Carb sizing and fuel efficiency
Thread Starter
Drifting
Joined: May 2001
Posts: 1,295
Likes: 2
From: Surprise Arizona
Carb sizing and fuel efficiency
I have been thinking about removing the 750 Holley off the big block and replacing it with an Edelbrock 1405, 600 CFM carb a buddy of mine has, and isnt using. The Holley has seen better days, it needs a complete overhaul. My mileage with the Holley has been absolutely horrible. (a lot of reasons for that 
)
My question is will my mileage go up with the smaller Eddy? Or will the power just go down with no appreciable gain in MPG? My goal here is better MPG sacrificing power if need be.
What do you guys think?
) My question is will my mileage go up with the smaller Eddy? Or will the power just go down with no appreciable gain in MPG? My goal here is better MPG sacrificing power if need be.
What do you guys think?
Last edited by Paul G; May 13, 2008 at 04:56 PM.
Le Mans Master
Joined: Apr 2007
Posts: 7,353
Likes: 72
From: Graceland in a Not Correctly Restored Stingray
IMHO I'd rather ration the quantity rather than the quality of my time in my shark, and I'm betting you'll likely be more disappointed by the drop in performance than by the increase in mileage, as a 600 is just way too small for any BB Corvette. I'd suggest overhauling the Holley and then putting a proper fine tune on that engine, as that may be all you really need.
BTW, the most efficient carb setup I ever had on a BB was the Tri-power (w/vacuum secondaries), which flies in the face of the smaller carb is better notion for mpg. Just my $.02...
BTW, the most efficient carb setup I ever had on a BB was the Tri-power (w/vacuum secondaries), which flies in the face of the smaller carb is better notion for mpg. Just my $.02...
Last edited by TheSkunkWorks; May 13, 2008 at 12:29 AM.
Melting Slicks
Joined: Sep 2007
Posts: 2,429
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From: Tucson AZ
Race Director
Joined: Oct 2000
Posts: 15,009
Likes: 79
From: central FL, near the beach.
did u read my carb page?
http://community.webtv.net/MATTGRU/carb
i'd try an 800cfm 4165 double pumper with a 4 holer & no cut down center divider.
http://community.webtv.net/MATTGRU/carb
i'd try an 800cfm 4165 double pumper with a 4 holer & no cut down center divider.
Last edited by Matt Gruber; May 13, 2008 at 06:26 AM.
Drifting
Joined: Apr 2008
Posts: 1,540
Likes: 51
From: Lexington Park Maryland
Rebuild your 750....., tune the car, and try to keep your foot out of it unless the situation warrants it (eg. some clown in a late model Mustang is next to you at a red light !!) OR as 7T1vette suggests......, leave it in the garage for awhile. You don't want a "slow" Vette !!
Melting Slicks
Joined: Mar 2007
Posts: 2,100
Likes: 12
From: Frederick Maryland
I like Edelbrock carbs, but a 600 is simply too small for a big block. Either have your Holley rebuilt or find a replacement of 750-800 cfm airflow (Edelbrock, Holley, Q-Jet or Demon).
You're going to be sorely disappointed with too small a carb, but you can stay at a Holiday Inn Express!
You're going to be sorely disappointed with too small a carb, but you can stay at a Holiday Inn Express!
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Racer
Joined: Apr 2006
Posts: 477
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From: Millbrae California
One of the best carbs for fuel mileage is a q-jet, it has very small primarys so as long as you can keep your foot out of the secondarys you should get good fuel mileage. Tune the ignition spark advance and air/fuel mixture curves and you should get decent mileage.
Henry @ olescarb
Henry @ olescarb
Tech Contributor
Joined: Aug 1999
Posts: 14,373
Likes: 6,371
From: At my Bar drinking and wrenching in Lafayette Colorado
Henry and I agree on that one. A Q-Jet, in stock or near-stock format, is actually jetted to provide pretty fair mileage, and you can get a lot of tuning and mileage efficiency out of getting your ignition curve tuned right.
