[GTOLou]

I've run the tomahawk/hurricane and HSD w/ shaker intakes plenty of times. I can usually get a .5inch spacer with a drop aircleaner. I've really not been able to run a shaker w/ drop and a 1" and an HSD intake.

Even w/ a drop air cleaner base - I have trouble w/ a full RPM. I've got a guy locally who hates milling .2" or so off of an RPM carb pad - but for me, that works best:

Drop air cleaner base/shaker TA/RPM w/ a bit milled off. - Seat of the pants is far better than an HSD/tomahawk w/ .5spacer. Sorry, no dyno numbers.

[Steve C.]

For interest.
Dyno numbers for my Holley Street Dominator intake, runner & plenum work by Dave Bisschop. Intake port matched to the approximate 2.300" tall port opening on the cylinder heads.
No effort to tune to perfection, we used the same jetting and timing as the RPM intake tested prior to the HSD. This was on my 4.210" stroke pump gas engine....

HSD / no carb spacer:
577.9 hp at 5700 rpm, 581.0 ft.lbs. at 4400 rpm.

HSD / 1/2" open spacer:
589.4 hp at 5600 rpm, 589.0 ft.lbs. at 4600 rpm.

HSD/ 1" open spacer:
589.8 hp at 5700 rpm, 590.8 ft.lbs. at 4400 rpm

I know peak numbers don't express much, really need to look at the curve with each different spacer.
The improvement going from the 1/2" spacer to the 1" spacer wasn't the big hit. However track testing could prove different.


.

[Cliff R]

Without a spacer running my Holley 850DP carb the Tomohawk didn't fair well at the track. It was WAY down across the entire run. Adding a 1" spacer with no other changes netted a solid 2mph improvement on top end, and it ran nearly 2 tenths quicker than with no spacer at all.

My Q-jet absolutely HATED that intake. With no spacer at all it induced a 'stumble/hesitation/bog on the starting line that would NOT tune out. Adding a 1" spacer helped, but it still didn't rival the Holley carb with a 1" spacer. I suspect that the huge secondary throttle plates sticking deep into the plenum areas cause some sort of turbulence or distribution issues compared to square flange Holley style carb. Not sure, but it's a "turd" with a Q-jet sitting directly on it, and picked up nicely with the Holley carb once a 1" spacer was added.

A dyno will NOT show you hesitation/stumble/bog, or other issues that effect going from idle to full power with good traction as we don't load the engine that low or allow it to rev quickly to get into the "good " power.

Something else very few folks test associated with these things are drop base air cleaners. You can loose a LOT more power than you ever hoped to gain going to all intakes and/or spacers if you move the air cleaner lid too close to the carburetor. I've found that you need at least 3" from the air cleaner base gasket surface to the lowest part of the air cleaner lid.......FWIW........

[scott70]

I forgot to mention when I drove home (about 50 miles) from the track I noticed a noticeable hitch at low rpms and slightly accelerating. Once the rpms came up some it was fine but I didnt really notice it before with the spacer in. Why would just taking the spacer out cause this? It didnt do this with the 1/2" spacer or the 4 hole 11/16" spacer,,,,or it didnt do it enough for me to notice.

[Cliff R]

Spacers on dual plane intakes can and will cause all sorts of running issues. Not sure what combination of things you were trying but spacers on dual plane intakes should have dividers in them. Open spacers that I've tested cause distribution issues effecting how well things work in the "normal" driving range, plus I've ran into scenarios where they induced stumble/hesitation/bog going quickly from idle to full throttle that would NOT tune out......

[Formulajones]

From your description it sounds like the problem arose without the spacer.
That could be a difference in low rpm off idle fuel distribution. The primaries may be experiencing less pull or low signal on the boosters and changing fuel delivery just a bit.

That's a big reason why Jim hand always modified his intakes with a small throat on the primaries matching the carb throat with a wide center divider there. It gave better low throttle drivability.
I've found the same results on the street.

As far as open spacers on a dual plane my experience differs from Cliffs. At least on rpm air gap intakes they have always worked best with an open spacer for me.
Many guys run a thick open carb gasket on the Pontiac intakes, acting like a small open spacers where the primaries can see each other. I assume that's what you currently have after removing the divided spacer?

I've wanted to try that at the track but the excellent low speed drivability with my divided spacer is what has kept me from trying it since I drive the thing daily and it sees more street time than track time.

[Cliff R]

I've had perfect results with 1/4" thick open gaskets on dual plane intakes allowing one side to see the other, but too much of a good thing can and will cause other issues.

