Hot Rod Forum : Hotrodders Bulletin Board - Reply to Topic
Hotrodders.com -- Hot Rod Forum



Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Transmission - Rearend> Poor fuel mileage
User Name
Password
lost password?   |   register now

Thread: Poor fuel mileage Reply to Thread
Title:
  
Message:
Trackback:
Send Trackbacks to (Separate multiple URLs with spaces) :

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Additional Options
Miscellaneous Options

Topic Review (Newest First)
11-06-2004 09:51 PM
87442lover GM's answer to this problem was the TH-200's, TH-200C's, 4R's, and TH-350C's Try getting either a lockup TH-350C rebuilt for yourself for a decent highway boost in performance and fuel mileage. If your not happy with that than go down to a 200-4R. Lock up trans, overdrive, and you wont be wasting power like with a 350 or 400.

Check out DRW's website for more info on the 200 series.
http://www.drwtransmission.com/
11-06-2004 07:37 PM
Pantload
I feel your pain

I just bought a junker mid-eighties Camaro that has the same problem. The previous owner let me have it real cheap because he couldn't get it to run worth a darn. The person he bought it from went to the hot rod store and put one of every single thing in that store on the car. I bought it because it has a fresh engine with all kinds of internal goodies, I figured I can sort out the rest.

The thing was getting the mileage of a top fuel dragster, until yesterday. Here are the problems (see how many match your setup).

1. Square bore Edelbrock carb. Mine isn't a 750 cfm, but it would run a lot worse if it were. Since the things are adjustable, that means you have to adjust it, properly, or it will run like doggie doo. I had to re-jet the thing to run leaner on the primaries and a lot richer on the secondaries. Made a big difference. Next thing I'm going to do is put a Quadrajet on it. Better mileage, much better street performance, and just as much horsepower, on every one I've ever had. The Edelbrock is pretty, so maybe it'll bring a good price on Ebay.

2. Cam. Loping idle, doggy acceleration below 3,000 RPM. I don't know what cam mine has (still haven't gotten the info from the original builder yet) but I thought at first it must be way overdone. But that wasn't the case. If the idle is loping badly, you have two things happening, most likely. Timing (I'll get to that in a minute), and idle adjustment. You will have to advance the base timing to smooth things out some, then adjust the idle mixture and idle speed. If you get the combination of too lean idle mixture, to wide throttle opening, and too retarded timing, the thing will lope and gallop and sound great, but it won't run worth a darn. This is because the vacuum falls off, and the carb enrichment circuits think you are trying to accelerate, so the metering rods pull out and let gas through. The result, you are not running on the idle cicruits at all. The thing lopes because it is chugging gas. So, advance the timing, get the vacuum up a little, then adjust the idle properly. It might get you through until you can get yourself a nice Quadrajet (or at least a 600 CFM something-or-other, if you must).

3. Timing. Mine has a gorgeous top-of-the-line MSD system on it, complete with the box, rev limiter, coil, and billet distributor (pretty wires, too). The guy paid over $600 for all of it. And it didn't help it run any better. The guys at the speed shop probably ought to be shot for selling anyone a distrubutor without vacuum advance on it for street use. First, I recurved it. (meaning lots more advance, sooner). That in conjunction with the jetting on the carb made the thing develop power for the first time since it was rebuilt several years ago (tee hee). Lots of power! It still chawed gas like a hungry dog, though. So, since there is no vacuum advance on it, I ended up running the base timing way up there, off the scale, to a point I never would have tried on a stock setup. Still no pinging or detonation, but the idle smoothed out, the pep came back at low rpm, and now it sips gas. This car WILL get a vacuum advance distributor, before it gets the Quadrajet, so that I can set the timing up properly, don't want any holes burnt through the pistons, right?

