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Does anyone have any dyno info on a spacer on an rpm air gap for big block. I told my guys about this and they do not think it is worth it. Like to see what the members here have found.

RH
 

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Ryan
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Agree with Malibu SS 64. What’s the combo?
 

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As was said above it’s all about the combo.
I’ve tried them twice on my own engine at the dyno.First time there was almost 10 HP.Second time was very little gain.
They can also cut into your hood clearance.
Guy
 

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I agree on the hp being hit or miss. It’s not consistent from engine to engine. But I have seen low speed drivability increase with the 1” open spacer.
 
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1” inch 4 hole tapered spacer will favor low end torque. 1” in open spacer will favor higher rpm HP.

There’s no reason not to run one if you have the clearance. It also separates the carb from the intake manifold reducing ambient heat transferred to carb.
 

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Does anyone have any dyno info on a spacer on an rpm air gap for big block. I told my guys about this and they do not think it is worth it. Like to see what the members here have found.

RH
I never did back to back testing with JUST the spacer, but I do run an open spacer on my Weiand dual plane with a carb, and then with the Fitech EFI. I then did some minor plenum work and cut the divider down. Here is my dyno progression if it can help at all. I've also switched to an Air-Gap this year, and it seems to run the same as the Weiand.

454 BBC - stock 820 heads - Comp 280H camshaft

Green line - 3310 750 cfm carb, 2.5" exhaust/Flowmaster mufflers, no spacer, had a tear in the vacuum secondaries
Blue line - 3310 750 cfm carb - fixed, 3" exhaust/Hooker mufflers, 1" open spacer
Red line - Fitech EFI, 1" open spacer, new 924 springs - correct spring pressures and tool steel retainers
Black line - Fitech EFI, 1" open spacer, cut down divider, clutch fan, switched from 4 speed/3.31 gears to 6 speed/3.91 gears

I can't say the open spacer helped a ton, but im sure it didnt hurt either. Every combo is different, but I find an open spacer helps more often than it hurts.

 

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The usual correlation is that a single plane intake benefits more from a 4-hole spacer and a dual plane intake benefits more from a open spacer. Exceptions support that rule.

There are some hotrod articles regarding spacer tests, just google a bit.
Me personally i would always use as much spacers as my hood clearance allows (and thats not much).
Up to 2" you rarely do something wrong so it seems.

I used 4-hole and open on a performer 2-O intake and the open one was way better regarding behaviour of the engine down low.
On my performer rpm air gap now i also use open spacer. Thats what the engine builders recommends (mark jones) and what edelbrock basically virtually implements themselves by cutting down the plenum divider a bit..
 

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Does anyone have any dyno info on a spacer on an rpm air gap for big block. I told my guys about this and they do not think it is worth it. Like to see what the members here have found.

RH
What is your total combination? Are you ready to dyno? When will you be going to the dragstrip?

What shows the most power on the dyno might not go down the strip faster.
 

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I agree to disagree.
MPH shows all
If I do 4 runs at the track, my MPH will be different on all 4 runs. No changes in parts or tune. No way I'll accurately be able to measure the small power differences from an open spacer.
 

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Ryan
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I don’t think I’ve ever seen an open spacer cost power on a dual plane.
 
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If I do 4 runs at the track, my MPH will be different on all 4 runs. No changes in parts or tune. No way I'll accurately be able to measure the small power differences from an open spacer.
Must be because you have a stick car ;)
My car is pretty consistent at the track and so is the gold 69 SS
Very easy to measure the difference in performance.
 

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Must be because you have a stick car ;)
My car is pretty consistent at the track and so is the gold 69 SS
That's true mine is a stick car. Though I've had days where it could be a bracket car. In any case, it's extremely rare to see anyone pulling mph's down to the tenth back to back, let alone over 4 runs. There are just way too many variables. A dyno will be a much more accurate way to measure small changes. A spacer might be worth 5 horsepower + or - in most cases, and you will pretty much never feel or see that difference at the drag strip. But if you find 3 or 4 different ways to gain 5 hp, you will start to see those differences.
 

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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.
Rectangle Slope Font Line Plot


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