, I could not find it [but I know it's here somewhere, I just don't know the magic search terms]. What I did find, though, was a thread entitled, DOT 3 Castrol RR363 Brake Fluid, which took quite a few interesting drifts over its life and a great many posts were by well-respected folks, some still frequently here and others not.

Brian
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John Beech
Prolific User
Username: jbeech

Post Number: 108
Registered: 10-2016
Posted on Monday, 05 December, 2016 - 23:19:   Edit PostDelete PostView Post/Check IP

Hmmm, not the response I anticipated but then again, I don't ask because I want my opinions and beliefs parroted back at me but to invite discourse and refine my thoughts. Speaking of which, many thanks for the thoughtful and considered responses (and David, you were right, the General Discussion 'is' a better forum for this than SY).

Robert Noel, I have more interest in the EFI than in any of the carburetors. However, I mentioned them in light of the fact Vladimir's car has a Holley (presumably replacing a Solex). Plus, I have zero interest in a turbo (and loads of experience tuning carburetors). Moreover, my query about the modification of the manifold is 'principally' an open invitation to those with more familiarity with the breed (you, for example) to tell me what part of the picture I am missing. I wouldn't engage in modifying the cooling system's water flow unless I 'cannot' do it with RR parts. Speaking of which, I have just received this image.
Mulsanne Turbo thermostat housing assembly
- Mulsanne Turbo thermostat housing assembly

. . . and thus, I wonder this; are these parts compatible with the existing water pump and radiator setup? E.g. if I buy them will adding them plus the Mulsanne intake manifold result in an SY1 with an intact and functioning cooling system - and ready for a 4-barrel/EFI - or am I still missing some of the picture? To be clear, the idea is fitting the Holley EFI instead of a carburetor.

Omar, yes the dampers are functioning perfectly. I may try using a lighter oil than is presently in the dashpots (3-in-1), e.g. ATF, which is supposed to be very light (like the recommended 20W which I cannot readily find) and would thus, open the needles a little more quickly under rapid acceleration. However, I suspect this is more on the order of fine tuning and thus, I don't really think it will give me the rush of a 4-barrel when the secondaries open. We'll see because I intend to empty the dashpots and try lighter oil. And FWIW, I've noticed the engine is somewhat slow to resume idle RPM after accelerating it whilst in neutral. I may have the mixture a little bit lean (I opened then closed the fuel needle screw - both directions - until it stumbled and set it at about the mid-point, which was also maximum RPM) and the air needles are set at about 2-1/2 turns.

Bob (and Geoff), the acceleration is OK for a 5000 pound car . . . it's just that when I give it the boot the response is more like an electric-motor than the get up and scoot, which I had with my other SuperPesante, a 1973 Chrysler New Yorker. That car was quite satisfying when nailing the throttle because it engaged passing gear, the secondaries opened, and heaved itself in an elephantine bull rush around whatever I was passing. The Roller should do about the same because engine displacement and total mass are similar. The difference in my view is the constant vacuum carburation versus the primary/secondary kludge of the fixed venturi carburetor. I could be wrong, of course.

Christian, this really isn't much money in the grand scheme of things. First, an early Roller isn't considered very valuable by the market and prices reflect this (however, this may change and thus, my interest in the easy mechanical reversibility of whatever I may do). Moreover, thus far the expenditure consists of an intake, which is an asset that may be subsequently re-sold to convert it back into cash - net effect zero. As for the Holley EFI, I can always throw it on a carbureted-truck I own for improved efficiency, so that's not lost money, either (though I don't drive the truck much and certainly not enough for me to buy one of these expressly for it). And yes, I am liquid (and admittedly it's better than the alternative) but it's still not a huge sum we're speaking of here. And certainly not on the order of spending $40k to restore an MGA subsequently worth $20k at best. Moreover, consider this; I don't drive much (and am far more apt to take my Harley Sportster versus something with 4-wheels) and this car is just for fun (added to which, I've had friends run this much money up their noses and have nothing whatsoever to show for it after a weekend). I prefer farting away my money on cars.

Finally, Brian, thanks for trying to find more on the 2-stage but let's not clutter this thread with this. I'll start another for that purpose.

John, who doesn't view Tootsie as a museum piece, either
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Jeff Young
Prolific User
Username: jeyjey

Post Number: 288
Registered: 10-2010
Posted on Tuesday, 06 December, 2016 - 00:10:   Edit PostDelete PostView Post/Check IP

Hi John,

Check the block part numbers between the SY and Mulsanne Turbo. If they're the same, then I'd say the thermostat housing pieces would definitely be equivalent.

