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8 & 10 cyl Bristol cars Type 407 onwards - restoration, repair, maintenance etc

Holley Sniper

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Old 12-10-22, 04:12 PM
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Default Holley Sniper

Hi all, new member here with first post. It's so exciting..... I've recently bought a 411 S3 and am beginning to get over the shock of the fuel consumption. There's plenty of play in the carb throttle shaft yet it runs very rich so am assuming the carb is well worn.
Am probably going to get a Holley Sniper master kit, as I want the driveabilty of efi. So am very interested in anyone's experiences, good or bad, of them - particularly if you did it yourself, as I plan to do.
If you have one, what was fitting it like? Did you choose an in-tank or in-line pump? If in-line, what did you do for a fuel reservoir? What driveability difference did fitting it make? Etc etc.
Sorry if I've missed an existing thread about this topic.
Thanks in anticipation
Cheers Mark
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Old 12-10-22, 04:18 PM
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Welcome! Sorry, I can't help you but I have a 408 with non-standard 360 and performance camshaft that gets horrible mileage and am considering the Sniper too. I will be interested to see how people propose fitting the fuel return into the tank.

David
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Old 13-10-22, 09:20 PM
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I too am dismayed by the fuel my 411 & 412 use, so to that end I made a study of various fuel injection systems . Many U TUBES and articles latter these are my conclusions comparing a well set up carby verse an after market efi

1/ Your fuel economy will not improve
2/ Your motor will run more reliably(starting hot and cold, no choke issues and perform more smoothly )
3/ The cost and issues of setting it up isnt as easy as it looks
4/getting it tuned and set once again isnt that easy.
5/ Given the miles I travel in my Bristols and the cost of an EFI i decided to stick with what I have.

Do your research there is a lot on U TUBE and the US forums . Keep us informed.
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Old 13-10-22, 09:26 PM
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Quote:
Originally Posted by peter dowdle View Post
I too am dismayed by the fuel my 411 & 412 use, so to that end I made a study of various fuel injection systems . Many U TUBES and articles latter these are my conclusions comparing a well set up carby verse an after market efi

1/ Your fuel economy will not improve
2/ Your motor will run more reliably(starting hot and cold, no choke issues and perform more smoothly )
3/ The cost and issues of setting it up isnt as easy as it looks
4/getting it tuned and set once again isnt that easy.
5/ Given the miles I travel in my Bristols and the cost of an EFI i decided to stick with what I have.

Do your research there is a lot on U TUBE and the US forums . Keep us informed.
I suspect you are correct and that not much, if any, economy improvements would be had and one would, at best, have to drive a lot to recoup the cost via fuel savings.

A friend of mine has suggested that I might improve my car's economy (and horrible muscle car-like idle) by reverting to a stock camshaft but I think that would be too intimidating for this home mechanic!

David

Last edited by dwomby; 13-10-22 at 09:36 PM.
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Old 14-10-22, 01:20 AM
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David my brother Geoffrey had a 411 mk 1 with the 383 motor which had been set up by a friend of ours in Sydney, Keith would know more about Chrysler cars and motors than any one in Australia .Geoff fitted an alloy manifold and had made a set of extractors . This car with a very mild sports cam would go like the wind and return 18 to 20 mpg.

I have spoken to Keith about my 411 and he has suggested reverting to a standard sports cam as supplied by Bristol and use either a 600 or 650 Edelbrock carbie. Edelbrock have a new range of carbies which are meant to improve economy and performance.

I had a hotter cam fitted to my car and wish I hadnt

Your car being a Mk3 had a slightly detuned motor than the Mk 1 and 2 but I have no idea what cam was used. Chrysler at the time were detuning their motors in the 70s and eventually upgraded them to the 400 motor which had low compression and no go. My 412 is very slow compared to the 411.
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Old 14-10-22, 05:40 AM
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Morning Mark - congrats on your new acquisition - apart from the fuel consumption I hope you're pleased with your car?
There's an interesting thread on here titled Fuel Consumption where you can see what different cars are achieving.
12/13 MPG seems achievable on a big block with a new carb and everything else bang on - I'd imagine the only thing that's going to alter that dramatically is an LPG conversion.
EFI + LPG would be great and a nice winter project for you!
Cheers
Andrew
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Old 14-10-22, 10:49 AM
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Quote:
Originally Posted by peter dowdle View Post

I had a hotter cam fitted to my car and wish I hadnt
My 408 came with it. The car lost its original engine sometime in its history and the 360 from a 1978 Dodge Monaco was rebuilt by a Mopar performance expert and fitted. He fitted the following (all I can make out from the 1992 photocopy of a handwritten receipt!):

Mopar Performance Cam 4452761.
Lifters unknown.
Mopar Performance Intake Manifold P4529116.
Piston rings 4.030"
Pistons unknown
Exhaust valve 1863

It is now fitted with:

Summit Racing Carb SUM-M08600VS. 600cfm
Distributor Pertronix PNX-D141701.
Coil Pertronix PNX-45001.

