EDGE

I know how to match Lift and LSA to a cylinder head, but what determines the duration? Still haven't quite figured that out. I have 5.7 .020 over. Edelbrock intake and runners and I'm going with Trick Flow 195 64CC heads. I know what I think I want in terms of lift but I'm out to lunch on duration. It's a street motor so I just want the power band to be in that 1500 to 5000 range.

Orr89RocZ

iTrader: (20)

Duration is time to fill cylinder. Based on air demand which comes from a number of factors, including cubic inches, head flow and induction cross sectional areas, rpm, estimated VE, etc. more duration is needed for more rpm, typically. Lift is kinda tied into that, as part of the area allowed for airflow to pass thru the valve. Its a time area function so they work together.

given that and those engine parts and rpm, a 5.7 will need 210-212 degrees depending on runner length. I mean stock cam in a 350 is 207/213 deg and with a short runner intake with stock heads will peak at 5100 ish. Bigger head more flow could likely make that power band with abit less but anywhere in the 210-218 deg imo is a good size

EDGE

Great info 👍🏻 Thanks!

Orr89RocZ

iTrader: (20)

Longer runners typically need more time so if sticking with tpi, could add 5-8 deg more on intake imo. A good compression 350, 220-224 deg on intake is an excellent street cam imo. Tpi just holds back rpm potential

EDGE

Am I reading these duration numbers a .050 or the advertised duration. Because the 218 @ .050 is something like 276 advertised.

Orr89RocZ

iTrader: (20)

Sorry, yeah at .050” which is typical catalog specs and industry standard. Also seems more impactful on performance output compared to just advertised numbers alone

EDGE

Great thanks for the info.

EDGE

I was just going through the head specs and at .600 the head is flowing at 258 CFM. So the cam I'm after should be in the high .500 some odd range because at .500 it's flowing 257. That being said, that's the cam lift without factoring the 1.5 rocker ratio. Now when matching the cams lift to the heads flow rate are you just going by the cams spec or do you add the rockers lift? So for say a .500 lift you'd actually get a .300 something lift. Does that even exist?

vorteciroc

To keep things simple...

Lift should really be chosen/ selected by the Flow Rates of the Cylinder-Head being used.
Selecting a Lift measurement near or at the most efficient Number... and not going past, or into a significant drop in Flow.

Duration, Lobe Separation Angle, and Installed position relative to the Actual Intake Lobe Centerline...
All correlate/ determine the Valve Events, which determine the Engine Behavior/ Performance Potential.

Duration figures are a horrible way to catalog and market Camshafts.
I truly wish the Industry would convert to using Valve Events instead.

vorteciroc

You really need to look at the entire Flow chart to make those decisions... and don't just pick the highest flowing Lift Number.
That is not the way to do it!

Those Lift Numbers are normally published as the Number via a Stock Ratio Rocker Arm.

Orr89RocZ

iTrader: (20)

Cam specs are typically given assuming a standard rocker ratio. For sbc cams that’s typically 1.5 ratio. So the total lift seen at the valve not including any lifter preload would be the lift seen in the cam spec. So if the catalog says 218/224 deg at .050 and lift is .510/.520” that typically is with 1.5 rocker at the valve. The cam lobe itself would be .340/.346 or so. Some cam lobe families like comp cams xfi efi cams are listed with 1.6 ratio rocker and are in the .560-.575” lift range.

depending on the hp goals and rpm you don’t necessarily need to lift to max flow point on the heads. Only on max effort applications is that typically needed. Valve diameter and lift make for flow area, and if thats large enough to support the rpm range then thats all you need and more might not do anything for you

EDGE

Thanks for help everyone. Really clears up some of the mystery!

Fast355

iTrader: (2)

With a 195 port that 350 is going to want to make peak power in the 6,000-6,500 rpm range. Why limit it to 5K? My stock Vortec 350 truck motor had WOT upshifts at 5,200 and when I put decent springs and a little more cam in it I ran it to 5,800.

F-BIRD'88

Buy and install a Melling #22280 hr cam. When degreeing it in move it slightly more advanced than cam card to enhance torque . 104/116 vs 107/113
Use 1.6 in rockers and 1.5 ex.
Enjoy the car.. Then you can analyze the how and why all to hell, as much as you want.

EDGE

Now I've gone down the rabbit hole. The heads I'm settling on run a single 1.470" valve spring and can handle a valve lift of .540. I'll be somewhere in the neighborhood of .500 or a tad less. The next step up is dual spring .600. More than I'll go. The last option is a single 1.250 .480. My question is: Is single strong enough? I haven't messed with heads for quite some time and back in the day it was dual spring to control float etc...etc. A lot of that also came from "I heard a guy say" so I don't know what the real deal is. What's your experience on the subject? This isn't a 7000 RPM motor either.

