Product Review #6 - Edelbrock Carb - Power & Economy?

[TonyBrown]

Product Review # 6

This is where we look at a promising product and give you a preliminary evaluation prior to any in depth evaluation we may subsequently do in our Product Spotlight Series.

Edelbrock Carb – Do we have Economy with Power?

By

Tony Brown
Atlantic Racing Speed Shop

Dragging my racer out to the track means getting out my old but trusty 454 big block Chevy powered 12,000 lb motor home and hooking up my enclosed trailer. The trailer, like the motor home, when loaded with the car plus all the other stuff like tools etc, comes in at another 12,000 lbs. So that 454 is working pretty much full time to haul this 24,000 load to and from the track. When GFN tech editor Vizard asked if I would like to test the Edelbrock 800 cfm carb (part # 1413) I naturally asked what the test was intended to show and DV tells me we are looking to see what this carb does for both power and fuel consumption.

As it happens the 1413 carb is, as stated by Edelbrock, calibrated for performance so I would not have normally considered this as a way to more mpg. However in discussing this with DV he explained that his tests years ago when Edelbrock first came out with this carb is that he had seen some promising though hardly world shattering results with this style of carb. It seemed that he was able to get the light to relatively wide open part throttle mixture such as to give good economy without measurably impeding the carbs ability to produce pretty decent output.

But things have moved on considerably since then and all this sounded like it was worth a try as swapping out a carb is a relatively quick undertaking. From my point of view I needed more power to pull that big load but like every racer I want it all and that meant extra fuel economy would also be very welcome.



Before getting into results let me say that my 1987 motor home’s 454, with only 39,000 miles on it, is in near pristine condition. The carb, a Q-Jet, is not perfect as wear and time have taken a toll but it is far from being worn out. The situation is that I will be replacing a respectably sound carb for a brand new one.

OK now for some results. First economy. On the Q-Jet the mileage, without the trailer was right on 5 mpg. You can figure that to be right within 0.2 mpg. After the swap to the Edelbrock carb (out of the box – no tuning) the mileage went to 7 mpg – again the figure can be trusted to within 0.2 mpg. When towing the mileage on the Q-Jet was 4.5 mpg. This climbed to 5.5 mpg on the Edelbrock.
What we have here, allowing our test error of 0.2 mpg is an improvement of between 30 and 40%! Towing mileage showed an improvement of between 13 and 22%.

I would typically sell this carb out of my shop at about $390. A quick calculation shows that with the present fuel costs (and you know it will go up) I would, assuming a conservative 15% improvement in mileage (instead of the near 20% I am actually seeing), get my money back on this carb in just 3500 miles. Over the course of 20,000 miles I will have saved better than $1800 and that is assuming no further increase in fuel costs (as of June 2008) – and you know how likely that is to happen!

So as you might suppose, I am really pleased with the mileage improvement. It is far better than either I or Tech Ed Vizard thought we would see and that cautioned against either of us making a carte-blanch statement. What I am able to say is that these carbs certainly work well but the results you get could be different to a measurable extent depending on application and your driving habits.

But how about power? Now if you think I am going to load this motor home up on a chassis dyno then think again. I figured that since I drive race cars I would have a good feel for the way this 6 ton motor home performed. This is especially so since I drive over the same roads to each of the tracks so I know just how much pedal I am giving this old lady on any particular grade. As things turned out the difference in power was so obvious that it took no skill on my part to realize it to be so. I am going to stick out my neck here and say for sure there was at least a 15% increase in torque in the rpm range I use. Overnight, towing a 12,000 lb trailer with a 12,000 motor home got to be a whole a lot more fun!

As good as all this sounds I don’t want to stick my professional neck out any further than I am comfortable with. I am confident the numbers I am using here are correct within the tolerance mentioned earlier. Although this 454's existing Q-Jet looked to be in more than reasonable condition there just might have been a minor calibration issue that influenced results. Although I think the Q-Jet carb was, in reality, reasonably well calibrated that possibility should be kept in mind. With that caution in mind I am confident that this Edelbrock Carb, used in the fashion I did here, does offer the end user the potential for much better mileage and power.

If power is not so much of an issue Edelbrock does have carbs in the 750 cfm down to about 500 cfm that are calibrated specifically for mileage. Go to their web site and check them out.

As far as results go on my motor home I have to say that when it comes to Edelbrock carbs I have a new found confidence in their capability.

Tony Brown
Atlantic Racing.

[MAP]

Greetings Tony,

Interesting review - thanks very much. Since about six months ago, Mr. Vizard promised that this was coming, so I looked forward to it quite eagerly (see the "34:1 Afr?!" thread.) I'm looking for a cost-effective fuel delivery system for my 383 SBC, that I'm redesigning for a big improvement in economy, with a minimal loss of power.

