Yet another comparison (air-gap carb spacers)

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gumper

gumper

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Put the air gap back on. Decided I'd port-match it before the 3rd reinstall. I usually run a 1" open wood spacer with the AG. I have a 1/2" oval split spacer I want to try out to see if it jives better with the split manifold design. I've read a lot of 'talk' about the differences, but no actual numbers. I'm going to track test the two spacers to see what happens. Anyone else do this comparison on the track or a dyno? I'm interested in just the open vs split spacer.
 
Especially if you keep the 2 levels/planes separated with a spacer, check your plug coloring with clean plugs after a few runs. If you see a slight but obvious coloring pattern showing the plugs being fed by the upper level/plane a bit darker than the ones fed by the lower level/plane, you should benefit from adjusting the jetting from side-to-side by a couple of numbers. Lean the upper level, richen the lower level or split them. My theory is that the lower level contains a larger volume of space and reduces the vacuum signal, requiring slightly larger jets to compensate.

I found this pattern on a Weiand Stealth I ran for a while and it seemed to help ET's by about .05.

Being a "modern" manifold, I don't know if the Air-Gap may have built-it features to compensate for this. But plug coloring patterns would help determine that, if the carb is jetted the same side-to-side to start with.
 
Locomotion said:
Especially if you keep the 2 levels/planes separated with a spacer, check your plug coloring with clean plugs after a few runs. If you see a slight but obvious coloring pattern showing the plugs being fed by the upper level/plane a bit darker than the ones fed by the lower level/plane, you should benefit from adjusting the jetting from side-to-side by a couple of numbers. Lean the upper level, richen the lower level or split them. My theory is that the lower level contains a larger volume of space and reduces the vacuum signal, requiring slightly larger jets to compensate.

I found this pattern on a Weiand Stealth I ran for a while and it seemed to help ET's by about .05.

Being a "modern" manifold, I don't know if the Air-Gap may have built-it features to compensate for this. But plug coloring patterns would help determine that, if the carb is jetted the same side-to-side to start with.
Click to expand...

Interesting theory. I'm starting with the split spacer with slightly smaller jets than the open spacer liked. I can't play at all this weekend unfortunately because the whole state is getting soaked with endless rain.
 
Yea, it's a lot of work to make sure you get valid results. Different type and height spacers can affect the accelerator pump shot requirements too!

Jet for MPH and adjust squirters & (to a lesser degree) pump cams for 60' times.
 
I can tell you with the air gap all my plugs were the same light tan colour on the insulator , think number 8 was a touch lean as is was a bit lighter colour . Not running a spacer , but thinking of adding one .
 
The thing I'm curious if port matching did anything positive as well. I had been running it out of the box for 5 years, and decided I'd use the carbon marks as guides to match things up. I had to take a lot out of some ports, probably .080" in some parts.
 
After some street testing the split spacer does not like nearly as much fuel as the open spacer. In theory, if you run bigger jets with cleaner plugs does that mean more power? Looking for thoughts.

I also squired an HVH super sucker 1" 4 hole spacer to test with the other two.
 
Have a link? I believe the open is the best between it and divided just from a little street time. The super sucker spacer will be interesting though.
 
I've read that article before. The open spacer did make a big difference, but there wasn't a spacer comparison. I've also seen spacer shootouts, but not with the air gap. I want to see if a true open spacer works better than letting the dual plane be itself with a split spacer. Then see if the HVH spacer is up to its hype.
 
gumper said:
In theory, if you run bigger jets with cleaner plugs does that mean more power? Looking for thoughts.
Click to expand...
No, could mean not as efficient combustion ,fuel mixing or carb signal
 
Depends if your airgap has an equalizer at the top. If not i would recommend an open spacer.
 
No, it doesn't have the cutout. It's all part of my testing, but so far without track testing I can feel the open is much better than splitting the planes at the carb base.
 