The exhaust manifolds are stock cast iron things.

The cam gives the car a bit of a Muscle Car-like performance and sound. I think I'd be happier with a stock cam as I am told it would quieten the idle and improve economy but the car can certainly pick up its skirts and shift itself!

David
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Old 14-10-22, 02:08 PM
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Andrew/David/Peter (in alphabetical order!)
Many thanks for your replies, from across the world by the looks of it. I'm intrinsically attracted to efi vs a carb from my experiences with other cars: currently I've got a '90 Chevy truck with a 5.7L/350 small chevy and a 5-speed manual, and a '95 Corvette 5.7L LT-1 auto which I'm supposed to be selling to make way for the Bristol. The truck is 2-barrel tbi, does about 19-22mpg imperial and revs at 2200 at 80mph. It weighs 100kg more than the Bristol & has worse aerodynamics. The Corvette is port injection, does 22-30mpg and has the same rpm at 80mph as the truck. Prior to the truck I had a '54 Ford Popular (Anglia to David I'd guess) with a stroked (to 6.3L/383) small Chevy, 3 speed auto and a Holley vac secondary carb, which did 11-15mpg, can't remember the gearing alas. Admittedly the Pop hot rod was a hoon-around sort of car but the truck and the 'Vette both use almost half the fuel of both the Pop and the Bristol. The Bristol revs at c.2900 rpm at 60, so with a 5500rpm red line that gives a theoretical top speed of c.120mph. I attribute the huge fuel consumption differences to 2 things: the gearing and efi. Surely even tbi will atomise the fuel much more finely, and control the mixture much more? Plus the Holley's self-learning via it's wide-band oxygen sensor (once initial paremeters are entered) suggests it will continually refine and control it's fuelling? So I'm thinking that even a modern carb will be less efficient than efi?
But I'm not an engineer - far from it, I'm just someone who's fscinated by how cars work and loves making them run better. So keep sending in the advice! I have lots to learn.....
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Old 15-10-22, 02:47 PM
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Hello, I am an engineer (trust me !). I have spent most of my career running two companies, one of which is a well-known builder of Rover V8 engines (which were originally Buick 215 c.i.). Our most common production now is a fairly sophisticated 4.8 litre (actually 4.75, 290 c.i.) with a long-runner manifold, single motorised throttle, modern injectors, and using the best of aftermarket EFI computers. This an expensive set-up but it suits certain applications.

We have recently started using Holley Snipers on some 'cheaper' engines. So where we are not aiming to produce the rather luxurious broad torque curve of the long-runner manifold, we can let the engine be more like a sports-car engine with maximum torque and power developed at higher rpm. For this the Sniper is ideal. Where we're building 4.8 or 5.0 litre engines with around 300 bhp we use the 4-barrel Sniper on an Edelbrock manifold. For smaller engines we are a bit stuck because the 4-barrel is too large, and there aren't any 2-barrel manifolds available. We have made a very good 2-barrel manifold by modifying the standard carburettor manifold for the engine, which had 2 SU or Stromberg carbs, but the modification is quite complicated and therefore expensive.

The Sniper range seems to be intended for more highly tuned engines, as even the simplest 4-barrel is said to be adequate for up to 650bhp, and the basic 2-barrel for 350 bhp. We have found that its self-learning is very good as long as the lambda sensor is in good shape (which I suppose is obvious). The tuning control allows for you to add more information and precise parameters in certain running areas. We haven't tried the ignition timing feature at all, but as that is a fairly simple output I would be surprised if it wasn't good as well.

My Bristol 409 has the original 318 in it but with a mild cam and gas-flowed heads. It currently uses an early aftermarket programmable EFI system, but it needs a thorough up-date. I am very tempted to either use the original cast iron 4-barrel manifold or find a good aluminium one, together with a 4-barrel Sniper. The original cast-iron manifold would need to have the inlet holes re-shaped and smoothed to match up with the Sniper.

