Mounting Thermoquad to air gap style intake. What adapter?

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JoePole1

A dude in a B body
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I have a 75 850 TQ (larger secondary) that I would like to mount on dual plane square bore intake for my small block 360. Going to be a learning experience including the TQ rebuild. This is strictly a street engine. Hood clearance may be a factor with the tall manifold. For those who have done this, what are you using???
I was thinking of the Mr Gasket 1932 and hog it out if necessary. I did shave down the plenum divider a bit on the intake.

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71-74 Chargers are notorious for not having much room for even a taller air cleaner.

I sold a guy a hood that already had the crossmember cut out for his 440 car with IIRC an RPM intake.

His factory hood wouldn't close and he didn't want to cut it.
 
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72 Satty and small block should give me a little more room. Currently has an edelbrock 1906 600 cfm. I will measure what I have now and add difference with TQ and spacer. Spacer above is .750".
 
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Curve of hood is a bit different on Plymouths.

There is about 3/8 inch more room.

This is just from me eyeballing a 73 RR hood I have installed on a 72 Charger.
 
I have a 75 850 TQ (larger secondary) that I would like to mount on dual plane square bore intake for my small block 360. Going to be a learning experience including the TQ rebuild. This is strictly a street engine. Hood clearance may be a factor with the tall manifold. For those who have done this, what are you using???
I was thinking of the Mr Gasket 1932 and hog it out if necessary. I did shave down the plenum divider a bit on the intake.

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I think you are on the right track. Smart of you to know there may be some modifying that may need to be done.
 
That adapter (any adapter like that) is a power killer. If you want to run the TQ, get a different manifold.

Again, those things cause more issues than can be fixed.
 
That adapter (any adapter like that) is a power killer. If you want to run the TQ, get a different manifold.

Again, those things cause more issues than can be fixed.
If it's for a dual plane get one with the bar right down the center, to keep the distribution as close as possible to stock
 
I love TQ's.
I tried the 850 on my 360HO with the AirGap and adapter.
IMO; for street use with street gears, this combo is a waste of time.
I tried several other carbs as well, but I found the 750DP was about the best on my combo, if a little large.

However; that same 850 on a proper small-port 2P intake, is dynomite on my Smog 318.

If you try this, make sure the secondaries don't snag on the adapter, at WOT! That adapter, altho it works, the transition is just too abrupt. Mine needed a thick gasket for secondary clearance.
If I had to guess, that adapted 850 made about the same WOTpower, as my 600 Holley, or the AVS off a 340car(580?).

BTW,
From my research:
Carter carbs are rated differently than Holleys, and because of that, you cannot directly compare an 850TQ (Carter) to an 850 Holley. I thought I used to have a conversion factory in my notes, but can't find it. Going from memory, the 850 TQ compares to a smaller Holley.
Does it matter?
Only if your 360 is a big-cammed, high-compression, free breathing, HotRod engine. The stocke lo-compression 360 can't hardly pull a 500/550 down at WOT.
 
Maybe I'll look around for a weiand action plus. Would be nice to check operation of the TQ before pulling the manifold. I know they are difficult to dial in especially being a novice.
 
Joe,
Congrats on using the excellent TQ. Use the Holleys as a weight on the trash can lid to stop the wind blowing it away....
You say strictly street use. If usable power is to be 5500 or under, then the Performer is a better choice & no spacer/adapter is reqd. Bolt on deal. Be realistic with the rpm expectations, which will depend on cam & other parts. Nothing to be gained, only losses, fitting a 6500 rpm intake [ the RPM ] on a 5500 rpm engine...
Because the carb pad is lower on the Perf, you may be able to add a 1" spacer [ divided or 4 hole, NOT open ]. This often adds a few upper end hp, with no loss down low. A free lunch...
 
I modified an offenhauser to accept a quadrajet. Looked legit. Never did run it though. Just a thought.
 
Maybe I'll look around for a weiand action plus. Would be nice to check operation of the TQ before pulling the manifold. I know they are difficult to dial in especially being a novice.
You will not regret taking the time to tune a Thermoquad for STREET use
 
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You will not regret taking the time to tune a Thermoquad for STREET use
I'm setting up a dual TQ set up for a 426 wedge, the Edelbrock 4 hole adapter looks to be the least restrictive and best matching. As you can see here, the adapter positioning will cause uneven flow and turbulence as it hits the metal between the 4 holes using the Mr Gasket adapters .the Edelbrock 4 hole adapter will be a closer match to the existing 4 holes on the intake.
Yes I know that the air gap is not 4 hole but I think it would be the best existing match if you can't find an adapter with a bar down the middle Ithe 4 Edelbrock is $ $33 on Amazon

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The Holley Street Dominator is an excellent choice if you decide to go to another mannyfold. It's a low rise single plane, but gives up nothing on the bottom end and has a spread bore carburetor pad.
 
