Author Topic: Poor Mileage (Read 7571 times)

Gewehr43 · « **on:** Mar 17, 2005, 12:33:30 PM »

I have an '82 Toyota 4x4. Last summer I had the engine rebuilt. It now has a Downey header, Competition Cam, LC Engineering Adjustable cam gear and I also have a NWOR 2 1/4" Exhaust system. I had a Custom High flow cat installed because my basically fell apart. My stock carburator was also rebuilt. It used to get around 20mpg. It now gets around 14. Would restricting my exhaust help any? I have heard that that much exhaust flow is what is killing the mileage.

CTENG in KS · « **Reply #1 on:** Mar 17, 2005, 01:50:09 PM »

Gas mileage was 20 after all the engine mods?? or before. If you were getting it after the engine mods then changing the exhaust isn't gonna fix your problem. ZIf it is a before and after deal then, this is what happens when you add things like more intake duration...your engine uses more gas...unfortunatly the law of conservation of energy says if you want more power out of your engine you gonna hafta burn some more gas...assuming something hasn't become gunked up and drastically changed the efficiency of your engine.

Boy am I rambling...

BigMike · « **Reply #2 on:** Mar 17, 2005, 06:39:50 PM »

I was thinking the same thing, 20 mpg from a carb engine with those mods, specifically the cam, seems very high.

14 is actually about the norm for a modified carb 22R. I doubt it's the restrictive nature of your exhaust system, which in my opinion, could be a 2.5" for that size engine. Question: Is your muffler a rat trap design (like a flowmaster) or is it a straight through design (like a Dynomax / Magnaflow)?

One thing that's nice and in your power to try is to change your cam timing. Single cams are a-whole-nother bread with cam timing as compared to twin cams, but try to decrease the valve to piston overlapping if possible. With twin cams you can decrease or increase valve to valve overlap by changing the timing of each cam, but on a single cam, the valve to valve overlap is predetermined by the grind on the cam itself, and it's not adjustable. But what you are still able to do is change the relationship of the valves to the strokes..

Try to get the exhaust valves closing sooner before the intake stroke comes. You can do this by advancing your cam timing. However this will also cause your intake valves to open up sooner on the intake stroke, which may defeat the whole purpose, which would be to decrease the amount of time that the exhaust stroke and intake stroke, with relation to the cam timing, is open at the same time allowing incoming intake charges to escape with the departing exhaust gasses.

Again, Im not sure how much of an affect this will make on a single cam engine, but its worth a try. Retard your cam by 5 degrees and then reset your ignition timing. Then drive around for a couple of tanks and compare the mileage. Then try it in the other direction, advance your cam 10 degrees (from -5 retarded) so that the cam is then +5 degrees advanced from the initial starting point (aka today), and do the same method to gather data and compute your gas mileage.

See what happens, always worth it to tune for perfection

BigMike

79coyotefrg · « **Reply #3 on:** Mar 17, 2005, 06:56:38 PM »

Then try it in the other direction, advance your cam 10 degrees (from -5 retarded) so that the cam is then +5 degrees advanced from the initial starting point

whats the lift , duration and centerline on that cam
on my hrbrid, .460, 280, (240@.050 lift) , 102 intake 118 exhaust

Uncle Jesse · « **Reply #4 on:** Mar 19, 2005, 12:01:02 PM »

Keep in mind that all those mods make you want to step on the throttle more. Especially the muffler- you want to hear that throaty sound. Pay attention to how you drive the truck now, that might help you a bit.

kneedownnate · « **Reply #5 on:** Mar 19, 2005, 01:40:10 PM »

Whoever told you that you'd get better mileage with a more restrictive exhaust is a moron. The more back pressure you have the harder the engine has to work to push the truck, the more open and free flowing it is the easier it is on the engine, hence the better you mileage will be. And like BigMike said, with your setup I'd be running a very free flowing 2.5" exhaust. Don't listen to nwor on their theory of bigger exhaust hurting performance, this is simply not true, ask me how I know! I'm with everybody else on the mods, with all that you did I think 14 mpg is pretty good, my 80 usually gets around 15 with very minimal mods.

Hyena · « **Reply #6 on:** Mar 19, 2005, 02:49:52 PM »

My 84 was getting around 16 with no engine mods, just lift and tires. Don't know what i am getting now. i want to get a bigger exhaust becasue mine sounds like

now.

79coyotefrg · « **Reply #7 on:** Mar 19, 2005, 03:30:44 PM »

Hyena will you PPLLLEEEEEAAAAAASSSSSSSEEEEEEEEE put your other avitar back up

79coyotefrg · « **Reply #8 on:** Mar 19, 2005, 03:31:53 PM »

or better yet email me the full size version

79coyotefrg · « **Reply #9 on:** Mar 19, 2005, 03:34:51 PM »

ok back on topic, befor my truck killed over dead, i was getting 15 mpg running 75 on the interstate 50 mile commute with a 4 spd so i was always turning around 3800-4000 rpm and considering i could jump to 90 in a heart beat i was happy with 15 mpg

Yota4life · « **Reply #10 on:** Mar 19, 2005, 10:40:03 PM »

i got 2 1/4 with flowmaster 40... Sounds sick

lilbuddy · « **Reply #11 on:** Mar 19, 2005, 10:46:05 PM »

