Holley Sniper EFI vs MP484 cam

I have a friend wanting me to do an EFI conversion on .69 GTX 440 automatic trans,A/C car. It was my old boss' car and he gave it to his son to use years ago and driveability needs some help.I suggested a newer type carb (stock AVS now)and electric fuel pump to help but I think he really wants to go EFI.This engine we rebuilt back in the early '90's to mostly stock specs sans a Mopar Performance 284/.484 lift 108 cam,not many miles on it since. I don't remember where it was installed +/- or straight up on the 108.This cam has a good lope,maybe a bit much but actually runs well when ran out to a high RPM.Might this cam be a bit too agressive or difficult to tune for the Sniper EFI? If we do this I'm thinking a swap the OE iron intake for a single plane unit might be necessary,not sure if this would help tame the 484 cam characteristics.Engine is stock iron headed w/906 castings and exhaust manifolds,dual exh with an H-pipe.Of course the first thing with the cam will be a visual inspection of the lobes,car is driven infrequently and who knows how the lobes look.Any suggestions on a better cam spec/preferred LSA cam for this stocker with Sniper EFI are welcome! TIA for any and all input. ~RT

That will be fine with it...You should see what I run with mine......Drivability will greatly improve.

You need to install a Hyperspark distributor with the Sniper so you can control timing. Once you can control timing and fuel it becomes fairly easy to dial in the tune. The tuning capability of EFI makes it much easier to get a big cam to work on the street.

Even for an EFI novice like the OP?

Can't tell you how yours will turn out, but mine idles and drives fine with 10-11" of vacuum. Cam is 247-251@ .050". Got the Sniper X flow and a locked factory dist. I'm controlling timing too. Being able to "give it what it wants" without distributor removal& surgery makes a huge difference.

The Sniper can be laptop tuned even for those "unfriendly" cams. Holley doesn't push the laptop capability because it's supposed to be totally self tuning, but if you don't have enough vacuum or there are other issues, I can connect a laptop remotely and tune it like it was an HP. When the Sniper was announced I thought I might never tune one, but now I remotely tune several every week. The laptop tuning capability is one of the strengths of the Sniper.

Sure, as long as he is willing to learn. It only took me a few days to figure out how to tune a Sniper. Not that difficult really. Read the instructions, watch some videos and then start trying things.

Are you sure that cam is one of the later ones ground on the 108 LSA and not one of them ground on the 104 LSA?
The early ones ground on 104 LSA installed advanced to 102 ILC don't, won't, have much vacuum at 900 RPM idle speed, maybe 5.0 inches
Did I tell you I hate those Purple Shaft cams

They have a button in the software for a race cam wth next to no vacuum...That's the mode I am running in without any timing control.

You don't need a Hyperspark distributor for timing control if you already have a MSD distributor. You can lock out the advance mechanism on the MSD and use a adjustable rotor to phase it properly. Also need to pay attention to good wiring practices with magnetic timing control as it is more prone to EMI.

I tried that when the Sniper first came out and it didn't work very well. It turns out that the MSD distributor isn't a very good match for the Sniper. The MSD produces a sine wave signal but the Sniper wants a square wave signal which is why Holley developed the Hyperspark. The Hyperspark uses a Hall effect sensor to produce a square wave digital signal that works well with the Sniper. The Holley forum is full of people who have had trouble getting their MSD distributors to work with the Sniper. The common advice now is for people to sell their MSD distributors and use the money to buy a Hyperspark.

I wouldn't think the 284/484 cam would be rowdy in a 440; in a 383/727 RR I had, it was soggy off-idle but things got happy after 3000RPM.
What is this AT & AC GTX used for ? Is it a restored/#s car or a hot rod ?
Changing the cam to something more modern would gain everywhere and require less crutching & less $$$.

can the Hyperspark distributor be used on the MSD box ?
i need to buy a distributor, and i don't want to do this twice.
however, if i use the MSD 6AL i have now [before switching over to the Sniper system, which i can't afford at this time] i have a couple of factory distributors i could modify.

Yes the Hyperspark distributor can be used with a MSD ignition box and a MSD coil. The Hyperspark distributor plugs into the Sniper and then the white wire (points output) from the Sniper triggers the MSD ignition box.

I had the same issue with my ancient 950 Commander.

The solution was to run the MSD pickup through an GM HEI module first. That converts the sine wave to a square wave.

I think it was in the installation instructions.

Kevin

Actually it works okay with a magnetic MSD distributor. Magnetic to Holley means sine wave. When I remote tune I sometimes have to be a remote mechanic as well, and what I run into with people that want to use their MSD dizzy is that the default Holley values for a magnetic pickup are wrong. The software defaults to a minimum signal voltage of zero volts. However, the instructions DO say that you should start at .35V. After I change that, my experiences have been very good. Then we have the rotor phasing issue that is mentioned above. That also must be done because the distributor must output at 50 - 60 degrees BTDC yet the rotor should be phased to its terminal at about 25 degrees BTDC. The most common reason that MSD distributors don't work well is that people didn't know where to find the instructions. I do one more thing not mentioned in the instructions - use shielded wire with the shield grounded at the Holley end.

