I understand why you need a narrow Lobe Separation Angle, but Degrees of Valve Overlap is a little more of a precise measurement than just a LSA Angle.

At what point is the overlap degree too much? For A Blower that is. 5*?

 

I don't know what is to much?
Mine has 33* overlap @ .050" and 77* overlap seat to seat, 114 LCA
I see -10 on the vacuum/boost guage, w/idle at about 1050rpm.

You can hear the lump in my idle a few times in this vid.
http://www.youtube.com/watch?v=ISMBSgMaWEM

The EFI works fine, but it's to old to need any smog test, it would never pass.

---Bill.

 

As far as FI, I meant Forced induction.. 33* GOOD LORD!

SO I'm thinking I can blow this cam... 224/228 .637 .639 110LSA.. BUT with that Duration, lobes and the LSA, it only has 5* of overlap.. This thing is a TQ monster, I can only imagine it with a blower!!

 

Mine is from Comp, solid roller, it's shown in there catalog as a Blower/Turbo cam.
http://store.summitracing.com/partde...8&autoview=sku

---Bill.

 

Hmm.. I figured havign little overlap would help keep the fuel air mixture in the chamber and prevent it from being blown out the exhaust during overlap.. -Am I trackin here?

 

LSA doesn't matter, only overlap. Only the slowest 10% of us don't get that.

People tend to agree that overlap is bad for Forced Induction, but no one seems to know exactly how much is too much. Surely, it depends on a multitude of things such as boost level, exhaust backpressure, port geometry, etc. . .

One thing that makes you go "hmmm" is the fact that an optimized turbo system will have the same amount of exhaust pressure (or less) as boost. In this case, you cam it just like it's naturally aspirated because the dynamics are unaffected.

Very little dyno testing has been published on FI cams. One guy who tested 4-5 cams in a twin turbo LT1 with a 2/1 backpressure/boost ratio concluded that his gained power every time he added overlap, up to +5 deg. However, he never went over +5 deg @ .050. It may very well continue to improve beyond that.

Mike

 

Choose your cam based on RPM range. Most cams have a designed torque curve and almost all will work with forced induction. Decide if you want a screamer or a low rpm torque monster. All you are doing is moving the rpm range up or down with a cam. When I went from a 112 LSA cam to a 114 LSA cam I lost a little power off the top end but gained substantially in the mid range.

 

97WS6Pilot I have a really good memory, but didn't you go to a smaller duration cam??

 

I went from a CC503 to a CC304. Check out the published rpm ranges. It says that my CC304 will peter out at 5000 rpm. I can tell you that it doesn't stop making power until 6200. Why? I believe that the supercharger spreads out the powerband and adds to the top end. So IMHO one does not need a big cam with forced induction. My car is much more enjoyable to drive with the CC304 because it makes power right off idle all the way to 6200 with no dead spots. Also with the powerband dipping down to 1000rpm gas mileage is much better.

Part Number: CCA-07-503-8
Cam Style: Hydraulic roller tappet
Basic Operating RPM Range: 1,800-5,800
Intake Duration at 050 inch Lift: 224
Exhaust Duration at 050 inch Lift: 230
Duration at 050 inch Lift: 224 int./230 exh.
Advertised Intake Duration: 276
Advertised Exhaust Duration: 281
Advertised Duration: 276 int./281 exh.
Intake Valve Lift with Factory Rocker Arm Ratio: 0.503 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio: 0.510 in.
Valve Lift with Factory Rocker Arm Ratio: 0.503 int./0.510 exh. lift
Lobe Separation (degrees): 112
Intake Valve Lash: 0.000 in.
Exhaust Valve Lash: 0.000 in.
Computer Controlled Compatible: No
Grind Number: LT1 XR276HR-12


Part Number: CCA-07-304-8
Cam Style: Hydraulic roller tappet
Basic Operating RPM Range: 1,000-5,000
Intake Duration at 050 inch Lift: 210
Exhaust Duration at 050 inch Lift: 220
Duration at 050 inch Lift: 210 int./220 exh.
Advertised Intake Duration: 266
Advertised Exhaust Duration: 276
Advertised Duration: 266 int./276 exh.
Intake Valve Lift with Factory Rocker Arm Ratio: 0.500 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio: 0.510 in.
Valve Lift with Factory Rocker Arm Ratio: 0.500 int./0.510 exh. lift
Lobe Separation (degrees): 114
Intake Valve Lash: 0.000 in.
Exhaust Valve Lash: 0.000 in.
Computer Controlled Compatible: No
Grind Number: LT1 266HR-14

 

Yea I agree with ya, I have a 224/230 in my 383. It does seem that blowers extend the range of cams, been noticing that for a while too.

 

I've seen a rule of -8 to +8 and a blower is more forgiving than a turbo,, but everyone that has tested at all has always seen large gains up top by going bigger.

Just like an NA motor you are shifting your power band upwards. I know of drag cars with massive turbos and 20* or more overlap. But they are leaving on a transbrake and that is all they are setup for.

I have a 218/224 on a 112. Its perfectly happy spinning past 6.

 

Great info! would a 230-230 dur @50 on a 107 give me 23* of overlap? Just trying to see if I calculated it right.

 

just for your fyi.
Any cam with an LSA under 110 will most likely be a bad choice.

 

Ya I knew that but I wanted to compare to get a better understanding. Im planning on something in the 112 range

 

I have a custom Bret Bauer Cam. I asked Bret for spec's but he said he was tired of being asked to go thru the trouble, then people either ignoring his advice or buying the cam he recommended elsewhere. I paid up and the cam I have is just absolutely perfect for what *I* want. That being, 600+rwhp at 12 to 14 psi, civil drivability/street manners on a car that would be 80%/20% on street/strip. Below boost, it feels like a stock 95 Z28. Smooth driving, gobs of torque, good gas mileage. But accelerate into boost? It hits 10 psi quick before you've even rev'd it very far. And this is in an M6 with 4.10's. I haven't had a chance to dyno it because I'm still tuning (running a tad rich at 11.x) but once I get the dyno, then slicks, I'll have a more complete impression/measurement to portray.