Holley Sniper

[Thor]

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.

[Green411]

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.

[Thor]

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.

[Green411]

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....

[roybatute]

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.

[Green411]

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......

[David C]

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.