Engine builders, need help
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Joined: Apr 2000
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From: Houston,Texas
Engine builders, need help
I need some advice degreeing this cam. When I use the centerline method, it comes in very, very close. + or - 1/2 a degree. But, when I go to check the intake opening and closing @ .050" lift, on each side of the intake lobe, I'm off over approx. 40****!!!!!!! For example, I'm looking for the intake opening @ .050" lift to be 30* BTDC, instead it's like 6* ATDC!! I have checked my TDC pointer about five times. I install my positive piston stop and roll the engine in both directions with the degree wheel and pointer installed. Say the piston hits the stop 12* ATDC and 10* BTDC, for a total of 22*. I roll the engine 11* toward the middle{TDC} and reset the pointer at TDC. What the heck am I doing wrong here???
Melting Slicks
Joined: Dec 2000
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From: Carmichael CA
Re: Engine builders, need help (Holeshot)
I've never played with a degree wheel before, but your piston stop procedure looks fine. The 6ş ATDC reading for a mild cam even looks right.
Correct me if I'm wrong, but at 30ş BTDC the #1 cylinder should be either in compression stroke or exhaust stroke and the intake should be totally closed. However, at 6ş ATDC the #1 cylinder should be either in intake stroke or power stroke. Thus, according to what I can see your cam timing is fine, unless you have some overlap in which case it may be off about 10ş or so. If there is an overlap then I would suspect something around 6ş BTDC for the valve to begin opening....30ş BTDC is a very aggressive cam timing for the intake valve. What cam is it? The stock L48 would probably open ATDC while the L82 would probably open BTDC.
Correct me if I'm wrong, but at 30ş BTDC the #1 cylinder should be either in compression stroke or exhaust stroke and the intake should be totally closed. However, at 6ş ATDC the #1 cylinder should be either in intake stroke or power stroke. Thus, according to what I can see your cam timing is fine, unless you have some overlap in which case it may be off about 10ş or so. If there is an overlap then I would suspect something around 6ş BTDC for the valve to begin opening....30ş BTDC is a very aggressive cam timing for the intake valve. What cam is it? The stock L48 would probably open ATDC while the L82 would probably open BTDC.
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Joined: Apr 2000
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From: Houston,Texas
Re: Engine builders, need help (69Rat)
It's a big flattappet solid. 265/273 @ .050 with .660 .654 lift. Yes, a lot of overlap. Looking for the intake valve to open 28.5 BTDC. I just hate to tell you this, but it's going in a 440 70 Challenger that has been running 10.6 @ 126mph. Hoping for some 10.4s. :chevy :D
Team Owner
Joined: Apr 1999
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From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Re: Engine builders, need help (Holeshot)
Your correct in how you figured actual TDC. this might be a stupid question: Are you running the dial indicator on the top of the lifter?
Todays cams are so much nicer than years ago. I've found all of my last few to be exactly what the cam card said for valve event numbers.
Todays cams are so much nicer than years ago. I've found all of my last few to be exactly what the cam card said for valve event numbers.
Race Director
Joined: Dec 1999
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Re: Engine builders, need help (gkull)
what are you using to turn the crank both ways? First one way to TDC then the other way around to TDC again. If you use a crank centerbolt that also has 2 nuts on it to clamp the degree wheel your wheel may be turning. Turb the crank with another means than the centerbolt if the degree wheel is on it.
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Joined: Apr 2000
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From: Houston,Texas
Re: Engine builders, need help (gkull)
Yes, I have a lifter on the intake of the #1 piston. I have a mag. base holding a dial indicator reading off the lifter. .050" on the opening of the lobe and .050" on the closing side of the lobe. Funny thing is, I checked the cam at 105.5* centerline method. This is 2.5* advanced, card says 108* Also checked intake and exhaust open and closing events, right on 2.5* advanced.
I did a compression check {200 psi}, checked valve to piston clearance, {good} and then decided to advance the cam 4* more, for the same checks. All I changed was a small offset bushing that fit on the timing gear. My centerline method shows another 1.5* advance 104* but now the valve events are way, way off and they repeat :smash:
I did a compression check {200 psi}, checked valve to piston clearance, {good} and then decided to advance the cam 4* more, for the same checks. All I changed was a small offset bushing that fit on the timing gear. My centerline method shows another 1.5* advance 104* but now the valve events are way, way off and they repeat :smash:
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,444
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Re: Engine builders, need help (Holeshot)
something changed when you decided to advance the cam. I'd get a second opinion from a real builder.
Jim lives down your way. e-mail him. Very Knowledgable:)
http://forums.corvetteforum.com/zerothread?id=610772
Jim lives down your way. e-mail him. Very Knowledgable:)
http://forums.corvetteforum.com/zerothread?id=610772
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Thread Starter
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Joined: Apr 2000
Posts: 57
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From: Houston,Texas
Re: Engine builders, need help (gkull)
WEll, I figured the problem out. My indicator was sticking. I don't understand why it was repeating though. I changed indicators and that fixed the problems. I degreed the cam in staight up, 2* adv., 4*adv, and 5.5* adv...
Checked compresion and V/P clearance in all positions. I'm going to install it 2* advanvced since the car weighs 3650#. Looking for some 10.4s!!! Thanks for the help on a Mopar :chevy :D
Checked compresion and V/P clearance in all positions. I'm going to install it 2* advanvced since the car weighs 3650#. Looking for some 10.4s!!! Thanks for the help on a Mopar :chevy :D
Race Director
Joined: Jun 2000
Posts: 10,036
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From: FL
Re: Engine builders, need help (Holeshot)
Yes, I have a lifter on the intake of the #1 piston. I have a mag. base holding a dial indicator reading off the lifter. .050" on the opening of the lobe and .050" on the closing side of the lobe.
Team Owner
Joined: Apr 1999
Posts: 21,953
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From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Re: Engine builders, need help (Holeshot)
Hey i'm glad that you got it figured out. I've owned two hot rodded mopars. 71 Sat. Sebring 383 magnum. I bought it when it was 4 years old and 17,000 miles. Then just a few years ago 67 charger R/T 440 - Well lets just say it was better to look at than drive. Being a modified Vette man. old Mopars that weight 4000 lbs with a big bad to the bone engines don't inspire much driving confidence with only a lap belt and low back bucket seats. The big unresponsive steering wheel, small brakes, and lots body roll.
They both could really blow smoke off the tires. I'm running a fairly large solid roller cam and I installed it 4 degrees retarded - I just thought that I would try it ans if I don't like it it will go back to straight up.
Good luck on the lower numbers :seeya
They both could really blow smoke off the tires. I'm running a fairly large solid roller cam and I installed it 4 degrees retarded - I just thought that I would try it ans if I don't like it it will go back to straight up.
Good luck on the lower numbers :seeya
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Joined: Apr 2000
Posts: 57
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From: Houston,Texas
Re: Engine builders, need help (gkull)
Yeah, the valve lift is quoted with 1.5 rockers. The cam card will also give a lobe lift, say .420", .420" X 1.6 = .672" of lift. It's usually better to degree directly off the tappet, if possible.
This Mopar is only made to go in a straight line. The only Mopar I've ever rode in that had nice handling for it's day, was a 70 AAR cuda. Quick ratio steering and very little body roll. Thanks again for all the help.
This Mopar is only made to go in a straight line. The only Mopar I've ever rode in that had nice handling for it's day, was a 70 AAR cuda. Quick ratio steering and very little body roll. Thanks again for all the help.
