Jump to content
HybridZ

Help with cam choices.


Recommended Posts

I've having a bit of a problem figuring out what to do about cam choices. I'm looking for a bit more power, but not increase where the power lies. I would like to keep my rev's to ~6500. I would also like a somewhat lopier idle.

 

Ok my current setup includes

 

Chevy 350 bored to 355

Holly systemax II package

Holly 750 carb

~10:1 compression

I forget what type of headers

etc...

 

With the systemax II came this cam: http://store.summitracing.com/partdetail.asp?part=LUN%2D07104LUN&autoview=sku

07104LUN Duration 235/240 @ .05" Lift .49/.49 I'm assuming from the spec sheet that center line of lobe is the LSA which is 108* however the website says it should be 112* Assuming I'm correct I should have 21.5* of overlap.

 

Now, I've found some cams below with more lift, and more overlap, but will I see that much of a power increase from ~.01"to .03" more lift?

 

Cam 1

http://store.summitracing.com/partdetail.asp?part=CCA%2D12%2D224%2D4&autoview=sku

248/248 @ .05" Lift .504/.525 LSA 110 Overlap 28*

 

Cam 2

http://store.summitracing.com/partdetail.asp?part=LUN%2D00012&autoview=sku

246/246 @ .05" Lift .515/.515 LSA 108 Overlap 30*

 

Cam 3

http://store.summitracing.com/partdetail.asp?part=CCA%2D12%2D250%2D3&autoview=sku

240/246 @ .05" Lift .507/.510 LSA 110 Overlap 23*

 

Cam 4

http://store.summitracing.com/partdetail.asp?part=LUN%2D07102&autoview=sku

235/235 @ .05" Lift .507/.507 LSA 108 Overlap 19*

 

Or should I just stick with what I have? Thanks for the help.

Link to comment
Share on other sites

You haven't mentioned what your heads are; they are the key to power.

These are nice, but you'll need to compute your CR:

http://store.summitracing.com/egnsearch.asp?Ntt=BRO-1021001&searchinresults=true&N=700+400033+316186+115

 

You are running a pretty healthy cam already:

http://www.holley.com/data/Catalogs/SysteMAX%20Engine%20Kits.pdf

It does have 112 degree lobe center separation, so you could get more lope (and maybe less gas mileage due to increased overlap) by closing that a bit. I've not looked closely at the overlap figures you provided, but they seem way low... the need to be figured from advertised durations, not .050.

 

This is a Harold Brookshire (was Ultradyne) design with similar .050 and tighter centers: http://holley.com/60104.asp I think they are the newest designs that Lunati/Holley has.

 

If you are all about sound, Check out the "Thumper" cams. Not for me.

 

I'll back off and let the experts give you a hand.

 

 

<>

Link to comment
Share on other sites

take your time and read thru these

 

http://www.newcovenant.com/speedcrafter/tech/camshaft/1.htm

 

http://www.chevyhiperformance.com/techarticles/95298_camshaft_lobe_phasing/

 

http://www.symuli.com/vw/camp1.html

 

http://www.symuli.com/vw/camp2.html

 

http://www.popularhotrodding.com/tech/0607phr_camshaft_basics/

 

digest that and you won,t get confused

 

look a cam does nothing more than control the valve timing, for a given rpm, displacement ,compression, port size,scavaging length on the headers,ETC. theres a narrow range that will maximize the cylinder fill efficiency, in most cases thats a lower total durration and tighter LCA than most guys sellect, because the wider LCA runs smoother at low rpms and they want more durration to compensate to get the overlap into the effective range, this tends to cause some problems, like reversion, yes youll still have reversion with a tight LCA but the power comes on faster and the low rpm torque tends to be better

 

 

look heres two nearly identical cams

 

http://www.cranecams.com/?show=browseParts&action=partSpec&partNumber=114681&lvl=2&prt=5

 

http://www.cranecams.com/?show=browseParts&action=partSpec&partNumber=110921&lvl=2&prt=5

 

top makes a better street combo, the bottom makes a better race engine, look at the timing and figgure out WHY and youll be well on your way......BTW HINT cylinder pressure/piston location/scavaging

Link to comment
Share on other sites

take your time and read thru these

 

http://www.newcovenant.com/speedcrafter/tech/camshaft/1.htm

 

http://www.chevyhiperformance.com/techarticles/95298_camshaft_lobe_phasing/

 

http://www.symuli.com/vw/camp1.html

 

http://www.symuli.com/vw/camp2.html

 

http://www.popularhotrodding.com/tech/0607phr_camshaft_basics/

 

digest that and you won,t get confused

 

look a cam does nothing more than control the valve timing, for a given rpm, displacement ,compression, port size,scavaging length on the headers,ETC. theres a narrow range that will maximize the cylinder fill efficiency, in most cases that a lower total durration and tighter LCA than most guys sellect, because the wider LCA runs smoother at low rpms and they want more durration to compensate to get the overlap into the effective range

 

 

BTW that lopey idle indacate the engine in reversion, NOT A GOOD THING

Link to comment
Share on other sites

Yea, I calculated those overlaps at .05, I'll edit the orig. post here in a min.

 

A link to the systemax II package, with some details

http://store.summitracing.com/partdetail.asp?part=HLY%2D300%2D503%2D1&autoview=sku

 

Valve Angle: 20º Intake Runner Volume: 184cc

Exhaust Runner Volume: 68cc

Combustion Chamber Volume: 68cc

Intake Valve Diameter: 2.02"

Exhaust Valve Diameter: 1.60"

CFM flow @.5" lift 223/173

Deck thickness: .5"

 

It looks like my Compression is 9.55:1 4.03" Bore, 3.38" Stroke, .039" compressed head gasket, and 68cc cylinder head vol. Stock pistons

Link to comment
Share on other sites

I ran that same package on a 350 with flat top pistons in a 3600lb chevelle with a stock converter. The cam didn't come on until about 4000rpms. I was really unhappy with it. In a lighter car with a stick shift, it would probably be a lot more fun though. The holley heads are supposedly the same as the brodix track1 heads....an entry level aluminum head, along the lines of the edelbrock performer. The heads are good for about 450hp in stock trim. If you are running it with an automatic, run a higher stall converter and you'll probably be fine with the cam that came with the package.

Link to comment
Share on other sites

You guys really know your cams !

 

Can someone help me out and make a couple of cam suggestions for a LT1 with stock Aluminum heads and 8.5 CR ( turbo motor build ) ?

Revs will be limited to under 6000. Boost target is 12 - 15 PSI. 42lb injectors, after market computer. Low stall speed , street car.

 

Thanks a bunch!

-Les

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...