Should I Change the Cam?

[2FAST4U]

When I started building my engine, I intended on using Weber 48 IDA carbs. I installed a cam that Jim Inglease blessed. It is a Lunati hydraulic roller (.571/.587 lift, 282/290 adv duration, 112 LSA). But then the prices of Webers shot up and I can no longer afford them. So I went with a Blue Thunder dual quad setup. Now I'm thinking of changing the cam to a wilder one compatible with carbs. I've been looking at Crane Cams hydraulic rollers (.595/.595 lift, 306/318 adv dur, 110 LSA; or .574/.595 lift, 298/306 adv dur, 110 LSA).

I'm wondering if all the work to change out the cam is worth it.

[Wayne Presley]

Did you spec the pistons/CR based on the original cam or have you bought your pistons yet?

[2FAST4U]

Yes I did. They're installed

[Wayne Presley]

Will the CR support the extra overlap without killing the dynamic CR?

[Bob Cowan]

I would use whichever one gives you the best dynamic compression.

[2FAST4U]

Static compression is 11.5:1

[2FAST4U]

The dynamic C/R with the current cam is 8.8:1. That's a tad high

The dynamic C/R with one of the new cams would be 8.3:1. That is much safer

[Bob Cowan]

Well, there you go. The answer is in the math. Best to make the change now while it's easy.

[2FAST4U]

I know Bob. But I just hate having to partially tear down a brand new engine. But I do have the advantage of time and the engine on a stand

[Big Blocker]

Wait . . . the engine is on a stand?? . . . why are we even discussing this . . . flip it over . . . pull the pan . . . pull the rocker covers . . . take the rocker adjuster nuts all the way to the top of the stud . . . take off the front timing cover and chain . . . rotate the cam a few times and the lifters will move out of the way . . . swap the cam . . . turn engine over and lifters will fall back into place . . . tighten rocker nuts . . . put the rest of it back together and . . . Wha-La! Brewski time . . . A few gaskets, a little time and a few adjustments to re-do . . . Hmmmmm.

Don'tcha just love the old guys, old school, ways of shade tree mechanics??

Swap the cam, Bill, now's the time.

Doc

[Wayne Presley]

Originally Posted by Bob Cowan

Well, there you go. The answer is in the math. Best to make the change now while it's easy.

You mean math/physics over rules subjective opinion, tell me it's not true!!!!!!!!!!

[Sanford]

If the spider retainer for the roller lifters is not used, but it is a neat idea.

[Erik W. Treves]

Originally Posted by Wayne Presley

You mean math/physics over rules subjective opinion, tell me it's not true!!!!!!!!!!

yup and my turbo is too small

[Big Blocker]

OOOOPS . . . I was under the impression that Bills' engine was an early 289 block . . . not roller cammed.

If I'm wrong, I stand corrected . . . the shade tree "fix" won't work with the spider installed.

Although, hmmmmmmm, even if roller cammed, the spider allows the lifters to lift enough to follow the highest lift available so should be able to let them "fall" low enough (engine inverted) to get the cam out. The spider is to keep the rollers from twisting, not lifting.
Guess it would depend on the way the lifters are kept from twisting . . . forks and a spider (factory FORD) or cross-bars attached to the lifter. Either way, it should work (?).

Doc

My BAD . . . I went back and read Bills first post . . . he's looking at a "roller" cam

[Lex]

I've got a pretty wild Anderson Motorsports roller cam I'll sell you. It's .576 lift int & exh with 232 int 240 at .050 duration on 110 degrees seperation. I ran this in my 347 with a 750 carb and Vic Jr heads and intake and made 547 hp at the flywheel.
http://www.andersonfordmotorsport.co...emart&Itemid=1

[BostonBuster]

What cylinder heads ?

[2FAST4U]

Originally Posted by Lex

I've got a pretty wild Anderson Motorsports roller cam I'll sell you. It's .576 lift int & exh with 232 int 240 at .050 duration on 110 degrees seperation. I ran this in my 347 with a 750 carb and Vic Jr heads and intake and made 547 hp at the flywheel.
http://www.andersonfordmotorsport.co...emart&Itemid=1

I'm not ready yet. We're in the midst of moving. Plus I need to put your cam specs in the dynamic C/R formula to see what it comes up with.

[2FAST4U]

Originally Posted by BostonBuster

What cylinder heads ?

Trick Flow CNC'd 205cc aluminum heads

[Bob Cowan]

Originally Posted by 2FAST4U

I know Bob. But I just hate having to partially tear down a brand new engine. But I do have the advantage of time and the engine on a stand

Yeah, but it will be worth it. Getting the DCR down to a reasonable level will make the car so much more fun to drive.

Originally Posted by Wayne Presley

You mean math/physics over rules subjective opinion, tell me it's not true!!!!!!!!!!

Follow the math, but only if it Feels right. We want the numbers to add up, but only if the feng shui matches and the aura is mellow.

