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Old 03-01-2020, 06:40 PM
1980 TA 1980 TA is offline
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Default FITECH and different carb spacers

I thought I'd share the results of switching carb spacers with my FITECH.

The original combo is a 455 with 6x8 heads, performer intake, 041 cam with Rhodes lifters. FITECH running the timing through an MSD distributor. The original carb spacer was 3/4 inch tall split plenum. The car would idle at 800 rpm with about 14.5-15.5 inches of vacuum.

I switched to a 3/4 tall open plenum spacer. I expected to see it rev a little quicker and be a little softer down low.

With just the spacer change, the AFR trim was showing the system pulling out 10% or more of the fuel pretty consistently for the trip to town and back, about 10 miles round trip, some highway and some city. I expected it to be lean with the open spacer not rich. The system was spot on before the switch with trims 0-3 under normal driving.

Idle vacuum jumped to 16-16.5 and saw 17 a few times. I really did not expect an increase in vacuum with the open spacer.

Overall the car was more responsive and smoother throughout the rev range. I did expect it to rev a little better, but did not expect it to be smoother at 1600-2000 rpms in 5th. I did not expect it to be so much smoother on take off either.

If the weather cooperates next, weekend, I'll think I can fit the 1 inch open spacer under the shaker and see what it does.

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Old 03-01-2020, 07:40 PM
JLMounce JLMounce is offline
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Great info. You’ve got my tempted to try my 1” open spacer. I’ve been running the FiTech directly on my tii since I installed it. Just need a drop base filter.

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Old 03-01-2020, 09:09 PM
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I was just watching some video comparing carbs to throttle body EFI and they were testing all of them on the dyno with and without spacers.

They were single plane intakes and much like we've already found with carbs and single plane intakes, they respond best with a super sucker style spacer.

Sure enough the holley throttle body also responded very well to the super sucker spacer.

Usually from what we've found on the dyno, single plane intakes don't see a bunch of change with an open style spacer using a carb, and I'd suspect that would still be the case with the throttle body. However open spacers do work well on dual plane intakes from what we've tried. Single plane intakes seem to really wake up with a super sucker or taper style spacer with some engines we've tested gain as much as 24 peak HP and TQ and a nice increase throughout the rpm range.

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Old 03-02-2020, 02:56 PM
fairwayhit fairwayhit is offline
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Do 2” open spacers gain additional over 1”?

Is there a point of diminishing returns regarding spacer height?


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Old 03-02-2020, 03:55 PM
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Generally speaking any time you can increase the plenum volume you'll find gains. The time consuming part is finding which style works best for a particular combo, open, divided, 4 hole, taper, etc... and then having the hood clearance to take advantage. Some intakes work well with some spacers and not so much with others.

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Old 03-03-2020, 10:12 AM
1funride 1funride is offline
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Good information. I have a Crosswinds Intake Manifold (like performer rpm), it also has a notch in the divider plate. Does a super sucker work well with this manifold? Not sure I can fit anything else under my hood, but this information is quite interesting.

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Old 03-03-2020, 10:42 AM
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Quote:
Originally Posted by 1funride View Post
Good information. I have a Crosswinds Intake Manifold (like performer rpm), it also has a notch in the divider plate. Does a super sucker work well with this manifold? Not sure I can fit anything else under my hood, but this information is quite interesting.
That's one spacer/intake setup I plan to test at the track when I get the one car here with an RPM air gap to the track. Right now that one has a 1" open spacer and works very well, but I've always wondered if the super sucker would work better. The trend, I'm told, is that these intakes tend to like the 1 inch open.

Trial and error.

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Old 03-07-2020, 08:02 PM
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Swapped in the 1 inch spacer today. I was impressed.

It started out extremely rich and rough. AFR trim was 20 to 30% and the system was not happy. Once the motor hit 160 it started smoothing out but was still 10% rich or so. After about 10 more minutes of driving it settled in consistently 5 % rich.

MAP readings were drastically lower. With the 3/4 divided spacer it would cruise at MAP of 45 to 50. Now, anything above 1500 rpms on level ground was right around 40. Once rpms got closer to 2000 rpms, MAP would be around 30-35. Car cruises real nice. Off idle transitions are more responsive.

The real fun is at full throttle. It used to pull alright to 4800, maybe 5000. Now it rips to 5500 if I'm not careful. Recovery between shifts at full throttle is much smoother. Motor is much much smoother and quiet at full throttle now.

Its finally becoming the street engine I had hoped for.

Idle vacuum on a warm motor is pretty solid at 16.5 to 17 now. Pretty amazing to me for a RAIV cam.

I enjoy having the extra data of the fuel injection to monitor changes. Next thing I want to check is gas mileage as I would expect normal driving to go up.

I do have to get the cold starts leaned out as the next tuning step. I'm almost tempted to log down all my current settings and start over with a baseline map from a one step smaller cam profile.

If I do, is there a way to label and save the current tune so I could reload it?

Idle vacuum on a warm motor is

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Old 03-07-2020, 08:05 PM
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That's certainly good news.

Spacers are a wonderful thing and crazy how they can change characteristics of the engine. You just need the hood space and the desire to try different styles to see what works.

Did you use a 1" open or a 1" super sucker?

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Old 03-07-2020, 08:12 PM
1980 TA 1980 TA is offline
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Just a simple open spacer. I'm not familiar with the super sucker. Given the name, it would make me think it might work better than a simple open spacer. Tell me more about the super sucker and I might change to one and post the results.

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Old 03-07-2020, 08:16 PM
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Quote:
Originally Posted by 1980 TA View Post
Just a simple open spacer. I'm not familiar with the super sucker. Given the name, it would make me think it might work better than a simple open spacer. Tell me more about the super sucker and I might change to one and post the results.
Okay that is pretty much in line with what I've found on dual planes and divided plenum intakes then, the 1" open seems to work really well in those scenarios.

The super sucker starts out as a 4-hole and then quickly tapers towards the center of the carb basically forming an open spacer towards the bottom. Sort of the best of both. But my experience with them has always been on single plane intakes where they really make a difference. I have yet to even try one on a dual plane but from what I've been told they don't work as well on a dual plane. I plan to test that theory for myself at the next track outing.

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Old 03-08-2020, 09:29 AM
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I've done a LOT of spacer testing, street, strip and on the dyno.

W/O exception all single plane intakes I've tested respond very well to a fully open 1" spacer nicely blended into the plenum area.

I've noticed smooth off idle and at lower RPM's with 4 hole and fully divided spacers on dual plane intakes for "normal" driving. Fully open spacers on dual plane intakes have never tested well anyplace. I've also observed hesitation/stumble/bog going very quickly to full throttle using them on dual plane intakes.

On the dyno spacer testing the best to date has been a semi-open 1" spacer similar to what is shown in Jim Hand's Book. The same spacer also logged the highest MPH at the drag strip verifying the engines we've ran them on really like that deal in the upper mid-range and top end.

At the track w/o exception 4 hole spacers on dual plane intake were the worst at every point on the track.

Kind of interesting but on several private track rentals using two different cars we did carb and spacer testing. On my car the best ET was with no spacer at all! Highest MPH and just about as quick in ET was using a Tomahawk intake with a 1" fully open spacer and Holley 850 DP carb. It ran a solid 2mph faster than all other intake/spacer combinations tested but gave up enough in 60' and short times that my factory intake, Q-jet and no spacer ran just a tad quicker (.02-.03" seconds) in ET.

I'd add here that ALL street or "seat of the pants" testing favors 4 hole and fully divided spacers on dual plane intakes. They "feel" very smooth right off idle and at very light throttle openings but take a back seat at WOT and making best power across the loaded RPM range.

From what I've seen you have to be very particular about how much area you can allow for one side of a dual plane (divided) intake to see the other side. I've lost count of how many folks I've helped out putting dividers back in dual plane intakes when their engine builder or beer drinking buddies removed them!

We even had a FAST Class iron intake evaluated after being professionally ported by a very well known Pontiac "guru". They removed the entire divider in the intake. This resulted in a couple more HP on the dyno WAY up at the shift point (5900rpm's), but the engine was WAY down in mid-range torque, nearly 40 ft lbs nearly as I can remember. With the divider missing it was also IMPOSSIBLE to launch the car as not having it there produce a HUGE hesitation going quickly to full throttle, which instantly went away when we made an aluminum divider for the intake putting all the material back in it.

Track testing on my own engine shows that it is beneficial to remove about half a 50 cent piece right between the secondaries and run a 1/4" thick fully open gasket. To date this set-up has produced the best ET, MPH and average power on the dyno......FWIW.........Cliff

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Old 03-08-2020, 10:01 AM
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"W/O exception all single plane intakes I've tested respond very well to a fully open 1" spacer nicely blended into the plenum area."

True for qjets and holleys? (Is that statement a bit carb dependent?)

Great info as always - Cliff!

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Old 03-08-2020, 10:16 AM
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Fwiw we have had very good results with 1" open and 1" tapered spacers on our 406 with the RPM intake

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Old 03-08-2020, 10:53 AM
1980 TA 1980 TA is offline
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Do you think the fuel injection is responding differently than a carb? It seems like conventional wisdom is that the TBI unit should behave like a carb.

From reading the Pontiac engine building books and all the posts I could find from guys like Cliff that have extensively tested and documented changes, I expected the open spacers to cause idle quality to suffer and off idle response to be sluggish. I expected vacuum to be lower and MAP readings to be higher. I did expect a better seat of the pants at upper rpms.

