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Carb dilema #2854980
12/03/20 09:56 PM
12/03/20 09:56 PM
Joined: Mar 2012
Posts: 29
Plano, TX
hkestes Offline OP
member
hkestes  Offline OP
member

Joined: Mar 2012
Posts: 29
Plano, TX
OK, this horse may have been beat to death but here it goes anyway.

I have a 95 model basically stock 5.9 360 in my 37 Plymouth coupe that has been converted to a carb with an airgap intake. Only other modification is a set of long tube headers. The Edelbrock 600cfm that was on it when I bought it was OK nothing special. However, I had an electrical fire and I guess the chemicals in the fire extinguisher caused a lot of corrosion on the body of the carb and it looked like hell. Never could get it to clean up. Buddy had a new Quick Fuel 680 that he was going to use on a build, but changed direction. I have been running the 680 for the time being. Does seem to be too much off idle as it stumbles a bit. At cruise it seems to be OK, but has backfired a time or two when I let off to come to a stop. All that said I am no carb expert by any stretch of the imagination so not sure if jet or accelerator pump changes could solve the issues or not.

Looking for a new carb and when I plug info into the CFM calculators based on 360 with 5500 RPM and use their suggested 83% volumetric efficiency I get 475cfm or at 100% VE it would be 572cfm. Yet multiple 5.9 magnum build articles talk of running 750cfm to as much as 850cfm with decent looking dyno number. I get that most of these have aftermarket heads and upgraded cams, but do those really allow the engine to use as extra 30% cfm boost over what the calculators show as the proper carb for a 100% volumetric efficiency (impossible to reach by the way) carb or are the calculators just wrong or maybe calibrated for a weak Chevy?

What cfm range have you had success running on a fairly stock 360?

Re: Carb dilema [Re: hkestes] #2855027
12/03/20 11:19 PM
12/03/20 11:19 PM
Joined: May 2019
Posts: 6,175
nowhere
S
Sniper Offline
master
Sniper  Offline
master
S

Joined: May 2019
Posts: 6,175
nowhere
Dynos test for max power, what may be great on a dyno can be rotten for driveability.

That said, on my LA .360 I ran an Edelbrock 1306 carb, 600cfm, and an Edelbrock 1407 carb, 730 cfm. Both tuned for the application.

The differences I noted were as follows.

With the 600 cfm carb top speed was 115 mph, highway mileage was routinely mid 20's.

With the 750 cfm carb top speed was 125 mph, highway mileage would touch 20 on a perfect day.

Driveability was the same for the most part. No stumbling or popping or anything out of order.

In my case, since it was my work car that spent about 80% of it's time on the highway I went with the 600 cfm carb.

All in all, with any aftermarket carb you will need to tune it.

Re: Carb dilema [Re: hkestes] #2855166
12/04/20 11:09 AM
12/04/20 11:09 AM
Joined: Jan 2003
Posts: 11,894
Benton, IL.
D
DaveRS23 Offline
Special needs idiot
DaveRS23  Offline
Special needs idiot
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Joined: Jan 2003
Posts: 11,894
Benton, IL.
This is a good Engine Masters episode on carb sizing. The only problem with it is that you have to subscribe to get the ending. But there is still some good info in it.

www.youtube.com/watch?v=OMdsh9-PBRU

Different size and different design carbs will display different strengths and weaknesses. One may drive better around town while another may put up better numbers at the track. 50 years ago, carbs were going to the spreadbore design and the center sections were going to materials that resisted heat transfer. Think Thermoquad. Today, those designs have even more positive effects that they did then.

I have said this numerous times in threads like this, the best street carbs out today are the Street Demons. They have features and benefits that the other, older design carbs do not. I have installed several and they are the best carbs I have ever installed on mild, primarily street cars (and trucks).

www.youtube.com/watch?v=IHWJpZCmUAk&t=31s

www.youtube.com/watch?v=YNAlVFtUFL4

www.youtube.com/watch?v=DPOuEOkazVc&t=308s

There are a tons more reviews on these carbs on Youtube. Either the 625CFM or the 750CFM would work on a mild 360. One might have advantages over the other that the OP would prefer. But the only real way to find out would be to test both on the vehicle. The primaries are the same on both size carbs. Only the secondaries are different between the 625 and the 750. So both would drive similarly around town and cruising. The difference would be at the secondary opening and at WOT. Does the engine need or even like the 125 extra CFM.

In considering these two carbs, if the OP wanted all he could possibly get from his engine, I would recommend the 750 knowing that it might require a bit more tuning. Maybe and then maybe not. If every last horse wasn't that important, then the 625 would almost guarantee a plug and play install.


Master, again and still






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