mileage motors

[streetstar]

Kind of a funny topic under other circumstances, but this is a forum board full of people with 10 mpg vehicles. I like to drive my truck more than let it sit, and was wondering if any of you remember if the 305 Chevy motors from the mid '80's had any special cam grinds or anything that helped them get decent mileage. My '84 with an OD tranny got 18-19 bone stock back when i was in high school (late 80's) ---- My '06 F150 doesnt even get that good.

Anyway -- what tricks do i need to know to build a replica of my '84 setup for a '75 C10? I have a stock 305 motor from that era, but i suspect most of the efficiency came from the overdrive tranny, which i am willing to pony up for, but i am wondering if i need to use any special cam profiles or torque converters or anything.
(i will be pissed if i spend $1500 and take 100 hp's away from my truck to go from 10 mpg to , 12 or 13)

[Omnivec]

I don't know much on the cam grinds, but gm like to use swirl port heads on there low end 305s to help mix air and gas.

[GREASEMONKEY72]

tighter compression and smaller cubes would be my guess

[rwgregory]

Try an Isky "Mile-a-Mor" cam. I have personally never used one, but I have heard good things about them. Good performance and better fuel mileage, hmmm, what a concept...

[combustion]

Originally Posted by rwgregory

Try an Isky "Mile-a-Mor" cam. I have personally never used one, but I have heard good things about them. Good performance and better fuel mileage, hmmm, what a concept...

its called varible valve timing

lol

=P

[Longhorn Man]

just get a bigger motor.
I have a way outta tune 425 big block (worn thirtey over) with a non overdrive and 4.10 gears, and I get 12.5 on the freeway at 70.

[mrein3]

Originally Posted by Longhorn Man

just get a bigger motor.
I have a way outta tune 425 big block (worn thirtey over) with a non overdrive and 4.10 gears, and I get 12.5 on the freeway at 70.

The real beauty of a big block - other than gobs of torque - is that if you're geting 12.5 on the freeway now, you'll get 12.5 with a head wind. Also with a tail wind. Also towing a boat or trailer full of toys.

If you're getting 10 mpg now, don't expect anything better than 13 with an overdrive. Typical OD ratios are .7:1 verses the 1:1 with non-overdrive.
(For the math challenged that is a 30% better ratio in OD, 30% of 10mpg is 3mpg, 10+3= 13mpg)
However you won't see EXACTLY 30% because until you get to overdrive and the torque converter locks up, you're still slipping away some mileage in the coverter.

If you are sitting at 10mpg now, you may want to tune it up good. Set the carb right. Leave the engine you got. Install the OD.

You may want to get a tach before you go OD. Some folks with 308 rear end gears have found a LOSS of gas mileage with an OD tranny. You can get too LOW of an RPM on the highway and actually hurt your mileage.

[streetstar]

If you are sitting at 10mpg now, you may want to tune it up good. Set the carb right. Leave the engine you got. Install the OD.

.[/QUOTE]


I probably would leave it alone and suffer at the pumps, but the current 350 in the truck is locked up, --- the 305 is doing nothing and would be a cheap swap for a semi-daily driver. But as i said in an earlier post -- i sure hate to lose hp's unless i gained some mpg's somehow.

Besides, my 75 is a driver, i have a 496 thats "set to kill" in my '69 for when i want to go fast in a straight line.

[GREASEMONKEY72]

Originally Posted by Longhorn Man

just get a bigger motor.
I have a way outta tune 425 big block (worn thirtey over) with a non overdrive and 4.10 gears, and I get 12.5 on the freeway at 70.

i though you had a 500?

[streetstar]

Thanks for the responses --- the 305 i have is a low mileage motor - (45,000) and i have replaced the gaskets and valve seals to prepare it for use again. I will look into that Isky cam -- sounds like what i need. I was attempting a mild performance re-build on the motor a year ago, but lost interest in the 305, but i am more than willing to yank the lumpy cam i installed under the circumstances. The stock intake is long gone, but i have an aluminum one from a mid 70's corvette i can use if i can dig up a Quadra jet. (current intake sitting on the engine is a Performer RPM- which i am also willing to shelve in favor of a more fuel efficient engine if i have to)

The current engine in the truck uses an Edelbrock carb, but i was wondering if the '84 Q-jet could be re-built to be used in a non computer controlled vehicle?

I assume the transmission in my recipient vehicle is a basically stock TH350. Does anyone know what difference a lockup vs. non-lockup converter would make as well with a mildly tuned 305?

Lot of questions - i know

[68K20 x Drill]

Lockup TC will make a difference, more difference with higher stalling convertors.
A 2bbl carb can help, but TBI would probably be better. Overdrive will make more difference than either. Hang one of those plastic craps under the front bumper, fold mirrors in at speed. Install a vacuum guage so you can tune and drive for the highest vac reading at criuse. i once gave my friends 82? Sub 3MPG by hooking up the smog system...The 5 port valve in the thermostat housing, don't bother with the AIR unless you need it to pass inspection. YMMV

[Longhorn Man]

a 2bbl would kill the MPG on a truck/car with a carefull driver.

[mnunn454]

Since we're all tossing in opinions, if I were in your shoes, here's how I'd go about seeking higher MPG.