This carburetor might work well, but I wonder whether the context of your evaluation holds much generality for other applications. Here's what I'm most concerned about: at 5-7-ish mpg, and with anything even remotely like a 14:1 AFR, you must be operating your carburetor with significant throttle opening, where the idle circuit might not be making a significant contribution to overall carburetor function.

I'm aiming for 25-ish mpg at 60mph on a flat surface with no surface wind, where I believe I'll be operating the carburetor mostly off of its idle circuit. It's this range of operation that concerns me, namely, the quality of fuel atomization here, and transient behavior based on the efficacy of the pump shot, in combination with an unusually lean steady-state off-idle AFR.

As such, to put it very crudely, I suspect you're using mostly 2/3 of the range of operation of your carburetor, whereas I'd be using 3/3, with an emphasis for economy on the 1/3 that you're not using. (Please correct me if I'm wrong about that, since I'm by no means trying to minimize your claims! You did, after all, begin the review with the qualification that it was preliminary.)

Do you have further insights in this regard?

Thank you,
Mark

[Tony Brown]

Considering this motorhome probably has a rear gear ratio of 4.10, and uses a 400 Turbo (of course with a 1:1 final gear), you are absolutely correct that I am rarely using the 1/3rd of the carb's functions that include much to do with the idle circuits. With that said I believe you are also correct that my testing does not hold any generality other than in towing circumstances. By the change in "responsiveness" over the Q-jet, I would bet the performance of the Edlebrock would be plenty for your 383 project. With the parameters of no wind, flat surface, 60 mph, etc., it would be hard for me to predict how this Edlebrock would compare with other Edlebrock types, or with other options altogether. I would suspect that final drive ratio including "most" proper transmission and gear ratio, along with tire diameter is going to have the most to do with your 25 mpg goal. I would bet that an overdrive trans is in your plans. Of course, with the type of final gearing required to get to this goal you may have to sacrifice a little on the performance end. BUT, that leads me right back to the purpose of the motorhome experiment. In this case, (pulling a substantial load), better performance led to better economy for the age old obvious fact that it was easier for the motorhome to pull itself and its load with the Edlebrock over the factory Q-jet, which led to better fuel mileage due to less of a struggle. Keep us all informed on your project. Maybe David has more insight on this.

Thanks,
Tony Brown

[MAP]

Greetings Tony,

I don't want to dominate the discussion here, so if I should posting instead under the "Engine Technology" forum, then please affect this, or let me know that I should transition there, and I will gladly do so.

My plans for 25mpg with a 383 SBC in a 1978 Chevrolet Malibu:
1.) Much lower front ride height, and extended forward bumper, to improve aerodynamics on what is admittedly something only slightly more curvaceous than a brick.
2.) 200R4 OD lock-up auto trans - you were quite right.
3.) 2.73:1 or 2.93:1 rear ratio vs. 3.42:1 now.
4.) Much shorter, but higher-lift, hydraulic roller cam than currently.
5.) As lean a cruising A/F as I can tolerate.

David says if the car is too slow after all this, then add nitrous!
Another aspect to your article: you compared the Edelbrock unit with the Q-jet. Why did you pick this particular carburetor, and not some other? And, if the Edelbrock is calibrated for performance, what might happen if you tailored the metering rods for an unusually lean A/F at cruise, while preserving the existing enrichment under WOT, which is to say, make the taper on the rods more pronounced? (This is apart from tinkering with the idle circuit, of course.)

Thank you,
Mark

[Tony Brown]

Over the years, I have sold many Edelbrock 1406 carbs and they have proven themselves to be very reliable, maintenance free and relatively lean calibrated compared to the traditional Holley. So, when David Vizard mentioned the Edelbrock test, I had plenty of confidence in their products already. Leaning the mixture at cruise would definitely help the mileage issue (in my opinion) on a non-towing application. As far as the motorhome experiment goes, I am unsure if the probable loss of power (although most likely slight) would hamper its ability to pull the amount of weight I am dealing with. Of course, a lot of towing mileage will always depend on "creative" driving (hitting the hills at the best speeds that the law will possibly allow) to help stay out of the near wide open throttle portion of the carb. In your case, I would try the 1406 out of the box and calibrate as necessary. Let us know if you end up needing the bottle to help with the performance.

[bigseth]

I'm running a 383 with a performer rpm and a 750 quick fuel double pumper. With a t-5 tranny and 2:73 gears, along with a lot of carb and vacuum advance tuning I'm getting around 24mpg on the highway at 65 mph 1800 rpms or so. Now my average around town and daily interstate commute of 60 miles Im getting on average 20-21 mpg, but that can go way down if I put my foot into it, which I am often temped to do. I am actually thinking of going to an 850dp and I don't really expect my mileage to drop off very much either. The biggest improvement I made as far as mileage is concerned was dialing in my vacuum advance. I was averaging about 21 mpg the highway and tuning on that vacuum advance brought it to 24 and greatly increased performance while cruising at low rpms in 5th gear and it idles tons better. Thats just my $.02 on this.

Seth