Holley Sniper

[Green411]

Howdy y'all. Hope this update is of interest.
On a recent 140 mile round trip on single-carriageway A & B roads, 18-20*c, not exceeding 65 mph, mostly at 50-60mph, but several roundabouts and junctions to accelerate away from (gently, letting the torque do the work), driving on the gently side of normally (with no hyper-miling tricks) and measuring from a hot start I got 19 mpg. From a 383! Driveability absolutely perfect.

[David C]

Brilliant! Thank you for the update.

[Thor]

That does seem like a good MPG figure. Thank you for this information. I'm hoping to get a Sniper onto my 409, and also a gearbox with lock-up torque converter. With the smaller engine I would hope to be into the 20s on MPG.

[Green411]

At first it did seem too good to be true, but I double-checked my sums and actually erred on the side of caution!
Thor, I'm sure that with a smaller engine, o/d transmission and a lock-up tc you'll beat me easily - assuming your engine is in stock/mild state of tune. On a 40 mile drive at 60-70mph, hot start, I once got 31mpg from my o/d auto '95 Corvette, which had a diff ratio of c.3.00:1 and did 2200rpm at 80mph.

[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

[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

[TonyK]

Good evening all, my first post on the forum. I’m in the process of acquiring a Beaufighter and in my research came across a PWM fuel pump controller, VaporWorks, which runs the pump depending on demand so should be much quieter, just a thought.