Seems to depend on the engine's requirements. A buddy of mine had a pretty hot 340 with a AG and he tried an open spacer and it didn't like it. I have a mild 408 in my Cuda and tried all three ways, no spacer vs. a 4 hole vs. an open spacer and it liked the open the best. I don't have a dyno test or track time to verify it, just seat of the pants feel so take it as you will.
 
I'm personally not a fan of spacers, period. In the 70's when I was first starting out, I tried several sizes/types on a few different street/strip combo's. The results were so mixed between all of them, as far as power & drivability, that I just got frustrated with the whole deal and swore off of them. I found much more satisfaction changing intakes, but then again, I wasn't looking for a "hun" or two...lol.

Back to modern times :D, and the fact that your more focused on track times, i'd think the open spacer on the AG will still give you the best of both worlds. That intake is so strong down low, I think opening the plenum a hair will help upstairs more then it will hurt down low. I know others have had similar results with it.

Good luck! I know we've been thru the big intake go round for the 1/8th mile, and hopefully with the AG and whatever spacers you test, you'll find what you're looking for. :thumbrig:
 
I have tried spacers on dozens of engines. SOme with success some with no gain at all. I remember one 505 I built a long time ago, I tried 5 different types of spacers. We saw no real gain. All they did was lean out the engine about 1-2 jet sizes. I had another 416 that gained 25HP with a 1/4 4 hole merge spacer. But lost 10HP with a 2" open.

All I can say is TEST TEST TEST. There is no "This spacer always makes power" its BS. SOme combos like them, some dont.
 
What ever happened to just goin to the track and havin fun?
 
Part of the fun is seeing how fast you can make the car go by tweaking/optimizing the little things about a combo rather than going out and changing cams, heads, carbs, etc.

Also, any time you change something, like a spacer, carb jetting may need to be changed to get the most out of it. And that's if your jetting was close to optimum to begin with! i.e.: If you install an open spacer and it goes faster, you may have been on the rich side without it.
It can be harder to figure things out at the track because most people don't have A/F meters. Drag strip times aren't a tell-all either because you have to be aware of many varying conditions that can affect the changes you made - temps, wind, shift points, etc. Your change may help. But if you, the weather or something else about the car isn't consistent, the comparison between runs may not be valid.

Like Mike said, "TEST, TEST, TEST". But you have to be aware of other influencing factors around you too.
 
Tested two spacers Friday night at the track. The split spacer didn't even make it that far, I could tell from driving around town the engine was not happy with it. So, I made two passes with each spacer (open wood and HVH super sucker tapered 4-hole, both 1"). Best pass with the open wood was 7.89, best pass with the HVH was 7.86 about a half mph faster. This is on an 1/8 mile track, with a 6800' corrected altitude (5335 uncorrected) within 15 minutes with those two runs. I also massaged the center divider so fuel wouldn't puddle on the flat factory casting, and the outer edges were matched to the spacers. Thought I'd have to mess with jetting, but the plugs all looked the same between the two spacers. I also ran out of time because I entered the mixed class gambler race. Wound up winning and being $500 richer, so that paid for the weekend, parts and then some.

The car is also a solid tenth faster in the 1/8 than the super victor manifold. Not sure how much carries over to the 1/4, but I'd say at least that judging by the mph.
 
Guess what kind I liked on my airgap? My 408 with xe275hl would hit real hard at 2200 and was rough below that (stick car). The three hole spacer was the best of both worlds drivability wise. Plus it makes a funny face!
 
I wanted to get my hands on one, but couldn't find who makes a good one. Whats that one?
 
It's just a mr gasket or whatever from the little hot rod section at pep boys. You know the display with the chrome dice valve caps and starter blankets. I took the 4 hole and cut open the back two holes into one hole. It comes with the open and 4 hole- the plastic insert is slightly tapered to drop into the aluminum square casting.

I really liked the 2 hole on the primaries for street driving.

Good luck!

Radar
 
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