If they're different, that doesn't mean it won't work, you'll just have to determine if any of the changes between the two were for the thermostat housing mounting.

(Oh, and my opinion? Tinker away; it's your car and your money. Besides that, seeing different things and different approaches makes the hobby more interesting -- at least for me.)

Cheers,
Jeff.
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Jonas TRACHSEL
Prolific User
Username: jonas_trachsel

Post Number: 104
Registered: 2-2005
Posted on Tuesday, 06 December, 2016 - 03:02:   Edit PostDelete PostView Post/Check IP

It is interesting that R-R over the decades more or less constantly were on the search for more power for their engines without loosing smoothness and refinement. The V8 is no exemption to this. The most probate method was always "more cid", i.e. increase from 6.25 to 6.75 liters in the case of the SY engine. When R-R was developing the SZ series cars they wanted more power, but they found that this engine was not willing to produce more oomph without a radical redesign. This led to the turbocharged versions of the V8. Even Cosworth (the racing engine company) could not extract much more HP from this OHV unblown engine.
What is the essence of my deliberations here? I doubt that putting a 4-barrel Holley/Solex/Rochester carby on this engine will markedly improve the performance. You can be assured that the R-R Development Dept tried all the then available carby options before deciding on SU as the best compromise.
Jonas
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Bob Reynolds
Grand Master
Username: bobreynolds

Post Number: 435
Registered: 8-2012
Posted on Tuesday, 06 December, 2016 - 03:39:   Edit PostDelete PostView Post/Check IP

"I may try using a lighter oil than is presently in the dashpots (3-in-1), e.g. ATF, which is supposed to be very light (like the recommended 20W which I cannot readily find) and would thus, open the needles a little more quickly under rapid acceleration."

This will have the opposite effect of what you're trying to do.

The whole point of the dampers is to cause the dashpots to rise slowly and lag behind the throttle movement. This causes a greater depression above the jet and sucks out more fuel, providing a temporary enrichment of the mixture.

Using a lighter oil will reduce this effect and provide enrichment for a shorter period of time.
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Omar M. Shams
Grand Master
Username: omar

Post Number: 934
Registered: 4-2009
Posted on Tuesday, 06 December, 2016 - 05:06:   Edit PostDelete PostView Post/Check IP

Perhaps the difference between the collective experience of contributors of lots of torque compared to what John is experiencing is the one thing that is indeed different to all our cars.......
The gearbox!! (tranny in America).
I do invite John to take a late Shadow for a test drive to compare.
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Patrick Ryan
Grand Master
Username: patrick_r

Post Number: 740
Registered: 4-2016
Posted on Tuesday, 06 December, 2016 - 06:54:   Edit PostDelete PostView Post/Check IP

Not that I have seen it myself, but I have read numerous items where people describe the total loss of the "waftability" that only the torque produced by this engine fitted with well sorted SU's can deliver. Bob's email nailed it.
The mascot lifts like the bow of a boat and the low rev, minimum throttle input & immediate rush of torque is awesome. Like a modern diesel car.
Losing this will destroy what the car is all about for me. So the SU's are the way to go for SRH12255.

When I train people about our truck products I tell them they should not be looking at the horsepower rating but the torque curve.

The torque produced by a standard 6.75L Rolls Royce v8 is awesome even by todays standards.
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Robert Noel Reddington
Grand Master
Username: bob_uk

Post Number: 1215
Registered: 5-2015
Posted on Tuesday, 06 December, 2016 - 09:45:   Edit PostDelete PostView Post/Check IP

Hence the term lazy 8

Horse power is a function of torque and RPM.

The torque readings on a dynometer are taken at various RPMs on FULL throttle which gets plotted on a graph with RPM on the X axis ( the time element of BHP) with torque on the y axis.

Only way to increase power is to increase RPM or torque.

The shadow engine at a guess is 280 ftlbs at 3000 rpm and 220bhp at 4500 rpm. more revs would result in no more power because the torque is dropping off if the torque could be made to hold out at 280 lbs to 5252 RPM then the BHP will be 280ftlbs. But this usually robs the low rpm torque and bang goes the waft mode. which lures me in when driving I love the way the car gathers speed on a staedy gas pedal on good roads I have seen 70mph on a hint of gas pedal and on the way to work there is a slight down hill straight 2 miles long and if allowed the car will go to 90 mph but a slight hill will knock it back to 70mph. good mile muncher.
Equally on the bendy bits in 2nd gear the plot does quite well.