I did not expect the results that I posted as they were opposite of what I expected. One other thing that seems to have changed with the open spacer is that the AFR adjustments are smoother. I have a dash gauge for AFR as well as the injection hand held. With the divided spacer, the analog gauage was real jumpy. It would jump high and low around the desired readings but was never smooth. Now it is much smoother and linear in its readings. With the divided spacer, the system seemed slower to respond. For example, if I'd change AFR set points it would take a trip or two to town and back to where trims would stabilize around +/- 3%. With the open spacers, adjustments seem to come faster. After each spacer change, the trims would be back in range within a half trip to town.

My goal in testing has been to play with different combos and see how much clearance I might have to make a performer RPM fit as I figured the larger runners and taller plenum might work for my combo. I figured on a street driven engine keeping the plenums separate would be better hence wanting an RPM intake.

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Old 03-08-2020, 11:07 AM
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Quote:
Originally Posted by slowbird View Post
Fwiw we have had very good results with 1" open and 1" tapered spacers on our 406 with the RPM intake
Is that used in conjunction with each other?

I ask because I have a theory from the testing I've done with the RPM intakes that has me thinking the taper spacer (as so many call them, I call them super suckers) speaking of the short 1" taper spacer, doesn't always work on a dual plane intake, but it might work well if it were open underneath, hence a 1" open spacer used under it.
Which has me wanting to try a 2" super sucker or even a 1 1/2" super sucker which is basically a completely open spacer underneath the taper portion. It accomplishes the same thing with one spacer that I believe you are doing above with two of them..

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Old 03-08-2020, 11:15 AM
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There wouldn't be any real differences between these TBI systems and carburetor. All the dyno testing I've observed (personally and on U-Tube) favor carburetors for highest peak numbers w/o exception.

It's a wet-flow system either way, and turbulence and incoming distribution issues created by dividers, removing dividers, types of spacers, open, divided or 4 hole gaskets and all combinations of them would yield pretty similar results.

What is interesting with ALL the testing I've done is how well a stock dual plane intakes works with a carb bolted directly to it, vs adding all sorts of spacers and modifying dividers, etc. I'd also add here in case anyone missed it that I'm doing this sort of testing on a 455 making over 500hp. Imagine jumping thru all sorts of "hoops" with your 350-400hp smaller CID engine to get some sort of spacer in place or high single plane intake/spacer under the hood where more often than not it's bringing NOTHING to the table anyplace, and probably hurting power more than helping it.

Case in point. A few years back we dyno's a 428 engine built here. Oliver rods, Ross pistons, tight squish, out of the box 74cc KRE aluminum "D" ports. I did nothing more to the heads than a very minor clean-up under the valves, didn't remove more than a teaspoon of material per head. We selected a custom ground HR cam with 236/242 @ .050" specs with .361" lobes and 1.6 Crower rockers.

On the dyno we ran my iron intake, RPM, and a nicely cleaned up reproduction HO manifold. The iron intake made 497hp, the RPM made 491hp and the HO made 487hp. This clears show that a factory iron intake is PLENTY for at least 500hp and using a larger intake with more plenum area actually hurt power rather than help it.

With this in mind look at how many folks stick RPM (or other aftermarket aluminum manifolds), often with spacers on 350's and 400's with iron heads making a LOT less power. In many cases to use taller intakes they have to do considerable "cobbling" to get everything to fit.

I'd also add that many of the "cobbling" includes drop based air cleaners which move the air filter lid too close to the carb which also hurts power considerably (verified by dyno and drag strip testing).......FWIW.......Cliff

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Old 03-08-2020, 12:28 PM
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Quote:
Originally Posted by Formulajones View Post
Is that used in conjunction with each other?

I ask because I have a theory from the testing I've done with the RPM intakes that has me thinking the taper spacer (as so many call them, I call them super suckers) speaking of the short 1" taper spacer, doesn't always work on a dual plane intake, but it might work well if it were open underneath, hence a 1" open spacer used under it.
Which has me wanting to try a 2" super sucker or even a 1 1/2" super sucker which is basically a completely open spacer underneath the taper portion. It accomplishes the same thing with one spacer that I believe you are doing above with two of them..
No not together. We currently run the 1" tapered with a 1/2" open but there wasn't any performance difference.

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Old 03-08-2020, 06:13 PM
1980 TA 1980 TA is offline
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Got some time to put in some miles today. Good even mix of city and highway. Mileage was 15.8 MPG. The car was pretty consistent at 11-12 for the same mix of city and highway before the spacer change.

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Old 03-08-2020, 06:38 PM
Chief of the 60's Chief of the 60's is offline
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If you think the previous posts are surprising, you would be amazed at what a Wilson Manifolds spacer can do. Not cheap, but the results are worth every dime.

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