1) measure tire diameter and ring and pinion to determine drive ratio with two different trannies (1:1 TH350 and a 0.7:1 TH200 or TH700). Choose the driveline option that comes the closest to letting your engine spin about 2000 revs at 65-70 MPH.

2) If the above can be done with a TH350, make sure get one with a lock up converter (TH350C). The TH200/700s come with lockup.

3) Use a stock converter or one made for an RV. Not a high stall.

4) Choose a cam grind that has a lot of LSA (Lobe Separation Angle) to minimize valve overlap. Ideally one that's been prescribed for your application. Talk to the experts.

5) Choose your headers carefully. For the stock 305 you'll want very long and relatively small diameter (about 1-1/2") primary tubes for best torque.

6) Make sure you use an MSD box in conjunction with your HEI distrib. Below 3000 RPMs, it sparks multiple times and burns the fuel more efficiently.

7) Install an O2 sensor and A/F meter and jet the primaries on your carb for 14.7:1 A/F ratio while cruising at highway speeds.

8) if bucks are still available, use an Edelbrock "Performer" or similar high torque/low RPM dual plane aluminum manifold.

9) If there's still more of that green candy in your pockets, find out which heads you have now and consider upgrading them to ones that'll yield about 9.5:1 one compression ratio.

Of course, all this assume emissions requirements aren't an issue. If they are, then it'll require a different choice of emissions legal parts, but the strategy is still the same.

Hope it helps.

[streetstar]

Cool --

thanks for the replies --

Cashflow isnt that much of an issue to an extent (lets call it a grand for the project-more or less)---- but if i had unlimited resources, i would just have a shop swap in a newer vette or z28 efi motor and tranny combo and be done with it.


As for exhaust, i was just gonna use rams horns for appearance issues - i have a set of long skinny flow-techs, but don't relish the idea of how fugly they look after 6 months and ceramic coating them is out of the question

[Longhorn Man]

it was makin death noises, so it came out. This was back in march

[GREASEMONKEY72]

Originally Posted by Longhorn Man

it was makin death noises, so it came out. This was back in march

ah ok, any difference between the 500 and the 425?



retselgerg - 511.000 miles, man thats alot of miles

[Longhorn Man]

Originally Posted by GREASEMONKEY72

ah ok, any difference between the 500 and the 425?



retselgerg - 511.000 miles, man thats alot of miles

yeah, about 75 cubes!

Well, neither engine was really all that sound. So I *try* to resist from getting into it too much. I have noticed a slight decrease in torque, but I'm not sure if it's the junk engine, the crappy carb, or what. i wanted to get the 500 rebuilt, but the sticker shock tossed the engine off the tailgate into the scrap yard. Got a whopping 45 bucks out of it. I'l probably gonna go look at a couple deralict caddys I've noticed around town, maybe one will actually run good and be cheap. Who knows.

[GREASEMONKEY72]

Originally Posted by Longhorn Man

yeah, about 75 cubes!

smartass

[Brad]

Anyone check out the current issue of Camaro Performers? There's an article about how to add 150hp to the 305. There key component was the use of EngineQuest Lightning cyclinder heads milled .030 along with an Edelbrock Performer AirGap intake and a Barry Grant 650 carb. They made 372hp at 6100rpm. Pretty interesting read and I'd totally do it if I had a 305!

[Brad]

Hey Andy, you can always get a 6!

[cameeks]

I'm getting a TPI kit from First Fuel Injection

[Longhorn Man]

I've driven many 6 cylinder trucks, and there was only one that I think I would be happy with, but the turbo and intercooler alone are worth more than everything I own.

[Tmiller]

I wish i had the pecs but I know my cousin whom i go to the drags with gets 23 mpg on the highway, and this is a stout 480hp 350 chevy. I know he's running a 700r4, 10.5:1 comp, a 750 holley and some 5.13 gears. I'd find it hard to believe but my gas guzzlin 11mpg big block will suck a tankfull to get to the stip but his only use a half. I'm sure theres alot to do with tunning because he can sure tune the hell outta that thing.

[mnunn454]

Originally Posted by Tmiller

I wish i had the pecs but I know my cousin whom i go to the drags with gets 23 mpg on the highway, and this is a stout 480hp 350 chevy. I know he's running a 700r4, 10.5:1 comp, a 750 holley and some 5.13 gears. I'd find it hard to believe but my gas guzzlin 11mpg big block will suck a tankfull to get to the stip but his only use a half. I'm sure theres alot to do with tunning because he can sure tune the hell outta that thing.

It's mostly in adjusting the air fuel ratio to be stingy with gas when you don't need it without compromising too much driveability. 5.13 rear gears with a locked up 700R4 means he's running a drive ratio in the 3.6 range. Couple that with tall tires, and you're right in the sweet spot for a 350 SBC to get decent mileage. Still, 480 HP (all on gas I assume) AND 23 MPG is really impressive and getting close to perfection, I think.

Slowing the engine revs down, opening up the exhaust, raising the compression some, tuning the a/f ratio to average about 14.7:1 on the highway should go a long way toward reaching your goals. I'd think a 25% to 30% improvement isn't unreasonable for our trucks.

[Pyrotechnic]

Use a QuadraJet. I know they are a little strange to work on, but once rebuilt and tuned properly those small primaries will get you great gas mileage. When you need to pass someone or have a little fun, you have those huge secondaries.

I think a 3.08 gear out back was the standard option in the 80's as well.