Lars
Thread Starter
Drifting
Joined: May 2001
Posts: 1,295
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From: Surprise Arizona
I went for a ride with the borrowed Eddy 600. Man what a difference! No spitting, backfiring, hesitation problems or any of that. It idles smooth and accelerates nice and smoothly. Only thing is a very noticeable loss of power. I am going to borrow it for a tank full of gas and see what the mileage turns out to be. The Holley 750 was giving me around 6.5 MPG. If the Eddy 600 gets me close to 10 I may just stick with a little carb for a while.
Granted owning and driving a big block is going to be expensive, but with 91 octane over $4.25 a gallon, 6.5 mpg just has to make me stop and think twice about driving the car as much as I would like. Giving up some HP to save some fuel is the responsible thing to do for now.
Granted owning and driving a big block is going to be expensive, but with 91 octane over $4.25 a gallon, 6.5 mpg just has to make me stop and think twice about driving the car as much as I would like. Giving up some HP to save some fuel is the responsible thing to do for now.
Thread Starter
Drifting
Joined: May 2001
Posts: 1,295
Likes: 2
From: Surprise Arizona
You know, the more I think about it, wouldnt it be smart to have a little fuel efficient carb for cruise nights and car shows and all that, and have the big Holley to swap back on if we go to the track.
What are your thought on that?
What are your thought on that?
Le Mans Master
Joined: Apr 2007
Posts: 7,353
Likes: 72
From: Graceland in a Not Correctly Restored Stingray
I got ~14mpg city with those 3x2 BB setups in my heavy SA which I mentioned earlier, whenever I could keep my foot out of the secondaries. Even the 1050 cfm progressive mechanical Dom could manage ~9mpg on a fairly moderate 427, so I wouldn't exactly be dancing about over 10mpg from that 600. (Note: these examples were all with 1:1 top gear manuals) Sounding more and more like you need a tune up. Food for thought...
Last edited by TheSkunkWorks; May 13, 2008 at 06:02 PM.
Drifting
Joined: Apr 2008
Posts: 1,305
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From: Lewisburg WV
thegazman
Lars and Henry are right. I bought a 750 Q-jet rebuilt by Jet Performance from Jegs. I installed it along with a Performer spread bore intake.I get good gas mileage, great idle, acceleration, and power when I put my foot in it and open up the rear bores. I bought their level 2, which is designed for better acceleration from off of idle.
Ken
Ken
Race Director
Joined: Apr 2000
Posts: 17,676
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
If you are getting 10mpg in anything less that a ProMod race car you need to tune your carb properly. An LM-1 wideband will pay for itself in a couple of months. I got 25mpg on the highway with 550HP small block @ 80mph.
Partly because of the overdrive tranny but the carb (825 Dragrace Demon) was tuned properly. When I got my engine back after being at the dyno shop I thought I had a hole in my gas tank the way the gas gauge was moving, I thought I could see it move, I am not kidding either, I went under and took a look for a leak. Turned out the carb was waaayy to rich, when I hooked up the LM-1, tune the carb and you should see double the gas mileage
Partly because of the overdrive tranny but the carb (825 Dragrace Demon) was tuned properly. When I got my engine back after being at the dyno shop I thought I had a hole in my gas tank the way the gas gauge was moving, I thought I could see it move, I am not kidding either, I went under and took a look for a leak. Turned out the carb was waaayy to rich, when I hooked up the LM-1, tune the carb and you should see double the gas mileage
Safety Car
Joined: Oct 2005
Posts: 3,570
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From: Algonac Michigan
One of the best carbs for fuel mileage is a q-jet, it has very small primarys so as long as you can keep your foot out of the secondarys you should get good fuel mileage. Tune the ignition spark advance and air/fuel mixture curves and you should get decent mileage.
Henry @ olescarb
Henry @ olescarb
Melting Slicks
Joined: Sep 2007
Posts: 2,429
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From: Tucson AZ
Not to hijack, but I got my new 80508S carb today, a 750cfm 4150 I think. Put it on and it idles at 4-500 rpms, if I wanted it too (turned it back up after). My vacuum has come up from 10" to 13-14". Response is great, acceleration is fine, a great all around carb, and especially in comparison to the other one I had. Holley really fouled up with quite a few carbs. Alot of them had "bubbles" on the inside of the fuel bowls and metering plates. Very happy now, runs like a 454/365 should!!!