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Discussion Starter #1
Looking for some help. Im trying to figure out if I can change my cam without changing my valve springs. I currently have aluminum trick flow heads w/ max valve lift of .540 inches. The cam currently in the motor(383)flat tappet- is 228/234 [email protected] in ;.480/.494 in lift w/1.5 rockers. my question is would I be able to use the following cam w/o having to change the springs; lunati cam 227/233 dur .489/.504 in lift. The rpm range for this cam is 1800-6200. Im running a th350 w/ a 3000 stall. If this cam is not good what do you all recommend. this is a street / strip car. More street than strip. thanks for the help.

Len:chev:
 

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If the springs on your heads are rated at a higher lift than your cam you are fine and wouldn't have to change them.
 

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If the springs on your heads are rated at a higher lift than your cam you are fine and wouldn't have to change them.
Technically we would need to know the spring rates (pressure at seat and lift) as well since the voodoo series is a pretty aggressive hydraulic flat tappet cam. You don't want any valve float at high rpm, that makes all sorts of bruises. :no:

But, if I had to guess, if you haven't experienced any valve float with the cam in it now, you might be ok.

-Dan
 

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The correct people to answer this spring question is LUNATI.

If me, for what your trying to do. You might look at just changing to 1.6 rockers with the current cam.

Al
 

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Spring dynamics are much more complicated than most novice hotrodders would guess. Cam lobes have a rate of change between lift and degrees of rotation. Springs have a rate of change between lift and pounds force.
Cam designers know what spring rate, seat force and max lift force is required to keep the lifter in contact with the lobe and the valve stable during the total rpm range. Springs have a natural frequency that must be accounted for and one reason for dual (or triple) springs that have different frequencies that cancel out harmful harmonic effects.
The bottom line is valve springs must be compatible with the specific lobe design to get best results. If they aren't compatible you can have excess wear, valve float, valve bounce and dynamic pressure loss.

Part Number: 60103 Hydraulic. The most awesome 268 cam ever produced! Out-powers all others! This High Performance street cam likes 2400 RPM stall, 700 cfm carb, dual plane intake and headers. Makes un-equaled power to 6200 RPM with proper valve springs. If you're looking for a Very Strong cam with great street manners then this cam is it.

* Advertised Duration (Int/Exh): 268/276
* Duration @ .050 (Int/Exh): 227/233
* Gross Valve Lift (Int/Exh): .489/.504
* LSA/ICL: 110/106
* Valve Lash (Int/Exh): Hyd/Hyd
* RPM Range: 1800-6200
For the Voodoo cam you are looking at, Lunati specs spring #73943.
Lunati Intro Series™ valve spring set

* Spring Type: Single w/damper
* Outside Diameter: 1.266 in.
* Inside Diameter: 0.883 in.
* Seat Load: 108 lbs @ 1.750 in.
* Open Load: 339 lbs @ 1.250 in.
* Coil Bind: 1.060 in.
* Spring Rate: 462 lbs/in.
If you do not know the specs on the springs in those trick flow heads there's no way to know if they are suitable. I checked out the Lunati web site and they don't say which of the 16 spring part numbers they use (and I'm not sure what specific head you have). Unless you are knowledgeable in the subject of springs, I would recommend you use the springs Luntati calls for.
 

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if it wuz me

a 383 outta be able to stand more cam than the 268 i think ,, saw some use the antique , but good 292 comp cam , run mid to low 7's in heavy cars with 35-3800 stalls , with 373 gears ,

I just wouldn't leave anything on the table with a cam as small as the 268
 

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Spring dynamics are much more complicated than most novice hotrodders would guess. Cam lobes have a rate of change between lift and degrees of rotation. Springs have a rate of change between lift and pounds force.
Cam designers know what spring rate, seat force and max lift force is required to keep the lifter in contact with the lobe and the valve stable during the total rpm range. Springs have a natural frequency that must be accounted for and one reason for dual (or triple) springs that have different frequencies that cancel out harmful harmonic effects.
The bottom line is valve springs must be compatible with the specific lobe design to get best results. If they aren't compatible you can have excess wear, valve float, valve bounce and dynamic pressure loss.



For the Voodoo cam you are looking at, Lunati specs spring #73943.

If you do not know the specs on the springs in those trick flow heads there's no way to know if they are suitable. I checked out the Lunati web site and they don't say which of the 16 spring part numbers they use (and I'm not sure what specific head you have). Unless you are knowledgeable in the subject of springs, I would recommend you use the springs Luntati calls for.
Paul,
I'm disappointed..... You didn't mention how the total valve-trail weight on the valve side needs to be taken into account as well.:devil:
I wouldn't run that recommended spring.:no: Lunati's guilty of the same thing as a lot of the other commonly mentioned cam companies.:yes: Their "Recommended" spring is just a baseline generic spec spring for whatever application, normally a small valve'd stock head.:yes:

Looking for some help. Im trying to figure out if I can change my cam without changing my valve springs. I currently have aluminum trick flow heads w/ max valve lift of .540 inches. The cam currently in the motor(383)flat tappet- is 228/234 [email protected] in ;.480/.494 in lift w/1.5 rockers. my question is would I be able to use the following cam w/o having to change the springs; lunati cam 227/233 dur .489/.504 in lift. The rpm range for this cam is 1800-6200. Im running a th350 w/ a 3000 stall. If this cam is not good what do you all recommend. this is a street / strip car. More street than strip. thanks for the help.

