Holley Sniper

[David C]

Andrew is getting 25MPG on a run and Dick used to get a bit better on a continental trip in the same car. 410 with overdrive, Edelbrock carb and standard distributor.

It wouldn't be too much of a reach to hope for 30MPG or more if driven carefully with a Sniper EFI and Hyperspark distributor.

I'm still waiting to get my car back with overdrive. If that goes as well as hoped I will fit Sniper, Hyperspark and SLJ headers. Very much hoping to report with real world figures early next year.

[Green411]

They're all very good figures, especially for 50+ year old cars with (by modern standards) poor aerodynamics.
If only we could help DWomby with his dismal consumption! If I recall correctly David struggles to get into double figures with a 360 cid engine? Makes my own tribulations seem small. I looked up the cam specs of his Mopar Performance 4452761 and they don't seem too outlandish.
So wrong timing/timing curve? Vacuum advance missing/not working? Cam incorrectly installed? Carb leak? Other leak? Fuel evaporating? Engine fault? Over-rich carb? Blocked air filter?

[dwomby]

Originally Posted by Green411

They're all very good figures, especially for 50+ year old cars with (by modern standards) poor aerodynamics.
If only we could help DWomby with his dismal consumption! If I recall correctly David struggles to get into double figures with a 360 cid engine? Makes my own tribulations seem small. I looked up the cam specs of his Mopar Performance 4452761 and they don't seem too outlandish.
So wrong timing/timing curve? Vacuum advance missing/not working? Cam incorrectly installed? Carb leak? Other leak? Fuel evaporating? Engine fault? Over-rich carb? Blocked air filter?

You do recall correctly although most of my driving is suburban. So higher numbers may be possible on longer runs. Unfortunately, my car has been off the road since late last year while the front suspension is out (see the saga so far here: http://www.bristolcars.info/forums/8...r-removal.html

I expect to start reassembly in another week or two when temperatures and humidity here have made working in the garage possible. I hope to get her back on the road before Christmas and the fuel consumption/tuning issue will no doubt need addressing then and I'll welcome all help!

David

[AndrewA]

As everything beds down I'm finding 25 mpg relatively easily achievable and a nearer 30 on long runs driven sensibly.
I do however enjoy making full use of kickdown when running around locally - it's difficult to resist - and then I'm back in the high teens.

[dezelsky]

These are great results. Thank you for sharing. All the more reason for us to enjoy our cars!

[David C]

A bit more reading on Mopar forums about Sniper upgrades has led me off on a bit of a tangent. Changing to EFI requires a fuel pump that can draw up to 20 Amps. Air conditioning can add about another 15 Amps.

These two upgrades alone can double the original current draw. The easy fix is to upgrade to a newer high output one wire alternator and do away with the original external voltage regulator. This is great but leaves the ammeter in circuit, wired with cable which isn't adequate for the new load and now a fire risk.

Maybe the best solution is to do away with the ammeter and find a period voltmeter to replace it.

Another option if keeping the original charging system would be to fit LED headlamps and wire the air conditioning to disable the heated rear screen when in operation.

[Green411]

Interesting point DavidC makes, so I checked my own car. My '73 411/3 has a voltmeter, albeit a slow-reacting one. As a precaution I'd renewed the separate solid-state regulator at the time I fitted the Sniper. Alternator looks original-ish and there's no sign of an upgrade or replacement in the history file.
I checked the charging with my voltmeter, and with fans on (and electric fuel pump obviously) it charges at 12.75v (shows just over 13v on the dash gauge) and 12.25v with the headlights on main beam, as well as the fans. Normal running shows c.15v on the dash gauge, which reads a bit high in relation to my multi-meter. Exec summary: it seems to work.

Referring to David C's earlier post about intake manifolds I experimented by trying my car without the (Holley-reccomended) divider-less Wieand sealer plate between the stock cast-iron spreadbore divided manifold and the square bore Sniper. I used a gasket with a divider strip. It ran ok at first but soon developed an air-leak that I couldn't cure so I went back to the original setup of open sealer plate with a gasket above & below, and it's running fine again. Whew....

[Green411]

Thought you might be interested in an update after 18 months or so.

The car still has the original Torqueflite 3 speed auto transmission and original back axle. With the original carb I got 13-14 mpg imperial on a run and about 11-12 mpg running around locally with 10-20 mile drives. Driveability left a lot to be desired and starting under most circumstances was poor.

With the Sniper I get 15-18 mpg on a run (absolute best of 19mpg at no more than 60mph and no harsh acceleration) and 13-15 mpg running around, all imperial.
Drivability and starting are greatly improved on top of the 10-15% fuel consumption improvement.

It's all based on the Sniper's self-learning, with no manual tuning done. The original ECU failed after about an hour of running, but Holley accepted liability immediately and I got a free replacement from Summit which has been fine.

I've had a couple of instances of a spit-back through the throttle body while pulling away during warm-up. This was traced to tbi mounting bolts loosening up for some reason, presumably causing a slight air/vacuum leak.
I use the recommended sealing plate between the square-bore throttle body base and the stock spread-bore intake manifold. Have tried it without it, but got an air leak.

Overall I'm very pleased. Would I do it all again? Yes, in a heartbeat.

[dwomby]

Thanks for the update. Tempting.

David

[David C]

Very pleased to hear all is still well. I have been keeping an eye on the internet for tales of woe about the updated Sniper and have seen few if any.
My installation of overdrive gearbox on the 410 has dragged on for various reasons but I hope to have it back on the road in the next week or so. If all goes well then Sniper and Hyperspark will be next.

[Green411]

I forgot to say in the last post that the fuel pump is a bit noisy, too. I used a Holley 12-131 returnless drop-in fuel module, which has a 255 lph in-tank pump. I added a Hydra-Mat, too, in lieu of a reservoir/swirlpot. All seems to work very well.

[David C]

Do you think it would be a good plan to put some neoprene or similar under the fuel tank and also between the straps and the tank?
Perhaps a bit of Dynamat on top of the tank to damp any ringing.

[Green411]

Hmmm......I must say I hadn't considered anything between straps and tank, or below tank, but I have put as much sound deadening as will fit between the tank front and seat back, and above tank.

[David C]

Next time you have access I suggest you place a hand on the top of the tank with the pump running. If you notice any lowering of noise level then one or two pieces of Dynamat or similar about 6" squareish may well help. If you can feel the pump vibration then decoupling the tank from the bodywork with something resilient is worth a go.

[Green411]

Sorry David C, for some reason (ineptitude?) have only just seen this.
Sounds like sound advice.