Home » Public Forums » GMCnet » [GMCnet] Power Drive
| Re: [GMCnet] Power Drive [message #327282 is a reply to message #327206] |
Tue, 19 December 2017 09:08   |
BobDunahugh
Messages: 2465
Registered: October 2010
Location: Cedar Rapids, IA
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Senior Member |
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On steep grades. I shift manually to first, or sec. Run the engine RPM's up to the point that I just keep moving.. Then what till I get to the top. And don't care how fast, or how long it takes. There is one point that hasn't been covered. Your trans temps are lower with the 3:70, or 4:10 because there's less load on the trans. And the trans fluid pump is flowing more fluid to the trans cooler. As to engine life with higher RPM's back years ago. Remember. Our engines back then used carburetors, and ran different clearances. PVC systems weren't as good. They were dirty engines back then. Engines will run longer with EFI systems installed. Bob Dunahugh 78 Royale Iowa Member GMCMI
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From: Bob Dunahugh
Sent: Sunday, December 17, 2017 10:03 AM
To: gmclist@list.gmcnet.org
Subject: RE: Power Drive
Vadim. You covered the subject well. The T425 with a 3:07 FD, 14 inch tires, and a 4,000 lbs car was a good combination. GM had the peak HP for the 427, and 455 reached in the 3,600 to 4,200 RPM range. So higher RPM's in the 4200 range, and above isn't an issue. We have 16 inch tires, and 12,000 lbs as you covered. And a different cam profile. That's another can of worms. Till about 2003 we only had the 3:07, and 3:21. I think there was a 3:42 from Cinnabar? So the Power Drive was a way to get the RPM's up to get out of luging our engines years ago. But as you mentioned. The PD is adding more load on the T425. Then Jim K at Applied GMC came out with some great FD ratio choices up to a 4:10 ratio. These ratios ended the luging. And allow the engine/trans to work more efficiently. Some say the PD,or a lower FD ratio are the same. No. Not at all. Is the PD bad? No. It's better then nothing. In your situation. I'd leave things as they are till you have trans issues. Then change the FD ratio. I'm thinking of going to 4:10 from my 3:70. Towing, or not. I'd recommend 3:70. When I'm pulling my enclosed trailer with a car in it. A 78 Royale 403, and the 3:70 FD. My GVW is about 21,000lbs. As a side note. My mileage went up with the 3:70. As to newer engines at 1500 RPM's at 65 MPH. Their design is another kind of animal. Bob Dunahugh Member GMCMI.
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