Bottom line; that carb might be too big to get tuned properly, but you can almost count on it not being jetted properly. If you set up the timing and jetting, you should be able to make it drive around town without drinking up your paycheck. You might have to advance the timing far enough that you can't floor it because of knocking, if that happens, you need to swap out that carb. If the distributor is a pretty aftermarket one, it is probably curved wrong, get the kit and set it up for 35 degrees at 3000 to 3500 RPM, as a starting point. And if it doesn't have a vacuum advance, it will never get very good mileage or throttle response. You can reach a compromise, like I have going on now, but the vacuum advance was a pretty well engineered feature, in my opinion.

Yep, you got something that is all adjustable, now you have to adjust everything.

Once the thing runs right, then you can decide whether overdrive will help.

I came upon this forum looking for information because this car I bought, they completely jacked the transmission around, too. Sorry if my first post here is off topic, guys, and sorry for giving amateur advice (I'm not a professional tuner or anything, hehe), but I found this guy's problem here and so I'm trying to help here.

Good luck with that 327.

Last point -- I've had a few muscle cars in my life, they all outran my buddies' muscle cars, mostly because they put double pumper whatchamajig carbs on, while I kept my Quadrajets. Mine had more pep in normal driving, better mileage, just as much all out power, better cold starts, less flooding, less backfiring, and better reliability. I still laugh about that bogging sound! Anyone wanna buy a nice shiny Edelbrock 1405 with no choke, so I can get a rebuilt Quaddie?
11-02-2004 07:15 PM
ChevelleSS_LS6 Here's what I'd do...
1. park the truck and drive a boring economical car as a daily driver
2. save money
3. get OD tranny, 600 CFM carb, more streetable converter, and a cam designed for torque (a fairly mild cam); the 327 if I'm right is more of a midrange-hi rpm performer. Then, it should get better mpg.

750cfm is wayyy too big for a 327 unless that thing was built to kill.
11-02-2004 01:17 PM
Siggy_Freud Well short of changing the internals it seems the only big increase you'll see is going to be from an overdrive, and/or a MPFI system. Both of which are going to run you 1000+ bucks. You have your answers, its up to you to decide what to do with them.
11-01-2004 09:11 PM
lightemup Not changing the cam because im not gonna take the engine out and apart.
11-01-2004 09:07 PM
poncho62 Sure...if you want to spend the money. Why not go with a more streetable cam, converter....................you will be further ahead for less money.

If you are not worried about the money, don't worry about mileage.
11-01-2004 09:06 PM
Siggy_Freud Yes. Worth a couple of MPG.
11-01-2004 09:04 PM
lightemup Yeah, that is part of it, but also having a 3 speed tranny doesnt help at all either. Don't you think it would be much better with a tranny that had an overdrive.
11-01-2004 09:02 PM
poncho62 OK...that and the hi stall converter (slippage) are probably the reason for the bad mileage.
11-01-2004 09:00 PM
lightemup Its pretty radical....

It would idle in neural, not drive. Every time i came up to a stop light i would have to put it in neutural.
11-01-2004 08:58 PM
poncho62 Even with a fairly radical profile cam, it should still idle.
11-01-2004 08:55 PM
lightemup poncho, it wouldnt idle with the stock stall converter because of the cam. its a 1/2ton

We really dont know much about the engine....it doesnt run very good. We dynoed it and it made 240hp and 260ftlbs@RW. not very impressive at all....

It was very rich so we put new jets and rods in the carb(which is too big, 750). I think that made a difference...but not much.
11-01-2004 04:54 PM
troy-curt Don't add overdrive, replace the transmission with an overdrive transmission.

10 is not bad for a hotrod.

If it has a big cam there is no telling what kind of compression or carb. and jets it has.

Troy
11-01-2004 03:39 PM
poncho62 If it's a 1/2 ton you should be getting better than 10..............3/4 or 1 ton, I could see 10.

Do a tune up, check to see that the choke is opening all the way.............could be a number of things.

The fact that it wouldn't idle tells a lot...............
11-01-2004 02:51 PM
lightemup It only gets 10 on the hw...not throught stoplights. We looked at the overdrive, but thats more than a new transmission. And for the cam.....we prolly will change it if we ever rebuild the engine.
This thread has more than 15 replies. Click here to review the whole thread.

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


All times are GMT -6. The time now is 05:47 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.