CFM for this engine. There is a quadrajet on there now and was thing about going to an edelbrock. Input will help. Ted
- posted
19 years ago
CFM for this engine. There is a quadrajet on there now and was thing about going to an edelbrock. Input will help. Ted
save you money
the 307 is a real dog ............ 283 bore 3.875, 327 stroke 3.25
was designed as a 'low-smog' engine, in the mistaken belief that smaog was caused by 'cooler combustion chamber temps close to the cylinder wall'........the small bore long stroke made the wall per CU IN ratio better
also made it doggy
'220 HP'.......HA
Blank A 500 Performer on a Performer intake, a set of 1 1/2inch primary tube full length headers, dual 2inch or single 2 1/2inch ekhaust, HEI ignition(plugs and wires too(dont forget the 12ga 12V source wire)), and a good cold air air intake would make a world of difference. You will still have a fairly small, low power engine. A GM crate engine with 2pc rear seal would run ya about 12-1500bucks and the same accesories you have now would bolt right on(short or long waterpump though?. Run a performer intake, 600 performer carb, 1 5/8inch full length headers, dual 2 1/2inch or single 3inch exhaust, and an HEI ignition set up and you would have a solid runner!
BlankTo answer your question thanks to Car Craft Magazine:
street carb cfm = rpm x displacement / 3456 x 0.85
For example....
3000 X 307 / 3456 X .8592100 / 2937.6
313.52 CFMBlankI found another formula, a bit easier.
theoretical cfm = rpm x displacement / 3456
3000 X 307 / 3456921000 / 3456
266.49 CFMDont' sound like 220HP to me
Blank
for this engine. There is a quadrajet on > there now and was thing about going to an edelbrock. Input will help. Ted
Go with a 600cfm with a vacuum secondary. You may have to play with the jetting to get it to run good. But then I've put 600cfm carbs. on 302 Fords that ran OK.
Brian
Seems like too much.......
$street carb cfm = rpm x displacement / 3456 x 0.85
For example....
3000 X 307 / 3456 X .85 92100 / 2937.6 313.52 CFMtheoretical cfm = rpm x displacement / 3456
3000 X 307 / 3456 921000 / 3456 266.49 CFMDont' sound like 220HP to me
I have seen 780CFM Holley Double Pumpers on 4.3V6 Chevys...Doesnt mean that its not too big just because it was there and it ran strong!
$Volumetric Eficiance is not always 85%! As for turning the engine at only 3000RPM isnt very realistic.
street carb cfm = rpm x displacement / 3456 x 0.85
For example....
3000 X 307 / 3456 X .85 92100 / 2937.6 313.52 CFMSure it would run...And I am sure it was pumping raw fuel out the tail pipe. Now THAT's efficient......
Guys who build racing engines would not just slap a carb on there jest because 800 is bigger than 600 so it MUST be better....they use the formulas, and use all the data based on thier engine components to make it run with the most power. If that means a 600 with bigger jets vice 800 with smaller jets will pull more power on the dyno, thats what the builder would recommend.
Not just slap it on till it runs strong.
So lets look at this then......with said formula (Used by many more great engine tuners than you or I) lets put in some more realistic numbers
Again "theoretical" cfm = rpm x displacement / 3456 using MY 4.3 V6
Lets cruise at 60 MPH....which is about 2000...give or take depending on uphill or down, overdrive or not..etc.
2000 X 262 / 3456524000 / 3456
Only 151.6 CFM is needed. Any more at that speed and the motor will begin to run rich, and eventually choke.
Mash down on the gas to pass slow poke in front of me and CFM required will obviously increase. I liken it to a stereo...may have 1000 peak watts, but it's not needed to sound good and available when warrented
don't forget that the infamous 307 had tiny valves (to fit inside the smaller bore) and anemic heads, so voumetric efficiency was probably in the dumper to start out
Agreed. But to be honest the only thing I know about the Chevy 307 is that it is a DOG, and not worth it to hop up. Olds 307 has some potential, but not much. Better off with the 350, or the 403 if you can find one with the forged crank. But as the original poster asked....what is the proper CFM for his anemic motor.
no more than 450-500
and I'd like to find a re-buildable 307, for my Dad's 1971 C-10, sitting alongside the shop................
I know of a rebuildable 327 in NC. He MAY have a 307 out there in the yard as well. So far he has had almost everything I have asked for. Except an Olds 350 Diesel.
OK, here is where your screwing up the formula...the RPM to be used is MAXIMUM RPM, NOT cruise RPM!!!
For originality I assume? I can't imagine any other reason that you'd want to do anything with a 307 other than attach a chain to it and throw it overboard...
'71 Chevy huh? You're making me drool. I want my next project vehicle to be a 1967-72 Chevy. Mine will definately NOT have a 307 in it when I'm done with it though. More like a 350 or 400.
-Tony
yeah, I'd like to get it back to 'stock'
Ok Spanky, quit your yelling. First, the FORMULA is not screwed up, I didn't invent that. Lets do it your way.
My 4.3 redlines at 5 grand, so lets go 6 so I can chuck a rod or spin a bearing. We'll stay with 4.3s, cause you mentioned them earlier....
6000 x 262 / 34561,572,000 / 3456
454.86 CFM MAXHappy??? Still about 325 CFM short of 780, as you touted earlier.
WAIT...lets do the 307...this should be fun!!
7000 X 307 / 3456621.8 CFM MAX...but we all know with the tiny weenie valves it would never push that much air, and I threw in an unrealistic 7000 RPM cause that would be fun too!!
ooooooohhhhh, foiled again Bob..............
There is only one thing you got close in your posts, and I'll give you that......
Quote ". A GM crate engine with 2pc rear seal would run ya about
12-1500bucks and the same accesories you have now would bolt right on(short or long waterpump though?. Run a performer intake, 600 performer carb, 1 5/8inch full length headers, dual 2 1/2inch or single 3inch exhaust, and an HEI ignition set up and you would have a solid runner!"It would still take tweaking on the carb/timing to hit the sweet spots. No formula is ever going to truly replace a finely tuned machine, and everyone knows that. BUT you have to at least be in the ball park to have a chance to hit a homer.
Now go get us a kegger....the race is on the Speed channel.
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