[Argess]

Suppose one picks a cam that has too high a lower band, say 2500-5500, and then wants to bring that down a bit. From what I understrand, advancing the cam a bit can do this. One thing I read is an advancement of 4 degrees will only move the powerband down by about 200 rpm. So for anything more significant, it would seem that it would be best to switch to another cam instead, even though I have timing gears that allow up to 9 degrees via a number of keyways.

I have read a couple of forum posts, ...can't remember where... of the Crane Fireball cam (which I have...294 adv) really bringing an FE BB alive if advanced 4 degrees. Do you think that's a valid point?

One other thing, a lot of what I read seems to overly complicate matters for me. I assume that 4 degrees advanced means advanced with respect to crankshaft degrees. But then some say, 4 degrees is built into some cams as the lobe centerline is off by 4 degrees,, hence a deviation from "straight-up". Seems to me that a person wanting to advance a cam by 4 crankshaft degrees means just that, 4 degrees advanced from the zero position recommended by the cam manufacture regardless of where the lobe center angle is.

Comments are most welcome. Thank-you.

 

[FmrStrtracer]

Ive advanced a couple of cams 4 degrees over the years, and it made a noticable improvement in lower and midrange RPM's.

But, unless you degree the camshaft during installation, changing its degree of advance or retard is a crapshoot. Its a absolute neccesity to degree the cam. Just a couple thousands of an inch in a machining error can retard the cam significantly, causing crappy performance. All performance cam and timing gear makers recommend that you check the cam timing to verify correct opening and closing positions. They all have great Quality Control, but sometimes a piece of tooling becomes worn, and something gets machined wrong, generally its the locating hole, or a keyway, thats off a few thou.

Makers of timing sets offer the multiple keyways so that it is easier degree the cam in the first place.

Id recommend that you degree your cam, if its where it should be, than go ahead and advance it 4*. Makesure you have enough piston to valve clearence before running.

If the cam's current setup is actually retarded, Id install it correctly to see how it runs, before Id advance it any.

 

[Rustydawg]

What about cranking compression as an indicator? Would it point towards a late-closing valve?

I would be tempted to do a before & after compression test if changing the cam timing.

 

[Argess]

Makers of timing sets offer the multiple keyways so that it is easier degree the cam in the first place.

I was suspicious that might be the case, but forgot to ask in the original post.

I did originally degree the cam and it was bang on....used the zero slot in the gears and checked against the cam card. But that was quite a few years ago and no doubt the chain has stretched a bit since then.

I started this thread jsut looking for general answers, but as RustyDawg asked, my CR is 9.5:1 and cranking compression is just under 200 psi...196 - 198 range on all 8 cylinders. I'm not sure what to make of that figure regarding cam timing, but it's a healthy compression number, none the less....chuckle.

Thanks for the replies guys.

 

[Argess]

Thanks for all the info. And I think I even understand it.

As I said, I did degree (verify) the cam years ago....degree wheel, dial indicator on a lifter, etc. and checked it against the cam card. It probably isn't quite the same any more as when i checked it the timing gears and chain were all new. Probably a little stretch by now. So if I wanted to pick 4 deg, I could re-check it now, and use that base to see what's closest to 4 with the selections available.

The car is very driveable, docile down low, and tons of power once up in the low/mid 2000 rpm range, and above. But I have to admit, for a street car, it lacks the tire squealing torque down low, and as has a standard transmission, 1st gear should be a little more fun than that.

The FE BB is a pain to change the cam timing on, although I suppose it is on most engines, so I wanted some more "experienced" views before I tried it. Thanks again.

 

[Argess]

294-294 [email protected]" 114.5 LSA .523-.523" lift crane mechanical
is this the cam you are using?

What is the compression ratio, rear gear ratio and tire diameter?
Intake manifold?

Yes, that is the cam, although I'd have to double-check on the LSA figure.

