RPM question
Thread Starter
Drifting
Joined: Mar 2002
Posts: 1,877
Likes: 39
From: cincinnati ohio
Cruise-In V Veteran
RPM question
What is normal rpm at highway speeds?At 65 miles per hour my 75 runs 3000 rpm,70 mph 3300 rpm,and 75 mph 3500 rpm.I am considering changing the rearend gear.What gear ratio should i use?Im thinking lower rpm would reduce highway heat.
Thanks
Wayne
Thanks
Wayne
Le Mans Master
Joined: Sep 2000
Posts: 5,635
Likes: 4
From: Orlando Floriduh
Re: RPM question (jlsru75)
There is a ratio calculator on http://www.tirerack.com or http://www.idavette.net
Melting Slicks
Joined: Aug 2000
Posts: 2,310
Likes: 1
Re: RPM question (jlsru75)
I guess you have the 3.36 with your combo, YES?. Your RPM numbers aren't much different than mine (with a TH350 and 3.08). Acctually, they're probably a little better than mine. If you go below 3.xx you may not like the car's performance. You may also want to check out what type of trans swap you could do; that might be more effective in lowering highway RPMs and even increase performance. Just a thought.
BTW, if you're just doing this for a highway heat problem, have you checked some of the threads on "overheating" or "running hot"? Two common reasons (there are others) for running hot under speed are a missing "chin" spoiler and a faulty fan-clutch.
Good Luck.
[Modified by jerryp58, 7:15 PM 7/7/2002]
BTW, if you're just doing this for a highway heat problem, have you checked some of the threads on "overheating" or "running hot"? Two common reasons (there are others) for running hot under speed are a missing "chin" spoiler and a faulty fan-clutch.
Good Luck.
[Modified by jerryp58, 7:15 PM 7/7/2002]
Thread Starter
Drifting
Joined: Mar 2002
Posts: 1,877
Likes: 39
From: cincinnati ohio
Cruise-In V Veteran
Re: RPM question (jerryp58)
Jerry58;Yes I am considering this swap due to highway heat.I have followed every post on overheating I have seen.I have installed new radiater,hoses, thermostat,checked chin spoiler and radiater seals and removed converter.I am not sure what rear end I have.According to calculator I used on another site I have 3.55:1 to 3.70:1.My car was supposedly 30,000 mile original when I bought it 4 yrs ago.I did not think these gear ratios were available with L48.Does anyone know?
Thanks
Thanks
Le Mans Master
Joined: Sep 2000
Posts: 5,635
Likes: 4
From: Orlando Floriduh
Re: RPM question (jlsru75)
Sometimes a heat problem is a result of retarded ignition timing. Ten radiators won't help in that case. Check the center part of the distributor, It must be free to advance as the wieghts fly open. HEI distributors have a habbit of the center shaft freezing and you get little or no advance. A retarded engine WILL run hot. Even retarding the timing so you can run 87 octane fuel has an affect on the temperature the engine runs at.
Melting Slicks
Joined: Aug 2000
Posts: 2,310
Likes: 1
Re: RPM question (jlsru75)
I don't know how "correct" it is but, according to my Vette Vues book, your L48 could have a 3.70 in it if it was a automatic without AC.
If you actually had an L82 originally, both a 3.55 or a 3.70 would be possible.
There's always the chance it's not original.
Have you checked the codes on the rear housing?
What temp are you running on the highway?
If you've got the cooling system in order (which it sounds like you do) , then Silvervetteman's thought on timing may be the problem.
Good Luck.
[Modified by jerryp58, 9:45 PM 7/7/2002]
If you actually had an L82 originally, both a 3.55 or a 3.70 would be possible.
There's always the chance it's not original.
Have you checked the codes on the rear housing?
What temp are you running on the highway?
If you've got the cooling system in order (which it sounds like you do) , then Silvervetteman's thought on timing may be the problem.
Good Luck.
[Modified by jerryp58, 9:45 PM 7/7/2002]
Thread Starter
Drifting
Joined: Mar 2002
Posts: 1,877
Likes: 39
From: cincinnati ohio
Cruise-In V Veteran
Re: RPM question (jerryp58)
jerryp58;You may be correct about rear gears not being original.I think maybe a previous owner installed a different gear to get alittle more umph out of the L48.I am going to check the timing first as per silvervetteman suggestion.The reason I thought it may be rear gear is because it feels like it needs to shift again after 4th gear.
Thanks
Thanks
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Le Mans Master
Joined: Sep 2000
Posts: 5,635
Likes: 4
From: Orlando Floriduh
Re: RPM question (jlsru75)
The timming advances as the engine speeds up, and would be more likely noticed AT hiway speed than just sitting at idle It's easty to check out the distributor. The initial timing may be fine so you need to look at the distributor inside. Take the cap off and try twisting the rotor. It should move several degrees with very slight resistance and snap back, If not then you need some distributor work.
[Modified by silvervetteman, 5:46 AM 7/8/2002]
[Modified by silvervetteman, 5:46 AM 7/8/2002]