Lowering rpms - suggestions?
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Joined: Jul 2001
Posts: 71
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From: Frederiksberg, Denmark
Lowering rpms - suggestions?
Hey,
I cruise the local highways on a regular a basis. At around 70 mph the engine is doing around 3500 rpms. I would to lower these rpms in order to improve top speed and general fuel economy at legal cruising speed.
I've heard that I should consider swapping the TH350 with a 700R4 with overdrive. But I've also heard that a mere change of differential gear ratio will do the job. I think I'm having a 3.70 gear right now. Should I go to 3.08 or even lower?
Enjoy the autumn!
I cruise the local highways on a regular a basis. At around 70 mph the engine is doing around 3500 rpms. I would to lower these rpms in order to improve top speed and general fuel economy at legal cruising speed.
I've heard that I should consider swapping the TH350 with a 700R4 with overdrive. But I've also heard that a mere change of differential gear ratio will do the job. I think I'm having a 3.70 gear right now. Should I go to 3.08 or even lower?
Enjoy the autumn!
Safety Car
Joined: Aug 2001
Posts: 3,685
Likes: 202
From: Waterford Mi
Re: Lowering rpms - suggestions? (Vettelaw)
With your setup, changing the trans would be the best thing to do. Yes the gear swap would do the same thing at top end but you would loose any low end performange you are now use to. I had the 3.08 gears and they suck. Even grandma's stationwagon could start out from a traffic light better than my Vette. Evryine was beating me off the line and most of them di'nt even know we were racing :lol: . I would cahnge the trans if I had one availlable.
Race Director
Joined: Mar 2001
Posts: 11,322
Likes: 1
From: Living in the Hartland
Re: Lowering rpms - suggestions? (redwingvette)
With your setup, changing the trans would be the best thing to do. Yes the gear swap would do the same thing at top end but you would loose any low end performange you are now use to. I had the 3.08 gears and they suck. Even grandma's stationwagon could start out from a traffic light better than my Vette. Evryine was beating me off the line and most of them di'nt even know we were racing :lol: . I would cahnge the trans if I had one availlable.
Melting Slicks
Joined: May 1999
Posts: 2,897
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From: Moon Township PA
Re: Lowering rpms - suggestions? (Vettelaw)
Changing differential ratios will lower the engine rpm and give you a more economical ride. This is a pretty straight forward job and requires a bit of knowledge and regard to safety with respect to the rear spring. It is not difficult though, mostly grunt work. I can't comment on the auto tranny though - no experience there.
Try the following web site to see what will happen to rpms with changine ratios: http://www.idavette.net/tech/ratioc.htm
I use 26" for the tire diameter, then make the requisite changes in the data.
Gary
Try the following web site to see what will happen to rpms with changine ratios: http://www.idavette.net/tech/ratioc.htm
I use 26" for the tire diameter, then make the requisite changes in the data.
Gary
Le Mans Master
Joined: Feb 1999
Posts: 8,351
Likes: 75
From: Tampa Bay FL
Re: Lowering rpms - suggestions? (Vettelaw)
If you decide to go the trans swap route, check with these folks. They specialize in the 2004R/700R4 swap into C3's:
http://www.700r4.com
http://www.700r4.com
Le Mans Master
Joined: Mar 2002
Posts: 7,456
Likes: 2
From: Coming home from Luckenbach Texas
Re: Lowering rpms - suggestions? (Vettelaw)
I think the most amazing thing about the tranny swap is the major increase in fuel economy. I haven't done any scientific testing, but I do know that I'm driving a LOT farther, somewhat faster, and using a LOT less gasoline to do it!
It's the most wonderful feeling to cruise down the highway at 80 mph (130 km/h) at 2300 rpm! I strongly believe that any C3 owner who does a lot of highway driving and had a chance to experience this would run out and do the tranny swap too! :yesnod:
It's the most wonderful feeling to cruise down the highway at 80 mph (130 km/h) at 2300 rpm! I strongly believe that any C3 owner who does a lot of highway driving and had a chance to experience this would run out and do the tranny swap too! :yesnod:
