I was under the impression the stock carb on these engines is crap, the 670 is only 20 cfm larger, ive been told that a good 600 cfm carb is better than the stock one.

 

Actually it is 70 CFM larger. A stock carb is an Holley built emissions 600 CFM carb. Replacing it with a standard 600 improves things.

 

Lot's of great info, here. Thanks especially to Brad Johnson for the detailed and well-thought out (and well-researched) cam suggestions.

 

As for gas mileage the 4180 600 CFM STOCK CARB, is alittle better on gas mileage, than a replacement 4160 600 CFM out of the box. One reason the 4180 has a 2 stage power valve and a few internal things that were for gas mileage.

 

Just swap the dual stage power valve into the new carb. Then you will be ahead because with the 4160 or even a 4150 you has infinite idle mixture adjustment where on the 4180 you are extremely limited to a lean conition.

 

Just out of curiosity, how accurate are Desktop Dyno estimates usually? The only reason I ask is, the claims Edelbrock makes for their performer cam/intake package are nowhere near those numbers.

I've got a set of headers (1 3/4" I believe, not certain though), dual 2 1/4" exhaust, and a Holley 750 in the truck now. Could I realistically expect numbers like those by swapping in one of the cams you mentioned?

Thanks,
Richard

 

Only as accurate as the input info, especially head flow numbers. Given good info it usually comes within a few percent. However... remember that it's still a sim, and presumes sea-level altitude and a perfect tune. Also, it's crank HP. You have to deduct for driveline losses to get wheel HP.

Also remember that the sim for this thread presumes stock heads. The Edelbrock packages are usually quoted using their aftermarket heads (which aren't bad, by the way). The late 60's factory 429 and 460 specs hovered around 350-360 HP and 450-475 lb-ft torque. You should be able to at least duplicate that, and possibly improve on it, with some specific bolt-ons and careful tuning.

Brad

 

Come to think of it they changed the heads a couple times in the eighties, this engine is older, and has D3VE heads, will this change things at all, or are the numbers still similar.

 

Does that mileage ever sound familiar!! Differences being 4X2, professionally rebuilt 4180 carb and, with the exception of low restriction exhaust and recurved distributor, it's all stock. My old trailer ran ~7,000#. The new(er) one is closer to 9,000#; a little longer, a little higher but I really don't notice a difference in mileage so far.

I'm toying with the idea of changing over to 4.10's since most of my mileage is towing. If it wasn't such a hassle I'd like to try 3.73's first but might as well go all the way if I'm going to do it. I've even been told I might pick up a little mileage with the stouter gears because the engine wouldn't be working as hard to do the same job.

Brad Thanks for the input. You've laid out a plan I'd really like to follow when the $$$ are available ... provided we can afford to even drive these things in the future

Lead_Foot Interesting that you're thinking about getting out of 4.10's and I'm looking to go into them for the same reason ...

Roger

Clyde S Dale, my chestnut brown & tan 5th wheel workhorse is a
1984 F250HD XLT RCLB 4X2 8600 GVW
460 C6 3.55's
68,500 original miles (and counting)

 

I never mentioned a gear change, im happy with my gearing, if i go larger tires i'll go an even lower gear, probably 35's with 4.56 gears.

EDIT my gas mileage is better than i thought, although i still dont know what it is under normal conditions because my mom has been driving my truck for two months, but towing a 6k lb trailer, including stump pulling, and crawling up a few miles in 4L i got 9.5 MPG, im fairly happy with it the way it is.

 

I stand corrected. It was Bear who mentioned the gear change as a way to lower the rpm.

Roger