Author Topic: Cam shaft help!  (Read 3532 times)

Offline Sldpulr

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Cam shaft help!
« on: May 11, 2017, 12:17:23 PM »
Hey guys, I need the advice of a engine builder. I am currently running the comp cams XE294H cam (part number 12-254-3). The motor runs great and has TONS of power all through the rpm range. I do however have a few issues. First problem is my brakes. I can only pull about 6hg of vacuum at idle. I have tried a vacuum canister but after about 2-3 brake cycles I am out of vacuum. I have visited with a vendor about switching to a wilwood master cylinder to fix that issue but I am planning on going to a Fitech 600hp power adder EFI kit. Which brings me to another problem the Fitech EFI kit will not work with my current cam shaft due to the choppy idle.

So I am looking for a cam shaft that will keep me at my current HP/torque levels, work with a EFI kit, and possibly pull enough vacuum to run a brake booster. From the research I have done I have not been able to find a cam that will meet all of my needs. So does anyone know of a cam that might work.

Link to current cam
http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=89&sb=2

SBC 383
BORE: 4.030
STROKE: 3.750
DECK HEIGHT: .025
CYLINDER HEAD VOLUME: 72CC
HEADS: 190CC RUNNERS
HEAD MATERIAL: ALUMINUM
GASKET THICKNESS: .032
COMPRESSION RATIO: 10.03:1
PISTON: FLAT TOP SINGLE VALVE RELIEF
CAM: COMP CAM XE294H
TIMING CHAIN: DOUBLE ROLLER
ROCKER ARMS: COMP CAMS ALUMINUM 1.5
DIST: MSD PRO BILLET/MSD 6AL
INTAKE: RPM AIR GAP
CARB: 750 HOLLEY DP MANUAL CHOKE
TRANS:TH350C
CONVERTER:HUGHES 3000 STALL
HEADERS: 1 3/4 LONG TUBE
EXAHUST: 3" WITH X-PIPE
MUFFLERS: 3" BORLA OFFSET/OFFSET
GEARS: 3.08:1 (I think they are 3.08, I will be swapping to 3.73 or 4.10 gears soon)

Picture for entertainment.....

« Last Edit: May 11, 2017, 12:20:12 PM by Sldpulr »
1980 C10 383 STROKER

Offline rich weyand

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Re: Cam shaft help!
« Reply #1 on: May 20, 2017, 01:00:01 AM »
Simulation says you are running something like 340hp @5000 and 400ftlb @2500.  The torque curve starts at maybe 140ftlb @1000, hits 340ftlb @2000, and holds above 360 ftlb from 2200 to 4800.  The vacuum problem is shown by the low torque at 1000 rpm.  Comp Cams recommended rpm range for this cam is 2800 to 7000 rpm, but in reality your hp begins rolling off at 5600 rpm.

You can get better horsepower and torque numbers, with more torque and better vacuum at 1000 rpm by going to a less aggressive cam.  Your idle will smooth out some, giving you better vacuum, and your top rpm will come down a little.

12-209-2 may be a good fit.  335hp @4500, 445ftlb @2500.  The torque curve starts at 300ftlb at 1000, hits 400ftlb @2000, and holds above 400ftlb from 2000 to 4400 rpm.  This should have much better vacuum at idle.  Comp Cams shows the rpm range on this cam at 2000 to 6000 rpm.  In reality, your horsepower starts rolling off at 4500 rpm, but from a 335hp peak.  Idle will be "choppy to mild-rough" according to Comp Cams, instead of "rough to very rough".

Depending on where the TH350C is shifting now, shifts will move down automatically with more vacuum, but you should be prepared to change a weight in the governor to change the shift points as required.
Rich

"Working Girl": 1978 K-10 RCSB 350/TH350/NP203 +2/+3 Tuff Country lift

Offline SkinnyG

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Re: Cam shaft help!
« Reply #2 on: May 20, 2017, 05:50:19 AM »
If you can find an EFI kit that can run Alpha-N instead of Speed-Density, you could make a low-vacuum engine work.  Alpha-N looks at throttle position to read engine load.  I run Alpha-N on one of my cars with ITB's - Speed Density can't tell the difference between cruise at 94kPa (needs to be lean) and full throttle at 96kPa at my altitude (needs to be rich).  And by golly I tried to make it work.  Alpha-N made it infinitely better to drive.

A vacuum pump would be a way to get your power brakes back.  Or fit a hydro-boost system.

However, I'm with Rich - your cam is scary big.  I would love to hear it idling!  The one he suggests is a good choice. You will want a stock converter. 3.08's would probably be fine with this combo in a 383.
The Crusty Chevy: 1977 Silverado, shortboxed & dropped, potato-potato.

Offline VileZambonie

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Re: Cam shaft help!
« Reply #3 on: May 20, 2017, 06:37:07 AM »
If you are happy with the cam and the engine performance then see what happens after you change the ring and pinion before changing the camshaft. What are you using for a vacuum reservoir and have you verified the check valve is working and booster holds vacuum? I have engines with higher profile cams that run vacuum assist without this issue.
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Offline rich weyand

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Re: Cam shaft help!
« Reply #4 on: May 20, 2017, 09:14:49 PM »
... have you verified the check valve is working and booster holds vacuum?

^^^ this.

Also, there are electrical vacuum pumps you can mount to run the power brake booster.
Rich

"Working Girl": 1978 K-10 RCSB 350/TH350/NP203 +2/+3 Tuff Country lift