I dont worry about the power I go by the driving and some cars on paper appear to be under powered but never the less acquit themselves quite well within their design intentions.

I once overtook a Ferrari doing 40mph in a Citroen 2CV doing 55mph. Then a guy in a mini cooper zoomed past.

70 mph in a turbo is much the same as 70mph in a non turbo car.

With heavy vehicles torque is paramount for good performance.

I dont push cars past about 1/2 pedal and most times I am light footed on the gas and in traffic its the easiest way.

I get 12 to 16 mpg I once got 19 mpg on a motor way at 55mph no cruise control. If I hoon the car around with lots of carpet pedal mashing then 8mpg.
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Patrick Ryan
Grand Master
Username: patrick_r

Post Number: 743
Registered: 4-2016
Posted on Tuesday, 06 December, 2016 - 12:20:   Edit PostDelete PostView Post/Check IP

The higher speed roll on throttle response when merging onto a motorway (110kph) in my SSI is so glorious I will go around the entire area just to merge back on again. All this at very low throttle input or noise or fuss.

I can easily out drag almost any car from 80kph to 160kph without engaging the kick down.
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ross kowalski
Prolific User
Username: cdfpw

Post Number: 208
Registered: 11-2015
Posted on Tuesday, 06 December, 2016 - 13:39:   Edit PostDelete PostView Post/Check IP

John,

What about the stock manifold and a 90's GM tbi with stock management?

I would think the stock manifold is fine, make up an adapter plate and there you go.

Gm tbi is basically free and extremely well documented.

Using 3456, the RR should be needing no more than 550cfm so I wouldn't think you would even need to go to the big block tbi.

It will be good to get a seat of the pants before and after review of this modification.
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David Towers
Frequent User
Username: xtriple

Post Number: 69
Registered: 6-2010
Posted on Wednesday, 07 December, 2016 - 02:09:   Edit PostDelete PostView Post/Check IP

Good on yer for trying something different. As has been said: its your car, money and time so entirely up to you.

I have never been a fan of SU carbs, not sure why, just never seemed to get the attraction, whereas a nice 4 barrel (especially with accelerator pumps) does indeed, float my boat.
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John Beech
Prolific User
Username: jbeech

Post Number: 115
Registered: 10-2016
Posted on Thursday, 08 December, 2016 - 03:34:   Edit PostDelete PostView Post/Check IP

Based on the advice of many I've decided to live with the SU carbs a while and see if they grow on me, or put another way, don't fix what ain't broke. Moreover, given the Holley EFI system is less than a year old, this gives me time to watch that product mature. In any case, I view it as significant that Rolls-Royce evolved the induction system over the years. I'm not saying an EFI system won't be an improvement, just that I am adopting a wait and see attitude.
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Patrick Ryan
Grand Master
Username: patrick_r

Post Number: 750
Registered: 4-2016
Posted on Thursday, 08 December, 2016 - 08:23:   Edit PostDelete PostView Post/Check IP

I think you are doing the right thing John.
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Mark Luft
New User
Username: bentleyman1993

Post Number: 4
Registered: 10-2016
Posted on Friday, 09 December, 2016 - 02:02:   Edit PostDelete PostView Post/Check IP

John, I say go for it. I've always wondered why my 3.8l Jaguar had three two inch SU's and the 6.25l Bentley had just two. I understand they were two completely different engines, one fast and high revving and the other slow and all torque. But I think a spread bore carb., or FI system would add the the engine.
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John Beech
Prolific User
Username: jbeech

Post Number: 130
Registered: 10-2016
Posted on Sunday, 25 December, 2016 - 00:26:   Edit PostDelete PostView Post/Check IP

Yesterday I visited my friend Larry Garry. I brought along the 4-barrel intake manifold for test fitting to a 6.75L engine, which he has sitting in storage. It dropped into place perfectly, which wasn't a surprise as I expect RR to use parts without editing them for as long as possible and the center dimensions of the block had me expecting they could bore and stroke the engine easily without resorting to a new casting (Tootsie's engine is the 380ci variety instead of the 411ci of later versions like he has in storage). Now the search is on once again for another manifold. This time because Larry wants one too. And FWIW, he owns several Shadows and Clouds plus a 1946 Bentley Speedster and a 1958 Silver Wraith HJM long wheel base, left hand drive (one of two), which was once used to transport the Queen (this, because it was an embassy car in DC, used during the 1959 visit with VP Nixon to Chicago).

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