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I’ve ran a few different spacers on my different engine combos. The reason I ran them was to cool down the fuel in the carb. Here in Florida the under hood tem would get so high the fuel would boil. Coolcarb.com makes a nice one designed to lower carb temperatures. My car ran a lot better and it looks pretty damn good.
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67 Camaro SS/RS L78 M20 Convertible
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Here is my dyno buildup. Baseline is no spacer, with a Qjet on a ported Performer dual plane, center divider intact. Next was a 1/2" phenolic semi-divided spacer; divided between primaries, and open betweeen secondaries. Gain over baseline was 5 peak hp. Next was a 1/2" phenolic open spacer. Gain over semi-divided was 8 hp at peak. Next was an aluminum 1" open spacer. Gain over 1/2" open was 3 peak hp. So gain on the 1" aluminum open was 16 hp peak over baseline.

The manifold has a removable center divider between the secondaries only. The engine did not like that regardless of the spacer used. View attachment 740014

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Thats some proper testing right there well done
 

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And that is only good for his engine. Hp gains are dependent on how bad a combo is to start.
I wouldn’t say bad tho. Maybe a certain combo needs a smidge more plenum volume?
Like you and others mentioned the gains aren’t huge and IF you only pick up a few hp I feel your pretty close to start with.
On my 355 it was I think a 10th on the infamous air gap. Ironically it had the same results with the hurricane. Different rental.
Either waythe OTB hurricane was quicker without the spacer then the ag with it.
60’ exactly the same as the ag.
Yes driving around town I did notice the ag a smidge but on the track it did nothing.
 

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Discussion Starter · #25 ·
Sir that is a lot of good information you did. Thank you. Like the members has said most will differ yet probably along the same lines maybe just more or lesser amounts.

My combination consists of my l88 shortblock, zl1 cam and ported 215 heads. Present i have a strip domintor intake. It did dyno at 580 horsepower. My guy likes the dual planes and have been getting power out of them. So he is asking me to switch to an original l88 intake and i like to spacer idea to help a bit more to get close to the strip dominator upper rpm performance. He just isn't sold on that idea of a spacer.

RH
 

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I wouldn’t say bad tho. Maybe a certain combo needs a smidge more plenum volume?
Like you and others mentioned the gains aren’t huge and IF you only pick up a few hp I feel your pretty close to start with.
On my 355 it was I think a 10th on the infamous air gap. Ironically it had the same results with the hurricane. Different rental.
Either waythe OTB hurricane was quicker without the spacer then the ag with it.
60’ exactly the same as the ag.
Yes driving around town I did notice the ag a smidge but on the track it did nothing.
And that is what happened with mine. My friend had this spacer that on his 555 pump gas engine I think they found 20hp. Now this was a healthy 860 hp on 93 octane. I forget the details if it was over another spacer, no spacer whatever. I had a tapered 4 hole on my engine and we put the miracle spacer on. It made 4 hp. I then put a 1” spacer that was blended to the intake plenum and it made the same as the miracle spacer. On the circle track motors we built the 1” tapered 4 hole spacers made 8-10 over a 1” open. On my motor it did nothing compared to a plain open spacer. Now on the dyno it made stuff. In the car, it probably amounted to nothing.
 
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In the '69 with a stock hood, adding a spacer (tried both 4 hole and open) on AG intake added nothing at the track on the 469". 540" had a tall single plane that barely allowed the hood to close with an air filter installed, spacer on that combo was completely out of the question. FWIW, running without an air filter made no difference, I ran a very low restriction K&N 14" filter. I think if you are under carb'd open spacer could help?
 

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I don't know how you all are running carb spacers. I can't use more than 1/2" spacer before the air cleaner hits the hood. BBC with Edlebrock RPM Performer.
 

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I don't know how you all are running carb spacers. I can't use more than 1/2" spacer before the air cleaner hits the hood. BBC with Edlebrock RPM Performer.
This works for me:


1967 - 1969 Correct Chevy Camaro Open Element Air Cleaner Base

New open element air cleaner base for your Camaro. Exact fit for all high performance models with an open element air cleaner breather. Correct deep design for hood clearance. Lower valve cover vent tube pre-welded as original. High quality reproduction. Lower breather tube attached. Superior quality reproduction of original special high performance air cleaner four barrel base. Gloss black body with attached breather tube (1" hose). Officially Licensed GM Restoration Parts.

Originally found on: 67, 68 and 69 Camaro 302 & 396, 68 - 69 Nova 396, 66 - 69 Chevelle 396, 65 - 69 Fullsize Chevy 427, and 65 - 72 Corvette.

My setup is:
  • RPM Air Gap (7561)
  • Carb gasket
  • 1" spacer
  • Carb gasket
  • Throttle bracket plate (also acts as a heat sink
  • Carb gasket
  • Carb (Holley 3310 750 or 0-80531 850)
  • 3" Air cleaner and OEM style lid (appears there is room for a 3.5" thick filter too, I have one on order if it ever arrives).

This is with flat hood on '70 Monte Carlo, hood is not lifted in the rear.
 
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I could never fit a one-inch spacer under my Quadrajet carb on my dual plain Quadrajet intake.

I think the best way to gauge power is on the street. I wish I had a dollar for every car I ruined the overall power to by installing drag strip parts for a streetcar. However I know a few guys who use the drag strip and they do real well. It's just different ways to get the same over all..

Its not about the horsepower in one spot like 6500 rpm or 6000 rpm, its about total power from idle to 6000..

I like to remove every part that doesn't do anything. The air condition and heater ducting is the worst! My el Camino runs so much better with an uncluttered engine bay and a 14 x 4 open element air cleaner with a heat diverter in the front.
I tried all kinds of different ways to run fresh air to the carb. All those extra parts did was hold heat and this heated the fresh air going into the carb.


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Here is my dyno buildup. Baseline is no spacer, with a Qjet on a ported Performer dual plane, center divider intact. Next was a 1/2" phenolic semi-divided spacer; divided between primaries, and open betweeen secondaries. Gain over baseline was 5 peak hp. Next was a 1/2" phenolic open spacer. Gain over semi-divided was 8 hp at peak. Next was an aluminum 1" open spacer. Gain over 1/2" open was 3 peak hp. So gain on the 1" aluminum open was 16 hp peak over baseline.

The manifold has a removable center divider between the secondaries only. The engine did not like that regardless of the spacer used. View attachment 740014

Sent from my SM-G991U using Tapatalk
Thanks for sharing good data.

When we dyno’d my first engine, we couldn’t really claim an improvement with the spacer since we changed a few things at the same time, and we didn’t go back and validate the results. From a logical perspective, added plenum volume on a modest RPM Air Gap-style intake manifold can only help the mixture and allow both sides of the engine to see both sides of the carb. If nothing else, a 1” spacer has to help even the A/F ratio to each cylinder, and help insulate the carb from heat.
 
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