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Holley sniper 4150 vs Quadrajet 12A performance / channels and open adapter
Hi guys,
I'm looking at putting a Holley sniper on my 79' 12A street port and I'm just wondering if the holley sniper EFI (square bore) or the sniper quadrajet (spreadbore) would be better.
Some things I've been considering:
Would the small primaries on the quadrajet be better for vacuum? They'd probably be better for more granularity in the low end, right? Maybe give a better idle, too?
What would be the effect of those small primaries at the higher end? Possibly limiting airflow on the primary side?
How would an open adapter change things? Maybe it would solve the potential restrictions at the high end. I can probably look this up, but figured I'd mention it. I seem to remember Rad potential did a video on this.
Is there something else out there that's cheaper and the same ease of installation and tuning?
The FB doesn't have an ecu that needs chipping, right?
I'll probably think of more questions, but we'll start with this for now.
Thanks!
Edit: I found this about the open spacer. Seems to be answering that question, so far. https://www.rx7club.com/1st-generati...te-12a-893128/
Edit2: Here's RadPotential's video that helps understand what would happen with the spacer.
i don't have definitive answers, but i can give you something just as good. well ... maybe that wasn't true. i can offer you something nowhere near as good, and those are ... my thoughts.
anyway, i suspect that you may be able to alter (albeit slightly) the torque curve with the spread bore setup, but i doubt you'll be losing anything upstairs or getting a better idle. RB manifolds are square bore and they idle just fine with a carburetor in place. i can't imagine they will idle worse with fuel injection. i am assuming your questions are because you want to get the best low end response. is that correct? if so, then i would refer you to RP's videos on the 12A Sniper install. i think he did a pretty good job covering it. i think you would be just fine using the spread bore on your streetport 12A, but again, if you were to get the square bore setup, i doubt you'd be looking at a night and day difference.
as far as your open spacer question goes, i'm not sure how much of it applies to fuel injection, since fuel supply is not (totally) dependent on the vacuum signals. i would defer to someone with more knowledge on that particular topic though.
the FB does not have an ECU that needs chipping.
EDIT: apparently, i'm missing at least 3 videos, but they shouldn't be hard to find.
Thanks!
I actually wasn't aiming for anything particular just yet. Only wanted to have decent street driving while limiting the performance impact as much as possible. I suppose low end torque would be helpful in that respect.
I have heard in a couple places that the holley carb doesn't work well with individual runners unless it's been tuned very well for it (like with the racing beat carb). If you plan to use a more normal holley 600 or 465cfm, they say it works better with the open spacer.
Since you say the performance won't really be much different either way, it would probably make the most sense to just get the square bore sniper.
RP/s videos on the 12A sniper install is actually what made me decide to go that route in the first place. But it's been awhile since I've seen them and I'm sure I've forgotten a lot of what he said. Now that I've done some more research, a review of it might be pretty enlightening.
I didn't think the FB needed chipping, but someone mentioned it on the Reddit group, so I second guessed myself. Thanks for the confirmation.
That's fine that you missed some videos. It won't be hard to find. There's a whole playlist on RP's youtube that has them all.
Thanks for the reply! It's rather helpful and certainly eases my mind that pretty much either way I go won't be a terrible decision.
I ran a spreadbore Edelbrock 500cfm on my stock port 12 for a while. To mount a spreadbore carb onto RB's intake manifold (squarebore) you will need some kind of spacer/adapter because the secondary butterflies are larger than the RB's runners. I used a 1" phenolic spacer and bored/tapered the secondaries to match the Eddy on top, and the RB intake on bottom.
The carb ran great on the primaries but fell on it's face when the big secondaries opened, and I could never get it jetted right (and I really like Eddy carbs). I had much better luck with a Holley 390cfm square bore, so I'd recommend the square Sniper.
That's interesting. Thanks.
Do you think the problems with the secondaries was related to fuel mixture? Cause I'd assume the automatic tuning on the sniper would take care of that. Or do you think maybe it was just not enough flow through the venturis to pull the fuel out? Which I think would also be solved with efi. Is there something else that could have caused that?
I wonder if you could use basically any size intake if you have fuel injection. I should do some research to make sure the sniper doesn't need a certain amount of vacuum to function. I guess with no vacuum, there would be problems with the brake booster and ignition advance.
And now that I think of the ignition advance, I wonder if I need to change the way that works. RP didn't mention that in his video, but he had a two barrel sniper.
I don't have the #'s in front of me, but a healthy na 12A pulls less than 400cfm at full throttle (7-9000 rpm). Again, I don't have that data in front of me right now, so anyone else can please correct me. The RB 465 is oversized. Guys running 600 Holly's are WAY oversized (on stockish 12A's). The 390 Holly I have runs pretty good.
I think the square bore sniper will be your best bet simply because it will physically fit the RB manifold. The Quadrajet spreadbore will not fit the RB manifold. Not without an adapter.
I wonder if you could use basically any size intake if you have fuel injection. I should do some research to make sure the sniper doesn't need a certain amount of vacuum to function. I guess with no vacuum, there would be problems with the brake booster and ignition advance.
from what i've seen (in the RP videos), the Sniper system is throttle body injection, so it does have some properties of carburetion - the relevant one being that fuel begins mixing upstream of the intake port. however, that's about it. high pressure fuel is still being pulsed by a pair of injectors and so there is no Bernoulli effect - i.e. it doesn't have to pull fuel out with a pressure differential. the fuel is injected/squirted, just like any other EFI. as long as air is flowing through all 4 ports, you should get no disruption in fuel supply because they are not linked.
intake size still matters, but matters less with fuel injection because carburetors can't adjust for certain things like a computer-controlled fuel injector can. the actual mixing may be affected, but i don't know to what degree.
the Holley manifold has a provisions for vacuum, so your brakes and ignition should work just fine.
Ok. I heard that the sniper released the fuel into a ring, but it looks like that's just to help aeration, not to actually release the fuel. Thanks for clearing that up.
intake size still matters, but matters less with fuel injection because carburetors can't adjust for certain things like a computer-controlled fuel injector can. the actual mixing may be affected, but i don't know to what degree.
Good to know that efi isn't as affected by intake size. Especially since the sniper is quite a bit too large for this engine.
the Holley manifold has a provisions for vacuum, so your brakes and ignition should work just fine.
So I guess the intake size won't affect vacuum hg much, then?
Several of us are playing with these ideas. The smaller primaries would increase the air flow rate and overall reduce the amount of over carburation. I went with the square bore on a street ported 12A. I do not know if the primaries are full port as well. Tried 2 different 600 and one 500 CFM elberbrock with varying results and LOTS of tuning effort.!!!!! even with and Air fuel ratio gauge. The Sniper was awesome. Installed on a stock intake manifold with Holley adaptor. for the last 2 weeks. Working through the learning curve.
Just got in a new Race Beat manifold Saturday that I plan to install after I get more of a feel on the stock intake manifold properties and power curves. I also got the 40% delay linkage in for setting up the primary port only up to 40 % throttle to see if that helps or hurts drivability and mileage.
Overall impression of the Sniper is I wish I had done it 6 months ago. Cranks in cold weather, Idles well at 1400 rpm and working in lower as I play with it. Runs very strong. The temperature gauge read 15 degrees hotter than my old gauge. ( I added an extra temperature gauge in the water line off of the oil cooler) It ran 5 degrees hotter than the old gauge and is now 10 degrees cooler that the sniper gauge. Spacing for the temperature sender and the throttle body is very tight on the stock manifold set up. Hoping for more space with the Race Beat one.
07-07-22, 03:11 PM
