Low Vacuum on Holley Sniper EFi

Is there anybody running a Sniper that has low vacuum with good results? My Comp cam is a XR-286-HR producing 8 hg at the Intake and 7-8 hg at the carb at 900 RPM idle.

Sure, lots of people. Here is a video of a RoadRunner that I installed a Sniper on. This is a 700 hp engine with a big solid roller and it has open exhaust. https://www.youtube.com/watch?v=sNeBSOqpO40

There are some tricks to make it work since the Sniper won't run on a low vacuum engine right out of the box. You'll need a laptop and the CAN to USB cable as well as the Sniper software. Once you have all of that you'll need to adjust the base fuel table, adjust the ignition tables and you might need to run it in open loop at idle. If you don't know how to do any of this tuning then give Rich at FAST Man EFI a call and he'll set you up with a tune.

My 512 RB with Solid Roller has about 8 inches of vacuum and it runs awesome with the Sniper.

I would turn the idle speed up until I got what I liked
1200 RPM out of gear and 1000 RPM in gear works good for me

Are you controlling timing with the Sniper? If not you should be. If you are then throw a lot of idle timing at the engine. Start at 25 degrees and then test 28 and 30 to see how it responds. Watch the MAP and IAC values as you change the timing since those two numbers will show you if the engine is getting happier.

Running a Sniper 4500 here....Raise your idle to 950....And yes. My Cam might scare you....and maybe add idle timing....

Thanks for the reply’s everyone and AndyF your car sounds great. Yes I plan of timing the car through the Sniper as I bought the Hyperspark distributor. I’ll definitely give Rich a call when I get to that point because the tuning is probably way over my head as I haven’t a clue about any of it.

I have a friend who fought his Sniper with a big cam for quite awhile. He called Rich and he helped him fix the problem. . He said he wished he would have done that from the beginning.

Yeah it only takes a few minutes for a pro to dial in a big cam tune on a Sniper so it is a good investment. Holley kind screws up the deal by telling people that a laptop is not required to tune a Sniper. That is true if you have a stock 350 chevy, but it isn't true if you have a big engine, or a big engine with a big cam. When you have a big cam you have to use a laptop to tune the spark and fuel tables. Good news is that it only takes a few keystrokes to fix the tune, bad news is that Holley doesn't provide any instructions. There are a few videos on youtube that kind of show part of the process but nothing very professional. Just guys in their backyards taking shaky videos with their cell phones. Someone like Rich can dial in a tune in 15 or 20 minutes.

got a 250/250° on 108 LSA cam in my 408 SB, more cam than the mentioned comp......no problem at all with the sniper.

https://www.youtube.com/watch?v=rxRAb0NxAww

Michael

Good lord that is nasty!!! Love it! I can’t wait to get the Sniper on there now!

that DOES sound good !

100 years ago, I got a Holley "tech" person n the phone ($$$) about the new EFI system. I asked where the input for engine vacuum was, what was the range of A:F, Hg" adjustments, etc.
He had no idea what I was talking about, even enough to say "there isn't one".
No, I didn't buy one.

The Sniper has an internal MAP sensor. It is ported into the base of the throttle body so it sees the top of the intake manifold. Holley includes a little kit to block that port on a supercharged engine so the MAP sensor can be connected to a port under the supercharger. I'm not clear on what your other question was. Something about AFR range?