Carb conundrum

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Darthomas said:
The late 1970s factory racing "direct connection" book noted that no performance increases were ever noted over the OEM intake manifold, save for weight considerations.I really, really like Thermoquads and AFBs.
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It's 2016. Just saying.. There are designs in intakes, carburation, ignition, heads, cams, etc that simply didn't exist 40 years ago.
 
Darthomas said:
The factory cast iron 340 manifold and TQ screamed for me every time I asked it to.

The late 1970s factory racing "direct connection" book noted that no performance increases were ever noted over the OEM intake manifold, save for weight considerations.I really, really like Thermoquads and AFBs.
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I agree except in the case of the LD-340. Build dependent of course. Once you start to go beyond the OE abilty, the LD-340 is really nice.

I have one modified as per the D.C. book. TQ equipped as well. Best described in a word? WHIOA!
 
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Well.....the Holley/Demon Street Demon looks like a TQ and bolts onto a square bore intake.

If I were to ever stray from my Holley, this would probably be the first carb I would try.
 
Captainkirk said:
What happens if those areas are left uncovered? Does anyone know?
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Same as if it were on the factory CI manifold or another spread bore manifold. The notches and troughs between the port and the throttle bores allow for vacuum to pass from a sideways perspective. On an open spacer or open manifold, the ports are just exposed from the bottom instead.
 
I have to be honest...... I have never really given a second thought about a TQ..... I have a pile of them (and some hard to find one I am sure) but never had an interest in making one work for performance reasons. But my pop's did and I decided last week to ditch the thought of FI and try one of these things out for a while.

It was the only carburetor he used in his racing days and did fine with it and have no reason to change course at this point short of a return line to the tank. I even like the idea of keep the Stock Intake. It will look good with a Fogger plumbed in it lol....

JW
 
the Holley strip dominator is a single plane open plenum intake for a thermoquad carb. worth about 10 horse over stock, and lighter. suggested by mopar for the 13-10 second car. those passages on the underside of the carb have U confused.
 
A strip Dominator worth 10 hp over stock? LOL, maybe for his build.
 
I vote for the iron and TQ. Hey it's easy enough to change if you dont like it. Air gap could be welded but why. The adaptor makes for a bad transition IMO. [do you think it looks good?]
 
rumblefish360 said:
LMAO!
Considering yours is a very mello build, those numbers are probably pretty accurate.
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I find this somewhat amusing, as back in the day, you were really stretching it to get 1HP per cube out of a performance street motor. The best Chrysler could do on the 340 was 275 in '68 (yes, I realize this was de-rated from a more realistic 325). IIRC, their most powerful engine was the 425HP dual quad 426 hemi...1 horse short of a "square" engine. Nowadays a a 400 horse 340 is considered a "mello build".
I think of it in terms of a "wild ride". Maybe I'm just getting old...
 
i've seen stock hi comp. 340 builds dyno around 280 making the factory rating realistic.I think the engines using the thermoquad carb peaked a bit higher.
I know of one 426 hemi built to stock specs that dynode 465 hp at nearly 6000 rpm without water pump,alternator,fuel pump or fan and had open headers.With accessories this would be very close it the factory rating of 425
i'm not convinced that a 400 hp 340's are common or as easy as some claim...
 
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This is the Weiand Stealth and a oem style TQ gasket. I pushed the gasket to the left and to the right and ran the pen in close. This gives a thick line that I have shown the measurements as recorded with a mic. There is very little room for error and a minimal sealing area, but it is doable. Or should be.


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Captainkirk said:
I find this somewhat amusing, as back in the day, you were really stretching it to get 1HP per cube out of a performance street motor. The best Chrysler could do on the 340 was 275 in '68 (yes, I realize this was de-rated from a more realistic 325). IIRC, their most powerful engine was the 425HP dual quad 426 hemi...1 horse short of a "square" engine. Nowadays a a 400 horse 340 is considered a "mello build".
I think of it in terms of a "wild ride". Maybe I'm just getting old...
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The 1hp per cube was a factory high water mark for the public and I agree it was a lot for the time and considering all things, it was good.

I was making 400hp builds in my 20's back in the 80's. It was easy like an E-Z bake oven.
 
Wow...that's pretty close, Rob! Not much meat left there. I will try the same experiment just for snicks and grins. But just eyeballin' it tells me it's not gonna work, plus the A/G RPM has only one set of stud holes...Holley pattern.
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I suppose the most reasonable approach would be this:
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...or the TQ mounted on the Chrysler stocker SB manifold. I am media blasting and cleaning that one up as well so I have a number of options. Frankly, the TQ choke thing is a definite issue and wouldn't be if using the stock manifold with the choke well.
Thinking, I am.

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rumblefish360 said:
This is the Weiand Stealth and a oem style TQ gasket. I pushed the gasket to the left and to the right and ran the pen in close. This gives a thick line that I have shown the measurements as recorded with a mic. There is very little room for error and a minimal sealing area, but it is doable. Or should be.
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Do you have a TQ to put that gasket against? I wonder if the throttle bores stretch to the outer limits of the spread bore gasket. Maybe try and line a square bore gasket up to the bottom of the TQ and see how much of the gasket you would need to trim up to just uncover the throttle bores. Then, line it up to the manifold and mark that.
 
The TQ gasket on a big primary TQ. Tight fit!

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Clearance can be claimed with this MP 1/4 tuning spacer and 1/16 gasket to seal to the carb when used with the OE gasket.

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No OE gasket???
Your basic aluminum spacer adapter or 2 MP tuning spacers and the 3-1/16 gaskets will do it.

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But it's looking a little ugly in there as far as smooth air flow is concerned.
You could try and blend it. A die grinder to bevel the carb pad edge to the gasket line.


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Looks like a good option. LD340 rates pretty high for flow numbers, doesn't it?
Did you blend that one or is it stock?
 
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