Cam timing
10-16-2003, 09:51 AM
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Cam timing
If I want to move the torque curve down the rpm range by using the 4 degree advance in timing sprocket, are there any general "rules" on the effect this will have. ie estimated rpm change at peak torque.
I'm thinking about putting a 5 speed OD in my 68 vette, 327, 300hp motor, 4 speed. Would like lower rpm torque peak for driving in 5th.
Gary
I'm thinking about putting a 5 speed OD in my 68 vette, 327, 300hp motor, 4 speed. Would like lower rpm torque peak for driving in 5th.
Gary
10-16-2003, 12:46 PM
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If you have the stock camshaft in the 300 hp engine you probably will get into detonation very quickly. The camshaft duration is very short and you probably still have the stock 10.25:1 compression ratio. You would end up backing out the ignition timing considerably to keep it from knocking on pump gas. This really hurts performance. Check the engines cranking compression. If it is at 190 or more now, it probably won't work.
Dennis Moore
Dennis Moore
10-16-2003, 01:04 PM
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Dennis,
I know the engine was rebuilt with lower compression pistons. It's around 165 psi and I can run 36 total (no vacuum advance) advance w/o detonation on 91 octane. I'm guessing around 9:1 CR. Not sure on the cam specs on the rebuild, may be original. Runs like a bat out of hell over 3000 rpm, but I'm afraid would be too sluggish at 2400 rpm overdrive, 75 mph cruise. I was hoping advancing the cam would be an easy way to lower the torque curve to make it a better hiway car with the 5 speed.
Gary
I know the engine was rebuilt with lower compression pistons. It's around 165 psi and I can run 36 total (no vacuum advance) advance w/o detonation on 91 octane. I'm guessing around 9:1 CR. Not sure on the cam specs on the rebuild, may be original. Runs like a bat out of hell over 3000 rpm, but I'm afraid would be too sluggish at 2400 rpm overdrive, 75 mph cruise. I was hoping advancing the cam would be an easy way to lower the torque curve to make it a better hiway car with the 5 speed.
Gary
10-16-2003, 05:01 PM
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Gary,Remember 5th is an overdrive gear meant for cruising.I have a 75 280Z (Datsun,2500lbs) with an LT-1 and a 6speed.6th is sluggish at 80mph BUT downshift to 4th and everything starts to blur quickly;plus downshifting is easier that advancing the cam.BOB
10-16-2003, 09:16 PM
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Bob, that's a sweet setup, I've always thought the Z's were ahead of their time in styling etc. Did you do the engine swap with your own bracketry or a pre-fabbed setup?
Brian
Brian
10-17-2003, 11:44 AM
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Martiniboat,Thanks.It definally is a sleeper and I love when people pick on my "poor little 6cyl".I used "Jags that run" templet for the motor mounts,everything else was done in house.BOB