Orr89RocZ

iTrader: (20)

You pick springs based on desired loads needed to control the cam, not necessarily the lift spec. But there is some need to consider lift, as you dont want too much gap between cam lift and spring max lift in a perfect setup. This is distance from coil bind and is necessary for optimal valvespring control

the dual spring is likely the idea spring for hyd rollers. I would not run a single spring as they probably are designed for flat tappets.
The single 1.470 spring may be enough depending on its load pressures and what cam you run. Mild stock like hyd rollers at low rpm could be fine. A comp xtreme energy or xfi lobe would likely need alot more pressure

skinny z

One school of thought suggests that duration is the RESULT of the other cam specs.
Overlap first. This is determined by the engine/vehicle application. A little for a tow truck. A lot for a racing engine. The combination of engine parts obviously plays into this. This is followed by LSA. LSA is selected by CID, cylinder head flow coefficient of discharge (or intake valve diameter in a pinch), compression ratio and if you're so inclined, the general purpose of the engine. But if maximum torque is your objective, the choice of LSA is better defined.
The duration falls in place after that.
As for valve events, the ICL in particular can be manipulated via where the cam is timed in. The duration split is impacted by the efficiency of exhaust system as well as the intake to exhaust ratio of the heads in use.
Of course, other methods have proven successful but the above has a solid rep as a good way to go.

F-BIRD'88

Just looking at the basic stated specs on the
package 2 springs 1.47" single with damper and 1.80" installed height .540" lift limit recomended.
They should be fine for with the Melling #22280 cam . Use the 1.6 rockers ONLY ON THE INTAKE SIDE. the 1.5 ratio is fine on the exhaust.
Itis up to you as the builder to check verify spring installed height (1.80") And coil bind height of the spring.. But that #2 package looks ok to me .
This Melling hr cam is not super critical on valve springs. (unlike some cams like the Comp XFI series can tend to be.
This popular Melling high perf street roller cam is used in a lot of various Crate engines. It works and is not hard to deal with.
This does not educate you much about cam duration choice for an engine application (for you)
but does get you a great cam for your statedd purpose. You can analize all this on your own..
The single spring with damper is fine.
If it did not have the damper my recomendation will be different.
You can consult TrickFlow directly on all this before purchase decision.
Just realize it is up to you to clean and check certain things on any assembled head package.

skinny z

I've asked before I think. What's Melling's method of measuring their seat to seat numbers? Not .006" at the lifter. That much I recall.

F-BIRD'88

You don't really want a over the top cam lobe design that needs critical radical valve springs as the OEM type HR lifters are not intended to work with extreme valve spring seat or open force.
The specialized HR lfters (limited travel etc etc) cost a fortune and are intended really for racing.

Keep it real.. those 1.47" springs are fine.
For your purpose with the street friendly Melling HR cam and OEM type sbc HR lifters.
It will GLH.

F-BIRD'88

The Melling cams use the SAE spec method for seat duration .006" (+lash) @the valve.
(not the same as Comp cams method)
Don't worry. The design is right for this purpose.
Its plenty spunky. Like I said. stick it in on 104/116 centers and hang on tight.

Fast355

iTrader: (2)

Agreed! Basically a cheaper LT4 hotcam with a little tighter LSA. I degreed a few hot cams into L31s at 105 ICL. They would run!

skinny z

This conversation sounds familiar!

I expect it to be plenty lively when I start to lay out my cam options. I'm hoping to see some participation from all of the usual suspects.

Fast355

iTrader: (2)

Yes sir! My current cam in the 383 is a slightly quicker ramped, higher lift "Hotcam" with 1.7 rockers and a 108 LSA. It flies for what it is. Its not going to run any 13 second passes with a 3.73 gear but the torque is abundant through the whole rpm range and it cruises effortlessly. Comp was trying to suggest a 206/212 @ 0.050 with alot less lift and a 112 or even 114 LSA. I am glad I knew better. Keep in mind I have the Rhoads V-Max lifters and my cam is smaller than Comps suggestion at low rpm as it sits. The tiny cam they suggested would have resulted in 305 peanut cam like specs at low rpm and probably 240-250 psi cranking compression. The guy on the phone at Comp also thought I was crazy only wanting 2° of cam advance. This is what the 383 pulls with a 4L85E that has a custom built stock diameter converter that flashes 2,800 rpm and 3.73 gears with tires nearly 32" tall.

EDGE

I was actually looking at the Comp 08-502-8 to go with the Trick Flow Super 23 195 Cylinder Heads TFS-30410003-M64

skinny z

Have you determined your compression ratio?

EDGE

I physically haven't calculated it. Other than what's published no. It's the factory stroke of 3.48" with a 4.020 bore. The factory heads are on it right now. I think that's 62CC. That's going to change with 64 CC a bit and I don't know how thick my head gasket is going to be yet. I'm still in the research phase for parts.

skinny z

I'm in much the same boat although the shortblock is sitting on a stand and the heads are on the work bench.
I've got the piston below deck numbers, valve relief volume as well as chamber CC's. I'd like to do a little clean up work on those chambers and then CC them again.
Some of the simulation programs I've used, Torque Master in particular, are sensitive to a couple of tenths swing in the CR. LSA and the resulting duration change as that CR value goes up or down, which is to be expected. The tighter I can get with that CR number, the better.

FWIW, I'm not necessarily chasing every last tenth for a given CR as the difference in output between 10:1 and 10.2:1 would barely be measurable at the track. But the cam spec could be, however that spec gets calculated. I'll take my simulations and bounce them off of a cam grinder like Mike Jones (Jones Cams) and see how it all shakes out.