The thing that would really improve the fuel-consumption, however, is a more sophisticated gearbox. We need at least 5 gears and a lock-up torque converter. I see no reason why any of the small-block Bristols should not then comfortably exceed 20 mpg. My company frequently uses the Ford 6R80 6-speed auto in other applications. The calibration is a bit time-consuming, but we can get impressive results. It might seem a bit heretical to use a Ford gearbox on a Chrysler engine but in fact nearly all of the these modern gearboxes are fundamentally ZF designs made under licence, so I feel there shouldn't be too big a culture-shock.

SO if we're using a Sniper and a Ford gearbox, you might question why you would keep that heavy iron 318 lump, especially if you have a VERY lightweight Rover V8 at 5.0 litres to hand, but there's something rather endearing about the 'Poly-sphere' 318, so I'm inclined to keep it.
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Old 15-10-22, 06:36 PM
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Thor makes some interesting points and he's clearly brighter than I am! in reverse order, re the trans updates, Ultrabell in the USA make bellhousings to fit anything to anything else, but in the case (pun intended...) of the TF727's successor the A-518 (small-block only) I think the old TF bellhousing has to be cut off and then the Ultrabell bolts in it's place, possibly using the A518's front pump bolts? But the A518 only has a 0.7:1-ish overdrive, and a torquey old lump like a 383 would pull a 0.5:1 with ease I think - on a light throttle my car gets into top at 20mph. On the other hand a 0.7:1 is 30% better than 1:1. Ho hum....I spoke to a very helpful chap with the improbable name of Nutty Professor Transmissions, who specialises in Mopar stuff. He says 518s are v rare in the UK so it'd be a case of being v nice to the few american contacts I have to find one from a 2wd vehicle and then get it shipped over somehow. He also thought that the controllers needed for modern 5/6 speed auto double-overdrive transmissions would be a task and a half for mortals like me, although by the sounds of it possibly less so for the no doubt mighty Thor!
Re efi, my best friend has a Lotus Carlton (drool....although it has the world's heaviest clutch). He says that they used a Bosch external fuel pump which was relatively quiet, so my latest thoughts are to buy a Spreadbore/Q-jet Sniper, but not the full Kit and get a Lotus Carlton-type Bosch pump, some hardline supply & return pipes (Holley only provide rubber one in their kit) and fittings in the UK (there's a company in the midlands who do NPT stuff), which might reduce the hammering I'm going to get from the exchange rate at the mo.
Thor, on both your customer's cars and your own 409 do you use the in-tank pump or external? If external: where & how does the supply exit the tank? What did you do about a swirl-pot? And I know what you mean about the character of american V8 engines.I'm a small-block Chevy lover myself, and am gradually getting used to mopars - took several days to get over the shock of the distrubutor rotating anti-clockwise!
Thanks to all, do please keep 'em coming
Btw, if anyone knows of a prospective buyer of good user-quality '95 Corvette auto with 80k I'd appreciate it - I need the space.
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Old 16-10-22, 04:35 PM
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Please excuse the silly name, but many years ago, when we had the more clunky precursor to this forum, a member used the pseudonym 'Bellerophon' who was the Greek god who rode 'Pegasus' the winged horse, and hence was the driver of a Bristol car as the cars have Pegasus logos inherited from the Aeroplane Company. I thought that as an 'injunear' I would use the name Thor as one who wields a hammer.

I have considered using a later Chrysler gearbox with lock-up and more gears, but as soon as I get to the point of needing to add electronics, I feel I might as well use a gearbox for which I have the technology. There are makers of other products which claim to be easy to set up for the Ford, but again I'll stick to what we know. There are also controllers for the GM 6-speed, which is also a ZF design licensed out. You and the Nutty Professor are right, the electronic calibration set up of anything with more than 4 gears is extremely involved.

The Sniper can be bought with a fitting kit which includes a pump. The rubber hose is fine and push-on fittings are also perfectly OK at the pressure the thing runs at. It has its own internal pressure regulator valve. I don't remember the pressure just now but it is about 50 p.s.i.

So, yes, you need a swirl pot arrangement. On cars which have internal fuel pumps in the tank it is possible to modify these and do everything inside the tank, but for older cars we use a low-pressure lift pump and a swirl pot. We use the Facet Posi-Flow pumps, but mount it on very wobbly bobbins to insulate the knocking noise from the body. A good value swirl pot can be bought from someone like 'Alloy Racing Fabrications' or similar. The feed from the LP pump and the return from the Sniper go in on the upper tangential ports, the HP pump is fed from the bottom, and the top port just goes back to the tank.

