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Best cam events for big bore/small valve

General engine tech -- Drag Racing to Circle Track

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4banger
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Best cam events for big bore/small valve

Post by 4banger » Tue May 19, 2020 4:57 am

2006 (gen 4) LQ4 .6.0L. Bored 0.030 with new flat (LQ9) top pistons. All new parts.....Summit ls truck cam. (205/217 500/500 112+2) , hyd. Lifters, melling oil pump, injectors, 560 beehive springs,
I'm putting the 5.3 (862) heads on it to raise compression with a 1.89 intake valve. The intake runner flows 210ish.
I'm looking low end tongue as this is in a 1999 GMC Sierra 2500HD with 4l80.
Is there a better cam or is this one as good as it gets? Summit has a similar cam with more intake duration(213/217 500/500 112+1).
What difference will a little more intake duration make with 1 degree less LSA than the first cam?
I thought I was wrong once but I was mistaken...

jeff swisher
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Re: Best cam events for big bore/small valve

Post by jeff swisher » Sat May 23, 2020 12:54 am

You need to look beyond the numbers you posted.
The second cam with more intake duration could possibly close the intake valve a lot later in the cycle and that would hurt low end power which you want for the extra pulling power out of the hole.
Pick the cam with the earlier closing intake lobe.
The second cam may be that cam and it could be the first cam also.. you need to research them and see.

I had a friend grind a cam for a buddies LQ9. I ported his stock heads and used the old cam and ground an old Hot cam grind onto it.
The Hot cam with 1.5 rockers is 218-228 @ .050 on a 112 LSA and .492" lift.
With the 1.7 rockers the duration at .050 will be up about 4 numbers more.

Now it is in a 4000 lb chevy truck from the 70's with TH350. It needed more grunt for sure.
So the cam grinder ground the cam on a 109 LSA and the intake valve actually closed earlier than the LQ9 stock cam and cranking pressure was up also because of that change.
Not the best grind for best MPG but it does pull an 8 foot bed full of sand quite well and it is quite peppy.

He got more power in the low end of the RPM scale and the top end of the scale.
Win Win.

I have had custom cams made that closed the intake valve quite early like grinding one on a 106LSA and then move the exhaust lobe to make said cam an actual 112LSA.
An experiment I had to try..I figured the power would fall off quick after the peak and it did but it got better MPG by 5+ MPG over the same lobes on another cam with the same closing time on the intake lobe and move the exhaust lobe to make it a 106LSA cam.
The 106 sure was a thirsty cam.
Cam lobes used were the old 286H 218@ .050 and the intake valve closed sooner than if I had ran the 260H.

You could call some cam companies and have special cams made.
you probably know that though.

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