| [GMCnet] Re; Big increase in power in my 1977 403ci engine. [message #318552] |
Mon, 05 June 2017 20:46  |
BobDunahugh
Messages: 2465
Registered: October 2010
Location: Cedar Rapids, IA
Karma: 11
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David.There's an old saying that goes. There's always more then one way to skin a cat. And you covered another method of performance timing. I build, and race engines that are out on the edge of maximum torque at full throttle in the 7 to 8,000 RPM range. I'm looking to get every half a foot pound of torque at the end of the crank. And there have been times that I've twisted the end of the crank off. I machine down my oil pumps to reduce the oil volume out put of that pump. That detail helps to increase engine torque out put. I set the 4 carbs, and timing to the air temps, humidity, barometric pressure, and gas that I'm using THAT day. ( As I bring my own tested gas with me ) All these change from day to day. I'm so close in timing that a settings I use one day. May blow the top of the piston out the next. Bringing this close of settings this close to our GMC's bring it's own issues. As the gas we get one day. May not be the same the next day. And all the items listed above have changed. And with all of these changing ranges. How close to maximum timing advance do you want to get. The GM factory specs are listed to handle all of these changing conditions. With a safety factors included. So is one way better then the other. That is all in your comfort range. As for me. My stock 78 Royale, 403 with a 2-1/2 exhaust, no headers, and a 3:70 FD. With Linda's lift van I have a GVW of 17,000 lbs. With the enclosed race trailer I'm at a GVW of 21,000 lbs. All with factory stock timing. That's my own personal comfort zone. Bob Dunahugh
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| [GMCnet] Re; Big increase in power in my 1977 403ci engine. [message #318616 is a reply to message #318552] |
Tue, 06 June 2017 23:46  |
BobDunahugh
Messages: 2465
Registered: October 2010
Location: Cedar Rapids, IA
Karma: 11
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Senior Member |
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GM's big thing, and all manufactures. Is to have their engines perform for many, many years. That's what brings customers back. There isn't an engine built in the world that you can't get more horse power/torque out of. Manufactures are out for longevity. So their tuning parameters deliberately fall short of maximum HP/torque. There are two ways to operate any engine. 1. How fast can I climb the mountain. Or 2. How many mountains do I want to climb over how many years. We BS horse power. We drive torque. Tuning in it's true form is done on an engine dyno. I've run engines on a dyno for days to get an engine to it's absolute max. Thus lots of part changes along the way. And I've scattered my fair share of engines in the proses. But I'm not interested in longevity. I'm just interested in not seeing the back of someone's car at the end of the day. So. Putting on a bigger carb won't help. Big exhaust won't help. A cam change won't help. But putting on matching parts will bring out the magic. I have the knowledge, and equipment to build a killer 403 for my 78 Royale. Or any engine for that matter. My GVW is always in the 17 to 21,000lbs range. Our last 78 Royale 403 got that GMC 152,000 miles with no internal issues. It got done what I needed done from coast to coast. I'm happy. As a note. I'm not saying that anyone is right, or wrong. We all need to do what makes us comfortable in what we do. Bob Dunahugh
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From: Bob Dunahugh
Sent: Monday, June 5, 2017 8:46 PM
To: gmclist@list.gmcnet.org
Subject: Re; Big increase in power in my 1977 403ci engine.
David.There's an old saying that goes. There's always more then one way to skin a cat. And you covered another method of performance timing. I build, and race engines that are out on the edge of maximum torque at full throttle in the 7 to 8,000 RPM range. I'm looking to get every half a foot pound of torque at the end of the crank. And there have been times that I've twisted the end of the crank off. I machine down my oil pumps to reduce the oil volume out put of that pump. That detail helps to increase engine torque out put. I set the 4 carbs, and timing to the air temps, humidity, barometric pressure, and gas that I'm using THAT day. ( As I bring my own tested gas with me ) All these change from day to day. I'm so close in timing that a settings I use one day. May blow the top of the piston out the next. Bringing this close of settings this close to our GMC's bring it's own issues. As the gas we get one day. May not be the same the next day. And all the items listed above have changed. And with all of these changing ranges. How close to maximum timing advance do you want to get. The GM factory specs are listed to handle all of these changing conditions. With a safety factors included. So is one way better then the other. That is all in your comfort range. As for me. My stock 78 Royale, 403 with a 2-1/2 exhaust, no headers, and a 3:70 FD. With Linda's lift van I have a GVW of 17,000 lbs. With the enclosed race trailer I'm at a GVW of 21,000 lbs. All with factory stock timing. That's my own personal comfort zone. Bob Dunahugh
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