I talked to my lokal tune shop today about the choice of my camshaft he told me that using the standard issue cam would be more appropiate since the increase of duration would decrease boost. this made me confusued since it didn´t correspond to what you guys said in my earlier thread. :confused:
need some help!!!! :nopity

 

well i was told to run a cam that is 114 or 116 sla then say a cam that is 112 or 110 sla because with a blower it is hard to keep it idleing? not so much about losing power?

What kind of cam where you looking at getting?

 

With a blower cam you don't want or need a cam that has a lot of overlap that would bleed off the boost from the blower. Also you would want a cam with more exhaust duration to keep the exhaust valve open a bit longer to get the spent exhaust gases out. It also depends on your engine displacement. If you have a 383 or a 396 stroker you will want more intake duration to match the longer stroke event of the crankshaft.

LPE makes a blower grind that is a 215/220 @.050 lift with .530/.530 lift ground on a 114 LSA. This cam makes great power, nearly 600HP on a supercharged small block with a SR manifold on very modest boost levels. It does idle nearly like a stock cam as well.

I am running a 224/236 custom ground Comp Cam which was ground on a 112 LSA. But I have a 396 displacement LT1 as well.


[Modified by tjwong, 9:27 AM 1/5/2004]

 

Yes i agree with TJWong... i was told by comp cam to run a cam that does not have a lot of over lap! Also a friend of mine from UTI told me it is about the heads and cam.... what i was told is you want a cam that will match your heads and application (SC/NA). For example my cam is a custom grind of 218/230 @.050 with 114 sla and with 1.6 roller tip rockers it 534/ 54?....

So you dont want a big cam with stock heads you will not make good power and then again you dont want a small cam that will not utilized the heads to there max potential!

I would call a cam rep and see what they recommend! What do you have done? is the block stock with stock heads or ?

 

I too run a 224-236 cam. I run a 114 LSA...that gives me 1 degree of overlap @ .050"...see below for formula:

((224 +236)/4)-114 LSA = 1 degree of overlap at .050" lift

An increase in duration without a corresponding increase in LSA will result in less boost...stock cams usually do well as blower grinds.






[Modified by Brand-X, 3:55 PM 1/5/2004]

 

Thanks for the responses so far, I thought that maybe some mor info on my combo would help you in choosing a cam...

It's a l98, with a D1 procharger @10psi, ATI intercooler. Stock intake, stock bottom end, Ported heads, with bigger combustionchambers to lower the compression. 1.5 roller rockers on the intake, 1.6 on the exhaust. Long tube headers. I'will be changing the torque converter, and installing a shiftkit.

 

Brand-x could you explain to me why you devided the duration by 4??
((224 +236)/4)-114 LSA = 1 :confused: :D

 

I run a 248I/254E duration custom Comp Cams solid roller with 112 Lobe Separation.

Based on the formula you have mentioned, I derive the following:
((248+254)/4)-112 LSA = 13.5° overlap

This is the first that I have seen of this formula, and it difers a bit (by 1/2) from what I derived from the cam card supplied from Comp. The cam card defines the valve timing events (@ 0.050") as follows:


Intake open - 12 BTDC Intake close - 56 ABDC
Exhaust open - 59 BBDC Exhaust close - 15 ATDC

Based on a 720° cycle for a 4 stroke engine, the following would apply.
Exh close - 15°, Intake close - 236°, Exh open - 481°, Intake open - 708°

To my understanding, the determination of everlap is while the exhaust valve is open following the power stroke (from 481° thru 15°), the intake valve just begins to open (from 708° thru 236°), causing some (more in the case of Forced Induction) of the fresh charge to exit the combustion chamber without being consumed.

In the above example, the overlap would be from 708° (IO) thru 15° (EC).
overlap = 15° - 708° (same as -12°)
overlap = 15° - (-12°)
overlap = 27°

Why does the difference of 1/2 exist? Your formula is certainly much simplified over plotting the valve timing events, but nonetheless, is different from what I had understood to be correct.In your cam, it would be the difference of 1° or 2° of overlap, which really is splitting hairs.

As a side note, I used your formula to calculate my old HR blower cam that made 545RWHP in a 350ci motor. ((228° + 228°)/4)-114 = 0° overlap.

Thoughts?

