Cam recommendation for mileage AND power.

[jamyers]

Understanding that any cam is a trade-off between mileage and power, how 'big' a cam can you go in a basically-stock 200 before you start to lose gas mileage?

Any guidelines or opinions gratefully accepted.

 

[XFlow_Fairlane]

prob about anything bigger than stock I would assume. a bigger cam is going to let more air and fuel in.

for a street car I would go with the smallest aftermarket grind you can find (basiclly the smallest cam that is bigger than stock) it will give you more lift and umph up top where the stocker runs out but won't hurt milage too bad.

 

[jamyers]

That's what I was thinking, but can't help wondering at how much performance I can gain before I start killing the economy.

I'm thinking of either a 250 cam, or one of the aftermarket ones. Looking at cam listings, there isn't much info on expected mileage except for the very smallest cams. With my Buick big-block, I went with a decent street performance cam (among a lot of other things), and it's actually helped the mileage a tad. I'm just wondering what people's experiences with various cams are as far as perf vs. economy.

ie, where's the "tipping point" in cams where mileage drops off dramatically?

 

[matt1967]

Isky makes a 252H cam for the small 6's it's probably the smallest cam you can get. 252/252 @ .50 and I belive it's .445/.445 on 110* LCA.

 

[addo]

Look at the "torque" and towing grade cams. Both will put you in the sweet spot of an otherwise stock-ish motor. Then consider gearing revisions to further suit.

 

[falcon fanatic]

The "tipping point" in cams ocurrs at the intersection between how much more responsive the engine becomes, and how much more you are going to "tip" your foot into the throttle as a result. Since pretty much any performance cam will make you car more fun to floor, there really is no hope...

 

[falcon60]

The "tipping point" in cams ocurrs at the intersection between how much more responsive the engine becomes, and how much more you are going to "tip" your foot into the throttle as a result. Since pretty much any performance cam will make you car more fun to floor, there really is no hope...

HaHa!,that's true. I really don't light-foot the Falcon since I built the 10:1 200 with the Carter YF,mild head porting and Mike's 264 cam. But you know,the darned car's getting an average 24 mpg as a daily driver work car....17 miles one way....and most of the time I don't even use 5th gear in the T5 since I'm running a 2.79 gear in the 8" rear. 4th runs about 2200 at 60 mph. The cam is a little rough at idle but as soon as you touch the throttle it pulls hard and is in a nice sweet spot at cruise.It can't be hurting the mileage any.Pretty soon I'll take it on a road trip and see what the highway mileage is.

Terry

 

[xctasy]

Past 270 to 280 degrees advertised duration is the point of no return. In tiny ohv Minis and Austin Healy Sprites, you can run a little over 268 degree cams and so no low end torque problems, and your economy is no changed from the stock 240 or 255 cams.

The main issue is

1) window lift area, must be less than 0.3 (valve diam divided by gross lift at valve)
2)The over lap where both vlaves are 30 thou off the seat must be minimised
3) the effective compression must exceed the stock cam.

Any 264 or 272 degree modern cam will fit the bill if the compression ratio is about 8.8:1. A set of stock lifter ratios will run fine with 272 degrres, but an aftermarket set of 1.6:1's or FE 427 style 1.75:1's will make even a 264 cam a point of no return.

The stock 240, 252 and 256 degree cams are trash, designed by conservative enginers in the 50's, 60's and 70's for long engine life. When retarded back 4 degrees like they were in 1972 on wards, any 264 or 272 degree cam will piddle all over any 256 Ford cam.

 

[jamyers]

...an aftermarket set of 1.6:1's or FE 427 style 1.75:1's will make even a 264 cam a point of no return.
...

Thanks for the info, that gives me something to go think about!

btw, I've never heard of using FE-style rockers on a 200...what about putting them on with a stock cam, what would that do besides higher lift (and slightly more duration?)? How hard would it be to install them?

 

[xctasy]

The rocker gear on an I6 is basically the same as the FE. They have lots of kick ass hard out rocker gear for them on account of Total Performance hangovers fropm the 60's....427 Shelby Cobras and GT40 427's and KR500 owners who want to retro fit 427's, and off road guys who insist that the old seven litre FE is the badest, most virile Ford V8 ever.(Which it probably was!)

The aftermarket Edelbrock 1.75's are basically more aggressive than Cleveland or Big Block Lima 1.73:1's. When placed on a small I6, they loose ratio because of rock ratio geometry. Something like 7% or so.

Any ways, the stock cams 240, 252, or 256, are low rent, and any lift via higher lift roller rockers is a bonus. 25 thou or so extra, maybee more is worth something if the cam is the performance limiter.

