| [GMCnet] More on final drive ratios [message #238033] |
Wed, 29 January 2014 20:50  |
glwgmc
Messages: 1014
Registered: June 2004
Karma:
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Senior Member |
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Hi Rob,
Yes, 3.5 chain means the Power Drive technology developed by a well known Porsche tuner turned GMC owner which he sold to Manny. It means the gears/chain that transfers power from the output shaft of the torque converter to the input shaft of the transmission are altered from the stock 1:1 ratio to a different ratio that results in an effective 3.5 over all ratio with the stock 3.07 final drive. In combination with the 3.21 final drive the effective over all ratio is .3.67.
Advancing the cam timing 4 degrees results in reducing the torque curve by about 400 rpm according to some, BUT NOT ALL, 455 knowledgeable engine folks. My experience is that it certainly has a beneficial effect according to the seat of my pants. No science here, just seat of the pants.
For flat land the 12 degrees of static distributor advance might well be ok, but where I live it would be too much unless one likes the tinkle sound of pinging. My ears are no longer good enough to hear such sounds reliably, so I tend to be more conservative. If I had a good knock sensor with auto retard I would advance further and let the electronics do their thing.
Jerry
Jerry Work
The Dovetail Joint
Fine furniture designed & hand crafted
in the 1907 former Masonic Temple building
in historic Kerby, OR
Http://jerrywork.com
541-592-5360
Cell 541-499-1027
.............
Message: 11
Date: Thu, 30 Jan 2014 11:18:21 +1100
From: "Robert Mueller" <robmueller@iinet.net.au>
Subject: Re: [GMCnet] More on final drive ratios
To: <gmclist@temp.gmcnet.org>
Message-ID: <5AB3F62674D448EFBA303C9DAD075C8D@DellDesktop>
Content-Type: text/plain; charset="iso-8859-1"
Jerry,
When you note "a 3.5 chain in the transmission" do you mean you have Manny's Power Drive installed? If yes with the 3.21 to 1 final
drive you've got a 3.67 ratio.
The cam set at 4? advance will have lowered your torque band (I couldn't say how much cause I'd be pulling the number out my nether
regions). What cam did you use?
The sheet Dick supplied with my distributor noted to set the advance at 12?
http://www.gmcmhphotos.com/photos/member-galleries/p32021-dick-paterson-s-distri.html
Which I set at a Slow Idle speed of 600 rpm Ref: X-7525 / Section 6M / ENGINE FUEL SYSTEM / Page 6M-23 / Figure 12 / Step 6.
Regards,
Rob M.
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
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Jerry & Sharon Work
78 Royale
Kerby, OR
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