TXCatfish

Why would the lift numbers be reversed on a cam? Example Tsunami cam.648 .609?

Kip Fabre

Those are not reversed. That is correct. .609 .648 is backwards. Thats left over from the Flat tappet days. Why would you open a EX valve more than the IN valve? Go look at any flow numbers the IN needs to be open more than the EX because its a bigger valve. So a 2.00 IN valve may need to be open .750 to get to its peek flow numbers while the 1.6 EX valve may only be needed to be opened .600 When I see numbers like that I have to think how do they come up with that? To much EX lift can KILL power.

HISS

iTrader: (52)

I have a feeling he's talking about a reverse split in duration. Example 233/244 vs 244/233. Lots of people talking about this nowadays.

JakeFusion

iTrader: (7)

Typically, the exhaust lobes used also have longer seat to seat duration and lower lift as they are milder lobes. Exhaust lobes need more duration to hold open the exhaust valve longer to expel the spend exhaust gas and typically need to be less aggressive to reduce the amount of valvetrain clatter when shutting the valves (you hear this echoeing in the header).

TXCatfish

Hey thanks Kip! Honestly I had to read this a few times to understand what you are talking about. I'm a idiot when it comes to numbers and camshafts.

Reason I said .648 .609 are reversed is I thought most cam specs I've seen the Intake number is lower then the exhaust number. Another example and the reason for this thread I'm currently running a 222/224 .570 .580 112. So my lift numbers are reversed? And if I move up to a bigger lift cam does the intake need to be bigger then the exhaust?

Also can I tell you my specs and get your opinion on a cam and if it's worth changing?

Thanks!

TXCatfish

No I meant reverse in lift. I got confusted on the whole thing. So when people say reversed number cam they are talking about the duration not lift?

TXCatfish

Okay that makes sense. Again got the duration and lift confused.

Thanks

KCS

iTrader: (20)

Wouldn't more lift often times be a consequence of longer duration lobes since that's typically the trend with lobe designs?

How does too much lift kill power?

DREAMZ28

iTrader: (1)

I would assume at a certain lift, the port becomes turbulent and flow suffers. Especially on stock heads, I could see this being a place of diminishing returns. From the way his post is worded, I imagine he is referencing how much the valve itself shrouds the port, and how far out of the way it needs to be pushed in order to maximize flow. The intake valve is bigger, hence the lift needs to be higher since it is covering more surface area that is blocking/hindering flow.

Kip Fabre

I have not seen more lift on the intake kill power unless the duration get to high. On the EX side I have seen a 1.5 rocker work well switch to a 1.6 and the power goes down. I have also seen the 1.6 work better than the 1.5 but at a certain point when we have increased the duration with less lift it make more power than the higher lift on the EX side.This is the short answer.

Kip Fabre

One of the reasons you see camshafts with more exhaust lift than lift on the intake side is that with the flat tappet cams used in older production engines like Chevy and Ford the lifter diameter limits the lifter speed (velocity), so duration limits how much lift you can make without the lobe coming to a sharp “point”. When a series of lobes was designed as the duration was increased so was the lift. The cost of manufacturing a “master lobe” for a production machine was too prohibitive to make both the high lift intake lobe and a lower lift lobe for the exhaust. With our CNC cam grinder grinding off of a computer file instead of a master plate it has made this process much more cost effective. Basically we can computer design any lobe design we need and “email” it to the production machine and just takes minutes to be done! So if your cam guy recommends more lift on the exhaust you need to ask him “Why?”.

ringram

Some good threads on speedtalk about this.

Stalling the exhaust port seems one consideration.