Im having trouble deciding on what carb i want holley/BG/edelbrock but anyways i was wondering if 600cfm is not enough for my motor
406sbc wont see more than 5500
406sbc wont see more than 5500
machine shop tom said:Personally I think you would be happiest with a 750 vac. sec, Holley. It will pull a LOT harder than the 600 or 670.
tom
Here the formula, and 517 CFMs are okay?Hippie said:You must have plugged in 100% volumetric efficiency, 80% for a street motor will probably be more like it and that's optimistic. Using 80% it comes out to a 517 cfm.
But now a 750 CFM carb is okay?Hippie said:Why didn't you tell us you had a Q-Jet in the first place? I wouldn't consider switching an "upgrade", get Doug Roe's book and spend some time on the Q-Jet, it probably works "OK" right now but you still have a way to go to be perfect. Once you get it "perfect" the only thing better on the street is EFI. It doesn't have the visual appeal of other carbs but it sure does work and once you've experienced one properly dialed in you'll start thinking it looks pretty good after all. Just my $.02 but from what I've seen in other posts there are quite a few experienced rodders here that feel the same way.
lluciano77 said:Here the formula, and 517 CFMs are okay?
What is your problem? I'm not the one that argued with you about the formula, we disagreed about Holley 4010's being a "new" design vs. other carbs but I put it behind me, obviously you can't. The original question here was whether or not a 600 Holley was big enough for a 400 SBC, he didn't ask if a Q-Jet would be better or if a 750 was too big, he asked if the 600 was ENOUGH. From my personal experience it is. As far as a 750 being OK a vacuum secondary carb will only flow at WOT what the motor will pull, using the dreaded "formula" his 406 will probably only flow around 517 cfm assuming a volumetric efficiency of 80% at WOT, very few street motors exceed 80% . Could it be more, yes, but with the combination he eventually listed probably not much more and realistically how much time does a street motor spend at WOT, a few seconds a month at best? A 750 Q-Jet would be better choice over a 750 square bore carb due to it's smaller primaries. A 750 square bore would kill his gas mileage and throttle response because of it's large primaries and idle circuits, if he was racing? Hell yeah go for a 750 Holley, Demon, etc. but he's not. The Q-Jet is capable of excellent throttle response, mileage, etc. and my experience with Holley spreadbores has been that they can't hold a candle to a Q-Jet for those attributes regardless of what Holley claims. That didn't come from a formula, chart or some magazine article, that comes from real world experience. Even as much as you hate "formulas" they provide a pretty good baseline to use to start making comparisons, thousands of people use them with great success. They were developed over many years by people with a lot more education and experience than just about anybody on this board. As for your "A S S" chewing the other day that didn't come from me in fact even though I felt you were out of line I felt kind of bad for you, I thought the guy over reacted. I've changed my mind.lluciano77 said:But now a 750 CFM carb is okay?
If 750 is okay, that means the formula doesn't work. Didn't I just get an A S S chewing for doubting the carb formula the other day???
I wasn't recommending a 517 cfm but it does read that way doesn't it? That wasn't the point I was trying to make but you'd never guess it from that post. Guess part of the thought process didn't make it to the post.....my bad, "glorious results of a mis-spent youth" as they say........ but I stand my ground on 600 being "enough". Been there done it, no magazines or formulas involved. It WILL work and I wasn't the only one voicing that opinion. Again, I wasn't the one that initially disagreed with you about the formula but when I used it I'm the one you climbed all over in THREE different posts one of which was in a thread that had NOTHING to do with carburetors. What is up with that? That's not about "protecting" people from bad advice that's about your ego being bruised because someone had the audacity to disagree with you. Offended? That's a nice way of saying it and I probably wouldn't have been if it hadn't been for thislluciano77 said:What I meant was you can't just go by the formula to get an accurate result. It wasn't really in reference to an argument that DIDN't happen between you and I.
Too many people on this board go with the new Hot Rod Magazine, smaller is always better theory. That is not always the case. When people start saying it will be a good idea to run 517 CFMs on a 9.7:1 406, that is when I'll speak up and say something. When they get offended and jump all over me about saying something, I'll stand my ground. If they prove me wrong I'll admit it or at least concede.