Cab,I'm not sure of the exact LSA but I don't think it is a 104.From memory I'm thinking it was either 108 or106. It idles at a reasonable RPM in drive.a little lopey but not horrible.I put this together in the early 90's for my friend and haven't heard it run in probably two decades.Not sure what vacuum is but i will check when I work on it,wasn't a big concern when we put the cam in since it is a manual brake car.
Thanks RT

I learned that shielding lesson the hard way.

Kevin

This car is basically a restored numbers match GTX except for a set of wheels,current duty is just aa a cruiser.Engine has the stock AVS carb on a stock spec 440 rebuild except for the 484 cam.Ignition is the factory points distributor,exhaust is OE manifolds into stock style duals with an H-pipe.The automatic transmission was built by a local trans guy well versed in Mopars and shifted great. Very crisp and consistent shifts at 6200 RPM (if tach was accurate) in drive.It has had many gear swaps from the original 3.23 to 4.10 at different times. I drove it from Pittsburgh PA to the Indy Mopar Nats in 1993,ran it down the IRP strip too.It did a 13.9 ET which I thought was acceptable having the stock carb and all. I wouldn't mind updating the cam,I always thought it was a bit radical for the overall package being a basically stock engine plus having AC.If the 484 shows any signs of wear I willl replace it with a newer design,a bit less aggressive.
Thanks,RT

,
A Hyperspark ignition is definitely on the list with this job to replace the stock points distributor.It is one reason we decided on the Holley Sniper setup for the EFI/ignition tuning capability.
Thanks,RT.

I'm definitely a novice as far as these automotive EFI conversions are concerned.However I do have some EFI experience working with Harley motorcycles in my shop so I.m familiar with the general needs operations of the basic systems.Plenty of diagnostic repairs as well as some tuning on the HD's so I'm willing to learn the auto aspects too.
Thanks,RT

Good to know Rich! You may very well be employed for this adventure in he future.
Thanks for the reply,RT

I'm working on a RoadRunner conversion right now. If the owner wants the wiring harness to look stock then add a couple of full days of work to the job. You need to take the Sniper harness all apart and rebuild it and then wrap it with vinyl wrap so it looks stock. It isn't a super tough job, just takes time and some patience.

I just completed a Sniper install on one of my cars last week. Wasn't really sure what to expect since its 500 Cubic inch engine, 12 to 1 Indy 295 CNC SR heads with a 272/275 @ .50 solid roller cam and a Indy dual plane. Maybe 5 to 6 pounds of vacuum at idle... I'm using the MSD distributor with the adjustable rotor for timing control. Took a while to get the idle dialed in. I idle it pretty high at 950rpm, but I idled it high with a carb to keep a lot of oil moving around. So far I'm very impressed with the system. Throttle response is great and really like the drivability of it. Wasn't sure how the dual plane would work and I do have a 1/2 inch spacer under the Sniper. I have a nicely ported 337 manifold on the shelf if I want to change it up, but this is 100% street car that will never see the track and I like the torque of the dual plane.

I still have some tuning to dial it in further and I'm doing all the tuning through the Sniper software as opposed to the hand help unit.

To the OP I don't think you will have any issues with that combination.

Hey Andy, just to clarify on this one:

Can the Hyperspark distributor be used by itself *without* the Sniper EFI?

I'm in the same spot as he is where I need to buy a new distributor and Sniper EFI is in my future plans. If I could buy it and run it with an MSD in the interim that would be sweet.

Thanks, Sean

No I don't think that would work since the Hyperspark distributor doesn't have any advance mechanism. It is just an RPM signal generator for the Sniper. The Sniper computer then creates the ignition advance curve and sends it to the MSD box. If you hooked a Hyperspark up to a MSD box it would be like a crank trigger with a locked timing curve.

that was my question, and i was confused by andy's answer as well.
i'm going to be using my well sorted thermoquad to start with until i can afford a sniper system.
since i need to replace my gas tank, i replaced it with a stainless part from vans auto, and am installing an aeromotive 340lph pump in the tank, along with a 1/2" return line.
i also have an aeromotive regulator, so it will be a matched system when i can finally switch over to the sniper.
i guess i'll just modify a stock distributor for now, and either use a gm HEI adaptation, or use the stock distributor to trigger the MSD, using a "ford F150 style" coil that matches whatever ignition system i decide on using, then when i can afford the sniper setup, i'll get the hyperspark distributor.