After kicking this around over the winter I think I am going to bag this idea and use my TQ on a LA 360 that I have for a future project. That engine has a Eddy Performer manifold. Now what to use on my current air gap style intake? Right now I am running an Eddy 1406 600cfm carb. I think it is under carbureated. I also have a factory refurb 670 street avenger but have not heard good things about them. Leaning towards an AVS2 650 or a 750 DP. I know nothing about Holleys but no expert on Edelbrocks either. I need choke and would rather have mechanical secondaries.
Recap..engine is 9.3:1 360 Magnum with small valve EQ's and reground 218/224, 270/277, 525/535, 108. Hughes springs. Street driven with AC
so idle rpm is an issue. Please don't let this get into a Holley vs Eddy battle.
 
Edelbrock has two different spreadbore adapters, QJet-2692, and TQ-2691. Go back to Bill Crowells post on Feb 3 2021, (Squarebore V spreadbore). I added several pictures on the difference. I would use an adapter on a 340-360 before I would use the Edelbrock 318-360 Performer with the 318 size ports, plus that 318-360 Performer in down right ugly! Go back to Bill's post-very informative, if I say so myself.
 
Plugging your numbers into the Wallace Calculator, it predicts your CCP to be 155psi and your Dcr to be 7.79
My thoughts;
That modest pressure means your engine might be a tad soft at sub-3000/3500 rpm,
which means together with the modest camshaft, she really wants the bottom-end to be picked up; unless you have a higher than 3000 stall Convertor.
The small-valves and modest cam are gonna limit useful top-end.
The 108LSA predicts ~58* of overlap, so that will want headers to plump up the midrange, and it squeezes a bit more power over the nose. That usually steals bottom end, but in your case @218/224/108, this will not be an issue.
The AG intake is a very good intake, working thru-out the rev range, and to beyond 5500, where, normally, a Single-Plain would be called for. But in your case, that small cam is peaking at about 4800, and the 108Lsa is gonna run down the backside of the power curve pretty quick. So it's not likely that your engine is ever gonna take advantage of the best feature of that AG intake. And so, IMO, that AG-style intake, squeezed under the factory hood, is overkill for your engine anyway, and so swapping it out opens up other options.
Options like; with the carb lowered, you can run a filter box with an air-straightener under/inside it, and a cold-air intake, both of which should plump up the entire rev-range with a lil bump at the top to compliment the 108LSA.
Taking all those factors into account, and the need for hood-clearance; my Suggestion would be to swap that AG-style off, in favor of a low-rise, midrange intake, that is set up for your head-ports, and then install that bad-boy Thermoquad.
The big 850TQ is overkill for your combo, but, properly adjusted, will NOT be a problem. I run those on 318s all the time. With the factory-stock cam even. The TQ will allow your small-cam/modest pressure 360LA to continue to pull a lil further up the rev range before "falling off the cam"
I just don't see your engine taking advantage of the AG's top-end capability, so swapping it out, for me, is a non-issue. It won't hurt your combo in any way, but I doubt if you will miss it after it's gone...... unless you install a real dog of an intake, I guess........
So that just leaves the decision as to which intake to run; and several good recommendations have already been offered; just make sure it comes with the right spread-bore mounting pad.
If you have a factory iron spreadbore intake, I would give that a try; they are a pretty decent piece, and come with a choke-well, and maybe all the mounting points for the A/C stuff.
This 360LA short-block with the 218/224/108 cam, will make plenty of vacuum no matter what street-intake you install.

BTW-1
as previously mentioned, I heard/read, that Carter carbs are rated differently than Holleys, so the 850TQ, a Carter, cannot be directly compared to a Holley. Maybe that's part of why they can be installed on just about any engine; IDK.
But one thing I do know, is that the TQ has ~11.5 square inches of throttle-valve, versus ~9.6 in the 750DP........ whatever that means, lol.
If you have an automatic, the DP is not that desirable a feature.

BTW-2
A streeter is usually a two-gear car, running to well past 65mph in Second gear. Meaning it only goes thru the power peak ONCE to get there and usually, with a 360, the tires are spinning thru first gear anyway. So then I see NO point in top-end power.
If you are running an automatic trans and say 3.23s, then in Second gear, with 27" tires, 65mph @WOT = 3800@zero-slip, say 4200 on the tach. So what's more important to you; power at 4800(75 mph), or power at 4200(65mph)?
But if you are running 4.10s, Second gear at 65 mph comes to ~5300, which is an excellent rpm for your engine combo. ..... And the AG is still not working hard .......

BTW-3
If you have a 3000 or higher stall, then the bottom-end is less important, almost not important at all.

These are my thoughts;

Happy HotRodding
 
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