Cam Specs for Chev 350 sb

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rbezdon

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Does any one know what the standard camshaft lift specification is for a 1988 OMC 5.7L with Rochester Quad?? How does that compare with the lift specs for a Chevt truck with TBI for the same year?? Last year I bought a remanufactured long block and ordered a marine engine. I am having top end problems (bogging) when the rear barrels open up. I have replaced with new every part in the fuel system and tested it. It is working including the new carb. I am beginnig to think I got screwed and the remanufacturer sent me a Chevy truck engine instead of a marine engine. I have heard the cam are different and if the engine can't breathe in that monster carb (650 CFM) it could be the problem.
 
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Ralph 123

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Re: Cam Specs for Chev 350 sb

**********************************************<br />Stock Marine Specs - Flat-based lifter<br /><br />GM Part No: 340284, Merc Part No 431-5943<br /><br />Duration @ .050: 200 intake, 212 exhaust<br />Valve lift in inches: .400 intake, .410 exhaust<br />Lobe centerline degrees: 108 ATDC, 112 BTDC<br />Lobe Separation Angle in Degrees: 110<br /><br />**********************************************<br /><br />Stock Marine Specs - roller lifter<br /><br />GM Part No: N/A, Merc Part No 431-811658<br /><br />Duration @ .050: 197 intake, 207 exhaust<br />Valve lift in inches: .430 intake, .450 exhaust<br />Lobe centerline degrees: 106 ATDC, 112 BTDC<br />Lobe Separation Angle in Degrees: 109<br /><br />**********************************************<br /><br />Source: Small Block Chevy Marine Performance: Engine Modifications for Maximum Boating Performance by Dennis Moore
 
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rbezdon

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Re: Cam Specs for Chev 350 sb

Thanks for the info. Do you know how the specs you gave would compare to the 1988 350 automotive engine (which at that time usually came with TBI instead of a monster 4bbl). I am in the process of purchasing a slightly higher performance cam (Comp 12-206-2) to try. My new engine runs fantastic until I push the throttle far enough to open the secondary throttle plates. Once open there is not even eough ait flow to actuate the carb plate covering the secondaries of the 4MV Quadrajet which controls the secondary metering rods. RPM actually drops slightly at WOT from the point where the secondary throttle plates are just actuated.
 
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rbezdon

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Re: Cam Specs for Chev 350 sb

Thanks for the info. Do you know how the specs you gave would compare to the 1988 350 automotive engine (which at that time usually came with TBI instead of a monster 4bbl). I am in the process of purchasing a slightly higher performance cam (Comp 12-206-2) to try. My new engine runs fantastic until I push the throttle far enough to open the secondary throttle plates. Once open there is not even eough ait flow to actuate the carb plate covering the secondaries of the 4MV Quadrajet which controls the secondary metering rods. RPM actually drops slightly at WOT from the point where the secondary throttle plates are just actuated.
 
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rbezdon

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Re: Cam Specs for Chev 350 sb

Forgot to mention, I have standard, flat hydrolic lifters.
 
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kenimpzoom

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Re: Cam Specs for Chev 350 sb

Your quardraget secondary barrels may be opening too quickly.<br /><br />Maybe the quadrajet experts can jump in, but I think it is real easy adjustment with a turn of a screw tightens the spring.<br /><br />Go to your local library and check out Rochestor carbs.<br /><br />Ken
 
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Ralph 123

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Re: Cam Specs for Chev 350 sb

**********************************************<br /><br />Stock auto Specs - flat lifter<br /><br />GM Part No: 3896929, Merc Part N/A<br /><br />Duration @ .050: 195 intake, 202 exhaust<br />Valve lift in inches: .390 intake, .410 exhaust<br />Lobe centerline degrees: 108 ATDC, 116 BTDC<br />Lobe Separation Angle in Degrees: 112<br /><br />**********************************************<br /><br /><br />All the other stock auto's listed are rollers except the 327 cid/350 hp auto<br /><br />GM Part No: 3863151, Merc Part N/A<br /><br />Duration @ .050: 222 intake, 222 exhaust<br />Valve lift in inches: .447 intake, .447 exhaust<br />Lobe centerline degrees: 110 ATDC, 118 BTDC<br />Lobe Separation Angle in Degrees: 114<br />**********************************************
 
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Ralph 123

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Re: Cam Specs for Chev 350 sb