You'd not ever just do a rocker shaft and arm swap unless you were going to do the timing chain, pushrods, lifters and cam. You'd potentially then run into spring bind, even with 25 thout extra lift. Ford doesn't even have 60 thou allowance for spring bind on most of its engines. For example, a 370 thou lift at the valve might have 60 thou allowance for spring bind with a 1.5:1 ratio. Add 1.6:1 rockers (which are likely to be more like 1,64 anyway), and you're half way to binding the tired springs, touching the keepers and vlave stem heads and all the rest of that jazz. And the vlave seals will hit the last 35 thou of the years of accumulated carbon, making them leak.

 

[jamyers]

Ahaaaa...thanks for the detailed info, I really appreciate your input here.

Didn't know the spring bind was so close. Guess it's just simpler to swap in a bigger cam and keep the stock rocker geometry then.

I'm going to need to rebuild the head sometime (leaking #6 valve guide fouling the plug every 300 miles), this gives me food for thought.

After all, can't just fix the head without tearing into something else, can I? Just wouldn't seem right.

 

[jamyers]

...
1) window lift area, must be less than 0.3 (valve diam divided by gross lift at valve)
2)The over lap where both vlaves are 30 thou off the seat must be minimised
3) the effective compression must exceed the stock cam.
...

Just to make sure;
#1, you're referring to the intake valve, correct?
#2, most cams report overlap at .050, will that figure work as well?
#3, I assume you're referring to measured static compression.

Thanks again!

 

[xctasy]

...
1) window lift area, must be less than 0.3 (valve diam divided by gross lift at valve)
2)The over lap where both vlaves are 30 thou off the seat must be minimised
3) the effective compression must exceed the stock cam.
...

Just to make sure;
#1, you're referring to the intake valve, correct?
#2, most cams report overlap at .050, will that figure work as well?
#3, I assume you're referring to measured static compression.

Thanks again!

1. Yep, intake lift at valve verses valve diameter. So a 1.75 valve intake times by 0.30 is 0.525" gross lift at valve, maximum.


2. The real problem on a street car with and auto or tall first gear four speed is when both valves are open at 30 thou according to Vizard. This is where a bog or 'hole' developes. 50 thou lift on some cams with good at lash duration can be less than another given cam, The better street cam is the one with less intense 30 thou figures, but the industry reports 50 thou figures for simplicity's sake. The less intense 30 thou figure is the better option for most street cars. There is a lot to cam design, and these were general precepts given to me some years back.


3. Nope, I'm refering to effective compression. On the web, there are sites that do the calculation for you. I think Jermey Diamnonds Panic site has a formula for effective compression calculation for a given cam, given stroke, given rod length, given lift. The valve closeing event defines the effectivie compression. You may have, say, 8.7:1 on your 250, but with a 252 cam and a 16/56 cam you input the effective compression for a given 56 degree valve shut event. The depth down the cylinder is calcuated, and the effective compression could come out at , say, 7.25:1. When you shove in a 272 cam with 26/66 timing, you need to come up to perhaps 9.2:1 to get the same effective compression as 7.25:1. If you do that, low end torque and drivablity is as good or better than stock.

If you change the advance or retard, the 56 or 66 degree close figure changes, and so does the effective compression. You can spike it perhaps 0.3 points if you retard or advance enough. For cars having a way to wild or way to mild cam, you can raise or lower effective compression to suit, which can help low speed tractability problems, or make them worse.

You can alter lash on solid and even some hydraulic cams too. If a cam is too agressive, you can open up the clearances to loose some effective compression, or if the car has a very soft cam, you can tighten the lash to give it a few degrees more duration.

Cam grinders have learned a heck of a lot of very smart tricks, and these days, its very hard to mess up a good aftermarket cam; the grinder will ask you some ultra tough questions that don't seam to have any relation to anything. The fact is the I6 is very hard to over cam, so thats why any sub 280 degree cam has a very good chance of being better than the original, and if its a smidgen too wild, you can always play with it to get it running well enough on the street.

I'll give you an example. Stock performance 3.3 Aussie Holdens ran 345 thou lift, 53 degree over lap, 266 total degree cams really nicely. For a bit more hard edge, they went to 429 thou lift, 84 degrees over lap, 309 total degree cams. It was still usable on the street. Thats where the limit is, so you won't get into any trouble with a 272 degree cam.

 

[jamyers]

Thanks for the clarifications, I appreciate it.

When researching my Buick engine build, I looked into 'fast-ramp' cams and other profiles, so the .030 number makes sense. I wish it was easier to get cam profile numbers, I guess most people just aren't interested in them though...

Effective compression = dynamic compression ratio. I'd seen Panic's article awhile back, I used Pat Kelley's downloadable calculator for the Buick with good results. http://cochise.uia.net/pkelley2/DynamicCR.html

Thanks again!