A fully open 1" spacer on a dual plane intakes fairs well on dyno days, but poorly on track days. On several different vehicles we've tried that set-up on they refused to leave "clean". We saw noticable transition issues from idle to full throttle (with good traction). Even when they car didn't "lay down" the transition was there and noticable, and instantly went away when we added a full divider, semi-open or four hole spacer.

I'd also note here that the semi-open spacer, or basically divided across the front and open between the secondaries was the overall winner when testing spacers. Jim Hand found out pretty much the same thing testing spacers. Our semi-open spacer was worth a solid 2 mph on top end on both 455 powered vehicles we tested it on at a private track rental........

[Formulajones]

Originally Posted by Cliff R

I've had perfect results with 1/4" thick open gaskets on dual plane intakes allowing one side to see the other, but too much of a good thing can and will cause other issues.

A fully open 1" spacer on a dual plane intakes fairs well on dyno days, but poorly on track days. On several different vehicles we've tried that set-up on they refused to leave "clean". We saw noticable transition issues from idle to full throttle (with good traction). Even when they car didn't "lay down" the transition was there and noticable, and instantly went away when we added a full divider, semi-open or four hole spacer.

I'd also note here that the semi-open spacer, or basically divided across the front and open between the secondaries was the overall winner when testing spacers. Jim Hand found out pretty much the same thing testing spacers. Our semi-open spacer was worth a solid 2 mph on top end on both 455 powered vehicles we tested it on at a private track rental........

Yes that's how I've been doing it on the factory OEM Pontiac and Chevrolet intakes. However even though it didn't seem to work out for Scott, I do want to go back to a 1/4" thick open gasket, dropping the carb down a bit, see how that runs, and while at the track, then switch the filter to raise the lid a tad and get the darn thing away from the choke horn and see if there is something there. But my situation is a bit different on the bird. Any other car here doesn't have the air cleaner issue.
If I find something, great. If not then I'll go back to what gives me the best drivability on the street.
Best part, this is all simple stuff that can be swapped around in the pits in minutes.

[scott70]

Yes the hitching or bucking at low rpm and accelerating slightly started when I took the spacer out. The spacer I started with and ran quite a while was a .5" 4 hole on a stock intake. Then this year I took the intake off and made the top look like a RPM intake and did the exact same to the spacer(pics in first post). The spacer also had a small notch between the secondarys which Ive always had there. All together with gaskets it measured like .71 " thick. I took it to the track with the modified intake and spacer and gained nothing in ET or MPH. Actually my 60ft seemed to be worse on the average. Then recently I bought a 11/16" thick 4 hole plastic spacer and put a small notch between the secondarys. Thinking the 4 hole might bring back some low rpm torque to get the 60ft back. That measured like .74 inches thick with the 2 thin gaskets I was using. Tried that at the track and about the same or maybe slightly worse as the modified intake/. 5" Spacer. Then before I left I took out the spacer and put in a 4 hole 1/8" gasket only. Immediately dropped a tenth to .12 off the 60 ft and ran the same mph. but now on the trip home if i lugged it a little and barley on the throttle it started bucking a little,,,like a rowdy cam likes to buck down low. Its a 4 speed so theres no cushion.

For the heck of it I bought a phenolic 1/4" 4 hole spacer and will cut out between the secondarys and do the same to the 2 gaskets. Maybe that will be a happy medium at the track and maybe eliminate the hitch..

[Formulajones]

Originally Posted by scott70

Yes the hitching or bucking at low rpm and accelerating slightly started when I took the spacer out. The spacer I started with and ran quite a while was a .5" 4 hole on a stock intake. Then this year I took the intake off and made the top look like a RPM intake and did the exact same to the spacer(pics in first post). The spacer also had a small notch between the secondarys which Ive always had there. All together with gaskets it measured like .71 " thick. I took it to the track with the modified intake and spacer and gained nothing in ET or MPH. Actually my 60ft seemed to be worse on the average. Then recently I bought a 11/16" thick 4 hole plastic spacer and put a small notch between the secondarys. Thinking the 4 hole might bring back some low rpm torque to get the 60ft back. That measured like .74 inches thick with the 2 thin gaskets I was using. Tried that at the track and about the same or maybe slightly worse as the modified intake/. 5" Spacer. Then before I left I took out the spacer and put in a 4 hole 1/8" gasket only. Immediately dropped a tenth to .12 off the 60 ft and ran the same mph. but now on the trip home if i lugged it a little and barley on the throttle it started bucking a little,,,like a rowdy cam likes to buck down low. Its a 4 speed so theres no cushion.

