Can someone explain the different numbers in heads / cams? I remember a post explaining them a while back, but can't find it. Also, what do the numbers mean in plain English. IE, how do they affect performance, driveability, etc. Finally, how about the 'accessories'? Are they necessary? Is it stupid to upgrade without new springs, etc?

For example:

1. Heads - 205 vs. 225?
2. Cams - Intake Duration, Exhaust Duration, Intake Lift, Exhaust Lift, LSA
3. Valve springs
4. Pushrods
5. Underdrive pulles

 

There is Wayyyyyyyyy too much to type. I would suggest that you can check out how stuff works:

http://auto.howstuffworks.com/camshaft.htm

and then after you have some understanding how camshafts work then ask more specific questions

 

Here's a great place to start:

http://www.ls1tech.com/forums/showthread.php?t=327734

 

Heads - the 205 and 225 refer to the volum of the intake runners. Larger number means more total flow (especially at higher RPMs), smaller number means higher velocity (better for low RPM throttle response). 205 is typically better for the street, 225 & up is better for racing. Other head specs refer to the flow at various inches of lift. Typical spec might be 300 CFM @ .580". More flow = more power.

Cams - duration refers to the number of degrees of rotation that the valves are open. More duration allows more time for the intake charge to flow into the combustion chamber, = more power. Too much duration causes poor idle & low speed response, loss of driveability, poor emissions quality & gas mileage. Lift refers to how hight the cam lifts the valves. Higher lift = more power, but also requires stiffer valve springs and hardened pushrods. Stiffer valve springs increase wear and valvetrain noise, and they don't last as long, need to be replaced. LSA refers to lobe separation angle, has to do with valve event timing. In general, a smaller LSA (110-112) has more valve overlap (both intake and exhaust valves open at the same time), resulting in a choppy idle, stronger mid-range power. A larger LSA (114-118) has less overlap, resulting in a smooth idle, low emissions, wider & smoother powerband.

Valve springs - stiffer springs are needed to control the higher lift, longer duration cams, especially at higher RPMs. Single springs such as the popular Comp Cams "918" springs are usually good for most cams up to .600" lift, dual springs are needed for larger cams.

Pushrods - hardened pushrods resist the stress of stiffer springs and high RPM operation. OEM pushrods can bend more easily. Pushrods also come in various lengths, to accommodate heads that have been milled for higher compression. Hence you will see ads for 7.35" and 7.4", and assorted other lengths.

Underdrive pulleys - these are sized differently so that they drive the alternator, waterpump, and other accessories at a lower speed, thus reducing the power consumed. The most gain comes from the crankshaft pulley, but the alternator and water pump pulleys can also be replaced. Typically results in a 8-10 HP gain. Downside is that your headlights may dim at idle, and if you have an aftermarket stereo system, amplifiers, subwoofer, etc. you may not have enough electrical power for them.

 

Thanks for that excellent explanation!

 

Anyone know the specs on the factory heads and cam for a C6 vs. a Z06?

 

Great explanation. Thanks

 

 

Great info, I love this place,

 

Hitman - I stand in awe of your knowledge

 

Contain the awe, please. What I posted was pretty basic stuff. There is a LOT more to it, and not everyone agrees on even the most basic stuff. I've seen 20 page threads on lobe separation angles alone. Not so much here though.

Read and learn, make up your own mind. Tolerate other's opinions, and keep an open mind. There are many others on this board who know a lot more than I do, the trick is to separate the truly knowledgeable from the opinionated.

Anyway, thanks......

 

Yes, a simple:

"T'warnt nuthin' ma'rm" <while scraping boot tip in circle>

would have done....

(seriously, good post! )

 

Only the tip of the iceberg ........ but It was very thoughtful of you to post an answer considering how opinionated we all can be with regard to the subject of picking a cam & heads.

Great advice

 

 

YUP its him again

 

Come on now...we all have our specialties...i am a dumb junk bond trader that knows nothing about cars...that is why I joined this forum

 

The point is HitMan, that YOU took the time to explain some basic and intermediate stuff to us NUBs, you know, the car challenged folks. Many would have not answered, referred us to some tech manual written in Greek or, worse yet, made disparaging remarks about our lack of automotive knowledge.

A sincere thanks for your help – we NUBs appreciate your efforts.

U R da Man . . .

 

Everybody was a noobie at some time, so I can relate. When I have the time, I enjoy sharing my opinions. Glad that you find it to be helpful.

 

Yeah, but JFTaylor is so old that he forgets he just learned something and must learn it again . . . and again . . . and again!
Just kidding John, and I agree with you that HitMan provided an excellent beginning in a very technical area!