?'s about cams, mileage, etc...

General engine tech -- Drag Racing to Circle Track

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roadrunner
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Re: ?'s about cams, mileage, etc...

Post by roadrunner »

Truckedup wrote:A lot of discussion about choked up exhaust affecting fuel mileage. Does running down the road at part throttle create that much exhaust volume???
Not in an aerodynamic 3000 pound car, but have a read of what this guy is running, it's a heavy truck with the aerodynamics of a brick...a very big brick.....running through an auto, and a choked up exhaust system, with an efi distributer curve, dual plane intake and has practically no quench or compression, and has a top end cam with a lsa wider than the grand canyon. How does that saying go...."you can't make a silk purse out of a sows ear"...or "you cant polish a turd" but you can roll the turd in glitter by at least freeing up some flow through a half decent exhaust system. Students generally don't have a lot of cash flow so most answers have taken this into consideration. If I were the owner of this combo and had no cash I would rig up a passive water injection system which would allow a better advance curve without running into pre-ignition problems, and just thrash it until it blew a hole in the block. Until that time came I would re-ring the original engine that had more power and got better mileage even though it has horrible blowby and refit it.
At an 800 rpm idle, this thing is a little rougher than I think it should be (at least until I found out that the seat to seat timing was so long). It actually has a slight lope to it.
Surely with a dual plane manifold there shouldn't be any lope present?
All the valves are moving...so no flat lobes
" Flat" lobes generally still lift the valves, just not very high, I would be looking for a tight lobe separation angle cam, around the fore mentioned Vizard specs.
I would also check the distributer for shaft play, vertical play means constantly shifting timing leading to a lopey idle.
Life's too short to not run a supercharger!
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Re: ?'s about cams, mileage, etc...

Post by jeff swisher »

I was in the same boat or close to it as you are.
Mine was a 1984 E150 dry weight 5900lb I jacked it up 3" and rearched the I beams to correct it all.
I ran synthetic wheel grease , synthetic trans fluid (AOD that never used the overdrive) Synthetic oil which was worth 2MPG
And synthetic diferential fluid.

Kept tires inflated to max psi.
I will kid you not.. when I installed the spare tire in front of the grill I gained 2MPG..Removed it and tried all kinds of stuff to get the lost MPG.. did not know it was the tire removal for a while..but when it hit me i stuck the tire back on the front of that big van and got my 2mpg back.

It got 17.6 most of the time..hit high 19's once and this had 3.50 gears.
I built the engine..a 1982 ford carbed 302 +.030 and tried the stock small cam like .376" lift or something really small.
I advanced it 4 and later installed a comp 260H and it made 2mpg better.. which is the MPG i got in the above 17.6.
It got this loaded on lake runs and city highway it also got the same.. was one of those not so picky deals.

My timing was all in my 2300 18 initial and 35 total.. it did not like any more ,,I tried many curves and also tried vacuum and it did not care for it at all.

Heads had the stock valves and i ported them and the intake was cast iron 2V and cast ported ex manifolds.
Big single exhaust.
I ran it at the track and it turned 18.0 in the 1/4 on 87 octane.. I was going to bump up the timing and run the 91 octane I had in my front tank if my buddy beat me in his 1991 Z71 but he ran 18.2...

I hauled some heavy stuff in it..6500lbs of rock a few times.
Wish i had better brakes.

I would do the 260H
Port the heads you have.. but make the intake runners ROUGH
I cruised at 2800-3100 to get that MPG
I wish i had more compression in that build.. my cranking pressure was about the same as yours 160psi.

after 13 years it developed a miss plugs were always white..I tried many carbs and after tweaking them they were all within 1/2 mpg.
I even tried many 4 barrels on an adapter and disconnected the secondaries in trial .. always within 1/2 mpg.

I stuck with a motorcraft 2V carb.
I fell if i had smaller chamber 289 heads my MPG would have been better.

Buddy tried 351 heads on his 302.. it killed the power..I suppose small chamber 1969 351W heads would have been the ticket.
That was a bit before the GT40 stuff.

Hard to beat the MPG of a cast iron intake
I tuned and tuned on my 350 chevy in my 47 dodge truck with aluminum dual plane intake.. many carbs including Qjets tried and many distributor curves.
best MPG was 15's
I installed an iron Qjet intake and MPG now is 18.6.
With a little bit of spirited driving.
That is what was going to replace the 302 when it developed a miss.
But i parted the van out gave the engine and trans to a buddy kept the rear end and a few other parts.
Then got a 97 geo metro off of craigslist for 750 jacked it up 3" and ported the head.. larger tires and i get 36-38mpg

If your timing curve comes in too quick but you like the end result you can always remove weight from the weights.

And with stiffer springs you can add weight to the weights to change the curve...just weld a small bead on one of them, or both ..and you can stagger the springs also.
Taller tires and try to drop the R's down a bit.. or maybe a 3.0 gear
wyrmrider
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Re: ?'s about cams, mileage, etc...

Post by wyrmrider »

had a bent exhaust pipe after backing into a pole in my 54 Ford hurt mileage and overheated if driven hard
Barry Burch
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Re: ?'s about cams, mileage, etc...

Post by Barry Burch »

F-bird88 knows what he's talking about. Take a look at the isky online catalog
on the smallblock mopar recommended cam for a 8.6 to 1 smog motor. vrs the
earler 9.2 motor.
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Re: ?'s about cams, mileage, etc...

Post by justahoby »

jeff swisher wrote:
Kept tires inflated to max psi.
I will kid you not.. when I installed the spare tire in front of the grill I gained 2MPG..Removed it and tried all kinds of stuff to get the lost MPG.. did not know it was the tire removal for a while..but when it hit me i stuck the tire back on the front of that big van and got my 2mpg back.

Some hypermilers build grill blocks as the air is better off going around after being built up, than be turned to drag going through. They usually leave enough for cooling .. Is like 1-2mpg on a geo metro
As I'm approaching 40,I still think I'm 20. What the hell is wrong with me?
wyrmrider
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Re: ?'s about cams, mileage, etc...

Post by wyrmrider »

what Barry said
Isky
on low compression motor 186 or 194 @50 on a 108- gear for 1000-3800
on 9.5 motor either 202 on 112 for 1500-4800
or 202-208 on a 110 for 1800-5000
course these are small lifter diameter cams, older and not to aggressive, but they work with older spring requirements
theory is the same but
you can do better
with a modern cam designed for the .875 Ford lifter
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Re: ?'s about cams, mileage, etc...

Post by Warpspeed »

I would agree with previous comments regarding raising the compression ratio and reducing exhaust back pressure as much as possible.

Don't underestimate changes you can make to the vehicle itself.
Rather a lot also depends on where and how you drive.
is it mainly stop go around the suburbs, or hours spent on the freeway out in dead flat terrain.
Or are you constantly going up and down steep grades, or carrying heavy loads ?
Aerodynamics, tire choice, and overall gearing may or may not make a significant difference, but you will never know until you try changing a few things.
On a heavy underpowered vehicle only driven from stop light to stop light in the suburbs, shorter gearing can sometimes improve both performance and economy. This would be a bummer for the freeway though.

For something like this, a long runner TPI inlet manifold with fully tunable electronic fuel injection would be easier to tune, for both fuel and spark, and have the potential for much better results.
Its not cheap, and there will be a big learning curve, but the results would be worth it if you do very high mileage.
Cheers, Tony.
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