Sniper EFI Dual-Plane Intake, Spacer or No?

[cv428]

I have a 5/8" open carb spacer under our Sniper EFI unit. It worked fine for N/A, but I'm in the process of finishing up the blower application. There's some hood clearance issues that I can't solve without either cutting a hole in the hood (not an option), or lowering the throttle body. This is on a 484ci FE with a Performer RPM intake. The intake manifold does have a center web that's not machined or recessed downward, and pulling an intake on an FE is not a quick process. Two years ago I read that a spacer helps equalize pressure between banks, so I put the 5/8" spacer in. This is an absolute beast of an engine, so I need every bit of streetability I can get.

Because of this hood clearance issue, I need to lower the throttle body about 1/4" to 3/8". I would like to get as much clearance as possible, but I don't want to create a new problem by going too short. I've read many threads on this forum on the subject, but there doesn't seem to be a consensus other than the Sniper EFI was developed for use on single and dual-plane intakes. I don't care about whistle, this isn't exactly a quiet car and the blower sounds like a jet as it is. I also don't care if a low profile spacer robs some power, there's plenty to spare.

TL;DR: How thin of an open carb spacer can I get away with without creating surging or idle issues? I need to have some spacer in there to help prevent heat transfer up into the Sniper ECU, just curious how short I can go. Any feedback is appreciated as always.

[Danny Cabral]

A 1/4" open spacer is fine. https://forums.holley.com/showthread...5359#post85359 (Holley Sniper EFI Dual-Plane Intake Manifold Use)

[cv428]

Awesome, that's good to hear! I actually read through that thread before posting, but everyone was saying 1/2", so I wasn't sure if there was established data on the subject. 1/4" would get me plenty of hood clearance. Appreciated!

[a b c]

What type of blower, centrifugal or Roots? If it's a Roots, no amount of spacer that's in a typical range will help with your heat problem, therefore I'd just leave it off unless they make a phenolic 1/4" one, as the constant psi from a Roots blower will dynamically change the airflow at idle in the manifold anyway.

[Danny Cabral]

I think he also wants airflow across the dual-plane plenum divider.
https://forums.holley.com/forum/holl...365#post289365 (Additional Roots Blower Cooling & MAP Sensor Info)

[cv428]

I think he also wants airflow across the dual-plane plenum divider.
https://forums.holley.com/forum/holl...365#post289365 (Additional Roots Blower Cooling & MAP Sensor Info)

Correct.

What type of blower, centrifugal or Roots? If it's a Roots, no amount of spacer that's in a typical range will help with your heat problem, therefore I'd just leave it off unless they make a phenolic 1/4" one, as the constant psi from a Roots blower will dynamically change the airflow at idle in the manifold anyway.

Centrifugal. I did find a 1/4" open phenolic from Summit. Plus, I'm running low boost (5 psi max, hopefully), the headers are JetHot coated, and there's a coating on the intake manifold as well. Radiant heat is minimal in that engine bay as opposed to the three turbo cars I've had.

Part of me wanted to go Roots just for the "bad ass" factor, but I didn't want to cut the hood, and the centrifugal is a little friendlier on the street. I've had every power adder at one point or another; centrifugal, single turbo, twin turbo, nitrous, twin screw, you name it.