Tuning help?
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Tuning help?
This winter I had a 383 built for my 1977 C3. Here are the stats, 10:1 compression / Dynamic 8.2:1. 195 AFR heads, Air Gap intake, Holley 750 Street Avenger, Comp Cam flat tappet - duration 227/240 LSA 107 - lift .479 .465 (I'm actually more with 1.6 rockers)
2004r trans 3200 stall
3.70 gearing
This engine replaced a 355 with SRT Pro topline iron heads and 9.6:1 compression and the 355 would have blown it away. It just isn't pulling like it should.
Fuel pressure is good. Timing is 36 deg all in at 2500, full manifold vacuum. Power jet is correct, float bowl level is correct, curb idle is set. I've reset the rockers, checked pushrod height, valve springs are matched to the cam. The cam was degreed and tdc was verified. I'm just stumped why this doesn't seem to pull like it should. 2 years ago I spun a bearing in a 418 H/P 383 and it ran like a scalded dog in the same car. This engine should easily be in the 400 h/p range and it's a slug. I'm stumped. Any suggestions would be appreciated.
2004r trans 3200 stall
3.70 gearing
This engine replaced a 355 with SRT Pro topline iron heads and 9.6:1 compression and the 355 would have blown it away. It just isn't pulling like it should.
Fuel pressure is good. Timing is 36 deg all in at 2500, full manifold vacuum. Power jet is correct, float bowl level is correct, curb idle is set. I've reset the rockers, checked pushrod height, valve springs are matched to the cam. The cam was degreed and tdc was verified. I'm just stumped why this doesn't seem to pull like it should. 2 years ago I spun a bearing in a 418 H/P 383 and it ran like a scalded dog in the same car. This engine should easily be in the 400 h/p range and it's a slug. I'm stumped. Any suggestions would be appreciated.
Last edited by 1977stroker; Apr 6, 2016 at 08:03 PM.
Drifting
Joined: Oct 2012
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From: Medina Ohio
Secondaries opening? Confirm AFR is all good.
I'm no cam expert, but 227/240 on a 107 sounds unique. Does it wake up up high in RPM, or a dog all together?
Was the cam broke in properly? Didn't wipe any lobes did you? (assume flat tappet based on the lift #'s ** Nevermind, you stated flat tappet)
I'm no cam expert, but 227/240 on a 107 sounds unique. Does it wake up up high in RPM, or a dog all together?
Was the cam broke in properly? Didn't wipe any lobes did you? (assume flat tappet based on the lift #'s ** Nevermind, you stated flat tappet)
Last edited by Ibanez540r; Apr 6, 2016 at 09:45 PM.
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Secondaries opening? Confirm AFR is all good.
I'm no cam expert, but 227/240 on a 107 sounds unique. Does it wake up up high in RPM, or a dog all together?
Was the cam broke in properly? Didn't wipe any lobes did you? (assume flat tappet based on the lift #'s ** Nevermind, you stated flat tappet)
I'm no cam expert, but 227/240 on a 107 sounds unique. Does it wake up up high in RPM, or a dog all together?
Was the cam broke in properly? Didn't wipe any lobes did you? (assume flat tappet based on the lift #'s ** Nevermind, you stated flat tappet)
That cams actually 2000-5000 rpm rated, it's supposed to be a mid range and torque based grind. I did proper break in, prepped everything so it would fire immediately, than ran it to 2000 rpms immediately. 3 cycles of 20 minutes. Comp cam break in oil. I guess it's possible, hard to tell if theres a miss or issue by ear because of the 107 LSA.
I reset the rockers after break in with the engine running. I assumed if I wiped out a lobe I'd have noticed but I guess it couldn't hurt to do a compression test.
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I also missed verifying that the secondarys are opening from the previous post, but thats another good idea.
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That cams actually 2000-5000 rpm rated, it's supposed to be a mid range and torque based grind. I did proper break in, prepped everything so it would fire immediately, than ran it to 2000 rpms immediately. 3 cycles of 20 minutes. Comp cam break in oil. I guess it's possible, hard to tell if theres a miss or issue by ear because of the 107 LSA.
I reset the rockers after break in with the engine running. I assumed if I wiped out a lobe I'd have noticed but I guess it couldn't hurt to do a compression test.
I reset the rockers after break in with the engine running. I assumed if I wiped out a lobe I'd have noticed but I guess it couldn't hurt to do a compression test.
Driving aroung normally it's fine. Basically I'm just tapping the pedal and coasting. It's when I get into it that it falls flat.
Safety Car
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From: New York
First I mean no disrespect , But why would you put in a cam that runs to 5000 ? A small block IS NOT a torque monster no matter what you here or read. A BB is a torque monster.
Anyway , how it is off idle , and when you floor it once in top gear ? How is it from a dead stop and you floor it ?
Anyway , how it is off idle , and when you floor it once in top gear ? How is it from a dead stop and you floor it ?
Race Director
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
You may have flattened a cam lobe. Who spec'd in that cam, it hase some pretty weird specs, and to finish off at 5000RPM, why did you want to that ? 
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First I mean no disrespect , But why would you put in a cam that runs to 5000 ? A small block IS NOT a torque monster no matter what you here or read. A BB is a torque monster.
Anyway , how it is off idle , and when you floor it once in top gear ? How is it from a dead stop and you floor it ?
Anyway , how it is off idle , and when you floor it once in top gear ? How is it from a dead stop and you floor it ?
A good buddy ordered this motor built for him. About the same time it was completed, his wife filed for divorce. I was working out of state and was also juggling a split window restoration. The last thing I wanted to do was tear into another car. I bought the motor to bail him out and flipped him some extra money to do the swap. The cam was installed and I didn't have the time or want to spend the money from my other project to switch over to a roller cam. The 5000 rpm range is actually fine. This is a street car and it'll never be run above that RPM range anyway, if I could get a true 400 hp out of it.
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Would a compression test be the easiest option to check for a wiped lobe? After the intial break in, I did reset the rockers with the engine idling. I didn't have any rockers at that time that were overly loose from the initial start up setting, maybe a quarter turn or so.
Drifting
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From: Chardon Ohio
I don't think a compression test would show a wiped lobe - compression could be fine. You would have to pull the valve covers and look for loose rockers, or measure the lift on all valves with a dial indicator. Or... just pull the intake and look.
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Melting Slicks
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From: Thunder Bay
I'm assuming you have the ignition curve worked out. Make sure TDC is accurate. I've seen situations where the timing pointer is mismatched with the mark on the balancer. If you are sure your advance curve is correct, then I think your problem may be a mismatch in parts. How sure are you that your compression is actually 10:1? There is a tendency for compression to be lower than calculated. Guys sometimes forget to allow for deck height and gasket thickness when calculating compression. If 10:1 is simply based on the piston manufacturer's advertised specs, I will guarantee your compression is not that high. Combine that with your heads and cam specs, and there's your problem. The cam is relatively long duration and with 107 LSA you've got a lot of overlap bleeding off compression. Combine that with 195 heads which are a little small for that cam and well its just a lot of little things stacking up against you. If the simple stuff checks out (timing curve, secondaries, etc.) I would be pulling a head to verify that compression and go from there.