You are surprisingly astute asking those questions as I know my answers are also responsible for some of my "docile" low rpm behaviour, so here goes:

9.5:1 CR

3.07 rear end ratio, however with the RG 5-speed, 1st gear must be considered, which is 3.28

295/50-15s, so that should be about 26.6" dia and a 83.5" circumference

Offy 360 deg manifold, divided plenum with single plane runner layout. Has dual 1460 vacuum Holley's, both 600 cfm with progressive linkage so you are on one for approx 30% of throttle travel, and sync'd to both open fully at WOT.

 

[Argess]

Thanks F-Bird88. Good info there.

On the manifold, to be fair, it's not exactly a single plane manifold as it has a divided plenum. On the other hand, it's not exactly a dual plane manifold as it doesn't allow for cylinder phasing. All the right hand carb barrels feed the right cylinders, and all the left hand barrels feed the left cylinder. But you are correct, the factory dual plane should be much better. What happened is I found the one I'm currently using fairly quickly (and very cheap), and stopped looking for the Ford unit. Maybe I'll start keeping my eyes open again for one.

My carbs are mounted 180 Deg out, i.e. backwards, just like the factory units and they have been modified, but not to the extent you mention. Essentially, the idle circuits have been leaned a bit to allow for a better idle, which I believe is common with quad set-ups. Jetting and PVs too.

I have been tinkering with the timing a bit and currently have it set at 20 intial and 38 max (no vacuum advance on dist). Havn't zeroed in 100% yet, but I know at 28 intial and 38 max, I am getting detoantion. Can't hear it over the exhaust, but I can feel the engine fighting me a bit.

The whole system seems to be OK if I was always in the higher rpms, like racing, but back to that low-end torque thing.....

So, 7 degrees of cam advance? I must look at the specs and try to understand about that 107 intrake center-line. I'd like to know how you came up with that number, but I suspect you might have to write pages on it to get the theory across to me...LOL.

Thanks again.

 

[Argess]

For the benifit of the readers, this is the intake I am currently using:

http://www.offyparts.com/product_info.php/cPath/1_6/products_id/195

There's a pic in the link page that can be enlarged. It's actually a pic of the low version. Carb pads are a bit higher on mine.

There is a few things wrong with this manifold other than low rpm response. To run Holley's, there are adapters required that move the carbs back to make room for the distributor. I have those, but even then, there is not enough room for a large diameter distributor, so I wound up using a Mallory YL (with a few modifications for other reasons), so crossfire potential is higher than with a large dia cap. Ports are tall and narrow compared to most Ford FE cyl heads, so there's a bad mismatch to deal with.

There are other alternatives to the original hard-to-find manifold. FPP, now out of business made them. Dove, ...I am unsure of their current status makes them. Blue Thunder makes them and seem to be still alive and kicking. There may be others.

I have no doubt that F-Bird has nailed the worst offender to my low rpm torque issue, however I did suspect that, although I must admit, I've never seen a manifold comparison review that showed much difference of anything down low in the rpm range. Perhpas that's because they were comparing dual plane to dual plane. Anyway, I was looking to see if a cam advance could make it up a little, as the engine is close to working to my satisfaction. And I think that was answered by F-Bird as well.

Interestingly, the engine idles perfectly, and has smooth off idle transition. Just a little low on grunt until over 2000 rpm. In one way, that's good...none of that lurching you get when driving a truck with an extra low 1st gear. But I was hoping to find an improvement somewhere between that and what I have now.

Thanks all. I appreciate all replies.

 

[sel2real]

after reading through this whole post, i agree with f-bird about the intake manifold, but i also think that engine is over-carb'd. i've built several FE390's and each one used a 750cfm holley (double pumper or vac) - which was plenty. cam choice was similar, all having a 4spd toploader (2.95 1st, i believe) and at least a 3.55 rear. yes, freeway cruising was horrible (65mph!) but torque and power off-idle was amazing! NEVER had an issue roasting the tires! my personal car has a stroked sb ford with a 5spd (3.31 1st) and a 3.55 rear.... 1st gear is useless....