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950 cfm carb
I have a stroked 427. I believe it has a 750 cfm carburetor I was thinking of a 950 cfm carburetor because of a large cam. I think, I would gain some horse power, just was wondering what others with more experience think. The previous owner, polished away the numbers so their is no stamp ,telling me the actual carb size.
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But based on these assumptions: 427 cu. in. (stroked small block) Lightly modified Mostly street driven 6000 RPM Redline 750 cfm is good. 950 cfm is too large unless it's a modified motor with high volumetric efficiency at redline. Also does the fuel delivery system have the flow capacity to feed a 950? Too large of carb will feel sluggish in street traffic where I assume most of your driving will occur. Could be an expensive letdown. Best method if you don't know specifics about your engine is to get the car on a dyno and decide based on the resulting imperical data. A quick and dirty ballpark method is Summit Racing's carb cfm size calculator: https://www.summitracing.com/newsand...cfm-calculator |
I have a 427 ci small block Chevy in my Cheetah. It was dynoed at 600 HP at 6100 RPM with a Holley Ultra XP 850 carb. It is not happy below 2000 RPM likely due to the weak air signal through the carb at low speeds. It is also cannot be equipped with a choke, so cold starts require some practice AND high RPM for a minute or so after start. . . Engine builders tend to use huge carburetors so they can boast of their big peak horsepower numbers, but those don't make for good street engines. . . . Keep in mind that peak horsepower plays a role in performance only at wide open throttle at peak speed, and that is only safely possible on a race track. At all lesser speeds it is engine torque that matters. So if you plan to drag race and you want to increase your trap speed, peak horsepower matters. On the street, responsiveness and torque matter most and the 750 is better for that.
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On my 427W I run a 780cfm from ProSystems. 4150 Dbl pumper, no choke or horn. 1-7/8" custom built headers and limited restriction sidepipes. Edelbrock Vic Jr., AFR 225 heads, Comp Cam custom grind 240 at .050, .610/.613, 108. Didn't like sub 2k RPM but would run very nicely at 2,200. About 535hp/tqe on an engine dyno, 440/435 on a Mustang wheel dyno (would be about 475 on a DynoJet).
My experience is similar to Tommy's. But I'll add that chokes are really unnecessary, in the way of a good air path and air cleaner options. I've tried a similar 940. Wow!!! did it scream at 7,000, not so hot under 5,000. Also tried 2" headers with similar effect. Sold the 940 carb. Told the friend with another 427W that bought it that it was too big. Took him a bit to believe me before he sold it. If I was going bigger it would be a Holley Ultra XP 850. Would like annular boosters abd would do this knowing that I will give up some low-end response and if switching to a Eldebrock Super Victor. But, I run to 7k RPM. In any normal world the 750/780 is great. Right now the plan is for the Vic Jr and PS 780. Not much future in messing with the combo that works. Need to build new headers for the Challenge Car. Jim |
When it comes to carburetors, bigger is not always better.
Instead of replacing the carb you have on the car now, why not spend some money have have a shop that uses a chassis dyno to properly tune and tweak it for the engine. Bill S. |
OK then I will not go bigger I have a Victor jr heads and a rpm Edlebrock manifold. Thank you all for your inputs.
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I started with a Performer RPM and Vic Jr. heads. Good combo, very drivable.
If you have a 4150 Mechanical/Double Pumper you're all set. If running a vac carb then switching to a DP will be a great kick in the pants upgrade. Might be what you're looking for. Jim |
I started with a Performer RPM and Vic Jr. heads. Good combo, very drivable.
If you have a 4150 Mechanical/Double Pumper you're all set. If running a vac carb then switching to a DP will be a great kick in the pants upgrade. Might be what you're looking for. Jim |
The carb on my Roush 427R is an 870 cfm Holley with vacuum secondary's. I thought it was too much so I made a call to Roush and they confirmed it was the correct carb.
Fred |
hauss,
Just checking in to see if you've made any progress or changes. Jim |
Here is what is happening if I jet it for close to sea level its a beast but in the mountains it does not want to run dam near fouled the plugs.That is why I thought bigger would be better. When jetted for mountains it looses power. In the motorcycle world there is a lectron carb and a smart carb that deals with these type of issues. just wondering what carb would be best in the car world?
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hauss, bigger won't solve those problems, sorry. Probably make it worse simply due to the 950 being TOO BIG. Air velocity will be slow and then compounding with less air. Nothing good will come of this.
I've run from a 700 ft tune (MI) into the Rockies but, much higher than 8,000 is a problem. I've had to drop jet sizes to average the tune out. Usually 2-3 sizes down takes care of things. What you need to be a bit careful of is tuning for altitude and then dropping to sea level, this is where it will lean out, maybe dangerously so. If changing altitude is a regular event you really are a prime candidate for EFI. Ouch, that really hurt but the truth is often uncomfortable. Jim |
In have a all aluminum 427 small block stroker 550 hp with a 850 demon works excellent
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