Which Carb For My Mopar Small Block 340

[Daveh]

Hi Guys I've decided on a Street Demon carb for my 340 Small Block. My question is which one? I have a slightly modified 340 MOPAR small block. You know cam, intake the normal things. Nothing outrageous. The P.O. build the engine and it ran very strong prior to me removing it to paint the car so I don't know the specs. All that I know is that it was upgraded a little and it felt like it was. Why a new carb? A buddy needed one so I gave mine to him and then he moved away so carb gone. No biggie I didn't expect to get it back and I was happy to help him.

Like I said I've decided on the Street Demon for it's plug and play features, reliability (so it seems) and ease of use. I'm not sure if I should go with the 625 CFM or the 750CFM. The 625 doesn't seem like enough. Although could the 750 be too much?

I'm leaning towards the 750 CFM. What are your thoughts? Thanks

https://www.summitracing.com/parts/dem-1901

https://www.summitracing.com/parts/dem-1904

[Cuda Cody]

Boy, without some specs on the engine it's really hard to say, but I would lean towards the 750.  But just a guess.     maybe @Chryco Psycho  has a better guess then me. 

[Daveh]

I agree but it ran so well prior to me taking the car apart that there was no need to tear the engine down.   I didn't get a lot of detail from the P.O. other than it was rebuilt with a hotter purple cam, upgraded pistons and redone heads.   Basically the normal stuff.

[RUNCHARGER]

Not really enough info to go on. We need gear ration, cam specs, headers? Automatic or 4 speed? Generally I like a 750 on a 340 with any mods, however for driveability when in doubt you should go to the smaller choice. You say it drove well before so I would find out what cfm that carb was and let that guide you.

[ChallengerHK]

I ran a 650 on my x-head 340 which was largely stock. Ran well, but I did have a bog on hard launch which may or may not have been fuel starvation.

[Daveh]

What was on the car was a Carter Thermoquad.  Like I said I don't know the CFM. 

I can answer a couple of the questions. 

1.   I'm converting it to a Tremec 5 Speed.
2.   Gear ratio is currently a Suregrip  with 3.23's in a 489 case.  But I'm considering upping it in the future to a 3.73 or 3.91.  I know  3.73's are for chevy's but I've had them before and I like them a lot.   

Thanks

[RUNCHARGER]

Hmm: Can you get the TQ back? I hate to say it but if they are right there is no better street carb. If you can't get it back I think a 650 vacuum is a safe bet although you might feel a bit less topend power.

[Chryco Psycho]

The Demons were problematic
I suggest a 650 Proform you can decide if you need a choke or not

[Spikedog08]

Funny that is the exact carb I recommended on the other site . .  . .

[lulurocks(Ken)]

The Demons were problematic
I suggest a 650 Proform you can decide if you need a choke or not

Before i built my stroker , i probably read every post CP made on a engine build subject.

I went with his proform sugestion  and all of his suggestions ,  very happy with his reccomdations ..

I did the proform 750  vac. Secondary  .  Tuning it has been easy so far , way easier then  my previous eddys ...

650 proform is a great choice ,  again i went vac  secondarys just by preferance only

[Chryco Psycho]

Wow not sure  what to say ......  but once you have built a few engines you kinda get things sorted out from experience as to what will & will not work well . I guess my passion is driving & building engines but not just any engine , I like to find any hidden Hp available ,, I simply cannot build a stock engine , it may look stock but I promise it is not !
I am glad you are happy with the result Ken   

[Daveh]

Unfortunately I can't go with a Proform because I have a shaker car and I'm told there would be major modifications to the baseplate to fit if at all.  The Edelbrock Thunder Series Carburetor fit well and the Demon looks just like the Edelbrock unit and I've heard a lot of good things about the new Street Demon carbs.  Just my 2 cents. 

[RUNCHARGER]

Do you have a stock thermoquad intake on this engine? If so you need a spacer to run a square bore carb, Shakers can make things difficult.

[Daveh]

I know I've been playing with the height issues for months with various carbs and intake measurements and I really won't know until I have the engine in and can experiment a little.  Thanks

[Chryco Psycho]

OK Spikedog has a Proform under his shaker no problem