[tirod]

It's been stated all over the 'net, aluminum heads allow more compression, up to 10.5 to one in terms of math. Since the dynamic compression is still under 9:1, it's still a pump gas motor.

What moving to dual quads will do is add more runner length compared to Webers, and improve torque. Shortening the LCA with a different cam could lose a lot of vacuum and force the idle higher, plus steal intake charge from the other cylinder that's open.

I'd run this by a cam designer familiar with Dave Vizard's theories and see what they recommend. It may well be trading off one incremental change for another, at the cost of a new cam. The net difference could be just a lighter wallet.

[Don Payne]

If you are looking to get just a little more umph on the DCR I would say you could lower the ICL or lower the duration a little. Since you are already at 106deg ICL (assuming 4deg built in advance) I would not move that anymore, but would lower the duration instead. This will allow the intake valve to close just a little sooner boosting your DCR to something like 8.5.

[Richard Oben]

Since we are throwing opinions out there, unless this thing is going to live above 5k rpm you likely have way too much head for the cubes. That is unless I do not know how many cubes you have. Remember this is a street car, that looks like a race car. JMHO, YMMV, Richard.

[Bob Cowan]

Originally Posted by tirod

It's been stated all over the 'net, aluminum heads allow more compression, up to 10.5 to one in terms of math. Since the dynamic compression is still under 9:1, it's still a pump gas motor.

Just because it's "all over the net", doesn't make it true. For pump gas, keep DCR well below 8.5. Remember, we're talking about Dynamic compression, not static compression.

Originally Posted by Don Payne

If you are looking to get just a little more umph on the DCR I would say you could lower the ICL or lower the duration a little. Since you are already at 106deg ICL (assuming 4deg built in advance) I would not move that anymore, but would lower the duration instead. This will allow the intake valve to close just a little sooner boosting your DCR to something like 8.5.

ICL isn't that important for DCR. It's mostly dependent on intake valve closing point. The later the valve closes, the lower the DCR is. A wide LSA creates less overlap, which will increase DCR.

Also, in CA it's tough to find anything better than 91 octane. On a hot day at sea level, a DCR of 8.5 can be a problem. If it was an EFI engine, you could set it up for E85, and then you can easily run a DCR of 8.5-9.0. But with carbs it's a lot more difficult.

[Don Payne]

Originally Posted by Bob Cowan

ICL isn't that important for DCR. It's mostly dependent on intake valve closing point. The later the valve closes, the lower the DCR is. A wide LSA creates less overlap, which will increase DCR.

Also, in CA it's tough to find anything better than 91 octane. On a hot day at sea level, a DCR of 8.5 can be a problem. If it was an EFI engine, you could set it up for E85, and then you can easily run a DCR of 8.5-9.0. But with carbs it's a lot more difficult.

I totally agree with the intake closing event being key to affecting the DCR. I was just trying to point out that both the ICL and durration affect it. The ICL and LSA are also very closely aligned since most off-the-shelf cams have a built in 4 deg advance.

That said, I would say that overlap only indirectly affects DCR because overlap is determined by lift, duration, LSA and ICL. I guess I am also going off the assumption that DCR is purely a mechanical metric similar to CR, where CR only deals with mechanical calculations of the rotating assembly and combustion chamber and DCR adds in the camshaft valve events. The Wallace Racing calculators for DCR are factoring in other variables that are non-mechanical like boost and atmospheric pressure, so my assumption may be incorrect.

What I don't know (and would love to hear more about) is how to answer Wayne's question of "Will the CR support the extra overlap without killing the dynamic CR?".

At the end of the day, I would have to follow your lead on what DCR is appropriate for pump gas. That seems to be THE metric that really determines whether or not you engine will live or die on pump gas, of which I don't know much about.

[2FAST4U]

Originally Posted by Don Payne

What I don't know (and would love to hear more about) is how to answer Wayne's question of "Will the CR support the extra overlap without killing the dynamic CR?".

My static compression is 11.5:1. So I have quite a bit of room to get the DCR down from 8.9 to 8.3.

[BostonBuster]

Use the cam you have , probably ground 4 deg advanced ? Install it straight up instead.Why spend another $400-$500 to pick up another 20-30 peak hp and sacrifice more hp down low , would reduce the dcr a little too .

[2FAST4U]

The more research I do, the more I'm inclined to leave everything alone. The car will be light and I'm using 4:10 gears.

[Bob Cowan]

I think you might regret that decision later on. The cam may be ground "4* advanced", or it may not be. You might be able to install it 4* retarded. Or, you might run into piston to valve clearance issues that way. Especially with a wide LSA.

Do the math, and follow the science.

The cam is the heart of the engine. If that doesn't match the rest of the engine, it's not going to perform well. My DCR is about 8.4; and that is right on the ragged edge of pump gas. It runs much better on E85.

[Chief]

May I sugest to take a little time off from the build, save up some more money, and stick with your original plan of Webbers. You know you want them and they'll look soo much better than the carbs.

[2FAST4U]

Retired. No extra money for Webers