Holley Sniper

[David C]

I should really have said that the Weiand is a divided single plane whereas the original is dual plane. Supposedly the longer tracts in the dual plane allow the mixture to slow further and give a more dense charge at lower RPM providing higher torque.
Looking at the original manifold, one half turns through a right angle almost immediately on entering the manifold so common sense suggests more puddling on one side than the other. Since the Sniper only uses an O2 sensor in one of the downpipes I struggle to see how it can get the mixture just right in both banks. Hence I decided on a symmetrical manifold.

If reading this gives the illusion that I know what I'm talking about, please don't be fooled. I very much welcome input from anyone who can see through my waffle and tell me where I'm going wrong.

[Green411]

Weeelll........I actually rang Holley tech and asked them about this before I bought mine. The Sniper has 4 x 100lb/hr injectors, one in each of the 4 barrels in the throttle body. 1 x O2 sensor in one down pipe, which tells the ecu what fuel to provide. The ecu commands all 4 injectors equally and at once. So unless there is a noticeable difference in the fuel distribution to each bank (eg engine v badly worn) then each bank, and each cylinder, gets pretty much the same fuel. I used an adaptor/spacer plate, which was open with no divider, so all cylinders can draw equally-ish.
That's my understanding, and all the plugs now look roughly the same colour - a nice light tan, rather than the thick soot they had beforehand.

[David C]

I think I'm in danger of over thinking it here. The important thing is that you have a much improved system that is working well for a reasonable outlay.

With any luck a few more of us will get EFI fitted and be able to report back and fine tune what is required for those who follow.

Thanks again for sharing !

[Green411]

Well over thinking is better than no thinking, which is the hole I sometimes fall into!

[Green411]

I just had a look at some forums, including Holley's 'Sniper efi' forum. The administrator and senior members (ie the ones who know the most I reckon) generally seem to think that a dual plane intake is fine with a Sniper. My own experience supports that.
I'm no expert, and I'm a VERY long way from knowing a zillionth of what a professional mechanic/engineer knows, but I firmly belive that a successful Sniper installation needs to be in a car with properly matched engine parts on an engine in reasonably good fettle with a good battery and charging system. It won't fix basic errors in matching cam and heads, for instance. Then just follow Holley's comprehensive instructions, particularly about electrical connections, and you should be ok.

[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.