For the heck of it I bought a phenolic 1/4" 4 hole spacer and will cut out between the secondarys and do the same to the 2 gaskets. Maybe that will be a happy medium at the track and maybe eliminate the hitch..

Ah crap, okay, so when you went gasket only, it was a 4 hole 1/8" gasket. My bad, for some reason I thought you tried a 1/4" thick open gasket.

If it were me, and it seems like you're leaning this way, I'd go back to the setup that gives best drivability. Trying a 1/4" phenolic modified like the intake, with a cutout for the secondaries may be a good way to go if you don't want the 1/2" setup on there. Sounds like this gave you a better low speed carb signal.

[Formulajones]

Here is how I do them, as Cliff explained above. This is a Chevrolet intake but the concept is exactly the same.
That's a one inch spacer but it can be done with a 1/4" or 1/2" spacer too. I thought for sure I posted this pic already but searched the thread and can't find it. Must be another intake thread somewhere.

Anyway, keeping the front primaries enclosed and the diameter close to the size of the throttle bores is what has given me best drivability on the street and crisp throttle response.

Whether or not this setup might run better with just a 1/4" thick open gasket with all this stuff removed remains to be seen, but something I may try.

[77 TRASHCAN]

Form, what cube engine is that BB intake/spacer on?
Looks like the intake that came on my 68 Chevy 396 pickup engine.

[scott70]

Originally Posted by Formulajones

Here is how I do them, as Cliff explained above. This is a Chevrolet intake but the concept is exactly the same.
That's a one inch spacer but it can be done with a 1/4" or 1/2" spacer too. I thought for sure I posted this pic already but searched the thread and can't find it. Must be another intake thread somewhere.

Anyway, keeping the front primaries enclosed and the diameter close to the size of the throttle bores is what has given me best drivability on the street and crisp throttle response.

Whether or not this setup might run better with just a 1/4" thick open gasket with all this stuff removed remains to be seen, but something I may try.

Yes your intake has a little more around the primaries. Thats why I thought Id try the slightly thicker 4 hole, might put me back to closer to your setup but it did nothing on mine.

[Cliff R]

The spacer in the pic above won spacer testing on two different private track rentals. I tried 4 different 1"spacers, 4 hole, fully open, fully divided and "semi-divided". I also ran one 1/4" thick open gasket.

The semi-open spacer ran the highest MPH for all runs. The 1/4" open gasket ran the quickest ET, but only by a very, very slight margin over the semi-open spacer set-up. Nearly as I can remember it was about .02-.03 seconds quicker with no spacer at all and only the open gasket.

So for all the "cobbling" involved to use a spacer in the first place on my set-up I just went back to the 1/4" thick open gasket. Related but another topic was testing drop based air cleaners, X-Treme lids, and combinations of both. Got my feelings hurt pretty bad on that deal, but that's a story for another thread........

[Formulajones]

Originally Posted by 77 TRASHCAN

Form, what cube engine is that BB intake/spacer on?
Looks like the intake that came on my 68 Chevy 396 pickup engine.

That one was on a 454

[scott70]

Originally Posted by Cliff R

The spacer in the pic above won spacer testing on two different private track rentals. I tried 4 different 1"spacers, 4 hole, fully open, fully divided and "semi-divided". I also ran one 1/4" thick open gasket.

The semi-open spacer ran the highest MPH for all runs. The 1/4" open gasket ran the quickest ET, but only by a very, very slight margin over the semi-open spacer set-up. Nearly as I can remember it was about .02-.03 seconds quicker with no spacer at all and only the open gasket.

So for all the "cobbling" involved to use a spacer in the first place on my set-up I just went back to the 1/4" thick open gasket. Related but another topic was testing drop based air cleaners, X-Treme lids, and combinations of both. Got my feelings hurt pretty bad on that deal, but that's a story for another thread........

So maybe Ill take the 1/4" 4 hole spacer Ive got coming...remove the divider between the secondarys and run 2 thin gaskets? Performance wise on my car setup doing that might be optimal? And maybe that will get rid of the hitch also by getting it back in the air a little bit. As far as the intake itself I ground the top to look like a RPM but I left the divider fully intact,,,no notching or cutting.

[Cliff R]

Since there aren't any rules with this sort of thing, and we know that at some point you can remove too much material causing negative results, I'd start with "baby steps" as far as removing material goes. I've always found with this sort of thing that once the material is removed, it's more difficult to put it back than not removing too much in the first place.......