GREGGPENN

CAM 88-89 L98 10066049 In/Exh Dur@.050" 207'/213' Lift (w/1.5) .415"/.430" LobSep 117'

The heads are the 113 heads.

I'm trying to figure out intake flow rate and the intake valve duration. Specifically, what will the head flow and how much time (with respect to the cam rotation) does it have to fill the cylinders?

I saw something suggesting 185-190 cfm non-ported. An increase to 210-215 cfm ported (for stock 113 heads).

I don't understand intake valve duration specs. I would guess it's related to how much of a 360-degree rotation a valve is open, how far it opens, etc... Please translate the top line into English.

I'm trying to figure out if the stock cam/head setup has all the air it needs from the stock TPI setup. Obviously most modders want to change cams/heads to create a "total" pkg. And, there's talk that the TPI (or plenum?) was designed for the 305 motor. But, no matter how much I look thru archives and thru 3rd gen, I can't find proof of anything.

For raw calculations, I recently stated that a 350CI motor needs 607cfm @ 6K rpms. Then, I thought the intake runners were amply sized because their combined flow rate was well above 607cfm (e.g., 200cfm * 8 cylinders = 1600cfm!). WAIT....

Then it was pointed out the duration of the intake valve "restricts" the flow considerably. In other words, the runners aren't always flowing. (I'm an idiot). So, I was asked to review the event stats of the cam. I assume they are on the first line. So, how much of the cam's 360-degree rotation is the intake valve open? Is the intake really "undersized"? If so, by how much?

BTW: I'm also understanding that the length determines as much as the cross-section of the intake ports. Longer = lower rpm maximums/Shorter = higher rpm maximums.....
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Bonus question #1
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For future reference, how do the upgraded heads compare to the stock 113 heads? IOW: how much more do they flow (ballpark)? How much will stock head flow with 1.6/1.7 RR? How much harder on the valves is this vs a bigger cam?
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Bonus question #2
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Finally, how weak do you think valve springs get in 18, 19, 20 yrs? (I never really considered this in the equation of owning an older, lower mileage car.

Thanks
Gregg

rodj

Only numbers I have seen have stock 113 heads at 196 /170cfm @.500

Stock cam is pretty whimpy at .430 lift

ZZ4 crate engine uses same heads with 208/221 .474 / .510 lift cam. Makes 355Hp (with carb) so obviously some potential there.

Most on this Forum don't consider the gains possible from porting 113"s worth the cost versus buying aftermarket heads that flow more; not withstanding finding someone who knows how to port 113"s correctly.

Bonus question #2.
If not going over .525 lift ;GM ZZ4/LT4 springs can be had for $35 from the dealership.
GM # 12495494 set of 16
Would not use 20yr old springs on any engine, period.

"I don't understand intake valve duration specs."

For comparision purposes, a valve is considered not to have any useful flow until it is off the seat by .050 lift.That is why you compare cam lift numbers at 0.050 lift.Apples with apples

A cam maker may grind a long ram on the cam so the "advertised" numbers look bigger even though it may have a smaller USEFUL duration than another brand with less "advertised" duration.

In/ Exh Dur @.050" 207'/213' Lift (w/1.5) .415"/.430" says

Intake Duration @.050" lift is 207 degrees with a max of .415 lift at the cam
Exhaust Duration @.050" lift is 213 degrees with a max of .430 lift at the cam

On the numbers above ,the intake valve opens for 207 degrees useful lift from .050 through a maximum of .415 lift to .050 on the closing side with a stock 1.5 ratio rocker.
Same idea for exh figures.

GREGGPENN

Don't understand the first sentence. What's 196/170? Is the flow 196 or 170. Also, is that flow never reached because the cam lift is only .43 (or do I need to multiply that by the rr ratio to get .645)?

Well, I guess so!!!!

From what I've read, 30HP.

Pfffffffftttt. Mine are only 18 yrs old! What do weak springs cause? (I have a guess/two but want to hear.)

Well, I was closer that I thought on my guess because I had guessed correctly. I just thought 207 degress out of a 360 rotation sounded like it was open too long. It's called a 4-cycle engine and only 1 of the 4 cycles is inputting air. 360/4=90 degrees.

I'm also assuming the lob sep is the number of degrees between the intake and exhaust lob peaks.

I've already guessed above... Does the 1.5 roller rocker need to be multiplied times the cam lift to get max valve opening?

Finally, over time, the springs bearings, oil pump, rings (have spring too), etc... get weaker and weaker. Modding a motor has to add stress to existing components -- increasing the odds of engine failure. That's obviously another reason to redo the whole thing or leave well enough alone.

Hey, did someone say something about the world running out of gas (petroleum) too? Naw, that will never happen....

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Dang. I'm coming up with as many reasons to leave it alone as to change it. Guess HR90 is right. Save up for a C6 or forget it!

gp