Aaron

 

You're right, the formula is off by 2x @ the overlap calculation. I'm an idiot when it comes to this stuff...this is how I understand it:

1. 248 crank degrees/2 (2:1 cam/crank ratio) = 124 cam degrees int.
2. 254 crank degrees/2 (2:1 cam/crank ratio) = 127 cam degrees exh.
3. 124 + 127 = 251 total cam degrees open
4. 251/2 lobes = 125.5 average open cam degrees per lobe
5. 125.5 - 112 (known lobe separation) = 13.5 overlap in "cam degrees"
6. 13.5 * 2 (2:1 crank/cam ratio) = 27 crank degrees of overlap

In the previous formula, I forgot to include the formula for converting ioverlap to crank degrees. The corrected formula should read:

(((int+ext)/4)-lsa)*2=overlap

Please note: A negative overlap number would represent the overlap occuring at some point less than the expressed lift value used in the calculation (e.g., @ 0.050"). I hope this this helped.

The formula works if it is understand that LSA is expressed in cam degrees and duration is expressed in crank degress.
CT







[Modified by Brand-X, 10:51 PM 1/5/2004]

 

(((224+236)/4)-114)*2= 2 degrees of overlap

Just testing!!

My cam card says:

-2 BTDC Int. open (or 2 degrees ATDC)
4 ATDC Exh. close

-2 - 4=2 degrees overlap

 

SO what do you guys think about the LT4 hot cam, would that be a good cam for my engine??
hot cam spec: 218/228 lift @.50" is .525"/.525"

 

I thought the hotcam was designed for NA applications. As for na cam in blower car, I used to run the CC305 cam in my 355 LT1...it had 220-230 w/114 lsa...worked fine! If I was gong to buy a cam, I'd buy one that was cut specifically for a blower application. I know CompCams makes a blower grind in a very similar profile to what you're talking about (i.e., 218 Int. duration), have you given their techline a call?

 

No I haven't called comp's techline... Do you think it would bee wise to contact them??
:crazy:

 

It couldn't hurt...here are some of their blower grinds (a cut and paste from racenet):

Competition Cams LT1 Xtreme Energy Nitrous & Supercharger Cams Xtreme Energy Cams are Comp Cams newest series of hydraulic cams. They are designed to take advantage of the latest improvements in valvetrain components and the newest developments in camshaft design. Their ggresive lobe design produces better throttle response and top end horsepower than other cams with the same duration @ .050" while delivering increased engine vacuum. Comp Cams Xtreme Energy Cams can be used in any street or street/strip application where both throttle response and top end horsepower are desired. Maximize torque, acceleration, and throttle response providing excellent high RPM horsepower Faster intake valve opening increases engine vacuum and enhances throttle response Special intake closing ramps close valve earlier providing more cylinder pressure and torque without valve train noise Faster ramps achieve maximum velocity sooner, increasing the area under the lift curve and providing maximum horsepower

Part # Description Price:

CCA-212-224-14 mild applications good mid and upper RPM power
Dur@.050 212-224 | Lift .487-.503 | LSA 114 | RPM Range 1200-5600 245.95

CCA-218-230-14 High Performance street w-100-150 HP nitrous or blower
Dur@.050 218-230 | Lift .495-.510 | LSA 114 | RPM Range 1600-5900 245.95

CCA-224-236-14 Street-Strip 125+HP Nitrous needs converter, gears, choppy idle
Dur@.050 224-236 | Lift .503-.521 | LSA 114 | RPM Range 2000-6200 245.95

 

Do you realize that I do NOT have a LT1 engine, I've got a L98. Do the cam's you mentioned work on a L98???

 

I was looking at the hot cam for the above mentioned application. I know that the cam was designed for N/A but if I did the formula right here is what I got.

((218+228)/4)-112*2= -1

Is that so bad?

 

Do you now for sertain that the HOT cam has 112 LSA?? I couldn't find it on Summit' homepage...
:smash:

 

:iagree: it is 112. http://www.superchevyperformance.com and look at specs for hot cam kit.

 

My post was intended to give you some ideas of blower cams that are common in sbc applications...compcam can grind those lobes on a stick that will fit in your engine.
CT

 

I asked only because I already own a Hot cam and the springs,locks, and retainers. I am trying to shave costs anywhere I can. If I can use the hot cam and a turbo for awhile, I will. I realize that cams don't cost that much, but with new springs and a custom ground cam, it adds up...