Holley Sniper EFI and intake manifold plenum modification.
Thread Starter
Melting Slicks
Joined: Nov 2017
Posts: 2,358
Likes: 519
Holley Sniper EFI and intake manifold plenum modification.
Greetz All,
Now that I have my Edelbrock EPS (closed plenum) intake manifold off of the car... I am thinking about modifying it.
I have read that it is a good idea, if you are running a Holley Sniper EFI, to grind down one inch by one inch slot of material in the top of the plenum. Something about the O2 sensor readings be more accurate.
Aside the valve issues I have been having... my idle seems fine. I understand that is where this mod would make most of the difference... improved idle quality.
So, to do or not to do... please opine and drop some knowledge.
MTIADC3.
Now that I have my Edelbrock EPS (closed plenum) intake manifold off of the car... I am thinking about modifying it.
I have read that it is a good idea, if you are running a Holley Sniper EFI, to grind down one inch by one inch slot of material in the top of the plenum. Something about the O2 sensor readings be more accurate.
Aside the valve issues I have been having... my idle seems fine. I understand that is where this mod would make most of the difference... improved idle quality.
So, to do or not to do... please opine and drop some knowledge.
MTIADC3.
Last edited by DorianC3; May 27, 2026 at 11:34 AM.
Melting Slicks
Joined: Apr 2021
Posts: 2,707
Likes: 2,153
From: Minnesota
Personally I wouldn’t feel comfortable taking material off the intake while it’s installed on the engine, so if you’re removing it anyways you might as well replace it with a true single plane.
Race Director
Joined: Nov 2006
Posts: 13,225
Likes: 7,823
From: Sunshine Coast, Queensland, Australia
2025 C3 of the Year Finalist - Modified
2024 C3 of the Year Finalist- Modified
2022 C3 of the Year Finalist - Modified
Cruise-In VIII Veteran
I had my EFI on a Edlebrock duel plane manifold. Everyone said, cut out the divider. It'll run better, better MAP sensor readings.
I removed my intake. Milled out the divider. Reinstalled and properly resealed my intake. Couldn't notice any difference whatsoever.
Everyone said, you need a single plane manifold for your EFI, once again pulled intake. Installed single plane manifold.
Couldn't notice any difference whatsoever!
I removed my intake. Milled out the divider. Reinstalled and properly resealed my intake. Couldn't notice any difference whatsoever.
Everyone said, you need a single plane manifold for your EFI, once again pulled intake. Installed single plane manifold.
Couldn't notice any difference whatsoever!
Thread Starter
Melting Slicks
Joined: Nov 2017
Posts: 2,358
Likes: 519
I had my EFI on a Edlebrock duel plane manifold. Everyone said, cut out the divider. It'll run better, better MAP sensor readings.
I removed my intake. Milled out the divider. Reinstalled and properly resealed my intake. Couldn't notice any difference whatsoever.
Everyone said, you need a single plane manifold for your EFI, once again pulled intake. Installed single plane manifold.
Couldn't notice any difference whatsoever!
I removed my intake. Milled out the divider. Reinstalled and properly resealed my intake. Couldn't notice any difference whatsoever.
Everyone said, you need a single plane manifold for your EFI, once again pulled intake. Installed single plane manifold.
Couldn't notice any difference whatsoever!
Race Director
Joined: Nov 2006
Posts: 13,225
Likes: 7,823
From: Sunshine Coast, Queensland, Australia
2025 C3 of the Year Finalist - Modified
2024 C3 of the Year Finalist- Modified
2022 C3 of the Year Finalist - Modified
Cruise-In VIII Veteran
No, it's runs fantastic. Still does.
Safety Car
Joined: May 2001
Posts: 4,757
Likes: 1,647
From: Fairfax Virginia
I agree with doing the machining work out of the engine compartment. There are so many ways to get trash into your engine.
Have you ever looked at the information regarding the Holley Snipers at: EFIsystempro.com. Their website has a LOT of great information regarding the Sniper systems.
I am using a Edelbrock RPM Air Gap Intake manifold on my 427 and it works great despite being a bit too tall. The Air Gap has the notch already machined into the plenum. I have had no bad effects caused by using the dual plane Air gap intake, probably because of the notch in the divider inside the plenum.
Best regards,
Chris
Have you ever looked at the information regarding the Holley Snipers at: EFIsystempro.com. Their website has a LOT of great information regarding the Sniper systems.
I am using a Edelbrock RPM Air Gap Intake manifold on my 427 and it works great despite being a bit too tall. The Air Gap has the notch already machined into the plenum. I have had no bad effects caused by using the dual plane Air gap intake, probably because of the notch in the divider inside the plenum.
Best regards,
Chris
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Le Mans Master
Joined: May 2007
Posts: 5,025
Likes: 1,120
From: North tonawanda NY
Notching the divider will only help performance even if you didn't have the sniper a lot of the EFI systems such as the aces throttle body injection I just installed on my C3 have a special gasket to allow some crossover for the map sensor so you're not just getting half of the pressure readings the the largest functional difference between the performer RPM and and theair gap is that notch.
Last edited by augiedoggy; May 28, 2026 at 06:22 PM.
Team Owner
Joined: Jun 2001
Posts: 23,375
Likes: 1,066
From: Virginia USA
Just FYI, I switched from my stock dual plane ZZ4 manifold shortly after I installed my Sniper 2 EFI to a single plane Weiand Team - G manifold and it really woke up my engine. It was a big improvement going from EFI on a dual plane to EFI on a single plane. At least in my case.
Burning Brakes
Joined: Feb 2008
Posts: 769
Likes: 343
From: Mooresville NC
That. I have a pretty detailed section on the single plane vs the dual plane with throttle body EFI in post #1 section 2d (Sniper for Dummies - level 2). Of the folks that I know that made the switch with TBI NONE would go back to a dual plane. However, it's easy to spend other peoples money. Creating a space or grinding down the divider (which the edelbrock RPM air gap does already) will help if you intend to stay with the dual plane. The shortest Team-G intake manifold is similar in dimensions to the Edelbrock Air Gap manifolds which is the real show stopper if you can't make it fit.
Last edited by Halfnium; Today at 09:27 PM.
Team Owner
Joined: Jun 2001
Posts: 23,375
Likes: 1,066
From: Virginia USA
That. I have a pretty detailed section on the single plane vs the dual plane with throttle body EFI in post #1 section 2d. Of the folks that I know that made the switch with TBI NONE would go back to a dual plane. However, it's easy to spend other peoples money. Creating a space or grinding down the divider (which the edelbrock RPM air gap does already) will help if you intend to stay with the dual plane. The shortest Team-G intake manifold is similar in dimensions to the Edelbrock Air Gap manifolds which is the real show stopper if you can't make it fit.
My Weiand Team - G fits under my 1971 stock base model hood with the original air filter housing on it. The closest my air cleaner gets to the hood is about a 1/4. Weiand Team G 7530WND
Hood clearance with clay:
Team Owner
Joined: Jun 2001
Posts: 23,375
Likes: 1,066
From: Virginia USA
No it's just the stock 1971 dual snorkel air cleaner. I'm probably leaving a little HP on the table running the dual snorkel. I'm thinking of going drop base with a 2 or 3 inch filter but I prefer the stock look.
Thread Starter
Melting Slicks
Joined: Nov 2017
Posts: 2,358
Likes: 519
Do you have a picture of that, please. I would prefer a stock look as well. Don’t mind leaving a few HP on table. I’d be interested in drop base and filter element height
Team Owner
Joined: Jun 2001
Posts: 23,375
Likes: 1,066
From: Virginia USA