If you're buying rubber hose make sure it is entirely resistant to ethanol. We always used SAE R6 type hose but we have moved on to R9 type as we have more confidence in it. With R6 we have seen the outer rubber perish quite quickly, and although to be fair the inner rubber it still OK, it doesn't seem right to have the braiding exposed.

Last edited by Thor; 16-10-22 at 04:40 PM.
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Old 19-10-22, 10:56 AM
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No need to apologise for a user name, young man, they seem to be silly almost by definition! I use Lankybloke on the Classic Corvette Club site, which I thought was both descriptive, for I am both, and gently amusing too. Mrs Lankybloke, however, had firm opinions so I migrated to an equally descriptive but automotive-based one here, hence Green411.
Lots of very useful stuff in Thors post - many thanks. And I imagine that in the cold, pitiless light of a dyno test your 5.0L Rovers are going to make more hp than the '60s technology of a Mopar 383? But less torque?
Re your note on swirl pots and how you do stuff:
Could the stock chrysler mechanical pump act as the lift pump?
What volume of fuel tends to be returned to the main tank with Snipers?
I appreciate all cars are different, but where do you tend to locate the swirl pot, the HP pump and the lift pump?
I'm wary of the noise level from the Holley pump - with Snipers what HP pump do you use? How noisy is it?
I've been looking at the swirl pot/submersed pump combos from the USA, such as FiTech
https://www.vitesse-ltd.com/collecti...roducts/40004; what's your view on these?
Re Transmissions, it occured to me (ie my knowledgeable mate thought that) if Ultrabell and the various adaptor manufacturers (eg JVX Racing) make stuff to fit any USA trans to any USA engine then it would be simpler in some ways to get a more widely-available GM TH700r4 - 4 speed o/d, plentiful and relatively cheap, not electronially controlled, and provided the tv cable is adjusted correctly they seem reliable. My Corvette has the later electronically controlled version of the 700r4, the 4L60E, and that's a cracking transmission. I know it's 'un-Chrysler' and thus await torrents of abuse (or what I imagine is the Bristol owners equivalent, such as a raised eyebrow...), but it seems worth a thought if nothing else....
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Old 23-10-22, 04:36 PM
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Default Torque converter

A huge torque converter and no lock up clutch is where a lot of power gets lost. The wonderful driving experience where the car hardly ever changes gear and proceeds so effortlessly is down to the torque converter but unless the torque converter can lock up you will always have the disappointing fuel economy.
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Old 14-11-22, 06:09 PM
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Hi all, just a quick update on my fuel consumption and efi thoughts:
Firstly fuel - my car has averaged 13.9mpg , including a c.150 mile drive home from Warminster to near Cambridge on mostly dual-carriageway (what a wonderfully old-fashioned expression!). My intial horror at a fag-packet calculation of 10mpg came from assuming the fuel gauge was accurate, but it seems a tad on the pessimistic side. Unless it doesn't take account of the reserve?
Otherwise I absolutely luuurve the car. I adore idiosyncratic touches like the plaited leather glove-box handle, the weight of the switches, the flip-up front wings and the lovely chrome seat brackets. It's really comfortable, the ride is good now that I've got the (new) rear dampers on their softest setting, the brakes and steering are great and I've solved a lot of the (terrible) windnoise from the driver's door. I'm hoping that the rest of the windnoise (or most of the rest, in view of the age of the shape) will be solved when I get the driver's door hinges rebuilt over the winter. I haven't started on the oil leaks yet, (in a sense it's free rustproofing) so the only really annoying thing is it's reluctance to start when cold......
So I've thought long and hard about the cost/benefits of a new Carb vs an aftermarket efi, originality vs efficiency, and so on. In the end I summed it up in my mind as shotgun/carb vs rifle/efi: both are effective but the rifle is more controllable, more precise and less wasteful. With efi the fuel/air ratio is essentially commanded via sensor input, especially with a wide-band oxygen sensor covering a wider spectrum of A/F ratios. If I've understood a carb correctly the A/F is reactive - dependent on pressure drop & jet sizes. So I've pretty much decided on a Holley Sniper 550-516; and a Holley in-tank drop-in returnless fuel module with a 255lph pump and Hydramat reservoir 12-131. I hope to use the existing supply line and I won't need a return line. The engine bay will still look largely the same, especially if I leave the existing machanical fuel pump in place (without the pushrod, and with a new gasket to stop the oil leak!) so it acts as the block-off plate. Any rubber lines will be R9. So I'll have a stealthy ethanol-proof system that seems to get good reviews and is 40+ years more advanced than the worn-out Carter which is currently in place. Will order from Summit Racing and do the deed over winter. Will report back then. And yes, I will have a grown-up holding my hand in case you're worried......
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Old 15-11-22, 05:31 PM
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Some interesting points raised here. After much research I too came to the conclusion that a newer transmission is the best way to keep the original character of the car but to significantly improve fuel economy.
For 409 and 410 the obvious upgrade is to a later Mopar 'box with overdrive and lockup. For a few glorious years there were hydraulically controlled models that can be automatically controlled with a couple of pressure switches and a vacuum switch.