Here is Moore's recommended specs for a stock 350 w/ flat lifters<br /><br />Duration:<br />202-208 degrees intake duration measured @ 050" lift<br />208-216 degress exhaust duration measured @ .050" lift<br /><br />Lift:<br />0410-0430" intake valve lift with 1.50:1 rocker arms0420-.460" exhaust valve lift with 1.50:1 rocker arms<br /><br />Timing:<br />109-110 degrees intake to axhaust lobe centerline separation angle in camshaft degrees<br />108-110 degrees after to dead center intake lobe centerline position in crankshaft degrees<br />109-112 degrees before top dead center exhaust lobe centerline position in crankshaft degrees<br /><br />************************************************<br /><br />Suggested high performance aftermarket camshaft. Competition Cams XE 250 H Xtreme Energy Hydraulic<br /><br /><br />Duration:<br />206 degrees intake duration measured @ .050" lift lobe #5440<br />250 degrees intake duration measured @ .006" lift (advertised duration)<br />212 degrees exhaust duration measured @ .050" lift lobe #5207<br />260 Degrees exhaust duration measured @.006" lift (advertised duration)<br /><br />Lift:<br />.432" intake valve lift with 1.50:1 rocker arms<br />.288" intake lobe lift at the lifter<br />.444" exhaust valve lift with 1.50:1 rocker arms<br />.296"exhaust lobe lift at the lifter<br /><br />Timing:<br />110 degrees intake to axhaust lobe centerline separation angle in camshaft degrees<br />108-110 degrees after to dead center intake lobe centerline position in crankshaft degrees<br />110-112 degrees before top dead center exhaust lobe centerline position in crankshaft degrees<br />************************************************<br /><br />You owe me big time for doing all this typing :)
 
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rayjay

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Re: Cam Specs for Chev 350 sb

There is a secondary lock out lever that is actuated by the choke. This locks the secondary butterflies closed. I have seen the plastic cam that lifts the secondary metering rods break. Lots of trucks came with q-jets. A non-restricted Q-jet is rated at 750cfm. W-30's, certain 455 Buicks and 455 SD's came with a special 850 Q-Jet. <br /><br />Doug Roe wrote the definitive Rockefeller carb book.
 
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xltier

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Re: Cam Specs for Chev 350 sb

any exhaust restrictions?the intake cant come in any faster than the exhaust can exit.possibly flappers stuck???????would act like a plugged catyletic convertor in a car engine.hth
 
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rbezdon

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Re: Cam Specs for Chev 350 sb

boy, you guys came up with more specs than I ever expected. Thanks and I do owe some of you for all of the typing. <br /><br />It is obvious that if the rebuilder did give me a automotive engine instead a marine, the cam would be much smaller. I have decided to put in a bigger cam just to try it out. With the Edelbrock dual plane intake I put on last ytear, this should be helpful no matter what.<br /><br />One other thing I have noticed while tearing down the engine to put in the cam is that the Edelbrock Performer (2104) has seperation between the dual planes. Basically, one side of the carb feeds 4 cylinders and the other side the rest. On the old cast iron manifold there was a 1/2 inch thick gasket completely open between the sides of the carb. I bought a replacement gasket like it when I rebuilt the engine. What this does is raise the carb 1/2 inch from the machined mounting surface of the Edelbrock. Now there can be some "mixing" of the feed from the two sides of the carb. Could this be the problem?? Should I get a flat gasket which has a web between the sides of the carb to garantee separation of the sides?? Any other inpuyts would be appreciated.<br /><br />By the way, on the exhaust thing, I was missing a flapper but the guy who serviced my drive pulled it out a few years ago. When I rebuilt the engine I replaced them. It is not likely the exhaust is blocked but it is remotely possible. I have checked everything up to the Y pipe (in fact I repalced the exhaust manifolds and risers when I rebuilt). If there is soimething in there it is at the exit from the drive.
 
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rbezdon

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Re: Cam Specs for Chev 350 sb

By the way, Ralph, I did buy a Comp Cam before I got your recommendation. I talked it over with a local speed shop guy and we dicided to get the .444 lift on both valves, same duration you recommended and 110 degree seperation. Thanks for thr input, we came to almost exactly the same conclusion.
 
jimmbo

jimmbo

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Re: Cam Specs for Chev 350 sb

Using an open spacer/thick gasket on a two plane manifold will reduce the strength of the signal the carbs sense and will lean the mixture, it should in theory help high rpm performance at the cost of some bottom end torque
 
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