Cam duration

[Steve.k]

Id have to look and see if i wrote that down craig. Figure it out as if Im good on clearance if you like. Even more duration could make it close to ii guess.

[CamKing]

Piston valve be tight for much more.

If Piston to Valve clearance is the issue, adding duration will have much more of an effect then adding lift will, to P2V clearance. You could increase the valve lift by .100" and only reduce the P2V by the same amount you would, if you increased the duration by just 4 degrees.

[Steve.k]

Mike do you think the head flow and intake suggest more cam? Although the current setup is not bad can't help but wonder if more available. The engine setup can easily handle more rpm.The engine is out I'll recheck pv clearance.

[CamKing]

Mike do you think the head flow and intake suggest more cam? Although the current setup is not bad can't help but wonder if more available. The engine setup can easily handle more rpm.The engine is out I'll recheck pv clearance.

For your size engine, you can use more cam with those heads.
If you don't want to have to cut the pistons, measure total valve drop from closed, to where it hits the piston at TDC, and 10 degrees after TDC.
When you get that, fill out my cam recommendation form: http://jonescams.com/drag-race/

Put the valve drop measurements in the "Comments" box, and I can design a cam to get you the most out of the engine, without having to cut the pistons.

[Steve.k]

Ok I'll get some info by next week. Thanks everyone for help.

[groberts101]

If you don't want to have to cut the pistons, measure total valve drop from closed, to where it hits the piston at TDC, and 10 degrees after TDC.
When you get that, fill out my cam recommendation form: http://jonescams.com/drag-race/

Put the valve drop measurements in the "Comments" box, and I can design a cam to get you the most out of the engine, without having to cut the pistons.

Thank you so much for posting that little tidbit, Mike. Quick question. Is there an overlap or convergence point where XXX amount of duration and XXX amount of lift equates to a minimum free drop requirement?

Have seen a few "well seasoned" builders do it through the years and I've also used valve free-drop measurements during rough mock-ups to approximate whether parts will likely need clearancing. Unfortunately, never quite figured out the exact crank position to use as rule of thumb. Mostly because I don't do enough cam installs, but it definitely seem's that with many FT cam's below 240°around .550"-.600" lift anything well above about .120" free drop gets by just fine. Of course, better/lighter valve-train lets us sneak closer towards the edge too.

Just mocked up my SBF with no gaskets this morning and got free drops of .180" intake/.240" exhaust into the valve reliefs. Small 1.98" valve head with tons of radial clearance(clayed it) and only .570" lift @ 228° solid FT cam should fit the existing valve reliefs with room to spare.

[CamKing]

Thank Quick question. Is there an overlap or convergence point where XXX amount of duration and XXX amount of lift equates to a minimum free drop requirement?

Unfortunately, no.
Lift, duration, and centerlines won't tell you what the lift will be 10 degrees after TDC. Too many other variables.

I was just looking at two different profiles of mine. Both are 312@ .012", and 262@ .050". One is a .417" Lobe Lift, and the other in .480" Lobe Lift.
I assumed the .480" lobe lift profile would have more lift at 10atdc, if they were on a 104 intake centerline. I was wrong. The .480" lift profile actually had .006" less lift at 10atdc.
The lift curves were totally different. The .417" lobe reached max velocity at 10atdc, and the .480" lobe didn't reach max velocity until 19atdc. The .480" lobe didn't overtake the .417" lobe until .250" Lobe Lift, but it was 5 degrees bigger at .300", and 40 degrees bigger at .400".

[groberts101]

Thanks for the reply, Mike. I kinda figured it was a dead end question but you can't blame a guy for trying to find new tricks!

[groberts101]

You can play around with this
Estimate Cam Intake Duration Needed @ 0.050" http://www.magneticlynx.com/carfor/calccam.php

Stan

Hi Stan. Love the tool but maybe I broke it. Is it even possible that my 310" SBF would only require 173° duration @ 7500 rpm with 100% VE through 350cfm cylinder heads?

If I use my other "normal heads" flowing 250 cfm it seems damned close.

[MadBill]

Thanks for the reply, Mike. I kinda figured it was a dead end question but you can't blame a guy for trying to find new tricks!

The more customer-focused cam grinders can provide lift at TDC data for the lobes, rocker ratios, LCA and index you might be considering. Even though the minimum P/V will likely be 5-10°ATDC for intake and BTDC for exhaust, it will get you in the ballpark.
I don't think I'm setting the bar too high here, but given the valve drop numbers and the R/S ratio, a full custom boutique shop like camking's can probably provide the exact minimum P/Vs and relevant CAs for your specs*, as inferred from his 11:55 AM today post. (*Of course it makes far more sense to just leave the whole works in his hands...)

[Stan Weiss]

You can play around with this
Estimate Cam Intake Duration Needed @ 0.050" http://www.magneticlynx.com/carfor/calccam.php

Stan

Hi Stan. Love the tool but maybe I broke it. Is it even possible that my 310" SBF would only require 173° duration @ 7500 rpm with 100% VE through 350cfm cylinder heads?

If I use my other "normal heads" flowing 250 cfm it seems damned close.

A SBF 310 ci (4.06" bore 3.0" stroke 5.09" rod) @ 7500 RPM has a peak piston flow demand of 276 cfm.

Calculate Engine / Piston Peak CFM Demand http://www.magneticlynx.com/carfor/calccfmd-r.php

Stan

[John Wallace]

Error message?

[randy331]

Hi Stan. Love the tool but maybe I broke it. Is it even possible that my 310" SBF would only require 173° duration @ 7500 rpm with 100% VE through 350cfm cylinder heads?

It's this type of results that make it useless.

Lower cfm and it just adds duration if ve is left the same.

It just doesn't work that way.

Randy

[77cruiser]

Stan where do you set the VE % at?
My 421 came out pretty close but the VE really throws the curveball.

[Stan Weiss]

Error message?

Thanks John

http://www.magneticlynx.com/carfor/calccfmd.php

Stan