What is the correct engine rpm at 65 mph?
#1
What is the correct engine rpm at 65 mph?
Hi, I am the owner of 2 1989 Iroc Z28's. I just bought one with the L98. I want to figure out if the previous owner installed a larger rear end gear (lost contact with original owner). My Camaro with the LB9 has a 2.77 rear end gear and runs almost 1700 rpm at 65mph. The Camaro with the L98 says on the parts sheet in the console that it has a 2.77 rear end gear and runs 2400 rpm at 65 mph. Here's an issue with the L98 camaro, the vss doesn't work (mph gauge not working), and I was using my GPS to tell me when it was running at 65 mph when the rpm gauge was at 2400 rpms. I can feel my car shifting into overdrive. So is not having a working vss messing with the rpms, am I running a higher gear, or is it normal for a L98 to run higher rpms than the LB9 at 65 mph with a 2.77 rear end gear?
#2
Senior Member
Joined: Feb 2010
Posts: 1,125
Likes: 1
From: San Diego, California
Car: Trailblazer EXT 4.2 (Firebird Form)
Engine: 5.1 4bbl
Transmission: 700R4 Mega Raptor Level 4
Axle/Gears: 2.73
Re: What is the correct engine rpm at 65 mph?
#3
Re: What is the correct engine rpm at 65 mph?
My next question is, What rpm are you L98 guys running at 65 mph with a 2.73 or 2.77 rear end gear?
#4
Joined: Dec 2005
Posts: 6,498
Likes: 26
From: Macon, GA
Car: 1992 Camaro RS
Engine: Vortec headed 355, xe262
Transmission: T56
Axle/Gears: 9-bolt 3.70
Re: What is the correct engine rpm at 65 mph?
The stock tachs are notoriously inaccurate at this point. I wouldnt trust them at all.
#5
Senior Member
Joined: Feb 2010
Posts: 1,125
Likes: 1
From: San Diego, California
Car: Trailblazer EXT 4.2 (Firebird Form)
Engine: 5.1 4bbl
Transmission: 700R4 Mega Raptor Level 4
Axle/Gears: 2.73
Re: What is the correct engine rpm at 65 mph?
you know... I should have mentioned this... but ... you should check your RPM with a timing light and then compare the numbers... ....
#6
Joined: Apr 2005
Posts: 7,734
Likes: 11
From: Not in Kansas anymore
Car: 82 Z28
Engine: 383 SP EFI/ 4150 TB
Transmission: T400
Axle/Gears: QP 9" 3.73
Re: What is the correct engine rpm at 65 mph?
Counting the number of times the driveshaft turns in relation to one turn of the wheel will ballpark rear end ratio
Do the maths
http://www.bgsoflex.com/rpmmph.html
#7
Re: What is the correct engine rpm at 65 mph?
I did some messing around, looks like someone did swap in a 3.73 gear. Thanks!
Counting the number of times the driveshaft turns in relation to one turn of the wheel will ballpark rear end ratio
Do the maths
http://www.bgsoflex.com/rpmmph.html
Counting the number of times the driveshaft turns in relation to one turn of the wheel will ballpark rear end ratio
Do the maths
http://www.bgsoflex.com/rpmmph.html
Last edited by 350Irocz28; 05-14-2010 at 11:43 AM.
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#8
On Probation
Joined: Oct 2008
Posts: 6,319
Likes: 18
From: Northern Utah
Car: seeking '90.5-'92 'bird hardtop
Engine: several
Transmission: none
Axle/Gears: none
Re: What is the correct engine rpm at 65 mph?
With a 3.73:1 axle, and 245/50R16 tires, and a 700R-4 automatic, you should be doing 2200 rpm at 65 mph if the converter is locking as it should. This calls for a 15 tooth speedo drive gear, and a 44 tooth driven gear.
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