650 cfm too small?

Posted By: 73cuda340

650 cfm too small? - 07/05/09 09:34 PM

I just picked up a holley 650 double pumper real cheap but it is only 650 cfm. Is this too small for a 340? It has a comp xe268 cam, ld340, ported 2.02 J heads and hooker headers. Car is going to be mostly driven on the street with a few trips to the strip.

Posted By: MoparforLife

Re: 650 cfm too small? - 07/05/09 09:46 PM

Have good low end but the higher end will suffer.

Posted By: goldmember

Re: 650 cfm too small? - 07/05/09 09:48 PM

Good carb for that combo.

Posted By: Mr. T

Re: 650 cfm too small? - 07/05/09 09:48 PM

I think you would be happier with a 750-800 c.f.m.

Posted By: DaytonaTurbo

Re: 650 cfm too small? - 07/05/09 09:54 PM

650 will be fine unless you plan to rev over 6k.

Posted By: PJM

Re: 650 cfm too small? - 07/05/09 09:55 PM

650 is perfect in my opinion! Most people make the mistake of over carburating.

Posted By: Pacnorthcuda

Re: 650 cfm too small? - 07/05/09 09:55 PM

Double pump, on a 4speed--GO FOR IT.

Do the cfm math, I bet you'd really have to wind that little sucker up before the carb would be holding you back.

Posted By: RapidRobert

Re: 650 cfm too small? - 07/05/09 10:19 PM

Quote:

I just picked up a holley 650 double pumper real cheap Car is going to be mostly driven on the street

Should do good & you might consider going thru it(at least pull the bowls) just to make sure everything is correct(& clean).

Posted By: Dartcuda

Re: 650 cfm too small? - 07/06/09 02:37 AM

650 DP should work very well . Did you ever race that Subaru ?

Posted By: MY340

Re: 650 cfm too small? - 07/06/09 04:27 PM

It will run fine, have great response but will suffer on the top end compared to a 750-800cfm carb.

When I swapped from a 625cfm Carter to a 850 TQ on my old Duster with a built 340 I could really FEEL THE DIFFERENCE when I tromped hard on the gas pedal while cruising.

Bigger secondaries are nice to have!

Posted By: Paul_Fancsali

Re: 650 cfm too small? - 07/06/09 04:44 PM

Currently working on a 650vac sec carb on a 340.Good low speed response but little lacking on high end 650 dbl pumpers are just about perfect on a street 340 I have several and overall hard to beat over all. I like a 750 on a light car the 650 on heavier. I have just built another 800 dbl pumper and its great on high end and ok at low speed due to the 4.56 gears on my 340 Duster. I have not track tested it to see what the 60fts and 330 are like, your combo a 650 dbl pumper might be a little small but it will out perform most any other carb

Posted By: Mr.Yuck

Re: 650 cfm too small? - 07/06/09 05:29 PM

should be ok... if you need more mph you can always bump up the rear jets.

Posted By: 73cuda340

Re: 650 cfm too small? - 07/06/09 11:38 PM

Quote:

650 DP should work very well . Did you ever race that Subaru ?

Didn't race it yet, i will update that post when i do.

Posted By: 73cuda340

Re: 650 cfm too small? - 07/07/09 02:36 PM

How much will this 650 hold me back up top. Will it be enough to worry about or only a little bit.

Posted By: Mr.Yuck

Re: 650 cfm too small? - 07/07/09 02:50 PM

Quote:

How much will this 650 hold me back up top. Will it be enough to worry about or only a little bit.

with the 3.23's you'll be fine If you go to 3.91's you might need a little more. Make sure you run a spacer under the thing. A 1/2" 4 hole would do ya good.

Posted By: goldmember

Re: 650 cfm too small? - 07/07/09 03:04 PM

The carb will work fine with your mild combo,it won't hold you back if it's properly set up. Someone suggested bigger jets to help the top end power,very poor advice. Set it up to stock specs and it will work very well.

Posted By: Mr.Yuck

Re: 650 cfm too small? - 07/07/09 04:16 PM

Quote:

The carb will work fine with your mild combo,it won't hold you back if it's properly set up. Someone suggested bigger jets to help the top end power,very poor advice. Set it up to stock specs and it will work very well.

actually bumping them up a little can improve MPH. I wouldn't do it for regular driving but if he wants to blast it real good it might help.

Posted By: goldmember

Re: 650 cfm too small? - 07/07/09 04:24 PM

Adding jet doesn't make the carb act BIGGER or faster if its correct as is.If it's correct adding jet will slow it down.

Posted By: dustergirl340

Re: 650 cfm too small? - 07/07/09 04:30 PM

My 650 Holley DP seems to be perfect for my combo. XE274 cam, AirGap, stock X heads, 3.91 gears, 3,500# car runs high 12's with the 650.

Everyone said it would run quicker with a Holley 750, we put one on and the car slowed down 3 tenths, even with tuning. Swapped the 650 back on and the car jumped right back.

Posted By: Mr.Yuck

Re: 650 cfm too small? - 07/07/09 04:30 PM

Well...you can have a street set-up and a track set-up. I have found that some of MY vehicles enjoyed more timing and bigger secondary jetting at the track. All were run w/o air cleaner assemblies w/ fresh air hoods while racing. I also uncapped the exhaust. Adding a few gallons of 110 didn't hurt either.

Posted By: goldmember

Re: 650 cfm too small? - 07/07/09 04:46 PM

Not suprising to me dispite what others would lead you to believe.

Posted By: 73cuda340

Re: 650 cfm too small? - 07/07/09 11:42 PM

Quote:

Quote:

How much will this 650 hold me back up top. Will it be enough to worry about or only a little bit.

with the 3.23's you'll be fine If you go to 3.91's you might need a little more. Make sure you run a spacer under the thing. A 1/2" 4 hole would do ya good.

It came with a 1" open spacer also.

Posted By: dgc333

Re: 650 cfm too small? - 07/08/09 12:00 AM

Quote:

How much will this 650 hold me back up top. Will it be enough to worry about or only a little bit.

I have a 360 that is making approximately 370 HP. I have had a 600, 670, 725 and 750 on it. There is no difference in the top end between the 670, 725 or 750, the 600 is only slightly down on power above 4000 rpm. But there is a BIG difference in the low rpm throttle response. The 600 and 670 have it all over the 725 and 750.

The 670 is the carb I settled on it gives up noting to the 725 or 750 through 6500 rpm and the low rpm throttle response is as good as the 600.

The 650 for your 340 is about perfect. You might go a .1 faster in the 1/4 with a bigger carb but you won't be near as satisfied driving it on the street as you will be with the 650.

Resist the temptation to over carb you will be much happier.

Posted By: dustergirl340

Re: 650 cfm too small? - 07/08/09 01:24 AM

I agree on the much better low rpm throttle response. The 750 was sluggish at low rpm's while my 650 is very responsive.