Carb spacers. pros/cons

[1970pelle]

I apologize if your saying oh no not again.But with the cost of fuel. We,or I am looking at getting all I can get.There has been some VERY good threads on MPG.Nothing beats a well tuned engine,with new quality parts.Myself just dropping my speed has made a big differance.Anyway looking at carb spacers.Poweraid and Transdapt makes one with claims of improved proformance and MPG.I understand the tunnelram effect that is achieved with the use of a spacer.But is there really any MPG gain??I used one on my Dodge Ram PK(EFI) and noticed a proformance gain,really smoothed the truck out.But no way around it.It was a hog all day long.Loved fuel.Glad its gone.Anybody using a spacer?My Truck 86 SWB 305,4bbl,700R4,2.73 gears,all smog removed,duals with turbo mufflers,3 in K&N,has a/c hardly ever used.2 size over stock tires,open bed.Planning on going with a electric cooling fan set up.Still researching what type.And lowering the truck also.I all so noticed the tread on front bumper air dams.I'm currently not using one.Wouldn't that make a allready flat frontend flatter?Thanks all.Sure enjoy this place.Ken

[LONGHAIR]

While I realize that the 700r4/2.73 gear is a factory thing....that may very well be part of your fuel milage problem. It "sounds" like it would make sense to have the engine RPM as low as possible at highway speeds, but that is not always the case, especially with over-drive transmissions. "Lugging" the engine in an RPM range that is too low requires more throttle as well as the over-drive "searching" for the right gear are the results.
It sounds counter-intuitive, but a lower gear can take care of these problems.

As far as the original question, carb spacers are nearly impossible to judge w/o installing and testing. Height(thickness) and the center configuration can make for different results on the very same engine. Some like the 4-hole and others are better with an open center. Different thicknesses can work different too. Some engines don't show any improvement at all or may even get worse, others have measurable improvments in mileage and seat-of-the-pants driving. Testing on your engine, not your friend's recommendation, is the only way.

[1970pelle]

I don't have an issue with lugging.I simple don't let the truck do it.I'm getting decent milage now 13-14 MPGs on the average.Mostly in town driving.Sure its a crap shot on all the different carb spacers out there with out a lot of testing.But the 2 I mentioned have spent some time testing to make the claims on a marketed product.Just thought someone has been using one.Thanks

[LONGHAIR]

What I am saying is that it is very "individual" as to whether it works for you. Ten guys could use the same thing and love it, yet on your truck, nothing. Or it could work for you and not the next guy.

I would still be willing to bet that a lower gear would help you, but it depends on where you do most of your driving and at what speed. In mostly highway and at higher speeds, like a commuter situation, it might be ok. A full-sized truck is not exactly a commuter vehicle though. In lighter highway (55-65) or when loaded, that high gear (2.73) will cause the transmission to shift around looking for the right gear. This is not great for the trans or mileage. Lower gears help you to accelerate with less throttle and can keep the transmission in over-drive at the oppropriate RPM.

[Pyrotechnic]

Highway gears like 2.73's will DESTROY your city mileage, and could possible hurt highway mileage too.

The entire point of an overdrive transmission is to be able to run a numerically high gear like a 3.73 to multiply torque while accelerating and keep the load of the engine, but at the same time be able to shift into overdrive on the highway and keep RPM's down.

With 2.73's and a 3 speed 1:1 transmission, you are basically in overdrive in 3rd gear already. If you add a overdrive, thats just way too much gear reduction. It might be useful at 150 MPH, but your truck would have taken flight before that speed.

Trust me, with 28" to 30" tall tires, 3.73's gears are the sweet spot for a 700R4. If you are getting 13-14 MPG now, you would probably be up to 16-17 with 3.73's.

[1970pelle]

Most times when driving I'm in a 35 or 45 mph zones.I use drive most of the time.If I'm going any distance I'll use OD.I'm just playing with my truck,if I have to really go anywhere I drive the my car or the wifes mini van.I think I could gain a very small amount back by going back to a 235 75 15 tire.I my try one of the spacer plates.I make a good test pilot.I'm going to install a vacuum gauge and along with my tach I may find a sweet spot.On the truck that is.

[babyJay]

I put one on my DD (a Dodge Ram 250 Van) recently. At the same time though, I switched to all sythetic drive line lubrication. Royal Purple engine oil, sythetic trans flush with Valvoline ATF+4, and Castrol sythetic gear lube in the pumpkin. I gained almost 3 MPG. Not sure if the TB spacer or the syns did the trick. Just my 2 cents.