Quote from: Yota4life on Mar 19, 2005, 10:40:03 PM

i got 2 1/4 with flowmaster 40... Sounds sick

Me too. I have a header and a highflow cat also. I have 37's and 5.29s in it. When i had 38s, id run around town at 8 psi (some of you are gonna say im crazy but with my richard Cepek FC-Kevlars, anything above 12psi would make them bubble) i was only getting like 12 MPG. I got my new tires, put in 91 octane gas, cleaned airfilter, changed fuel filter and did something else, now im getting 18.5MPG. Not too bad IMO.

toybuilt · « **Reply #12 on:** Mar 19, 2005, 10:52:20 PM »

I have a 83 yota with a 22r in it with some mods and it gets around 14mpg

kneedownnate · « **Reply #13 on:** Mar 19, 2005, 11:52:22 PM »

Quote from: Yota4life on Mar 19, 2005, 10:40:03 PM

i got 2 1/4 with flowmaster 40... Sounds sick

Man, you could probably take it to the exhaust doctor and get it fixed. Is it a cough, a wheeze, or a cought with a wheeze? Nurse, I'm gonna need 80ccs of magnaflow, STAT!!!

79coyotefrg · « **Reply #14 on:** Mar 20, 2005, 08:06:41 AM »

toybuilt · « **Reply #15 on:** Mar 20, 2005, 03:54:30 PM »

$Beer Chug\'n$

yotaboy79 · « **Reply #16 on:** Mar 20, 2005, 08:16:24 PM »

ive got a 79 toy 20r headman header no cat and 2.25 with a flowy and with the 31in tires it got around 10-12.5 mpg depending on how much i got into it i dunno what its gunna get now with the 33in tires i havent got a chance to drive it yet im wating on a draglink that was also when the exauset was half assed a rusted out header and the tail pipe exiting at the back side of the cab now its done right with a new header and a full exaust

donkeykong · « **Reply #17 on:** Mar 21, 2005, 10:42:47 AM »

Join the crowd... I get about 13.5mpg. But I have a 22r/20r hybrid, with headers 2.5'' exhuast, 5'' of lift and 35 running 4.88's in the pumkin.

79coyotefrg · « **Reply #18 on:** Mar 21, 2005, 02:41:51 PM »

Quote from: yotaboy79 on Mar 20, 2005, 08:16:24 PM

ive got a 79 toy 20r headman header no cat and 2.25 with a flowy and with the 31in tires it got around 10-12.5 mpg depending on how much i got into it i dunno what its gunna get now with the 33in tires i havent got a chance to drive it yet im wating on a draglink that was also when the exauset was half assed a rusted out header and the tail pipe exiting at the back side of the cab now its done right with a new header and a full exaust

do you still have the 4.37 gears in that 79

or was yours one of the lucky ones that got the 3.90's

yotaboy79 · « **Reply #19 on:** Mar 21, 2005, 07:38:32 PM »

4.37's and a 4spd im driving it to work tomarow so ill let ya know what mialage it gets with the 33s and all the new goodies its still got the 4.37 gears and the 4 speed but i think the 33s will help alot! i took it out for a test drive and at 55 im doing 3k instead of 3700 rpms

Gewehr43 · « **Reply #20 on:** Mar 22, 2005, 10:12:54 PM »

Thanks for all the advice. Another Q. How many miles does it typically take to break a 22R in?
Check out this pic of the engine before I had it assembled!

BigMike · « **Reply #21 on:** Mar 23, 2005, 10:10:00 AM »

some ppl say to just drive a new engine like it wasn't, but I always wait until 1500 before I start climbing up on the revs and about 3000 is when i call it good.

toybuilt · « **Reply #22 on:** Mar 24, 2005, 09:05:30 AM »

One of my buds just has his engine hoped up and the guy tould him to go easy on it for 500 miles

firekiller · « **Reply #23 on:** Mar 25, 2005, 06:49:34 PM »

I've always used the 500 mark, changed the oil, run the valves , then give it hell. Once again my

Tico
$Beer Chug\'n$

brainlessfool · « **Reply #24 on:** Mar 25, 2005, 06:51:59 PM »

Well I'm of the other mind. If it won't stand up to it when its new, when will it? that taking of coures that it was put together right.

kyle_22r · « **Reply #25 on:** Mar 25, 2005, 09:39:09 PM »

i went easy on it for the first 500 miles or so, then i've driven like normal. i've been getting close to 20mpg lately. i did a little better on my 20R sometimes, but i think it was because my weber adapter had a huge vacuum leak and the engine always ran super lean(spark plugs were fried when i pulled the engine)

Gewehr43 · « **Reply #26 on:** Mar 28, 2005, 02:34:43 PM »

What should I do toy achieve better mileage? Fuel injection conversion or opt for a weber? I really want to get about 18-20. I am only riunning 30" tires. I plan on lifting and afraid the mileage will take a nose dive.

brainlessfool · « **Reply #27 on:** Mar 28, 2005, 08:31:18 PM »

maybe I missed it but, what gears does ya have? how big is your cam? and when your carb. was "overhauled" was the float set right?
and is your ing. timimg on? on what?

m44offroad · « **Reply #28 on:** Mar 30, 2005, 03:50:55 PM »

your gearing has alot to do with the mileage. we where talking about this in class today and the instructor was saying that the 22r needed the low gearing just to move but the gearing also causes the mileage to go down and it is normal to have that kind of mileage. another idea gewehr43 is to quit driving your 700 pound girlfriend around town in your truck

Gewehr43 [OP]

Gewehr43 [OP]

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