|05-20-2005 07:44 PM|
Also you may not believe this but with your combo that 2.73 might be hurting your mileage, a lower gear like a 3.08 or 3.23 may actually improve it and it certainly won't hurt the performance. With your cam you're probably having to give it a fair amount of throttle to get it rolling because it's not "up on the cam", in other words it isn't in the "fat" part of the torque curve yet. A loose converter doesn't help mileage either. A lower gear will help the torque multiplication and get it into the torque curve at a slower vehicle speed plus keep it in the curve at cruise RPM. That's where an OD transmission, lock up converter and a lower rear gear can really shine. I know there's a lot of argument that keeping engine RPM as low as possible is the key to good fuel economy but it's only part of the story. New cars are geared so incredibly high at least in part to reduce "emissions per mile", a slightly lower Final Drive Ratio in many cases would give better economy but increase emissions per mile. For example my '94 LeSabre has a 2.84 differential plus 30% OD for an FDR of 1.99 to 1 . It gets 25-26 HWY MPG when driven at a steady 55MPH, at a steady 70 MPH it gets a consistent 28-29. A swap to a 3.08 differential would boost my 55MPH gas mileage to 28-29 or even a tad better because of less wind resistance even though it increased engine RPM. I do most of my driving in that car at 55-60 and if it didn't have 176,000 on it I'd be swapping the differential. It's a piece of cake on a 4T60E.
|05-20-2005 06:41 PM|
Go with the 4010 600 CFM carb. You will get them cheaper then that on Ebay. You will get better mileage than the Avenger series, better idle quality, better cold starts, better atomization, and less leaks.
|05-20-2005 06:38 PM|
|85Sierra||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|
|05-20-2005 10:29 AM|
Gonig to try the 750
I think I am going to try the 750 with new rods and jets (yea, its a carter). I appreciate all the good info. That is why I keep finding myself back at this site!
|05-16-2005 08:14 PM|
Please note the "SMOG" 383 motor part of it. That kind of indicates on it's own that the engine we detuned.
|05-16-2005 07:26 PM|
To the smallblockGuy. I'd say the 600 was delivering purely because the mixtures were spot on. I reckon the 750 would be better if you had it dyno tuned and rejetted to suit. Surely a worked 383's gonna want more then what a 600 can give regardless of what any theory says!
Just going back to what I was saying in my last post about my 750 fed 327. I forgot to mention that when idling well with a sweet CO reading of 4.5%, not only did the CO drop to 1.5% when in gear but the HC ppm (hydrocarbons parts per million) went from about 400 to over a 1000! Excessive HC readings indicate high levels of unburnt fuel in the exhaust and that's what made the stink in the exhaust. Not because it was running too rich which I never said.
|05-16-2005 11:19 AM|
|Huskinhano||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!|
|05-16-2005 11:10 AM|
I hate to hy-jack the post but I have a question and comment.
First, HotRod did an article a while back where they put 350,650,750, and 850 on a NASCAR style engine and did dyno pulls the numbers were very similar. I don't remember the specifics and would not want to trust what memory I have.
My question or comment: I have a 383 in a 71 chevelle. 10.75 : 1, iron heads, 1 5/8 headers, Performer RPM intake, Dart heads, Roller cam with mucho overlap. I had a 600 CFM carter / Edelbrock on it. The tune was perfect, 14.5:1 cruise and idle, and 12.5:1 WOT. However, I installed a Cowl induction hood (vac activated) and found that it was not opening under WOT conditions. I installed a VAC gage and was pulling a vac under load. I then installed a spare (borrowed) 750 CFM Carter / Edelbrock. The cowl door now open very easily (as expected) but the entier system runs rich and I will have to lean it out.
To the point: I wanted to get some opinion for some guys who have more experience then me. Does that seem reasonable or is there something I am missing with the 600CFM. I don't mind re-roding and jetting the carter but I like the 600 and the response.
|05-16-2005 01:20 AM|
|club327||To answer you two, a carb will deliver the same quantity of fuel on any engine when the fuel signal reaches the same level. A 283 running at 1000 RPM would be similar to a 400 Idling at 650 RPM so to speak. So fuel draw and atomization on the bigger engine would be greater at lower RPM's. That I know you all agree. When the fuel signal drops below the desired level that's when problems arise. My 327 running the 750 would have the idle mixture screws turned out only 1/2 a turn to give an exhaust carbon monoxide reading of 4.5%. Yet, the CO reading would drop to a super lean 1.5% as soon as I put it in gear! Luciano that's when your theory of a 'bigger carb runs leaner' comes into play. The engine just could'nt pull enough fuel out when in gear, and the fuel that was pulled out was poorly atomized. What were my options? I could of screwed the idle mixture screws out more to get an eye watering 8% CO just to bring the idle mixture up to an acceptable level when in gear. That, was not what I wanted. So hence I've gone to the smaller 600 to address the problem.|
|05-15-2005 07:40 PM|
|stepside454||Club327, dont know what to tell yeah.as far as the 750 runnin to rich goes...it could be leaned to correct that, I mean, you could make a 1150 Dominator run lean...I can only assume its a mtter of tuning|
|05-15-2005 06:56 PM|
|05-15-2005 05:56 PM|
|steve t||save yourself some money, keep the Q jet if it works|
|05-15-2005 04:58 PM|
|club327||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.|
|05-14-2005 07:54 PM|
|stepside454||actually, sure, 517 probably will work..is it enough ? not in my opinion|
|05-14-2005 08:03 AM|
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