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    Results 21 to 31 of 31
    1. #21
      Join Date
      Apr 2003
      Location
      Central Valley, CA
      Posts
      900
      Country Flag: United States
      Quote Originally Posted by Mike Norris
      I guess I should stipulate that this is pretty much the norm for the LSx vehicles I build and and they work very well. I do not do any SBC cars and it is possible that they are quite a different beast, but my understanding was that the "traditional" split worked well for street cars with lower boost.

      I think some of this comes down to the old "ask five people and get five different answers" kind of question. The only way to know for sure what your combo wants is to actually try 2-3 or even 4 different cams, peferable on an engine dyno and see what you get if you are that paticular about the results. Turbo gurus such as Nelson and Kenny D should ahve a great baseline also.

      Hope this makes sense as I am better at building the cars the explaining theory

      Mike Norris
      Thanks Mike.

      I forgot to add that one of my data points is a friend's twin turbo LS2 that was all spec'd out by Wheel to Wheel; his cam was 236/231 @ .050.



      I'm sure the "ideal" cam split also has a lot to do with A/R of turbine housing, backpressure, and overall pressure ratio between turbine & compressor sides... but I need to do more research.
      1969 Chevelle
      Old setup: Procharged/intercooled/EFI 353 SBC, TKO, ATS/SPC/Global West suspension, C6 brakes & hydroboost.
      In progress: LS2, 3.0 Whipple, T56 Magnum, torque arm & watts link, Wilwood Aero6/4 brakes, Mk60 ABS, vaporworx, floater 9" rear, etc.


    2. #22
      Join Date
      Aug 2004
      Posts
      210
      My Procharged 542 inch Pontiac shortblock is almost complete. We will be at ~9.25:1 for the C/R. And we are coating the piston tops AND combustion chambers. Also intercooled. I figure my max boost should be somwhere in the 12-15# range. Should all work fine on premium pump.
      Another consideration in this equation is cylinder head material. Aluminum heads have definite advantages over iron.

    3. #23
      Join Date
      Jan 2005
      Location
      Dallas TX
      Posts
      1,633
      Gather all your specs and call Cam Motion. When I built my buddy's street truck it was a 461ci 9.0 to 1 iron 049 heads with 8lbs. The cam they got me made 703HP and its just a flat tappet. He has lots of fun at the truck beating up on race cars with his 4300lb street truck.

    4. #24
      Join Date
      Sep 2002
      Location
      So. Cal
      Posts
      1,179
      Quote Originally Posted by Blown353
      Mike, what's your reason for more exhaust than intake duration on a turbo build?
      My 2 pennies as I understand it.
      In a blown application, more exhaust duration allows more exhaust to be exhaled resulting in a better air fuel charge. (more horsepower) You have the blower to force air into the cylinder to overcome narrower intake duration. This is why blower cam like pushing out your exhaust duration and narrow the intake without going into overlap.
      In a N/A motor, it more critical for intake duration (or equal)
      .
      Ron DeRaad
      68 Camaro RSx
      Darton Sleeved LS9 - 434ci (4.155x4.00)
      AFR LSX245 Heads (12:1cr)
      660hp/588tq

    5. #25
      Join Date
      Sep 2002
      Location
      So. Cal
      Posts
      1,179
      Quote Originally Posted by ronracer
      My 2 pennies as I understand it.
      In a blown application, more exhaust duration allows more exhaust to be exhaled resulting in a better air fuel charge. (more horsepower) You have the blower to force air into the cylinder to overcome narrower intake duration. This is why blower cam like pushing out your exhaust duration and narrow the intake without going into overlap.
      In a N/A motor, it more critical for intake duration (or equal)
      .
      I would also llike to say that this is confirmed with the Desktop Dyno 2000 software as I ran thru thousands of cam profiles before I settled with the one I have.
      Ron DeRaad
      68 Camaro RSx
      Darton Sleeved LS9 - 434ci (4.155x4.00)
      AFR LSX245 Heads (12:1cr)
      660hp/588tq

    6. #26
      Join Date
      Apr 2003
      Location
      Central Valley, CA
      Posts
      900
      Country Flag: United States
      Ron, I hear what you're saying, but when I check TurboForums for cam specs and talk to people the overwhelming majority seem to have 4-6 degrees more intake than exhaust duration on their turbo builds. The guys with more exhaust duration seem to be in the minority.

      On a supercharged application I can see more exhaust duration-- I'm running 12 degrees more exhaust than intake duration on my Procharger build and it works great and makes perfect sense on a supercharged application where you don't have any backpressure in the exhaust from the turbo. I'm just questioning this logic when it comes to a turbo engine and want to know the reasoning.

      Quote Originally Posted by gearheads78
      Gather all your specs and call Cam Motion. When I built my buddy's street truck it was a 461ci 9.0 to 1 iron 049 heads with 8lbs. The cam they got me made 703HP and its just a flat tappet. He has lots of fun at the truck beating up on race cars with his 4300lb street truck.
      Looking at the cam specs sticky over at turbomustangs.com it seems that every Cam Motion custom grind guys have posted the specs to have anywhere from 6-10 degrees more intake duration than exhaust duration, both for Ford and Chevy builds.

      I'm not looking for someone to design a cam for me, I just want to better understand the reasoning and thought processes when it goes into picking a turbo cam.
      1969 Chevelle
      Old setup: Procharged/intercooled/EFI 353 SBC, TKO, ATS/SPC/Global West suspension, C6 brakes & hydroboost.
      In progress: LS2, 3.0 Whipple, T56 Magnum, torque arm & watts link, Wilwood Aero6/4 brakes, Mk60 ABS, vaporworx, floater 9" rear, etc.

