All Big Six Fabbing intake on efi lower.

Relates to all big sixes

pmuller9

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The 252 requires a very low compression ratio.
If you have to use a Comp Cam use the 260.

161Henry did 3 singles on a EFI lower intake.
He was going to use the center one as a primary and the outer two as secondaries but didn't follow through.
 

pmuller9

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Just to see if I'm following on this correctly, does that mean that the cfm requirements we get from online calculators are more of an average, where as the actual number needs to be taken during that short time that the cylinder is actually filling?
Yes. The 300 six as well as the other big straight sixes have always done well with larger carburetors than expected.
My last 300 six had a Quick fuel 650 mechanical secondary and had no problem breaking the tires loose in second gear at 1200 rpm and still got 17+ mpg on the highway in a 1977 2wd truck.
 

THE FRENCHTOWN FLYER

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What is very low, 8.1?
Keep it equivalent in DCR to the stock cam in terms of intake closing events
So figure the DCR for the stock cam events , then adjust the 252 SCR so the DCR is the same as with the stock cam.
Were it me, I would increase the cam events over stock with the addition of additional carburetion, not decrease it.
 
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BigBlue94

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Never been a fan of Comp's offerings for the 300. They all have a duration lower than the factory cam. Good for making a bit more torque cruising in the city, but not necessarily best for performance throughout the rpms. Schneider has a wonderful range of cams for the 300, but are out of cam cores currently.
 

pmuller9

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What is very low, 8.1?
8.0 if the cam is installed 4 degrees advanced per the cam card
The three Comp cam offerings require lower static compression than the other comparable .050" durations from the other cam companies.
The stock cam has a 268 duration and is also installed 4 degrees retarded allowing up to an 8.8 compression ratio with 87 octane pump gas.

Here is the cam list;
 

Frank

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This doesn't address peak flow requirements
The 300 six has 50 cu in cylinders the same as a 400 V8 that "gulp" much larger volumes of air during the intake cycle than a 300 V8.
It has been demonstrated multiple times that an internally stock 300 six responds well to increased induction along with increased exhaust breathing and scavenging.
Thank you for that! Good to know.
 

Dipstik86

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Yes. The 300 six as well as the other big straight sixes have always done well with larger carburetors than expected.
My last 300 six had a Quick fuel 650 mechanical secondary and had no problem breaking the tires loose in second gear at 1200 rpm and still got 17+ mpg on the highway in a 1977 2wd truck.
I might actually go up to a 450cfm or larger carb with my turbo build.
 

Evan76

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Theres a size thats less exspensive than the 390 and 450 cfm.

Ive been reading on floats whistles vent tubes n springs.
I think I can build a offroad carb for 150 that includes cost of carb rebuild parts n misc whistles n stuff.
 

Evan76

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I havent finshef this build yet, already thinking about building a second 300.
Have 2 more cranks and two blocks

Punch one .050 over and run some forged 360 pistons

Ones a 240 so I guess those rods are out.

Just thinking out loud.

You guys wanting me to run two garbs got me to thinking. Thats alot of carburation it requires a complete redo of the top of my intake would be a conglomeration of throttle linkages

I like simple. though what I did probly wont turn out to be simple. Bought a 600cfm 4160 for 70 bucks.
Ill set secondaries to come in late
Probly only be used while my foots on the floor with our 10k skidsteer in tow on the 5k goosekneck Trailer.

Ive bought the 252h cam but wouldnt be aposed to ordering something else. But I almost feel like I may have made the right deciseion since some say it is tourque but has less power on top. Isnt that what a came geard towards lower rpms does. Thats what im after.

I dont have to stay with the comp cam. Ive got a cam that is stock and one that I think is a stock replacement.

Im probly making all the wrong calls on how to spend my money but im atleast learing alot.
 

bubba22349

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Just some more info for you, the 352 FE Pistons are a 4 inch bore size the same as the 240 & 300.
 

BigBlue94

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Theres a size thats less exspensive than the 390 and 450 cfm.

Ive been reading on floats whistles vent tubes n springs.
I think I can build a offroad carb for 150 that includes cost of carb rebuild parts n misc whistles n stuff.
I bought a Quickfuel 450. Its a 4160 with lots of bonus features.

Vent whistle fit in one bowl but kept the seat open on the other. Dont recall which one. So I trimmed the one whistle to fit. Then I bought a $7 brass tube, bent it and drilled holes in the top, and replaced the stock vent tubes with it. It looks just like the tube on the holley truck avenger. Had zero problems with it out in Moab. Well, zero issues related to off camber fuel delivery lol.

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Cams for the 300 and 240 are rated for use on a 240. So when a cam says 2000-5500 rpm range, that is for a 240. The 300, due to different stroke length, will take about 750 rpms away from both of those figures, so 1250 to 4750 rpms. Yes, you want a cam with torque down low, but you also want it to not fall on its face at 3500 rpms. With nothing more than a 4bbl, intake, and headers, the stock cam I used to run would keep making power past 5000 rpms. I can be cruising in fourth gear at 70mph at 3000 rpms in the bronco, and when i mash the pedal, the rear squats and I can be to 90mph in a couple seconds. Or I can put it in granny 4 low, let out on the clutch, get out, and run circles around the bronco. Thats with this cam and 9.75:1 static compression.

Screenshot_20211202-112355.png
 

Evan76

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Dead blowcis better than a crescent wrench.

Im thinking about ordering bowl and metering plate and possibly adjustable power valve I think thats whats adjustable with a screw.

I might get stuck on the freeway everyounce in awhile ill go bat shit crazy if shes spinning over 2500rpm
Good thing it doesn't have a tack.
 
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