why are some cam lifts less on the exhaust side? say like with my cam, the way it is now its 226/232 559/565@50 thats with 1.6's now if I put 1.5 on the exhaust side and made it 559/535@50 whats the point of doing that? I have seen alot of cams set up this way and curious as to why?


thanks

 

Not sure I understand your question. The cam is ground with more lobe lift on the exhaust side. It would only have less gross lift if you chose to change only the E from 1.6 -> 1.5X, and left the I at 1.6X. Your math also appears to be a bit off.....

0.565 x (1.5 / 1.6) = 0.530"

The question would be "why do you want to reduce the gross lift on the exhaust side?"

 

The main reason is that the lift may not be needed on the exhaust side. The exhaust valve has a smaller diameter than the intake valve. Consequently, when opening the valve it reaces the point of max flow at lower lift. BTW - you often see gains going past the point of max lift. this is misleading. It occurs because to do you, the duration at lower lift points also usually increases.

Rich

 

If the cam is custom ground they do that because you have a strong exhaust port or good header/ex combo to go along with it. I see alot of that if the head has a 70% or better intake to exhaust flow ratio.

Also you have to consider this, the piston is chasing the exhaust valve when it is closing on the ex stroke.

My duration is straight across, but my lift is like .020 less on the ex side.

David

 

right!...why do you want to reduce the gross lift on the exhaust? and what is the benifit to do that? more power?

also my cam was custom ground for 1.52's and with those the lift @50 is 531/535 I just added the 1.6 to give me more lift since im thinking it should have been ground with higher.
my lobe lift is .34961/.35323 so my lift with the added 1.6's would be?

 

You seldom lose power with more valve lift. But you may run into piston to valve or other clearance issues and need to use more spring, put more stress on parts leading to breakage, etc. if you increase the lift. So, in general, there is a potential downside to using more lift than you need. IOW, don't use more lift than needed for max power. Indeed, it may make sense to use less to keep the thing intact, avoid clearance issues, etc.

Rich

 

I often wonder why someone buys a "custom" cam theoretically designed for the specific engine combination then changes things from what the cam guy specified. If the performance increased with the change I suspect the cam wasn't the right one in the first place.

It pays to choose yur cam guy carefully.

Jon

 

I agree Jon, but once the cam is installed you don't have much to play with when experimenting for maximum hp, and or results. As they say, each motor is different. Changing rockers isn't that bad. Cam timing for us less experienced can be a pain in the butt, but maybe worth a try. And in the end I believe that with a little trial and error you'll see if there are results worth the effort, and possably a cam change in order. Many have seen where the smallest change in a cam, even a mild one for the street (for example) can make a 10 to 20 hp difference. JMO, which isn't worth a whole lot.

 

If the cam guy didn't take into account a number of lift/duration/rocker ratio/advance/retard combinations in his "design", you probably have the wrong guy doing you cam.

If I had a cam designed specifically for my engine, installed it with the recommended valvetrain bits and the ICL specified by the cam designer, and I could pick up 20 hp (5% on a 400 hp engine) by varying his specs for rocker or advance retard, etc., I'd fire the cam guy and ask for a refund unless I was getting free cams to do his R&D. Well, I probably could get free cams, but that's a different stroy.

Jon

 

so will adding different rocker ratios to a custom cam made for a specific rocker ratio change the whole way the cam with perform? for the bad?

 

The only way to tell is to try it. But if, as Jon suggested, the specs were right in the first place it should already have been optimized for a specific RR and therefore not improve, or get worse, with a change. Of course, the original RR might have been chosen with something other than max power in mind. 1.6:1 may have been selected, for example, with consideration to max lift and spring life with full knowledge that going to 1.7:1 would produce more power. If you are talking about really aggressive lobes, they will have been designed and tested with a specific range of RR in mind. Such a lobe, regardless of what your motor wants, might exhibit stability problems with an increased RR. Or, OTOH, they may be designed with a very high RR in mind. There are lots of examples of this because some racing classes have "lift rules" that specify max lobe lift. To get more power, such a lobe may be designed to work with a RR of 2.0:1 or even higher. In that case, using a lower RR would result in very lazy valve motion and you would have a real turd on your hands - one that produced much less hp than the seat timing would suggest.

You might want to read the "custom cam" thread that is going on in "LT1 Tech" to get some more opinions about some of these issues. https://www.camaroz28.com/forums/sho...d.php?t=567918

Rich