    7. #27
      Join Date
      Sep 2002
      Location
      So. Cal
      Posts
      1,179
      Quote Originally Posted by Blown353
      Ron, I hear what you're saying, but when I check TurboForums for cam specs and talk to people the overwhelming majority seem to have 4-6 degrees more intake than exhaust duration on their turbo builds. The guys with more exhaust duration seem to be in the minority.

      On a supercharged application I can see more exhaust duration-- I'm running 12 degrees more exhaust than intake duration on my Procharger build and it works great and makes perfect sense on a supercharged application where you don't have any backpressure in the exhaust from the turbo. I'm just questioning this logic when it comes to a turbo engine and want to know the reasoning.



      Looking at the cam specs sticky over at turbomustangs.com it seems that every Cam Motion custom grind guys have posted the specs to have anywhere from 6-10 degrees more intake duration than exhaust duration, both for Ford and Chevy builds.

      I'm not looking for someone to design a cam for me, I just want to better understand the reasoning and thought processes when it goes into picking a turbo cam.
      ????Dunno

      I know different motor configurations require different cams profiles, but per the desktop dyno program, I did'nt see any differences between supercharger and turbo power (other then the hp belt loss vs turbo). They both reacted the same when I add more intake dur or exhaust. I originally thought that you needed more exhaust duration for the turbos due to the extra restriction the turbos made, but then when I input the data for the same supercharged engine, I saw the same hp gains with more exhaust duration. I would think if one had more restictive intake/heads, maybe more duration on the intake might compensate.
      It would be cool to see some dyno sheets with the different cam profiles.

      I can say that my motor loves the exhaust duration. 750-800hp out of a little 302 with 12-15psi boost is a pretty good indicator. RPM is an ugly factor....but it sure sounds bitchen...
      Ron DeRaad
      68 Camaro RSx
      Darton Sleeved LS9 - 434ci (4.155x4.00)
      AFR LSX245 Heads (12:1cr)
      660hp/588tq

    8. #28
      Join Date
      Dec 2007
      Location
      Springfield,MO
      Posts
      14
      You should be able to run 10 lbs fine on 9.0:1. We are running 15lbs on a NOVI2000 set-up with 10.2:1 compression using 93 octane.

    9. #29
      Join Date
      May 2008
      Location
      Rochester, NY
      Posts
      5
      Quote Originally Posted by Larry Callahan
      Is 9.0:1 compression ratio too high for 10lbs of boost on pump gas on a fuel injected 383?

      I am trying to pick out a cam and I am trying to figure out if I can get away with 9.0:1 compression ratio on pump gas with 10 pounds of boost. I know 8.0:1 or 8.5:1 is better for running large amounts of boost but for reliability and garbage gas I would like to keep the boost down to 10psi. I am afraid if I run 8 or 8.5 to 1 that it will be a lazy pig when not under boost.

      Thoughts?
      Larry -

      Its been a long time, but I am still out here! Nice project! Just my two cents on compression ....

      If you plan to drive the car a lot (as I suspect you will!), the lower your compression ratio the more the engine will struggle on its own with no boost. My BBC is running about 9.25:1 and I only run pump gas (93 octane). I have had no issues with thousands of miles and running as high as 12 psi with an innercooler. However, some things to keep in mind that are application dependent: (1) Your cam; (2) Your heads (3) SC/Turbo design (with regards to compression efficiency) (4) Timing curve. All will have some impact on on the effective CR and intake temp which will all affect what you can get away with.

      Hopefully I have not created more questions!

      - Tony

    10. #30
      Join Date
      Jan 2008
      Location
      some where's in Ohio
      Posts
      93
      Im new to turbo stuff, and the more Im reading the more Im thinking that my engine isnt going to last long. I have an s10, 406 sbc,t-56, EFI, intercooled twin turbo. Before the turbo's came along I was running edelbrocks efi ecm 10:1 compression running 93 octane with this cam http://www.iskycams.com/timingchart....ng_chart_id=98 .
      still have the same cam and engine, running the edelbrock intake and FAST ecm. I Have had the truck out a few times tuning it since the turbo's were installed and I dont understand why there is a problem with running a cam that wasnt designed for a turbo (LSA). Unless It is the tuning problem that I have when cruising but I think that is just a tuning issue. It loads up while cruising , otherwise it will scream. What problems does the wrong cam cause? Oh and Im not planning on running more than 10 psi boost. At least for now.

    11. #31
      Join Date
      Jul 2008
      Location
      Oklahoma City
      Posts
      18
      I have twin 70's on a PROBE FPS flat top 468, 990 open chamber heads. 8:1 compression, CSU blow through, intercooled, the cam is 244-252 @ .050 / .544-.560 lift 115 lobe separation. It has made 858 WHP on 91. I have the total timing at 36deg. I have always ran 91 pump gas in it with no issues. Turning down the timing just seems to mildly reduce power. I have lately started trying 89 fuel in it and can't really tell any difference. I am thinking of dynoing it again with the 89 to see if my seat of the pants is performing properly. This comination has been together for 3 years now and fails to dissapoint. I have some old pics of it on myspace at www.myspace.com/neokcterror.

      I would recommend you definitely speak to a turbo oriented camshaft company on your selection. I would further recommend David Crower at Crower cams to help you out in your camshaft selection needs.

      Oh yeah this combo is on 16 pounds of boost.

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