Dick Peacock converted his 410, changing to an A518 / 46RH 'box. This was a straight development of the 727 Torqueflite and as far as I know mounts straight on the back of the Poly engine. In standard form the 410 would do between 18 and 20MPG on a run. Dick told me that he was getting closer to 30MPG on long continental runs. I hope the current owner of the car will chip in with some accurate up to date figures.

I discussed the subject with the gents from Classic Bristol Car Parts and they told me that for 409 / 410 the factory preferred the A500 / 42RH 'box from a 1992 to 1996 Dodge Durango. This is a development of the 904 transmission which is less robust than the above unit but is good for the output of the 410 in standard trim and can be rebuilt with more clutch plates to beef it up. The 42RH has a smaller torque converter but still bolts up directly to the Poly in the 409 and 410. The original starter motor bolts straight up as the bellhousing is different. The flex plate and dust shield from the 42RH will be needed as they different to the 727. 407 and early 408 have different crankshaft and will not directly bolt to the 42RH.

Fitting an overdrive will probably not involve modification to the tunnel but will require modification of the chassis crossmember along with shortening the prop shaft by around 3 inches. As the engines have good torque the factory back axle ratio is likely to still be suitable. Non overdrive units used 5/16" cooler pipes whilst overdrive units use 3/8" It may also be necessary to replace or augment radiator transmission cooler.

46RH transmissions can still be found in the US for reasonable money. 42RH are very hard to source but not impossible. STS imports will get a transmission from Florida to Essex for about 200 which is probably a lot less than the cost of crating and transportation to Florida from elsewhere in the States.

If trying to track down a suitable transmission it may help to know that A518 is the series with subsets 46RH (hydraulic operation) and 46RE (electronic operation) Similarly A500 has subsets among others of 40RH, 42RH, 42RE and 44RE.

Back to the topic - inlet manifolds more suitable for fuel injection adapters were made for the Poly 318 - E.g Weiand 7503 - but are very hard to find and quite pricey now.
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Old 16-11-22, 04:45 PM
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I've got the car that was Mr P's - I get 18 mpg running around locally and around 25 mpg on a run.
That's with a 318, the gearbox with overdrive and lock up, new Edelbrock 500, rebuilt top end, electronic distributor, 2.8 rear, flat as a pancake cam and a fair amount of time on rolling road getting it all spot on.
Good luck with the efi!
Cheers
Andrew
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Old 17-11-22, 01:37 PM
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That is a good result. By today's standards a 410 is not a heavy car and the relatively small frontal area of a Bristol makes it (quite) aerodynamic, but a 5.2 litre petrol engine has certain limitations ! With a good deal of fiddling about a Sniper OUGHT to be able to do a bit better, but it is quite a challenge.
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Old 17-11-22, 01:53 PM
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Thanks - when the heads were off the chap that did them spent a lot of time getting them to flow as well as possible. The engine's quite poky - I'm apparently getting 245 brake at the wheels but have spent enough time with various cars on different rolling roads to know some are more generous than others!
The flat cam suits the car well btw - although the hot rodder part of me wouldn't mind a bit of lope!
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Old 17-11-22, 05:53 PM
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A bit of lope on a cam does sound good in the right car, but as you say a Bristol may not be the right home for such a cam! Didn't Comp cams do a ' Thumpr' series which had the lope at idle but with modern lobe design?
If I had a 318/340/360 then I'd probably have a 518 in it now, on the basis of the overdrive improving cruising more than efi would. But as discussed earlier a 383 will need an adaptor, which then opens up further debate about whether to stick with Mopar and the A518/46RH or go GM TH700R4/4L60E for it's relative availability, affordability and ease of getting replacement parts.
Lots of useful specifics in David C's post - thank you!
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