I'd rather piss someone off on this board off that may be giving bad advice, unknowingly. Than have someone not get the best answer to their question possible. If that takes debating between board members so be it. If that takes me standing up for my point and making an A S S of myself while doing so, so be it too.
Sorry I offended you Hippie, I'll keep it cooler next time.
What was that all about? Hmmmm? Prior to the 4010 vs. Q-Jet discussion in another thread I'm not sure what button I pushed that gave you such a dislike for me but it sure looks to me that's what this all boils down to. You seem to be a pretty smart guy and you do usually have pretty good input and while we may disagree on occasion we're usually not too far apart but you DON'T have to be an a-s-s to people to make your point, in fact they'd be a lot more inclined to see your side of things if you weren't. I can be pretty stubborn, I'm Irish, it can't be helped and maybe I got a little too wound up. Actually we probably aren't all that different, might be part of the problem . I'm sure we'll bump heads again, all I ask is if you're going to bump heads with me do it over things I said not what somebody else said. I'd rather get along but that's up to you, disagree with me all you want but stick to the discussion at hand. I think we've beat this one to death.lluciano77 said:[Quote:
Originally Posted by Hippie]
780 CFMs...But according to the formula it should have never worked on a 350. 400-something CFMs should have been more than enough...I have them somewhere at home but I'm at work right now. As far as hood clearance goes any available dual plane intake that I know of should clear with a dropped base air cleaner. The '70-1/2 through '72 Z-28 came equipped with the LT-1 350 which used the Z-28/LT-1 high rise, 780 Holley and the AC 14 x 3 inch open element air cleaner under the stock Camaro flat hood. The Holley 300-36 Street Dominator dual plane and Edelbrock Performer RPM are very similar intakes, (OK the Holley is almost an exact copy but hey, if something works why reinvent it?) they should have the dimensions for those on their websites.
Alright, I'll leave it alone now..
A smaller carb usually runs richer on a bigger engine. The opposite is true as well. A bigger carb on a smaller engine will run leaner.club327 said:I better enlighten you all about my resent downsizing from a 750 vac sec Holley to a 600 vac sec Holley on my 327. The main reason I went to downsize was that the 750 was too big for efficient mixture atomization, particularly when cold. The stench of fuel carbon deposits was overwhelming and would find its was into my home and clothes and I just had enough. So I bought a used 600 vac sec Holley and rebuilt it using Holley parts. I expected the engine to run a lot better when cold, but it's only slightly better. I guess the engine does'nt really like inhaling its own farts due to the extra cam duration. But once warm it's good and the low speed throttle control and smoothness of power delivery puts a smile on my face. However, when on full throttle I feel it's not as good as the 750. It does'nt sound as menacing and I sometimes wonder if the secondaries are opening at all. I've fitted the lightest secondary spring which had no real improvement. But what I find questionable is all of you who say that putting a Holley 750 on a 350 or whatever would cause problems because it's too big. In reality, my 750 allowed my engine to give stupendous bottom end torque (before I changed the cam lol). So much so that when I drove it for the first time I thought it had only a small Holley due to the grunt. So it came as a big shock when I found out that it had the 750. Yes, the mileage was poor but I never bought the car for commuting anyway.
I guarantee it would have made more with a bigger carb. My engine could make some respectable numbers with a 350 CFM 2 barrell.Huskinhano said:In the latest Popular Hotrodding mag, they have a 75 Camaro that they're doing a build on. They just dyno'd the new "smog" 383 motor. It made 402 hp using a 600 emission Holley. I'd say the other guys who recommended a 600 cfm carb are right on the money!
How much time have you spent dialing in the carb? Q-Jets are good but they aren't magic....... and the same goes for any carb you might try. You might get lucky and come close but the odds that it is optimal are pretty slim.85Sierra said:Well i have had the car out for a week now and it gets worse mileage then my truck even when i dont give'r, There is a 600 holley rebuilt in the local buy/sell for $100 might check that out