Len:chev:
Len,
I would contact Trick-Flow and see what spring they put on those heads. You should pull a couple and have them checked and SEE what pressures you're playing with. Comparing that actual measurement with the original spring specs will tell you a LOT.:yes:
With a mild hydraulic flat tappet, your spring choice isn't going to be that crucial. As long as your springs are in good shape you should be fine.:yes:
If we were talking solid roller or special solid flat tappet with hard faced lifters (using solid roller spring rates) and ridiculously high RPM levels, or any of the launcher series hydraulic rollers the story would be COMPLETELY different!!:yes: Some of those lobes are designed around a specific valvetrain mass and spring pressure (and rate!!).:yes:..
You can PM me for Harold Brookshire's number if you want his opinion as well. If that's in fact a VooDoo cam, then he's the man who designed the lobes!!
 

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Calling Harold is a good idea. Maybe Harold can explain how if Harold designed the Lunati lobe why the Lunati spec'd spring is not the correct spring.
I'd almost be willing to bet he's going to say that while there is some leeway on springs, the Voodoo grind has definite minimum spring requirements to maintain valvetrain stability.

The recommended Lunati spring has over 300 lbs pressure over the nose and a rate of 462 lbs/in...it isn't mild. The 1.250" OD Trick flow springs are only 300 lbs/in. Those aren't going to work. If he has the 1.460" trick flow springs there's only a few PN's that are "close" to Lunati spec, so the odds are not good that the existing springs are "close".

If I was going to deviate from the Lunati spring, I'd wouldn't buy a Trickflow rebranded spring. Better options are had elsewhere.

The question was can he use the existing springs with the Voodoo cam. We don't know what PN the springs are so it's all speculation at this point.
 

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True Tales Valve Spring Story

I once ported a set of SBF heads for a fellow engineer at Roush. He had a 5.0 Mustang he was building and asked me to help him out. I did and when it was time to assemble them he brought me some dual springs he got a "good deal" on.These were larger diameter than stock with a stiff rate.

He got the engine assembled and running and brought it by for a test drive. It ran real strong up to about 5,800 rpm and then stuttered like crazy. He was guessing everything from fuel pressure to ignition, but he didn't think it was valve float because the springs were so stiff.

The Mustang was stolen and later recovered. It had been used for street racing. The thief tried to solve the stuttering because it had a new ignition and fuel pump.

I mentioned that maybe the springs he used weren't compatible with the cam he selected. Long story short, that's what it turned out to be. At 5800 rpm, the valves were bouncing on the seats losing combustion pressure
Changing the springs to the correct rate solved the problem. It now pulls to 7,200.
 

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I once ported a set of SBF heads for a fellow engineer at Roush. He had a 5.0 Mustang he was building and asked me to help him out. I did and when it was time to assemble them he brought me some dual springs he got a "good deal" on.These were larger diameter than stock with a stiff rate.

He got the engine assembled and running and brought it by for a test drive. It ran real strong up to about 5,800 rpm and then stuttered like crazy. He was guessing everything from fuel pressure to ignition, but he didn't think it was valve float because the springs were so stiff.

The Mustang was stolen and later recovered. It had been used for street racing. The thief tried to solve the stuttering because it had a new ignition and fuel pump.

I mentioned that maybe the springs he used weren't compatible with the cam he selected. Long story short, that's what it turned out to be. At 5800 rpm, the valves were bouncing on the seats losing combustion pressure
Changing the springs to the correct rate solved the problem. It now pulls to 7,200.
No doubt. Been there!!!:rolleyes:

Brookshire's lobes generally have a pretty gentle closing side. VERY ASYMMETRICAL.:yes: So they're generally not near as finicky.:no: But like I suggested earlier, a call to him and Trick-Flow would be the end of the discussion.:yes:

As for the "Recommended" springs. They are generally just a reference since NO two cylinder heads are set up with the same springs, spring heights, valve/lock/retainer weights, etc... Even two of the same heads can vary slightly.:yes: Some of the cheaper Chinese stuff can be just absolutely DISGUSTING!!
There's definitely a learning curve involved and it's NICE to have a couple GOOD go-to guys like Earl, Brookshire and Chris over at PAC to get the inside scoop. Especially on some of the higher end solid flat tappets and hydraulic rollers!!

Pushrods can be just as detrimental in the higher end stuff but in this application.....not so much.:no: Just a GOOD .080 wall 5/16" stick will work just fine.:yes:

Notice ALL of the springs on PAC's web sight also list the spring's frequency along with all of the other specs. A conversation with Chris about figuring all of that (along with the resonate frequency of the pushrods, etc.) would even give a physics professor at Berkley a head-ache!!:eek:
 

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Discussion Starter #11
Thanks for all the info guys. This head and cam combo both came from trick flow as a match set. It is their 420 hp set. They claim they got 460 hp with this setup on a 383 w/ an air gap and a 750 carb. I think im going to just run the cam / heads in my new 383 and see how it is. I was just concerned that it might not be enough cam for the 383.... We'll see. Thanks again.

Len
 
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