340 intake questions

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furyus2

furyus2

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I see intakes for small blocks advertised for all small blocks. What about the port mis match with 340 heads?
Are the professional products intakes good for a mild 340?
The 69 340 intake has small bores, and I was thinking that I would like to try a Thermoquad carb.
 
There always some 'as in intake port is still smaller than the heads port' Also a little to one side a lot of times...but still smaller...so that you can work with it and equalize/match it. What IS a problem..is when the floor is lower than the head intake floor... fuel will shed and sit there.
Most side to side misalignment at the common wall/dividing wall lines up at the inner side on each pair, 3,5 for instance..so you match up 1,7 or 2, 8.
One place you can usually compensate for mismatch is the roof... because raising the roof always helps flow, while lowering the floor at the entrance can mostly hurt and imo cause fuel separation ..and wet intake gaskets.
 
furyus2 said:
I see intakes for small blocks advertised for all small blocks. What about the port mis match with 340 heads?
Are the professional products intakes good for a mild 340?
The 69 340 intake has small bores, and I was thinking that I would like to try a Thermoquad carb.
Click to expand...
Yep, you can not use a thermoquad with a 1969 oem 340 intake.
 
furyus2 said:
I knew that, and that is why I was thinking of changing the intake. Also would like to block the crossover at the same time.
Click to expand...
There are plenty of oem 71 and later intakes, to see if you like the TQ, but they're going up in price now.
 
The early intakes with the four holes are called square bore. Thermoquads use spreadbore. The stock 340 intake is an excellent intake minus the fact that it weighs a ton.
As far as port size, you have the 273/318 size and 340/360 size. You do not want to use the smaller port intake on a 340. Im not familiar with the professional products intake? Is that the air gap clone? Edelbrock RPM Air Gaps use the larger ports.
 
If you can find one, an LD340 that has been modded to a spread bore via the DC bulletin would certainly make you stand out at the car shows with the engine affectionados.
LD340 Spreadbore?
 
OldmanRick said:
I'd prefer a stock intake for your application also.

Maybe @RAT ROD AL could help you out. He's probably only about 150mi. from you?
Click to expand...
I do have a stock intake on it now. I was thinking of killing a couple birds at the same time.
I thought maybe get an aluminum intake for light weight, block the heat crossover, try a thermoquad, but I might just change the intake gasket since I don't need heat in the manifold.
 
The port mismatch red herring. Run what you can find. If you don't like the size of the port window, use a grinder.

If you can find a 71-73 340 intake, that will work. There are a bunch of aluminum intakes that will work. Some of the recommended intakes for 340-360 engines that are performance oriented, that get bounced around on this site, have the 318 port window in them. Go figure.
 
crackedback said:
The port mismatch red herring. Run what you can find. If you don't like the size of the port window, use a grinder.

If you can find a 71-73 340 intake, that will work. There are a bunch of aluminum intakes that will work. Some of the recommended intakes for 340-360 engines that are performance oriented, that get bounced around on this site, have the 318 port window in them. Go figure.
Click to expand...
That is what confused me. I wanted aluminum for weight, spread bore for flexibility, but I don't want the port mis match. It's not something I need to do, just something I wanted to.
 
Want a good intake that has a TQ base. Find a performer 318/360 and spend a half hour with a grinder/dremel and a gasket. Simple.

Those intakes go CHEAP because of the port window BS...
 
I have installed smallport intakes on bigport heads AND bigport intakes on smallport heads, and on the street you will be hard pressed to know the difference.
A smallport single-plain intake on a 340 with small port heads is dynomite on the bottom end. And with bigport heads seems to have a lil more in third gear. Cylinder pressure makes a big difference.

If you install a TQ, I highly recommend that you use a proper spreadbore intake, and NOT an adapter.

Defeating the cross-over, on the street, unless you have headers, is almost a waste of time; unless you have percolation issues.
A lot of work for very little gain. If the intake is coming off anyway, then yes I would defeat it..... in Florida.
 
A Great set of answers.
AJ/FormS said:
I have installed smallport intakes on bigport heads AND bigport intakes on smallport heads, and on the street you will be hard pressed to know the difference.
A smallport single-plain intake on a 340 with small port heads is dynomite on the bottom end. And with bigport heads seems to have a lil more in third gear. Cylinder pressure makes a big difference.

If you install a TQ, I highly recommend that you use a proper spreadbore intake, and NOT an adapter.

Defeating the cross-over, on the street, unless you have headers, is almost a waste of time; unless you have percolation issues.
A lot of work for very little gain. If the intake is coming off anyway, then yes I would defeat it..... in Florida.
Click to expand...
crackedback said:
Want a good intake that has a TQ base. Find a performer 318/360 and spend a half hour with a grinder/dremel and a gasket. Simple.

Those intakes go CHEAP because of the port window BS...
Click to expand...
 
Is the car driven in the winter? At night, I know your area will see some pretty cold temps for a short time.

furyus2 said:
I see intakes for small blocks advertised for all small blocks. What about the port mis match with 340 heads?
Are the professional products intakes good for a mild 340?
The 69 340 intake has small bores, and I was thinking that I would like to try a Thermoquad carb.
Click to expand...
 
rumblefish360 said:
Is the car driven in the winter? At night, I know your area will see some pretty cold temps for a short time.
Click to expand...
Yup, it gets into the 20s in the winter, but bounces back to the 70s. But I have an electric choke on the car, and I just drive it in nice weather, so I don't need the crossover.
 
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