cam thoughts

[AZGhost623]

Due to a problem with my P90 head, its getting fixed due to a bad gas incident a month ago resulting in a bent valve and leaving #5 with 0 psi on a compression test. While its there I am having the cam go through a regrind to what he thinks will be a good setup for what im looking for (mild, good street setup). He said it will give a lumpy idle, and strong pull all the way up to 7000 rpm. He is a local builder and this is a spec he uses on carb'd engines. Any thoughts? 

 

280 duration

.480 lift

106 lobe center

 

Valve Timing:
Intake: .010 lift opens at 31* BTDC closes 31* ATDC (62* overlap)
Exhaust: .010 lift closes at 69* ATDC / opens 69* BBDC

 

 

[jeffp]

Ok well, you did not say what the application is, but the specifications that you stated are more cam then you need. 62 degrees overlap will give you a soggy bottem end, and you should start making power in the 3-3500 rpm range. The lobe center is WAY off! you need to look at a 110-112 lobe center for the results you are looking for. Also the .480 lift could be a little higher say in the .500-.550 range.

 

This is a street car right? so what is better suited to your application is a short duration and high lift not the long duration short lift for the best results.

[AZGhost623]

Thanks Jeff

For whatever reason doing some homework on these cam spec's looks like most lobe centers for cars that are carb'd is 107 (ish). The lobe center for EFI seems to be around 112 like you said? Im not sure exactly what the lobe center does or how that contributes?

 

Yes, a streetcar primarily, weekend warrior, and occasional overnight trip type thing out of town. It will have some possible track use on occasion with HPDE and NASA.

[Leon]

280 duration

.480 lift

106 lobe center

 

Valve Timing:

Intake: .010 lift opens at 31* BTDC closes 31* ATDC (62* overlap)

Exhaust: .010 lift closes at 69* ATDC / opens 69* BBDC

 

My first thoughts are that you typed in the cam specs wrong. By those numbers, your intake/exhaust duration is 62/318. Hmmm...

 

I'm guessing:

EVO=69BBDC

EVC=31ATDC

 

IVO=31BTDC

IVC=69ATDC

 

That gives 280deg duration with 62deg of overlap. I'm with JeffP regarding lift and duration.

[ram75280z]

Thanks Jeff :)For whatever reason doing some homework on these cam spec's looks like most lobe centers for cars that are carb'd is 107 (ish). The lobe center for EFI seems to be around 112 like you said? Im not sure exactly what the lobe center does or how that contributes? Yes, a streetcar primarily, weekend warrior, and occasional overnight trip type thing out of town. It will have some possible track use on occasion with HPDE and NASA.

This is LSA (Lobe Separation Angle)

 

Generally the closer LSA will give you a better mid range, and less vacuum at idle(rough idle). Torque curve looks like a hump.

 

Wide LSA cams give a flatter torque curve(more like a plateau) and better idle vacuum, which is why injected cars have had them in the past, because they needed the low rpm vacuum to operate the fuel pressure regulator.

 

You can run either on a carbed car, but the carbs will need to be tuned accordingly. This is the single biggest factor in getting a built motor to have a clean idle for smog testing.

 

I should've added, i would agree with jeffp overall. Except with that much lift, i would go for at least 114 LSA. Which i think you'll find is what's necessary to have overlap around 50 with that much lift, but i haven't done the math.

Edited May 2, 2013 by ram75280z

[Leon]

As far as LSA goes, personally I don't care about it. If you know the important bits (valve events, lift), LSA doesn't really tell you much more...

 

It's really used more for degreeing than describing a cam's characteristics. Valve overlap degrees will tell you way more than LSA...

[Xnke]

I run a similar cam right now...and it's OK. Power comes in at 2800, really feels good about 3200 and pulls fine to 7000RPM and more...should make power to 8000RPM max, but my pistons won't go that high, so I set the limiter at 7100 most of the time.